The humanized "BLT" mouse is
created by introducing human bone marrow, liver and thymus tissues into animals
without an immune system of their own. The BLT mouse has a fully functioning
human immune system. Credit: University of North Carolina School of Medicine
More than 15 percent of new HIV infections
occur in children. Without treatment, only 65 percent of HIV-infected children
will live until their first birthday, and fewer than half will make it to the
age of two. Although breastfeeding is attributed to a significant number of
these infections, most breastfed infants are not infected with HIV, despite
prolonged and repeated exposure.
HIV
researchers have been left with a conundrum: does breast milk transmit the
virus or protect against it?
New
research from the University of North Carolina School of Medicine explores this
paradox in a humanized mouse
model, demonstrating that breast milk has a strong virus killing effect and
protects against oral transmission of HIV.
"This
study provides significant insight into the amazing ability of breast milk to
destroy HIV and prevent its transmission," said J. Victor Garcia, PhD,
senior author on the study and professor of medicine in the UNC Center for Infectious Diseases and
the UNC Center for AIDS Research. "It also provides new leads for the
isolation of natural products that could be used to combat the virus."
Garcia
and colleagues pioneered the humanized "BLT" mouse model, which is
created by introducing human bone marrow, liver and thymus tissues into animals
without an immune system of their own. Humanized BLT mice have a fully
functioning human
immune system and can be infected with HIV in the same manner as
humans.
In the
study, the researchers first determined that the oral cavity and
upper digestive tract of BLT mice have the same cells that affect oral
transmission of HIV in humans and then successfully transmitted the virus to
the mice through these pathways. When the mice were given virus in whole breast
milk from HIV-negative women, however, the virus could not be transmitted.
"These
results are highly significant because they show that breast milk can
completely block oral transmission of both forms of HIV that are found in thebreast milk of
HIV-infected mothers: virus particles and virus-infected cells," said
Angela Wahl, PhD, a post-doctoral researcher in Garcia's lab and lead author on
the paper. "This refutes the 'Trojan horse' hypothesis which says that HIV
in cells is more stubborn against the body's own innate defenses than HIV in
virus particles."
Finally,
the researchers studied the effectiveness of pre-exposure prophylaxis (PrEP)
with antiretroviral medication for oral transmission of HIV. Garcia and his
team have previously shown that PrEP is effective against intravenous, vaginal
and rectal transmission
of HIV in humanized BLT mice. In this study, they gave the mice
antiretroviral drugs for seven days (3 days before and 4 days after exposing
them to the virus) and found 100 percent protection against virus transmission.
These
latest findings provide important leads to alternative treatments that could be
used to prevent transmission.
"No
child should ever be infected with HIV because it is breastfed. Breastfeeding
provides critical nutrition and protection from other infections, especially
where clean water for infant formula is scarce," Garcia said.
"Understanding how HIV is transmitted to infants and children despite the
protective effects of milk will help us close this important door to the spread
of AIDS."
The
study appears in the June 14, 2012 issue of the online journal PLoS
Pathogens.
Provided
by University
of North Carolina Health Care
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