Tumor-specific regulatory T cells suppress lytic granule release of adoptively transferred cytotoxic effector T cells and inhibit tumor rejection

Aims: Regulatory T cells (Treg) interfere with the rejection of malignant tumors through cytotoxic T cells (CTL), but it is not well characterized at which levels of the T cell response: (i) initial activation at the priming site, (ii) trafficking to tumors, (iii) survival and proliferation in the tumor stroma or (iv) the execution of effector function, Treg-mediated suppression of CTL function predominantly occurs. Here we investigated the local influence of Treg on CTL effector function in tumors and tumor-draining lymph nodes by combining intravital multiphoton microscopy and flow cytometry-based population a…