Allogeneic stem cell transplantation (SCT) continues to provide the best chance of cure for selected patients with haematological malignancies. However, transplant-related mortality (TRM) and graft-versus-host disease (GVHD) offset the unique therapeutic advantage of the graft-versus-leukaemia (GVL) effect. Although T-cell-depleted (TCD) SCT results in lower TRM and GVHD rates, the disease-free survival is comparable with that of unmanipulated SCT because of a higher rate of disease relapse and graft rejection (Marmont et al, 1991). To offset these disadvantages, while conserving the beneficial effect of T-cell depletion, we have used a myeloablative TCD peripheral blood stem cell transplant (PBSCT) followed by a transfusion of donor lymphocytes (DLI) after a delay of 45-100 d. The rationale of this approach was to boost T-cell immunity while mitigating GVHD with the delayed lymphocyte infusion (Barrett et al, 1998). Several studies have drawn attention to the frequent occurrence of mixed haematopoietic chimaerism after TCD transplants and have linked relapse and unfavourable transplant outcome with the mixed chimaeric state (Walker et al, 1986;Schaap et al, 1997;Bader et al, 1998;Barrios et al, 2003;Lamba et al, 2004). However, the relative patterns of engraftment of T-cells and myeloid cells have not been well described after these myeloablative SCT. We therefore evaluated donor T-cell and myeloid chimaerism in our hybrid T-cell depletion and add-back protocol, correlating chimaerism results with transplant outcomes. T lymphocyte (CD3 + cells) and myeloid (CD14 + /CD15 + cells) lineage specific chimaerism was measured regularly in the first 3 months post-transplant. Here we describe factors associated with mixed chimaerism, and the relationship between early mixed chimaerism and transplant outcome in patients with haematological malignancies receiving TCD human leucocyte antigen (HLA)-identical PBSCT and delayed DLI.
SummarySixty patients with haematological malignancies received a myeloablative regimen of total body irradiation, cyclophosphamide and fludarabine followed by a T-cell-depleted peripheral blood stem cell transplant from a human leucocyte antigen identical sibling. To improve donor immune function, 1 · 10 7 CD3 + cells/kg were added-back between d 45 and 100. Tcell and myeloid chimaerism were monitored regularly to evaluate the effect of T-cell chimaerism on outcome. The major factor affecting outcome was disease risk, with significantly lower relapse and higher survival in 29 standard risk (SR) patients compared with 31 patients at high risk (HR) for treatment failure (relapse 4AE8 ± 5% vs. 59 ± 11%, P < 0AE0001, and overall survival 93 ± 5% vs. 39 ± 10%, P < 0AE0001, respectively). Donor myeloid chimaerism reached âĄ95% within 14 d of transplant, but in the first several months, donor T-cell chimaerism was frequently mixed. Full T-cell chimaerism was significantly more frequent in HR vs. SR patients. Landmark analysis at days 30 and 90 in HR patients with mixed versus full T-cell chimaerism, sho...