IT-16COMBINATION TREATMENT WITH DELTA24-RGD AND TEMOZOLOMIDE IMPROVES SURVIVAL AND AFFECTS INTRATUMORAL IMMUNE CELL SUBSETS IN A MURINE MALIGNANT GLIOMA MODEL.

INTRODUCTION: The oncolytic adenovirus Delta24-RGD specifically lyses tumor cells and is currently tested in clinical phase I/II trials for recurrent glioma. We recently showed that the efficacy of Delta24-RGD is mainly dependent on an induced anti-tumor immune response. As known, TMZ has pronounced effects on the immune system, which could hamper the viral-induced anti-tumor immune response. To assess the combined effects, we tested different treatment regimens in an immune competent glioma mouse model. METHODS: C57BL/6 mice were injected intracranially with GL261 cells. TMZ was given for 5 days before (pre-treatment regimen) or after (post-treatment regimen) intratumoral injection of Delta24-RGD. Mice were followed for survival or sacrificed at earlier time-points to assess intratumoral influx of immune cells. T-cell response directed to the tumor cells was assessed by co-culture of splenocytes with GL261 tumor cells and analysis of IFNgamma production. Furthermore, to assess the type of cell death induced by the treatments, western blotting for LC3 (autophagy) and caspase 3/7 analysis (apoptosis) was performed. RESULTS: In vitro, apoptosis is highly induced in virus and combination treated cells, whereas autophagy is induced by TMZ monotherapy. In vivo, both combination treatment regimens significantly improved survival compared to TMZ alone. The post-treatment regimen also prolonged survival significantly compared to virus only. In the pre-treatment group, influx of dendritic cells is reduced, followed by a diminished influx of CD8+ T-cells. Interestingly, splenocytes from mice of virus and both combination treatment groups recognize GL261 cells, indicating that the diminished influx of immune cells did not hamper T-cell activation. CONCLUSION: The addition of TMZ to Delta24-RGD treatment in immune competent mice improves survival compared to Delta24-RGD or TMZ alone. Contrary to the post-treatment regimen, administering TMZ prior to virus injection hampers the intratumoral influx of immune cells; however, with both regimens an effective anti-tumor immune response is elicited.