# Kolltan Pharmaceuticals
Kolltan Pharmaceuticals, Inc. was a clinical-stage biopharmaceutical company based in [New Haven, Connecticut](https://www.edgepedia.org/new-haven-connecticut), that developed antibody-based drugs targeting receptor tyrosine kinases (RTKs) for cancer. It was founded in 2007 by Dr. [Joseph Schlessinger](https://www.edgepedia.org/joseph-schlessinger) and Arthur Altschul, Jr., licensed its founding intellectual property from Yale University, and commenced operations in 2008.[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) In November 2016 it was acquired by Celldex Therapeutics in a stock deal worth up to about $235 million.[2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm)
| Fact | Detail |
|---|---|
| Founded | 2007, by Joseph Schlessinger and Arthur G. Altschul, Jr.; operations from 2008[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) |
| Headquarters | New Haven, Connecticut, adjacent to the Yale Medical School[3](https://www.prnewswire.com/news-releases/kolltan-pharmaceuticals-obtains-60-million-in-series-d-financing-252425461.html) |
| Sector | Biotechnology; antibodies against receptor tyrosine kinases for oncology[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) |
| CEO | Dr. Gerald McMahon (President and CEO)[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) |
| Total raised | About $75 million cumulative by early 2014[4](https://hartfordbusiness.com/article/startups-cancer-therapy-preps-for-2014-clinical-trials/) • [3](https://www.prnewswire.com/news-releases/kolltan-pharmaceuticals-obtains-60-million-in-series-d-financing-252425461.html) |
| Lead candidates | KTN3379 (anti-ErbB3, Phase 1/1b) and KTN0158 (anti-KIT, Phase 1 in GIST)[2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm) |
| Outcome | Acquired by Celldex Therapeutics; merger agreement November 1, 2016[2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm) |
## Founding and the Yale connection
Kolltan grew out of RTK research in the Yale laboratory of co-founder Dr. Joseph Schlessinger.[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) Fierce Biotech described Schlessinger and Altschul as two of the principals behind Plexxikon, and noted that CEO Gerald McMahon had worked with them at SUGEN before Pfizer acquired that company.[5](https://www.fiercebiotech.com/biotech/cancer-r-d-stars-pitch-an-86m-biotech-ipo-for-kolltan-pharma)
McMahon himself had been at SUGEN and MedImmune; while at MedImmune he was involved in developing KTN3379, which Kolltan later licensed from MedImmune.[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) That license, signed in July 2013, gave Kolltan exclusive rights to its lead product.[4](https://hartfordbusiness.com/article/startups-cancer-therapy-preps-for-2014-clinical-trials/)
## Pipeline and science
Kolltan's candidates were monoclonal antibodies designed to shut specific RTKs off.
**KTN3379** was a human monoclonal antibody against ErbB3 (HER3). The company described it as a dual-mechanism antibody, designed to block ErbB3 activation whether or not the receptor was being activated by its ligand, neuregulin.[3](https://www.prnewswire.com/news-releases/kolltan-pharmaceuticals-obtains-60-million-in-series-d-financing-252425461.html) It entered Phase 1 testing in adults with advanced solid tumors,[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) and by the time of the acquisition a Phase 1b study had shown meaningful responses and stable disease in cetuximab (Erbitux)-refractory patients with head and neck squamous cell carcinoma and in BRAF-mutant non-small cell lung cancer.[2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm)
**KTN0158** was a humanized antibody targeting KIT. Kolltan applied insights into the x-ray crystal structure of KIT from Schlessinger's Yale laboratory to find a distinct way to inhibit the receptor; KTN0158 prevents KIT activation by blocking receptor dimerization.[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) • [2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm) At the time of the acquisition it was in a Phase 1 [dose-escalation study](https://www.edgepedia.org/dose-escalation-study) in refractory gastrointestinal stromal tumors (GIST).[2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm)
## Funding history
Kolltan raised over $35 million in its Series A preferred stock financing, from investors including [Purdue Pharma](https://www.edgepedia.org/purdue-pharma), L.P., HBM Capital Partners, and the Pritzker/Vlock family, along with other private life science investors.[6](https://www.fiercebiotech.com/biotech/kolltan-pharmaceuticals-raises-over-35-million-series-a-financing) By late 2013 and early 2014 the company had raised about $75 million cumulatively.[4](https://hartfordbusiness.com/article/startups-cancer-therapy-preps-for-2014-clinical-trials/)
