Isolation of pure functionally active CD8+ T cells. Positive selection with monoclonal antibodies directly conjugated to monosized magnetic microspheres.

A monoclonal antibody of the IgM isotype, ITI-5C2, which binds with high affinity to CD8 molecules, was directly conjugated to the monosized magnetic microspheres M-450. This permits selective removal of the CD8+ T cell subset (T8) from peripheral blood mononuclear cell suspensions in a rapid one-step procedure. With a low ratio of microspheres to cells (2:1), functionally active T8 cells can be recovered. In vitro experiments involving such positively selected T8 cells or recombinations of isolated T8 and T4 subsets, demonstrate that the presence of M-450 microspheres coated with ITI-5C2 do not interfere with the immunological functions of the positively selected cells. The method has possible application in the isolation of all cell populations where high avidity mAbs of appropriate specificity are available.