<Li> Tissue resident memory T cells (T) occupy tissues (skin, lung, etc ...) without recirculating . One cell surface marker that has been associated with T is the integrin αeβ7 . </Li> <Li> Virtual memory T cells differ from the other memory subsets in that they do not originate following a strong clonal expansion event . Thus, although this population as a whole is abundant within the peripheral circulation, individual virtual memory T cell clones reside at relatively low frequencies . One theory is that homeostatic proliferation gives rise to this T cell population . Although CD8 virtual memory T cells were the first to be described, it is now known that CD4 virtual memory cells also exist . </Li> <P> Regulatory T cells (suppressor T cells) are crucial for the maintenance of immunological tolerance . Their major role is to shut down T cell - mediated immunity toward the end of an immune reaction and to suppress autoreactive T cells that escaped the process of negative selection in the thymus . Suppressor T cells along with Helper T cells can collectively be called Regulatory T cells due to their regulatory functions . </P> <P> Two major classes of CD4 T cells have been described--FOXP3 T cells and FOXP3 T cells . </P>

Name the cell from which all other cells are derived