Studies on the differentiation of T cells from hemopoietic stem cell.

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Differentiation of T cells from the hemopoietic stem cell was investigated. Since the stem cells have never been quantitatively analysed, we first deviced a method to quantity the stem cells for T cell lineage. C57BL (B6) mice were used as the recipient, and B10Thy1.1 mice were used as the donor. The recipients were either part-body-shielded (leg and tail, or thymus area) and irradiated (900 R) or whole body irradiated (800 R) and reconstituted with <10^7> syngeneic bone marrow cells. Donor cells were transferred eithter intravenously (i.v.) or intrathymically (i.t.). I.t. transfer method was much more (10 to 100 times) efficient for T cell generation than i.v. transfer method. By i.t. transferring serial dilutions of cells from various organs of B10Thy1.1 mouse, the frequency of the stem cells which have a potential to give rise to T cells (T-stem cells) was determined. The results are as follows: bone marrow, 1/8 x <10^3> ; fetal liver, 1/1.6 x <10^4> ; spleen 1/4.5 x <10^5> ; thymus, 1/7 x <10^5> .In the recipients given a limited number of bone marrow cells, it was shown that the donor type T cells were the progeny of a single stem cells. Both helper T cells and killer T cells were found to be derived from a single stem cell. We further showed that the repertoire diversification of T cells occurred at random.