Ionis Pharmaceuticals, Inc. (NASDAQ: IONS) and its affiliate Akcea Therapeutics, Inc. (NASDAQ: AKCA) today announced that they have entered into a definitive agreement under which Ionis will acquire all of the outstanding shares of Akcea common stock it does not already own, approximately 24%, for $18.15 per share in cash. This corresponds to a total transaction value of approximately $500 million on a fully diluted basis. The transaction has been approved by the Ionis and Akcea Boards of Directors, and by the independent Affiliate Transactions Committee of Akcea's Board of Directors. Akcea's Board of Directors has recommended to shareholders of Akcea that they tender their shares into the tender offer.

"This acquisition is another step forward in Ionis' evolution and creates a stronger, more efficient organization to the benefit of all stakeholders," said Brett Monia, Chief Executive Officer of Ionis. "We believe becoming one company – with one vision and one set of strategic priorities, led by one team – will deliver significant strategic value, enhancing the future success of our company, accelerating our next phase of growth and positioning us to most effectively deliver our medicines to patients. Following the completion of the transaction, Ionis will retain more value from Akcea's rich pipeline and commercial products, further strengthening our financial position and supporting continued investments in our future."

"Akcea values the skills, experience and expertise of our teams and I am proud of what we've accomplished in developing and delivering transformational medicines to patients," said Damien McDevitt, Chief Executive Officer of Akcea. "This acquisition by Ionis is a testament to the achievements of the Akcea team."

"This transaction delivers immediate and certain value with a premium to Akcea shareholders," said Barbara Yanni, Chair of the Akcea Affiliate Transactions Committee. "Our close collaboration with Ionis has been key to enabling the launch of two commercial antisense medicines in just two years as well as advancing a late-stage pipeline and securing important partnerships."

SIGNIFICANT FINANCIAL BENEFITS

This transaction also further strengthens Ionis' financial position:

• Ionis will realize more financial upside from Akcea's rich pipeline and commercial products.
• Ionis will gain full access to Akcea's significant cash on hand of approximately $390 million as of June 30, 2020 and future cash flows to further invest in the Company's future and further support Ionis' capital allocation strategy.
• Ionis will achieve meaningful cost synergies.

TERMS OF THE AGREEMENT

Under the terms of the agreement, Ionis will commence a tender offer for all outstanding shares of Akcea common stock not already owned by Ionis at a price of $18.15 per share in cash. The closing of the tender offer will be subject to a majority of Akcea's shares not already owned by Ionis, its affiliates or their respective directors and executive officers being tendered in the tender offer.

Promptly following the completion of the tender offer, Ionis will acquire all remaining shares of Akcea common stock at the same price of $18.15 per share in cash through a second-step merger. Ionis and Akcea expect to complete the transaction in the fourth quarter of 2020, subject to other customary closing conditions.

Ionis expects to fund the acquisition through existing cash resources. The transaction is not subject to any financing condition.

ADVISORS

Goldman Sachs & Co. LLC and Stifel, Nicolaus & Company, Incorporated are serving as financial advisors to Ionis, and Skadden, Arps, Slate, Meagher & Flom LLP is serving as legal counsel to Ionis. Cowen is serving as financial advisor to the Affiliate Transactions Committee of Akcea's Board of Directors, and Ropes & Gray LLP is serving as legal counsel to the Affiliate Transactions Committee of Akcea's Board of Directors.

ABOUT IONIS PHARMACEUTICALS, INC.

As the leader in RNA-targeted drug discovery and development, Ionis has created an efficient, broadly applicable, drug discovery platform called antisense technology that can treat diseases where no other therapeutic approaches have proven effective. Our drug discovery platform has served as a springboard for actionable promise and realized hope for patients with unmet needs. We created the first and only approved treatment for children and adults with spinal muscular atrophy as well as the world's first RNA-targeted therapeutic approved for the treatment of polyneuropathy in adults with hereditary transthyretin amyloidosis. Our sights are set on all the patients we have yet to reach with a pipeline of more than 40 novel medicines designed to potentially treat a broad range of diseases, including neurological, cardio-renal, metabolic, infectious, and pulmonary diseases.

To learn more about Ionis visit www.ionispharma.com or follow us on twitter @ionispharma.

ABOUT AKCEA THERAPEUTICS, INC.

Akcea Therapeutics, Inc., a majority-owned affiliate of?Ionis Pharmaceuticals, Inc. (NASDAQ: IONS), is a biopharmaceutical company focused on developing and commercializing medicines to treat patients with serious and rare diseases. Akcea is commercializing TEGSEDI® (inotersen) and WAYLIVRA®?(volanesorsen), as well as advancing a mature pipeline of novel medicines, including AKCEA-APO(a)-LRx, vupanorsen (AKCEA-ANGPTL3-LRx), AKCEA-APOCIII-LRx, and AKCEA-TTR-LRx, with the potential to treat multiple diseases. All six medicines were discovered by Ionis, a leader in antisense therapeutics, and are based on Ionis' proprietary antisense technology. TEGSEDI is approved in the U.S., E.U., Canada and Brazil, and WAYLIVRA is approved in the E.U. Akcea is headquartered in Boston, Massachusetts, and is building the infrastructure to commercialize its medicines globally. Additional information about Akcea is available at?www.akceatx.com and you can follow the Company on twitter at @akceatx.