CTIM-04. MODULATION OF THE INTRATUMORAL IMMUNE MICROENVIRONMENT BY LOCAL THERAPY WITH NATURAL KILLER CELLS ENGINEERED WITH A HER2-TARGETED CHIMERIC ANTIGEN RECEPTOR IN COMBINATION WITH SYSTEMIC ANTI-PD-1 CHECKPOINT INHIBITION IN PATIENTS WITH RECURRENT GLIOBLASTOMA

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Abstract Glioblastoma (GB) is characterized by a marked immunosuppressive tumor microenvironment. In the multicenter CAR2BRAIN phase I first-in-human clinical trial, we investigated the modulation of the tumor microenvironment by repetitive local injection of clonal chimeric antigen receptor (CAR)-NK cells (NK-92/5.28.z) targeting HER2 alone and in combination with systemic anti-PD-1 checkpoint inhibitor therapy in patients with recurrent HER2-positive GB. 6 patients were treated with repetitive doses of CAR-NK cells as monotherapy and 12 patients received a combination therapy with the anti-PD-1 checkpoint inhibitor ezabenlimab. In three of those, we were able to implement a biopsy-treat-resect-treat strategy. After initial biopsy, combination treatment was initiated before planned tumor resection, enabling analysis of the transformation of the tumor immune microenvironment by highplex multispectral fluorescent analyses and cytokine quantification. None of the patients developed a cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome. Profound alterations of the immune cell distribution in the cerebrospinal fluid (CSF) and in the tumor were observed. In CSF sampled from the resection cavity, combination immunotherapy induced a local immune response with elevated pro-inflammatory cytokines and cell counts. In post-treatment tissue samples, we observed an increase of CD4+ and CD8+ T cells, and a decrease of regulatory CD4+FoxP3+ T cells. The three patients treated following the biopsy-treat-resect-treat strategy achieved a median progression-free survival (PFS) of 24 weeks, compared to 10 weeks for patients with upfront resection. Local immunotherapy with HER2-targeted CAR-NK cells is feasible and safe both as monotherapy and in combination with the systemic checkpoint inhibitor ezabenlimab and induces local immune reactions in CSF and tumor tissue. Given the signal for possible clinical benefit provided by the increase in PFS in the patients of the biopsy-treat-resect-treat cohort, further trials are warranted.

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