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The Anti-CCR5 mAb004 Inhibits HIV-1 Replication Synergistically in Combination with Other Antiretroviral Agents but Does not Select for Resistance during in vitro Passage
Francoise Giguel*1, L Beebe2, T S Migone2, and D Kuritzkes1,3
1Massachusetts Gen Hosp, Harvard Med Sch, Boston, US; 2Human Genome Sci, Rockville, MD, US; and 3Brigham and Women's Hosp, Harvard Med Sch, Boston, MA, US
Background: CCR5mAb004
is a potent inhibitor of HIV-1 R5 isolates
in vitro. To determine the pattern and rate of emergence of resistance to
this antibody, R5 clinical isolates of HIV-1 were passaged
in human peripheral blood mononuclear cells (PBMC) in vitro in the presence drug for as long as 6 months.
Methods: We
passaged 2 R5 clinical isolates of HIV-1 (RM and JC)
in PMBC in the presence
of increasing concentrations of CCR5mAb004. Parallel cultures were maintained
in the absence of drug as a control. Isolates were passaged by subculturing
supernatants onto fresh cells every 4 to 7 days. Changes in HIV-1 susceptibility were monitored by comparing the IC50
values of the isolates passaged in the presence or
absence of the antibody.
Results: The
initial geometric mean IC50 for CCR5mAb004 was 0.055 mM for RM and 0.113 mM for JC. The IC50’s
of isolates passaged in the presence of antibody did
not differ significantly from the IC50 of viruses from control (no
drug) cultures at similar passage number. However, parallel increases in IC50
were observed for
control and drug-treated isolates over time, suggesting adaptation to
replication in vitro rather than drug selection. Passage of the JC isolate in
PBMC was halted after 19 to 20 weeks because of the emergence of syncytium-inducing viruses in the control cultures in the
absence of drug. Emergence of X4 virus was confirmed by inoculation onto
U87-CXCR4 cells. The RM patient isolate continued to week 24 (passage 33)
before there was suggestion of a tropism switch, again observed both in the
absence and presence of drug. Emergence of resistance is also being evaluated
in patient isolates in an R5 cell line.
Conclusions: The
inability to select HIV-1 variants with increased IC50 values after
in vitro passage in the presence of CCR5mAb004 for as long as 24 weeks suggests
that resistance requires multiple mutations and may be slow to emerge in vivo. Selection experiments using
cell lines lacking CXCR4 may avoid the problem of eventual emergence of X4
variants during prolonged in vitro
passage of R5 isolates on PBMC.
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