Pediatric Patients with Severe Aplastic Anemia Treated with Combined Immunosuppressive Therapy, Eltrombopag and Eculizumab and Their Clinical Course to Stem Cell Transplant

Acquired aplastic anemia (AA) in children is a rare disorder characterized by pancytopenia and hypocellular bone marrow. Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematopoetic stem cell (HCT) disorder characterized by complemented-mediated hemolysis, thrombosis and bone marrow failure secondary to deficiency of glycosylphosphatidylinositol-anchored proteins (GPI-AP) on hematopoetic stem cells. PNH and acquired AA are closely related; up to 50% of patients with AA have detectable PNH-clones at the time of diagnosis and small percentage of them can have clonal expansion throughout their disease course requiring close monitoring. Current standard therapy for severe aplastic anemia (SAA) patients without matched related donor (MRD) is immunosuppressive therapy (IST) regimen with anti-thymoglobulin (ATG), cyclosporine (CSA), and recent addition of eltrombopag. Eculizumab is a recombinant humanized monoclonal antibody that blocks complement protein C5 and prevents cell lysis. While it has been shown to be effective in children with PNH, concomitant treatment with IST for patients with SAA is unknown. To our knowledge, there has been no pediatric data on combined IST, eltrombopag and eculizumab treatment for children with AA with clinically significant PNH clones. Here we retrospectively reviewed three pediatric patients with SAA with PNH clones treated with IST, eltrombopag and eculizumab and their unique clinical courses. Two out of three patients had high PNH clone size and were started on eculizumab prior to IST with improvement in transfusion intervals. Of the two, one had decrease in PNH clone size after IST but the other patient's clone size continued to increase despite two courses of IST. Finally, the third patient had a minor PNH clone and was not started on eculizumab prior to IST. He remained asymptomatic for over a year until he developed symptomatic PNH with large clone size and aplastic bone marrow. His clone size continued to increase with no improvement in transfusion frequency despite being started on eculizumab. However, steroids were started based on anecdotal literature and his transfusion frequency decreased subsequently. All three patients are in the process of going through matched unrelated donor stem cell transplants. Several studies have reported the presence of a minor PNH clone at the time of AA diagnosis was associated a favorable response to IST. In this case series, the patient with the smallest PNH clone size at the time of diagnosis of SAA had the best response to IST compared to the other two patients who had larger PNH clone populations. These findings suggest that even though minor PNH population may lead to better response to IST compared to absence of the clone, the correlation between clone size and prognosis is unclear. Further study with larger sample size is needed to investigate this relationship. However, regardless of the population size, all three patients were able to prolong transfusion intervals using eculizumab without significant side effects. As the adoption of eltrombopag with standard IST is evolving with ongoing study, the efficacy of incorporating eculizumab to decrease transfusion frequency in patients with PNH-clone in addition to eltrombopag/IST regimen should be further investigated.