Chronic HIV-1 Infection Frequently Fails to Protect against Superinfection

Abstract

Reports of HIV-1 superinfection (re-infection) have demonstrated that the immune response generated against one strain of HIV-1 does not always protect against other strains. However, studies to determine the incidence of HIV-1 superinfection have yielded conflicting results. Furthermore, few studies have attempted to identify superinfection cases occurring more than a year after initial infection, a time when HIV-1-specific immune responses would be most likely to have developed. We screened a cohort of high-risk Kenyan women for HIV-1 superinfection by comparing partial gag and envelope sequences over a 5-y period beginning at primary infection. Among 36 individuals, we detected seven cases of superinfection, including cases in which both viruses belonged to the same HIV-1 subtype, subtype A. In five of these cases, the superinfecting strain was detected in only one of the two genome regions examined, suggesting that recombination frequently occurs following HIV-1 superinfection. In addition, we found that superinfection occurred throughout the course of the first infection: during acute infection in two cases, between 1–2 y after infection in three cases, and as late as 5 y after infection in two cases. Our results indicate that superinfection commonly occurs after the immune response against the initial infection has had time to develop and mature. Implications from HIV-1 superinfection cases, in which natural re-exposure leads to re-infection, will need to be considered in developing strategies for eliciting protective immunity to HIV-1. Superinfection with HIV-1 occurs when an individual infected with one strain of HIV-1 acquires a second strain, from a different partner. There are more than 20 published cases of HIV-1 superinfection. These cases have raised concerns for HIV-1 vaccine design because they indicate that the immune response generated against natural infection is not always sufficient to protect against later exposures to the virus. However, it remains unclear how often HIV-1 superinfection occurs, especially at times in infection after an immune response would be expected. We investigated the incidence of HIV-1 superinfection in a cohort of 36 high-risk women followed for approximately five years after their first HIV-1 infections. We found seven cases of HIV-1 superinfection. Five cases occurred more than a year after the initial infection, a time when the immune response would have had time to develop and broaden. In three cases, the initial and superinfecting viruses were classified as the same HIV-1 genetic subtype, indicating a lack of protection against closely related viruses. Our results suggest that natural HIV-1 infection does not always elicit a protective immune response, an important consideration in developing strategies for HIV-1 vaccine design and testing.