The first report of allogeneic haematopoietic stem cell transplantations for bone marrow failure performed in Sri Lanka

Aplastic anaemia (AA) is defined as pancytopenia with a hypocellular bone marrow without any abnormal infiltrate or fibrosis.¹ Haematopoietic stem cell transplantation (HSCT) is the only curative option for both inherited bone marrow failure syndromes (BMFs) and acquired AA (aAA) in children.² A routine therapeutic option in developed countries for many decades, the first allogeneic HSCT (allo-HSCT) to be performed in Sri Lanka was as recently as June 2014, for a child with transfusion-dependent thalassaemia (TdT). A civil war that plagued the scenic island for >26 years was one of the main obstacles that hindered development in most sectors, including healthcare.

In resource limited countries, such as Sri Lanka, managing AA can be challenging with one reason being the very limited access to advanced diagnostic tests, e.g. chromosomal fragility and next generation sequencing (NGS), to determine if the marrow failure is due to an inherited cause. Furthermore, timely provision of supportive care with blood products, suitable infrastructure and appropriate drugs to manage neutropenic sepsis and related complications are not readily available to all patients. Therefore, a significant morbidity and mortality is seen in children with BMFs. It is in this environment that we decided to expand our allo-HSCT programme for TdT to include children with BMFs. Infrastructure and facilities of our transplant centre conform to the minimum recommendations of the Worldwide Network for Blood and Marrow Transplantation (WBMT),³ including high-efficiency particulate air (HEPA)-filtered rooms with positive differential pressure. The programme director, a haematologist with HSCT training in the UK, and the transplant team had >3 years of experience in allo-HSCT in Sri Lanka. High-resolution human leucocyte antigen (HLA) typing, NGS and post-HSCT chimerism testing were done at accredited laboratories in India.

In the present study, we present a series of four consecutive children with bone marrow failure (Table I), successfully managed with allo-HSCT in Sri Lanka amidst many limitations, and is the first report of such HSCTs performed in the country. Dr Revathi Raj mentored these transplants remotely, from the Apollo specialty hospital, Chennai, India.

Case series

There are no randomised trials comparing conditioning regimens in AA. Bejanyan et al.⁴ evaluated conditioning regimens for consecutive matched sibling donor (MSD) and matched unrelated donor (MUD) HSCTs for severe AA reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). Data from 142 transplant centres worldwide, including 955 MSD transplants were analysed. Fludarabine (Flu)/cyclophosphamide (Cy)/anti-thymocyte globulin (ATG) or Cy/ATG had the best survival. The 5-year probabilities of survival with Flu/Cy/ATG, Cy/ATG, Cy6Flu, and busulfan/Cy were 91%, 91%, 80% and 84% respectively.

Case 1 and 4, with idiopathic AA underwent MSD HSCT following Flu/Cy/ATG conditioning. Graft-versus-host disease (GVHD) prophylaxis was a calcineurin inhibitor and ‘short’ methotrexate. Neither developed significant acute or chronic GVHD.

Case 2 had a heterozygous variation (chr7:g.92762233C>T; c.3052G>A) in exon 5 of the sterile alpha motif domain-containing 9-like (SAMD9L) gene by NGS. Studies suggest that the SAMD9L protein acts as a tumour suppressor.⁵ Monosomy 7 is the most frequent cytogenetic lesion in children with myelodysplastic syndrome (MDS), and in contrast to adults often occurs as the sole cytogenetic abnormality.⁶ Asou et al. identified SAMD9, its paralogue SAMD9L (SAMD9-like), and Miki/HEPACAM2 as commonly deleted genes within a 7q21 cluster in patients with myeloid neoplasms.^{7, 8}

Germline, heterozygous gain-of-function SAMD9L mutations p.H880Q, p.I891T, p.R986C, and p.C1196S were discovered in four pedigrees with variable degrees of neurological (ataxia, balance impairment, nystagmus, hyperreflexia, dysmetria, dysarthria) and haematological (single to tri-lineage cytopenias, MDS/-7) manifestations. Clinical presentations were compatible with ataxia-pancytopenia (AP) syndrome in most carriers. All SAMD9L mutations reported or identified found a total of six germline mutations (p.H880Q, p.I981T, p.R986H, p.R986C, p.C1196S, and p.V1512 M).⁸

