T cell receptor diversity in severe combined immunodeficiency following HLA-haploidentical bone marrow transplantation.

We have studied T cell receptor (TCR) diversity in a group of six patients with severe combined immunodeficiency (SCID) previously treated by HLA-haploidentical bone marrow transplantation (BMT). At the time of study, all patients had developed stable T cell chimerism and full reconstitution of T cell functions in the absence of acute or chronic graft-versus-host disease. Peripheral blood lymphocytes (PBL) were analysed by immunofluorescence using a panel of monoclonal antibodies (MoAb) against TCR variable (V) region epitopes including V beta 5, V beta 6, V beta 8, V beta 12, and V alpha 2. Our results showed that in each patient studied a low but significant portion of PBL reacted with each anti-TCR V region epitope MoAb used, in a manner that was, on statistical grounds, indistinguishable from results obtained with PBL from healthy controls. We conclude that within the experimental resolution of a limited number of anti-TCR V region epitope MoAb, T cell reconstitution following BMT for SCID, even when performed across a full HLA-haplotype barrier, leads to an apparently normal TCR diversity. These novel findings may be relevant in the evaluation of functional capacities of T cells that have differentiated from transplanted precursor cells in an HLA-haplodifferent environment.