DEVELOPMENT OF A METHOD OF THYMOCYTE DIFFERENTIATION OF BONE MARROW-ENRICHED CD34(- CELLS IN POSTNATAL ALLOGENEIC CULTURED THYMIC EPITHELIATO EVALUATE IMMUNODEFICIENCY DISORDERS()CD38)

An in vitro model of CD34(+)CD38(-) stem cell (SC) differentiation in postnatal cultured thymic epithelia fragment (CTEF) cocultures is desc ribed. Sequential phenotypic analysis of the progeny of the SC-CTEF de monstrated predominantly thymocytes and minor populations of promyeloc ytes, monocytes and natural killer cells. Triple-positive CD3(+)CD4(+) CD8(+), double-positive CD4(+)CD8(+), and mature single-positive CD4() and CD8(+) T cells, which were TCR alpha beta(+), were identified in dicating normal thymocyte maturation. In kinetic studies, mature singl e-positive CD4(+) T cells increased from 29% of total cells at one wee k to 54% at four weeks of coculture. These findings demonstrate that c oculture of bone marrow-derived SC acid allogeneic cultured thymic epi thelia in vitro results in continuous normal predominantly thymocyte d ifferentiation. The SC-CTEF cocultures were then infected with two dif ferent strains of human immunodeficiency virus. CD4(+) thymocytes were markedly decreased. However, inhibition of early thymocyte maturation steps was also suggested by the presence of increased triple-negative and CD44(+)CD25(-)CD3(-) thymocytes and decreased CD44(+)CD25(+) thym ocytes. This model system of thymocyte maturation will be useful in th e evaluation of primary T cell immunodeficiency disorders, gene therap y of SC and pharmacological augmentation of thymic function.