Human CD8+CD28− T Suppressor Cells Expanded by IL-15 In Vitro Suppress in an Allospecific and Programmed Cell Death Protein 1-Dependent Manner

Abstract

CD8+CD28− T suppressor cells (Ts) have been recently documented to play an important role in alloimmunity. Therefore, understanding and optimizing the conditions under which these cells are generated and/or expanded would greatly facilitate further research and potential clinical use. In this study, we describe rapid expansion of human allospecific CD8+CD28− Ts cells through coculture of CD8+ T cells with human leukocyte antigen-mismatched donor antigen-presenting cells plus IL-15 in a relative short period of time in vitro. Interestingly, IL-15 promotes the expansion of CD8+CD28− Ts cells through several parallel mechanisms. The expanded CD8+CD28− Ts cells upregulate expression of CD132, CD25, and programmed cell death protein 1 (PD-1), but downregulate expression of CD122, GZM-B, and perforin, while exhibiting no cytotoxicity. Most importantly, the expanded CD8+CD28− Ts cells vigorously inhibit CD4+ T cells proliferation in a contact-dependent and donor-specific manner both in vitro and in vivo. Interestingly, the co-inhibitory molecules PD-1 and programmed death-ligand 1 play an obligatory role in the mechanisms of CD8+CD28− Ts cells suppression. Taken together, our study report novel methodology for IL-15-induced expansion of human CD8+CD28− Ts cells and possible mechanisms. These findings may facilitate understanding of transplant rejection and promote clinical application of CD8+CD28− Ts cell-based strategies for inducing and monitoring transplant tolerance in the future.

CD8+ Tregs revisited: A heterogeneous population with different phenotypes and properties

“…In spite of the phenotypic heterogeneity of hCD8 + CD28 − T cells observed both in the steady state and in disease, it is clear that this population can give rise to cells with clear suppressive capacity in vitro. Induced CD8 + CD28 − suppressor cells occur after stimulation of peripheral blood mononuclear cells with allogeneic APCs and specific cytokines [68, 72, 91, 92], or tumor‐derived exosomes [93]. These cells are able to suppress both CD4 + helper and CD8 + killer effectors via modulating the expression profile of DCs towards their tolerogenic state [72, 75].…”

Post-hocassessment of the immunogenicity of three antibodies reveals distinct immune stimulatory mechanisms

“…Interestingly, CD8 T cell depletion enhanced the CD4 T cell proliferative response to most biologics with high immunogenicity (KLH, mAb1, and mAb2) without increasing the response to negative control mAb, suggesting that CD8 T cells in vitro hinder human CD4 T cell responses to immunogenic antibodies. Regulatory CD8 T cells have been shown to modulate in vitro the human CD4 T cell responses to autoantigens, 11 alloantigens, 22 and xenoantigens. 23 This is the first time, to our knowledge, that CD8 T cells have been shown to inhibit the human CD4 T cell responses to therapeutic mAbs.…”

Regulatory T Cells in Ovarian Carcinogenesis and Future Therapeutic Opportunities

“…Rare CD8 + CD28 − Tregs can transiently produce pro-inflammatory cytokines, such as IFN-γ, IL-17, and IL-10, and aid an immune response [ 10 , 11 , 67 ]. Although the infiltration of tumors by Tregs generally causes a reduction in the immune response to a tumor, infiltration of CD8 + Treg cells has been shown to inhibit naïve CD4 + T cell proliferation via TGF-β and IFN-γ secretion.…”

“…Tregs also express forkhead box P3 (FOXP3) transcription factor, a highly specific intracellular transcription factor essential in the development of Tregs. Although Tregs can be FOXP3 - , most are FOXP3 + [ 11 ]. Although there are many subtypes of Tregs expressing their specific surface markers, the typical Treg phenotype is CD4 + CD25 hi FOXP3 + [ 12 ].…”