What Xilio Therapeutics does

Xilio Therapeutics is a clinical-stage biotechnology company developing tumor-activated immuno-oncology therapies intended to be systemically administered but preferentially activated within the tumor microenvironment. Founded in 2016 and headquartered in Waltham, Massachusetts, the company is listed on NASDAQ under the ticker XLO and operates with a headcount of 51-100 employees following a 21% workforce reduction in March 2024. Its therapeutic candidates are built on a proprietary masking technology platform designed to limit the activity of potent immune-engaging molecules (checkpoint inhibitors, cytokines, bispecifics) to tumor tissue, with the goal of widening the therapeutic index relative to systemic counterparts.

The pipeline centers on Vilastobart (XTX101), a masked anti-CTLA-4 antibody in Phase 1 development including a NSCLC dose-expansion cohort; Efarindodekin Alfa (XTX301), a masked IL-12 program licensed to Gilead Sciences; XTX501, a masked IL-2 plus anti-PD-1 bispecific with an IND filing planned for mid-2026; and an early-stage set of masked T cell engagers targeting CLDN18.2 and a PSMA plus STEAP1 dual-antigen construct. Strategic collaborations with Gilead Sciences and AbbVie validate the platform externally and provide capital, with Xilio having achieved an AbbVie development milestone in Q1 2025.

Xilio's business model is pre-commercial: revenue is generated exclusively from licensing fees, milestone payments, and collaboration economics under its Gilead and AbbVie agreements rather than from product sales. 2025 revenue of approximately $43.8M and 2024 revenue of approximately $6.3M reflect this lumpy, partner-driven profile. The company has funded operations through a sequence of capital actions between March 2024 and February 2026 (a $11.3M private placement alongside the Gilead license, a $50.0M public offering in June 2025, $35.8M from Series B warrant exercises in January 2026, and a $40.0M pre-funded warrant offering in February 2026), ending 2025 with approximately $137.5M in cash and a stated runway through the end of 2027. A 1-for-14 reverse stock split executed in March 2026 maintained Nasdaq listing compliance, and market capitalization stood at approximately $49M as of April 2026.

Name

Xilio Therapeutics

Legal name

Xilio Therapeutics, Inc.

Website

https://xiliotx.com

Company type

Public

Founded year

2016

Operating status

Operating

Headcount range

51–100 employees

Short description

Xilio Therapeutics is a clinical-stage biotechnology company developing tumor-activated immuno-oncology therapies using a proprietary masking platform, with a pipeline spanning masked anti-CTLA-4, IL-12, and T cell engager programs partnered with Gilead and AbbVie.

Ownership category

akta.pro rank

Product category

Clinical-stage immuno-oncology therapeutics

NAICS

Biological Product (except Diagnostic) Manufacturing (325414), Pharmaceutical and Medicine Manufacturing (3254)

SIC

Biological Products, (No Disgnostic Substances) (2836), Pharmaceutical Preparations (2834)

akta.pro primary industry

Cytokines, Interferons & Immunomodulatory Proteins (HLAAAAAC)

akta.pro secondary industry

Personalized Therapeutic Design (neoantigen vaccines, individualized cell/gene therapies) (HLAAANAK)

Keywords

• Immuno-oncology therapies
• Tumor-activated biologics
• Masked cytokine therapy
• Cancer immunotherapy
• Clinical-stage biotechnology

Headquarters

HQ city

Waltham

HQ country

United States

HQ region

North America

Offices1 record

Markets served

GTM type

B2B

Offering type

Hardware or Manufacturing

Cost components

Technology or R&D, Personnel, Operations, Marketing or Sales, Infrastructure

Revenue model

1. Licensing and Collaboration Revenue: Xilio generates revenue through licensing agreements with pharmaceutical companies. The company entered into an exclusive license agreement with Gilead Sciences for its tumor-activated IL-12 program and has a collaboration with AbbVie for masked T cell engagers. Revenue includes upfront payments, milestone payments, and potential royalties on future product sales.

Go-to-market motion1 record

Distribution channels1 record

Marketing channels3 records

Core offering

Xilio Therapeutics is a clinical-stage biotechnology company developing masked immuno-oncology therapies designed to remain inactive in systemic circulation and be selectively activated by tumor-specific proteases within the tumor microenvironment. Its pipeline includes masked cytokines (IL-12, IL-2), a masked anti-CTLA-4 antibody, and masked T cell engagers, with multiple programs partnered with Gilead Sciences and AbbVie. Revenue is generated through licensing, collaboration upfront payments, development milestones, and potential future royalties.

Product overview

Xilio Therapeutics is a clinical-stage biotechnology company developing a pipeline of tumor-selective, masked immuno-oncology therapies. The company's differentiated approach uses proprietary masking technology to design molecules that remain inactive until they reach the tumor microenvironment, where they are activated by tumor-specific proteases. The core portfolio includes: Vilastobart (XTX101), a masked anti-CTLA-4 in Phase 1/2; Efarindodekin Alfa (XTX301), a masked IL-12 licensed to Gilead and in Phase 2; XTX501, a bispecific PD-1/masked IL-2 with IND planned mid-2026; and two masked T cell engager programs targeting CLDN18.2 and PSMA+STEAP1 in preclinical development. The company also maintains an Expanded Access Policy for clinical trial enrollment.

