Analysis of the development of T cells by transferring precursors into cultured fetal thymus with a microinjector.

Development of T cells from precursors in the bone marrow or fetal thymus cells was investigated by transferring these cells into deoxyguanosine (dGuo)-treated organ cultured fetal thymus (FTOC) with a microinjector (micro i.t. method). Donor type T cells could be generated after transfer by the micro i.t. method of precursors present both in bone marrow and fetal thymus. The kinetics of the generation of T cells from these precursors was similar to that found in in vivo intra thymus transfer systems. As low as 300 fetal thymus cells were shown to be sufficient to repopulate a dGuo-FTOC. On the other hand, in a hanging drop culture method only precursors from the fetal thymus but not from the bone marrow were effective in repopulating the lobes. The hanging drop method was ineffective in repopulating all lobes, even when higher numbers of fetal thymus cells were applied. Moreover the number of T cells recovered per repopulated lobes was 2 to 3 times lower in the hanging drop system than in the micro i.t. system. It was also observed that the development of T cells was significantly accelerated by adding adherent cells from either the thymus or the spleen.