Merck Acquires Harpoon Therapeutics for $680 Million To Diversify Cancer Immunotherapies

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Merck has announced a definitive agreement to acquire clinical-stage biotech Harpoon Therapeutics for $23 per share in an all-cash deal valued at approximately $680 million. The acquisition provides Merck with Harpoon’s promising pipeline of novel T-cell engager immunotherapies that harness the body’s immune system to treat cancer.

Harpoon’s lead asset is HPN328, an investigational T-cell engager targeting delta-like ligand 3 (DLL3) for the treatment of small cell lung cancer (SCLC) and other neuroendocrine tumors expressing DLL3. HPN328 directs a patient’s T-cells to kill tumor cells displaying DLL3. In October 2022, Harpoon reported positive interim data from the ongoing Phase 1/2 trial showing encouraging tolerability and early signs of efficacy for HPN328.

The acquisition expands Merck’s burgeoning oncology portfolio, adding a new modality to its toolkit. “This agreement reflects the creativity and commitment of scientists and clinical development teams at Harpoon. We look forward to further evaluating HPN328 in innovative combinations with other pipeline candidates,” stated Dr. Dean Y. Li, President of Merck Research Laboratories.

Harpoon’s TriTAC and ProTriTAC Platforms

Beyond HPN328, Merck also gains Harpoon’s proprietary TriTAC and ProTriTAC platforms for developing novel T-cell engagers. TriTACs (tri-specific T-cell activating constructs) are engineered protein therapies designed to recruit a patient’s immune cells to attack tumor cells. The ProTriTAC platform applies a prodrug concept to remain inactive until reaching the tumor site.

Harpoon has an extensive pipeline of TriTAC candidates against various cancer targets, including:

  • HPN217: Targets B-cell maturation antigen (BCMA) for relapsed/refractory multiple myeloma, currently in Phase 1.
  • HPN601: Targets epithelial cell adhesion molecule (EpCAM) for solid tumors expressing EpCAM.
  • HPN424: Targets delta-like ligand 4 (DLL4) for solid tumors.
  • Other preclinical TriTACs targeting tumor antigens like NaPi2b, FLT3, and DLL3.

The platforms offer modular designs to quickly generate and test new immunotherapies directed to disease-specific targets. Merck can leverage these platforms to strengthen its immunotherapy pipeline in cancer and possibly other disease areas.

Merck Building an Oncology Powerhouse

Cancer immunotherapies represent the next wave of innovation in oncology drug development. The Harpoon acquisition aligns with Merck’s strategy to establish leadership in immuno-oncology.

Merck already markets the blockbuster PD-1 checkpoint inhibitor Keytruda, approved for 30 different cancer indications. Keytruda generated $17.2 billion in sales in 2021. Now with Harpoon, Merck adds T-cell engagers to its arsenal. These therapies provide another way to leverage the immune system against hard-to-treat tumors like SCLC.

Merck is also developing numerous other novel agents across various modalities:

  • Cancer vaccines targeting specific tumor mutations (Personalized Cancer Vaccine, V590, V591)
  • Antibody-drug conjugates (belantamab mafodotin, ladiratuzumab vedotin)
  • Bispecific fusion proteins targeting both PD-1 and LAG-3
  • First-in-class inhibitors (MK-6482, KL-A)

Combined with its extensive capabilities in discovery research and clinical development, Merck is positioning itself as an oncology powerhouse able to take on cancers from all angles.

The Harpoon acquisition provides another building block in this strategy. In Harpoon’s pipeline and platforms, Merck gains cutting-edge T-cell engager capabilities to complement internal immuno-oncology programs. Merck can advance Harpoon’s therapies into new combination regimens and indications to maximize their potential.

Deal Details

Under the terms of the agreement, Merck will acquire Harpoon through a subsidiary, purchasing all outstanding Harpoon shares for $23 each in cash. This represents a premium of 118% over Harpoon’s previous closing share price.

The deal has been approved by Harpoon’s Board of Directors and is expected to close in the first half of 2024, pending shareholder approval and regulatory clearances. It will be accounted for as an asset acquisition by Merck.

Harpoon shareholders will vote on the acquisition at a future shareholder meeting. The waiting period under the Hart-Scott-Rodino Antitrust Improvements Act will also need to expire.

Advisors on the deal include Evercore Group for Merck and Centerview Partners for Harpoon.

With promising new immunotherapies and platforms adding to its robust oncology pipeline, Merck strengthens its leadership in the high-growth cancer drug market. The Harpoon acquisition provides Merck with new T-cell engager capabilities to help develop life-changing medicines for patients with cancer worldwide.


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