# Checkmate Pharmaceuticals
Checkmate Pharmaceuticals, Inc. was a clinical-stage immuno-oncology biotechnology company incorporated in Delaware in July 2015, headquartered in [Cambridge, Massachusetts](https://www.edgepedia.org/cambridge-massachusetts), and built around a single drug candidate, vidutolimod (CMP-001), a [Toll-like receptor](https://www.edgepedia.org/toll-like-receptor) 9 (TLR9) agonist delivered in a virus-like particle. [Regeneron Pharmaceuticals](https://www.edgepedia.org/regeneron-pharmaceuticals) acquired the company in May 2022 for $10.50 per share in cash, an equity value of approximately $250 million, and Checkmate's stock ceased trading on Nasdaq.[1](https://www.sec.gov/Archives/edgar/data/872589/000110465922066277/tm2215205d3_ex99-a5a.htm) • [2](https://www.sec.gov/Archives/edgar/data/1651431/000119312521244686/d201063d10q.htm)
| Key fact | Detail |
|---|---|
| Founded | July 2015, Delaware incorporation; headquartered in Cambridge, MA[2](https://www.sec.gov/Archives/edgar/data/1651431/000119312521244686/d201063d10q.htm) |
| Founder | Art Krieg, who first reported immunostimulatory CpG DNA in 1995[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm) |
| Lead product | Vidutolimod (CMP-001), a TLR9 agonist CpG-A oligonucleotide in a Qbeta bacteriophage virus-like particle[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm) • [4](https://www.sec.gov/Archives/edgar/data/1651431/000119312522088386/d275568d10k.htm) |
| Venture rounds | $20.0M Series A (2015); $27.0M Series B (2017) plus ~$22M extensions; $85.0M Series C (2020) (unverified)[5](https://biobase.whitefordresearch.com/companies/checkmate-pharmaceuticals) |
| IPO | August 2020, 5.0M shares at $15.00, $75.0M gross, ~$67.7M net, Nasdaq: CMPI[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm) • [2](https://www.sec.gov/Archives/edgar/data/1651431/000119312521244686/d201063d10q.htm) |
| Outcome | Acquired by Regeneron, announced April 19, 2022, completed May 31, 2022, ~$250M equity value at $10.50/share[6](https://www.sec.gov/Archives/edgar/data/872589/000110465922047376/tm2213041d1_ex99-1.htm) • [1](https://www.sec.gov/Archives/edgar/data/872589/000110465922066277/tm2215205d3_ex99-a5a.htm) |
## Founding and scientific origin
The company's science came from work done two decades before its founding. Art Krieg first reported the discovery of immunostimulatory cytosine-phosphate-guanine (CpG) DNA in 1995; with the later discovery of TLR9, the immune receptor that senses it, researchers recognized that synthetic CpG-A oligonucleotides could stimulate TLR9 therapeutically.[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm) Checkmate was incorporated under Delaware law in July 2015 to develop that idea as an injected cancer therapy.[2](https://www.sec.gov/Archives/edgar/data/1651431/000119312521244686/d201063d10q.htm)
## What vidutolimod is and how it works
CMP-001 paired a bacterial virus shell with immune-stimulating DNA. Vidutolimod consists of two components: a capsid protein produced by fermentation and derived from a Qbeta RNA bacteriophage, and a DNA oligonucleotide manufactured by solid-phase synthesis. The two intermediates, called Qb and G10, are combined in an aqueous salt buffer, where they self-assemble into virus-like particles (VLPs) before final purification.[4](https://www.sec.gov/Archives/edgar/data/1651431/000119312522088386/d275568d10k.htm)
Regeneron, after the acquisition, described vidutolimod as an advanced-generation CpG-A oligodeoxynucleotide TLR9 agonist delivered in a VLP that had demonstrated clinical responses as a monotherapy in patients with PD-1 refractory (melanoma that no longer responds to PD-1 checkpoint-inhibitor immunotherapy) melanoma.[1](https://www.sec.gov/Archives/edgar/data/872589/000110465922066277/tm2215205d3_ex99-a5a.htm) According to Checkmate's IPO prospectus, when injected into a tumor the VLP was designed to trigger the innate immune system, alter the tumor microenvironment, and direct activated anti-tumor T cells against both the injected tumor and distant tumors.[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm)
## Funding history and IPO
Checkmate raised three venture rounds before going public. A $20.0 million Series A had its first sale on August 11, 2015, from Sofinnova Ventures and venBio; the initial Form D reported $10.03 million sold before an amendment reported $20.0 million. A $27.0 million Series B followed on June 2, 2017, led by F-Prime Capital Partners with Sofinnova and venBio participating, and Series B extensions from November 2018 through January 2020 added roughly $22 million. In June 2020 the company completed an $85 million Series C, led by Longitude Capital with Novo Holdings, Omega Funds, Medicxi, Sofinnova, venBio, F-Prime, and Decheng Capital participating. These round figures come from a directory-style compilation of Form D and press records rather than the primary filings or independent reporting, and remain unverified.[5](https://biobase.whitefordresearch.com/companies/checkmate-pharmaceuticals)
