Harpoon Therapeutics stock (US4135961044): Merck takeover closes and delisting ends trading chapter

Harpoon Therapeutics has been acquired by Merck in an all?cash deal that has taken the cancer drug developer off the Nasdaq, ending its run as an independent public company. The transaction reshapes the future of its T?cell engager pipeline under big?pharma ownership.

Harpoon Therapeutics has completed its takeover by Merck in an all?cash transaction that has removed the oncology developer from public markets and ended trading in its shares on Nasdaq, according to a company announcement and related securities filings published in March 2024 and updated through the closing of the deal in early 2024 Merck news release as of 01/08/2024 and Harpoon Therapeutics investor news as of 03/20/2024.

As of: 05/14/2026

By the editorial team – specialized in equity coverage.

At a glance

• Name: Harpoon Therapeutics
• Sector/industry: Biotechnology / oncology drug development
• Headquarters/country: South San Francisco, United States
• Core markets: Experimental cancer therapies with a focus on the US and global pharmaceutical markets
• Key revenue drivers: Collaboration and licensing income plus potential future milestone and royalty streams from its T?cell engager pipeline
• Home exchange/listing venue: Formerly Nasdaq (ticker: HARP)
• Trading currency: US dollar (before delisting)

Harpoon Therapeutics: core business model

Harpoon Therapeutics has been a clinical?stage biotechnology company focused on developing T?cell engager therapies for solid tumors and hematologic cancers. Its technology platform has aimed to redirect a patient’s own immune cells to recognize and attack tumor cells, using engineered proteins designed to bring T cells and cancer cells into close proximity, according to corporate descriptions in its investor materials and regulatory filings that were active while the stock still traded on Nasdaq Harpoon Therapeutics company overview as of 12/31/2023.

The company’s strategy centered on discovering and advancing product candidates that could improve on traditional T?cell engagers in terms of safety, dosing convenience and tumor targeting. The pipeline included several investigational molecules targeting antigens associated with solid tumors, as well as earlier stage programs that had potential applications in hematologic malignancies and possibly autoimmune diseases, based on information provided in prior pipeline updates around late 2023 and early 2024 Harpoon Therapeutics pipeline snapshot as of 11/02/2023.

Harpoon Therapeutics operated in a capital?intensive segment of the biotech sector, which typically requires repeated access to the equity markets or to partnership financing to fund multi?year clinical programs. As with many early?stage oncology developers, it had no approved products on the market when Merck moved to acquire the company, and its historical revenues primarily consisted of collaboration and license income plus research funding from larger pharmaceutical partners.

Main revenue and product drivers for Harpoon Therapeutics

Before the Merck acquisition, Harpoon Therapeutics’ economics were strongly linked to its lead product candidates and related partnership structures. The company’s disclosures highlighted HPN328, a DLL3?targeting T?cell engager for certain tumors including small cell lung cancer, as a central asset. Another notable candidate, HPN217, targeted BCMA, a protein associated with multiple myeloma. Both candidates were in clinical development phases during 2023–2024, and their trial progress represented key value drivers, according to company updates on ongoing studies and collaborations Harpoon Therapeutics clinical overview as of 11/02/2023.

Revenue for Harpoon Therapeutics largely came from upfront and milestone payments under collaboration agreements with major pharmaceutical companies, as opposed to product sales. These agreements typically provided research funding and the potential for additional development, regulatory and commercial milestones, alongside royalties on future sales if product candidates were approved and commercialized. For US investors tracking the stock before its delisting, the timing and size of such milestone events often influenced sentiment around Harpoon’s cash runway and negotiating leverage.

Because the company was still loss?making when it agreed to be acquired by Merck, its earnings profile reflected significant research and development expenses, including clinical trial costs, manufacturing scale?up for investigational products and general corporate overhead. The ability to manage cash while advancing multiple assets was therefore central to its long?term outlook. The Merck deal effectively shifted those funding requirements from public shareholders to a diversified pharmaceutical group with substantially greater resources.

Merck acquisition and delisting reshape the investment story

Merck announced an agreement to acquire Harpoon Therapeutics in an all?cash transaction valued at approximately $680 million, with the deal structured as a tender offer followed by a merger. The announcement in January 2024 described the acquisition as part of Merck’s strategy to expand its oncology pipeline, particularly in the field of T?cell engagers, according to an official press release detailing the rationale and financial terms of the transaction Merck news release as of 01/08/2024.

The agreed per?share price represented a premium over Harpoon Therapeutics’ undisturbed trading price prior to the deal announcement, based on figures discussed in the merger communication and subsequent commentary in financial media. Following the tender offer and satisfaction of customary closing conditions, Harpoon became a wholly owned subsidiary of Merck, and its common stock ceased trading on Nasdaq. A related notice from the company and the exchange confirmed the delisting and termination of Harpoon’s public reporting obligations under US securities law Harpoon Therapeutics merger completion notice as of 03/20/2024.

For retail investors in the United States, the closing of the transaction marked the final opportunity to participate in Harpoon Therapeutics as a standalone equity story. Shareholders whose stock was not tendered before the closing date were typically cashed out at the deal price in the subsequent merger step, in line with standard practices for such all?cash acquisitions. After completion, Harpoon’s business, pipeline and employees became integrated into Merck’s broader oncology portfolio.

From Merck’s perspective, the acquisition added clinical?stage assets targeting difficult?to?treat cancers and complemented existing immuno?oncology programs. By absorbing Harpoon’s R&D infrastructure, Merck gained direct control over development timelines, trial design and partnering decisions. For former Harpoon shareholders, the takeover crystallized the company’s value at the agreed cash price, shifting any upside or downside from future clinical outcomes to Merck’s investors instead.

Implications for the former Harpoon Therapeutics stock and US investors

Because Harpoon Therapeutics is no longer listed, there is no ongoing public market price for the stock. Investors who followed the name while it traded on Nasdaq now primarily encounter it in the context of Merck’s oncology pipeline. For US investors, exposure to Harpoon’s underlying programs has effectively migrated into Merck’s diversified portfolio, which trades on the New York Stock Exchange and reflects a much broader mix of pharmaceutical and vaccine products alongside early?stage research initiatives.

The fact that a large pharmaceutical company was willing to acquire Harpoon Therapeutics for several hundred million dollars underscores how strategic T?cell engagers and similar immunotherapies have become within oncology. The deal highlights a common pattern in the US biotech ecosystem, where smaller, innovation?driven companies rely on partnerships or takeovers by larger players to move promising candidates through late?stage development and commercialization. In such scenarios, the public?market window for pure?play exposure to specific technologies can be short.

For investors reviewing past transactions in the biotech sector, the Harpoon case provides an example of how clinical?stage companies may deliver returns primarily through strategic deals rather than through long?term, standalone profitability. It also illustrates the importance of monitoring cash positions, partnership structures and big?pharma interest when evaluating similar oncology developers in the US market. Once an acquisition closes, liquidity and pricing are determined by the deal terms rather than ongoing trading activity.

Conclusion

The completed acquisition of Harpoon Therapeutics by Merck has closed the chapter on Harpoon as an independently traded biotech stock and shifted its T?cell engager programs into a large?cap pharmaceutical portfolio. For former shareholders and US investors more broadly, the transaction underlines how value in early?stage oncology often crystallizes through strategic deals rather than long?term standalone commercialization. Future progress of Harpoon’s former pipeline will now be reflected in Merck’s broader share performance rather than in a dedicated listing.

Disclaimer: This article does not constitute investment advice. Stocks are volatile financial instruments.