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Summary:CAMPATH-1H (C-1H) is widely used in vivo and/or in vitro for T cell depletion in hematopoietic SCT. This humanised monoclonal antibody is specific for CD52, a marker coexpressed on the majority of human lymphocytes with CD48 and other glycosylphosphatidyl-inositol (GPI) anchored proteins. We detected CD52/CD48 dual expression on 499% of CD3 þ lymphocytes from normal individuals and all 15 post-SCT patients whose transplants did not utilise C-1H. By contrast, 23/26 patients with transplants involving C-1H (in vivo, in vitro or both) exhibited populations lacking CD52 expression that accounted for 49.7% (4.2-86.2%) of the CD3 þ lymphocytes (median and range) in samples evaluated at a median of 2 months post-SCT. Most CD52 À cells also lacked CD48 expression. These GPI À T cells were of either donor or mixed donor/recipient origin. They were predominant in the early months after SCT at times of profound lymphopenia and inversely correlated with the recovery of the absolute lymphocyte count (r ¼ À0.663, Po0.0001). The presence of CD52 À cells has been correlated previously with clinical outcome after CAMPATH therapy for both malignant and nonmalignant diseases. Bone Marrow Transplantation (2005) 36, 237-244.

Summary. The accurate and rapid determination of the origin of haemopoietic cells may provide valuable information as to the aetiology of, and most appropriate therapy for, leucopenia following allogeneic bone marrow or peripheral blood stem cell transplantation. We describe an approach to the analysis of chimaerism post bone marrow transplantation (BMT) based on the immunomagnetic capture of white cells combined with microsatellite polymerase chain reaction (PCR) and resolution of products by polyacrylamide gel electrophoresis (PAGE). This non-isotopic method enables the chimaeric status to be determined from as little as 1 . 0 ml of profoundly leucopenic peripheral blood (WBC р0 . 1 × 10 9 /l) and has been applicable to all donor/recipient pairs tested so far. Results are available within 6 h of blood sampling and lineage-specific chimaerism is possible. Furthermore, blood transfusions do not interfere with the analysis.