Abstract 590: Humanized PD-1/LAG-3 mice for preclinical evaluation of combination therapy

Abstract

Abstract Lymphocyte activation gene 3 (LAG-3) is a member of the immunoglobulin superfamily which shares homolog with CD4 and binds to MHC II with higher affinity. It is expressed on activated T cells, regulatory T cells (Tregs), natural killer cells and plasmacytoid dendritic cells, and inhibits their activation. Blocking LAG-3 activity is expected to provide therapeutic benefits in the treatment of cancer, especially when combined with PD-1 blockade. Due to the low homology between human and mouse LAG-3 and PD-1 and in order to enable increased translatability of preclinical in-vivo efficacy evaluation of immune checkpoint antibodies, we generated double humanized mice by replacing the extracellular domain of mouse LAG-3 and PD-1 with the corresponding human sequences. Homozygous double humanized mice express chimeric LAG-3 and PD-1 at comparable levels to mouse LAG-3 and PD-1 respectively in wildtype mice. When treated with human LAG-3 antibody (anti-LAG-3) or human PD-1 antibody (anti-PD-1), CT26 tumor growth was inhibited in a dose-dependent manner, proving that both humanized proteins are functional. However, not all tumor types respond to anti-LAG-3 or anti-PD-1 the same. To identify the suitable tumor models for preclinical efficacy evaluation of anti-LAG-3 and anti-PD-1 combo therapy, we engrafted several syngeneic tumor models onto our mice. The growth of subcutaneously engrafted MC38 colon tumor was mildly inhibited by anti-PD-1, but strongly inhibited in the presence of anti-LAG-3. Similarly, B16F10 melanoma tumor showed modest growth inhibition when treated with anti-PD-1 or anti-LAG-3 separately, while combination therapy significantly repressed tumor growth. However, neither monotherapies of anti-LAG-3 and anti-PD-1 nor combination treatment effectively inhibited tumorigenesis of LLC1 derived lung cancer, indicating that this tumor is likely insensitive to PD-1 and LAG-3 blockade. Collectively, these data indicate that double humanized PD-1 and LAG-3 mice are a powerful tool to evaluate the therapeutic efficacies of anti-hPD-1 and anti-hLAG-3 treatment in different types of tumor in vivo. Citation Format: Feifei Duan, Xiaoliu Yang, Cunxiang Ju, Jing Zhao, Xiang Gao, Santi Suryani Chen. Humanized PD-1/LAG-3 mice for preclinical evaluation of combination therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 590.