Merck (MRK) - Get Report is throwing a cancer-immunotherapy party and has invited several friends. 

In three separate collaboration agreements announced Wednesday, Merck is planning clinical trials to combine its anti-PD-1 immunotherapy MK-3475 with complimentary anti-cancer compounds owned by Amgen (AMGN) - Get Report, Incyte (INCY) - Get Report and Pfizer (PFE) - Get Report. Financial terms of the agreements were not disclosed. 

The new collaborations are significant because they help Merck close the competitive gap with Bristol-Myers Squibb (BMY) - Get Report, which is largely viewed as the front runner in the race to develop the new class of anti-PD-1 immunotherapies, which work by releasing a brake on the patient's immune system to better recognize and kill tumors. 

Bristol has been developing its anti-PD-1 nivolumumab as a monotherapy and in combination with other drugs, including Yervoy. Merck is now mimicking that playbook, studying MK-3475 (also known as lambrolizumab) and in combination therapy. 

"Merck clinical scientists intend to explore the potential of our PD-1 inhibitor across a wide range of cancers, both as monotherapy and in combination," said Roger Perlmutter, Merck's top scientist in charge of R&D. "These new collaborations with Amgen, Incyte and Pfizer underscore our shared determination to evaluate treatment regimens with the potential to provide meaningful benefits to patients suffering from cancer."

The collaboration between Merck and Amgen is a homecoming of sorts for Perlmutter, who used to run Amgen's drug development operations. Merck will study MK-3475 in combination with Amgen's oncolytic vaccine T-Vec in a phase I/II study in patients with previously untreated advanced melanoma. Perlmutter was responsible for bringing T-Vec into Amgen through an acquisition, so it's a therapy he knows well.

Merck will also be collaborating with Incyte to combine MK-3475 with INCB24360, a so-called "IDO inhibitor," in a study of patients with non-small cell lung cancer and other metastatic cancers. 

Finally, Merck plans to evaluate MK-3474 with two Pfizer drugs -- Inlyta and PF-2566 -- in kidney and other cancers. 

"Merck now seems to get that the PD-1 cancer race is hyper-hyper-hyper competitive, and as such, now seems to be picking up the pace of its announcements," writes ISI Group analyst Mark Schoenebaum in an email to investor clients this morning. 

Earlier this month, Merck surprised investors by announcing that MK-3475 would be filed for approval with the FDA sooner than expected for skin cancer patients who no longer respond to Bristol's Yervoy. 

Of the three collaborations announced today, Schoenebaum points to the combination with Incyte's INCB24360 as the most significant because IDO inhibitors have "generated significant buzz among investors and doctors as a promising immuno-oncology approach that could be complimentary to PD-1."

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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