HIV preferentially infects HIV-specific CD4+ T cells

HIV infection is associated with the progressive loss of CD4(+) T cells through their destruction or decreased production. A central, yet unresolved issue of HIV disease is the mechanism for this loss, and in particular whether HIV-specific CD4(+) T cells are preferentially affected. Here we show that HIV-specific memory CD4(+) T cells in infected individuals contain more HIV viral DNA than other memory CD4(+) T cells, at all stages of HIV disease. Additionally, following viral rebound during interruption of antiretroviral therapy, the frequency of HIV viral DNA in the HIV-specific pool of memory CD4(+) T cells increases to a greater extent than in memory CD4(+) T cells of other specificities. These findings show that HIV-specific CD4(+) T cells are preferentially infected by HIV in vivo. This provides a potential mechanism to explain the loss of HIV-specific CD4(+) T-cell responses, and consequently the loss of immunological control of HIV replication. Furthermore, the phenomenon of HIV specifically infecting the very cells that respond to it adds a cautionary note to the practice of structured therapy interruption.     

Tat-specific cytotoxic T lymphocytes select for SIV escape variants during resolution of primary viraemia

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections are characterized by early peaks of viraemia that decline as strong cellular immune responses develop. Although it has been shown that virus-specific CD8-positive cytotoxic T lymphocytes (CTLs) exert selective pressure during HIV and SIV infection, the data have been controversial. Here we show that Tat-specific CD8-positive T-lymphocyte responses select for new viral escape variants during the acute phase of infection. We sequenced the entire virus immediately after the acute phase, and found that amino-acid replacements accumulated primarily in Tat CTL epitopes. This implies that Tat-specific CTLs may be significantly involved in controlling wild-type virus replication, and suggests that responses against viral proteins that are expressed early during the viral life cycle might be attractive targets for HIV vaccine development.     

Eventual AIDS vaccine failure in a rhesus monkey by viral escape from cytotoxic T lymphocytes.

Potent virus-specific cytotoxic T lymphocyte (CTL) responses elicited by candidate AIDS vaccines have recently been shown to control viral replication and prevent clinical disease progression after pathogenic viral challenges in rhesus monkeys. Here we show that viral escape from CTL recognition can result in the eventual failure of this partial immune protection. Viral mutations that escape from CTL recognition have been previously described in humans infected with human immunodeficiency virus (HIV) and monkeys infected with simian immunodeficiency virus (SIV). In a cohort of rhesus monkeys that were vaccinated and subsequently infected with a pathogenic hybrid simian-human immunodeficiency virus (SHIV), the frequency of viral sequence mutations within CTL epitopes correlated with the level of viral replication. A single nucleotide mutation within an immunodominant Gag CTL epitope in an animal with undetectable plasma viral RNA resulted in viral escape from CTLs, a burst of viral replication, clinical disease progression, and death from AIDS-related complications. These data indicate that viral escape from CTL recognition may be a major limitation of the CTL-based AIDS vaccines that are likely to be administered to large human populations over the next several years.     

Direct evidence of extensive diversity of HIV-1 in Kinshasa by 1960

Human immunodeficiency virus type 1 (HIV-1) sequences that pre-date the recognition of AIDS are critical to defining the time of origin and the timescale of virus evolution. A viral sequence from 1959 (ZR59) is the oldest known HIV-1 infection. Other historically documented sequences, important calibration points to convert evolutionary distance into time, are lacking, however; ZR59 is the only one sampled before 1976. Here we report the amplification and characterization of viral sequences from a Bouin's-fixed paraffin-embedded lymph node biopsy specimen obtained in 1960 from an adult female in Léopoldville, Belgian Congo (now Kinshasa, Democratic Republic of the Congo (DRC)), and we use them to conduct the first comparative evolutionary genetic study of early pre-AIDS epidemic HIV-1 group M viruses. Phylogenetic analyses position this viral sequence (DRC60) closest to the ancestral node of subtype A (excluding A2). Relaxed molecular clock analyses incorporating DRC60 and ZR59 date the most recent common ancestor of the M group to near the beginning of the twentieth century. The sizeable genetic distance between DRC60 and ZR59 directly demonstrates that diversification of HIV-1 in west-central Africa occurred long before the recognized AIDS pandemic. The recovery of viral gene sequences from decades-old paraffin-embedded tissues opens the door to a detailed palaeovirological investigation of the evolutionary history of HIV-1 that is not accessible by other methods.