Blood, Vol. 93 No. 10 (May 15), 1999:
pp. 3250-3258
Abrogation of the Hematological and Biological Activities of the
Interleukin-3/Granulocyte-Macrophage Colony-Stimulating Factor
Fusion Protein PIXY321 by Neutralizing Anti-PIXY321 Antibodies in
Cancer Patients Receiving High-Dose Carboplatin
Langdon L. Miller,
Edward L. Korn,
Diane S. Stevens,
John E. Janik,
Barry L. Gause,
William C. Kopp,
Jon T. Holmlund,
Brendan D. Curti,
Mario Sznol,
John W. Smith II,
Walter J. Urba,
Sarah E. Donegan,
Thelma M. Watson, and
Dan L. Longo
From the Frederick Cancer Research and Development Center, Biological
Response Modifiers Program, National Cancer Institute, Frederick, MD;
the Biometric Research Branch, Cancer Therapy Evaluation Program,
National Cancer Institute, Bethesda, MD; the Clinical Services Program,
SAIC Frederick, Frederick, MD; Immunex Research and Development Corp,
Seattle, WA.
This dose-escalation study was performed to evaluate the hematologic
activity, biological effects, immunogenicity, and toxicity of PIXY321
(an interleukin-3/granulocyte-macrophage colony-stimulating factor
fusion protein) administered after high-dose carboplatin (CBDCA)
treatment. Patients with advanced cancers received CBDCA at 800 mg/m2 intravenously on day 0 of repeated 28-day cycles. In
part A of the study, patients were treated with CBDCA alone during
cycle 1 and then received PIXY321 on days 1 through 18 of cycle 2 and later cycles. In part B, patients received 18 days of PIXY321 beginning
on day 1 of all CBDCA cycles, including cycle 1. PIXY321 was
administered subcutaneously in 2 divided doses. Total doses of 135, 250, 500, 750, and 1,000 µg/m2/d were administered to
successive cohorts of 3 to 6 patients in part A. In part B, patient
groups received PIXY321 doses of 750, 1,000, and 1,250 µg/m2/d. The hematologic effects of PIXY321 were assessed
in the first 2 cycles of therapy. Anti-PIXY321 antibody formation was
assessed by enzyme-linked immunosorbent assay (ELISA) and
neutralization assay. Of the 49 patients enrolled, 31 were fully
evaluable for hematologic efficacy. When comparing the first B cycle
(cycle B-1; with PIXY321) with the first A cycle (cycle A-1; without PIXY321), the fusion protein had no significant effect on platelet nadirs or duration of platelets less than 20,000/µL but was able to
speed the time of recovery of platelet counts to 100,000/µL (15 v 20 days; P = .01). Significant improvements in
neutrophil nadir and duration of ANC less than 500 were observed in
cycles A-2 and B-1 (with PIXY321) as compared with cycle A-1 (without PIXY321). Initial PIXY321 prophylaxis (cycle A-2 and cycle B-1), enhanced the recovery of ANC to greater than 1,500/µL by an average of at least 8 days as compared with cycle A-1 (without PIXY321; P 
.004). However, positive PIXY321 hematologic effects were lost in the second course of PIXY321 among patients treated in part B. ELISA analysis showed that 92% of patients had developed neutralizing
anti-PIXY321 antibodies by the completion of 2 PIXY321-containing cycles. The incidental action of PIXY321 to depress serum cholesterol levels was also abrogated during cycle B-2. We conclude that PIXY321 was active in speeding hematologic recovery but that neutralizing anti-PIXY321 antibody formation suppressed the hematologic and biochemical effects by the second cycle of PIXY321 administration. The
immunogenicity of this fusion protein provides a cautionary warning
that clinical development of bioengineered human molecules requires
thorough testing for immune neutralization.
