Xilio Therapeutics, Inc.

We are a clinical-stage biotechnology company discovering and developing masked immuno-oncology, or I-O, therapies with the goal of significantly improving outcomes for people living with cancer. Leveraging our clinically-validated masking technology and capabilities, we are developing I-O therapies designed to selectively activate within the tumor microenvironment to achieve durable efficacy without the severe side effects associated with systemically active I-O agents. Our integrated biology and protein engineering approach enables us to design and develop highly potent, masked biologics that are activated, or unmasked, by tumor-specific proteases within the tumor microenvironment. We are currently advancing multiple programs in preclinical and clinical development, including: XTX501, a PD-1/masked IL-2 bispecific; masked, multi-specific T cell engagers, or TCEs; and efarindodekin alfa, a masked IL-12. Our clinically-validated masking technology has enabled us to establish top-tier strategic partnerships, including with AbbVie Group Holdings Limited, or AbbVie, and Gilead Sciences, Inc., or Gilead.

XTX501: PD-1/masked IL-2 bispecific

XTX501 is a novel, investigational PD-1/masked IL-2 (alpha-optimized) bispecific antibody fusion protein that combines two complementary mechanisms in a single molecule: selective inhibition of the PD-1/PD-L1 pathway and potent IL-2-driven expansion of T cells. The PD-1 binding arm is designed to selectively direct IL-2 activity to PD-1 positive, antigen-experienced T cells and enhance their function. The IL-2 binding arm incorporates a masked, high potency IL-2 variant with an alpha-optimized receptor binding profile. By leveraging our proprietary masking technology, XTX501 aims to overcome IL-2 receptor-mediated clearance, peripheral activity, and tolerability challenges associated with non-masked IL-2 therapies. We are currently evaluating XTX501 as a monotherapy in patients with metastatic non-small cell lung cancer, or NSCLC, and select advanced solid tumors who have previously received anti-PD(L)-1 therapy in a first-in-human, multi-center, open-label Phase 1/2 clinical trial at multiple sites in the United States. We recently initiated patient dosing in the trial, and we plan to report initial Phase 1 data in patients with metastatic NSCLC in the fourth quarter of 2027.

Masked T Cell Engager Programs

We are leveraging our proprietary, clinically-validated masking technology and modular TCE architecture to advance two wholly-owned masked TCE programs, as well as an additional masked TCE program in collaboration with AbbVie. As part of the core design, our TCEs incorporate a masked CD3 binding domain, a tumor-associated antigen, or TAA, binding domain and built-in co-stimulation. Our modular architecture enables the flexibility to incorporate additional TAA binding domains and mask the TAA binding domain(s) and/or co-stimulatory signaling domain. Upon tumor-selective activation, the molecules are designed to release the mask(s) and deliver a potent TCE with a short half-life in the tumor microenvironment.

XTX602: dual-masked CLDN18.2-targeting multi-specific TCE with co-stimulation

XTX602 is a potential first-in-class, dual-masked CLDN18.2-targeting multi-specific TCE with built-in CD2 co-stimulation. CLDN18.2 is a TAA expressed in gastrointestinal cancers (gastric, pancreatic and esophageal). By incorporating masks for both the CLDN18.2 and the CD3 binding domain, XTX602 is designed to overcome potential gastrointestinal toxicity associated with non-masked CLDN18.2 targeting molecules. In addition, the CD2 co-stimulatory domain is built directly into the molecule to enable enhanced T cell activation, expansion and durability of T cell response. Investigational new drug application, or IND, enabling studies for XTX602 are ongoing, and we plan to submit an IND for XTX602 in the fourth quarter of 2027.

