Background CAR-T cell therapy against hematological malignancies demonstrated potent therapeutic efficacy, resulting in clinical application of these treatments. On the other hand, CAR-T cell therapy against solid cancers has yet to be fully developed, as only a few exceptional cases have been reported to demonstrate clinical efficacy. Potential hurdles for the effects of CAR-T cell therapy in solid cancers include heterogeneity of tumor-associated targets, insufficient migration and infiltration of CAR-T and endogenous immune cells into tumor tissues, and immunosuppressive nature of tumor microenvironment. To overcome these hurdles, we developed novel CAR technology enabling CAR-T cells to produce both interleukin-7 (IL-7) and CCL19, which induced the efficient accumulation and expansion of the transferred CAR-T cells and host immune cells inside tumor tissues, and demonstrated potent therapeutic efficacy in various mouse solid cancer models.¹

Methods In this study, we explored the immunological mechanisms of IL-7/CCL19-producing CAR-T (7x19 CAR-T) cells in solid cancers. We used mouse tumor cell lines expressing endogenous tumor antigens as well as CAR target, and examined whether administration of 7x19 CAR-T cells into the tumor-bearing mice induce epitope spreading to endogenous tumor antigens via cross presentation.

Results In the mice inoculated subcutaneously with B16F10 melanoma cells expressing OVA and CAR target, intravenous administration of 7x19 CAR-T cells induced T cells responses against OVA and endogenous melanoma antigens including TRP-1, TRP-2, and gp100. In another model using MC38 colon cancer cells expressing CAR target, treatment with 7x19 CAR-T cells also induced T cell responses against neoantigens in MC38, such as Dpagt1, Adpgk, and REPS1. In the OVA-expressing B16F10 model, the number of CD11b-negative, CD8α-positive dendritic cells (DC), which are known to have a capability of cross presentation, was increased by the administration of 7x19 CAR-T cells. In addition, DC harvested from these mice induced activation of OVA-specific OT-1 T cells without addition of OVA antigen. The mice inoculated with a mixture of CAR target-positive and negative B16F10 were successfully treated by 7x19 CAR-T cells, but not conventional CAR-T cells. Similar results were observed in the model using a mixture of CAR target-positive and negative 3LL lung cancer cells.

Conclusions Our findings substantiated that the epitope spreading is induced in the process of therapeutic responses in solid cancers by 7×19 CAR-T cells. Moreover, this response is associated with an increase of DC with a capacity of cross presentation to T cells, which is a crucial machinery for the epitope spreading.

Reference

1. Adachi K, Kano Y, Nagai T, Okuyama N, Sakoda Y, Tamada K. IL-7 and CCL19 expression in CAR-T cells improves immune cell infiltration and CAR-T cell survival in the tumor. Nat Biotechnol. 2018 Apr;36(4):346–351. doi: 10.1038/nbt.4086. Epub 2018 Mar 5.

Ethics Approval All mouse studies were conducted in accordance with national guidelines for the humane treatment of animals and were approved by the Institutional Animal Care and Use Committee (IACUC) at Yamaguchi University.