P06.12 Combination therapy of CAR-NK-cells and anti-PD-1 antibody results in high efficacy against advanced-stage glioblastoma in a syngeneic mouse model and induces protective anti-tumor immunity in vivo

Background Checkpoint inhibitors as well as adoptive cell therapy hold great promise for cancer therapy and encouraging treatment responses have already been demonstrated in different cancer indications. Glioblastoma (GB) is the most common and aggressive primary brain tumor. Standard therapy has very limited efficacy in the majority of patients. Analysis of the GB tumor microenvironment (TME) has shown prominent immunosuppressive features including expression of PD-L1 on tumor cells and increased frequency of FOX-P3 positive regulatory T cells. While the surrounding brain is HER2-negative, GB tumors are frequently HER2-positive, suggesting HER2 as a promising target for adoptive immunotherapy. Previous results from mouse glioma models showed efficacy of CAR-NK cells (NK-92/5.28.z) targeted against HER2 as monotherapy with relatively small tumors, but not with advanced late-stage tumors. Materials and Methods The murine glioma cell line GL261 was transfected with HER2. Tumor cells were implanted either subcutaneously or orthotopically into C57BL/6 mice and treated either with HER2-specific NK-92/5.28.z cells alone or in combination with an anti-PD-1 antibody. Effects on tumor growth and survival were determined. Lymphocyte infiltration and immunosuppressive TME were characterized in high-dimensional high-throughput analysis via RNAseq and multiplex IHC. Results Combined treatment with NK-92/5.28.z cells and anti-PD-1 checkpoint blockade resulted in synergistic effects with tumor regression and long-term survival even of advanced-stage tumor bearing mice. Analysis of TME showed enhanced cytotoxic lymphocyte infiltration and altered profiles of exhaustion markers in tumor and immune cells, leading to an altered TME after combined treatment with NK-92/5.28.z cells and anti-PD-1 antibody. Conclusions These data demonstrate that efficacy of NK-92/5.28.z cells can be enhanced in combination with checkpoint blockade, resulting in successful treatment of advanced tumors refractory to NK-92/5.28.z monotherapy. Furthermore, the combination therapy induces a cytotoxic rather than immunosuppressive TME, leading to a primed immune system. To address this question in a clinical setting, we are preparing a combination therapy cohort as part of our ongoing phase I clinical study (CAR2BRAIN; NCT03383978). Disclosure Information F. Strassheimer: None. M.I. Strecker: None. T. Alekseeva: None. J. Macas: None. M.C. Demes: None. I.C. Mildenberger: None. T. Tonn: None. P.J. Wild: None. L. Sevenich: None. Y. Reiss: None. P.N. Harter: None. K.H. Plate: None. W.S. Wels: None. J.P. Steinbach: None. M.C. Burger: None.