Haploidentical bone marrow transplant with posttransplant cyclophosphamide for sickle cell disease: An update

Low dose post-transplant cyclophosphamide and sirolimus induce mixed chimerism with CTLA4-Ig or lymphocyte depletion in an MHC-mismatched murine allotransplantation model

Allogeneic hematopoietic cell transplantation (allo-HCT) offers a curative option for patients with certain non-malignant hematological diseases. High-dose post-transplant cyclophosphamide (PT-Cy) (200 mg/kg) and sirolimus (3 mg/kg), (HiC) synergistically induce stable mixed chimerism. Further, sirolimus and cytotoxic T lymphocyte-associated antigen-4 immunoglobulin (CTLA4-Ig), also known as Abatacept (Aba), promote immune tolerance and allograft survival. Here, in a major histocompatibility complex (MHC)-mismatched allo-HCT murine model, we combined Aba and/or T-cell depleting anti-Thy1.2 (Thy) with a lower dose of PT-Cy (50 mg/kg) and Sirolimus (3 mg/kg), (LoC). While mice in the LoC group showed graft rejection, the addition of Thy to LoC induced similar donor chimerism levels when compared to the HiC group. However, the addition of Aba to LoC led to graft acceptance only in younger mice. When Thy was added to the LoC+Aba setting, graft acceptance was restored in both age groups. Engrafted groups displayed significantly reduced frequencies of recipient-specific interferon-γ-producing T cells as well as an increased frequency in regulatory T cells (Tregs) except in the LoC+Aba group. Splenocytes from engrafted mice showed no proliferation upon restimulation with Balb/c stimulators. Collectively, in combination with Aba or Thy, LoC may be considered to reduce graft rejection in patients who undergo allo-HCT.

Excellent outcome of stem cell transplantation for sickle cell disease

Many sickle cell disease (SCD) patients lack matched family donors (MFD) or matched unrelated donors (MUD), implying haploidentical donors (MMFD) as a logical donor choice. We used a reduced toxicity protocol for all donor types. We included 31 patients (2-22 years) with MFD (n = 15), MMFD (10), or MUD (6) HSCT and conditioning with alemtuzumab/ATG, thiotepa, fludarabine and treosulfan, and post-transplant cyclophosphamide for MMFD. After the initial six patients, treosulfan was replaced by targeted busulfan (AUC 65-75 ng*h/ml). After a median follow-up of 26 months (6-123), all patients are alive and off immunosuppression. Two MMFD patients experienced secondary graft failure with recurrence of SCD, both after treosulfan conditioning. Neither acute GVHD ≥ °III nor moderate/severe chronic GVHD was observed. The disease-free, severe GVHD-free survival was 100%, 100%, and 80% in the MFD, MUD, and MMFD groups, respectively (p = 0.106). There was a higher rate of virus reactivation in MMFD (100%) and MUD (83%) compared to MFD (40%; p = 0.005), but not of viral disease (20% vs 33% vs 13%; p = 0.576). Six patients had treosulfan-based conditioning, two of whom experienced graft failure (33%), compared to 0/25 (0%) after busulfan-based conditioning (p = 0.032). Donor chimerism was ≥ 80% in 28/31 patients (90%) at last follow-up. Reduced toxicity myeloablative conditioning resulted in excellent overall survival, negligible GVHD, and low toxicity among all donor groups in pediatric and young adult patients with SCD.

Sickle Cell Disease: From Genetics to Curative Approaches

Sickle cell disease (SCD) is a monogenic blood disease caused by a point mutation in the gene coding for β-globin. The abnormal hemoglobin [sickle hemoglobin (HbS)] polymerizes under low-oxygen conditions and causes red blood cells to sickle. The clinical presentation varies from very severe (with acute pain, chronic pain, and early mortality) to normal (few complications and a normal life span). The variability of SCD might be due (in part) to various genetic modulators. First, we review the main genetic factors, polymorphisms, and modifier genes that influence the expression of globin or otherwise modulate the severity of SCD. Considering SCD as a complex, multifactorial disorder is important for the development of appropriate pharmacological and genetic treatments. Second, we review the characteristics, advantages, and disadvantages of the latest advances in gene therapy for SCD, from lentiviral-vector-based approaches to gene-editing strategies.

Enrollment Lessons from a Biological Assignment Study of Marrow Transplantation versus Standard Care for Adolescents and Young Adults with Sickle Cell Disease: Considerations for Future Gene and Cellular Therapy Trials

We previously conducted a single-arm feasibility study (STRIDE1) of myeloablative bone marrow transplantation (BMT) in adolescents and young adults with sickle cell disease (SCD). The trial identified donors before entry, enrolled well, and found no unexpected regimen-related toxicity. Although many single-arm studies have been published, there are no controlled trials of either BMT or gene therapy in SCD. Therefore, we designed a comparative trial by biological assignment (available donor versus no donor). This multicenter National Institutes of Health-funded study (Blood and Marrow Transplant Clinical Trials Network 1503; STRIDE2) enrolled patients between 2016 and 2021 at 35 sites. Lagging recruitment led to study closure, and here we report the impediments to accrual. The BMT regimen and entry criteria were from STRIDE1, and 2-year survival was the primary endpoint. To minimize selection bias from prior HLA typing, STRIDE2 excluded individuals with previously identified donors. Accrual was stopped at 69% of target (138 enrolled; assigned 28 with donor, 96 with no donor). Barriers to enrollment included lower than expected frequency of HLA-matched related and unrelated donors; loss of enrollees owing to previously identified donors; conventional care arm dissuading some seeking BMT; challenging short-term endpoints in SCD, including incomplete documentation of sickle pain episodes; state Medicaid (primary insurers of SCD) denial of BMT coverage for adult SCD despite the study having secured Coverage with Evidence Development from the Center for Medicare & Medicaid Services; slowed accrual in 2019 to 2021 during the Coronavirus disease 2019 pandemic; and restriction of BMT resourcing for nonmalignant diseases by academic medical (cancer) centers. Social obstacles and access to BMT centers also limited entry, as did practitioner and participant concerns over suitability, cost, and toxicity. Planning for future controlled trials of curative therapy in SCD and other nonmalignant diseases likely will meet these enrollment challenges. Lessons from this trial may aid the development of future comparative studies.

