Role of maternal autologous neutralizing antibody in selective perinatal transmission of human immunodeficiency virus type 1 escape variants

Abstract

Perinatal human immunodeficiency virus type 1 (HIV-1) transmission is characterized by acquisition of a homogeneous viral quasispecies, yet the selective factors responsible for this genetic bottleneck are unclear. We examined the role of maternal autologous neutralizing antibody (aNAB) in selective transmission of HIV-1 escape variants to infants. Maternal sera from 38 infected mothers at the time of delivery were assayed for autologous neutralizing antibody activity against maternal time-of-delivery HIV-1 isolates in vitro. Maternal sera were also tested for cross-neutralization of infected-infant-first-positive-time-point viral isolates. Heteroduplex and DNA sequence analyses were then performed to identify the initial infecting virus as a neutralization-sensitive or escape HIV-1 variant. In utero transmitters (n = 14) were significantly less likely to have aNAB to their own HIV-1 strains at delivery than nontransmitting mothers (n = 17, 14.3% versus 76.5%, P = 0.003). Cross-neutralization assays of infected-infant-first-positive-time-point HIV-1 isolates indicated that while 14/21 HIV-1-infected infant first positive time point isolates were resistant to their own mother's aNAB, no infant isolate was inherently resistant to antibody neutralization by all sera tested. Furthermore, both heteroduplex (n = 21) and phylogenetic (n = 9) analyses showed that selective perinatal transmission and/or outgrowth of maternal autologous neutralization escape HIV-1 variants occurs in utero and intrapartum. These data indicate that maternal autologous neutralizing antibody can exert powerful protective and selective effects in perinatal HIV-1 transmission and therefore has important implications for vaccine development.

FIG. 1.

Maternal HIV-1 neutralizing antibody titer at delivery. Maternal neutralizing antibody titer to autologous virus from the time of delivery (A) and maternal neutralizing antibody to the mother's infant's first-positive-time-point HIV-1 isolate (B) are shown. □, Mothers treated with ZDV.

FIG. 2.

Heteroduplex mobility analysis of maternal HIV-1 env gene diversity. ΦX, DNA molecular weight markers. SS, single-stranded DNA. PB, maternal PBMC derived viral DNA PCR products; CC, maternal PBMC coculture cell-derived DNA PCR products; NE, maternal neutralization assay cell-derived DNA PCR products. The size (in base pairs) of the molecular weight markers is located to the right of the gel. IU, in utero transmitter; IP, intrapartum transmitter; NT, nontransmitter. CD4, maternal CD4 cell count. aNAB values are 50% neutralizing titers.

FIG. 3.

Heteroduplex comparison analysis of maternal neutralization escape and infant PBMC HIV-1 DNA. SS, single-stranded DNA. MNE, maternal aNAB escape; MPB, maternal PBMC-derived HIV-1 DNA PCR products; IPB, infant PBMC-derived HIV-1 DNA PCR products. (a) MB pair 10, aNAB < 10; (b) MB pair 4, aNAB < 10; (c) MB pair 8, aNAB = 40; (d) MB pair 11, aNAB = 640; (e) MB pair 14, aNAB < 10; (f) MB pair 16, aNAB = 160. MNEP, maternal neutralization escape probe; M+NE, maternal PBMC HIV-1 DNA mixed with maternal NE probe; I+NE, infant PBMC HIV-1 DNA mixed with maternal NE probe.

FIG. 4.

Maximum likelihood trees. Nucleotide sequences from maternal time-of-delivery PBMC (blue), maternal time-of-delivery aNAB culture cells (red), and infant first-positive-time-point PBMC (green). Horizontal branch lengths are drawn to scale, with the black bar representing 10% divergence. IU, in utero; IP, intrapartum.

FIG. 5.

Consensus protein alignment of HIV-1 gp120 V3 to V5 env gene regions. Shown is a comparison of regions V3 through V5 of a subtype B consensus sequence (top) and consensus sequences for mother time-of-delivery PBMC (MPBMC), mother neutralization escape (MNE), and infant first-positive-time-point PBMC (BPBL) for each of the nine MB pairs analyzed. Dashes indicate conserved residues relative to the subtype B consensus; dots indicate deleted residues; substitutions are indicated by the amino acid letter. ConB, clade B consensus sequence.