Merck to Buy Cancer Immunotherapy Biotech Harpoon for $680 Million

Pictured: Merck's headquarters in Kenilworth, New Jersey/iStock, JHVEPhoto

Merck is to acquire cancer drug developer Harpoon Therapeutics for about $680 million, a move that will bolster the pharma giant’s immunotherapy and oncology pipeline, Merck announced Monday. The purchase will help Merck “advance breakthrough science,” the company’s president, Dean Y. Li, said in the statement.

Harpoon has developed several T-cell engager drugs, antibodies engineered to redirect a patient’s T cells to recognize and kill cancer cells. Its lead T-cell engager candidate, HPN328, targets the ligand DLL3, which is expressed at high levels in small cell lung cancer (SCLC) and neuroendocrine tumors.

“We look forward to further evaluating HPN328 in innovative combinations with other pipeline candidates,” Li said.

HPN328 is currently in a Phase I/II clinical trial to check its safety, tolerability and pharmacokinetics in patients with advanced cancers associated with expression of DLL3. Harpoon, which saw its share price more than double on today’s news, presented positive interim tolerability and response data for HPN328 in certain patients with SCLC and neuroendocrine tumors in October last year.

The deal comes as Merck moves closer to losing key patents on its blockbuster immunotherapy drug, Keytruda beginning in 2028, and thus market share to competing biosimilars.

David Adam is a freelance science journalist based in the U.K. Reach him at

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