Expression of TCRs in CD8+ T cells from pmel-1 (A, gp100-Tet+) or OT-I (B, OVA-Tet+) transgenic mice. Splenocytes from the mice were stained with tetramers binding with TCR specific for gp100 (pmel-1) or OVA (OT-I), and antibody against CD8. Stained cells were analyzed with flow cytometry. The numbers in upright corner of the dot plots indicate the frequency (% of splenocytes) of gp100-targeting (A) or OVA-targeting (B) in CD8+ T cells.
ARTICLE ABSTRACT
Cancer cell heterogeneity and immunosuppressive tumor microenvironment (TME) pose a challenge in treating solid tumors with adoptive cell therapies targeting limited tumor-associated antigens (TAAs), such as CAR T-cell therapy. We hypothesize that oncolytic adenovirus Delta-24-RGDOX activates the TME and promote antigen spread to potentiate the abscopal effect of adoptive TAA-targeting T-cells in localized intratumoral treatment. Herein, we used C57BL/6 mouse models with disseminated tumors derived from B16 melanoma cell lines to assess therapeutic effects and antitumor immunity. gp100-specific pmel-1 or OVA-specific OT-I T-cells were injected into the first subcutaneous (s.c.) tumor, followed by three injections of Delta-24-RGDOX. We found TAA-targeting T-cells injected into one s.c. tumor showed tumor tropism. Delta-24-RGDOX sustained the systemic tumor regression mediated by the T-cells, leading to improved survival rate. Further analysis revealed that, in mice with disseminated B16-OVA tumors, Delta-24-RGDOX increased CD8+ leukocyte density within treated and untreated tumors. Importantly, Delta-24-RGDOX significantly reduced the immunosuppression of endogenous OVA-specific cytotoxic T lymphocytes (CTLs) while increasing that of CD8+ leukocytes and, to a lesser extent, adoptive pmel-1 T-cells. Consequently, Delta-24-RGDOX drastically increased the density of the OVA-specific CTLs in both tumors, and the combination synergistically enhanced the effect. Consistently, the splenocytes from the combination group showed a significantly stronger response against other TAAs (OVA and TRP2) than gp100, resulted in higher activity against tumor cells. Therefore, our data demonstrate that, as an adjuvant therapy followed TAA-targeting T-cells in localized treatment, Delta-24-RGDOX activates TME and promotes antigen spread, leading to efficacious systemic antitumor immunity to overcome tumor relapse.
