Phase II trial of recombinant immunotoxin RFB4(dsFv)-PE38 (BL22) in patients with hairy cell leukemia.
OBJECTIVE
To conduct a phase II trial in chemoresistant hairy cell leukemia (HCL) with BL22, a recombinant anti-CD22 immunotoxin which showed phase I activity in HCL.


METHODS
Eligible patients had relapsed/refractory HCL and needed treatment based on blood counts. Patients were stratified into three groups: response to cladribine less than 1 year, those with a response lasting 1 to 4 years, or no response and uncontrolled infection. Patients received BL22 40 microg/kg every other day for three doses on cycle 1. Those achieving hematologic remission (HR), defined as neutrophils > or = 1,500/mm(3), hemoglobin > or = 11 g/dL, and platelets > or = 100,000/mm(3), were observed. Patients without HR were re-treated at 30 microg/kg every other day for three doses every 4 weeks beginning at least 8 weeks after cycle 1.


RESULTS
Thirty-six patients were enrolled including 26, nine, and one in groups 1 to 3. The response after one cycle (CR, 25%; PR, 25%) improved when 56% were re-treated (CR, 47%; PR, 25%). CR rate was similar in groups 1 and 2 (P = .7). Twenty-two with baseline spleen height lower than 200 mm had higher CR (64% v 21%; P = .019) and OR rates (95% v 36%; P = .0002) compared to 14 with spleens either absent or higher than 200 mm. The only serious toxicity was reversible grade 3 hemolytic uremic syndrome, not requiring plasmapheresis, in two patients (6%). High neutralizing antibodies were observed in four patients (11%) and prevented re-treatment.


CONCLUSIONS
BL22 activity in HCL is confirmed. Best responses to BL22 after cladribine failure are achieved before the patients develop massive splenomegaly or undergo splenectomy.
Laboratory of Molecular Biology, Laboratory of Clinical Pathology, and Medicine Branch, National Cancer Institute, NIH, Bethesda, MD 20892, USA. kreitmar@mail.nih.gov
Robert J
RJ
Kreitman
Maryalice
M
Stetler-Stevenson
Inger
I
Margulies
Pierre
P
Noel
David J P
DJ
Fitzgerald
Wyndham H
WH
Wilson
Ira
I
Pastan
D000328:Adult; D000368:Aged; D000906:Antibodies / Q000008:administration & dosage / Q000627:therapeutic use* / Q000633:toxicity; D000970:Antineoplastic Agents / Q000627:therapeutic use; D017338:Cladribine / Q000627:therapeutic use; D004351:Drug Resistance; D004768:Enterotoxins / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use* / Q000633:toxicity; D005260:Female; D006801:Humans; D007943:Leukemia, Hairy Cell / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013154:Spleen; D016896:Treatment Outcome
D000906:Antibodies; D000970:Antineoplastic Agents; D004768:Enterotoxins; C431326:RFB4(dsFv)-PE38 recombinant immunotoxin; D017338:Cladribine