Dual targeting of CD155/ TIGIT and PD-L1/ PD-1 immune checkpoints potentiates NK cell-mediated cytotoxicity in medulloblastoma

BACKGROUND: Medulloblastoma (MB) is one of the most prevalent pediatric brain malignancies and makes up approximately 20% of all primary brain tumors in children. Current treatment options are not curative for approximately 30% of patients and leave survivors with an impaired quality of life. Immune checkpoint inhibition can offer a novel targeted therapy but largely remains understudied in MB. The aim of this study was to determine whether dual immune checkpoint inhibition can be used as a novel targeted therapy in MB. METHODS: We utilized single cell and single nuclei sequencing datasets of primary MB tumors, established Group 3 and Sonic Hedgehog MB cell lines and MB patient-derived xenograft (PDX) organoid models, and primary patient-derived MB tissue of all subtypes to study immune checkpoints and their blockade to target MB. RESULTS: We identified the expression of immune checkpoint protein CD155 on MB tumor cells and the expression of its inhibitory binding partner TIGIT on immune cells of MB patient-derived tissues, cell lines, and PDX MB organoids. In addition, while MB shows weak, if any, PD-L1 protein expression, we found that MB cells can upregulate PD-L1 expression upon stimulation by natural killer (NK) cells or interferon-γ as a putative immune evasive strategy. Subsequent immunotherapeutic interventions with FDA-approved antibodies Tiragolumab (anti-TIGIT), Durvalumab (anti-PD-1), and their combination potentiated primary NK cell activation and killing of MB cell lines and PDX-derived MB organoids. CONCLUSION: These data propose a translatable and novel immunotherapeutic strategy for children diagnosed with subgroups Sonic Hedgehog and Group 3 MB.