Xilio Therapeutics is a clinical-stage biotech developing cancer immunotherapies using a proprietary "masking" technology. The core idea is that many existing immune-oncology therapies — cytokines, T cell engagers, checkpoint inhibitors — are effective against tumors but cause serious systemic toxicity. Xilio's molecules are designed to remain inactive in circulation and only activate when they reach the tumor microenvironment, where tumor-specific proteases cleave off the masking domain. Xilio has four main programs: efarindodekin alfa (masked IL-12), XTX501 (a bispecific PD-1/masked IL-2), two masked T cell engagers targeting prostate and gastrointestinal cancers, and vilastobart (masked anti-CTLA-4), for which Xilio is seeking a partner. Xilio has no product revenue and funds operations primarily through partnership deals with large pharma. Gilead holds an exclusive license to efarindodekin alfa, generating $72.5M to date with up to $575M in additional contingent payments plus royalties. AbbVie has rights to masked T cell engager programs, generating $52M to date with up to ~$2.1B in additional contingent payments plus royalties. Xilio retains full rights to XTX501 and its T cell engager programs, bearing the full development cost but retaining the full commercial upside. The company contracts out manufacturing to third-party CDMOs and has no manufacturing facilities of its own.