Objective: To explore the effects of splenocytes on chimerism and GVHD after haploidentical MHC matched stem cells transplant with nonmyeloablative conditioning in murine model. Method: Thirty CB6F1 recipient mice were divided into group A

B and C. They were given 60Co of total body irradiation and infused with MHC haploidentical matched bone marrow plus different proportion of splenocytes. The level of the chimerism of the recipient mice was detected by flow cytometry. The manifestations and histopathological examination of GVHD were observed. The mortality of the recipient mice was observed. Result: Engraftments of group A and B were full donor chimerism after 21 days

engraftments of group C were full donor chimerism after 14 days. The clinical GVHD score in group C was obviously higher than that in group B(P<0.01)

and that in group B higher than in group A(P<0.01). All the mice survived over 90 days. Conclusion: The higher dose of MHC haploidentical matched splenocytes will help to be full donor chimerism earlier

but it may aggravate GVHD.