Oncolytic Virus Expressing Non-Secreted DR-18 Cytokine Induces Potent, Systemic Antitumor Immunity

A recent study published in

Molecular Therapy: Oncology (Vol. 33, Sept 2025) demonstrates the therapeutic potential of a novel oncolytic vaccinia virus (oVV) encoding a non-secreted, decoy-resistant IL-18 mutein (nsmDR-18). This engineered virus induced strong antitumor responses and systemic immune memory in preclinical mouse models — without the toxicity often associated with secreted cytokine therapies.

Study Overview: Improving Cytokine Delivery with Oncolytic Viruses

Cytokines are promising for cancer treatment but face challenges like short half-lives, high-dose requirements, and systemic toxicity. Cytokines also have natural inhibitors, such as IL-18 binding protein (IL-18BP), which suppresses IL-18 function.

Oncolytic viruses (OVs) provide a way to overcome these limitations by delivering cytokines directly to tumor sites, allowing for high local concentrations within the tumor microenvironment (TME).

The researchers engineered an oncolytic vaccinia virus (oVV) to deliver interleukin-18 (IL-18) and its variants, assessing their antitumor effects in various tumor models. The virus used was a double viral-gene-inactivated (tk- and vgf-) oVV, referred to as vvDD.

They evaluated multiple forms of IL-18, including:

vvDD-IL-18: Expresses wild-type murine IL-18.
vvDD-smDR-18: Expresses secreted decoy-resistant IL-18 mutein (DR-18).
vvDD-nsmDR-18: Expresses non-secreted, mature decoy-resistant IL-18 mutein (nsmDR-18).

Key Findings

The vvDD-nsmDR-18-expressing oVV showed potent antitumor efficacy with reduced systemic toxicity compared to other forms. In the MC38-luc peritoneal cancer model, the median survival time for mice treated with vvDD-nsmDR-18 was 41 days, which was a significant improvement compared to the 32 days for vvDD-DR-18 and the severe early death observed with vvDD-smDR-18 due to toxic effects. This improved safety was also evidenced by a lack of severe toxicity markers like lung edema and liver damage.

This treatment was found to have a significant effect on the tumor microenvironment (TME), transforming "cold" tumors into "hot" tumors.

The study found that vvDD-nsmDR-18 treatment led to:

Increased expression of antitumor factors like IL-2, interferon gamma (IFN-γ), granzyme B (GzmB), and perforin.
Expansion of tumor-reactive $C D 3 9^{+} C D 10 3^{+} C D 8^{+}$ T cells.
A reduction in severely exhausted $P D - 1^{+} T I M - 3^{+} C D 8^{+}$ T cells.
An increase in regulatory T cells (Tregs) and upregulation of immune checkpoint molecules (PD-1, PD-L1, and CTLA-4).

The study also showed that the antitumor effect of vvDD-nsmDR-18 was dependent on $C D 8^{+}$ T cells and IFN-γ, but not $C D 4^{+}$ T cells.

Combining vvDD-nsmDR-18 with anti-CTLA-4 antibody led to significantly improved outcomes.

The median survival time for mice receiving the combination therapy was 59 days, compared to 42 days for the group receiving a combination of vvDD and anti-CTLA-4 antibody, and 41 days for the vvDD-nsmDR-18 treatment alone.
In cured mice, re-challenging them with the same tumor cells resulted in complete tumor rejection in 60% of the mice, suggesting the establishment of systemic, tumor-specific antitumor immunity.
The combination therapy also resulted in a non-significant delay in the growth of irrelevant tumor cells, suggesting that factors like mouse age and shared tumor antigens may play a role.

ichorbio's Role in the Study

To test the hypothesis that CTLA-4 blockade could enhance the effects of vvDD-nsmDR-18, the researchers administered an anti-CTLA-4 antibody in combination with the virus. For this, they used:

Anti-CTLA-4 antibody (Clone 9D9, ichorbio).

The antibody was administered at a dose of 200 μg intraperitoneally (i.p.) on days 5, 7, 9, and 11 post-tumor cell inoculation.

This combination was critical to establishing the enhanced antitumor efficacy, demonstrating the utility of clone 9D9 in functional in vivo studies of immunotherapy.

Product Cited

Anti-CTLA-4 antibody – Clone 9D9
- In vivo functional grade
- View Product →

Read the Full Study

Ye et al. Molecular Therapy: Oncology (2025) https://doi.org/10.1016/j.omton.2025.201022