LAUSR

2536 Background: Cell-surface protein PSCA is upregulated in many solid tumors and correlates with disease stage. BPX-601, an autologous T-cell product expressing a PSCA-CD3ζ CAR and a rimiducid (Rim)-inducible MyD88/CD40 co-activation switch to augment T-cell proliferation and persistence, is designed to have enhanced efficacy in solid tumors vs traditional CARs. This ongoing first-in-human study assesses safety, biologic, and clinical activity of BPX-601+Rim in PSCA+ cancers. Updated results, including those from patients (pts) who underwent LD with Flu/Cy, are presented. Methods: BP-012 is a 2-part, open-label trial. Part 1 is a 3+3 dose escalation of BPX-601 (1.25–5.0x106 cells/kg; Day [D] 0) given prior to a single, fixed Rim dose (0.4 mg/kg; D7) in pts with previously treated PSCA+ metastatic pancreatic, gastric, or prostate cancers with measurable disease. Results: As of Jan-22-2019, 15 pts have received BPX-601±Rim. Two pts at the highest cell dose received Flu/Cy for LD on D−5 to D−3 before BPX-601; LD after Flu/Cy was 96.6% and 84.3%. Thirteen pts received Cy alone on D−3; in these pts, LD ranged from 0–68.6%. Rapid cell expansion by D4 was observed in all pts with peak vector copy number 8.3-fold higher with Flu/Cy (n = 2) vs Cy LD (n = 13). Serum IP-10, IL-6 and TNFα increased > 2-fold from baseline in ≥1 pt in all Rim cohorts, with 3- to 20-fold Rim-dependent cell expansion in 6 pts. No CRS or DLTs were reported. After Rim, one Flu/Cy pt experienced a serious Grade 2 AE (encephalopathy) related to BPX-601+Rim that resolved with IV steroids; despite time-matched nonserious Grade 1 pyrexia, the pt had no other CRS symptoms. After BPX-601+Rim and ≥1 scan, best responses were 8 SD and 3 PD (1 non-evaluable). With a median follow-up of 9.8 wks, time to next treatment (tx) after BPX-601 ranged from 2.7–22.1 wks (n = 8) and ongoing tx-free intervals range from 9.1–30.1 wks (n = 4). Conclusions: BPX-601+Rim was well-tolerated with manageable safety and early evidence of enhanced CAR T-cell expansion and prolonged persistence after Flu/Cy vs Cy. Additional pts will undergo Flu/Cy LD prior to BPX-601 with single- and repeat-dose Rim. Clinical trial information: NCT02744287.