<SEC-DOCUMENT>0000899243-20-017100.txt : 20200618
<SEC-HEADER>0000899243-20-017100.hdr.sgml : 20200618
<ACCEPTANCE-DATETIME>20200618172806
ACCESSION NUMBER:		0000899243-20-017100
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20200616
FILED AS OF DATE:		20200618
DATE AS OF CHANGE:		20200618

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Atlas Venture Fund X, L.P.
		CENTRAL INDEX KEY:			0001628098
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39319
		FILM NUMBER:		20973638

	BUSINESS ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQUARE
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		857-201-2700

	MAIL ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQUARE
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Atlas Venture Associates X, LLC
		CENTRAL INDEX KEY:			0001742765
		STATE OF INCORPORATION:			DE

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39319
		FILM NUMBER:		20973639

	BUSINESS ADDRESS:	
		STREET 1:		400 TECH. SQ.
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		857-201-2700

	MAIL ADDRESS:	
		STREET 1:		400 TECH. SQ.
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			ATLAS VENTURE ASSOCIATES X, L.P.
		CENTRAL INDEX KEY:			0001742766
		STATE OF INCORPORATION:			DE

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39319
		FILM NUMBER:		20973640

	BUSINESS ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQ.
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		857-201-2700

	MAIL ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQ.
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Atlas Venture Opportunity Fund I, L.P.
		CENTRAL INDEX KEY:			0001759241
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39319
		FILM NUMBER:		20973641

	BUSINESS ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQUARE, 10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		857-201-2700

	MAIL ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQUARE, 10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Atlas Venture Associates Opportunity I, L.P.
		CENTRAL INDEX KEY:			0001780065
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39319
		FILM NUMBER:		20973642

	BUSINESS ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQUARE
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		857-201-2700

	MAIL ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQUARE
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Atlas Venture Associates Opportunity I, LLC
		CENTRAL INDEX KEY:			0001780066
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39319
		FILM NUMBER:		20973643

	BUSINESS ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQUARE
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		857-201-2700

	MAIL ADDRESS:	
		STREET 1:		400 TECHNOLOGY SQUARE
		STREET 2:		10TH FLOOR
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Generation Bio Co.
		CENTRAL INDEX KEY:			0001733294
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				814301281
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		301 BINNEY STREET
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02142
		BUSINESS PHONE:		857-529-5908

	MAIL ADDRESS:	
		STREET 1:		301 BINNEY STREET
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02142
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc4.xml
<DESCRIPTION>FORM 4 SUBMISSION
<TEXT>
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    <documentType>4</documentType>

    <periodOfReport>2020-06-16</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001733294</issuerCik>
        <issuerName>Generation Bio Co.</issuerName>
        <issuerTradingSymbol>GBIO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001628098</rptOwnerCik>
            <rptOwnerName>Atlas Venture Fund X, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>400 TECHNOLOGY SQUARE, 10TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02139</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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    <reportingOwner>
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            <rptOwnerCik>0001742765</rptOwnerCik>
            <rptOwnerName>Atlas Venture Associates X, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>400 TECHNOLOGY SQUARE, 10TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02139</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001742766</rptOwnerCik>
            <rptOwnerName>ATLAS VENTURE ASSOCIATES X, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>400 TECHNOLOGY SQUARE, 10TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02139</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001759241</rptOwnerCik>
            <rptOwnerName>Atlas Venture Opportunity Fund I, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>400 TECHNOLOGY SQUARE, 10TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02139</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
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            <isOther>0</isOther>
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    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001780065</rptOwnerCik>
            <rptOwnerName>Atlas Venture Associates Opportunity I, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>400 TECHNOLOGY SQUARE, 10TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02139</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001780066</rptOwnerCik>
            <rptOwnerName>Atlas Venture Associates Opportunity I, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>400 TECHNOLOGY SQUARE, 10TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02139</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2020-06-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10040032</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12630758</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Series A Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-06-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>15051020</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>8521213</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Series C Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-06-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>268269</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1518819</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On June 16, 2020, the Series A Preferred Stock automatically converted into Common Stock on a 1.7663-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.</footnote>
        <footnote id="F2">On June 16, 2020, the Series C Preferred Stock automatically converted into Common Stock on a 1.7663-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.</footnote>
        <footnote id="F3">Includes 11,111,939 shares held by Atlas Venture Fund X, L.P. (&quot;Atlas Venture Fund X&quot;) and 1,518,819 shares held by Atlas Venture Opportunity Fund I, L.P. (&quot;Atlas Venture Opportunity Fund I&quot;). The general partner of Atlas Venture Fund X is Atlas Venture Associates X, L.P. (&quot;AVA X LP&quot;). Atlas Venture Associates X, LLC (&quot;AVA X LLC&quot;) is the general partner of AVA X LP. Each of AVA X LP and AVA X LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Venture Fund X, except to the extent of its pecuniary interest therein, if any. The general partner of Atlas Venture Opportunity Fund I is Atlas Venture Associates Opportunity I, L.P. (&quot;AVAO I LP&quot;). Atlas Venture Associates Opportunity I, LLC (&quot;AVAO I LLC&quot;) is the general partner of AVAO I LP. Each of AVAO I LP and AVAO I LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Venture Opportunity Fund I, except to the extent of its pecuniary interest therein, if any.</footnote>
        <footnote id="F4">The shares are held directly by Atlas Venture Fund X. The general partner of Atlas Venture Fund X is  AVA X LP. AVA X LLC is the general partner of AVA X LP. Each of AVA X LP and AVA X LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Venture Fund X, except to the extent of its pecuniary interest therein, if any.</footnote>
        <footnote id="F5">The shares are held directly by Atlas Venture Opportunity Fund I. The general partner of Atlas Venture Opportunity Fund I is AVAO I LP. AVAO I LLC is the general partner of AVAO I LP. Each of AVAO I LP and AVAO I LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Venture Opportunity Fund I, except to the extent of its pecuniary interest therein, if any.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Atlas Venture Fund X, LP, By: Atlas Venture Associates X, L.P., it's general partner, By: Atlas Venture Associates X, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan</signatureName>
        <signatureDate>2020-06-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Atlas Venture Associates X, LP, By: Atlas Venture Associates X, LLC, it's general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan</signatureName>
        <signatureDate>2020-06-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Atlas Venture Associates X, LLC, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan</signatureName>
        <signatureDate>2020-06-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Atlas Venture Opportunity Fund I, L.P., By: Atlas Venture Associates Opportunity I, L.P., its general partner, By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan</signatureName>
        <signatureDate>2020-06-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Atlas Venture Associates Opportunity I, L.P., By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan</signatureName>
        <signatureDate>2020-06-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Atlas Venture Associates Opportunity I, LLC, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan</signatureName>
        <signatureDate>2020-06-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</SEC-DOCUMENT>
