Background:γδ T cells, MHC unrestricted immune cells, target NKG2D ligands differentially expressed on tumor cells. DeltEx drug resistant immunotherapy (DRI), a novel ex vivo expanded, activated γδ T cell expresses MGMT, conveying TMZ resistance. NCT04165941, a phase 1 trial assessing the safety of single and multiple infusions of autologous DeltEx DRI cells presents updated safety and efficacy data. Methods: Adult newly diagnosed GBM patients with adequate organ function and KPS≥70% are enrolled. Cells engineered from apheresis after tumor resection were infused through a Rickham catheter placed during surgery. Cohort (C) 1, 2 and 3 receive 1, 3 and 6 doses of cells respectively on day (D) 1 of each 28-day maintenance cycle. Patients receive 1 x 10⁷γδ T cells intratumorally on D1 with 150 mg/m² of TMZ intravenously with the Stupp regimen. Primary endpoint is safety; secondary endpoints include progression free and overall survival. Immunologic and genomic correlative analyses are being conducted. Dose limiting toxicities (DLTs) are defined as treatment related ≥ grade 3 cardiopulmonary or hepatic toxicity, grade 4 toxicity exceeding 72 hours or neurologic deterioration that exceeds 2 weeks. Results: 12 patients (58% male; median age 66.5 (range: 21-76); 66.7% IDH-WT, 66.7% MGMT unmethylated) were enrolled with 6 dosed (3 in C1, 3 in C2). No patients had DLTs, cytokine release syndrome (CRS), or neurotoxicity. The most common adverse events (AEs) were Grade 1/2 events including fever, leukopenia, nausea, and vomiting attributable to TMZ or radiotherapy. One subject had Grade 3 treatment related AEs of UTI, dehydration, and thrombocytopenia. Three evaluable C1 patients have PFS of 8.3, 11.9, 7.4 months and OS of 15.6, 17.7 and 9.6 months respectively. In C2, three patients have been dosed, with one patient with stable disease at 8.2 months after receiving all three doses and no DLTs. Patient recruitment continues with anticipated completion in 2022. Conclusions: Data demonstrates that single, repeat doses of DRI T cells have manageable toxicity with encouraging trend in PFS.