Envelope sequence variation, neutralizing antibodies, and primate lentivirus persistence

Area of Science:

• Virology
• Immunology
• Molecular Biology

Background:

• Chronic lentivirus infections, including ungulate lentiviruses and simian immunodeficiency virus (SIV), are characterized by the emergence of viral variants over time.
• Previous studies suggested the immune system, particularly humoral immunity, acts as a selective force, but lacked molecularly cloned viruses for definitive proof.

Purpose of the Study:

• To provide definitive evidence that neutralization-resistant variants emerge during persistent primate lentivirus infection.
• To investigate the evolution of viral envelope sequences and the emergence of neutralization resistance in SIV-infected rhesus monkeys.

Main Methods:

• Cloning viral envelope genes from rhesus monkeys over time and collecting sequential serum samples.
• Performing reciprocal neutralization studies using parental and variant-specific sera.
• Utilizing molecularly cloned virus of defined sequence to demonstrate immune selection.

Main Results:

• Persistent infection with SIV and HIV exerts selective pressure for changes in discrete variable regions of the viral envelope.
• The host's neutralizing antibody response is a key selective force, driving sequence variation and the emergence of neutralization escape mutants.
• Neutralization domains of HIV and SIV correlate with variable regions (V1-V6), suggesting a direct link between antibody targets and sequence evolution.

Conclusions:

• Neutralizing antibodies play a crucial role in limiting lentivirus replication during the asymptomatic phase of infection.
• Sequence variation in viral envelopes, particularly in variable regions, is driven by host immune responses, leading to the emergence of escape variants.
• While antibodies are a major selective force, other factors like tropism and T-cell responses may also contribute to sequence changes in specific viral domains.