<SEC-DOCUMENT>0001144204-13-066571.txt : 20131210
<SEC-HEADER>0001144204-13-066571.hdr.sgml : 20131210
<ACCEPTANCE-DATETIME>20131210165441
ACCESSION NUMBER:		0001144204-13-066571
CONFORMED SUBMISSION TYPE:	SC 13G
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20131210
DATE AS OF CHANGE:		20131210
GROUP MEMBERS:		PETER KOLCHINSKY
GROUP MEMBERS:		RA CAPITAL HEALTHCARE FUND, L.P.

SUBJECT COMPANY:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Xencor Inc
		CENTRAL INDEX KEY:			0001326732
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				201622502
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SC 13G
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-87750
		FILM NUMBER:		131268885

	BUSINESS ADDRESS:	
		STREET 1:		111 WEST LEMON AVE
		CITY:			MONROVIA
		STATE:			CA
		ZIP:			91016
		BUSINESS PHONE:		626-305-5900

	MAIL ADDRESS:	
		STREET 1:		111 WEST LEMON AVE
		CITY:			MONROVIA
		STATE:			CA
		ZIP:			91016

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			RA CAPITAL MANAGEMENT, LLC
		CENTRAL INDEX KEY:			0001346824
		IRS NUMBER:				830406777
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SC 13G

	BUSINESS ADDRESS:	
		STREET 1:		20 PARK PLAZA, SUITE 1200
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		617-778-2500

	MAIL ADDRESS:	
		STREET 1:		20 PARK PLAZA, SUITE 1200
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
</SEC-HEADER>
<DOCUMENT>
<TYPE>SC 13G
<SEQUENCE>1
<FILENAME>v362686_sc13g.htm
<DESCRIPTION>SCHEDULE 13 G
<TEXT>
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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">UNITED STATES<BR>
SECURITIES AND EXCHANGE COMMISSION<BR>
Washington, D.C. 20549</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>SCHEDULE 13G</B></P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">Under the Securities Exchange Act of
1934</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center; text-indent: 0in"><B>(Amendment No.__)*</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center; text-indent: 0in">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><BR>
Xencor, Inc.</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(Name of Issuer)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Common Stock, par value $0.001 per share</B></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(Title of Class of Securities)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>98401F105</B></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(CUSIP Number)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>December 03, 2013</B></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(Date of Event Which Requires Filing of
this Statement)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Check the appropriate box to designate the rule pursuant to
which this Schedule is filed:</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="width: 100%; font: 10pt Times New Roman, Times, Serif">
<tr>
    <TD STYLE="padding: 3pt; width: 5%">[ &nbsp; ]</td>
    <TD STYLE="padding: 3pt; width: 95%">Rule 13d-1(b)</td></tr>
<tr>
    <TD STYLE="padding: 3pt">[<b>X</b>]</td>
    <TD STYLE="padding: 3pt">Rule 13d-1(c)</td></tr>
<tr>
    <TD STYLE="padding: 3pt">[ &nbsp; ]</td>
    <TD STYLE="padding: 3pt">Rule 13d-1(d)</td></tr>
</table>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">*The remainder of this cover page shall be filled out for a
reporting person&rsquo;s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment
containing information which would alter the disclosures provided in a prior cover page.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">The information required in the remainder of this cover page
shall not be deemed to be &ldquo;filed&rdquo; for the purpose of Section 18 of the Securities Exchange Act of 1934 (&ldquo;<B><I>Act</I></B>&rdquo;)
or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however,
see the Notes).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>


