A cure for murine sickle cell disease through stable mixed chimerism and tolerance induction after nonmyeloablative conditioning and major histocompatibility complex–mismatched bone marrow transplantation

Abstract

The morbidity and mortality associated with sickle cell disease (SCD) is caused by hemolytic anemia, vaso-occlusion, and progressive multiorgan damage. Bone marrow transplantation (BMT) is currently the only curative therapy; however, toxic myeloablative preconditioning and barriers to allotransplantation limit this therapy to children with major SCD complications and HLA-matched donors. In trials of myeloablative BMT designed to yield total marrow replacement with donor stem cells, a subset of patients developed mixed chimerism. Importantly, these patients showed resolution of SCD complications. This implies that less toxic preparative regimens, purposefully yielding mixed chimerism after transplantation, may be sufficient to cure SCD without the risks of myeloablation. To rigorously test this hypothesis, we used a murine model for SCD to investigate whether nonmyeloablative preconditioning coupled with tolerance induction could intentionally create mixed chimerism and a clinical cure. We applied a well-tolerated, nonirradiation-based, allogeneic transplantation protocol using nonmyeloablative preconditioning (low-dose busulfan) and costimulation blockade (CTLA4-Ig and anti-CD40L) to produce mixed chimerism and transplantation tolerance to fully major histocompatibility complex-mismatched donor marrow. Chimeric mice were phenotypically cured of SCD and had normal RBC morphology and hematologic indices (hemoglobin, hematocrit, reticulocyte, and white blood cell counts) without evidence of graft versus host disease. Importantly, they also showed normalization of characteristic spleen and kidney pathology. These experiments demonstrate the ability to produce a phenotypic cure for murine SCD using a nonmyeloablative protocol with fully histocompatibility complex-mismatched donors. IntroductionPatients with sickle cell disease (SCD) suffer from both episodic acute complications and chronic, progressive, multisystem decline. Although medical treatments are life-extending, only stem cell transplantation offers an effective cure. There are currently 2 major barriers to stem cell transplantation for SCD: (1) the high morbidity and mortality associated with conventional bone marrow transplantation (BMT) and (2) the scarcity of acceptable stem cell donors. 1,2 (1) Conventional BMT can cure SCD but requires toxic myeloablative preconditioning regimens to achieve donor cell engraftment. 3,4 These intensive preparative regimens have many toxic adverse effects, including potential organ failure and a long-term risk of malignancy. In heavily pretreated patient populations, the morbidity and mortality of transplantation can outweigh the morbidity and mortality of SCD. 2 A dilemma is now developing between early treatment with stem cell transplantation (shown to increase survival and disease-free survival when compared with transplantation after more disease-related complications have occurred) and a delayed approach, during which medical management ameliorates the symptoms of SCD until a later age when definitive therapy can b...

Primary and Secondary Immunocompetence in Mixed Allogeneic Chimeras

“…While hemopoietic chimerism has the potential to treat or cure life-threatening conditions (30) and to facilitate tolerance induction to transplants, it also has the potential to adversely affect the ability of a recipient to generate effective immune responses, particularly against intracellular pathogens. It is critical that we understand the degree to which chimerism-based tolerance induction regimens create immunologic blind spots and impair the ability of a recipient to effectively control intracellular pathogens, particularly those that cause persistent or latent infections.…”

A survey on patient perception of reduced-intensity transplantation in adults with sickle cell disease

“…However, this enthusiasm has been short-lasting owing to poor outcome with conventional allografting. 6 Recent developments in reduced-intensity conditioning (RIC) have rendered allogeneic haematopoietic stem cell transplantation (allo-HSCT) feasible in a wider group of patients who could potentially benefit from such a procedure, but who were considered ineligible for conventional conditioning owing to increased age or comorbidities. [7][8][9][10] Various RIC regimens have been employed with differing complications.…”

Reduced intensity allogeneic umbilical cord blood transplantation in children and adolescent recipients with malignant and non-malignant diseases

“…18,19 Several investigators have shown the potential of non-myeloablative or reduced intensity (RI) conditioning followed by AlloSCT to reduce regimen-related morbidity, regimen-related mortality (RRM) and potentially future late effects in patients with both malignant and nonmalignant disorders. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] A recent review by our group has summarized the results to date following RI conditioning for allogeneic stem cell transplantation (RI-AlloSCT). 35 Recently, successful engraftment has been demonstrated after reduced intensity UCBT (RI-UCBT) in adult recipients.…”