CTLA4 (cytotoxic T-lymphocyte-associated protein 4) is homologous to the co-stimulatory protein CD28, and both receptor binds to CD80 and CD86. Cancer cells can be recognized and destructed by the host’s immune system. In this setting, CTLA4 functions as a brake to dampen anti-tumor T cell responses, which promote cancer progression. Antibodies targeting CTLA4 was expected to subvert T cell inhibition. Moreover, regulatory T cells residing in the tumor microenvironment can be killed by anti-CTLA4 antibody since these cells have higher expression level of CTLA4 comparing with the activated T cells. Yervoy, an anti-CTLA4 antibody, was the first FDA-approved antibody targeting the immune checkpoint family, and it protects a fraction of cancer patients when either used alone or in combination with other drugs. We asked whether the efficacy of anti-CTLA4 antibodies could be evaluated in humanized mouse models. And if so, whether we can use in vivo assay to guide the development of potent antibodies targeting CTLA4.
Here, we generated humanized CTLA4 knock-in mouse (B-hCTLA4) with a chimeric PD-1 receptor and this mouse were validated by Yervoy. Then, we utilized humanized B-hCTLA mice and implanted syngeneic tumors subcutaneously, followed by treating mice with purified testing CTLA4 antibodies and Yervoy. Via this approach, we are able to discern several clones that have better efficacy than Yervoy. These clones were further selected for humanization. The cohort of recombinant humanized CTLA4 antibodies were screened in B-hCTLA4 mice.
We successfully generated B-hCTLA4 mouse for anti-human CTLA4 antibody in vivo efficacy evaluation. A cohort of CTLA4 specific antibodies were successfully generated and purified. The clones with better efficacy than Yervoy were screened using Biocytogen’s humanized mouse platform. These clones were humanized and screened by using B-hCTLA4 mice. Both the Fv and Fc portion of the lead antibody were optimized using the B-hCTLA4 mice, leading to the humanized form of the antibodies.
Using the platform established at Biocytogen, we successfully discovered two antibodies whose efficacy is equivalent or exceed that of Yervoy. The clinical evaluation of these new entities are wanted.
Yi Yang.
Beijing Biocytogen Co., Ltd.
All authors have declared no conflicts of interest.