CD34+selected bone marrow grafts are radioprotective and establish mixed chimerism in dogs given high dose total body irradiation

Background. Canine stem cell transplantation models have provided important preclinical information for human clinical studies. The recent cloning of cDNA for canine CD34 and the production of monoclonal antibodies that recog nize canine CD34 have been the basis for the development of techniques for the large-scale enrichment of canine hematopoietic progenitor cells. In thi s study, we evaluated the in vivo functional properties of canine bone marr ow CD34+ cells after a myeloablative conditioning regimen. Methods. After 920 cGy total body irradiation, three dogs received infusion of autologous CD34+ selected cells from the marrow, three dogs CD34+ deple ted autologous marrow cells, and two dogs received CD34+ autologous marrow cells that were immunomagnetically selected and then further purified by ce ll sorting. In addition, four dogs received allogeneic marrow enriched for CD34+ cells from dog leukocyte antigen-identical littermates to investigate long-term repopulating function of CD34+ cells. Chimerism studies were per formed using polymerase chain reaction to detect highly polymorphic microsa tellite markers, Results. In three recipients of autologous marrow enriched for CD34+ cells to between 29% and 70% (1.6x10(6) to 3.4x10(6) CD34+ cells/kg), prompt and full hematopoietic recovery occurred, whereas in three dogs that received m arrow depleted of CD34+ cells (1x10(7) cells/kg), no hematopoietic recovery was achieved. In two dogs that received highly purified CD34+ cells (purit y: 98% and 96%, 0.79x10(6) to 0.547x 10(6) CD34+ cells/kg), delayed but ful l hematopoietic recovery was seen. Three of four allograft recipients of 1. 75x10(6) to 6.8x10(6) CD34+ cells/kg engrafted and showed full hematopoieti c recovery, whereas one dog rejected the graft. The three long-term survivo rs showed stable mixed hematopoietic chimerism with predominantly donor hem atopoiesis. Conclusions. Transplantation of canine CD34+ cells after lethal total body irradiation provides radioprotection and gives rise to long-term hematopoie tic reconstitution. Stable donor/host mixed chimerism was observed in allog raft recipients most likely as a result of T-cell depletion of the grafts. Our findings suggest a future role for canine preclinical transplant studie s involving in vitro manipulation of hematopoietic progenitor cells.