Abstract 1641: Evaluating in vivo efficacy of bi-functional fusion protein anti-PD-1-IL21 in humanized B-hIL21R mice and B-hPD-1/hIL21R mice

Abstract

Abstract Interleukin 21 (IL21) binding to its receptor IL21R, results in downstream activation of multiple signaling molecules, including JAK1, JAK3, STAT1, and STAT3. Intriguingly, IL21 has been implicated in both positively and negatively regulating immune responses in a cell-type specific manner, suggesting drug candidates that target IL21/IL21R signaling has therapeutic potential. Specifically, recent reports suggest that antibodies targeting PD-1 fused to IL-21 has a synergistic anti-tumor effect. To generate a suitable animal model for in vivo assessment of a human anti-PD-1-IL21 fusion protein, Biocytogen developed humanized PD-1 and IL21R mice (B-hIL21R mice and B-hPD-1/hIL21R mice) by replacing the murine Il21r and PD-1 gene with the human IL21R and PD-1 counterparts via homologous recombination. Our data shows that human IL21R was detectable in sorted cells from homozygous B-hIL21R and B-hPD-1/hIL21R mice, while human PD-1 was detectable in B-hPD-1/hIL21R mice compared to wild type mice. Furthermore, STAT3 phosphorylation in splenocytes was successfully induced with mouse IL21 or human IL21 in homozygous B-hIL21R mice. In addition, percentages of T cells, B cells, NK cells, DCs, granulocytes, monocytes, macrophages, CD8+ T cells, CD4+ T cells and Tregs in homozygous B-hIL21R mice and B-hPD-1/hIL21R mice were similar to those in wild type mice, demonstrating that introduction of human IL21R and PD-1 genes in place of its mouse counterpart does not change the overall development, differentiation or distribution of these cell types. To evaluate in vivo efficacy of anti-mPD-1-hIL21 and anti-hPD-1-hIL21 fusion proteins, mouse colon adenocarcinoma MC38 cells were subcutaneously implanted into homozygous B-hIL21R mice (female, 6-7-week-old, n=6) or B-hPD-1/hIL21R mice (female, 6-7-week-old, n=6). Mice were grouped and treated when tumor volume reached approximately 100 mm3. Results showed that anti-PD-1-hIL21 fusion proteins were efficient at inhibiting tumor growth in B-hIL21R and B-hPD-1/hIL21R mice. Altogether, B-hIL21R and B-hPD-1/hIL21R mice are promising humanized mouse models for preclinical in vivo studies to assess novel drug candidates. Keywords: IL21/IL21R, humanized mice, fusion protein Citation Format: Ruili Lyu, Zhixia Li, Leila Kokabee, Jiawei Yao, Yanhui Nie, Chaoshe Guo. Evaluating in vivo efficacy of bi-functional fusion protein anti-PD-1-IL21 in humanized B-hIL21R mice and B-hPD-1/hIL21R mice [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 1641.