The depletion of T cells from haematopoietic stem cell transplants

Objective. In our laboratory, we have developed an immunorosette technique for the depletion of T cells from bone marrow transplants. Tetrameric compl exes of monoclonal antibodies are able to form very stable immunorosettes, which are efficiently depleted with the aid of a blood cell separator. Majo r improvements over the original sheep red blood cell depletion are the use of human (patient or donor derived) erythrocytes instead of sheep-derived cells, and the possibility of using a closed system for separation in a cel l separator. In contrast to bone marrow, mobilized haematopoietic stem cell transplants obtained after leucocytapheresis contain higher numbers of T c ells. Therefore, a different approach is necessary. Method. We have used two CD34 selection systems (Isolex(TM) 300SA and the C linimacs(R)) to perform T-cell depletions from peripheral blood stem cell ( PBSC) transplants. Results. Immunorosette T-cell depletion, with CD2/CD3 tetrameric complexes, of bone marrow transplants resulted in a mean 2.5 log depletion of T cells with a yield of 50% of the CD34(+) cell population. Stem cell selection of PBSC transplants using one of the CD34 selection procedures resulted in a 4.5 log depletion of T cells for both systems, but with different results f or the recovery of CD34(+) cells. An increased yield of CD34+ cells was obt ained with the Clinimacs(R) procedure (57.9 +/- 9.0%) in comparison to the Isolex(TM) procedure (40.1 +/- 12.5%). Conclusion. Our own immunorosette depletion technique and the two tested CD 34 selection methods for stem cell transplants both resulted in a very effi cient T-cell depletion with the recovery of 40-60% of the CD34(+) haematopo ietic stem cells present in the transplant.