Immune Reconstitution Following Myeloablative Allogeneic Hematopoietic Stem Cell Transplantation: The Impact of Expanding CD28^negCD8⁺ T-Cells on Relapse.

Allogeneic stem cell transplantation has become standard therapy for haematological malignancies through the positive immunologic graft-versus-leukaemia effect. Initial immune recovery relies on peripheral expansion of infused T-cells which switch to a memory-like phenotype. This study prospectively investigated whether changes in subset composition precedes late complications after myeloablative HLA-matched transplantation. Of 80 recipients, 51 experienced neither early infection nor acute graft-versus-host disease (GVHD), of whom 18 were still free of clinical complication throughout 395 – 1564 days of follow-up. Compared with this complication-free subgroup, patients who developed chronic GVHD as the only event recovered similar numbers of circulating T-cells with predominance of CD8⁺ T-cells lacking CC-chemokine receptor-7 and CD28 expression. Conversely, poor CD8⁺ T-cell recovery with diminished numbers of CD28^neg CD8⁺ T-cells (~1/4^th of that of relapse-free patients) preceded occurrence of relapse. In multivariate analysis, lower CD28^neg CD8⁺ T-cell counts by day 60 were associated with greater risk of subsequent relapse (HR 0.33; 95% CI 0.14 - 0.76; P = 0.01). Enumeration of CD28^neg CD8⁺ T-cells in patients without early clinical complication could assist in predicting risk of relapse and help build an algorithm for accelerating the immune recovery by reducing the immunosuppressive regimen and considering the introduction of prophylactic donor lymphocyte infusions.