Pre-Existing HSV-1 Immunity Enhances Anticancer Efficacy of a Novel Immune-Stimulating Oncolytic Virus

Abstract

Oncolytic viruses (OVs) can specifically replicate in the host and cause cancer cell lysis while inducing an antitumor immune response. The aim of this study is to investigate the impact of either pre-existing immunity against herpes simplex virus type-1 (HSV-1) or multicycle treatment with OVs on anticancer efficacy of VG161, an HSV-1 OV in phase 2 clinical trial. VG161 efficacy was tested in CT26 mouse models by comparing the efficacy and immune response in naïve mice or in mice that were immunized with VG161. Moreover, VG161 efficacy in HLA-matched CD34+ humanized intrahepatic cholangiocarcinoma (ICC) patient-derived xenograft (PDX) models was also tested in multicycle treatment and was compared to standard chemotherapy for this type of cancer (gemcitabine). The HSV-1-immunized mice significantly inhibited tumor growth in VG161-treated mice compared to control naïve treated mice. RNA expression profiling and ELISPOT analyses indicated changes in the tumor's immune profile in the immunized and treated group compared to naïve and treated mice, as well as enhanced T cell function depicted by higher numbers of tumor specific lymphocytes, which was enhanced by immunization. In the ICC PDX model, repeated treatment of VG161 with 2 or 3 cycles seemed to increase the anticancer efficacy of VG161. In conclusion, the anticancer efficacy of VG161 can be enhanced by pre-immunization with HSV-1 and multicycle administration when the virus is given intratumorally, indicating that pre-existing antiviral immunity might enhance OV-induced antitumor immunity. Our results suggest potential clinical benefits of HSV-1-based OV therapy in HSV-1-seropositive patients and multicycle administration of VG161 for long-term maintenance treatment.

Keywords: HSV-1; immunotherapy; oncolytic viruses.

Figure 1

Anti-HSV-1 response after immunization in CT26 mouse models: Before the tumor implantation, serum was randomly collected from 2 naïve mice and 20 immunized mice. The anti-HSV-1 antibody level was detected using Mouse/Rat HSV-1 IgG ELISA kit. ** p < 0.05.

Figure 2

Efficacy and survival of CT26 mouse model treated with mVG161. (A) The schema of treatment protocol for Balb/c mice used in the CT26 tumor mode, (B) Mean tumor volume in each group in mice treated with mVG161 (single tumor model) (C) Survival curve for mice treated with mVG161 or vehicle, either immunized or naïve mice (single tumor model). (D) Immunization and treatment regimen for Balb/c mice used in the CT26 bilateral tumor model (E) Mean tumor volume in each group in mice treated with mVG161 (bilateral tumor model). (F) Survival of mice treated with mVG161 (Bilateral tumor model).

Figure 2

Efficacy and survival of CT26 mouse model treated with mVG161. (A) The schema of treatment protocol for Balb/c mice used in the CT26 tumor mode, (B) Mean tumor volume in each group in mice treated with mVG161 (single tumor model) (C) Survival curve for mice treated with mVG161 or vehicle, either immunized or naïve mice (single tumor model). (D) Immunization and treatment regimen for Balb/c mice used in the CT26 bilateral tumor model (E) Mean tumor volume in each group in mice treated with mVG161 (bilateral tumor model). (F) Survival of mice treated with mVG161 (Bilateral tumor model).

Figure 2

Efficacy and survival of CT26 mouse model treated with mVG161. (A) The schema of treatment protocol for Balb/c mice used in the CT26 tumor mode, (B) Mean tumor volume in each group in mice treated with mVG161 (single tumor model) (C) Survival curve for mice treated with mVG161 or vehicle, either immunized or naïve mice (single tumor model). (D) Immunization and treatment regimen for Balb/c mice used in the CT26 bilateral tumor model (E) Mean tumor volume in each group in mice treated with mVG161 (bilateral tumor model). (F) Survival of mice treated with mVG161 (Bilateral tumor model).

Figure 3

Humanized ICC PDX model. (A) Implantation of different human white blood cells in the different mouse groups before treatment. (B) Tumor size after administering VG161 to female Hu-NPI mice bearing patient tumor tissue. Data points represent group mean; error bars represent standard error of the mean (SEM).

Figure 4

CT26 Balb/c mouse models. Splenocytes were collected from each mouse 10 days after administering mVG161 or vehicle control. Cells were co-incubated with CT26 cells. ELISPOT kit was used to detect IFN-γ expression. Data points represent number of spots for each mouse. Error bars represent standard error of the mean (SEM).

Figure 5

Cell scores in tumors treated with mVG161 comparing immunized vs. naïve mice (A,B). Pathway analysis shows the most significant changes in different pathways when the same tumors were analyzed (C). differential gene analysis of the most significantly up or down-regulated genes in the tumors of naïve and mVG161 treated mice compared to immunized and mVG161 treated mice in CT26 tumors. (D) Volcano plot of differentially expressed genes in tumors from naïve treated mice compared to immunized treated mice. This analysis was performed using the NanoString platform.

Figure 5

Cell scores in tumors treated with mVG161 comparing immunized vs. naïve mice (A,B). Pathway analysis shows the most significant changes in different pathways when the same tumors were analyzed (C). differential gene analysis of the most significantly up or down-regulated genes in the tumors of naïve and mVG161 treated mice compared to immunized and mVG161 treated mice in CT26 tumors. (D) Volcano plot of differentially expressed genes in tumors from naïve treated mice compared to immunized treated mice. This analysis was performed using the NanoString platform.