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A. Khalil et al.
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Figure 2. Scatter plots of anti-PEG IgM versus anti-PEG IgG levels determined in the reference and the acute lymphocytic leukemia cohorts. (A) Samples of the ref- erence cohort were taken from healthy infants. (B, C) Samples of acute lymphocytic leukemia (ALL)-cohort 1 were taken from patients treated according to the AIEOP- BFM ALL 2009 trial and were either collected prior to their first dose of PEG-asparatinase (ASNase) (B) or within 15 days after administration of the first PEG-ASNase dose (C). (D, E) Samples from ALL-cohort 2 (children with relapsed ALL treated according to the ALL-REZ BFM 2002 and the ALL-REZ BFM ALL observational study and biobank) (D) and samples from ALL-cohort 3 (adults treated according to the GMALL 07/2003 protocol) (E) were taken after administration of PEG-ASNase. Anti- PEG antibodies were determined by the level of mean fluorescent intensity (MFI). In (A) the dashed light blue vertical line represents the 95th percentile of anti-PEG IgM MFI and the dashed green horizontal line represents the 95th percentile of anti-PEG IgG MFI determined in the reference cohort. The solid reference lines rep- resent the defined cut-points after visual adjustment for anti-PEG IgM (light blue vertical line, MFI = 2) and anti-PEG IgG (green horizontal line, MFI = 8).
patients with pre-existing anti-PEG antibodies, the anti- body levels decreased a mean of about 2.7-fold for anti- PEG IgG and about 4.1-fold for anti-PEG IgM.
PEG-asparaginase activities
PEG-ASNase activities were determined in 1,183 sam- ples from 646 patients of ALL-cohort 1. Samples were col- lected within 15 days of the first administration of 2,500 U/m2 PEG-ASNase (maximum 3,750 U per dose) on day 12 of induction. Of these samples, 95.5% were collected at the scheduled times (day 7±1 and day 14±1 after adminis- tration). The mean (± standard deviation) PEG-ASNase activities determined were 911±311 U/L on day 7±1 and 527±200 U/L on day 14±1.
PEG-ASNase activities were significantly lower among patients with elevated anti-PEG IgG (MFI ≥8) or anti-PEG IgM (MFI ≥2) prior to their first dose of PEG-ASNase (P<0.05, Kruskal-Wallis one way analysis of variance on ranks, all pairwise multiple comparison procedures [Holm- Sidak method]). In addition, the PEG-ASNase activities decreased with increasing anti-PEG antibody levels prior to administration (Figure 3). To evaluate the effect of anti- PEG antibodies on PEG-ASNase activities in individual patients, mean PEG-ASNase activities were calculated for the respective day after administration and individual PEG- ASNase activities were categorized as above or below the respective means. Pre-existing anti-PEG IgG (MFI ≥8) as well as pre-existing anti-PEG IgM (MFI ≥2) increased the risk of PEG-ASNase activities below average (anti-PEG
IgG: odds ratio [OR]: 2.06, 95% confidence interval [95% CI]: 1.44-2.96; anti-PEG IgM: OR: 1.65; 95% CI: 1.27-2.15; P<0.001, χ2 test). No such associations were observed for anti-PEG IgG and IgM levels determined after PEG-ASNase administration. Pre-existing anti-PEG antibodies reduced but did not eliminate PEG-ASNase activities (Figure 3). Comparing the distribution of PEG-ASNase activities above and below 400 U/L, 100 U/L and the lower limit of quantitation (LLOQ = 5 U/L), significantly more samples with PEG-ASNase activities <400 U/L were found in patients with already existing anti-PEG antibodies (Table 2). No differences were observed for the distribution of PEG-ASNase activities above and below 100 U/L and the LLOQ (Table 2). Thus, silent inactivation of PEG-ASNase, which is defined by PEG-ASNase activities <100 U/L with- in 7±1 days and/or undetectable PEG-ASNase activities within 14±1 days after administration without signs of hypersensitivity reaction, was not affected by pre-existing anti-PEG antibodies.24,25 Anti-PEG antibodies did not inhibit the catalytic activity of PEG-ASNase and anti-PEG IgG and/or IgM had no effect on asparagine hydrolysis by PEG- ASNase (Online Supplementary Figure S4).
Anti-PEG antibodies prior to treatment with PEG-asparaginasese and hypersensitivity reactions to PEG-asparaginase
After initial exposure to PEG-ASNase, seven patients in ALL-cohort 1 (1.0%) showed hypersensitivity reactions (all Common Terminology Criteria for Adverse Events
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haematologica | 2022; 107(1)