The mutations in Case 2 have not been described previously. The patient, his sister (donor) and father, all had the same mutations, but no somatic features of AP syndrome. Therefore, it is difficult to conclude if these mutations contributed to the marrow failure. He received Flu/Cy/ATG followed by a MSD HSCT GVHD prophylaxis with tacrolimus and ‘short’ methotrexate.

Case 3 was a 7-year-old girl, the third child of healthy non-consanguineous parents. She presented at 1year 4 months with ecchymosis due to severe thrombocytopenia. Bone marrow was normocellular with markedly reduced megakaryopoiesis. She developed pancytopenia with a markedly hypocellular marrow 2 years later. Somatic features of inherited BMFs were not identified. Chromosome fragility test was negative. Karyotype showed 46,XX, inv(9)(p11q13), considered a normal variant. NGS showed two pathogenic mutations in the myeloproliferative leukaemia protein (MPL) gene at exons 3 and 8 (compound heterozygous). A diagnosis of congenital amegakaryocytic thrombocytopenia (CAMT) was made. A rare disorder presenting in infancy, usually not associated with somatic abnormalities⁹ and ~50% of patients with CAMT develop AA by the age of 5 years. She had several life-threatening bleeds, including a subdural haemorrhage, and was refractory to platelets due to high-titre HLA antibodies. There was no MSD. A MUD was identified from an Indian registry. However, the coronavirus disease 2019 (COVID-19) pandemic made it impossible to import donor stem cells from overseas. Considering her life-threatening situation, a haploidentical HSCT from her father was offered.

High-titre donor-specific antibodies (DSAs) of 9827MFI prompted five plasma exchanges, alternating with four intravenous immunoglobulin 0.4 g/kg doses and one dose of rituximab 375 mg/m² prior to HSCT.¹⁰ Conditioning was with rabbit ATG 4.5 mg/kg over 3 days, thiotepa 10 mg/kg in two divided doses, Flu 30 mg/m²/day for 5 days, Cy 14.5 mg/kg for 2 days and total body irradiation (TBI) 2 Gy single-fraction on day 1. Peripheral blood stem cells (PBSC) were used envisaging better engraftment in a haplo-HSCT setting with high DSAs and the increased risk of myelodysplasia/acute leukaemia in CAMT. GVHD prophylaxis was Cy on 3 days post-transplant (D + 3) and 4 days post-transplant (D + 4), followed by tacrolimus. Currently, 5 months after transplant, she remains GVHD free with normal haematological parameters and full donor chimerism.

Conclusion

While being a potential cure for many diseases, allo-HSCT is a resource intensive treatment modality and therefore a challenge to establish and sustain in countries such as Sri Lanka. When initiating HSCT in developing countries, emphasis should be given to more focussed, thoughtful care models, without compromising the quality of care.¹¹ Despite financial restraints, minimum quality standards should be maintained to ensure good ethical principles, with a keen focus on patient safety and a vision of long-term sustainability.¹²

We experienced that a mentoring programme, even remotely, is likely to pay rich dividends. Molecular diagnosis helps tailor treatment to each patient and probably improves outcomes. Haplo-identical donor transplants with post-transplant Cy have made allo-HSCT for BMFs in developing countries more accessible and cost effective.

Amidst many adversities and challenges, we successfully performed allo-HSCTs for four children with severe AA in Sri Lanka, the present report being the first.

Author contributions

Wasanthi Wickramasinghe: Literature review, acquired and analysed data, drafted the paper, read and approved the final version. Ruwangi Dissanayake: Conceptualised the paper, critically revised the paper, read and approved the final version. Revathi Raj: Critically revised the paper, read and approved the final version. Lallindra Gooneratne: Conceptualised the paper, critically revised the paper, read and approved the final version.