title: Immunogenicity of native or pegylated E. coli and Erwinia asparaginases assessed by ELISA and surface plasmon resonance (SPR-biacore) assays of IgG antibodies (Ab) in sera from patients with acute lymphoblastic leukemia (ALL).
abstract: BACKGROUND
  Therapeutic uses of asparaginases (ASNase) have been shown to elicit immune responses resulting in the development of potentially life-threatening human anti-bacterial antibodies (Ab). A robust screening enzyme-linked immunosorbent assay (ELISA) to detect binding Ab(+) against ASNase has been developed and validated for therapeutic monitoring to support clinical trials. Recently, a protein chip bioassay (Biacore) was developed for the Ab of these proteins. These methods were compared.
  
  
  METHODS
  A Biacore T-100 analyzer using a protein bioassay and an ELISA assay were used to determine the IgG immmuboglobulin Ab against ASNase in sera from 84 acute lymphoblastic leukemia (ALL) patients plus 6 controls (n=121 samples). These samples were characterized for anti-ASNase Ab neutralizing activity. Human E. coli ASNase, pegaspargase and Erwinase proteins were covalently coupled to the carboxy-methylated dextran matrix of a CM5 sensor chip (surface plasmon resonance, SPR). In the course of a nested experimental design, a wide range of human sera from patients who had obvious clinical allergic reactions after either native or pegaspargase treatments were tested. The data were fitted by a parametric logistic equation (+/-95% confidence interval, CI), which ranged from <3.0% to <14%.
  
  
  RESULTS
  The specificity of Ab(+) was evaluated using "spiked" human IgG antibodies. Both assays provide near excellent linearity and sensitivity of response (<0.8 to <500 ratio and 1-3000 resonance units [RU]) of anti-ASNase Ab in human sera with low variance. The bioassay method was ten times more sensitive than the ELISA Ab assay. The lowest limit of quantification of Ab(+) ratio for the SPR assay was 0.6 whereas the upper limit of quantification was 3000 RU. The SPR assay results were in excellent accord with both the Ab(-) and the Ab(+). Ab(-) by the ELISA method (<1.003 ratio) was related to a mean RU value of 8.1. Despite the narrow range of ambiguity around the 1.1 Ab(+) ratio values, the majority of the specimens (93.2%) were determined to be Ab(+) by either ELISA or SPR determination.
  
  
  CONCLUSIONS
  The vast majority (81/84 = 96.4%) of the IgG Ab(+) were neutralizing. The SPR Ab determination technique is reliable, accurate and more sensitive than the ELISA method.
authors.affiliation: CHLA Hematology/Oncology USC-Keck School of Medicine, Los Angeles, CA 90027, USA. vavramis@chla.usc.edu
authors.forename: Vassilios I
authors.initials: VI
authors.lastname: Avramis
authors.forename: Earl V
authors.initials: EV
authors.lastname: Avramis
authors.forename: William
authors.initials: W
authors.lastname: Hunter
authors.forename: Melissa C
authors.initials: MC
authors.lastname: Long