Evaluation of TCR Vβ subfamily T cell expansion in NOD/SCID mice transplanted with human cord blood hematopoietic stem cells

Examination of the T cell receptor ( TCR) gene repertoire is important in the analysis of the immune status of models, because clonal expansion of T cells permits the identification of specific antigen responses of T cells. Little is known about T- cell immunity in the humanized NOD/ SCID mouse model. TCR V beta repertoire usage and clonality were analyzed to investigate the distribution and clonal expansion of TCRV beta subfamily T cells in NOD/ SCID mice transplanted with human cord blood ( CB) hematopoietic stem cells. The NOD/ SCID mice were sublethally irradiated (Co-60, 300cGy) to eliminate residual innate immunity in the host. The experimental mice were transplanted intravenously with CB CD34(+) cells sorted by MACS. After 6 weeks, RNA was obtained from peripheral blood, bone marrow and thymus of the study animals. The gene expression and clonality of the TCR Vb repertoire were determined by RT- PCR and GeneScan techniques. A restricted range of TCR V beta usage was exhibited in the bone marrow of mice, which included TCRVb 1, 2, 9, 13 and 19. Further, oligoclonal expression of some TCR V beta subfamilies ( V beta 9, 13, 19) was identified by GeneScan technique. To investigate the reason for oligoclonal expansion of the TCR V beta subfamily T cells from CB in mouse models, the T- cell culture with tissue- antigen of NOD/ SCID mouse was performed in vitro. The cells from peripheral blood mononuclear cells and bone marrow, spleen, thymus in NOD/ SCID mice were frozen and thawed, and used as tissue- antigen. CB mononuclear cells were separately cultured with the component from those murine cells for 15 - 20 days. Oligoclonal expression or oligoclonal trend of some TCRV beta subfamilies ( V beta 10, 11 and V beta 2, 15, 16, 19) was detected in T cells after stimulation with tissue- antigen of NOD/ SCID mouse. Interestingly, a similar clonal expansion of the TCRV beta 11 subfamily was found in T cells cultured with peripheral blood, bone marrow and spleen respectively. The TCR Vb subfamily T cells could be reconstituted in humanized NOD/ SCID mouse transplanted with CD34(+) cells from CB. The restricted expression and clonal expansion of some CB T cell clones may be induced by tissue- antigens of NOD/ SCID mice.