Modulation of inhibitory signals in CAR T cells leads to improved activity against glioblastoma.

Abstract

3031 Background: Early clinical trials have demonstrated the safety of chimeric antigen receptor (CAR) T cells targeting glioblastoma (GBM), however, their efficacy remains limited by multiple obstacles including the immunosuppressive tumor microenvironment. Adoptively transferred CAR T cells remain susceptible to inhibition via the engagement of co-inhibitory receptors on their surface such as PD1, BTLA, CTLA4 and LAG3. The subsequent recruitment of Src homology region 2 containing protein tyrosine phosphatase 2 (SHP2) by these receptors to the immune synapse may represent a common mechanism of T cell inhibition, as SHP2 can de-phosphorylate key signaling molecules that mediate T cell activation (including CD28 and CD3ζ). We hypothesized that SHP2 deletion will simultaneously offset the effects of multiple co-inhibitory receptors, thereby improving the anti-tumor activity of CAR T cells. Methods: Electroporation of sgRNA/Cas9 ribonucleoprotein complexes into human T cells was used to knockout (KO) SHP2. Retroviral vector transduction was used to express a clinically-utilized second generation CAR (with a CD28 endodomain) targeting HER2. The phenotype of wild-type (WT) and SHP2KO CAR T cells was evaluated with mass cytometry and flow cytometry. Their anti-tumor function was tested in vitro using the xCELLigence assay (an impedance-based cytotoxicity assay), and in vivo, in an orthotopic xenograft mouse model of GBM. Results: Efficient and reproducible depletion of the SHP2 protein in human T cells was verified using western blotting. The Inference of CRISPR Efficiency (ICE) Assay confirmed efficient editing of the PTPN11 gene encoding SHP2. An anti-HER2 CAR was efficiently expressed in the SHP2KO T cells. SHP2 deletion did not significantly affect CAR T cell expansion, proliferation or baseline phenotype. However, following co-culture with HER2+ LN229-GBM cells, the CD8+ central memory (CCR7+ CD45RA-) and effector memory (CCR7- CD45RA-) subsets were enriched to a greater extent in the SHP2KO CAR T cells. The pattern of cytokine co-expression varied between donors in a single-cell analysis comparing SHP2KO to WT CAR T cells after encountering LN229 cells. Functionally, SHP2KO CAR T cells derived from the majority of healthy donor and patient peripheral blood eliminated LN229 cells more rapidly in vitro. In an orthotopic mouse model of GBM, SHP2KO CAR T cells showed better early control of established LN229 xenografts and improved survival in comparison to WT CAR T cells. Conclusions: SHP2 deletion in CD28ζ.CAR T cells improves their anti-tumor activity.