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    <TD STYLE="width: 46%; padding-right: 3pt; padding-left: 3pt; font-size: 10pt"><font style="font-size: 10pt">CUSIP No. <b>98401F105</b></font></td>
    <TD STYLE="width: 22%; padding-right: 3pt; padding-left: 3pt; font-size: 12pt; text-align: center"><font style="font-size: 12pt"><b>13G</b></font></td>
    <TD STYLE="width: 32%; padding-right: 3pt; padding-left: 3pt; font-size: 10pt">&nbsp;</td></tr>
</table>
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    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt"><font style="font-size: 10pt">1.</font></td>
    <TD COLSPAN="2" STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<br>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>RA Capital Management, LLC&#9;</b></P></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 1.45pt 3pt">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding: 1.45pt 3pt"><font style="font-size: 10pt">2. </font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</font></td></tr>
<tr>
    <TD STYLE="width: 4%; padding: 1.45pt 3pt 6pt">&nbsp;</td>
    <TD STYLE="width: 7%; padding: 1.45pt 3pt 6pt">&nbsp;</td>
    <TD STYLE="width: 6%; padding: 1.45pt 3pt 6pt"><font style="font-size: 10pt">(a)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<FONT STYLE="font-family: Wingdings">&#168;</FONT></font></td>
    <TD STYLE="width: 83%; padding-bottom: 6pt"></td></tr>
<tr>
    <TD>&nbsp;</td>
    <TD>&nbsp;</td>
    <TD STYLE="padding-left: 3pt"><font style="font-size: 10pt">(b)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<FONT STYLE="font-family: Wingdings">&#168;</FONT></font></td>
    <TD></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 1.45pt 3pt">&nbsp;</td>
    <TD STYLE="padding: 1.45pt 3pt"><font style="font-size: 10pt">3.</font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">SEC Use Only </font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 1.45pt 3pt">&nbsp;</td>
    <TD STYLE="padding: 1.45pt 3pt"><font style="font-size: 10pt">4.</font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font>&nbsp;<font style="font-size: 10pt"><b>Massachusetts</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
</table>


<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>
<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <td rowspan="7" style="width: 18%; padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Number of</font><br>
<font style="font-size: 10pt">Shares</font><br>
<font style="font-size: 10pt">Beneficially</font><br>
<font style="font-size: 10pt">Owned by</font><br>
<font style="font-size: 10pt">Each Reporting</font><br>
<font style="font-size: 10pt">Person With</font></td>
    <td style="width: 3%; padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">5.</font></td>
    <td style="width: 79%; font-size: 10pt"><font style="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">6.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>2,725,000 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">7.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">8.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>2,725,000 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
</table>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>










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    <TD STYLE="width: 4%; padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt; font-size: 10pt">&nbsp;</td>
    <TD STYLE="width: 7%; padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt; font-size: 10pt"><font style="font-size: 10pt">9.</font></td>
    <TD STYLE="width: 89%; padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>2,725,000 shares</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt; font-size: 10pt">&nbsp;</td>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt; font-size: 10pt; text-align: left; vertical-align: top"><font style="font-size: 10pt">10.</font></td>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><font style="font-size: 10pt">Check if the Aggregate Amount
        in Row (9) Excludes&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </font><FONT STYLE="font-family: Wingdings">&#168;</FONT></P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Certain Shares (See Instructions)</P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt; font-size: 10pt">&nbsp;</td>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt; font-size: 10pt"><font style="font-size: 10pt">11.</font></td>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>8.7%</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt; font-size: 10pt">&nbsp;</td>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt; font-size: 10pt"><font style="font-size: 10pt">12.</font></td>
    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>IA</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
</TABLE>

<P STYLE="margin: 0">&nbsp;</P>


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<tr>
    <TD STYLE="width: 46%; padding-right: 3pt; padding-left: 3pt; font-size: 10pt"><font style="font-size: 10pt">CUSIP No. <b>98401F105</b></font></td>
    <TD STYLE="width: 22%; padding-right: 3pt; padding-left: 3pt; font-size: 12pt; text-align: center"><font style="font-size: 12pt"><b>13G</b></font></td>
    <TD STYLE="width: 32%; padding-right: 3pt; padding-left: 3pt; font-size: 10pt">&nbsp;</td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
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    <TD STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt"><font style="font-size: 10pt">1.</font></td>
    <TD COLSPAN="2" STYLE="padding-top: 1.45pt; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<br>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>Peter Kolchinsky&#9;</b></P></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt">&nbsp;</td>
    <td style="vertical-align: top; padding: 1.45pt 3pt"><font style="font-size: 10pt">2. </font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</font></td></tr>
<tr>
    <td style="width: 4%; padding: 1.45pt 3pt 6pt">&nbsp;</td>
    <td style="width: 7%; padding: 1.45pt 3pt 6pt">&nbsp;</td>
    <td style="width: 6%; padding: 1.45pt 3pt 6pt"><font style="font-size: 10pt">(a)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<FONT STYLE="font-family: Wingdings">&#168;</FONT></font></td>
    <td style="width: 83%; padding-bottom: 6pt"></td></tr>
<tr>
    <TD>&nbsp;</td>
    <TD>&nbsp;</td>
    <TD STYLE="padding-left: 3pt"><font style="font-size: 10pt">(b)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<FONT STYLE="font-family: Wingdings">&#168;</FONT></font></td>
    <TD></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt">&nbsp;</td>
    <td style="padding: 1.45pt 3pt"><font style="font-size: 10pt">3.</font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">SEC Use Only </font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt">&nbsp;</td>
    <td style="padding: 1.45pt 3pt"><font style="font-size: 10pt">4.</font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font>&nbsp;<b>United States</b></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
</table>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>










