Fast hematopoietic recovery after bone marrow engraftment needs physiological proximity of stromal and stem cells

Relatively slow hematopoietic recovery after isolated bone marrow (I-BM) engraftment is probably caused by a disrupted microenvironment of stromal and stem cells. Thus, we compared the kinetics of hematopoietic recovery of lethally irradiated rats that received I-BM versus vascularized BM (V-BM). Total body irradiated (TBI; 8 Gy) Lewis (LEW; RT1(1)) rats were either injected IV with syngeneic sex-mismatched 80 x 10(6) I-BM or transplanted with 80 x 10(6) V-BM in orthotopic hind limb grafts. Ten days later, peripheral blood (PB) and mesenteric lymph nodes (MLN) of these recipients were examined for the presence of donor-derived hematopoietic cells with a panel of monoclonal antibodies by FACS. To detect male cells in sex-mismatched female recipients, PCR was performed using male Y chromosome primers. When examined in PB and MLN, recipients transplanted with V-BM displayed significantly faster recovery of leukocytes (CD43+), monocytes (CD14+), and T cells (CD5+) in comparison with I-BM recipients. In addition, only V-BM (but not I-BM) groups contained stroma-like male-positive cells in PB and MLN. Our results suggest that V-BM transplants provided superior hematopoietic recovery in comparison to I-BM transplants. We postulated that close proximity between stromal and stem cells in V-BM is essential for efficient repopulation with progenitors of different lines of leukocytes.