Nonantigen specific CD8+ T suppressor lymphocytes originate from CD8+CD28- T cells and inhibit both T-Cell proliferation and CTL function

Nonantigen specific CD8⁺ suppressor T lymphocytes (CD8 ⁺ Ts) inhibit T-cell proliferation of antigen-specific T lymphocytes. The impossibility to generate in vitro these cells has been correlated with the appearance of relapses in patients affected by autoimmune diseases, suggesting the involvement of these cells in immune regulation. This study was aimed to identify circulating precursors and to characterize the phenotype and mechanism of action of CD8⁺ Ts. We found that CD8⁺ Ts can be generated in vitro from CD8⁺CD28^- T lymphocytes, but not from CD8⁺CD28⁺ T cells. A key role in their generation is played by monocytes that secrete interleukin-10 (IL-10) after granulocyte macrophage-colony-stimulating factor (GM-CSF) stimulation. Cell-to-cell direct interaction between CD8⁺CD28^- T cells and monocytes does not play a role in the generation of CD8⁺ Ts. CD8⁺ Ts have a CD45RA⁺, CD27^-, CCR7 ^-, IL-10Rα⁺ phenotype and a TCR Vβ chain repertoire overlapping that of autologous circulating CD8⁺ T cells. This phenotype is typical of T lymphocytes previously expanded due to antigen stimulation. Their suppressive effect on T-cell proliferation targets both antigen presenting cells, such as dendritic cells, and antigen-specific T lymphocytes, and is mediated by IL-10. CD8⁺ Ts suppress also the antigen-specific cytotoxic activity of CTL decreasing the expression of HLA class I molecules on target cells through IL-10 secretion. These findings can be helpful for the better understanding of immune regulatory circuits and for the definition of new pathogenic aspects in autoimmunity and tumor immunology.