Immunogenicity assessment of HPV16/18 vaccine using the glutathione S-transferase L1 multiplex serology assay

The glutathione S-transferase (GST)-L1 multiplex serology assay has favorable properties for use in clinical trials and epidemiologic studies, including low cost, high throughput capacity, and low serum volume requirement. Therefore, we evaluated the GST-L1 assay as a measure of HPV16/18 vaccine immunogenicity. Our study population included 65 women selected from the Costa Rica Vaccine Trial who received the bivalent HPV16/18 virus-like particle (VLP) vaccine at the recommended 0/1/6-month schedule. We tested replicate serum samples from months 0/1/12 (i.e., after 0/1/3 doses) by GST-L1 and 3 other commonly used serology assays, VLP-ELISA, SEAP-NA, and cLIA. We calculated the percentage of women seropositive by GST-L1 by time point and HPV type (14 HPV types), and compared GST-L1 to other assays using Spearman rank correlation coefficients. After 1 vaccine dose, seropositivity by GST-L1 was 40% each for HPV16 and HPV18, increasing to 100% and 98%, respectively, after 3 doses. Seropositivity after 3 doses ranged from 32% to 69% for HPV types 31/33/45, for which partial vaccine efficacy is reported, though increases also occurred for types with no evidence for cross-protection (e.g., HPV77). GST-L1 correlated best after 3 doses with VLP-ELISA (HPV16 and HPV18 each = 0.72) and SEAP-NA (HPV16 = 0.65, HPV18 = 0.71) (all P<0.001); correlation was lower with cLIA. The GST-L1 is suitable for evaluating HPV16/18 vaccine immunogenicity after 3 vaccine doses, although in contrast to other assays it may classify some samples as HPV16/18 seronegative. The assay's utility is limited for lower antibody levels such as after receipt of 1 dose.