CAR T cells targeting C-C motif chemokine receptor 4 (CCR4) selectively deplete human Tregs ex vivo and in vivo

Regulatory T cells (Tregs) are essential for maintaining immune tolerance but also contribute to immune suppression within the tumor microenvironment (TME), dampening anti-tumor immunity in hematologic and solid tumors. As such, strategies aimed at depleting Tregs or reducing their suppressive activity are of great clinical interest. C-C Chemokine receptor 4 (CCR4) is highly expressed on intratumoral Tregs and mediates Treg migration into the TME. Although current therapies targeting CCR4 using monoclonal antibodies have shown some Treg depletion in clinical trials, their clinical efficacy has been limited. We therefore tested whether chimeric antigen receptor (CAR) T cell therapy could be used to deplete Tregs. We evaluated human-specific CCR4-directed CAR T cells (CCR4-CARTs) previously developed for T cell malignancies and determined whether these CARTs could deplete human Tregs ex vivo and in vivo. In patient-derived malignant pleural effusions and lung cancer tumor digests, CCR4 CARTs almost completely depleted Tregs, plus a small population of CCR4+ CD4+ non-Tregs, while sparing CD8+ T cells. When tested in vivo in humanized mice, a single dose of CCR4 CART led to nearly complete Treg depletion. These findings support the potential of CCR4 CARTs as a selective and effective approach to Treg modulation and warrant further clinical investigation.