Autologous BMT in high risk patients with CALLA-positive ALL: Possible efficacy of ex vivo marrow leukemia cell purging with monoclonal antibodies and complement

Autologous BMT (auto-BMT) has been conducted for 17 high-risk common ALL antigen (CALLA)-positive non-T cell type ALL patients. Ex vivo purging of leukemia cells from infused BM cells was performed using complement and three kinds of mouse monoclonal antibodies reactive to CALLA-positive leukemia cells: NL-1 (IgG2a), NL-22 (IgM), and HL-47 (IgM). Minimal residual leukemia cells in BM were examined by PCR method in Philadelphia chromosome (Ph¹)-positive ALL cases. BCR/ABL chimeric transcript, which was positive in BM samples before purging, was shown to be absent after ex vivo purging in all three cases tested. Among four Ph¹-positive cases transplanted in first CR, three cases survived in CR remission 77, 29 and 26 months after BMT, and one case died without relapse 4 months after BMT. The other four Ph¹-negative cases transplanted in the first CR also remained in CR except one who relapsed. The results of minimal residual leukemia cell studies and clinical data indicate the effectiveness of our ex vivo leukemia cell purging method and auto-BMT in the early stage of CR for patients with high risk ALL.