Differentiator

Problem solved

Functional benefit

Brands

• Efarindodekin alfa (XTX301): A masked IL-12 therapy for cancer immunotherapy, currently in Phase 2 clinical trial as monotherapy for advanced solid tumors
• Vilastobart (XTX101)
• XTX501
• Masked T Cell Engagers

Products and services

• Vilastobart (XTX101) A masked, Fc-enhanced anti-CTLA-4 monoclonal antibody designed to block CTLA-4 and deplete regulatory T cells only when activated in the tumor microenvironment, intended to reduce the systemic toxicity associated with conventional anti-CTLA-4 therapy. Currently in Phase 1/2 clinical trials in combination with atezolizumab for metastatic colorectal cancer.
• Efarindodekin Alfa (XTX301) A masked IL-12 cytokine designed to potently stimulate anti-tumor immunity and reprogram the tumor microenvironment of poorly immunogenic 'cold' tumors towards an inflamed 'hot' state. Licensed exclusively to Gilead Sciences and currently in Phase 2 clinical trials as monotherapy for advanced solid tumors.
• XTX501 A bispecific PD-1/masked IL-2 molecule designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function. IND submission planned for mid-2026.
• CLDN18.2 Masked T Cell Engager (XTX601) A potential first-in-class masked T cell engager targeting CLDN18.2 expressed in gastrointestinal cancers (gastric, pancreatic, esophageal) and lung cancer. IND submission planned for 2027.
• PSMA+STEAP1 Masked T Cell Engager A potential first-in-class dual-targeted masked T cell engager with built-in co-stimulatory signaling (SEECR format) targeting PSMA and STEAP1 in prostate cancer. Development candidate nomination expected Q2 2026.
• Clinically-Validated Masking Technology Platform Proprietary integrated biology and protein engineering platform for designing masked biologics (cytokines, antibodies, T cell engagers) that remain inactive systemically and are selectively activated by tumor-specific matrix metalloproteases and other proteases within the tumor microenvironment; supports multiple internal programs and external partnerships.

Quantifiable outcome

• Efarindodekin alfa demonstrated IL-1 pharmacology in patients with advanced solid tumors: pharmacodynamic data from first-in-human Phase 1 study.
• +2 more outcomes

Named customers1 record

Segments1 record

Ideal customer profiles3 records

Technology focussed Yes

API detail

Has API

No

API docs

API detail

Core technology

AI maturity

App detail

Feature5 records

Partnerships

Two partnerships are on record, tiered core.

• Gilead SciencescoreOEM/ Whitelabel/ Licensing Partner · 1 March 2024Exclusive license agreement with Gilead Sciences for Xilio's tumor-activated IL-12 program, including efarindodekin alfa (XTX301). Xilio received $17.5 million development milestone payment in 2025. Gilead also participated in multiple financing rounds as an investor.
• AbbViecoreStrategic or Co-development Partner · 1 March 2024Collaboration on wholly-owned masked T cell engager program. Xilio achieved a development milestone for its masked antibody-based immunotherapy program under the collaboration with AbbVie.

Scale indicators8 records

Recent moves7 records

Expansion highlights4 records

Direct peers

• Werewolf Therapeutics: Clinical-stage oncology biotech developing INDUKINE conditional-activation cytokine therapeutics. Closest analog to Xilio's masked/conditionally activated biologics platform with overlapping mechanism (protease-activated cytokines).
• Adagene: Clinical-stage biotech using SAFEbody and POWERbody masking technologies to conditionally activate antibodies in the tumor microenvironment. Directly comparable platform-level approach to Xilio's masking technology.
• Janux Therapeutics: Clinical-stage biotech developing masked T cell engager (TRACTr) therapeutics with tumor-selective activation. Directly comparable to Xilio's masked TCE pipeline in mechanism and target indications.
• Maverick Therapeutics: Develops COBRA conditionally active T cell engagers; acquired by Takeda in 2021. Direct mechanistic analog to Xilio's masked/conditionally activated T cell engagers in solid tumors.

Broad incumbents

• Harpoon Therapeutics: Developer of T cell engagers (HPN328, HPN217) acquired by Merck in 2024. Competes in the T cell engager space overlapping with Xilio's masked TCE programs (XTX601, PSMA/STEAP1), but without the masking/conditional activation layer.
• Bristol-Myers Squibb: Owns Yervoy (anti-CTLA-4), Opdivo, and a broad I-O franchise that competes directly with Xilio's masked anti-CTLA-4 vilastobart and other I-O candidates. Establishes the benchmark that any new CTLA-4 or PD-1 axis therapy must beat.
• Merck & Co. Owns Keytruda and has acquired Harpoon Therapeutics; competing incumbent in I-O and T cell engagers that Xilio's masked programs must either displace or combine with in clinical practice.
• Roche / Genentech: Major oncology incumbent with Tecentriq, a broad pipeline of I-O agents and T cell engagers, and significant internal masking/conditional activation research. Competes for the same indications and BD partnerships Xilio targets.

Emerging players

• Cullinan Oncology: Clinical-stage oncology biotech developing targeted therapies including immune engagers and oncology-focused biologics. Comparable as a similarly sized clinical-stage oncology platform with partnered and wholly-owned assets.
• Surface Oncology (Coherus Biosciences): Clinical-stage I-O company focused on next-generation immuno-oncology, acquired by Coherus. Comparable as a similarly small, focused I-O pipeline company whose strategic trajectory (acquisition) represents a plausible exit template for Xilio.

Market position

Strengths4 records

Weaknesses4 records

Competitive moat4 records

Key risks5 records

Key highlights6 records

Customer concentration

• LinkedInlinkedin.com/company/xilio-tx
• Xx.com/xiliotx

Revenue estimate

Valuation estimate

Number of profiles

Profiles14 records

Funding overview

Funding rounds8 records

Investors19 records

Funding detail is available on the Subscription and Enterprise plan.Contact sales →

M&A

Investments

M&A and investment is available on the Subscription and Enterprise plan.Contact sales →

Frequently asked questions about Xilio Therapeutics