--Data Support Advancing SGN-PDL1V and SGN-B7H4V into Phase 1 Studies, Increasing Robust Pipeline to 10 ADC Programs--

--Leverages Seagen’s Leadership in ADC Technology--

Seagen Inc. (Nasdaq:SGEN), today announced the presentation of two new vedotin-based antibody-drug conjugate (ADC) programs at the Society for Immunotherapy of Cancer (SITC) 36th Anniversary Annual Meeting, taking place in Washington, D.C. and virtually, November 10-14, 2021. Each program combines antibodies targeted to an immune checkpoint [PD-(L)1 or B7-H4] with the cytotoxic properties of the vedotin payload. Preclinical data demonstrate promising antitumor activity. Both ADCs are set to enter first-in-human phase 1 studies in 2022.

“We are excited to advance two novel immune checkpoint vedotin ADCs, SGN-PDL1V and SGN-B7H4V, into phase 1 studies. These programs utilize a clinically validated payload and have the potential to be first in class ADCs,” said Roger Dansey, M.D., Chief Medical Officer at Seagen.

SGN-PDL1V is a novel, investigational vedotin ADC directed to the T cell checkpoint ligand, PD-(L)1. PD-(L)1 is a target with limited normal tissue expression and clinically validated expression across a variety of malignancies, including non-small cell lung cancer (NSCLC) and head and neck squamous cell carcinomas (HNSCC). SGN-PDL1V is engineered for efficient delivery of the therapeutic payload, monomethyl auristatin E (MMAE), and is proposed to have distinct mechanisms of action from other PD-(L)1-directed therapeutics, including direct cytotoxicity against PD-(L)1-expressing cells, bystander killing, and immunogenic cell death. SGN-PDL1V demonstrates robust antitumor activity in xenograft models, including in tumors with low, heterogenous PD-(L)1 expression, supporting the potential to treat patients across a wide range of PD-(L)1 expression levels. (Abstract #783)

SGN-B7H4V is a novel, investigational vedotin ADC directed to the T cell checkpoint ligand, B7-H4. B7-H4 expression is limited on normal tissue and overexpressed on a variety of solid malignancies, including breast, ovarian, and endometrial tumors. SGN-B7H4V is designed to bind and internalize the B7-H4/ADC complex from the surface of the tumor cells and release the therapeutic payload MMAE, inducing MMAE-mediated direct cytotoxicity, bystander killing, and immunogenic cell death, as well as antibody-dependent cellular cytoxicity (ADCC) and phagocytosis (ADCP). SGN-B7H4V demonstrates strong activity in xenograft models, including models with heterogenous B7-H4 expression. (Abstract #854)

The abstracts published in advance of the SITC Annual Meeting can be found here. All data presentations will be available on-demand starting on November 9.

Details of Seagen Presentations at SITC Annual Meeting 2021:

About Seagen

Seagen is a global biotechnology company that discovers, develops and commercializes transformative cancer medicines to make a meaningful difference in people’s lives. Seagen is headquartered in the Seattle, Washington area, and has locations in California, Canada, Switzerland and the European Union. For more information on the company’s marketed products and robust pipeline, visit www.seagen.com and follow @SeagenGlobal on Twitter.

Forward-Looking Statements

Certain of the statements made in this press release are forward-looking, such as those, among others, relating to the therapeutic potential of SGN-PDL1V, SGN B7H4V and SEA-TGT, their possible safety, efficacy and therapeutic uses, anticipated development activities including clinical trial activities, and the company’s pipeline. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Factors that may cause such a difference include the difficulty and uncertainty of pharmaceutical product development, the risk of adverse events or safety signals, the inability to show sufficient activity in clinical trials and the possibility of adverse regulatory actions. More information about the risks and uncertainties faced by Seagen is contained under the caption “Risk Factors” included in the Company’s Quarterly Report on Form 10-Q for the quarter ended September 30, 2021, filed with the Securities and Exchange Commission. Seagen disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

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