High level expression of donor hemoglobin and decrease in the level of membrane associated denatured hemoglobin (madh) as an indicator of disease severity after in utero bone marrow transplantation in a murine model of βthalassemia

Introduction: β-Thalassemia (thai) major is characterized by abnormal hemoglobin (Hb) production resulting in decreased erythrocyte stability. In utero hematopoietic stem cell transplantation (lUHSCTx). a pontential therapeutic approach, has been shown to result in long term, multilineage, allogenic hematopoietic chimerism in animal models particularly under circumstances with a competitive advantage for donor cells. We hypothesized that decreased red cell survival and ineffective erythropoiesis in a β-thal model might provide a selective advantage facilitating donor erythroid chimerism after lUHSCTx. Methods: Knockout thai mice (H2kb) were transplanted i.p. at 14 day gestational age with 5x10' bone marrow light density mononuclear cells from SJL/J (H2k!) donors. Donor chimerism and Hb expression level were assessed by dual color flow cytometry and reverse-phase HPLC. MADH, an indicator of disease severity and RBC stability, was assessed by measuring the amount of hemichrome attached to RBC membranes. Results: Donor peripheral blood chimerism (0.17-2.02%) was found in 5 of 6 analyzed thai mice. All chimeric (chim) thai mice expressed higher levels of donor Hb (7.23-47.51 % of total Hb) than their respective levels of donor chimerism. The ratio of the donor Hb level to the total donor chimerism level in 5 thai chim mice (range 14.23-42.53) was higher than that in 4 wild type (wt) chimeric mice (1.54-3.41% donor chimerism) which ranged between 0.59-3.72. The MADH level in the 5 chim thai mice ranged between 0.08-0.41%. The average MADH levels of wt chim mice, wt non-chim mice and thai non-chim mice were 0.19%, 0.09% and 0.58% respectively. Analysis of the 6 analyzed thai mice by Peason's correlation coefficient test found significant correlation between the level of donor chimerism and the level of donor Hb (r=0.879, r0.05=0.811), and between the level of donor Hb and MADH level (r= -0.819, r0.05=0.811). Conclusion: 1) Donor Hb levels were selectively increased in the chim thai mice relative to chimeric wt controls. 2) The levels of donor Hb expression in the thai mice correlate with the level of donor chimerism. 3)Mice with a high level donor Hb expression had a lower level of MADH. These results support the potential of mixed chimerism created by lUHSCTx as a therapeutic strategy for the treatment of β-thal.