# Xilio Therapeutics
Xilio Therapeutics, Inc. is a clinical-stage biotechnology company headquartered in [Waltham, Massachusetts](https://www.edgepedia.org/waltham-massachusetts), incorporated in Delaware in June 2020 and traded on Nasdaq under the ticker XLO, which discovers and develops masked (tumor-activated) immuno-oncology therapies.[1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b) • [2](https://www.sec.gov/Archives/edgar/data/1840233/000119312526187691/2026_04_28_-_ars.pdf) • [3](https://www.biospace.com/press-releases/xilio-therapeutics-reports-second-quarter-2026-financial-results-and-provides-pipeline-and-business-updates) Its lead clinical asset is vilastobart, a tumor-activated anti-CTLA-4 antibody formerly designated XTX101, and its lead next-generation program is XTX501, a bispecific PD-1/masked IL-2 molecule that entered clinical development in 2026.[2](https://www.sec.gov/Archives/edgar/data/1840233/000119312526187691/2026_04_28_-_ars.pdf) • [3](https://www.biospace.com/press-releases/xilio-therapeutics-reports-second-quarter-2026-financial-results-and-provides-pipeline-and-business-updates)
| Fact | Detail |
|---|---|
| Legal name and listing | Xilio Therapeutics, Inc. (Nasdaq: XLO), incorporated in Delaware June 2020, HQ Waltham, MA[1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b) • [3](https://www.biospace.com/press-releases/xilio-therapeutics-reports-second-quarter-2026-financial-results-and-provides-pipeline-and-business-updates) |
| Origin | Began as Akrevia Therapeutics; rebranded to Xilio Therapeutics in 2020[4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics) |
| IPO | October 2021, 8,119,106 shares at $16.00, $116.4 million in proceeds[5](https://www.sec.gov/Archives/edgar/data/1840233/000155837023002687/R8.htm) |
| Lead clinical asset | Vilastobart (formerly XTX101), tumor-activated Fc-enhanced anti-CTLA-4[2](https://www.sec.gov/Archives/edgar/data/1840233/000119312526187691/2026_04_28_-_ars.pdf) |
| Major pharma deals | Roche trial collaboration (2023, $8.0M cost-sharing received); Gilead license ($43.5M upfront, 2024); AbbVie option-to-license ($52.0M upfront, up to ~$2.1B contingent, 2025)[1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b) • [4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics) • [6](https://www.prnewswire.com/news-releases/abbvie-and-xilio-therapeutics-announce-collaboration-and-option-agreement-to-develop-novel-tumor-activated-immunotherapies-302371535.html) |
| Financial position | Accumulated deficit of $429.1 million at September 30, 2025; going-concern doubt disclosed[1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b) |
| Status (August 2026) | Operating, publicly traded clinical-stage company[3](https://www.biospace.com/press-releases/xilio-therapeutics-reports-second-quarter-2026-financial-results-and-provides-pipeline-and-business-updates) |
## History and funding
The company originated as Akrevia Therapeutics and rebranded as Xilio Therapeutics in 2020; the legal entity Xilio Therapeutics, Inc. was incorporated in Delaware in June 2020.[4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics) • [1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b) As a private company it raised three reported venture rounds: a $30.0 million Series A closed September 27, 2018, led by F-Prime Capital Partners and Atlas Venture; a $100.5 million Series B closed March 2, 2020, with Takeda Ventures, SV Health Investors, MRL Ventures Fund, RiverVest, Bay City Capital, Solasta Ventures, M Ventures, Ipsen Ventures, F-Prime, and Atlas; and a $95.0 million Series C closed February 24, 2021, with Rock Springs Capital, Bain Capital Life Sciences, Deerfield Management, RA Capital Management, and others.[4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics) These round figures come from an industry database rather than the company's own filings.[4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics)
Xilio went public in October 2021. According to an SEC filing exhibit, the IPO closed with an aggregate of 8,119,106 shares sold, including 766,106 shares from a partial exercise of the underwriters' option, at a public offering price of $16.00 per share, generating $116.4 million in proceeds.[5](https://www.sec.gov/Archives/edgar/data/1840233/000155837023002687/R8.htm)
After 2023 the company relied on a sequence of partnerships and dilutive financings:
- **March 2024:** [Gilead Sciences](https://www.edgepedia.org/gilead-sciences) paid $43.5 million upfront ($30.0 million cash plus $13.5 million in equity at $1.97 per share) in a strategic license and equity investment; a same-day private placement raised $11.3 million gross from Bain Capital Life Sciences, Rock Springs Capital, and other existing investors at $0.64 per share.[4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics)
