Prognostic Analysis of Pre-Transplant CD26-Positive Lymphocytes and CD26bright/CD45RO-Positive Memory T-Cell Levels in Patients Receiving an Autologous Hematopoietic Progenitor-Cell Transplant.

The lymphocyte surface glycoprotein CD26 is involved in an array of diverse signalling pathways and costimulatory events. CD26positive cells possess dipeptidylpeptidase IV (DPP IV) activity, a serine protease known to inactivate SDF-1/CXCL12, a key mediator of stem cell homing and engraftment. Furthermore, CD26 modulates surface expression of CTLA-4 and contributes to T-cell migration through endothelial layers. CD26 has been attributed with a central role in alloantigen-mediated immune pathways and memory T-cell responses. The purpose of this study was to evaluate the levels of a distinct memory T-cell subset, CD26bright/CD45RO-positive, in autologous hematopoietic progenitor-cell transplant (HPCT) recipients. Between 2003 and 2006 we enrolled 42 patients scheduled to undergo high-dose chemotherapy and autologous HPCT (multiple myeloma, n=31; Hodgkin’s Disease, n=3; NHL, n=6; PNET, n=1; AML, n=1). Levels of memory and naïve CD26, CD34, CD4, CD8, as well as co-expression of CD4 or CD8 among CD26bright/CD45RO-positive cells were analyzed before autologous HPCT. In addition, the number of memory and naïve CD26-positive T cells transfused per kg body weight in the progenitor cell harvest were determined. The subsets of CD26-positive cells were correlated with kinetics of engraftment and with the occurrence of disease progression or relapse after autologous transplantation. With regard to kinetics of engraftment, only the number of CD34-positive cells transfused was associated with rapid engraftment (P=0.001). However, CD26-positive cells were of predicitve value for the occurrence of disease progression or relapse. Pre-transplant CD26-positive T-cell levels correlated with progression-free survival (PFS) (P=0.022). Specifically, the number of CD26bright/CD45RO-positive memory T-cells in the autograft correlated with PFS and, in regression analyses, emerged as the only variable predictive for the occurrence of diease progression or relapse (P=0.006). The prognostic effects of pre-transplant CD26bright/CD45RO-positive memory T-cells were independent of the type of disease and of the conditioning regimen applied. The analysis of antigens CD4 and CD8, respecively, on CD26bright/CD45RO-positive T-cells yielded no additional information. Our results suggest that pre-transplant levels of CD26-positive T cells, specifically a memory cell subset of CD26bright cells coexpressing CD45RO, may yield information with regard to outcome in autologous HPCT recipients. These observations may contribute to a prospective identification of those patients at higher risk of relapse, based on their immune status.