Refractory Autoimmune Hemolytic Anemia Following Hematopoietic Stem Cell Transplant (HSCT) in the Setting of Impaired Immune Reconstitution Among Pediatric HSCT Recipients
Authors: Scherer Lauren , Grimes Amanda Bell , Kim Taylor , Martinez Caridad A. 
Published: October 2019

Abstract
Background: Autoimmune hemolytic anemia is a well-recognized complication of hematopoietic stem cell transplant (HSCT). While occurring in only ~2-6% of pediatric patients receiving HSCT, it is associated with significant morbidity and mortality of up to 50%. Post-transplant AIHA is poorly studied due to small patient numbers. Therefore, risk factors for the development of post-transplant AIHA are not well delineated and optimal treatment strategies are not known. Disease course is often refractory and multiply relapsing, with current treatment approaches remaining empiric. The most commonly utilized immunomodulatory therapies include glucocorticoids, intravenous immune globulin (IVIG), and rituximab; and potentially repeat bone marrow transplantation. Better understanding of the underlying immunobiology in post-transplant AIHA is imperative, as it may uncover the potential for newer, more effective targeted treatment options and better elucidate pre-disposing risk factors which could be modified for future HSCT patients, resulting in overall improvement in clinical outcomes among this group of high-risk patients.
Objective: Through retrospective chart review of a large cohort of pediatric patients developing post-transplant AIHA, we aim to better describe the clinical characteristics, treatment responses, and long-term outcomes of patients with this rare and poorly-studied HSCT complication in order to highlight important areas for future research. Furthermore, we aim to describe correlating immunobiology in a sub-population of patients experiencing refractory AIHA post-HSCT to elucidate potential therapeutic targets and identify peri-transplant immune modulation modifications which may be beneficial in preventing this complication.
Methods: We completed a retrospective chart review including patients aged 0 - 18 with post-transplant AIHA over a recent 6-year period (2012 - 2018) at a large pediatric transplant center. Potential patients were identified via query of the electronic medical record (EMR), and further stratified according to eligibility criteria for further full review. AIHA was defined as the presence of hemolytic anemia (as evidenced by at least 2 of the following parameters: elevated LDH, elevated bilirubin, low haptoglobin, reticulocytosis, or evidence of hemolysis on the peripheral smear) and positive Coombs or Direct Antiglobulin Test (DAT). Patients diagnosed with autoimmune hemolytic anemia prior to first HSCT or found to have an alternate etiology of hemolytic anemia were excluded. Eight patients from among this cohort of post-transplant AIHA patients were enrolled in a biology study with the aim of evaluating T cell recovery in this population as compared to that in matched post-transplant control patients in whom AIHA did not occur. T cell subsets, including sub-analysis of CD4+ T helper cells, CD8+ cytotoxic T cells, and FoxP3+CD25+ T regulatory cells, were measured at monthly time-points following enrollment. Both studies were conducted in accordance with institutional IRB-approved protocols.
Results: Thirty-six pediatric patients with post-transplant AIHA were identified (median age 6.3 years). Median time to the onset of AIHA following HSCT was 188 days (range 37 - 563 days). Among patients treated for AIHA, 48% had documented disease resolution, while 52% did not achieve resolution of AIHA and had an average disease duration of 822 days. Mean duration of disease for all those achieving resolution of post-transplant AIHA was 472 days. Importantly, mortality among our cohort of post-transplant AIHA patients was 33%. Among the sub-population of patients in whom phenotypic immune reconstitution was monitored, we demonstrated a trend toward statistically significantly reduced T regulatory cell populations in post-transplant AIHA patients as compared to matched post-transplant control patients (Figure 1).
Conclusions: Autoimmune hemolytic anemia following HSCT is characterized by a refractory and relapsing course and high associated morbidity and mortality rates with limited effective therapeutic options. Impaired immune reconstitution following HSCT, specifically delayed T regulatory cell re-population, may be implicated in the complex immunopathology of post-transplant AIHA development and persistence, thereby representing an important area for future research and potential therapeutic targeting.

Disclosures
No relevant conflicts of interest to declare.