Identification of diverse HIV type 1 subtypes and dual HIV type 1 infection in pregnant Ugandan women

Vertical (mother-to-child) transmission accounts for the majority of pediatric HIV-1 infections. Many factors are involved in vertical transmission, however it is not clear which factors are most important for determining whether a mother will transmit HIV-1 to her infant. It has been suggested that HIV-1 subtype may influence vertical transmission and that subtype D viruses may be less likely to be transmitted in this setting. We analyzed HIV-1 gp120 V3 region sequences from the plasma of 20 pregnant Ugandan women of known transmission status who did not receive antiretroviral prophylaxis. V3 regions were cloned, sequenced, and subtyped by phylogenetic analysis. Among 11 women who transmitted HIV-1 to their infants, we detected subtypes A, C, D, and G. Two of the transmitters had dual infection with subtypes A and D. In addition, a third was infected with two distinct strains of subtype G viruses. HIV-1 subtype A and D viruses were found in 9 women who did not transmit the virus to their infants. This study reveals that pregnant Ugandan women harbor diverse HIV-1 subtypes, including women who transmit HIV-1 to their infants. Transmission of HIV-1 with subtype D V3 regions was confirmed in 4 of the 11 transmitters, including 2 who had dual infection with subtype A and D HIV-1.

Improved detection of human immunodeficiency virus type 1 variants by analysis of replicate amplification reactions: relevance to studies of human immunodeficiency virus type 1 vertical transmission

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1)-infected individuals typically harbor mixtures of HIV-1 variants. For HIV-1 transmission studies, methods used for genotypic analysis should reliably detect variant mixtures. Such studies typically analyze complementary DNAs (cDNAs) from a single polymerase chain reaction (PCR) amplification. This approach may fail to detect variant mixtures in some samples because of analytic bias.

METHODS

To evaluate the impact of analytic bias on the detection of HIV-1 variants, we analyzed samples from a mother and infant known to contain both subtypes A and D HIV-1. The env third variable region of HIV-1 gp120 (V3 region) was amplified and cloned in five replicate experiments using a single plasma sample from each individual. Ten cDNAs from each experiment were analyzed.

RESULTS

The subtype mixture was detected in only four of 10 amplification experiments (three of five for the mother and one of five for the infant). Sequencing of uncloned PCR products showed that a single subtype, either A or D, was preferentially amplified in each experiment. However, the subtype mixture was detected for each sample by analyzing the five replicate experiments as a group.

CONCLUSIONS

This shows that mixtures of HIV-1 variants may be more readily detected when replicate amplification reactions are analyzed. This approach may be useful for characterizing HIV-1 variants for studies of HIV-1 transmission.

The amino acid following an asn-X-Ser/Thr sequon is an important determinant of N-linked core glycosylation efficiency

Many eukaryotic proteins are modified by Asn-linked (N-linked) glycosylation. The number and position of oligosaccharides added to a protein by the enzyme oligosaccharyltransferase can influence its expression and function. N-Linked glycosylation usually occurs at Asn residues in Asn-X-Ser/Thr sequons where X not equal Pro. However, many Asn-X-Ser/Thr sequons are not glycosylated or are glycosylated inefficiently. Inefficient glycosylation at one or more Asn-X-Ser/Thr sequons in a protein results in the production of heterogeneous glycoprotein products. These glycoforms may differ from one another in their level of expression, stability, antigenicity, or function. The signals which control the efficiency of N-linked glycosylation at individual Asn residues have not been fully defined. In this report, we use a site-directed mutagenesis approach to investigate the influence of the amino acid at the position following a sequon (the Y position, Asn-X-Ser/Thr-Y). Variants of rabies virus glycoprotein containing a single Asn-X-Ser/Thr sequon at Asn37 were generated. Variants were designed with each of the twenty common amino acids at the Y position, with either Ser or Thr at the hydroxy (Ser/Thr) position. The core glycosylation efficiency of each variant was quantified using a cell-free translation/glycosylation system. These studies reveal that the amino acid at the Y position is an important determinant of core glycosylation efficiency.