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Background CD19-targeted chimeric antigen receptor (CAR) T-cell therapy has transformed the treatment of relapsed/refractory diffuse large B-cell lymphoma (r/r DLBCL). Despite these advances, up to 60% of patients fail to achieve a complete response. To investigate factors underlying therapeutic response, we conducted single-cell transcriptomic profiling of infusion products from r/r DLBCL patients treated with axicabtagene ciloleucel.Methods Infusion products from eight r/r DLBCL patients with varying clinical outcomes were analyzed using single-cell RNA sequencing. Differential transcriptional signatures between complete responders and patients with progressive disease were examined. Insights from these analyses informed the development of an ex vivo CAR T-cell manufacturing strategy involving type I interferon (IFN-I) stimulation. To prevent potential in vivo adverse effects, IFN-I was withdrawn prior to infusion. Both CD28- and 4-1BB-based CAR constructs were incorporated in the study. Functional performance of CAR T cells was assessed through in vitro assays and in vivo xenograft tumor models.Results Complete responders exhibited elevated IFN-I-associated transcriptional signatures compared to patients with progressive disease. The impact of IFN-I priming on CAR T-cell function was dose-dependent. Low-dose IFN-I enhanced cytotoxic activity in vitro without affecting transduction efficiency. In contrast, high-dose IFN-I triggered apoptosis and reduced cell viability. Low-strength IFN-I did not impair cell expansion and maintained viability. Additionally, CAR T cells primed with low-dose IFN-I demonstrated superior antitumor activity in vivo across both CD28- and 4-1BB-costimulated constructs. These enhancements were consistent across multiple donors.Conclusions Low-dose IFN-I priming represents a costimulation-independent strategy to augment CAR T-cell function. This approach leverages an FDA-approved cytokine, avoids in vivo toxicity through cytokine removal prior to infusion, and integrates seamlessly with existing CAR platforms. The results support the clinical potential of IFN-I-enhanced CAR T-cell therapies for patients with r/r DLBCL.Ethics Approval Deidentified patient biospecimens were collected under Institutional Review Board (IRB)-approved protocols at the University of Chicago Medicine (IRB #18-0025), with informed consent obtained from all patients or their legal guardians in accordance with institutional and federal guidelines. PBMCs from healthy donors were collected under IRB #15-0102 with informed consent. All animal experiments were approved by the Institutional Animal Care and Use Committee (IACUC) at the University of Chicago (ACUP #72707) and conducted in compliance with institutional guidelines.