CD4+T cell activation distinguishes response to anti-PD-L1+anti-CTLA4 therapy from anti-PD-L1 monotherapy

Cancer patients often receive a combination of antibodies targeting programmed death-ligand 1 (PD -L1) and cytotoxic T lymphocyte antigen -4 (CTLA4). We conducted a window -of -opportunity study in head and neck squamous cell carcinoma (HNSCC) to examine the contribution of anti-CTLA4 to anti -PD -L1 therapy. Singlecell profiling of on- versus pre-treatment biopsies identified T cell expansion as an early response marker. In tumors, anti -PD -L1 triggered the expansion of mostly CD8 + T cells, whereas combination therapy expanded both CD4 + and CD8 + T cells. Such CD4 + T cells exhibited an activated T helper 1 (Th1) phenotype. CD4 + and CD8 + T cells co -localized with and were surrounded by dendritic cells expressing T cell homing factors or antibody -producing plasma cells. T cell receptor tracing suggests that anti-CTLA4, but not anti -PD -L1, triggers the trafficking of CD4 + naive/central-memory T cells from tumor -draining lymph nodes (tdLNs), via blood, to the tumor wherein T cells acquire a Th1 phenotype. Thus, CD4 + T cell activation and recruitment from tdLNs are hallmarks of early response to anti -PD -L1 plus anti-CTLA4 in HNSCC.