Oncolytic virus-initiated protective immunity against prostate cancer

Abstract

Recently reovirus-based oncotherapy has been successfully implemented for the treatment of prostate cancer. In this report, we show that apart from its primary direct cancer-killing activity, reovirus oncotherapy overrides tumor-associated immune evasion strategies and confers protective antiprostate cancer immunity. Prostate cancer represents an ideal target for immunotherapies. However, currently available immune interventions fail to induce clinically significant antiprostate cancer immune responses, owing to the immunosuppressive microenvironment associated with this disease. We show here that during the process of oncolysis, reovirus acts upon prostate cancer cells and initiates proinflammatory cytokines and major histocompatibility complex (MHC) class I molecule expression. In an immunocompetent transgenic adenocarcinoma of mouse prostate (TRAMP) model, reovirus oncotherapy induces the homing of CD8(+) T and NK cells in tumors and the display of tumor-associated antigens (TAAs) on antigen-presenting cells (APCs), and endows dendritic cells (DCs) with a capacity to successfully present TAAs to tumor-specific CD8(+) T cells. These newly generated immunological events lead to the development of strong antiprostate cancer T cell responses, which restrict the growth of subsequently, implanted syngeneic tumor in an antigen-specific, but reovirus-independent manner. Such reovirus-initiated antiprostate cancer immunity represents a clinically valuable entity that can promote long-term cancer-free health even after discontinuation of the primary oncotherapy.

Figure 1

Susceptibility of mouse transgenic adenocarcinoma of mouse prostate-C1 (TRAMP-C1) cells to reovirus-mediated oncolysis in vitro and in vivo. (a) BPH-1 and TRAMP-C1 cells were cultured in the presence of live reovirus [LRV; 1–10 multiplicity of infection (MOI)] or phosphate-buffered saline (PBS) (control) for 18–24 hours and then analyzed microscopically. Confocal microscopy (top panel, red: reovirus) and light field contrast (bottom panel) images display reovirus-infected and apoptotic cells, respectively. (b) Total (T) and activated (A) Ras in prostate cancer cells were pulled down using conjugated Raf-domain and detected by anti-Ras antibody. Levels of β-actin served as an internal control. (c) Human and mouse prostate cancer cells were cultured in the presence of PBS or LRV for 24 hours, stained with antireovirus antibody or annexin-V/7-AAD and analyzed in flow cytometry. The numbers indicate the percentages of reovirus-infected (histograms: filled, PBS; open, reovirus) and apoptotic (dot-plots) cells. (d) NOD/SCID mice were subcutaneously (s.c.) implanted with 1 × 10⁶ TRAMP-C1 or 5 × 10⁵ BPH-1 cells and evaluated for tumor growth. When tumors reached a diameter of 25 mm², mice were intratumorally (i.t.) administered with 5 × 10⁶ plaque-forming units (pfu) of UVRV/LRV or PBS at the time points indicated by arrows, and then monitored for tumor growth. (e) Immunocompetent C57BL/6 mice were implanted with 5 × 10⁶ TRAMP-C1 cells. When tumors reached a diameter of 25 mm², mice were administered i.t. with 5 × 10⁸ pfu of UVRV/LRV or PBS, at every indicated time point, and monitored for tumor growth. The data is a representative of three independent experiments.

Figure 2

Reovirus induces homing of immune cell into prostate tumors. C57BL/6 mice-bearing transgenic adenocarcinoma of mouse prostate-C1 (TRAMP-C1) tumors were administered with therapeutic regimen of phosphate-buffered saline (PBS)/UV-inactivated reovirus (UVRV)/live reovirus (LRV). On day 3 post last injection (p.l.i.), tumor-infiltrating lymphoid cells (TILs) were isolated, stained, and directly analyzed in flow cytometry to determine the frequency of (a) H2Kb⁺ immune cells, (b) CD3⁺, CD8⁺ T cells, and (c) NK cells. Numbers listed on dot-plots indicate the percentages of cells present in a respective quadrant, while bar graphs represent the cumulative data from three independent experiments for respective cell subtype.