<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <td rowspan="7" style="width: 18%; padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Number of</font><br>
<font style="font-size: 10pt">Shares</font><br>
<font style="font-size: 10pt">Beneficially</font><br>
<font style="font-size: 10pt">Owned by</font><br>
<font style="font-size: 10pt">Each Reporting</font><br>
<font style="font-size: 10pt">Person With</font></td>
    <td style="width: 3%; padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">5.</font></td>
    <td style="width: 79%; font-size: 10pt"><font style="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">6.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>2,725,000 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">7.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">8.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>2,725,000 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="border-bottom: Gray 1.5pt solid; padding-right: 3pt; padding-left: 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
</table>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>










<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <td style="width: 4%; padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</td>
    <td style="width: 7%; padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">9.</font></td>
    <td style="width: 89%; padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>2,725,000 shares</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</td>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt; text-align: left; vertical-align: top"><font style="font-size: 10pt">10.</font></td>
    <td style="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><font style="font-size: 10pt">Check if the Aggregate Amount
        in Row (9) Excludes&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </font><FONT STYLE="font-family: Wingdings">&#168;</FONT></P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Certain Shares (See Instructions)</P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">11.</font></td>
    <td style="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>8.7%</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">12.</font></td>
    <td style="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>IN</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
</table>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B></B></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD STYLE="width: 46%; padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">CUSIP No. </FONT>&nbsp;<FONT STYLE="font-size: 10pt"><B>98401F105</B></FONT></TD>
    <TD STYLE="width: 22%; padding: 1.45pt 3pt; font-size: 12pt; text-align: center"><FONT STYLE="font-size: 12pt"><B>13G</B></FONT></TD>
    <TD STYLE="width: 32%; padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD></TR>
</TABLE>


<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B></B></P>
<hr size="2" noshade align="center" style="width: 100%; color: gray">
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>







<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <td style="padding: 1.45pt 3pt">&nbsp;</td>
    <td style="vertical-align: top; padding: 1.45pt 3pt"><font style="font-size: 10pt">1.</font></td>
    <td colspan="2" style="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<br>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>RA Capital Healthcare Fund, L.P.&#9;</b></P></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt">&nbsp;</td>
    <td style="vertical-align: top; padding: 1.45pt 3pt"><font style="font-size: 10pt">2. </font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</font></td></tr>
<tr>
    <td style="width: 4%; padding: 1.45pt 3pt 6pt">&nbsp;</td>
    <td style="width: 7%; padding: 1.45pt 3pt 6pt">&nbsp;</td>
    <td style="width: 6%; padding: 1.45pt 3pt 6pt"><font style="font-size: 10pt">(a)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<FONT STYLE="font-family: Wingdings">&#168;</FONT></font></td>
    <td style="width: 83%; padding-bottom: 6pt"></td></tr>
<tr>
    <td style="padding-bottom: 6pt">&nbsp;</td>
    <td style="padding-bottom: 6pt">&nbsp;</td>
    <TD STYLE="padding-bottom: 6pt; padding-left: 3pt"><font style="font-size: 10pt">(b)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<FONT STYLE="font-family: Wingdings">&#168;</FONT></font></td>
    <td style="padding-bottom: 6pt"></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt">&nbsp;</td>
    <td style="padding: 1.45pt 3pt"><font style="font-size: 10pt">3.</font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">SEC Use Only </font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt">&nbsp;</td>
    <td style="padding: 1.45pt 3pt"><font style="font-size: 10pt">4.</font></td>
    <td colspan="2" style="padding: 1.45pt 3pt"><font style="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font>&nbsp;<font style="font-size: 10pt"><b>Delaware</b></font></td></tr>
<TR>
    <TD STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">&nbsp;</TD>
    <TD STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">&nbsp;</TD>
    <TD COLSPAN="2" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">&nbsp;</TD></TR>
</table>


<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>









<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <td rowspan="7" style="width: 18%; padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Number of</font><br>
<font style="font-size: 10pt">Shares</font><br>
<font style="font-size: 10pt">Beneficially</font><br>
<font style="font-size: 10pt">Owned by</font><br>
<font style="font-size: 10pt">Each Reporting</font><br>
<font style="font-size: 10pt">Person With</font></td>
    <td style="width: 3%; padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">5.</font></td>
    <td style="width: 79%; font-size: 10pt"><font style="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">6.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font>&nbsp;<font style="font-size: 10pt"><b>2,180,000 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">7.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="2" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">8.</font></td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font>&nbsp;<font style="font-size: 10pt"><b>2,180,000 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
</table>


