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VRC01 antibody delays but does not prevent HIV rebound after antiretroviral treatment interruption
Liz Highleyman, 2016-04-08 07:50:00
VRC01, a broadly neutralising antibody
targeting HIV's CD4 binding site, was able to modestly delay the return of
viral replication following interruption of antiretroviral therapy (ART), according
to a study presented at the recent Conference on Retroviruses and
Opportunistic Infections (CROI 2016) in Boston. VRC01 did not maintain viral
suppression on its own, but it may play a role in combination therapy for HIV
treatment or a functional cure.
Studies of antibodies for HIV prevention and
treatment have mostly been disappointing because the virus is highly variable.
The recent discovery of a number of broadly neutralising monoclonal antibodies,
or bNAbs, that can target multiple HIV strains has given new impetus to this
line of research. Antibodies for HIV prevention or treatment was the topic of a
plenary lecture by John Mascola as well as a talk at the
Community HIV Cure Research Workshop preceding CROI. (See this overview of those presentations.)
Katharine Bar of the University of
Pennsylvania and fellow investigators with the AIDS Clinical Trials Group A5340 team evaluated
whether one of the most promising bNAbs, known as VRC01, could delay or prevent
the return of HIV vireamia after ART interruption.
VRC01 attaches to the CD4 binding site of HIV's envelope protein,
preventing the virus from binding to the CD4 surface receptor that it uses to
gain entry to T-cells. The CD4 binding site is conserved, or consistent across HIV
strains, and VRC01 neutralises around 90% of diverse viral isolates from
multiple clades in laboratory studies.
This open-label study looked at the safety,
tolerability, pharmacokinetics and antiviral activity of VRC01 in HIV-positive
people with suppressed viral load (< 50 copies/ml) for more than six months
on an ART regimen containing a protease inhibitor or integrase inhibitor.
The study enrolled 14 participants. All were men, half were
American and the median age was 38 years. They had well-preserved
immune function with a median CD4 count of approximately 900 cells/mm3
and a CD nadir (lowest-ever level) above 200. They had been on ART for a median
of 4.7 years.
Participants received intravenous (IV) infusions of 40mg/kg VRC01 every three
weeks for three doses. They started a carefully monitored analytical treatment
interruption one week after the first infusion. ART was restarted if their
viral load rose to > 1000 copies/ml or their CD4 count fell below 350
cells/mm3. One patient stopped ART before the first VRC01 dose and
was excluded from the efficacy analysis.
VRC01 was generally safe and well-tolerated, with no grade 3 or 4
(severe) adverse events, nor any grade 2 (moderate) events considered related
VRC01 remained at adequate concentrations (> 50
mcg/ml) for eight
weeks after stopping ART.
Despite high antibody levels, a majority of participants experienced
rebound by week five of the treatment interruption. The remaining two
participants maintained viral suppression for eight and 11 weeks off ART before
rebounding. Participants re-established viral suppression after restarting ART.
However, viral rebound was delayed compared to the time it took for
virus to return in people who stopped non-NNRTI ART regimens in prior ACTG
studies. At four weeks after the treatment interruption, 38% of VRC01
recipients maintained viral suppression compared to 13% of historical control
subjects, a significant difference. At eight weeks, 8% of VRC01 recipients
still maintained viral suppression compared to 3% of historical controls, which
was no longer significant.
Time to viral rebound was not associated with VRC01 level, age, baseline
or nadir CD4 count, or duration of ART.
Genetic sequencing of rebounding virus suggested that in some cases
VRC01 restricted clonality (number of different strains) and in other cases it
selected for pre-existing VRC01-resistant variants in the viral reservoir.
"The passive immunization of VRC01 is safe and well tolerated, modestly delays
the return of viremia when compared to historical controls, but does not
maintain viral suppression in the majority of patients," the researchers