The target antigen determines the mechanism of acquired resistance to T cell based therapies

Immunotherapy is a revolution in cancer treatment. Despite its success, cancer patients eventually progress due to the emergence of resistance. In this scenario, the selection of the tumor antigen is important and can be decisive in the success of the clinical response, particularly when resistance emerge. T cell bispecific antibodies (TCBs) are engineered molecules that include, within a single entity, binding sites to the T cell receptor and to a tumor-specific or a tumor-associated antigen. It is assumed that, as all TCBs have the same mechanism of action, mechanisms of resistance are independent of the tumor antigen. Using gastric CEA+/HER2+ MKN45 cells as a model and TCBs directed against CEA or HER2, here we show that the mechanism of resistance to a T cell-based therapy is dependent on the tumor antigen. Acquired resistant models to a high-affinity CEA-targeted TCB exhibit a reduction of CEA antigen levels due to transcriptional silencing, which is reversible upon 5-AZA treatment in vitro and in vivo. In contrast, a HER2-TCB resistant model maintains HER2 levels as HER2 downregulation led to an impairment of proliferation. Furthermore, using this latter model, we identify the disruption of the interferon-gamma signaling as the cause of resistance to killing by active T lymphocytes. Our results unveil different mechanisms of acquired resistance to TCBs depending on the selected antigen, which will help in the design of combinatorial strategies to increase the efficacy of cancer immunotherapies and to anticipate and overcome resistances. Comparative gene expression profiling analysis of RNA-seq data for gastric cell line MKN45 and its immunotherapy resistant derivatives MKN-HER2R (resistant to a HER2-TCB) and MKN-CEAR (resistant to a CEACAM5-TCB)