Effects of X-rays and γ-rays on reconstitution of hematopoiesis and immunity after allogeneic bone marrow transplantation

Objective To determine the conditioning regimen suitable for mice allogeneic hematopoietic stem cell transplantation (allo-HSCT).Methods Twelve BALB/c mice were randomly divided into 2 equal groups to undergo X-ray irradiation by linear accelerator at the dose of 7.0 Gy (pure X-ray group) or 60Co source irradiation at the dose of 7.0 Gy (pure γ-ray group).Thirty mice were randomly divided into 2 equal groups to undergo X-ray irradiation and then infusion of bone marrow from donor mice via caudal vein (X-ray + transplantation group) or γ-ray and then infusion of bone marrow via caudal vein (γ-ray + transplahtation group).3,5,7,10,15,20,and 30 d later peripheral blood samples were collected to calculate the number of white blood cells (WBCs) and detect the chimeric rates of lymphocytes by flow cytometry.5,10,and 20 d after irradiation 15 mice were killed with their lung,liver,small intestine,spleen,and femurs taken out to undergo pathological examination.Results The survival rates during the period 5-15 days of the γ-ray + transplantation group were all significantly higher than those of the X-ray + transplantation group.The pathological changes of organs of the X-ray +transplantation group were all more severe than those of the γ-ray + transplantation group.Since the fifth day after transplantation cells originating from the donor began to appear in the peripheral blood.The chimeric rate of the γ-ray + transplantation group 10 days after transplantation was (95.53± 2.57) %.The chimeric rates 5,10,and 20 days after transplantation of the γ-ray + transplantation group were all significantly higher than those of the X-ray + transplantation group (t = 15.263,3.256,P < 0.05).The WBC count of both irradiation groups decreased to the lowest level 5 d later and began to increase 10 days after transplantation and the WBC counts of the γ-ray + transplantation group 10 and 20 days aftertransplantation were both significantly higher than those of the X-ray + transplantation group (t = 3.624,6.695 ,P < 0.05).The chimeric rats of the peripheral lymphocytes 10 and 20 days after transplantation of the γ-ray + transplantation group were both significantly higher than those of the X-ray + transplantation group (t = 12.317,8.295,P < 0.05).The homogeneity rate of transplantation of the γ-ray +transplantation group was better than that of the X-ray + transplantation group.Conclusions As a conditioning regimen in allogeneic hematopoietic stem cell transplantation γ-ray irradiation causes milder injury and accelerated reconstitution of hematopoiesis and immunity,in comparison with X-ray irradiation. Key words: X-rays;  γ-rays;  Allogeneic hematopoietic stem cell transplantation; Immune reconstitution