T CELL REPERTOIRE COMPLEXITY IN SEVER COMBINED IMMUNODEFICIENCY PATIENTS AFTER BONE MARROW TRANSPLANTATION

Objective. To study thymus-dependent T cell development and T cell repertoire in human sever combined immunodeficiency (SCID) patients after HLA-identical or haploidentical T cell-depleted allogeneic bone marrow transplantation (BMT). Methods. Blood samples were obtained from 15 SCID patients before transplantation and at varying intervals thereafter. Quantitative competitive PCR assay and immunoscope analysis of the T cell receptor (TCR) Vβ repertoire were performed. Results. Before and within the first 100 days after transplantation, patients' peripheral blood mononuclear cell (PBMC) presented an oligoclonal or polyclonal skewed T cell repertoire, low T cell receptor excision circles (TRECs) values and predominance of CD45RO+ T cell. In contrast, the presence of high numbers of CD45RA+ T cells in bone marrow(BM) circulation reconstituted SCID patients (＞100 days post-transplantation) correlated with active T cell production by the thymus as revealed by high TREC values, and a polyclonal T cell repertoire demonstrated by a Gaussian distribution of Vβ-specific peaks. Conclusions. Within one year after BMT, a normal T cell repertoire develops in SCID patients as a result of thymic output. The T cell receptor diversity is highly and positively correlated in these patients with TREC levels.