- **February 2025:** AbbVie collaboration and option-to-license agreement on tumor-activated, antibody-based immunotherapies including masked T-cell engagers: $52.0 million in total upfront payments including a $10.0 million equity investment, with eligibility for up to approximately $2.1 billion in contingent payments plus tiered royalties.[6](https://www.prnewswire.com/news-releases/abbvie-and-xilio-therapeutics-announce-collaboration-and-option-agreement-to-develop-novel-tumor-activated-immunotherapies-302371535.html)
- **June 2025:** a follow-on public offering of prefunded warrants and accompanying common stock warrants brought initial gross proceeds of $50.0 million, with potential for up to $100.0 million more on cash exercise at $0.75 per warrant.[1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b)
- **January 2026:** Series B warrant exercises brought $35.8 million gross at $0.75 per share from Coastlands Capital, Frazier Life Sciences, and Gilead Sciences.[4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics)
- **February 2026:** a follow-on offering raised $40.0 million gross ($37.3 million net) from Coastlands Capital, OrbiMed, Perceptive Advisors, and Gilead Sciences.[4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics)
The trajectory of pricing is stark: the IPO priced at $16.00 per share in 2021, while the 2024 private placement priced at $0.64 and the 2025–2026 financings at roughly $0.75.[5](https://www.sec.gov/Archives/edgar/data/1840233/000155837023002687/R8.htm) • [4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics) As of September 30, 2025, the company reported an accumulated deficit of $429.1 million and net losses of $45.4 million for the first nine months of 2025, and its 10-Q stated there is substantial doubt about the company's ability to continue as a going concern within twelve months of issuance.[1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b)
## Technology and pipeline
Xilio's platform consists of masked biologics that remain inactive until they reach the tumor microenvironment, where they are unmasked by tumor-specific matrix metalloproteases (MMPs) and other tumor-specific proteases.[7](https://xiliotx.com/) The intent is to confine immune activation to tumors and avoid the systemic toxicity that has limited conventional immuno-oncology agents; the company frames the problem against the history of non-masked CTLA-4 therapy dating to ipilimumab's first FDA approval in 2011.[2](https://www.sec.gov/Archives/edgar/data/1840233/000119312526187691/2026_04_28_-_ars.pdf)
**Vilastobart (formerly XTX101)** is an investigational tumor-activated, Fc-enhanced, high-affinity anti-CTLA-4 monoclonal antibody designed to block CTLA-4 and deplete regulatory T cells when activated in the tumor microenvironment.[2](https://www.sec.gov/Archives/edgar/data/1840233/000119312526187691/2026_04_28_-_ars.pdf) Its dual mechanism combines CTLA-4 blockade and co-stimulation, which lower the threshold for priming naive T cells against lower-quality neoantigens, with regulatory [T cell](https://www.edgepedia.org/t-cell) depletion that reduces immune-suppressive signaling and drives polyclonal CD8 T cell expansion.[2](https://www.sec.gov/Archives/edgar/data/1840233/000119312526187691/2026_04_28_-_ars.pdf)
**XTX501** is a bispecific PD-1/masked IL-2 antibody fusion protein, described by the company as a potential foundational "backbone" therapy for combination treatment. In preclinical studies it demonstrated robust monotherapy activity, including in settings insensitive to PD-1 therapy, and tumor-selective pharmacodynamics consistent with its intended mechanism.[8](https://www.globenewswire.com/news-release/2026/05/12/3292720/0/en/Xilio-Therapeutics-Reports-First-Quarter-2026-Financial-Results-and-Provides-Pipeline-and-Business-Updates.html) The FDA cleared its investigational new drug application for a Phase 1/2 trial, with dosing in metastatic non-small cell lung cancer and select advanced solid tumors expected to begin in the second half of 2026 and initial Phase 1 NSCLC data planned for the second half of 2027.[3](https://www.biospace.com/press-releases/xilio-therapeutics-reports-second-quarter-2026-financial-results-and-provides-pipeline-and-business-updates)
The company is also building masked T-cell engagers in two formats: the ATACR format, which masks the CD3-binding domain, and the SEECR tri-specific format, which adds co-stimulatory signaling. Wholly owned programs target the tumor-associated antigens PSMA, CLDN18.2, and STEAP1, alongside an additional program in collaboration with AbbVie.[9](https://ir.xiliotx.com/news-releases/news-release-details/xilio-therapeutics-announces-pipeline-and-business-updates-and-9)