<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>









<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <td style="width: 4%; padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</td>
    <td style="width: 7%; padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">9.</font></td>
    <td style="width: 89%; padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>2,180,000 shares</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</td>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt; text-align: left; vertical-align: top"><font style="font-size: 10pt">10.</font></td>
    <td style="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><font style="font-size: 10pt">Check if the Aggregate Amount
        in Row (9) Excludes&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <FONT STYLE="font-family: Wingdings">&#168;</FONT></P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Certain Shares (See Instructions)</P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">11.</font></td>
    <td style="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>7.0%</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <td style="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</td>
    <td style="padding: 1.45pt 3pt; font-size: 10pt"><font style="font-size: 10pt">12.</font></td>
    <td style="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>PN (Limited Partnership)_</b></P></td></tr>
<tr>
    <TD COLSPAN="3" STYLE="padding-right: 3pt; padding-left: 3pt; border-bottom: Gray 1.5pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
</table>


<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">CUSIP No. <FONT STYLE="font: 10pt Times New Roman, Times, Serif"><B>98401F105</B></FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 1.</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">(a)&#9;<B>Name of Issuer:</B> Xencor, Inc. (the &ldquo;Issuer&rdquo;).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">(b)&#9;<B>Address of the Issuer&rsquo;s Principal Executive
Offices:</B> 111 West Lemon Avenue Monrovia, California 91016.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 2.&#9;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(a)&#9;<B>Name of Person Filing: </B> This
joint statement on Schedule 13G is being filed by Peter Kolchinsky, RA Capital Management, LLC (&ldquo;Capital&rdquo;), and RA
Capital Healthcare Fund, L.P. (the &ldquo;Fund&rdquo;). Mr. Kolchinsky, Capital and the Fund are collectively referred to herein
as the &ldquo;Reporting Persons.&rdquo;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(b)&#9;<B>Address of Principal Business Office:</B>
The principal business office of the Reporting Persons is c/o RA Capital Management, LLC, 20 Park Plaza, Suite 1200, Boston, MA
02116.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(c) &#9;<B>Citizenship:</B> Capital is a Massachusetts
limited liability company. The Fund is a Delaware limited partnership. Mr. Kolchinsky is a United States citizen.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(d)&#9;<B>Title and Class of Securities: </B>Common
stock (&ldquo;Common Stock&rdquo;).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(e)&#9;<B>CUSIP Number:</B> 98401F105.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 3.&#9;If this statement is filed pursuant to &sect;&sect;240.13d-1(b)
or 240.13d-2(b) or (c), check whether the person filing is a:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 4. &#9;Ownership:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Provide the following information regarding the aggregate number
and percentage of the class of securities of the issuer identified in Item 1.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse">
<TR STYLE="vertical-align: top">
    <TD STYLE="width: 6%; padding-right: 2.7pt; padding-left: 2.7pt; font-size: 10pt">(a)</TD>
    <TD STYLE="width: 94%; padding-right: 2.7pt; padding-left: 2.7pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Amount Beneficially Owned:**</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC - 2,725,000 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky - 2,725,000 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P. - 2,180,000
        shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt; font-size: 10pt">(b)</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt; font-size: 10pt">Percent of Class:**</TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC &ndash; 8.7%</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky &ndash; 8.7%</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P. &ndash;
        7.0%</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt; font-size: 10pt">(c)</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt; font-size: 10pt">Number of shares as to which such person has:</TD></TR>
</TABLE>


