468 Characteristics of toripalimab: a next generation anti-PD-1 antibody with potent T cell activation and enhanced clinical efficacy irrespective of PD-L-1 status

BackgroundToripalimab is a PD-1 targeting humanized IgG4 monoclonal antibody (mAb) that is currently pending approval by US Food and Drug Administration (FDA) for first-line treatment of nasopharyngeal carcinoma (NPC) in combination with chemotherapy. While currently approved PD-1 mAbs have demonstrated significant clinical benefit particularly in patients with PD-L1 expressing tumors, in three on-going clinical trials, toripalimab in combination with chemotherapy has demonstrated good clinical efficacy irrespective of the PD-L1 status. Thus, we investigated the molecular and functional characteristics of toripalimab and compared it to pembrolizumab, a PD-1 mAb that is approved in the largest number of indications in the PD-1 mAb class.MethodsPost-hoc analysis was performed for three clinical trials namely JUPITER-02, JUPITER-06 and CHOICE-01, where patients were treated with toripalimab plus chemotherapy or placebo plus chemotherapy. Two PD-L1 scoring criteria: tumor proportion score (TPS) or combined positive score (CPS) were utilized. Binding affinity and kinetics for PD-1 mAbs toripalimab and pembrolizumab were determined by performing surface plasmon resonance (SPR) experiments. The ability of the PD-1 mAbs to activate T cells was characterized using T-cell based assays: 1) staphylococcal enterotoxin B (SEB) stimulated human peripheral blood mononuclear cells (PBMCs) and 2) anti-CD3 and anti-CD28 activated human CD8+ T cells. Efficacy was further tested in an ex-vivo system using dissociated tumor cells from treatment naïve non-small cell lung cancer (NSCLC) patients in the presence of anti-CD3/CD28 antibodies. Activation of PD-1 receptor by the PD-1 mAbs was determined using a Jurkat cell based SHP1/SHP2 recruitment assay.ResultsToripalimab plus chemotherapy improved overall survival (OS) irrespective of PD-L1 status in NPC (JUPITER-02), advanced NSCLC (CHOICE-01) and advanced esophageal squamous cell carcinoma (JUPITER-06) (table 1, figure 1). Toripalimab exhibited 12-fold higher binding affinity for PD-1 (figure 2) and significantly enhanced T cell activation in-vitro when compared to pembrolizumab (figure 3 and figure 4). Furthermore, toripalimab treatment showed an upregulated IFN-g gene signature in comparison to pembrolizumab in the ex-vivo system with NSCLC tumors (figure 5 and figure 6). Lastly, toripalimab demonstrated lower agonistic potential than pembrolizumab upon binding to PD-1, by recruiting lower levels of SHP-1 and SHP-2 in Jurkat-P