Correction of murine hemoglobinopathies by prenatal tolerance induction and postnatal nonmyeloablative allogeneic BM transplants

Abstract

Key Points• IUHCT induces DST in murine models of sickle cell and b-Thal.• IUHCT combined with postnatal nonmyeloablative allogeneic BM transplants corrects the disease phenotype in SCD and Thal mice.Sickle cell disease (SCD) and thalassemias (Thal) are common congenital disorders, which can be diagnosed early in gestation and result in significant morbidity and mortality. Hematopoietic stem cell transplantation, the only curative therapy for SCD and Thal, is limited by the absence of matched donors and treatment-related toxicities.In utero hematopoietic stem cell transplantation (IUHCT) is a novel nonmyeloablative transplant approach that takes advantage of the immunologic immaturity and normal developmental properties of the fetus to achieve mixed allogeneic chimerism and donorspecific tolerance (DST). We hypothesized that a combined strategy of IUHCT to induce DST, followed by postnatal nonmyeloablative same donor "booster" bone marrow (BM) transplants in murine models of SCD and Thal would result in high levels of allogeneic engraftment and donor hemoglobin (Hb) expression with subsequent phenotypic correction of SCD and Thal. Our results show that: (1) IUHCT is associated with DST and low levels of allogeneic engraftment in the murine SCD and Thal models; (2) low-level chimerism following IUHCT can be enhanced to high-level chimerism and near complete Hb replacement with normal donor Hb with this postnatal "boosting" strategy; and (3) high-level chimerism following IUHCT and postnatal "boosting" results in phenotypic correction in the murine Thal and SCD models. This study supports the potential of IUHCT, combined with a postnatal nonmyelablative "boosting" strategy, to cure Thal and SCD without the toxic conditioning currently required for postnatal transplant regimens while expanding the eligible transplant patient population due to the lack of a restricted donor pool. (Blood. 2015;126(10):1245-1254 IntroductionSickle cell disease (SCD) and b-thalassemia (Thal) are the two most common hemoglobinopathies worldwide. They are autosomal recessive disorders, which can be diagnosed prenatally. SCD results from a missense mutation in the b-globin gene that causes hemoglobin (Hb) to polymerize resulting in RBC deformation, "sickling," and subsequent severe hemolytic anemia and vaso-occlusive disease. Thal is caused by genetic defects that reduce b-globin protein levels resulting in severe anemia. Although there have been significant improvements in the management of SCD and Thal, hematopoietic stem cell transplantation (HSCT) remains the only curative treatment. [1][2][3] The standard protocol, a myeloablative HLAidentical matched transplant, is limited by the lack of an HLA-matched donor for most patients as well as graft-versus-host disease (GVHD) and treatment toxicities. [4][5][6][7][8][9] Recent attempts to expand the donor pool by using haploidentical donors and decrease transplant-related toxicities by using minimally myeloablative regimens, although promising, still require immunosuppression and are subj...

The Intravenous Route of Injection Optimizes Engraftment and Survival in the Murine Model of In Utero Hematopoietic Cell Transplantation

“…It has the potential to expand the donor pool, while treating any disorder that can be diagnosed prenatally and is currently managed with mixed chimerism. For IUHCT to reach its full clinical potential, donor cells must be safely and efficiently delivered to fetal hematopoietic organs, resulting in postnatal donor cell engraftment at levels that treat the target disease or reliably induce DST for postnatal nonmyeloablative cellular transplantations [1,7,10]. Intrinsic to the evaluation of the optimal delivery of donor cells is the route by which the cells are administered.…”

“…Clinically, IUHCT may result in high enough levels of engraftment to treat the target disease, such as sickle cell anemia. Alternatively, DST associated with low levels of engraftment may permit postnatal same-donor nonmyeloablative transplantations to increase engraftment to therapeutic levels [7][8][9][10]. Despite the potential of IUHCT, clinical success has only been seen in cases of severe combined immunodeficiency [11][12][13][14].…”

New insights into sickle cell disease

“…An explosion of microfluidics technology has reached SCD research, and quantitative microfluidic microscopy methods were unveiled to study vaso-occlusion and retention of erythrocytes in the spleen in SCD [52, 53]. Innovative strategies were used in SCD mice to induce immune tolerance before birth, followed by curative postnatal non-myeloablative allogeneic hematopoietic stem cell transplant [54]. Finally, more progress was gained in gene therapy correction of the sickle cell disease mutation in human hematopoietic stem cells and progenitor cells [55].…”

Cellular therapy for sickle cell disease

“…However, there will have to be significantly more work done before this approach can be applied at the embryonic level. In utero transplant is currently being explored in animal models with some success[63]. However, gene editing of the endogenous beta globin gene in human embryonic stem cells led to significant off-target mutations, illustrating demonstrating how catastrophic such an approach could be if not rigorously tested in preclinical models [64].…”