CD9 is an unreliable antibody for bone marrow purging

Various procedures are useful in purging bone marrow of pre-B lineage contamination prior to autologous bone marrow transplantation. Specific monoclonal antibodies are used in combination with complement, magnetic microspheres, chemotoxins, phototherapy or lectins. In this setting, the usual monoclonal antibody cocktail consists of CD9 (DU-ALL-1), CD10 (WCMH 15.14) and CD19 (HD37). Antigens reacting with all three monoclonal antibodies are present on early and mature pre-B lymphocytes. However, CD9 positive antigens have also been shown to be present on megakaryocytes, platelets and mature granulocytes. In our studies, we have found that CD10 and CD19 expression predictably vary according to disease status, with low positivity in remission and higher positivity in relapse. CD9 expression, however, varies independently of disease status and is frequently inconsistent within individual patients. As such, use of CD9 for marrow purging may result in the removal of a broad range of cell populations not related to the underlying disorder.