AN ALTERNATE PATHWAY FOR T-CELL DEVELOPMENT SUPPORTED BY THE BONE-MARROW MICROENVIRONMENT - RECAPITULATION OF THYMIC MATURATION

In the principal pathway of alpha/beta T cell maturation, T cell precu rsors from the bone marrow migrate to the thymus and proceed through s everal well-characterized developmental stages into mature CD4(+) and CD8(+) T cells. This study demonstrates an alternative pathway in whic h the bone marrow microenvironment also supports the differentiation o f T cell precursors into CD4(+) and CD8(+) T cells. The marrow pathway recapitulates developmental stages of thymic maturation including a C D4(+)CD8(+) intermediary cell and positive and negative selection, and is strongly inhibited by the presence of mature T cells. The contribu tion of the marrow pathway in vivo requires further study in mice with normal and deficient thymic or immune function.