Are CD8+CD122+ cells regulatory T cells or memory T cells?

We identified CD8+CD122+ regulatory T cells in the mouse. Some immunologists consider CD8+CD122+ cells to be memory T cells despite our report of their regulatory function. Here, we propose a dual phenotype of these cells. Murine CD8+CD122+ T cells demonstrate both memory and regulatory features in their functional profiles. Human CD8+CXCR3+ T cells, which are thought to be the human counterpart of murine CD8+CD122+ regulatory T cells, do not match human central memory T cells of the CD8+CD45RA−CCR7+ phenotype. Thus, we must consider human CD8+ regulatory T cells and murine CD8+ regulatory T cells separately. Of human CD8+ regulatory T cells, CD8+CXCR3+ regulatory T cells can be divided into further subsets and we may be able to distinguish memory T cells and regulatory T cells. Of murine CD8+CD122+ regulatory T cells, it seems to be impossible to divide CD8+CD122+CD44+CD62L+ regulatory T cells into further subsets at present, indicating that this single population of cells has activities of both regulatory T cells and memory T cells.