Inhibition of specific Akt isoforms in CD8+ T cells promotes favored differentiation into memory versus effector cells, the former of which are superior in mediating anti-tumor immunity. In this study, we investigated the role of upstream PI3K isoforms in CD8+ T cell differentiation and assessed the potential use of PI3K isoform-specific inhibitors to favorably condition CD8+ T cells for adoptive cell therapy. The phenotype and proliferative ability of tumor antigen specific CD8+ T cells was assessed in the presence of PI3K-α, -β, or -δ inhibitors.Inhibition of PI3K-δ, but not PI3K-α or PI3K-β, delayed terminal differentiation of CD8+ T cells and maintained the memory phenotype, thus enhancing their proliferative ability and survival while maintaining their cytokine and granzyme B production ability. This effect was preserved in vivo after of ex vivo PI3K-δ inhibition in CD8+ T cells destined for adoptive transfer, enhancing their survival and also the anti-tumor therapeutic activity of a tumor-specific peptide vaccine.Our results outline a mechanism by which inhibitions of a single PI3K isoform can enhance the proliferative potential, function and survival of CD8+ T cells, with potential clinical implications for adoptive cell transfer and vaccine-based immunotherapies.

Significant progress has been made in treating cancer with immunotherapy, although a large number of cancers remain resistant to treatment. A limited number of assays allow for direct monitoring and mechanistic insights into the interactions between tumor and immune cells, amongst which, T-cells play a significant role in executing the cytotoxic response of the adaptive immune system to cancer cells. Most assays are based on two-dimensional (2D) co-culture of cells due to the relative ease of use but with limited representation of the invasive growth phenotype, one of the hallmarks of cancer cells. Current three-dimensional (3D) co-culture systems either require special equipment or separate monitoring for invasion of co-cultured cancer cells and interacting T-cells.Here we describe an approach to simultaneously monitor the invasive behavior in 3D of cancer cell spheroids and T-cell cytotoxicity in co-culture. Spheroid formation is driven by enhanced cell-cell interactions in scaffold-free agarose microwell casts with U-shaped bottoms. Both T-cell co-culture and cancer cell invasion into type I collagen matrix are performed within the microwells of the agarose casts without the need to transfer the cells, thus maintaining an intact 3D co-culture system throughout the assay. The collagen matrix can be separated from the agarose cast, allowing for immunofluorescence (IF) staining and for confocal imaging of cells. Also, cells can be isolated for further growth or subjected to analyses e.g. for gene expression or Fluorescence Activated Cell Sorting (FACS). Finally, the 3D co-culture can be analyzed by immunohistochemistry (IHC) after embedding and sectioning. Possible modifications of the assay include altered compositions of the extracellular matrix (ECM) as well as the inclusion of different stromal or immune cells with the cancer cells.

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