Background: PSCA, a cell surface protein, is upregulated in many solid tumors and correlates with disease stage. BPX601 is an autologous, T-cell product engineered to contain a PSCA-CD3ζ CAR plus the small molecule rimiducid (Rim)-inducible MyD88/CD40 costimulatory domain. BPX601 is optimized for antigen-directed and independent T cell activation, proliferation and persistence, potentially enhancing efficacy in solid tumors versus traditional CARs. This first-in-human study assesses the safety, biological and clinical activity of BPX601 plus Rim in select PSCA-positive cancers. Methods: NCT02744287 is a two-part, open-label trial. Part 1 is an ongoing 3+3 cell dose escalation to identify the recommended BPX601 cell dose (Day 0) given in combination with a fixed, single Rim dose (0.4 mg/kg; Day 7). Eligibility criteria include previously treated metastatic pancreatic cancer (mPDAC) with measurable disease & positive PSCA expression. Results: Patients received only cyclophosphamide (CTX) for lymphodepletion (LD) within three days before BPX601 infusion. Nine adults have been treated across three cell dose levels (cells/kg): 1.25x10⁶ (cells only), 1.25x10⁶+Rim, 2.5x10⁶+Rim. All had mPDAC with ≥ two prior therapies. Common AEs were fatigue and nausea. No DLTs, related SAEs, neurotoxicity or CRS events were reported. Rapid cell engraftment by Day 4 was observed in all patients. No evidence of LD with CTX was seen. Of six patients that received Rim: two had cell expansion 10- to 20-fold within seven days; two had cell persistence > three weeks; all had elevated serum cytokines (IP-10, TNFα) correlated with cell expansion. Best response after ≥ one scan was 4 SD ≥ eight weeks with two minor responses (not confirmed; one patient had matched CA19-9 decrease) and 2 PD. Disease control without new therapy was 16 and > 11 weeks (ongoing) in one and two patients, respectively. Conclusions: BPX601 with single-dose Rim was well-tolerated and resulted in enhanced T cell expansion and prolonged persistence in some patients despite lack of LD. Evidence of clinical benefit in this heavily pretreated mPDAC population was seen. Part 2 is planned to open soon and will include CTX/fludarabine LD to maximize engraftment as well as gastric and prostate cancers. Clinical trial information: NCT02744287