Augmentation of antitumor responses by adoptively transferred CD8+ cells in the lymphopenic host by administration of HSV amplicons Free

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Cytotoxic treatments may directly affect cancer cells and frequently induce lymphopenia. Expansion of T cells in the setting of lymphopenia may affect T cell repertoire and response. The specific effects of lymphopenia on adoptively transferred T cells in the setting of established tumors has not been extensively studied. We studied the adoptive transfer of transgenic ovalbumin-specific CD8+ OT-1 T cells into irradiated immunocompetent mice, or into RAG-1 ^-/- mice and the effect of intratumoral injection of HSV amplicons on immune response. C57BL/6 mice were injected with E.G7 (Ovalbumin expressing mouse EL4 thymomas) in the right flank and treated with 550 cGy to induce lymphopenia, once the tumor diameter reached 5mm. Tumor implants were protected from direct irradiation by a 5 half-value layer lead shield. One day following irradiation, tumors were injected with HSV amplicons encoding β-galactosidase(HSVlac) or PBS. RAG-1 -/- mice were injected in both flanks with tumors and right-sided tumors received unilateral intratumoral injections of HSVlac or PBS. OT-1 cells were adoptively transferred one day after the first intratumoral injection in both models. 6/10 irradiated mice bearing E.G7 treated by the combination of OT-1 transfer and intratumoral HSVlac injection were cured of tumor compared to 1/9 cured by OT-1 transfer alone and 0/7 cured by HSVlac injections alone. 5/8 mice cured by the combination of induced lymphopenia, HSVlac injection and OT-1 transfer rejected a subsequent rechallenge with the parental EL.4 tumor, implying epitope spreading. In contrast in RAG-1^-/- mice, contralateral E.G7 growth was initially reduced in mice treated with OT-1 transfer and HSVlac compared to OT-1 alone, but eventually all E.G7 tumors regrew. In repeated experiments higher percentages of OT-1 cells from irradiated mice bearing E.G7 and treated with intratumoral HSVlac injection secreted interferon-g following restimulation in vitro (73.1 +/− 13.4%)) compared to controls treated without HSVlac injection (36.1+/−13.1%) p< 0.025). The combination of transferred CD8+ cells and HSVlac was moderately more effective in treatment of established EL-4 tumors in irradiated mice than CD8+ cells alone (p = 0.036) for tumor size at day 20. Preliminary results suggests that CD8 cells lacking interferon-g were less effective at inducing tumor rejection in this setting. These experiments suggest that a strong local innate stimulus such as HSVlac injection may potentiate the immune response seen with adoptively transferred T cells in the setting of lymphopenia