KaliVir reports a 71% response rate with VET3-TGI in advanced cutaneous cancers, including melanoma and Merkel cell carcinoma, in Phase 1/1b STEALTH-001.
Written By: Sravani Pamanji, PharmD
Reviewed By: Pharmacally Editorial Team
KaliVir Immunotherapeutics has reported preliminary clinical findings from its Phase 1/1b STEALTH-001 trial, demonstrating an objective response rate (ORR) of 71% (5 of 7 patients) with intratumoral VET3-TGI in patients with advanced cutaneous malignancies. All seven patients had experienced disease progression following previous anti-PD-1/PD-L1 treatment.
Across the overall response-evaluable population of 12 patients, the ORR was 41.7% (5 of 12), with a disease control rate (DCR) of 75% (9 of 12). Notably, tumor regression was observed in both injected and non-injected lesions, raising the possibility of antitumor activity beyond directly treated tumors.
The findings were presented at the Society for Immunotherapy of Cancer (SITC) 2026 Annual Meeting on November 6.
STEALTH-001: Study Design and Patient Population
STEALTH-001 (NCT06444815) is an ongoing, open-label, non-randomized Phase 1/1b study evaluating VET3-TGI alone and in combination with atezolizumab in patients with advanced solid tumors.
The study investigates two administration routes: intratumoral injection and intravenous (IV) infusion. Its four treatment groups comprise intratumoral VET3-TGI monotherapy (Group A), intratumoral VET3-TGI plus atezolizumab (Group B), intravenous VET3-TGI monotherapy (Group C), and intravenous VET3-TGI plus atezolizumab (Group D).
The Phase 1 component primarily evaluates safety, tolerability and maximum tolerated dose (MTD) for the respective administration routes. Phase 1b expansion cohorts further investigate preliminary antitumor activity at selected doses, with RECIST version 1.1 used for response assessment. The sponsor identifies safety and tolerability as primary study objectives and preliminary antitumor activity as a secondary objective.
The preliminary efficacy dataset comprised 12 response-evaluable patients treated through intratumoral administration, including seven with advanced cutaneous malignancies: three with Merkel cell carcinoma, three with advanced melanoma and one with cutaneous squamous cell carcinoma. All seven had received at least one previous line of systemic therapy and experienced progression following anti-PD-1/PD-L1 treatment.
The study has a planned enrollment of approximately 60 participants.
Antitumor Activity Across Cutaneous Malignancies
The reported 71% ORR (5 of 7) represents the central efficacy finding in the cutaneous cancer subgroup.
All three patients with Merkel cell carcinoma achieved an objective response, while two of the three patients with advanced melanoma also responded. Among the five responders, four received VET3-TGI monotherapy and one received VET3-TGI in combination with atezolizumab. The reported efficacy dataset relates to intratumoral administration rather than the intravenous treatment groups.
One patient with Merkel cell carcinoma was reported to have achieved a complete response (CR).
In the overall response-evaluable population, the ORR was 41.7% (5 of 12), and the DCR was 75% (9 of 12).
Another important observation was tumor regression in non-injected lesions. In immuno-oncology, this type of response is often discussed in the context of a potential abscopal effect, in which local treatment may be associated with antitumor activity at distant sites. However, the observed regression does not independently establish a systemic immune-mediated mechanism.
All five responders remained on treatment at the data cutoff, with treatment durations ranging from 10 to 19 months. Responses continued to deepen in some patients. These observations warrant further investigation, although treatment duration should not be interpreted as an established duration of response.
VET™ Platform and Mechanism of Action
VET3-TGI is built on KaliVir’s proprietary VET™ (Vaccinia Enhanced Template) platform, an engineered vaccinia virus backbone designed to improve tumor targeting, systemic delivery and tumor-selective viral replication.
The platform incorporates genetic modifications intended to support viral delivery to tumors and enhance replication within tumor cells. VET3-TGI additionally carries two therapeutic transgenes: interleukin-12 (IL-12) and a transforming growth factor-beta (TGF-β) inhibitor.
IL-12 is intended to stimulate antitumor immune activity, while the TGF-β inhibitor is designed to block immunosuppressive signaling within the tumor microenvironment. KaliVir describes this inhibitor as a modified molecule that binds the TGF-β type II receptor.
By combining direct tumor-cell destruction through viral oncolysis with immune modulation, VET3-TGI is designed to address both tumor growth and local immune suppression. This provides a biological rationale for investigating the therapy in malignancies that have progressed following checkpoint inhibitor treatment. Nevertheless, the contribution of each component to the clinical responses remains to be established.
Preliminary Safety Findings
The reported safety findings showed no dose-limiting toxicities (DLTs). Treatment-related adverse events were predominantly Grade 1 or Grade 2, and no treatment-related deaths were reported.
These observations provide an initial indication of tolerability in the evaluated population. However, the small dataset cannot exclude uncommon, delayed or dose-dependent adverse events. Continued clinical evaluation will be necessary to characterize the safety profile of VET3-TGI as monotherapy and in combination with atezolizumab.
Clinical Interpretation
The STEALTH-001 findings provide an early clinical activity signal for VET3-TGI in advanced cutaneous malignancies following checkpoint inhibitor treatment. Responses in all three patients with Merkel cell carcinoma and two of three patients with melanoma are noteworthy given their previous treatment histories.
The regression of non-injected lesions adds another dimension to the findings, raising the possibility of an abscopal effect following intratumoral administration. However, the biological mechanism and clinical significance of this observation require further investigation.
The results remain preliminary, involving only seven patients in the cutaneous cancer subgroup and 12 patients overall. STEALTH-001 is an ongoing early-phase, non-randomized study without a comparator arm. Consequently, these response rates cannot establish comparative efficacy or demonstrate superiority over existing treatments.
VET3-TGI remains investigational, and its safety and effectiveness have not been established. Larger clinical cohorts and longer follow-up will be required to determine whether the preliminary response signal translates into durable clinical benefit.
Reference
KaliVir Immunotherapeutics Reports 71% Objective Response Rate in Patients with Advanced, Cutaneous Malignancies in Phase 1/1b STEALTH-001 Trial, KaliVir Immunotherapeutics, 06 November 2026
A Study of VET3-TGI in Patients with Solid Tumors (STEALTH-001), ClinicalTrials.gov ID NCT06444815
About the Writer
Sravani Pamanji is a PharmD (LinkedIn) professional with experience in scientific writing, medical literature review, drug profile preparation, and clinical case documentation. She has contributed to scientific publication and presented at the 74th Indian Pharmaceutical Congress. Her training includes ICH GCP E6(R3), scientific research, and medication safety. She is passionate about evidence-based medical communication and accurate dissemination of clinical and pharmaceutical information.