Oncolytic poxvirus CF33-hNIS-ΔF14.5 favorably modulates tumor immune microenvironment and works synergistically with anti-PD-L1 antibody in a triple-negative breast cancer model

Abstract

Triple-negative breast cancer is the most aggressive subtype of breast cancer and is difficult to treat. Breast cancer is considered to be poorly immunogenic and hence is less responsive to immunotherapies. We tested whether the oncolytic poxvirus CF33-hNIS-ΔF14.5 could modulate tumor immune microenvironment and make the tumors responsive to the immune checkpoint inhibitor anti-PD-L1. We found that virus infection causes the upregulation of PD-L1 levels on triple-negative breast cancer cells in vitro as well as in vivo in mice. In a mouse model of orthotopic triple-negative breast cancer, the virus was found to increase tumor infiltration by CD8+ T cells. Likewise, in mice treated with CF33-hNIS-ΔF14.5 high levels of proinflammatory cytokines IFNγ and IL-6 were found in the tumors but not in the serum. The levels of immune modulation were even higher in mice that were treated with a combination of the virus and anti-PD-L1 antibody. While CF33-hNIS-ΔF14.5 and anti-PD-L1 antibody failed to exert significant anti-tumor effect as a single agent, a combination of the two agents resulted in significant antitumor effect with 50% mice experiencing complete tumor regression when both agents were injected intra-tumorally. Furthermore, the 'cured' mice did not develop tumor after re-challenge with the same cancer cells suggesting that they developed immunity against those cancer cells. Taken together, our study shows that CF33-hNIS-ΔF14.5 favorably modulates tumor immune microenvironment in triplenegative breast cancer model making them responsive to the immune checkpoint inhibitor anti-PD-L1, and hence warrants further studies to determine the clinical applicability of this combination therapy.

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“…The chimerization, cloning, competitive selection and sequence of CF33 backbone virus have been described previously [ 10 , 11 , 13 , 35 ]. In brief, 9 strains of orthopoxvirus were co-infected and 100 resulting viral plaques were clonally isolated and purified.…”

“…Subsequent manipulations of CF33 backbone virus have ensued. Insertion of the hNIS expression cassette or firefly luciferase under the control of the vaccinia H5 synthetic early (SE) promoter at the J2R locus has also been described [ 11 , 12 ], as has the deletion of the F14.5L gene [ 13 , 35 ] and insertion of the anti-PD-L1 transgene at the F14.5L locus [ 16 ]. Previous experiments have demonstrated minimal-to-no differences in viral function with in vitro between parent CF33 and CF33-hNIS or CF33-hNIS-anti-PD-L1 or CF33-hNIS-ΔF14.5 [ 12 , 16 ].…”

“…Capable of rapidly recruiting immune and inflammatory cells, viroimmunotherapy is gaining traction as a clinically useful treatment modality, particularly in immunosuppressed tumors devoid of effector immune cells [ 8 ]. We have created a recombinant orthopoxvirus as previously described [ 9 , 10 , 11 , 12 , 13 ] and have demonstrated pre-clinical promise against colon cancer [ 11 , 12 ].…”

“…Our group and others have demonstrated additive/synergistic effects of combining OVs with immune checkpoint inhibition [ 13 , 14 , 15 , 16 ]. Specifically, our group has used a CF33-derivative, CF33-hNIS-ΔF14.5 in combination with systemically delivered anti-PD-L1 to induce durable tumor-specific cure in a breast cancer model [ 13 ].…”

“…Our group and others have demonstrated additive/synergistic effects of combining OVs with immune checkpoint inhibition [ 13 , 14 , 15 , 16 ]. Specifically, our group has used a CF33-derivative, CF33-hNIS-ΔF14.5 in combination with systemically delivered anti-PD-L1 to induce durable tumor-specific cure in a breast cancer model [ 13 ]. However, in immunosuppressed tumors with substantial fibrosis, delivery to sequestered tumor cells may still represent a cure-limiting factor for immunogenic therapies like OVs [ 17 , 18 ].…”