On March 26, 2014 Kolltan announced a $60 million Series D financing led by a new Boston-based institutional asset manager and existing investor KLP Enterprises, with [Deerfield Management](https://www.edgepedia.org/deerfield-management), Franklin Berger, HBM Healthcare Investments, Purdue Pharma, and [Osage University Partners](https://www.edgepedia.org/osage-university-partners) participating. Proceeds were earmarked to advance KTN3379 into Phase 2 trials; the company had initiated its first clinical trial in January 2014.[3](https://www.prnewswire.com/news-releases/kolltan-pharmaceuticals-obtains-60-million-in-series-d-financing-252425461.html) Elm Street Ventures, an early investor, listed Fidelity, KLP Enterprises, Gilead Sciences, and Auven Therapeutics among its co-investors across the Series A and Series D.[7](https://www.elmvc.com/project/kolltan/)
In 2014 Kolltan filed a Form S-1 for an initial public offering that Fierce Biotech reported as an $86 million offering; the IPO was later withdrawn and the company raised the private Series D instead.[1](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm) • [5](https://www.fiercebiotech.com/biotech/cancer-r-d-stars-pitch-an-86m-biotech-ipo-for-kolltan-pharma)
## Acquisition by Celldex Therapeutics
On November 1, 2016 Celldex Therapeutics agreed to acquire Kolltan in a stock-for-stock transaction. The upfront payment represented an equity value of approximately $62.5 million in Celldex stock, with Kolltan shareholders eligible for up to $172.5 million in additional payments on development, regulatory, and commercial milestones, a potential total of about $235 million.[2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm) Endpoints News framed the deal as a bolt-on acquisition of a clinical-stage antibody developer, executed after a Celldex Phase III failure.[8](https://endpoints.news/post-phiii-implosion-celldex-buys-oncology-drug-developer-kolltan-in-235m-deal/)
With the acquisition, Celldex's clinical pipeline grew to seven drug candidates, including therapeutic antibodies, antibody-drug conjugates, and immune system modulators.[2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm)
## Business and traction
Kolltan ran a licensing-plus-discovery model: it initiated clinical trials for its first drug, licensed from MedImmune, while building an internal pipeline from Yale-anchored RTK research.[7](https://www.elmvc.com/project/kolltan/) The company worked in close collaboration with Schlessinger's laboratory and with Yale's medical and scientific community, and was located adjacent to the Yale Medical School.[2](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm) • [3](https://www.prnewswire.com/news-releases/kolltan-pharmaceuticals-obtains-60-million-in-series-d-financing-252425461.html)
## References
1. [Kolltan Pharmaceuticals Form S-1 (SEC EDGAR, 2014)](https://www.sec.gov/Archives/edgar/data/1442835/000104746914007587/a2221359zs-1.htm)
2. [Celldex Therapeutics press release, acquisition announcement and terms (SEC 8-K exhibit, Nov 1, 2016)](https://www.sec.gov/Archives/edgar/data/744218/000110465916153723/a16-20866_1ex99d1.htm)
3. [Kolltan Pharmaceuticals Obtains $60 Million in Series D Financing (PR Newswire, March 26, 2014)](https://www.prnewswire.com/news-releases/kolltan-pharmaceuticals-obtains-60-million-in-series-d-financing-252425461.html)
4. [Hartford Business Journal: Startup's cancer therapy preps for 2014 clinical trials](https://hartfordbusiness.com/article/startups-cancer-therapy-preps-for-2014-clinical-trials/)
5. [Fierce Biotech: Cancer R&D stars pitch an $86M biotech IPO for Kolltan Pharma](https://www.fiercebiotech.com/biotech/cancer-r-d-stars-pitch-an-86m-biotech-ipo-for-kolltan-pharma)
6. [Fierce Biotech: Kolltan Pharmaceuticals Raises over $35 Million in Series A Financing](https://www.fiercebiotech.com/biotech/kolltan-pharmaceuticals-raises-over-35-million-series-a-financing)
7. [Elm Street Ventures — Kolltan project page](https://www.elmvc.com/project/kolltan/)
8. [Endpoints News: Post-PhIII implosion, Celldex buys oncology drug developer Kolltan in $235M deal](https://endpoints.news/post-phiii-implosion-celldex-buys-oncology-drug-developer-kolltan-in-235m-deal/)
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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 › Biologics and antibody developers › Oncology biologics developers › Radiopharma and targeted oncology biologics*
*Initially written Sep 17, 2026 · Edited: Oct 11, 2026; Oct 15, 2026; Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license