Lineage specific treatment of adult patients with acute lymphoblastic leukemia in first remission with anti-B4-blocked ricin or high-dose cytarabine: Cancer and Leukemia Group B Study 9311.

Background: Anti-B4-blocked ricin is an immunotoxin comprised of an anti-CD19 murine monoclonal antibody (B4) conjugated to blocked ricin, which has cytotoxic activity in patients with lymphoid malignancies.

Methods: Adults with untreated acute lymphoblastic leukemia (ALL) were treated with a previously developed and tested chemotherapeutic regimen. Patients with CD19 positive ALL were given anti-B4-blocked ricin as 2 7-day continuous infusions 1 week apart. Patients with CD19 negative ALL received high-dose cytarabine. Serial polymerase chain reaction (PCR) assays of BCR-ABL, immunoglobulin heavy chain (IGH), and T-cell receptor (TCR) genes were used to measure the impact of lineage specific intensification treatment on minimal residual disease.

Results: Eighty-two adults were enrolled, and 78 were eligible. The median age was 34 years (range, 17-81 years). Sixty-six patients (85%) achieved complete remission. Forty-six patients received the anti-B4-blocked ricin, which generally was well tolerated; 80% were able to receive both courses. The most common toxicity was asymptomatic transient elevation of liver function tests in 72% of patients. Lymphopenia occurred in 46% of patients. Two patients developed antibodies to the anti-B4-blocked ricin. Molecular monitoring before and after the experimental course of intensification did not show a consistent change in the number of leukemia cells remaining, and the immediate posttreatment PCR studies did not correlate with remission duration.

Conclusions: Intensification therapy with anti-B4-blocked ricin is feasible for patients with CD19 positive ALL, although there is little evidence of an additional clinical benefit from the anti-B4-blocked ricin. Cancer 2003;97:1471-80.