Influence of regulatory T cells on the TCR Vβ repertoire following hematopoietic cell transplantation. (A) TCR Vβ profile of donor FVB (unpublished data) or C57Bl6 (shown) CD3⁺ T cells from Balb/c recipients on day 30 following transplantation. Flow cytometry shows a broad overall Vβ usage in all groups, with a higher percentage of donor CD3⁺ T cells at the majority of Vβ regions in animals that received Tregs in addition to Tcons. TCR Vβ profiles of untreated age-matched C57Bl/6 animals (Untreated) and of Balb/c recipients which received only C57Bl/6 T cell–depleted bone marrow cells (BM) served as controls. Data presented as the mean plus or minus SE (3 to 4 mice per group). (B) CDR3 size spectratyping analysis was performed using C57Bl/6-specific Vβ primers to generate PCR products from purified splenic cells from untreated C57Bl/6 wild-type controls (WT) or transplant recipients which received TCD-BM alone, with Tcons (Tcon) or with Tcons and Tregs (Tcon + Treg), on day 30 following transplantation. Shown are representative spectratypes of Vβ2, 4, 6, 8.3, 10, 12, and 16 in the histogram format. Histograms (blue peaks) depict CDR3 sequence length (abscissa) vs frequency of occurrence (ordinate). Red peaks within each histogram represent nucleic acid reference sequence of defined length. Data are representative of at least 3 animals per group, from one of 2 experiments.