Performance of a redesigned HIV Selectest enzyme-linked immunosorbent assay optimized to minimize vaccine-induced seropositivity in HIV vaccine trial participants

Abstract

Vaccine-induced seropositivity (VISP) or seroreactivity (VISR), defined as the reaction of antibodies elicited by HIV vaccines with antigens used in HIV diagnostic immunoassays, can result in reactive assay results for vaccinated but uninfected individuals, with subsequent misclassification of their infection status. The eventual licensure of a vaccine will magnify this issue and calls for the development of mitigating solutions in advance. An immunoassay that discriminates between antibodies elicited by vaccine antigens and those elicited by infection has been developed to address this laboratory testing need. The HIV Selectest is based on consensus and clade-specific HIV peptides that are omitted in many HIV vaccine constructs. The assay was redesigned to enhance performance across worldwide clades and to simplify routine use via a standard kit format. The redesigned assay was evaluated with sera from vaccine trial participants, HIV-infected and uninfected individuals, and healthy controls. The HIV Selectest exhibited specificities of 99.5% with sera from uninfected recipients of 6 different HIV vaccines and 100% with sera from normal donors, while detecting HIV-1 infections, including intercurrent infections, with 95 to 100% sensitivity depending on the clade, with the highest sensitivities for clades A and C. HIV Selectest sensitivity decreased in very early seroconversion specimens, which possibly explains the slightly lower sensitivity observed for asymptomatic blood donors than for clinical HIV cases. Thus, the HIV Selectest provides a new laboratory tool for use in vaccine settings to distinguish the immune response to HIV vaccine antigens from that due to true infection.

FIG 1

HIV Selectest assay configuration. A mixture of 5 biotinylated peptides is immobilized, via a streptavidin bridge, to the wells of a 96-well biotin-coated microplate. Serum antibodies are detected with a human IgG-specific horseradish peroxidase (HRP) conjugate and a chromogenic substrate.

FIG 2

HIV Selectest signal/cutoff (S/CO) values for 671 HIV-1-infected individuals (A, ◊), 400 normal blood donors (B, □) and 1,183 uninfected HIV vaccine trial participants, including 778 vaccine recipients (C, △), 255 placebo recipients (D, ○), and 150 preimmune subjects (E, ☒). The cutoff value is indicated as a horizontal dashed line.

FIG 3

HIV Selectest signal/cutoff (S/CO) values versus infection recency in the clade C early-infection panel. The extremely early group (signal/cutoff values of <4) is to the left of the vertical line. The cutoff value is indicated by the horizontal dashed line.