A Predictive Model for Synergistic Oncolytic Virotherapy: Unveiling the Ping-Pong Mechanism and Optimal Timing of Combined Vesicular Stomatitis and Vaccinia Viruses

TL;DR

This study develops a seven-variable ODE framework to quantify the synergistic anti-tumor effects of combining Vaccinia Virus and Vesicular Stomatitis Virus, mediated by the B18R-driven neutralization of interferon-$\alpha$ and a ping-pong enhancement of viral replication. Through nondimensionalization, quasi-steady-state reduction, and bifurcation analysis, the authors identify critical thresholds in viral burst sizes and B18R inhibition that govern therapy success, and define viral basic reproduction numbers $\mathcal{R}_0^1$ and $\mathcal{R}_0^2$ that exceed unity by large margins in calibrated tumor models. Numerical simulations show that VV-VSV combination achieves complete tumor clearance in about 50 days, an 11% improvement over VV monotherapy, with VSV contributing the dominant oncolysis once the interferon barrier is lowered. The optimal administration strategy favors immediate VSV delivery followed by VV after 1–19 days, a sequence that exploits VV’s immune-modulating effects to maximize VSV spread, and provides a quantitative framework for experimental design and clinical translation in precision oncolytic virotherapy.

Abstract

We present a mathematical model that describes the synergistic mechanism of combined Vesicular Stomatitis Virus (VSV) and Vaccinia Virus (VV). The model captures the dynamic interplay between tumor cells, viral replication, and the interferon-mediated immune response, revealing a `ping-pong' synergy where VV-infected cells produce B18R protein that neutralizes interferon-$α$, thereby enhancing VSV replication within the tumor. Numerical simulations demonstrate that this combination achieves complete tumor clearance in approximately 50 days, representing an 11\% acceleration compared to VV monotherapy (56 days), while VSV alone fails to eradicate tumors. Through bifurcation analysis, we identify critical thresholds for viral burst size and B18R inhibition, while sensitivity analysis highlights infection rates and burst sizes as the most influential parameters for treatment efficacy. Temporal optimization reveals that therapeutic outcomes are maximized through immediate VSV administration followed by delayed VV injection within a 1-19 day window, offering a strategic approach to overcome the timing and dosing challenges inherent in OVT.

Figures (15)

• Figure 1: Schematic representation of the mathematical model describing the synergistic interaction between Vaccinia Virus (VV) and Vesicular Stomatitis Virus (VSV) with tumor cells. The model consists of seven state variables: uninfected tumor cells ($T_u$), VV-infected tumor cells ($T_1$), VSV-infected tumor cells ($T_2$), free VV particles ($V_1$), free VSV particles ($V_2$), B18R protein concentration ($C_1$), and interferon-alpha concentration ($C_2$). Solid lines denote direct processes: viral infection, cell lysis, virus production, and molecular synthesis. Dashed lines represent inhibitory interactions. Key interactions include: proliferation of uninfected tumor cells ($T_u$) atm a rate $\alpha$ with carrying capacity $K$; infection of tumor cells by VV and VSV with Michaelis-Menten kinetics and infection rates $\beta_1$ and $\tilde{\beta}_2(C_2)$ respectively; lysis of infected tumor cells at rates $l_1$ and $l_2$; (4) virus production with burst sizes $b_1$ and $b_2$; virus clearance at rates $\gamma_1$ and $\gamma_2$; B18R production by VV-infected cells at rate $\alpha_1$ and B18R decay at rate $\mu_1$; IFN-$\alpha$ production by VSV-infected cells at rate $\alpha_2$ and IFN-$\alpha$ decay at rate $\mu_2$; inhibition of IFN-$\alpha$ by B18R at rate $\lambda$. The synergy arises as VV-infected cells produce B18R, which binds to and inhibits IFN-$\alpha$, thereby reducing the inhibitory effect on VSV infection described by $\tilde{\beta}_2(C_2) = \beta_2/(1 + C_2/C_2^*)$.
• Figure 2: Optimization of virus injection timing for VV-VSV combination therapy. (a) Final tumor burden as a function of VV injection time $\tau_1$ shows optimal therapeutic window between 1-19 days when VSV is administered immediately ($\tau_2 = 0$). (b) Final tumor burden increases monotonically with VSV delay $\tau_2$, indicating immediate VSV administration is optimal. The combined results establish the optimal strategy: immediate VSV followed by delayed VV injection (1-19 days).
• Figure 3: Optimization of virus injection timing for VV-VSV combination therapy. (a) Temporal tumor dynamics demonstrate that immediate VSV injection ($\tau_2 = 0$) yields lower tumor concentrations across treatment timeline. (b) Temporal tumor dynamics demonstrate that delayed VV injection ($\tau_1 > 0$) yields lower tumor concentrations across treatment timeline. Collectively, these analyses establish the optimal strategy: immediate VSV injection followed by delayed VV administration within 1-19 days.
• Figure 4: Monotherapy limitations in tumor clearance. (a) VSV alone fails to achieve complete tumor eradication, with residual tumor burden persisting beyond 250 days due to IFN-$\alpha$-mediated antiviral responses. (b) VV monotherapy achieves complete tumor clearance in approximately 56 days. These results show the complementary strengths of each virus and the rationale for combination approach.
• Figure 5: Synergistic enhancement of VSV efficacy through VV-mediated interferon suppression. Both models demonstrate the "ping-pong" mechanism where VV-infected cells produce B18R protein, which binds to and neutralizes IFN-$\alpha$, creating a permissive environment for enhanced VSV replication. (a) Full model simulations show molecular interactions and population dynamics. (b) Quasi steady-state model captures synergistic dynamics with reduced computational complexity. The increased population of VSV-infected tumor cells ($T_2$) in both models shows the biological mechanism of synergy.

Theorems & Definitions (8)

• Theorem 1: Well-posedness
• Theorem 2
• Theorem 3
• Theorem 4
• proof : Proof of Theorem \ref{['thm:well-posedness']}
• proof
• proof
• proof