ABSTRACT: Tumors remodel extracellular matrix (ECM) and glycosylation, yielding epitopes with restricted or limited detectability in normal adult tissues. Here, we evaluated the O-glycosylated IIICS domain of fibronectin (Tn-FN) as a chimeric antigen receptor (CAR) T cell target. FDC6-BBζ CAR T cells recognizing Tn-FN were benchmarked against EDB-FN-targeted L19-BBζ and Tn-MUC1-targeted 5E5-BBζ. FDC6-BBζ mediated robust, antigen-dependent activation and cytotoxicity, outperforming L19-BBζ and matching 5E5-BBζ in vitro and in NSG xenografts of prostate cancer. FDC6-BBζ and 5E5-BBζ CAR T cells achieved durable tumor control with increased intratumoral CD3⁺ infiltration and reduced tumor-collagen overlap. Cytotoxicity required intact tumor interferon-γ (IFNγ) receptor 1; L19-BBζ further depended on Fas, whereas FDC6-BBζ and 5E5-BBζ were less Fas-dependent. Tumoral toll-like receptor (TLR) 2/6 or TLR4 agonism restored FDC6-BBζ killing of IFNγR1-deficient targets and induced broad inflammatory and stress-response programs. Pharmacologic perturbation implicated caspase-dependent mechanisms and a contribution from inflammasome-linked signaling, whereas ferroptosis blockade did not abrogate restored killing. These findings establish Tn-FN as a glycoform-restricted, ECM-derived CAR target and show that innate agonists can reprogram tumor state to overcome resistance from impaired IFNγ signaling.