## Partnerships
In July 2023, Xilio and F. Hoffmann-La Roche entered a clinical trial collaboration under a clinical supply agreement to evaluate vilastobart in combination with atezolizumab (Tecentriq) in a Phase 1/2 trial: Phase 1 dose escalation in advanced solid tumors and Phase 2 in microsatellite-stable metastatic colorectal cancer. As of September 30, 2025, Xilio had received $8.0 million in Roche cost-sharing payments and retains global development and commercialization rights to vilastobart.[1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b) The Gilead license of March 2024, reported by an industry database, and the company-announced AbbVie option-to-license of February 2025 are described above.[4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics) • [6](https://www.prnewswire.com/news-releases/abbvie-and-xilio-therapeutics-announce-collaboration-and-option-agreement-to-develop-novel-tumor-activated-immunotherapies-302371535.html)
## Clinical traction and status
Vilastobart remains in a Phase 1c combination dose escalation with atezolizumab in advanced solid tumors and a Phase 2 trial in metastatic microsatellite-stable colorectal cancer, with and without liver metastases, under the co-funded Roche collaboration.[9](https://ir.xiliotx.com/news-releases/news-release-details/xilio-therapeutics-announces-pipeline-and-business-updates-and-9) As of August 2026 the company is operating and publicly traded, with XTX501 cleared to enter the clinic and two wholly owned masked T-cell engager programs plus the AbbVie-collaborated program in progress.[3](https://www.biospace.com/press-releases/xilio-therapeutics-reports-second-quarter-2026-financial-results-and-provides-pipeline-and-business-updates)
**What has changed since 2023** is the balance between validation and financial strain. The Gilead and AbbVie deals, together with roughly $126 million of 2025–2026 financings, indicate continued external confidence in the masked platform; the same period saw the share price fall from the $16.00 IPO level to the $0.64–$0.75 range at which later rounds priced, and the company disclosed going-concern doubt in its Q3 2025 10-Q.[5](https://www.sec.gov/Archives/edgar/data/1840233/000155837023002687/R8.htm) • [4](http://biobase.whitefordresearch.com/companies/xilio-therapeutics) • [1](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b)
Several questions the sources do not settle remain open: whether vilastobart or XTX501 has demonstrated proof of tumor selectivity and clinical benefit in patients (no kept source reports patient-level efficacy data); how Xilio compares with other masked-cytokine developers such as Werewolf Therapeutics, Anaveon, and Potenza; and whether the going-concern doubt disclosed in 2025 has been resolved.
## References
1. [Xilio Therapeutics Form 10-Q (Q3 2025)](https://ir.xiliotx.com/static-files/d6597718-db23-4e7f-9aa8-6ec8e3e1738b)
2. [Xilio Therapeutics 2025 Annual Report to Stockholders](https://www.sec.gov/Archives/edgar/data/1840233/000119312526187691/2026_04_28_-_ars.pdf)
3. [Xilio Therapeutics Reports Second Quarter 2026 Financial Results (BioSpace)](https://www.biospace.com/press-releases/xilio-therapeutics-reports-second-quarter-2026-financial-results-and-provides-pipeline-and-business-updates)
4. [Xilio Therapeutics — Whiteford Research Biobase](http://biobase.whitefordresearch.com/companies/xilio-therapeutics)
5. [SEC filing exhibit — Xilio Therapeutics IPO closing (2021)](https://www.sec.gov/Archives/edgar/data/1840233/000155837023002687/R8.htm)
6. [AbbVie and Xilio Therapeutics Announce Collaboration and Option Agreement (PR Newswire)](https://www.prnewswire.com/news-releases/abbvie-and-xilio-therapeutics-announce-collaboration-and-option-agreement-to-develop-novel-tumor-activated-immunotherapies-302371535.html)
7. [Xilio Therapeutics company website](https://xiliotx.com/)
8. [Xilio Therapeutics Reports First Quarter 2026 Financial Results (GlobeNewswire)](https://www.globenewswire.com/news-release/2026/05/12/3292720/0/en/Xilio-Therapeutics-Reports-First-Quarter-2026-Financial-Results-and-Provides-Pipeline-and-Business-Updates.html)
9. [Xilio Therapeutics Q2 2025 Pipeline and Business Update](https://ir.xiliotx.com/news-releases/news-release-details/xilio-therapeutics-announces-pipeline-and-business-updates-and-9)
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*Initially written Sep 17, 2026 · Edited: Oct 15, 2026; Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license