Study of thymic size and function in children and adolescents with treatment refractory systemic sclerosis eligible for immunoablative therapy

Abstract Following hematopoietic stem cell transplantation (HSCT), thymic reconstitution of peripheral T lymphocytes is essential to avoid a chronically immunodeficient state and disease recurrence. The purpose of this study was to determine if children and adolescents with treatment refractory SSc, awaiting HSCT, have sufficient thymic function to reconstitute T lymphocyte function after transplantation. Thirteen children with systemic scleroderma were enrolled and assessed by physical exam, chest MRI, measurement of autoantibodies, B and T cell immuno-phenotyping, and quantization of T cell receptor rearrangement excision circles (TREC) as a marker of thymopoiesis. MRI detected thymic tissue in 9/13 children. TREC levels were detectable in all but one child but were significantly reduced ( p < 0.001) when compared to a control population. SSc patients also had a reduced percentage of naïve (CD45RA + CD31+) CD4+ T lymphocytes, further indicating diminished thymopoiesis. Our data suggest that thymic function in children with SSc might be insufficient for an adequate immunoreconstitution following transplantation in some patients. A thorough evaluation of immune and thymic functions to identify those patients prior to HSCT is recommended.