ROBERT J. KREITMAN: THURSDAY 30 MARCH 2006, 16:00
Therapy of chemoresistant hairy cell leukemia patients with recombinant immunotoxin BL22
Robert J. Kreitman, Wyndham H. Wilson, Maryalice Stetler-Stevenson, Pierre Noel, David J.P. FitzGerald, and Ira Pastan
National Cancer Institute,
Laboratory of Molecular Biology,
Clinical Immunotherapy Section,
Bethesda, Maryland, USA
Fifty-one patients with hairy cell leukemia (HCL) previously treated with CdA were treated with recombinant anti-CD22 immunotoxin BL22, containing truncated Pseudomonas exotoxin fused to the variable domains of an anti-CD22 monoclonal antibody. Of 31 patients on phase I, 19 (61%) achieved complete remission (CR) and 6 (19%) had partial response (PRs). The median (range) duration of CR was 36 (5-66) months and 8 (42%) patients are still in CR at a median 48 (range 32-66) months. Of 30 with cytopenais, 22 (73%) acheived hematologic remission (HR) (neutrophils, platelets, and hemoglobin at least 1500, 100,000, and 11) and 11 (50%) are still in HR at a median of 48 (33-66) months. Of 18 HCL patients on phase II, 10 were followed at least 4 months, 6 (60%) achieved CR, and 1 relapsed. The major toxicity of BL22 (Phase 1+ 2 special exemption) was hemolytic uremic syndrome (HUS), observed in 5 HCL patients during cycle 2 or 3. HUS in all 5 completely resolved after 6-12 daily plasmapheresis treatments without recurring at a median of 52 (29-70) months. Phase II patients were retreated at least 8 weeks after cycle 1 and only if not achieving HR, and none had HUS requiring plasmapheresis.