Nonmyeloablative Allogeneic Stem Cell Transplantation In H-2 Haploidentical Murine Models

Nonmyeloablative allogeneic hematopoietic stem cell transplantation(NST) is a new approach to allogeneic transplantation. It bases on the traditional transplantation and the transplantation immunology developed in the past few years. Compared to traditional ablative transplantation, this approach utilizes enhanced immunosuppression rather than myeloablative cytotoxic conditioning, and the stably mixed chimerism established by it will decrease the possibility of GVHD through induction of transplantation tolerance.Although HLA-haploidentical transplantation makes many patients with hematological malignancies who were born in family with only one child get the opportunity for transplantation, at present, it's application is still limited because of high morbidity and mortality related to transplantation, such as GVHD, graft rejection and so on. If nonmyeloablative conditioning is used in HLA haploidentical transplantation , related-mortality will be decreased without doubt. Based on this assumption, nonmyeloablative allogeneic stem cell transplantation was established in H-2 haploidentical murine models, trying to obtain some useful information for clinical application of HLA haploidentica transplantation with nonmyeloablative conditioning in treatment of hematological malignancies.In the present experiment, The H-2 haploidentical nonmyeloablative allogeneic stem cell transplantation between the parental generation and filial generation was conducted , the recipient mice of each group received different conditioning regimens. Group A was given the myeloablative conditioning regimens(10.5GY), group B and C were given different nonmyeloablative conditioning regimens. The recipients were pretreated with Ara-C+C Y+ TBI(2Gy)in group B and C, and with fludarabine in C group. All the recipients were injected the marrow cell from C57BL/6 mice through tail vein on day 0, and the mixed suspension of marrow and spleen cells, control group of each group was not processed the cell transplantation, then the hematopoietic recovery, engraftment and the GVHD were observed in the recipients.The results showed that the recipients of group B and C which were not infused donor stem cell regained its hematopoietic recovery on day 14 post-transplant, mixed chimerism was detected on day 7 post-transplant by flow cytometry assay in the recipients after transplantation, the proportion of chimerism increased gradually, and kept more than 50% stably.Chimera detection after transplantation showed that the engraftment of Group A remained full donor chimerism, and the Group B and Group C were associated with mixed chimerism or full donor chimerism, but the chimerism of Group C is stable up to 90% , and remained above 50% even on day 50 post-transplantation; the chimerism of Group B after transplantation remained less than 70%, and tended to decrease to below 30% after day 50.GVHD occurred in all the recipient mice with infusing the mixed suspension of bone marrow and spleen cells to different extent due to failure of prevention, wherein, acute GVHD occurred in all of the recipients in group A, the occurrence rate of GVHD in Group B and Group C were 75% and 62.5% respectively, obviously lower than that of Group A (p<0.01), and there was no difference between Group B and Group C. The occurrence of GVHD in group C was the lowest since CSA and MTX were given for prevention of GVHD.Our results indicate that our nonmyeloablative regimens were safe and well-tolerated. The recipients in group C given nonmyeloablative regimens but noinfusion of donor cells were achieved hematopoietic recovery and the transplanted recipients with stable mixed chimerism in vivo, and GVHD was mild. There is no significant difference in ratio of GVHD between different nonmyeloablative regimens. Comparatively, conditioning regimen in group C is the best one because of the successfully established donor cell graft.