Treatment of human B-cell precursor leukemia in SCID mice using a combination of the investigational biotherapeutic agent B43-PAP with cytosine arabinoside

Combined immunochemotherapy regimens using the investigational biotherapeutic agent B43(anti-CD19)-poke-weed antiviral protein (PAP) immunotoxin may offer an effective treatment for refractory B-cell precursor leukemias. The purpose of the present study was to explore and identify effective combinations of B43-PAP with standard chemotherapeutic drugs, including the anthracyclin doxorubicin, the epipodophyllotoxin etoposide, the nitrosurea carmustine, and the antimetabolite cytosine arabinoside. Here, we report that the B43-PAP plus cytosine arabinoside combination has potent antileukemic activity against human B-cell precursor leukemia in SCID mice and leads to 100% long-term event-free survival from an otherwise invariably fatal leukemia. Surprisingly, none of the other treatment protocols tested, including combinations of B43-PAP with carmustine, doxorubicin, or etoposide, proved more effective than B43-PAP alone.