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Characterization of cells with T cell markers in athymic nude bone marrow and of their in vitro-derived clonal progeny. Comparison with euthymic bone marrow.

Evidence is presented that early steps in T cell differentiation, to the point of TCR expression, can occur in athymic nude bone marrow (BM) and perhaps also in normal BM. Low density nylon wool nonadherent BM from 5- to 8-wk-old nude and normal mice was found to contain dim CD3+ CD4- CD8- cells. This subpopulation was not found in scid/scid low density nylon wool nonadherent BM but was present at similar frequency in both nude and normal BM and expressed comparable fluorescence intensity. With the use of additional markers, a difference between nude and normal dim CD3+ CD4- CD8- cells was found: the ratio of J11d+/J11d- cells was at least threefold higher in nude than in normal BM. Whereas 60% of nude J11d+ CD3+ cells expressed a TCR-alpha/beta and 40% expressed a gamma/delta TCR, almost no TCR-gamma/delta expressing cells were detected in dim CD3+ cells from normal mice in either the J11d+ or J11d- subpopulation. The majority of those cells express a TCR-alpha/beta. We established that nude dim CD3+ CD4- CD8- cells were distinguishable from mature recirculating T cells and developed an in vitro clonal culture system that supported the growth of these cells. When these cells were cocultured in vitro in a limiting dilution system with inactivated anti-CD3 mAb-secreting cells, in the presence of rIL-2 and rIL-4, one in 5 x 10(2) to 1 x 10(3) cells were growth inducible. Most progeny cells expressed a CD3+ CD8+ CD4- surface phenotype. Cultures displayed nonspecific cytolytic reactivity. With the use of a sensitive dot-blot technique, transcripts coding for C alpha, C beta, VC gamma, and C delta TCR genes were detected in these cultures. Rehybridization experiments demonstrated mutually exclusive expression of either C alpha or C delta mRNA transcripts in the majority of clones selected for a high probability of clonality. Most (greater than 95%) of T cell clones derived from normal BM expressed the C alpha transcript with approximately 5% expressing the C delta transcript. In contrast, about 40% of T cell clones derived from nude BM expressed the C delta transcript whereas the remaining 60% expressed 10-fold lower C alpha message than normal BM-derived clones.