Figure 3

Reovirus enhances the expression of major histocompatibility complex (MHC) class I molecules on prostate tumors and display of tumor-associated antigens (TAA) on antigen-presenting cells (APCs). (a) Transgenic adenocarcinoma of mouse prostate-C1 (TRAMP-C1) tumors from C57BL/6 mice were excised, digested with collagenase, and prepared as single-cell suspension. These TRAMP-C1 tumor cells, in parallel with in-vitro cultured cells, were stained with anti-H2Kb antibodies and analyzed in flow cytometry. (b) Single-cell suspensions prepared from the phosphate-buffered saline (PBS)/UV-inactivated reovirus (UVRV)/live reovirus (LRV)-treated TRAMP-C1 tumors (as per protocol described in Figure 1e) were stained with anti-H2Kb antibodies and analyzed in flow cytometry. Cumulative data from three experiments is shown. (c) TRAMP-C1 tumors expressing a surrogate TAA ovalbumin (ova; TRAMP-C1-ova) were grafted on C57BL/6 mice. The resultant tumors were injected with PBS/UV-inactivated reovirus (UVRV)/live reovirus (LRV) (PBS/UVRV/LRV) (as per protocol in Figure 1e). On day 5, TILs were isolated and stained with 25D1.16 antibody. Numbers on dot-plot represent the percentages of cells expressing the SIINFEKL–H2Kb complexes. Cumulative data from three independent experiments is shown in a bar graph. (d) TRAMP-C1 cells cultured in the presence or absence of splenocytes were added with PBS/UVRV/UVRV for 24 hours, stained with anti-H2Kb antibodies and analyzed. TRAMP-C1 cells stimulated with 10 units/ml of IFN-γ were used as a positive control. Events were separated based on size scatter properties to evaluate the expression of MHC class I on tumor cells. Data is representative of three independent experiments.

Figure 4

Reovirus enhances the presentation of prostate tumor-associated antigen (TAA) to tumor-specific CD8 T cells. (a) 1 × 10⁵ bone marrow-derived dendritic cells (BMDCs) cultured in the presence of 1 × 10⁵ native TRAMP-C1 or TRAMP-C1-ova tumor cells were incubated with phosphate-buffered saline (PBS) or 1 multiplicity of infection (MOI)/cell of UV-inactivated reovirus (UVRV) or live reovirus (LRV) for 24 hours. Then, 5 × 10⁴ B3Z cells were added to these cultures for an additional 18 hours and then evaluated for the breakdown of β-galactosidase substrate to define CD8 T cell activation. (b) Native or ova-expressing TRAMP-C1 tumor-bearing C57BL/6 mice were treated with PBS/UV-inactivated reovirus (UVRV)/live reovirus (LRV) (PBS/UVRV/LRV) (as per Figure 1e). On day 5 p.l.i., tumor-infiltrating dendritic cells were isolated and assessed in the B3Z antigen presentation assay (see Materials and Methods section). Data is representative of four independent experiments.

Figure 5

Reovirus oncotherapy initiates antiprostate T cell immunity. Native or ova-expressing transgenic adenocarcinoma of mouse prostate-C1 (TRAMP-C1) tumor-bearing C57BL/6 mice were injected with phosphate-buffered saline (PBS)/UV-inactivated reovirus (UVRV)/live reovirus (LRV) (PBS/UVRV/LRV) (as per Figure 1e). On day 7 post last injection (p.l.i), tumor-infiltrating lymphoid cells (TILs) were isolated. (a) TILs were labeled with CFSE from native or ova-expressing tumors were stimulated with SIINFEKL or TRAMP-C1 tumor lysate, respectively, and then analyzed in proliferation assay. (b) TILs from PBS/UVRV/LRV-treated TRAMP-C1-ova tumors were stimulated with SIINFEKL for 6 hours and then evaluated in interferon-γ (IFN-γ)/CD107a assay. (c) B6.PL-Thy1^a/CYJ mice (thy1.1⁺; congenic to C57BL/6) were injected with TRAMP-C1-ova tumor cells, allowed to develop tumors and then injected with PBS/UV-inactivated reovirus (UVRV)/live reovirus (LRV) (PBS/UVRV/LRV) (as per Figure 1e). After 5 days p.l.i., these thy1.1⁺ mice were injected (i.v.) with naive, CFSE-labeled ova-specific transgenic T cells isolated from the spleens of OT-1 mice (thy1.2⁺). After 7 days, the lymph nodes of recipient thy1.1 mice were harvested, stained with anti-thy1.2 and CD3 antibodies, and assessed in CFSE assay. Histograms display characteristic halving of CFSE fluorescence in proliferating CD3⁺, thy1.2⁺ OT-1 donor cells as analyzed with ModFit LT. Sequential daughter cell generations present in proliferating donor cells are represented by various shades/colors in histograms. Bar graph represents a cumulative data from three independent experiments.

Figure 6

Oncotherapy-initiated antitumor immunity protects against subsequent tumor challenge. (a) C57BL/6 mice were subcutaneously (s.c.) injected with phosphate-buffered saline (PBS) or transgenic adenocarcinoma of mouse prostate-C1 (TRAMP-C1) cells, and then administered with therapeutic regimen of PBS, UV-inactivated reovirus (UVRV), or live reovirus (LRV) at indicated time points. Seven days p.l.i., splenocytes were harvested and adoptively transferred into naive C57BL/6 mice. (b) After additional 7 days, recipient mice were further challenged with either 5 × 10⁶ TRAMP-C1 or 5 × 10⁵ Lewis lung carcinoma (LLC) tumor cells and monitored for tumor growth to determine survival.