Dual-Target Oncolytic Immunotherapy for Solid Tumors

Highlights from 2025 American Society of Gene and Cell Therapy (ASGCT) Annual Meeting

A next-generation cancer immunotherapy developed by KaliVir Immunotherapeutics combines two powerful mechanisms: inhibition of the immunosuppressive cytokine TGF-β and localized expression of the immune-stimulating cytokine IL-12. Delivered through a systemically administered a vaccinia virus-based immunotherapy viral platform, this approach addresses a central challenge in oncology, the immunosuppressive tumor microenvironment. It also overcomes the paradox where IL-12-induced IFN-γ leads to compensatory TGF-β upregulation, limiting therapeutic impact. In preclinical models, this therapy achieved 100% tumor clearance at doses far below anticipated clinical levels while maintaining a strong safety profile.

Platform Design and Tumor-Targeted Delivery

The therapy is based on a specially engineered viral platform (VET3-TGI) optimized for systemic delivery and precise tumor targeting. A key innovation involves inserting the chemokine receptor CXCR3 into the viral genome. This enables infected hematopoietic cells to express CXCR3 and migrate to tumors that produce matching chemokines.  The VET3-TGI also features an innovative therapeutic transgene combination that includes a TGF-β1 inhibitor (TGF-β mini-monomer, TGFβMM) and IL-12 expression. This dual approach counteracts TGF-β1–mediated immunosuppression while boosting type-1 immune responses within the tumor microenvironment, resulting in significantly enhanced anti-tumor immunity and durable complete responses. This targeting mechanism has been validated in vitro and in vivo, including in models with prior immunity or treatment exposure.

This strategy ensures high tumor delivery and minimizes off-target toxicity, a major barrier in systemic viral therapies. Post-mortem studies confirmed improved tumor localization and reduced systemic effects compared to control vectors.

TGF-β: A Barrier to Immune Activation

TGF-β plays a major role in immune evasion, acting initially as a tumor suppressor but later promoting tumor progression, metastasis, and immune suppression. It inhibits CD8+ T cell cytotoxicity, fosters regulatory T cells (Tregs), and suppresses NK cell activity. Blocking TGF-β restores effective immune surveillance, making it a high-value target in cancer immunotherapy.

IL-12: Driving Type-1 Immune Responses

IL-12 is a potent immune activator that enhances IFN-γ production through the JAK2/TYK2-STAT4 pathway, boosting CTL and NK cell function. It also promotes Th1 cell development, crucial for robust anti-tumor responses. However, systemic delivery of IL-12 causes toxicity, which this platform avoids by enabling tumor-localized expression for potent effects with reduced risk.

TGF-β and IL-12 Crosstalk

TGF-β suppresses IL-12 activity by blocking early signaling events such as JAK2/TYK2 and STAT4 phosphorylation, weakening IFN-γ production. Although IFN-γ can induce Smad7 to inhibit TGF-β signaling, this is often insufficient in tumors. Moreover, IL-12-induced IFN-γ may paradoxically upregulate TGF-β, creating a negative feedback loop. This supports the rationale for co-targeting both pathways.

A Synergistic Therapeutic Strategy

The therapy integrates TGF-β inhibition using a mini-monomer to reverse immune suppression, alongside IL-12 expression to promote robust type-1 immune responses. This dual action enhances CD8+ T cell and NK cell function, suppresses Tregs, and prevents the feedback-driven TGF-β rebound commonly seen with IL-12 monotherapy. Treated tumors show increased cytotoxic T cell infiltration, elevated inflammatory chemokines, and decreased expression of immunosuppressive genes.

Preclinical Performance and Clinical Readiness

Across multiple solid tumor models—including melanoma, colorectal, renal, and mammary carcinomas—the therapy achieved complete tumor elimination even at low doses. It remained effective despite pre-existing antiviral immunity and showed a strong safety profile with reduced systemic toxicity.

The data presented at the ASGCT 2025 meeting mark a key milestone in the clinical development of this approach. Its rational design, robust efficacy, and favorable safety position it as a promising candidate to reshape the future of multi-mechanistic immunotherapy for solid tumors.

Further Reading

  1. Mechanisms of synergy between TGF-beta inhibitor and IL12 expression from the systemically deliverable clinical oncolytic immunotherapy VET3-TGI: ASGCT 2025 Meeting Abstracts
  2. Novel oncolytic viral immunotherapy VET3-TGI displays enhanced systemic delivery and inhibits TGFb-signaling while augmenting type-1 immune response in the tumor.
  3. A novel oncolytic immunotherapy, VET3-TGI, overcomes TGFB1 mediated immunosuppression, augments type-1 immune response, and displays potent therapeutic activity in multiple mouse tumor models.
  4. Therapeutic targeting of TGF-β in cancer: hacking a master switch of immune suppression. 
  5. TGF-β and immune cells: an important regulatory axis in the tumor microenvironment and progression.
  6. IFN-γ and TGF-β, Crucial Players in Immune Responses: A Tribute to Howard Young.
  7. New insights into IL-12-mediated tumor suppression.
  8. Downregulation of interleukin-12 (IL-12) responsiveness in human T cells by transforming growth factor-beta: relationship with IL-12 signaling. 

 

About Marin Biologic Laboratories

Our Recent Publication/Meeting Presentation on Gene Therapy

1.  Development of a Pharmacokinetic (PK) Mouse Serum GLP ELISA for an Anti–CD19–AntiCD3 Diabody
bioRxiv 2025.03.19.644217; doi: https://doi.org/10.1101/2025.03.19.644217
2. Cell-Based Potency Assay for Anti-CD3-Anti-CD19 Diabody. bioRxiv 2025.04.15.648836v1 https://www.biorxiv.org/content/10.1101/2025.04.15.648836v1
3.  American Society of Hematology (ASH) Annual Meeting 2024.
Abstract link: Using Gene Therapy to Solve Challenges with CAR-T Cell Immunotherapy: Lead Selection and Preclinical Development of an Adeno-Associated Virus with Reduced Immunogenicity  Exhibiting Efficient and Long-Term Expression of an Anti-CD19 T-Cell Engager.

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Download the full presentation: Development of Custom Cell Based and In vitro Potency and Pharmacokinetics (PK) Assays for AAV vectors- Marin biologic Laboratories

 

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