FIXED ASSETS

Fixed assets, summarized by major category, consist of the following (in thousands):



	June 30,			December 31,
	2017			2016
Machinery and laboratory equipment	$	35,224		$	34,309
Leasehold improvements	34,327			33,787
Computer equipment and software	7,298			5,623
Office furniture and equipment	1,603			1,606
Construction in progress	67,443			63,201
Total	145,895			138,526
Less: accumulated depreciation	(42,656		)	(37,510		)
Fixed assets, net	$	103,239		$	101,016

For the three months ended June 30, 2017 and 2016, depreciation expense was $3.7 million and $3.2 million, respectively. For the three months ended June 30, 2017 and 2016, capitalized interest on the construction of manufacturing sites was $0.2 million and $0.4 million, respectively.

For the six months ended June 30, 2017 and 2016, depreciation expense was $6.8 million and $6.3 million, respectively. For the six months ended June 30, 2017 and 2016, capitalized interest on the construction of manufacturing sites was $0.4 million and $0.7 million, respectively.

At June 30, 2017 and December 31, 2016, total fixed assets, net, includes leasehold improvements and manufacturing process equipment located in England in the amount of $52.1 million and $33.7 million, respectively.