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 precursors from the bone marrow migrate to the thymus and proceed through several well-characterized developmental stages into mature CD4+ and CD8+ T cells. This study demonstrates an alternative pathway in which the bone marrow microenvironment also supports the differentiation of T cell precursors into CD4+ and CD8+ T cells. The marrow pathway recapitulates developmental stages of thymic maturation including a CD4+CD8+ intermediary cell and positive and negative selection, and is strongly inhibited by the presence of mature T cells. The contribution of the marrow pathway in vivo requires further study in mice with normal and deficient thymic or immune function.