Serial Analysis of Whole Blood Cell and CD3⁺ T-Lymphocyte Chimerism Following Allogeneic Stem Cell Transplantation with Alemtuzumab Containing Reduced-Intensity-Conditioning (RIC).

Serial analysis of haemopoietic chimerism can be used to predict outcome after allogeneic SCT using a RIC regimen and guide post-transplant intervention. Although alemtuzumab is increasingly used as a component of RIC regimens, there have been few studies of its impact on chimerism status post-transplant. We have therefore measured chimerism following allogeneic SCT in whole blood/marrow nucleated cells (WB) and magnetically selected CD3⁺ T-lymphocytes in 64 patients with lymphoid (8 high-grade NHL, 18 low-grade NHL, 5 myeloma, 3 mantle cell lymphoma, 9 Hodgkin’s lymphoma) or myeloid malignancy (14 AML, 3 MDS, 1 myelofibrosis, 3 CML) conditioned with alemtuzumab and either fludarabine with melphalan (n=46), BEAM (carmustine, etoposide, cytarabine and melphalan) (n=16) or fludarabine/busulphan (n=2). Forty-seven patients received a transplant from an HLA compatible sibling donor and 17 from a matched unrelated donor. All patients achieved neutrophil and platelet engraftment. Donor chimerism was quantified within the first year post-allograft as well as following donor lymphocyte infusions (DLI) by FISH or PCR-based analysis of polymorphic microsatellite regions. 85% of patients demonstrated full donor chimerism (FDC, defined as ≥ 95% cells of donor origin) in WB within the first 90 days post-transplant. By contrast FDC was only present in the CD3⁺ compartment of 45% of patients. The proportion of patients with WB FDC declined to 64% by 12 months post transplant whilst the proportion of patients with CD3⁺ FDC remained constant. Thirteen patients received DLI using escalating CD3⁺ doses for management of mixed chimerism (MC) including 6 with evidence of disease relapse. Following DLI, 7 patients achieved FDC in WB and CD3⁺ compartments and 4 failed to switch to FDC. Seven patients developed acute GVHD post-DLI. Acquisition of FDC in the CD3⁺ compartment within 90 days post-transplant correlated with the presence of acute GVHD (p=0.003). Sixteen patients relapsed of whom 13 exhibited MC in WB or CD3⁺ compartments. Three patients relapsed despite the presence of FDC in WB and CD3⁺ cells. There was a trend towards improved disease free survival in patients who achieved FDC in WB within 90 days of transplantation compared to patients with MC (median 30 months v 11 months respectively). These data define a different pattern of WB and CD3⁺chimerism after alemtuzumab regimens compared with T-replete RIC regimens and confirm a correlation between chimerism status and outcome post-transplant.