The IPO closed on August 11, 2020: 5,000,000 shares at $15.00 per share for $75.0 million gross, $69.75 million before expenses after $5.25 million in underwriting discounts, and approximately $67.7 million in net proceeds including the underwriters' overallotment of 109,861 shares exercised on September 3, 2020.[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm) • [2](https://www.sec.gov/Archives/edgar/data/1651431/000119312521244686/d201063d10q.htm) The company listed on the Nasdaq Global Market as CMPI and held approximately $80.3 million in cash as of June 30, 2020.[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm)
A note on totals: the itemized rounds above sum to roughly $154 million, and the record does not fully reconcile that total with all of the company's reported offerings.[5](https://biobase.whitefordresearch.com/companies/checkmate-pharmaceuticals) • [7](https://www.biospace.com/checkmate-pharmaceuticals-secures-85-million-in-series-c-financing)
## Clinical program
By mid-2020 CMP-001 had been studied in more than 200 melanoma patients, with adverse events described as generally manageable, consisting primarily of flu-like symptoms and injection site reactions.[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm) In the Phase 1b study of CMP-001 combined with pembrolizumab in anti-PD-1 refractory melanoma, the company reported a best objective response rate of 28% as of June 1, 2020, including post-progression responders.[3](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm) In the Phase 1b program, documented abscopal responses, regressions at distant, un-injected lesions, were also observed.[6](https://www.sec.gov/Archives/edgar/data/872589/000110465922047376/tm2213041d1_ex99-1.htm) The $85 million Series C was announced as funding development in anti-PD-1 refractory melanoma, front-line melanoma, and head and neck squamous cell carcinoma; the company also claimed CMP-001 was the only CpG-A oligonucleotide in clinical development at the time, a company statement rather than independent verification.[7](https://www.biospace.com/checkmate-pharmaceuticals-secures-85-million-in-series-c-financing)
## Acquisition by Regeneron and outcome
On April 19, 2022, Regeneron and Checkmate announced a definitive agreement for Regeneron to acquire Checkmate at an all-cash price of $10.50 per share, valuing the company at approximately $250 million in total equity.[6](https://www.sec.gov/Archives/edgar/data/872589/000110465922047376/tm2213041d1_ex99-1.htm) The tender offer expired one minute after 11:59 p.m. ET on May 27, 2022, with 18,471,314 shares, approximately 83.8% of outstanding shares, validly tendered. Regeneron paid $10.50 per share and completed the transaction through a second-step merger on May 31, 2022; Checkmate's stock ceased trading on Nasdaq.[1](https://www.sec.gov/Archives/edgar/data/872589/000110465922066277/tm2215205d3_ex99-a5a.htm)
## References
1. [Regeneron press release: Regeneron Completes Acquisition of Checkmate Pharmaceuticals (May 31, 2022)](https://www.sec.gov/Archives/edgar/data/872589/000110465922066277/tm2215205d3_ex99-a5a.htm)
2. [Checkmate Pharmaceuticals Form 10-Q (2021)](https://www.sec.gov/Archives/edgar/data/1651431/000119312521244686/d201063d10q.htm)
3. [Checkmate Pharmaceuticals Form 424B4 IPO Prospectus (August 2020)](https://www.sec.gov/Archives/edgar/data/1651431/000119312520213729/d913691d424b4.htm)
4. [Checkmate Pharmaceuticals Form 10-K (2022)](https://www.sec.gov/Archives/edgar/data/1651431/000119312522088386/d275568d10k.htm)
5. [Checkmate Pharmaceuticals — Whiteford Research Biobase](https://biobase.whitefordresearch.com/companies/checkmate-pharmaceuticals)
6. [Regeneron/Checkmate acquisition announcement (April 19, 2022)](https://www.sec.gov/Archives/edgar/data/872589/000110465922047376/tm2213041d1_ex99-1.htm)
7. [Checkmate Pharmaceuticals Secures $85 Million in Series C Financing — BioSpace (June 2020)](https://www.biospace.com/checkmate-pharmaceuticals-secures-85-million-in-series-c-financing)
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*Topic: Encyclopedia › Society and history › Economics and business › Business and work › Business and work overview › Companies and corporations › Venture-backed startups and growth companies › Health, biotech, and medtech startups › Small-molecule and chemical drug developers › Oncology drug developers › North American and European oncology drug developers*
*Initially written Sep 17, 2026 · Edited: Oct 11, 2026; Oct 15, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license