Long Prime-Boost Interval and Heightened Anti-GD2 Antibody Response to Carbohydrate Cancer Vaccine

Abstract

The carbohydrate ganglioside GD2/GD3 cancer vaccine adjuvanted by β-glucan stimulates anti-GD2 IgG1 antibodies that strongly correlate with improved progression-free survival (PFS) and overall survival (OS) among patients with high-risk neuroblastoma. Thirty-two patients who relapsed on the vaccine (first enrollment) were re-treated on the same vaccine protocol (re-enrollment). Titers during the first enrollment peaked by week 32 at 751 ± 270 ng/mL, which plateaued despite vaccine boosts at 1.2-4.5 month intervals. After a median wash-out interval of 16.1 months from the last vaccine dose during the first enrollment to the first vaccine dose during re-enrollment, the anti-GD2 IgG1 antibody rose to a peak of 4066 ± 813 ng/mL by week 3 following re-enrollment (p < 0.0001 by the Wilcoxon matched-pairs signed-rank test). Yet, these peaks dropped sharply and continually despite repeated boosts at 1.2-4.5 month intervals, before leveling off by week 20 to the first enrollment peak levels. Despite higher antibody titers, patients experienced no pain or neuropathic side effects, which were typically associated with immunotherapy using monoclonal anti-GD2 antibodies. By the Kaplan-Meier method, PFS was estimated to be 51%, and OS was 81%. The association between IgG1 titer during re-enrollment and β-glucan receptor dectin-1 SNP rs3901533 was significant (p = 0.01). A longer prime-boost interval could significantly improve antibody responses in patients treated with ganglioside conjugate cancer vaccines.

Keywords: anti-GD2 IgG1 titer; beta-glucan; dectin-1 SNP rs3901533; ganglioside GD2/GD3 carbohydrate vaccine; high-risk neuroblastoma.

Figure 1

This was an open-label, single institutional phase I/II study of the GD2/GD3 vaccine in combination with oral β-glucan for high-risk neuroblastoma (clinicaltrials.gov NCT00911560). The vaccine treatment schema identified the prime and boost intervals, with a total of 7 injections spanning 52 weeks. Each subcutaneous vaccine injection consisted of 30 µg GD2 plus 30 µg GD3 conjugated to carrier protein KLH (keyhole limpet hemocyanin), mixed with 150 µg/m² OPT-821 (immunological saponin adjuvant). β-glucan (adjuvant) at 40 mg/kg/day was given orally starting from week 6, at a 2-week on and 2-week off schedule until the end of treatment or disease progression.

Figure 2

Thirty-two patients who were treated with the vaccine had relapsed. Upon achieving clinical remission, they were re-enrolled in the same vaccine protocol. Their anti-GD2 IgG1 titer was measured by ELISA and expressed as mean ± SEM. Using the Wilcoxon matched-pairs signed-rank test, a statistically significant difference was observed at week 1, week 3, week 8, and week 20 for these patients by comparing their antibody titers during their first vaccine therapy and their second vaccine therapy. *** p ≤ 0.002, **** p ≤ 0.0001.

Figure 3

Illustration of three representative patients who relapsed on first vaccine therapy, and they re-enrolled in the same vaccine therapy after achieving clinical remission. The anti-GD2 IgG1 titer was quantified for patients #1, #2, and #3 from their first injection at the first enrollment () to the last injection at re-enrollment (). The timing of prime and boost was indicated. Months from the last upfront vaccine to the first injection during re-enrollment were as follows: 16.6 m for patient #1, 13.4 m for patient #2, and 12.0 m for patient #3.

Figure 4

Relationship between the interval in months from the last upfront vaccine to the first injection during re-enrollment and the fold increase from the last titer in the first enrollment to the peak titer in the re-enrollment for individual patients. Two patients with no detectable antibody titer throughout their two vaccine treatments were excluded from this analysis.

Figure 5

Anti-KLH IgG1 titer among patients who relapsed on vaccine and re-enrolled in the same vaccine therapy after achieving clinical remission. Their anti-KLH IgG1 titer was measured by ELISA and expressed as a mean ± SEM. Using the Wilcoxon matched-pairs signed-rank test, a statistically significant difference was observed when comparisons were made between different time points. * p = 0.04, **** p ≤ 0.0001.

Figure 6

Association between antibody titer and SNP rs3901533 of dectin-1 (CLEC7A) polymorphism among 32 relapsed patients. The average antibody titer from week 8 after the initiation of β-glucan to the end of vaccine treatment or disease progression was tabulated for individual patients. Statistical analyses were performed using the Kruskal–Wallis test. First enrollment (p = 0.14); re-enrollment (p = 0.01).

Figure 7

Survival outcome after second vaccine therapy among 32 relapsed vaccine patients; progression-free survival (PFS) and overall survival (OS).