Background: Allergic disorders are more common in pediatric heart transplant (HTx) recipients than non-transplanted children, with young age at HTx and thymectomy being risk factors. We hypothesized that thymectomy and immunosuppression at an early age affect development of T and B cell subsets, especially regulatory T cells (Tregs), which are key in maintaining peripheral tolerance. We investigated the impact of thymectomy and lymphocyte-depleting induction on lymphocyte subsets, and allergic disorders after HTx. Methods: Flow cytometry phenotyping was used to determine lymphocyte subset proportions in peripheral blood from pediatric HTx patients. Demographic and clinical data were collected in standardized questionnaires and from medical charts. An age-matched, immune suppressed but non-thymectomized liver transplant (LTx) comparison group was included. Results: 69% of thymectomized patients experienced new or worsening asthma and eczema post-transplant, compared to 33% of non-thymectomized patients. CD45RA+CD27+ naïve Treg proportions within the CD4+CD25+CD127low Treg population was lower in thymectomized patients although not significantly. Patients with asthma and eczema had significantly lower naïve Treg proportions than patients without (p=0.038), and showed increased memory CD4+ populations with age. Memory CD4+ and CD5+CD1d+ “B10” populations were higher in thymectomized patients although not significantly. 71% of thymectomized patients were EBV carriers compared to 29% of non-thymectomized patients. Comparison to the LTx group is pending due to small sample size. Conclusions: Lower percentages of naive Tregs are found in children with allergic disorders after pediatric HTx and likely result from thymectomy. Persisting EBV infection was more common after thymectomy and may impact T cell maturation. Memory and “B10” populations may also contribute. A larger sample size may help quantify the independent risk of these factors and allow us to stratify the type and intensity of immunosuppression.

CITATION INFORMATION: Kim T., Ionescu L., Avdimiretz N., Larsen M., Murdoch F., Motyka B., Gilmour S., West L., Urschel S. Lymphocyte Proportions Post Thymectomy Are Associated with Allergic Disorders in Heart Transplanted Children Am J Transplant. 2017;17 (suppl 3).

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