Purging of T-lymphocytes with magnetic affinity colloid

There is a well-documented correlation between the number of T-lymphocytes in the bone marrow graft and subsequent development of acute graft-versus-host disease after allogeneic bone marrow transplantation. The incidence of acute graft-versus-host disease may be decreased with elimination of mature T-lymphocytes from the bone marrow graft. We have developed an immunomagnetic separation procedure using an avidin-based magnetic affinity cobalt colloid. Bone marrow cells were incubated with a combination of CD2, CD3, CD4, and CD8 monoclonal antibodies. The cells were washed and then incubated with the biotinylated, affinity-purified IgG fraction of goat anti-mouse immunoglobulins followed by an avidin-based magnetic affinity colloid. The cells were then run through a high-magnetic gradient separation column utilizing an external samarium cobalt magnet. The number of residual T-lymphocytes was assessed by limiting dilution analysis of clonogenic T-lymphocytes. This procedure produces an approximately 1.7-log reduction of antibody-reactive cells with 45% recovery of hemopoietic progenitors (granulocyte-macrophage colony-forming cells, GM-CFC). This causes a reduction of T-lymphocytes in the bone marrow graft to approximately 5 x 10⁵ cells/kg body weight.