A laboratory comparison of T cell depletion by CD34+ cell immunoaffinity selection and in vitro Campath-1M treatment: clinical implications for bone marrow transplantation and donor leukocyte therapy

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Abstract
Donor leukocyte infusions (DLI) have been used effectively to induce remission in patients who relapse after BMT. Using CD34+ cell immunoaffinity enrichment, donor T cells may be captured in the unadsorbed (residual) fraction and we assessed this as a potential source of functional T cells for post-BMT immunotherapy. We extended our study to compare CD34+ cell selection and antibody-mediated cell lysis using Campath-1M and measured T cell-depletion, CD34+ cell recovery and relative progenitor proliferative potential. The recovery of CD3+ cells (responsive to IL-2 or PHA) in the unadsorbed fraction was 84 ± 12% (mean ± s.d.) using a laboratory scale CD34+ cell selection process (CEPRATE LC). The immunoselected (CD34+ cell enriched) product contained 55 ± 12% of the starting CD34+ cells (purity, 75 ± 6%) with recoveries of 44 ± 12% and 42 ± 13% for CFU-GM and BFU-E respectively. T cell depletion was 99.8 ± 0.2% (FACS) and the frequency of clonable T cells estimated at 1:640 (limiting dilution assay). In comparison, Campath-1M-treated marrow samples gave recoveries of CD34+ cells, CFU-GM and BFU-E of 50 ± 7%, 78 ± 20% and 79 ± 18%, respectively. The frequency of clonable T cells was 1:2700 despite an estimated T cell depletion of 98.4 ± 1.9%. Data obtained from four BM harvests processed on the clinical grade CEPRATE SC system was comparable in every respect to the laboratory scale system. The yield of 1259 ± 222 × 106 CD3+ cells in the unadsorbed fraction would allow for multiple graded incremental T cell aliquots for DLI for patients with acute leukaemia.

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