HLA-Class II Expression identifies functionally distinct human CD8+ regulatory T cells

ARRUVITO L; PAYASLIÁN F; PODHORZER, A; PANDOLFI J; FAINBOIM L

Los Cocos. Córdoba

Congreso; LXI Reunión Científica Anual de la SAI.; 2013

# Introduction: Human suppressor T cells were defined within the CD8+ T-cell compartment in early 80s by us. However, since the characterization of the CD4+FOXP3+ Tregs, CD8+ Tregs fall into an ill defined subset of regulatory T cells. In the present study we re-evaluated our first description of a subset of induced CD8+HLA-DR+ cells with a strong suppressor activity. # The main aim was to identify this subset in resting CD8+ T cells from peripheral blood as a counterpart of natural CD4+FOXP3+ Tregs.   # Material and Methods: PBMCs were sorted into CD8+HLA-DR+ and CD8+HLA-DR- subsets, and its regulatory activity was evaluated by adding these two subsets to autologous T cells stimulated with anti-CD3 plus anti-CD28 ab. Phenotypic characteristics of CD8+ Tregs were performed using antibodies against: FOXP3, CD25, CD28, CTLA-4, CD62L, CCR7, GrzA, CD107a, IFN-γ, IL-10. Cytokine secretion was also assessed by ELISA. # Results and Conclusion: CD8+HLA-DR+ T cells represent ~ 15% of total peripheral blood CD8+ T cells. After being purified by cell sorting only CD8+HLA-DR+ cells showed a strong suppressor activity that was partially abrogated by anti-IL-10 ab, and was not altered by anti-HLA-class II ab. In contrast, CD8+HLA-DR- cells induced an enhanced proliferation on responder cells. We also found that CD8+ HLA-DR+ subset displayed an effector-memory T phenotype (low expression of CD62L and CCR7) and did not show the classical regulatory CD4+ T cell markers (CD25, FOXP3 and CTLA-4) in resting conditions. However, these markers could be induced and maintained throughout 15 d of culture at significant levels in contrast with those CD8+HLA-DR- cells. Furthermore, they secreted cytotoxic molecules (GrzA) and pro-inflammatory cytokines (IFN-γ). Our study represents an important advance in the field of Immune Tolerance and contributes to define the quality of the regulatory response within the CD8 compartment.