Background: Temozolomide (TMZ) transiently upregulates NKG2D ligands targeted by innate immune effector cells. Lymphodepletion impairs this immune response, however, genetic modification of ex vivo expanded γδ T cells with an MGMT-expressing lentivector confers resistance to TMZ, allowing concurrent chemotherapy and γδ T cell infusion, thereby targeting the tumor when NKG2DL are maximally expressed. This Drug Resistant Immunotherapy (DRI) is currently being evaluated in a Phase 1 first in human study (NCT04165941) and interim safety and biologic correlative analysis are detailed here for the first dosing cohort. Methods: Adults with newly diagnosed, untreated glioblastoma (GBM), adequate organ function, and a KPS≥70% will be enrolled. Subjects undergo subtotal resection and placement of a Rickham reservoir followed 3-4 weeks by apheresis from which γδ T cells are expanded, transduced with an MGMT-expressing lentivector, harvested, and cryopreserved. Standard of care induction TMZ/radiation therapy is initiated followed by 6 cycles of maintenance TMZ. Intravenous TMZ (150mg/m²) and intracranial dosing of 1 x 10⁷γδ T cells occur on day 1 of each maintenance cycle. Daily oral TMZ 150mg/m² follows for Days 2-5. Dose level 1 (DL1) subjects receive 1 fixed dose of γδ T cells and DL2 receive 3 doses administered on Day 1 of each of first 3 cycles of TMZ dependent on absence of dose limiting toxicity. Primary endpoint is safety; secondary endpoints include progression free and overall survival. Immunologic and genomic correlative analyses are being conducted at specific time points from peripheral blood and cerebral spinal fluid collected from the Rickham. Results: Six subjects (4 females, 2 males) have been enrolled in DL1. All subjects were IDH1-WT with 5 subjects MGMT unmethylated and 1 methylated. Of these, 1 generated inadequate gd T cells and 2 withdrew consent prior to DRI treatment. For the 3 that received DRI, treatment-related adverse events with maximum CTCAE Grade 3 occurred in 1 subject; UTI, dehydration, and thrombocytopenia. The most common Grade 1/2 events included: fever, leukopenia, nausea, and vomiting which were attributable to TMZ or radiotherapy. Circulating T cells remained below normal range throughout maintenance phase in 2/3 subjects. NK and gd T cell numbers remained within low normal range for 3/3 and 2/3 subjects, respectively. Serum Th1 (IFNg, IL-2, TNFa) and Th2 (IL4, IL5, IL-10) cytokines were within clinical range although TNFa remained elevated from the gdT cell infusion through day +30 in 2 subjects. Conclusions: Administration of MGMT-gene modified gdT cells and TMZ as DRI is feasible in lymphodepleted subjects during TMZ maintenance phase and sufficiently safe to warrant further investigation at additional doses. Clinical trial information: NCT04165941