Abstract 3779: Clonal tracing reveals different mechanisms of resistance to immune checkpoint blockade

Immune checkpoint blockade (ICB) therapy has improved patient survival in a variety of cancers, but its resistance presents a major clinical challenge. It remains unclear whether therapeutic resistance is driven predominantly by refractory clones of cancer cells or by immunosuppressive microenvironment. To address this, we utilized syngeneic transplantation model and performed clonal tracing of cancer cells to monitor the response to ICB. Different cancer clones displayed variable sensitivity to ICB treatment, reflecting intratumoral heterogeneity in therapy response. Furthermore, different recipients manifested distinct resistance mechanisms. ICB-responders developed resistance through selection and expansion of pre-existing ICB-resistant cancer clones, whereas non-responders presented with irresponsive microenvironment rather than dominance of resistant cancer clones. Extrapolation of the tumor-infiltrating immune repertoire revealed that higher IgG and lower IgA strongly correlated with better ICB response. This biomarker was further validated in multiple clinical cohorts. Our approach discriminates different sources of resistance to ICB, and identifies humoral immunity as biomarker of ICB response. Citation Format: Shengqing Gu, Xihao Hu, Xiaoqing Wang, Peng Jiang, Ziyi Li, Nicole Traugh, Xia Bu, Xiaofang Xing, Gordon J. Freeman, Myles Brown, Xiaole S. Liu. Clonal tracing reveals different mechanisms of resistance to immune checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3779.