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Testing vilastobart alone and with atezolizumab in advanced solid tumors

A First-in-Human, Multicenter, Phase 1/2, Open-Label Study of Vilastobart (XTX101) Monotherapy and Vilastobart (XTX101) and Atezolizumab Combination Therapy in Patients With Advanced Solid Tumors

Phase1; Phase2 Interventional Xilio Development, Inc. · NCT04896697

This study is testing a new treatment called vilastobart, both on its own and with another drug called atezolizumab, to see if it helps people with advanced solid tumors who haven't had success with other therapies.

Quick facts

PhasePhase1; Phase2
Study typeInterventional
Enrollment136 (estimated)
Ages18 Years and up
SexAll
SponsorXilio Development, Inc. Industry-sponsored
Drugs / interventionsbevacizumab, cetuximab, panitumumab, chemotherapy, atezolizumab
Locations19 sites (Phoenix, Arizona and 18 other locations)
Trial IDNCT04896697 on ClinicalTrials.gov

What this trial studies

This is a first-in-human, Phase 1/2, multicenter, open-label study designed to evaluate the safety and tolerability of vilastobart (XTX101), a tumor-selective anti-CTLA-4 antibody, both as a standalone treatment and in combination with atezolizumab for patients with advanced solid tumors. The study will be conducted in multiple parts, including dose escalation and evaluation of specific biomarkers. Patients with various advanced solid tumors who have failed standard therapies will be enrolled to assess the effectiveness of these treatments.

Who should consider this trial

Good fit: Ideal candidates include patients with advanced solid tumors who have failed standard therapy or for whom no curative options are available.

Not a fit: Patients with early-stage tumors or those who have not yet undergone standard treatment may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could provide a new treatment option for patients with advanced solid tumors that have not responded to existing therapies.

How similar studies have performed: Other studies have shown promise with similar immunotherapy approaches, suggesting potential for success in this novel combination.

Eligibility criteria

Show full inclusion / exclusion criteria 
Inclusion Criteria:

Disease Criteria -

* Part 1A and 1C: Any histologically or cytologically confirmed solid tumor malignancy that is locally advanced or metastatic and has failed standard therapy, or standard therapy is not curative or available;
* Part 1B:

  * Any histologically or cytologically confirmed solid tumor malignancy for which anti-PD-1 or anti-PD-L1 treatment is approved and has progressed on or after prior anti-PD-1 or anti-PD-L1 therapy.
  * Patients with metastatic castrate-resistant prostate cancer if they have progressed on at least 2 lines of systemic therapy
  * Patients with extensive stage small cell lung cancer (SCLC) after at least 1 line of prior therapy
  * Patients with microsatellite stable colorectal cancer after at least 2 lines of prior therapy
* Phase 2: Patients with histologically confirmed metastatic MSS CRC are eligible to enroll in Phase 2 as follows:

  * Patients must have had at least 1 prior chemotherapy regimen for metastatic CRC including all of the following agents: a fluoropyrimidine, irinotecan, oxaliplatin, bevacizumab or biosimilars, an anti epidermal growth factor receptor antibody (cetuximab or panitumumab), and v-raf murine sarcoma viral oncogene homolog B1 inhibitor/BRAF (encorafenib), if applicable
  * Patients with MSI-H/dMMR are excluded
* ECOG performance status of 0 or 1
* Adequate organ function
* Part 1B, Part 1C, and Phase 2 only: measurable disease per iRECIST

Exclusion Criteria:

* Received prior treatment with anti-CTLA-4 therapy
* Received prior immune-checkpoint therapy and experienced Grade 3 or greater toxicity lasting greater than 6 weeks
* Received prior approved systemic anticancer therapy within 4 weeks prior to study treatment
* Received prior radiotherapy within 2 weeks prior to study treatment
* Phase 2 only: Received prior anti-PD-1/L1 therapy or any investigational checkpoint inhibitory therapy
* Has a diagnosis of immunodeficiency
* Has known malignancy (other than disease under study) that is progressing or has required active treatment within the past 3 years
* Has an active autoimmune disease that has required systemic treatment in past 2 years, including the use of disease modifying agents, corticosteroids or immunosuppressive drugs
* Has an active infection requiring systemic intravenous therapy within 4 weeks prior to study treatment, or oral therapy within 2 weeks prior to study treatment
* Has a history of severe hypersensitivity reaction (≥ Grade 3) to any study intervention and/or any of its excipients
* Has a known psychiatric or substance abuse disorder that would interfere with the participant's ability to cooperate with the requirements of the study
* Phase 2 only: symptomatic bowel obstruction

Where this trial is running

Phoenix, Arizona and 18 other locations

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Advanced Solid Tumor
Last reviewed 2026-06-15 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.