Immunomagnetic microsphere mediated purging of cALLa positive leukemic cells from bone marrow for autologous...

Bone marrow from sixteen patients with cALLa positive ALL have been treated with a monoclonal antibody (MoAb) cocktail which includes DuALL-1 (CD9), WCMH15.14 (CD10) and HD-37 (CD19). Following antibody treatment, marrows were incubated (30 minutes) with anti-murine-IgG1 (Fc) coated magnetic microbeads and passed through a graded magnetic field chamber. Two problems have had to be addressed: (1) More marrow cells must be processed than in marrows from patients with neuroblastoma, for which the separation chamber was originally developed, requiring the use of more beads, causing occlusion of the chamber's collection surface. This has been corrected by using a large surface area pre-magnet for the elimination of excess microbeads prior to processing in the main chamber; (2) Up-modulation (up to 40% positive cells) of the CD9 associated antigen has been detected. To avoid difficulty, marrows are being routinely screened prior to harvest for purging, and purging is delayed for patients with elevated CD9 levels. Eight patients have been reinfused, with no morbidity or mortality associated with the purging or other ex vivo handling of the marrow.