Clonally Expanded CD8+ T cells in Allogeneic Bone Marrow Transplantation

Allogeneic bone marrow transplantation (BMT) is a potentially curative therapy for patients with haematologic malignancies. Several lines of evidence demonstrate that donor T cells are involved in the antitumour effects observed after BMT. Thus, patients receiving T‐cell‐depleted BMT have a higher risk of leukaemia relapse compared to patients receiving nonmanipulated BMT, and patients experiencing graft‐versus‐host disease (GVHD) have a lower risk of disease relapse than patients who do not experience GVHD. Although the importance of donor T cells for the curative action of BMT has been established, the exact mechanisms and molecules involved in this graft‐versus‐tumour effect remain largely unknown. In a recently initiated project, we have conducted a longitudinal study of T‐cell clonotypes in patients who received peripheral blood stem cell grafts after nonmyeloablative conditioning. Peripheral blood samples were obtained sequentially after transplant, and the mononuclear cells (MNCs) were isolated and cryopreserved. CD8+ T cells were isolated from the MNCs by use of immunomagnetic beads or FACS and analysed for the presence of clonally expanded cells by T‐cell receptor clonotype mapping based on RT‐PCR and denaturing gradient gel electrophoresis (DGGE). Using this gel‐based methodology, clonally expanded T cells were monitored after transplant and compared to the clinical data of the patients. The preliminary results demonstrates the presence of clonally expanded CD8+ T cells at all time points analysed. Furthermore, a number of clonotypes persisted for more than 6 months, and other clonotypes emerged during this period. The appearance of newly emerged clonotypes which coincided with clinical GVHD could indicate a role for these T cells in the pathogenesis of GVHD.