THYMUS-GRAFTED SCID MICE SHOW TRANSIENT THYMOPOIESIS AND LIMITED DEPLETION OF V-BETA-11+ T-CELLS

To seek direct evidence for the notion that stem cells in the thymus need to be constantly replenished from the bone marrow (BM), fetal (day 13) thymuses from normal BALB/c mice were grafted into T and B cell-deficient C.B-17 SCID mice (both H-2d, I-E+). The thymus grafts in these mice showed normal thymopoiesis for the first 3 wk postgrafting but then developed sudden atrophy with near complete loss of CD4+8+ cells by 4-5 wk. Such atrophy was not seen when the thymus-grafted mice were cotransplanted with normal BM cells. The lymph nodes of SCID mice receiving thymus grafts alone contained mature T cells but virtually no B cells. This lack of B cells was associated with aberrant I-E-restricted V-beta deletion: the depletion of V-beta-3+ and V-beta-5+ T cells was near complete, whereas V-beta-11+ cells showed only marginal depletion.