Does Mixed Chimerism After Allogeneic Hematopoietic Cell Transplantation in Pediatric Patients With Fanconi Anemia Impact on Outcome?

Two decades of stem cell transplantation in patients with Fanconi anemia: Analysis of factors affecting transplant outcomes

Allogeneic hematopoietic stem cell transplantation (HSCT) is currently the only curative treatment for the hematological complications of patients with Fanconi anemia (FA). Over the last two decades, HSCT outcomes have improved dramatically following the development of regimens tailored for FA patients. In this study, we analyzed genetic, clinical, and transplant data of 41 patients with FA who underwent HSCT at Hadassah Medical Center between November 1996 and September 2020. Overall survival (OS) was 82.9% with a median follow-up time of 2.11-years (95% CI, .48-16.56). Thirteen patients (31.7%) developed acute graft-versus-host disease (GVHD), three of them with grades 3-4. Nine patients developed chronic GVHD, five had extensive disease. Twelve patients (29.3%) developed stable mixed-chimerism with complete resolution of bone marrow failure (BMF); none of them had acute nor chronic GVHD. Significantly higher GVHD rates were observed in transplants from peripheral blood stem cell grafts as compared to other stem cell sources (p = .002 for acute and p = .004 for chronic GVHD). Outcome parameters were comparable between HSCT from matched-sibling (n = 20) to other donors (n = 21), including survival rates (p = .1), time to engraftment (p = .69 and p = .14 for neutrophil and platelet engraftment time, respectively), chimerism status (p = .36 and p = .83 for full-donor and mixed chimerism, respectively), and GVHD prevalence (p = 1). Our results demonstrate the vast improvements in HSCT outcomes of patients with FA, narrowing the gap between matched-sibling versus alternative donor transplantations. Our data identifies factors that may significantly affect transplant outcomes such as graft source and chimerism status.

Unresolved issues in allogeneic hematopoietic cell transplantation for non-malignant diseases

Allogeneic hematopoietic cell transplantation (HCT) can be curative for a variety of non-malignant diseases (NMDs) as well as hematological malignancies. However, there are several fundamental differences between HCT for NMDs and hematological malignancies, which may necessitate the use of alternative HCT strategies. For example, these diseases differ in the intensity of conditioning regimen sufficient to improve disease. In addition, patients with NMDs are at higher risk of graft failure or mixed chimerism following HCT, and gain no or little survival benefit from graft-versus-host disease. Because more than 80% of patients with NMDs become long-term survivors, greater attention has been paid to late adverse effects and decreased of quality of life after HCT. This review addresses several unresolved issues in allogeneic HCT for patients with NMDs, such as (1) stem cell source, (2) conditioning regimen, (3) use of serotherapy or low-dose irradiation, and (4) therapeutic intervention for mixed chimerism. Resolving these issues may improve transplant outcomes in patients with NMDs.

The significance of mixed chimaerism and cell lineage chimaerism monitoring in paediatric patients post haematopoietic stem cell transplant

Haematopoietic stem cell transplants (HSCTs) are carried out across the world to treat haematological and immunological diseases which would otherwise prove fatal. Certain diseases are predominantly encountered in paediatric patients, such severe primary immunodeficiencies (PID) and diseases of inborn errors of metabolism (IEM). Chimaerism testing for these disorders has different considerations compared to adult diseases. This review focuses on the importance of cell-lineage-specific chimaerism testing and examines the appropriate cell populations to be assessed in individual paediatric patient groups. By analysing disease-associated subpopulations, abnormalities are identified significantly earlier than in whole samples and targeted clinical decisions can be made. Chimaerism methods have evolved over time and lead to an ever-increasing level of sensitivity and biomarker arrays to distinguish between recipient and donor cells. Short tandem repeat (STR) is still the gold standard for routine chimaerism assessment, and hypersensitive methods such as quantitative and digital polymerase chain reaction (PCR) are leading the forefront of microchimaerism testing. The rise of molecular methods operating with minute DNA amounts has been hugely beneficial to chimaerism testing of paediatric samples. As HSCTs are becoming increasingly personalised and risk-adjusted towards a child's individual needs, chimaerism testing needs to adapt alongside these medical advances ensuring the best possible care.