In Heterosexuals, Transmitted HIV Strains Often Resemble Original Infecting Virus
Transmitted Strains May Have Evolutionary Advantage, NIH Scientists Suggest
September 20, 2012
A new study has found that even though HIV diversifies widely within infected individuals over time, the virus strains that ultimately are passed on through
heterosexual transmission often resemble the strain of virus that originally infected the transmitting partner. Learning the
characteristics of these preferentially transmitted HIV strains may help advance HIV prevention efforts, particularly with
regard to an HIV vaccine, according to the scientists who conducted the study. The research was led by Andrew D. Redd,
Ph.D., staff scientist, and Thomas C. Quinn, M.D., senior investigator, both in the Laboratory of Immunoregulation
of the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.
Dr. Redd and colleagues examined particular genetic sequences of HIV in blood samples collected between 1994 and 2002 from
hundreds of HIV-infected heterosexuals participating in the Rakai Community Cohort Study in Rakai District, Uganda. The scientists
found a significant increase in population-wide HIV genetic diversity among infected individuals during the 8-year period, yet
the amount of genetic change was significantly greater within individuals than across the population as a whole. To explain
this phenomenon, the scientists hypothesized that the genetic diversity of HIV at the population level was limited
because only certain strains of the virus within each person were responsible for subsequent sexual transmissions.
To test this hypothesis, the scientists examined the genetic relatedness of HIV strains in 31 couples where heterosexual
transmission occurred. Through three increasingly comprehensive analyses, they compared HIV strains in the transmitting partner at
points before and around the estimated time of HIV transmission with the strain in the newly infected partner around the time of
transmission. In 22 of the couples, or 71 percent of those studied, the virus strains in the blood of the newly infected
partner were more closely related to those found in the blood of the transmitting partner at the earliest available
time point than to strains present around the time of transmission. According to Dr. Redd, this finding
demonstrates that in the heterosexual transmission of HIV, the frequent natural selection of viral
strains from early in the infection of the transmitting partner reduces viral diversity at the population level.
Moreover, in four couples, the newly acquired strain was highly similar or identical to specific variants found in the
transmitting partner at both the earliest time point and the time of transmission. The scientists hypothesize that these highly
transmissible HIV strains from early infection were sustained in the blood at low levels or sequestered in certain cells for
transmission at a later time.
Related research by other scientists shows that HIV strains found in infected individuals during the early stages of
infection have diversified little from the strain that caused infection. Thus, the fact that these early HIV strains somehow are
maintained or persist at low levels for transmission later suggests they may have an evolutionary advantage at crossing the
genital barrier and causing infection, compared with HIV strains that predominate later in infection, according to Dr. Redd.
This research was co-funded by the NIAID Division of Intramural Research; NIAID grants numbers R01A134826, R01A134265
and R01AI077473; the World Bank STI Project; the Henry M. Jackson Foundation; the Fogarty Foundation; and the Bill and Melinda
Gates Institute for Population and Reproductive Health.
AD Redd et al. Previously transmitted HIV-1 viral strains are preferentially transmitted during subsequent sexual transmission. Journal
of Infectious Diseases DOI 10.1093/infdis/jis503 (2012).
Anthony S. Fauci, M.D., NIAID director and chief of the NIAID Laboratory of Immunoregulation; and Andrew D. Redd, Ph.D., staff scientist
in the NIAID Laboratory of Immunoregulation, are available for comment.
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NIAID conducts and supports research-at NIH, throughout the United States, and worldwide-to study the causes of infectious
and immune-mediated diseases, and to develop better means of preventing, diagnosing and treating these illnesses. News releases, fact
sheets and other NIAID-related materials are available on the NIAID Web site at www.niaid.nih.gov.
About the National Institutes of Health (NIH):
NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human
Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is
investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its
programs, visit www.nih.gov .
Source: NIH News
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