Self-renewal and maturation of immature T-cell progenitors within PHA-induced agar T-cell colonies

T-cell colonies derived from peripheral blood mononuclear cells plated in agar with phytohemagglutinin (PHA) contain about 5-7% E-, OKT3-, OKT6-, TdT-, SIg- cells phenotypically similar to bone marrow precursors since they are also RFB1+, OKT10+, HLA-DR+, and PNA+. These cells can generate secondary E+, OKT3+ T-cell colonies when replated in the presence of both PHA and a colony-promoting activity distinct from the T-cell growth factor, Interleukin 2. These observations suggest that E-, OKT3- cells detected in primary PHA-induced T-cell colonies belong to a pool of prethymic cells which are able to mature into T-lymphocytes of T4 and T8 type in the absence of the thymic microenvironment.