Efficacy of the anti-CD22 recombinant immunotoxin BL22 in chemotherapy-resistant hairy-cell leukemia

N Engl J Med. 2001 Jul 26;345(4):241-7. doi: 10.1056/NEJM200107263450402.


Background: Hairy-cell leukemia that is resistant to treatment with purine analogues, including cladribine, has a poor prognosis. We tested the safety and efficacy of an immunotoxin directed against a surface antigen that is strongly expressed by leukemic hairy cells.

Methods: RFB4(dsFv)-PE38 (BL22), a recombinant immunotoxin containing an anti-CD22 variable domain (Fv) fused to truncated pseudomonas exotoxin, was administered in a dose-escalation trial by intravenous infusion every other day for a total of three doses.

Results: Of 16 patients who were resistant to cladribine, 11 had a complete remission and 2 had a partial remission with BL22. The three patients who did not have a response received low doses of BL22 or had preexisting toxin-neutralizing antibodies. Of the 11 patients in complete remission, 2 had minimal residual disease in the bone marrow or blood. During a median follow-up of 16 months (range, 10 to 23), 3 of the 11 patients who had a complete response relapsed and were retreated; all of these patients had a second complete remission. In 2 of the 16 patients, a serious but completely reversible hemolytic-uremic syndrome developed during the second cycle of treatment with BL22. Common toxic effects included transient hypoalbuminemia and elevated aminotransferase levels.

Conclusions: BL22 can induce complete remissions in patients with hairy-cell leukemia that is resistant to treatment with purine analogues.

Publication types

  • Clinical Trial
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Aged
  • Antibodies
  • Antineoplastic Agents / administration & dosage*
  • Antineoplastic Agents / adverse effects
  • Cladribine / therapeutic use
  • Dose-Response Relationship, Drug
  • Drug Resistance
  • Enterotoxins
  • Exotoxins / administration & dosage*
  • Exotoxins / adverse effects
  • Female
  • Hemolytic-Uremic Syndrome / chemically induced
  • Humans
  • Immunotoxins / administration & dosage*
  • Immunotoxins / adverse effects
  • Leukemia, Hairy Cell / drug therapy*
  • Male
  • Middle Aged
  • Pseudomonas
  • Recurrence
  • Remission Induction / methods


  • Antibodies
  • Antineoplastic Agents
  • Enterotoxins
  • Exotoxins
  • Immunotoxins
  • RFB4(dsFv)-PE38 recombinant immunotoxin
  • Cladribine