Spatially selective depletion of tumor-associated regulatory T cells with near-infrared photoimmunotherapy.

Current immunotherapies for cancer seek to modulate the balance among different immune cell populations, thereby promoting antitumor immune responses. However, because these are systemic therapies, they often cause treatment-limiting autoimmune adverse effects. It would be ideal to manipulate the balance between suppressor and effector cells within the tumor without disturbing homeostasis elsewhere in the body. CD4(+)CD25(+)Foxp3(+) regulatory T cells (T-regs) are well-known immunosuppressor cells that play a key role in tumor immunoevasion and have been the target of systemic immunotherapies. We used CD25-targeted near-infrared photoimmunotherapy (NIR-PIT) to selectively deplete T-regs, thus activating CD8 T and natural killer cells and restoring local antitumor immunity. This not only resulted in regression of the treated tumor but also induced responses in separate untreated tumors of the same cell line derivation. We conclude that CD25-targeted NIR-PIT causes spatially selective depletion of T-regs, thereby providing an alternative approach to cancer immunotherapy.