Global perspectives on cellular therapy for children with sickle cell disease

PURPOSE OF REVIEW

Low-income and middle-income countries (LMICs), primarily in sub-Saharan Africa (SSA), predominantly experience the burden of sickle cell disease (SCD). High frequency of acute and chronic complications leads to increased utilization of healthcare, which burdens fragile health systems. Mortality for children with limited healthcare access remains alarmingly high. Cellular based therapies such as allogeneic hematopoietic stem cell transplant (HSCT) are increasingly used in resource-rich settings as curative therapy for SCD. Broad access to curative therapies for SCD in SSA would dramatically alter the global impact of the disease.

RECENT FINDINGS

Currently, application of cellular based therapies in LMICs is limited by cost, personnel, and availability of HSCT-specific technologies and supportive care. Despite the challenges, HSCT for SCD is moving forward in LMICs. Highly anticipated gene modification therapies have recently proven well tolerated and feasible in clinical trials in resource-rich countries, but access remains extremely limited.

SUMMARY

Translation of curative cellular based therapies for SCD should be prioritized to LMICs where the disease burden and cost of noncurative treatments is high, and long-term quality of life is poor. Focus on thoughtful modifications of current and future therapies to meet the need in LMICs, especially in SSA, will be especially impactful.

Sickle Cell Transplantation Evaluation of Long-term and Late Effects Registry (STELLAR) to Compare Long-term Outcomes After Hematopoietic Cell Transplantation to Those in Siblings Without Sickle Cell Disease and in Nontransplanted Individuals With Sickle Cell Disease: Design and Feasibility Study

BACKGROUND

There are sparse data on the long-term and late effects of hematopoietic cell transplantation (HCT) for sickle cell disease (SCD).

OBJECTIVE

This study aims to establish an international registry of long-term outcomes post-HCT for SCD and demonstrate the feasibility of recruitment at a single site in the United States.

METHODS

The Sickle Cell Transplantation Evaluation of Long-Term and Late Effects Registry (STELLAR) was designed to enroll patients with SCD ≥1 year post-HCT, their siblings without SCD, and nontransplanted controls with SCD to collect web-based participant self-reports of health status and practices by using the Bone Marrow Transplant Survivor Study (BMTSS) surveys, health-related quality of life (HRQOL) using the Patient-Reported Outcomes Measurement Information System (PROMIS) Pediatric Profile-25 or Pediatric Profile-29 survey, chronic graft-versus-host disease (cGVHD) using the symptom scale survey, daily pain using an electronic pain diary, the economic impact of HCT using the financial hardship survey, sexual function using the PROMIS Sexual Function SexFSv2.0 survey, and economic productivity using the American Time Use Survey (ATUS). We also piloted retrieval of clinical data previously submitted to the Center for International Blood and Marrow Transplant Research (CIBMTR); recorded demographics, height, weight, blood pressure, waist and hip circumferences, timed up and go (TUG) test, and handgrip test; and obtained blood for metabolic screening, gonadal function, fertility potential, and biorepository of plasma, serum, RNA, and DNA.

RESULTS

Of 100 eligible post-HCT patients, we enrolled 72 (72%) participants aged 9-38 (median 17) years. We also enrolled 19 siblings aged 5-32 (median 10) years and 28 nontransplanted controls with SCD aged 4-46 (median 22) years. Of the total 119 participants, 73 (61%) completed 85 sets of surveys and 41 (35%) contributed samples to the biorepository. We completed ATUS interviews of 28 (24%) participants. We successfully piloted retrieval of data submitted to the CIBMTR and expanded recruitment to multiple sites in the United States, Canada, the United Kingdom, and Nigeria.

CONCLUSIONS

It is feasible to recruit subjects and conduct study procedures for STELLAR in order to determine the long-term and late effects of HCT for SCD.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/36780.

Evolving Strategies in the Management of Sickle Cell Disease in the 21st Century and the Role of the Pediatrician

Sickle cell disease (SCD) is one of the most common genetic disorders in the United States. Once a fatal disease of childhood, the majority of patients born with SCD who live in a developed country will survive to adulthood (albeit with slightly shortened life spans). Despite numerous novel therapeutic advancements in recent years that serve to mitigate the symptoms associated with SCD, the only cure for SCD is a hematopoietic stem cell transplant. The overall survival for patients with a matched sibling donor transplant is greater than 90%. However, fewer than 20% of patients with SCD in the US have a 12/12 human leukocyte antigen (HLA) matched sibling donor. In contrast, most patients have at least one HLA haploidentical first-degree relative, which expands the donor pool for patients who have diseases amenable to stem cell transplantation such as SCD. [Pediatr Ann. 2022;51(1):e34-e39.].