<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">CUSIP No. <FONT STYLE="font: 10pt Times New Roman, Times, Serif"><B>98401F105</B></FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="width: 100%; font: 10pt Times New Roman, Times, Serif; border-collapse: collapse">
<TR STYLE="vertical-align: top">
    <TD STYLE="width: 6%; padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt"><FONT STYLE="font-size: 10pt">&nbsp;</FONT></TD>
    <TD STYLE="width: 6%; padding-right: 2.7pt; padding-left: 2.7pt">(i)</TD>
    <TD STYLE="width: 88%; padding-right: 2.7pt; padding-left: 2.7pt">sole power to vote or to direct the vote **</TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt"><FONT STYLE="font-size: 10pt">&nbsp;</FONT></TD>
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt">&nbsp;</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P. - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt"><FONT STYLE="font-size: 10pt">&nbsp;</FONT></TD>
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt">(ii)</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt">shared power to vote or to direct the vote**</TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt"><FONT STYLE="font-size: 10pt">&nbsp;</FONT></TD>
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt">&nbsp;</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC - 2,725,000 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky - 2,725,000 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P. - 2,180,000
        shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt"><FONT STYLE="font-size: 10pt">&nbsp;</FONT></TD>
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt">(iii)</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt">Sole power to dispose or to direct the disposition of**</TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt"><FONT STYLE="font-size: 10pt">&nbsp;</FONT></TD>
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt">&nbsp;</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P. - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt"><FONT STYLE="font-size: 10pt">&nbsp;</FONT></TD>
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt">(iv)</TD>
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt">shared power to dispose or to direct the disposition of**</TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt"><FONT STYLE="font-size: 10pt">&nbsp;</FONT></TD>
    <TD STYLE="padding-right: 2.7pt; padding-bottom: 12pt; padding-left: 2.7pt">&nbsp;</TD>
    <TD STYLE="padding-right: 2.7pt; padding-left: 2.7pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC - 2,725,000 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky - 2,725,000 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P. - 2,180,000
        shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
</TABLE>


<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">** Shares reported herein for the Fund represent shares of Common
Stock beneficially owned and held of record by the Fund. Shares reported herein for Capital represent (a) the above-referenced
shares of Common Stock reported for the Fund, for which the LLC serves as the sole general partner, and (b) shares of Common Stock
held in a separately managed account for which Capital serves as investment adviser. Shares reported herein for Mr. Kolchinsky
represent the above-referenced shares of Common Stock reported for Capital, for which Mr. Kolchinsky serves as the manager. Each
of the Reporting Persons disclaims beneficial ownership of the shares reported herein except to the extent of its or his pecuniary
interest therein.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 5.&#9;Ownership of Five Percent or Less of a Class:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 1in; text-indent: -1in"><B>Item 6.&#9;Ownership of More than
Five Percent on Behalf of Another Person:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 1in; text-indent: -1in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 7. &#9;Identification and Classification of the Subsidiary
Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">CUSIP No. <FONT STYLE="font: 10pt Times New Roman, Times, Serif"><B>98401F105</B></FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 8.&#9;Identification and Classification of Members of
the Group:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 9.&#9;Notice of Dissolution of Group:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 10.&#9;Certification:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">By signing below I hereby certify that, to the best of my knowledge
and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing
or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant
in any transaction having that purpose or effect.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>


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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: left">CUSIP No. <FONT STYLE="font: 10pt Times New Roman, Times, Serif"><B>98401F105</B></FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: left">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>SIGNATURE</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">After reasonable inquiry and to the best
of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">Date: </FONT>December
10<FONT STYLE="text-transform: uppercase">, 2013</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><BR>
RA CAPITAL MANAGEMENT, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: /s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Manager</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">PETER KOLCHINSKY</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">/s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">RA CAPITAL HEALTHCARE FUND, L.P.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: RA Capital Management, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in; text-indent: 0.5in">General Partner</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: /s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Manager</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>


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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><U>Exhibit 1</U></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><U>JOINT FILING AGREEMENT</U></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">This Joint Filing Agreement, dated as of
December 10, 2013, is by and among RA Capital Management, LLC, Peter Kolchinsky and RA Capital Healthcare Fund, L.P. (the foregoing
are collectively referred to herein as the &ldquo;Filers&rdquo;).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Each of the Filers may be required to file
with the United States Securities and Exchange Commission a statement on Schedule 13G and/or 13D with respect to Common Shares,
par value $0.01 per share, of Xencor, Inc. beneficially owned by them from time to time.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Pursuant to and in accordance with Rule
13(d)(1)(k) promulgated under the Securities Exchange Act of 1934, as amended, the Filers hereby agree to file a single statement
on Schedule 13G and/or 13D (and any amendments thereto) on behalf of each of such parties, and hereby further agree to file this
Joint Filing Agreement as an exhibit to such statement, as required by such rule.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">This Joint Filing Agreement may be terminated
by any of the Filers upon one week&rsquo;s prior written notice or such lesser period of notice as the Filers may mutually agree.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Executed and delivered as of the date first
above written.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">RA CAPITAL MANAGEMENT, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: /s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Manager</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">PETER KOLCHINSKY</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">/s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">RA CAPITAL HEALTHCARE FUND, L.P.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: RA Capital Management, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in; text-indent: 0.5in">General Partner</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: /s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Manager</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"></P>

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