Selective outgrowth of CD45RO+ V gamma 9+/V delta 2+ T-cell receptor gamma/delta T cells early after bone marrow transplantation

Before and after bone marrow transplantation (BMT) for hematologic malignancies, peripheral blood mononuclear cells from 10 patients were obtained. The relative and absolute numbers of CD3+ T-cell receptor gamma delta+ (TCR gamma delta+) cells, as defined by the reaction of monoclonal antibodies (MoAbs) directed against CD3 and the TCR gamma delta (anti-TCR gamma delta-1), were determined. Before transplantation, eight of nine patients tested had less than 10% CD3+TCR gamma delta+ cells. Consistent increased numbers of gamma delta cells up to eightfold the pretransplant level can be seen in four of nine patients tested within the first 4 months after BMT. The large majority of early posttransplant gamma delta and alpha beta T cells express the CD45RO antigen, which is usually expressed on “memory” cells only. The V-region usage of the TCR gamma delta+ T cells was analyzed using fresh mononuclear cells and MoAbs against known V gamma and V delta regions. For more detailed analysis, CD3+TCR gamma delta+ cells were sorted and cultured in bulk and cloned. Using fresh cells and bulk cultures, mainly V gamma 9+V delta 1-V delta 2+ cells were found during engraftment. Only after 6 weeks post-BMT, V gamma 9-V delta 1+V delta 2- cells appear. Analysis of the V gamma and V delta usage at the clonal level confirmed the observation that early after BMT only V gamma 9+V delta 2+ cells are present, whereas gamma delta T- cell clones expressing other gamma delta TCR phenotypes can only be detected 4 to 6 weeks post-BMT. The predominance of V gamma 9+ cells during early engraftment could be explained by several mechanisms: (A) sequential rearrangements during T-cell development, leading to an early wave of V gamma 9+ cells, or (B) selective outgrowth of preexisting V gamma 9+V delta 2+CD45RO+ TCR gamma delta cells in the bone marrow graft, possibly as a result of antigen driven expansion due to exposure to environmental antigens.