Rumour mill says MSD is hunting Harpoon Therapeutics

MSD’s 2023 run of pipeline-building deals looks like it could continue into this year, with reports already emerging that the company is in talks to buy Harpoon Therapeutics and its T-cell engager programmes.

The rumour, first reported by Bloomberg, puts a price tag of around $700 million on Harpoon, which had a market cap of around $180 million based on its last closing share price of just over $10. The stock has, however, rocketed to more than $21 in pre-market trading on the back of the report.

Harpoon has developed a new class of ‘TriTAC’ T-cell engagers – based on engineered trispecific proteins that recruit the body’s immune system to target and kill cancer cells – and is developing its own pipeline of candidates, as well as partnering with Roche and AbbVie.

The TriTACs are designed to have an extended serum half-life and be about one-third the size of a monoclonal antibody, making them more likely to penetrate solid tumours and potentially easier to make and administer than personalised or cell-based cancer immunotherapies.

One of its lead candidates – DLL3-targeting HPN328 – is being tested alongside Roche’s PD-L1 inhibitor Tecentriq (atezolizumab) for small cell lung cancer (SCLC), neuroendocrine prostate cancer (NEPC), and other neuroendocrine tumours in phase 1 trials.

It has also started clinical testing of a BCMA-directed candidate called HPN217 as a potential therapy for blood cancer multiple myeloma, and its preclinical portfolio includes an AbbVie-partnered TriTAC that has emerged from a 2019 alliance between the two companies worth up to $2.4 billion.

In December, Harpoon reported phase data on HPN217 at the ASH haematology meeting that showed encouraging signs of efficacy and safety in heavily pre-treated relapsed/refractory multiple myeloma patients, including an overall response rate of 63%.

MSD – known as Merck & Co in North America – is reported to be planning an offer of $23 per share for Harpoon, with a deal ready for announcement within the next few days, according to Bloomberg, which has cited people familiar with the matter.

If the deal goes through, it will extend a series of bolt-on deals for MSD in 2023, headed by an alliance with Daiichi Sankyo on antibody-drug conjugates for cancer that included a whopping $4 billion upfront payment and a top-line value of up to $22 billion.

Other deals that were announced or closed last year included a $10.8 billion buyout of immunological drug developer Prometheus Biosciences, a $1.35 billion takeover of Imago BioSciences and its portfolio of blood cancer candidates, and a $610 million takeover bid for neurodegenerative disease specialist Carraway Therapeutics.