XTX701: masked PSMAxSTEAP1 targeting multi-specific TCE with co-stimulation

XTX701 is a potential first-in-class, masked PSMAxSTEAP1-targeting multi-specific TCE with built-in CD2 co-stimulation. PSMA and STEAP1 are TAAs collectively expressed in approximately 95% of metastatic castration-resistant prostate cancer. Targeting these two TAAs is intended to address heterogeneity of expression of PSMA and STEAP1 across prostate tumors and limit resistance and lack of durability of response due to antigen escape. By incorporating a mask for the CD3 binding domain, XTX701 is designed to minimize toxicity due to peripheral T cell activation and on-target, off-tumor engagement associated with non-masked molecules. In addition, the CD2 co-stimulatory domain is built directly into the molecule to enable enhanced T cell activation, expansion and durability of T cell response. IND-enabling studies for XTX701 are ongoing, and we plan to submit an IND for XTX701 in the fourth quarter of 2027.

Efarindodekin alfa: masked IL-12

We are evaluating efarindodekin alfa as a monotherapy in an ongoing Phase 2 clinical trial in patients with advanced solid tumors under our license agreement with Gilead and expect to deliver an option data package to Gilead in the first half of 2027.

Liquidity Overview

To date, we have financed our operations primarily from proceeds raised through private placements of equity securities; sales of common stock in our initial public offering, or IPO, and through “at-the-market” offerings; the sale of prefunded warrants in our June 2025 and February 2026 follow-on offerings; the exercise of certain common stock warrants issued in connection with our June 2025 follow-on offering; development event payments under our co-funded clinical trial collaboration with F. Hoffmann-La Roche Ltd., or Roche; and upfront payments and milestone payments under our collaboration and license agreements with AbbVie and Gilead. All of our programs are in early clinical or preclinical development. As a result, we have not generated any revenue from product sales and do not expect to generate any revenue from product sales for at least the next several years, if at all. Our ability to generate product revenue sufficient to achieve profitability will depend heavily on the successful development and eventual commercialization of one or more of our product candidates, if approved. Because of the numerous risks and uncertainties associated with product development, we are unable to predict the timing or amount of increased expenses or when or if we will be able to achieve profitability. Even if we are able to generate revenue from product sales, we may not become profitable.

Since inception, we have incurred significant operating losses, including net losses of $21.9 million and $45.4 million for the nine months ended September 30, 2026 and 2025, respectively, and a net loss of $35.0 million for the year ended December 31, 2025. As of September 30, 2026, we had an accumulated deficit of $440.6 million. We expect to continue to incur significant expenses and operating losses for the foreseeable future, particularly to the extent we:

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continue to advance our current research programs and conduct additional research programs;

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advance our current product candidates and any future product candidates we may develop into preclinical and clinical development;

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seek marketing approvals for product candidates that successfully complete clinical trials, if any;

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obtain, expand, maintain, defend and enforce our intellectual property;

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continue to discover, validate and develop additional product candidates;

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continue to manufacture increasing quantities of our current or future product candidates for use in preclinical studies, clinical trials and for any potential commercialization;

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acquire or in-license other product candidates, technologies or intellectual property;

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hire additional personnel to support current or future programs;

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establish a commercial and distribution infrastructure to commercialize products for which we may obtain marketing approval, if any; and

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incur additional costs associated with current and future research, development and commercialization efforts and operations as a public company.

As a result, we will need substantial additional capital to support our continuing operations and pursue our strategy. As of September 30, 2026, we had cash and cash equivalents of $122.2 million. Based on our current operating plans, we anticipate that our existing cash and cash equivalents as of September 30, 2026 will be sufficient to enable us to fund our operating expenses and capital expenditure requirements into the first quarter of 2028. This estimate excludes up to $36.2 million in additional gross proceeds in the fourth quarter of 2026 if all outstanding Series C warrants are exercised at their current exercise price and any potential additional milestone payments, option-related fees or other contingent payments under our collaboration and license agreements with AbbVie and Gilead, including up to $31.0 million in near-term milestones and option extension fees that could be achieved under the AbbVie collaboration through the first half of 2027.

In addition, we have based our estimates on assumptions that may prove to be wrong, and we could exhaust our available capital resources sooner than we anticipate. We expect our operating losses and negative operating cash flows to continue for the foreseeable future as we continue to advance our pipeline of novel, masked I-O molecules through preclinical and clinical development, maintain the infrastructure necessary to support these activities and continue to incur costs associated with operating as a public company.