Abstract P3-11-01: Oncolytic herpes simplex virus immunovirotherapy eradicates breast cancer and prevents tumor relapse
Authors: Nguyen Hong-My , Almanza Othon , Saha Dipongkor 
Published: March 2022

Syngeneic mouse tumor models are critical to investigating new immunotherapeutic modalities and providing a rationale for clinical translation. Oncolytic herpes simplex virus (oHSV) is an emerging treatment strategy for breast cancer. Genetically modified oHSV selectively replicates in cancer cells (sparring healthy cells), induces immunogenic cancer cell death, and stimulates innate/adaptive anti-tumor immune responses. The therapeutic success of oHSV depends on a dynamic interaction between oHSV, the tumor, and the host. Here, we evaluated the anti-tumor effects of G47Δ-IL12, a genetically engineered oHSV expressing interleukin-12 (IL-12), in two orthotopic immunocompetent mouse models of breast cancer, E0771 (some classified this model as luminal B subtype and some as triple-negative) and EMT6 (triple-negative subtype), which are syngeneic to C57BL/6 and BALB/c mice, respectively. Intratumoral G47Δ-IL12 treatment led to complete eradication of orthotopic E0771 and EMT6 mammary tumors and prevention of lung metastases, resulting in 100% long-term survivors, which remained tumor-free during the observation period (&gt;100 days following the last G47Δ-IL12 treatment). In a contralateral orthotopic mammary tumor model, G47Δ-IL12 treatment of primary tumors led to the eradication of both treated and untreated distal tumors, confirming the abscopal and anti-metastatic effect of G47Δ-IL12 virotherapy. All cured mice from G47Δ-IL12-treated groups rejected lethal tumor re-challenge in the contralateral naïve mammary fat pad, indicating successful generation of a protective memory response. In both E0771 and EMT6 models, cell-specific IFN-γ responses and the presence of effector memory T cells (CD4+CD44highCD62Llow phenotype) in spleens of long-term survivors, possibly contributing to tumor relapse prevention. G47Δ-IL12-mediated anti-tumor efficacy was associated with significant increases in CD4+ and CD8+ tumor-infiltrating lymphocytes (TILs) (vs. mock group) in both E0771 and EMT6 tumor lesions. G47Δ-IL12 monotherapy also led to a significantly increased CD8+/FoxP3+ ratio (an important parameter for immunotherapy success) in both tumor models. Interestingly, immune cell depletion studies demonstrated that efficacy requires both CD4+ and CD8+ T cells in the E0771 model while only CD8+ T cells were required in the EMT6 model. Conclusions: G47Δ-IL12 monotherapy was effective in eradicating both orthotopic and metastatic tumors and generating long-term protective memory responses in two syngeneic breast cancer models. Treatment efficacy of G47Δ-IL12 was associated with significant immunologic alterations of the TME. G47Δ-IL12 utilized distinct immunologic mechanisms of action to eradicate tumors: CD8+ T cell-dependent action in the EMT6 model, whereas CD4+ and CD8+ T cell-dependent efficacy in the E0771 model. Altogether, our data suggest that G47Δ-IL12 is an efficient inflammatory modulator and beneficially exploits the immune system to eradicate breast tumors. These studies provide the necessary supporting evidence for the clinical translation of this agent into breast cancer patients.

Citation Format: Hong-My Nguyen, Othon Almanza, Dipongkor Saha. Oncolytic herpes simplex virus immunovirotherapy eradicates breast cancer and prevents tumor relapse [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-11-01.