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CompletedNCT04896697Updated Sep 10, 2026

Vilastobart (XTX101) Monotherapy and Vilastobart and Atezolizumab Combination Therapy in Advanced Solid Tumors

A Phase 1/2 interventional study of vilastobart (XTX101) and Atezolizumab in Advanced Solid Tumor, sponsored by Xilio Development, Inc.. Completed at 19 sites in United States. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-10.

Sponsored by Xilio Development, Inc. · Phase 1/2, Interventional, and Treatment

Phase
Phase 1/2
Study type
Interventional
Enrollment
125
Allocation
Non-randomized
Ages
18 Years and older
Sex
All
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Study summary

This is a first-in-human, Phase 1/2, multicenter, open-label study designed to evaluate the safety and tolerability of vilastobart (XTX101) as monotherapy and vilastobart (XTX101) and atezolizumab combination therapy in patients with advanced solid tumors.

Read the detailed description

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, as monotherapy and vilastobart (XTX101) and atezolizumab combination therapy in patients with advanced solid tumors.

Part 1A will examine vilastobart (XTX101) monotherapy in an accelerated and standard 3+3 dose escalation design. Based on the results of Part 1A, patients with select advanced solid tumors will be enrolled in Part 1B, which will evaluate vilastobart (XTX101) monotherapy in relation to specific PD biomarkers.

Part 1C will examine vilastobart (XTX101) in combination with atezolizumab in a standard 3+3 dose escalation/dose de-escalation design. Part 1C may include a dose expansion cohort to further evaluate the safety, PK, and PD of dose levels that were previously cleared.

Phase 2 will examine vilastobart (XTX101) in combination with atezolizumab in patients with metastatic microsatellite stable colorectal cancer (MSS CRC) at the RP2D(s) defined in Part 1C.

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Conditions studied

  • Advanced Solid Tumor
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In context

Lead sponsor

Xilio Development, Inc. is the lead sponsor of 4 studies on the registry; 2 are open to participants now.

Counted across the registry records on this site, refreshed daily.

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Who can participate

Ages eligible
18 Years and older
Sexes eligible
All
Accepts healthy volunteers
No

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

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
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Study design

Phase
Phase 1 / Phase 2
Primary purpose
Treatment
Allocation
Non-randomized
Intervention model
Sequential assignment
Masking
None (open label)
Enrollment
125 participants (actual)

Study arms

  • Experimental
    Part 1A - vilastobart (XTX101) Monotherapy Dose Escalation

    Part 1A Dose Escalation of vilastobart (XTX101) administered in ascending doses to patients with advanced or metastatic solid tumors to find the recommended phase 2 dose (RP2D).

    Drug: vilastobart (XTX101)

  • Experimental
    Part 1B - Pharmacodynamic (PD) Dose Expansion

    Part 1B vilastobart (XTX101) at the RP2D will be administered to further examine vilastobart (XTX101) as monotherapy in patients with select advanced solid tumors.

    Drug: vilastobart (XTX101)

  • Experimental
    Part 1C - vilastobart (XTX101) Dose Escalation and Dose Expansion in Combination with Atezolizumab

    Part 1C will receive a labeled dose of atezolizumab in combination with vilastobart (XTX101).

    Drug: Atezolizumab · Drug: vilastobart (XTX101)

  • Experimental
    Phase 2 - vilastobart (XTX101) Dose Expansion in Combination with Atezolizumab

    Phase 2 will receive a labeled dose of atezolizumab in combination with vilastobart (XTX101) at the RP2D(s) in patients with MSS CRC.

    Drug: Atezolizumab · Drug: vilastobart (XTX101)

Interventions

  • Drugvilastobart (XTX101)

    vilastobart (XTX101) monotherapy

  • DrugAtezolizumab

    1200 mg administered every 3 weeks in combination with vilastobart (XTX101)

  • Drugvilastobart (XTX101)

    In combination with Atezolizumab

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What researchers measure

Primary outcomes

  1. Incidence of Dose Limiting Toxicities (DLTs) in Part 1A

    Time frame: Cycle 1 Day 1 up to just prior to the second dose of study drug at Cycle 2 day 1 (approximately 3 weeks)

  2. Incidence of Dose Limiting Toxicities (DLTs) in Part 1C

    Time frame: Cycle 1 Day 1 up to Cycle 3 Day 1 (approximately 6 weeks)

