Improved performance of seroconversion with a 4th generation HIV Antigen/Antibody assay

https://doi.org/10.1016/S0166-0934(99)00086-5Get rights and content

Abstract

Recently a new fourth generation microELISA for large scale blood screening has been described in which HIV p24 Ag detection was integrated in an anti-HIV-1/-2 and anti-HIV-1 group O assay based on a direct assay format: (Vironostika HIV Uni-Form II Ag/Ab (Van Binsbergen et al., (1998)). When compared to the third generation a-HIV assay (Vironostika HIV Uni-Form II plus O), the seroconversion window was narrowed with more than one week. A more precise window estimation based on seroconversion series with short sampling time intervals of up to 7 days, is described in parallel with that for the single HIV p24 Ag assay. It was found with 10 relevant seroconversion series that the HIV p24 Ag assay closes the seroconversion window with 6.2 days as compared to the 3rd generation a-HIV assay, while a window reduction of 4 days was found with Vironostika HIV Uni-Form II Ag/Ab. These seroconversion data show that with the new assay two-thirds of the current p24 Ag window is closed. There was no statistical difference in seroconversion sensitivity between the HIV p24 Ag and the new assay format. An extended evaluation of the new assay with subtype HIV-1 M and group O p24 Ag strains and with anti-HIV antibodies obtained from individuals infected with different HIV-1 subtypes showed that all subtypes of HIV-1 M and HIV-1 group O p24 antigen were detected as well as of HIV antibody.

Introduction

Recently, as the follow up of third generation anti-HIV assay sensitivity, the fourth generation of direct HIV large scale screening assays was introduced in which HIV p24 Ag detection is combined with anti-HIV-1/-2 and anti-HIV-1 group O detection, (Gürtler et al., 1998, Van Binsbergen et al., 1998, Weber et al., 1998). In one of these new screening assays, Vironostika HIV Uni-Form II Ag/Ab, native HIV-1 gp160 (HIV-1 CDC4, subtype B) is used for the detection of anti-HIV-1 M antibodies, in combination with HIV-1 group O gp41 (HIV-1 group O ANT70) and HIV-2 gp36 (HIV-2 ROD) peptides, derived from the immunodominant region, for the detection of anti-HIV-1 group O and anti-HIV-2, respectively. For the implementation of p24 Ag detection, two anti-p24 mouse monoclonal antibodies were selected providing the highest analytical p24 Ag sensitivity. This assay concept will improve further the safety of blood transfusion, particularly in highly endemic regions in Asia and Africa (Van Binsbergen et al., 1998).

Just as in the 3rd generation assays, the 4th generation assay microELISA Vironostika HIV Uni-Form II Ag/Ab is a direct sandwich assay combining user- friendliness (total assay time is 90 min, conjugate present in the well as lyophilised sphere) with control on pipetting steps by clearly visible and spectrophotometrically measurable color changes.

The advantage of HIV Ag detection has been demonstrated in early seroconversion. Compared with the 3rd generation Vironostika HIV Uni-Form II plus O (Van Binsbergen et al., 1996, Van Binsbergen et al., 1997), the window period between infection and the first anti-HIV antibody response is narrowed with about 1 week with the Vironostika HIV Uni-Form II Ag/Ab, without compromising anti-HIV sensitivity (Van Binsbergen et al., 1998).

This report describes a further evaluation of Vironostika HIV Uni-Form II Ag/Ab focussing on seroconversion series containing samples obtained with short sampling intervals to give a realistic view on the extent of narrowing the seroconversion window, and to extensively analyse HIV p24 Ag and anti-HIV-1 antibody subtype sensitivity.

Section snippets

Sample panels

The worldwide HIV-1 Performance panel (WWRB301) was obtained from Boston Biomedica Inc. (BBI), West Bridgewater, MA. It contains HIV-1 samples which were subtyped by their reactivity with tests that use gp120 V3 loop peptide sequences from various subtypes (group M subtypes A through F and Group O) as antigen (Centers for Disease Control, CDC, HIV Branch, Atlanta, GA) (Schable et al., 1994) and which were genotyped by the Heteroduplex Mobility Assay, HMA (Delwart et al., 1993).

HIV

Anti-HIV-1 and HIV-1 p24 Ag subtypes

To ensure maximum safety of blood supply for transfusion, the current 3rd generation a-HIV assays are designed to detect all currently known HIV-1 subtypes with the highest sensitivity. An evaluation of subtyped anti-HIV-1 group M, group O and anti-HIV-2 positive samples was carried out with the Vironostika HIV Uni-Form II plus O showing detection of all subtypes (Van Binsbergen et al., 1997). In the successor of this assay, the 4th generation Vironostika HIV Uni-Form II Ag/Ab, the major

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