Insights into the mechanisms of serplulimab: a distinctive anti-PD-1 monoclonal antibody, in combination with a TIGIT or LAG3 inhibitor in preclinical tumor immunotherapy studies

Background: Anti-PD-1 therapy has become a cornerstone of tumor immunotherapy. Over a dozen of anti-PD-1/PD-L1 antibodies have currently been marketed. However, these agents exhibit notable disparities in their characteristics and clinical performance. For instance, in the field of small cell lung cancer (SCLC) where the majority of anti-PD-1 antibodies yielded limited success, Serplulimab produced impressive survival improvements and has been approved by NMPA. The marketing authorization application has also been validated by EMA. Nevertheless, the molecular mechanism underpinning Serplulimab's superiority over its competitors remains elusive. Methods: We characterized the difference of Serplulimab with approved PD-1/PD-L1 inhibitors such as Pembrolizumab and Nivolumab on their antibody binding features and funcations in vitro and anti-tumor activity in vivo. We also investigated the potential cellular pathways underlying the efficacy of Serplulimab in combination with other immune checkpoint inhibitors. Results: In comparison to competitors, Serplulimab robustly induces PD-1 receptor endocytosis while fostering weaker PD-1-CD28 cis interactions. This phenomenon could mitigate the dephosphorylation of CD28 by SHP2, thereby facilitating sustained and robust T cell activation. Notably, Serplulimab and Pembrolizumab exhibited similar performance in both in vitro Mixed Lymphocyte Reaction assays and in vivo efficacy studies. However, upon co-administration with anti-TIGIT or anti-LAG3, the Serplulimab-containing combination consistently demonstrated superior tumor killing efficacy compared to the Pembrolizumab-based combination. Moreover, our mechanistic investigations have unveiled that the Serplulimab combination effectively reduces tumor microenvironment Treg cell populations, augments effector and memory T cell populations, and more potently modulates genes associated with diverse facets of the immune system, surpassing the effects of the Pembrolizumab combination. Conclusions: In summary, our data underscore Serplulimab as a highly differentiated PD-1 monoclonal antibody with best-in-class therapeutic potential Overall design: HuGEMM human PD-1 and TIGIT double knock-in mice (BALB/c background) were used to inoculate CT26 tumor cells subcutaneously inoculated in the right flank with 0.5 × 106 cells in 0.1 mL PBS. Treatment was initiated 8 days later when tumors reached 90–100 mm3. The mice were randomized into groups so that the average tumor sizes of all groups were similar, and treatment by intraperitoneal injections was initiated on day 8. Vehicle group received saline solution (10 µL/g) twice weekly, other group received tested antibodies treatment twice weekly. Tumor tissue RNA was purified and performed with 2x150 paired-end sequencing on MGISEQ-2000RS (MGI).