Significance: Regulatory T (Treg) cells expressing the transcription factor FOXP3 play a critical role in suppressing antitumor immune responses. Here we found that, compared with peripheral blood T cells, tumor-infiltrating T cells contained a higher frequency of effector Tregs, which are defined as FOXP3^hiand CD45RA⁻, terminally differentiated, and most suppressive. Effector Treg cells, but not FOXP3^loand CD45RA⁺naïve Treg cells, predominantly expressed C-C chemokine receptor 4 (CCR4) in both cancer tissues and peripheral blood. In vivo or in vitro anti-CCR4 mAb treatment selectively depleted effector Treg cells and efficiently induced tumor-antigen-specific CD4⁺and CD8⁺T cells. Thus, cell-depleting anti-CCR4 mAb therapy is instrumental for evoking and enhancing tumor immunity in humans via selectively removing effector-type FOXP3⁺Treg cells.

Increasing evidence indicates that the gut microbiota is closely associated with acute graft-versus-host disease (aGVHD) in stem cell transplantation (SCT). Fecal microbiota transplantation (FMT) could represent an alternative treatment option for aGVHD. However, FMT for SCT patients carries a potential risk of infection by infused microbiota because of the severely immunosuppressed status. We therefore conducted a pilot study to evaluate the safety of FMT in SCT. A total of 4 patients with steroid-resistant (n = 3) or steroid-dependent gut aGVHD (n = 1) received FMT. No severe adverse events attributed to FMT were observed. All patients responded to FMT, with 3 complete responses and 1 partial response. Temporal dynamics of microbiota seemed to be linked to the gut condition of patients and peripheral effector regulatory T cells also increased during response to FMT. FMT was safely performed in our patients and might offer a novel therapeutic option for aGVHD. This trial was registered at the University Hospital Medical Information Network (https://upload.umin.ac.jp/cgi-open-bin/icdr_e/ctr_view.cgi?recptno=R000017575) as #UMIN000015115. Publisher9s Note: There is an Inside Blood Commentary on this article in this issue. Key Points FMT was safely performed in SCT patients, with 3 complete responses and 1 partial response. Temporal microbiota dynamics seem linked to gut condition and effector regulatory T cells also increased during response to FMT.

Immunological tolerance to self requires naturally occurring regulatory T (T _reg ) cells. Yet how they stably control autoimmune T cells remains obscure. Here, we show that T _reg cells can render self-reactive human CD8 ⁺ T cells anergic (i.e., hypoproliferative and cytokine hypoproducing upon antigen restimulation) in vitro, likely by controlling the costimulatory function of antigen-presenting cells. Anergic T cells were naïve in phenotype, lower than activated T cells in T cell receptor affinity for cognate antigen, and expressed several coinhibitory molecules, including cytotoxic T lymphocyte–associated antigen-4 (CTLA-4). Using these criteria, we detected in healthy individuals anergic T cells reactive with a skin antigen targeted in the autoimmune disease vitiligo. Collectively, our results suggest that T _reg cell–mediated induction of anergy in autoimmune T cells is important for maintaining self-tolerance.

Significance: Anti–CTLA-4 mAb is able to augment tumor immunity despite CTLA-4 expression by functionally opposing T cell populations: activated effector T (Teff) cells and FOXP3⁺CD4⁺Treg cells. Here we show that anti–CTLA-4 mAb engineered to be cytotoxic depleted Treg cells effectively in vitro in humans and in vivo in mice. It expanded antigen-specific CD8⁺Teff cells when tumor-antigen stimulation was delayed several days to protect them from killing by the mAb. Anti–CTLA-4 mAb modified to exhibit a lesser or no cell-depleting activity failed to show such effects. This strategy of differentially controlling Treg and Teff cells by cytotoxic anti–CTLA-4 mAb to evoke effective tumor immunity will help in designing cancer immunotherapy targeting other molecules commonly expressed by Treg and Teff cells.