  3. Incidence of treatment-emergent adverse events in Part 1

    Time frame: Up to 24 months

  4. Incidence of changes in clinical laboratory abnormalities in Part 1

    Time frame: Up to 24 months

  5. Investigator-assessed objective response rate (ORR) per iRECIST in Phase 2

    Time frame: Up to 24 months

Secondary outcomes

  1. Investigator-assessed objective response rate (ORR) per iRECIST in Part 1

    Time frame: Up to 24 months

  2. Antidrug antibody (ADA) occurrence and titer in serum in Part 1

    Time frame: Up to 24 months

  3. Plasma concentrations of vilastobart (XTX101) (total and intact) in Part 1 and Phase 2

    Time frame: Up to 24 months

  4. Maximum observed plasma concentration (Cmax) in Part 1 and Phase 2

    Time frame: Up to 24 months

  5. Time of maximum observed concentration (Tmax) in Part 1 and Phase 2

    Time frame: Up to 24 months

  6. Trough concentrations (Ctrough) in Part 1 and Phase 2

    Time frame: Up to 24 months

  7. Area under the curve (AUC) in Part 1 and Phase 2

    Time frame: Up to 24 months

  8. Half-life (T1/2) in Part 1 and Phase 2

    Time frame: Up to 24 months

  9. Systemic clearance (CL) in Part 1 and Phase 2

    Time frame: Up to 24 months

  10. Volume of distribution (Vd) in Part 1 and Phase 2

    Time frame: Up to 24 months

  11. Investigator-assessed ORR per RECIST in Phase 2

    Time frame: Up to 24 months

  12. Duration of response per iRECIST in Phase 2

    The time from first documented confirmed response to first documented disease progression

    Time frame: Up to 24 months

  13. Disease control rate in Phase 2

    The percent of patients who achieve complete response per iRECIST (iCR), partial response per iRECIST (iPR), or stable disease per iRECIST (iSD)

    Time frame: Up to 24 months

  14. Progression-free survival per iRECIST in Phase 2

    The time from first dose to first documented disease progression or death

    Time frame: Up to 24 months

  15. Overall survival in Phase 2

    The time from first dose to death due to any cause

    Time frame: Up to 24 months

  16. Incidence of treatment-emergent AEs in Phase 2

    Time frame: Up to 24 months

  17. Incidence of changes in clinical laboratory abnormalities in Phase 2

    Time frame: Up to 24 months

07

Study locations

19 sites
  • Mayo Clinic Hospital
    Phoenix, Arizona 85054, United States
  • City of Hope
    Duarte, California 91010, United States
  • California Cancer Associates for Research and Excellence, cCARE
    Encinitas, California 92024, United States
  • City of Hope-Lennar
    Irvine, California 92618, United States
  • USC/Norris Comprehensive Cancer Center
    Los Angeles, California 90033, United States
  • California Cancer Associates for Research and Excellence, cCARE
    San Marcos, California 92069, United States
  • UCLA Hematology/Oncology- Santa Monica
    Santa Monica, California 90404, United States
  • City of Hope-Upland
    Upland, California 91786, United States
  • Mayo Clinic Hospital
    Jacksonville, Florida 32224, United States
  • Sarah Cannon Research Institute at Florida Cancer Specialists
    Orlando, Florida 32827, United States
  • Massachusetts General Hospital
    Boston, Massachusetts 02114, United States
  • Mayo Clinic Hospital
    Rochester, Minnesota 55905, United States
  • Duke University Medical Center
    Durham, North Carolina 27710, United States
  • Carolina BioOncology Institute
    Huntersville, North Carolina 28078, United States
  • University of Pittsburgh Medical Center- Hillman Cancer Center
    Pittsburgh, Pennsylvania 15232, United States
  • Next Oncology
    Austin, Texas 78758, United States
  • Mary Crowley Cancer Research
    Dallas, Texas 75230, United States
  • Tranquil Clinical Research
    Webster, Texas 77598, United States
  • NEXT Virginia
    Fairfax, Virginia 22031, United States
08

References and documents

Publications

  • Jenkins KA, Park M, Pederzoli-Ribeil M, Eskiocak U, Johnson P, Guzman W, McLaughlin M, Moore-Lai D, O'Toole C, Liu Z, Nicholson B, Flesch V, Qiu H, Clackson T, O'Hagan RC, Rodeck U, Karow M, O'Neil J, Williams JC. XTX101, a tumor-activated, Fc-enhanced anti-CTLA-4 monoclonal antibody, demonstrates tumor-growth inhibition and tumor-selective pharmacodynamics in mouse models of cancer. J Immunother Cancer. 2023 Dec 12;11(12):e007785. doi: 10.1136/jitc-2023-007785. PubMed 38164757 ↗

Individual participant data

Plan to share: No

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Updates

Tracking since Sep 25, 2026
No changes since tracking began. The registry record was last updated on Sep 10, 2026, before this site started recording changes on Sep 25, 2026. Its history is on ClinicalTrials.gov ↗
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Registry details

Key details

Study ID
NCT04896697
Lead sponsor
Xilio Development, Inc.
Collaborators
Hoffmann-La Roche
Responsible party
Sponsor
First posted
May 21, 2021
Start date
Sep 13, 2021
Primary completion
May 18, 2026
Completion
May 18, 2026
Last update
Sep 10, 2026

Oversight

Data monitoring committee
No
FDA-regulated drug
Yes
FDA-regulated device
No
View the source record on ClinicalTrials.gov ↗

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This study is completed, as verified in Sep 2026. You cannot join it, but the record below documents what was studied.

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