The effect of thymectomy on the competitive potential of C57BL/6 bone marrow graft.

When a mixture of bone marrow cells derived from mice of the CBA-T6T6 and C57BL/6 strains and Lewis rats is injected into lethally irradiated (C57BL/6 X CBA-T6T6)F1 hybrid recipients, a process of cell interaction takes place, which in less than 2 weeks leads to the complete and permanent take over in hematopoietic and lymphoid organs by the C57BL/6 cell population. This is shown by the chromosome marker technique (T6) analysis. Adult thymectomy of F1 hybrid hosts prior to irradiation and bone marrow transplantation does not alter the competitive potential of the C57BL/6 donor cell population. However, neonatal thymectomy of the prospective C57BL/6 donors significantly impairs their "superiority" as donor cells, and CBA-T6T6 dividing cells persist at all times in all tissues analyzed. The results lend support to the concept of thymus-dependent precursor cells residing in "prethymic" hematopoietic tissue.