Segment Information and Concentration of Business Risk

We have two reportable segments Ionis Core and Akcea Therapeutics. In July 2017, Akcea completed an IPO and therefore beginning in July 2017, we no longer own 100 percent of Akcea. As of July 19, 2017, the closing of the IPO and at March 31, 2018, we owned approximately 68 percent of Akcea. Segment income (loss) from operations includes revenue less operating expenses attributable to each segment.

In our Ionis Core segment we are exploiting a novel drug discovery platform we created to generate a broad pipeline of first-in-class and/or best-in-class drugs for us and our partners. Our Ionis Core segment generates revenue from a multifaceted partnering strategy.

Akcea is a biopharmaceutical company focused on developing and commercializing drugs to treat patients with rare and serious diseases.

The following table shows our segment revenue and loss from operations for the three months ended March 31, 2018 and March 31, 2017 (as revised) (in thousands), respectively.

Three Months Ended March 31, 2018	Ionis Core		Akcea Therapeutics			Elimination of Intercompany Activity			Total
Revenue:
Commercial revenue:
SPINRAZA royalties	$	41,081	$	—		$	—		$	41,081
Licensing and other royalty revenue		942		—			—			942
Total commercial revenue	$	42,023	$	—		$	—		$	42,023
R&D revenue under collaborative agreements	$	90,517	$	17,108		$	(5,229	)	$	102,396
Total segment revenue	$	132,540	$	17,108		$	(5,229	)	$	144,419
Total operating expenses	$	105,544	$	47,435		$	(5,259	)	$	147,720
Income (loss) from operations	$	26,996	$	(30,327	)	$	30		$	(3,301	)

Three Months Ended March 31, 2017 (as revised)	Ionis Core		Akcea Therapeutics			Elimination of Intercompany Activity			Total
Revenue:
Commercial revenue:
SPINRAZA royalties	$	5,211	$	—		$	—		$	5,211
Licensing and other royalty revenue		2,590		—			—			2,590
Total commercial revenue	$	7,801	$	—		$	—		$	7,801
R&D revenue under collaborative agreements	$	153,382	$	6,094		$	(51,477	)	$	107,999
Total segment revenue	$	161,183	$	6,094		$	(51,477	)	$	115,800
Total operating expense	$	78,352	$	69,470		$	(51,507	)	$	96,315
Income (loss) from operations	$	82,831	$	(63,376	)	$	30		$	19,485

The following table shows our total assets by segment at March 31, 2018 and December 31, 2017 (as revised) (in thousands), respectively.

Total Assets	Ionis Core		Akcea Therapeutics		Elimination of Intercompany Activity			Total
March 31, 2018	$	1,349,044	$	252,466	$	(301,950	)	$	1,299,560
December 31, 2017 (as revised)	$	1,342,578	$	268,804	$	(288,608	)	$	1,322,774

We have historically funded our operations from collaborations with corporate partners and a relatively small number of partners have accounted for a significant percentage of our revenue. Revenue from significant partners, which is defined as ten percent or more of our total revenue, was as follows:

	Three Months Ended March 31,
	2018		2017
				(as revised)
Partner A		47 %		4 %
Partner B		36 %		25 %
Partner C		12 %		5 %
Partner D		0%		56%

Contracts receivables from one significant partner comprised approximately 87 percent of our contracts receivables at March 31, 2018. Contracts receivables from two significant partners comprised approximately 84 percent of our contracts receivables at December 31, 2017.