Approved anti-CD19 chimeric antigen receptor T-cell treatments (CART19) demonstrate effectiveness in treating advanced B-cell non-Hodgkin lymphoma (NHL), although relapse occurs in the majority of cases. Multiple factors drive treatment failure, including emergence of CD19-negative disease and impaired CAR T-cell activity. Each of the four licensed CART19 therapies relies on the FMC63 single-chain variable fragment (scFv), which binds a membrane-distal CD19 epitope with slow binding (on) and release (off) kinetics. We postulated that an innovative anti-CD19 scFv directed at a distinct membrane-proximal CD19 epitope—unrelated to the FMC63 binding site—and exhibiting rapid on- and off-rates might reduce instances of CART19 failure and enhance therapeutic outcomes. An autologous CART19 therapy incorporating 4-1BB costimulation was engineered using a new humanized avian-derived antibody (h1218). This antibody recognizes a membrane-proximal CD19 epitope and shows quicker on/off kinetics relative to FMC63. Performance of h1218-CART19 was evaluated in vitro and in vivo against models refractory to FMC63-CART19. A multicenter first-in-human phase I trial was initiated to assess AT101 (GMP-grade h1218-CART19) in individuals with relapsed/refractory (r/r) NHL. In preclinical studies, h1218-CART19 alone—unlike FMC63-CART19—successfully eliminated lymphomas bearing CD19 point mutations (L174V and R163L) or those co-expressing FMC63-CAR19, as observed in relapses following FMC63-CART19 therapy. Moreover, h1218-CART19 displayed superior cytotoxicity against B-cell tumors both in vitro and in vivo versus FMC63-CART19. At the mechanistic level, h1218-CART19 demonstrated lower activation-induced cell death (AICD) and superior proliferation relative to FMC63-CART19, attributable to its rapid on- and off-rates. Guided by these findings, a phase I dose-escalation study was conducted, evaluating three dose levels (DL) of AT101 (GMP h1218 product) in a 3 + 3 scheme. Across 12 enrolled patients (7 DLBCL, 3 FL, 1 MCL, and 1 MZL), AT101 exhibited an acceptable safety profile, including 8.3% grade 3 CRS (n = 1) and 8.3% grade 4 ICANS (n = 1). Overall response rate reached 91.7% with a complete response rate of 75.0%, rising to 100% at DL-2 and -3. Peak AT101 levels correlated with complete response and B-cell depletion. An innovative, well-tolerated, and highly active CART19 therapy has been created that targets a membrane-proximal CD19 region with rapid binding and release kinetics, delivering robust activity and favorable safety in relapsed B-cell NHL cases.
