P01.43.a Pd-L1 and B7-H3 Checkpoint Inhibitor Blockade in Glioblastoma

Abstract BACKGROUND Glioblastoma (GBM) is an aggressive primary brain tumor with a short patient survival and is often associated with highly immunosuppressive tumor microenvironment. The B7 family of immune checkpoint receptors are valuable targets for anti-tumour immunity and their blockades have revolutionized the field of cancer immunotherapy. MATERIAL AND METHODS Glioblastoma tumors in newly diagnosed patients (n=80) were processed using enzymatic kits and gentleMACSTM Dissociator (Miltenyi Biotec Inc.) and tumor cells phenotyped for the immune checkpoint inhibitor ligands B7-H1 (CD274) and B7-H3 (CD276) by multicolor flow cytometry. Glioblastoma cells were cultured in presence of PD-L1 inhibitor (atezolizumab, avelumab and durvalumab) or B7-H3 inhibitor (omburtamab) and subsequently used in killing assays with magnetically sorted innate immunity effector lymphocytes NK and γδ T cells, both with known prominent reactivity against GBM. The B7-H3 blocking studies were also performed using the CRISPR/Cas9. Next, we used Luminex xMAP technology to quantify plasma levels of PD-L1 and B7-H3 in patient samples at diagnosis (n=48), prior chemo/radio therapy (n=23), post therapy (n=22) and during disease progression (n=13). RESULTS We showed that B7-H1 and B7-H3 i) were highly expressed on primary GBM tumor cells at diagnosis and expression correlated with patient survival, ii) blockades modulated NK and γδ T cell cytotoxic activity against glioblastoma cell lines and primary tumor cells, iii) are directly involved in GBM-mediated suppression of tumor control, and iv) were significantly elevated levels in patients at diagnosis compared to age-matched healthy controls (HD, n=15) and remained significantly increased throughout the therapy. CONCLUSION Our study highlights the specific blockades of B7-H1 and B7-H3 immune checkpoint inhibitor ligands resulted in significant NK cell- and γδ T cell - mediated GBM tumor cell lysis, which could be exploited in novel immunotherapeutic interventions to improve patient survival. DISCLOSURE This study was supported by Ministry of Health, Czech Republic (grant NV19-05-00410 to AK) by Ministry of Health, Czech Republic-Conceptual Development of Research Organization (FNBr, 65269705). All rights reserved.