STEALTH-001 Trial Tests VET3-TGI Oncolytic Virus in Solid Tumors

A first-in-human clinical trial is testing whether an engineered oncolytic virus called VET3-TGI can help the immune system attack advanced solid tumors, including mesothelioma.

The STEALTH-001 trial (NCT06444815), sponsored by KaliVir Immunotherapeutics, is a Phase 1/1b study designed to find a safe and effective dose of VET3-TGI, given both on its own and in combination with the checkpoint inhibitor atezolizumab. It plans to enroll about 60 people and is currently recruiting in the United States.

What the Trial Is Testing

STEALTH-001 is a dose-escalation and expansion study. Its central goal is to identify the highest dose of VET3-TGI that patients can tolerate, delivered two different ways, and to measure safety when the drug is given alone and alongside atezolizumab.

VET3-TGI is an oncolytic immunotherapy. According to KaliVir, it is designed to selectively infect and kill tumor cells while expressing an immune-stimulating transgene payload made up of interleukin-12 and a TGF-beta inhibitor. The clinicaltrials.gov record describes it as an oncolytic vaccinia virus engineered with immunomodulatory transgenes. Atezolizumab is an anti-PD-L1 antibody, a checkpoint inhibitor already approved for several other cancers.

The trial assigns participants to one of four groups:

• Group A: VET3-TGI alone, injected directly into a tumor (intratumoral), given as four doses with booster injections permitted for up to two years
• Group B: VET3-TGI injected into a tumor and combined with atezolizumab given intravenously
• Group C: VET3-TGI alone, given by intravenous infusion as six doses with booster infusions permitted for up to two years
• Group D: VET3-TGI given intravenously and combined with atezolizumab

The combination groups use the highest tolerated VET3-TGI dose identified in the matching monotherapy group. Expansion cohorts may add patients to evaluate early signs of activity once a dose is selected.

Where Mesothelioma Fits In

STEALTH-001 is a basket trial. Rather than focusing on one cancer, it enrolls people across a range of advanced solid tumors. The conditions listed on clinicaltrials.gov include microsatellite stable colorectal cancer, head and neck squamous cell carcinoma, cervical cancer, kidney and renal cell carcinoma, stage IV melanoma, Merkel cell carcinoma, non-small cell lung cancer, cutaneous squamous cell carcinoma, urothelial carcinoma, and mesothelioma.

Mesothelioma is one eligible condition among many. The trial is not a mesothelioma-specific study, and at this early stage the design treats all of these tumor types together while researchers establish the dose and safety profile.

Who Can Participate

The trial is open to adults aged 18 and older with pathologically confirmed advanced, unresectable, or metastatic solid tumors who have already exhausted or cannot tolerate standard treatments such as chemotherapy, immunotherapy, or targeted agents. Key requirements listed on clinicaltrials.gov include:

• Measurable disease by RECIST 1.1 criteria
• At least one tumor that can be safely injected or biopsied
• ECOG performance status of 0 or 1
• Adequate organ function

People are excluded if they need anticoagulant or anti-platelet therapy that cannot be paused for injections and biopsies, have untreated central nervous system metastases, have a history of myocarditis, have known HIV or active hepatitis B or C, or are taking high-dose immunosuppressive medication.

Study Locations

According to the trial record, STEALTH-001 is enrolling at the following U.S. sites:

• USC Norris Comprehensive Cancer Center, Los Angeles, California
• UC Irvine Health, Orange, California
• University of Miami, Miami, Florida
• Community Health Network, Indianapolis, Indiana
• UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania
• Mary Crowley Cancer Research, Dallas, Texas
• University of Texas MD Anderson Cancer Center, Houston, Texas

Why This Trial Matters

Oncolytic viruses are a different approach from the checkpoint inhibitors that have reshaped mesothelioma care over the past several years. Instead of releasing a brake on the immune system, an oncolytic virus is engineered to infect and destroy tumor cells directly while delivering signals that draw immune cells to the tumor. The idea behind combining VET3-TGI with atezolizumab is that the virus may make a tumor more visible to the immune system, and the checkpoint inhibitor may then help sustain the immune response.

KaliVir dosed the first patient in STEALTH-001 on October 8, 2024. In May 2025, the company reported that an independent Data Safety Committee had reviewed the first cohort and approved continued dosing in the next intratumoral and intravenous groups. The company has not reported efficacy results, and as an early-phase safety study, STEALTH-001 is not designed to prove that the treatment works.

Limitations to Consider

This is a Phase 1/1b trial. Its primary purpose is to assess safety, identify dose-limiting toxicities, and recommend a dose for later study, not to demonstrate benefit. With a target of roughly 60 participants spread across four groups and many tumor types, it cannot establish how well VET3-TGI works against mesothelioma specifically.

VET3-TGI is investigational and has not been approved by any regulator. The trial is open only at a small number of U.S. academic and specialty centers, which may limit access for people who live far from those sites. Meaningful results will take years to emerge, with the study’s estimated completion in late 2027.