Oral Abstract Session 01 - Global HIV Vaccine Enterprise

Topic 5: HIV Transmission and Viral Diversity
P05.03
Low Selection Rate of HLA-Anchor Escape Mutations
in HIV After Transmission of Subtype B and
Recombinants BF Strains Patients from Argentina
G. Damilano 1 , E. Socias 2 , C. Magneres 2 , G. Turk 1 , M. Gomez-
Carrillo 1 , H. Salomon 1 , D. Dilernia 1
1 Argentinean Reference Center for AIDS, Buenos Aires,
Argentina; 2 HUESPED Foundation, Buenos Aires, Argentina
Background: The immune response of HIV-infected individuals
shapes the evolution of the virus by selecting escape mutation.
After transmission to a new host, the HLA-mediated immune
pressure changes. The objective of our study was to characterize
the dynamics of HLA-anchor escape mutations after transmission.
Methods: We studied 6 transmission events between members
of serodiscordant couples collecting blood samples from the
donor and the previously seronegative-partner at the moment
of seroconversion, and a second sample at least 6 months postinfection.
HLA-I typing was performed by the SSOP-PCR method.
The viral gene gag was amplified by RT-PCR and cloned into the
pGEM-T vector for viral quasiespecies analysis. Transmitted
strain was identified by phylogenetic analysis. Escape mutation
was defined as viral polimorphisms located in HLA-anchor
position that eliminate an epitope predicted by the NetMHC (CBS
Prediction Server). Significant variations in the number of escape
mutations were assessed by Poisson´s probability distribution.
Results: Of the total epitopes available in transmitted gag for
recognition by the recipient HLA alleles, a mean 7.25% of them
selected escape mutations by the moment of the second sample
collection in an anchor position of the epítope. Of the total of HLAanchor
escape mutations present in the second sample and absent
in the subtype consensus, a mean 79,8% were already present in
the first sample of the recipient and in the sample of the donors.
Also, the majority (84%) of the escape mutations to the donor’s
HLA alleles persisted in time after transmission without reversion,
even in the absence of the selecting HLA allele.
Conclusion: The low rate of newly selected escape mutations
could be due in part to lack of immune pressure, but considering
the high rate of transmission and persistence, our results suggest
a high level of viral adaptation to the HLA system in subtype B
and recombinants BF circulating in Argentina.
P05.04
AIDS Vaccine 2012
Posters
The Efficiency of Bridging Sheet Recruitment
Determines HIV-1 R5 Envelope Sensitivity to Soluble
CD4 and Macrophage Tropism
O. O’Connell 6 , A. Repik 6 , J.D. Reeves 1 , M.P. Gonzalez-Perez 6 ,
B. Quitadamo 6 , M. Duenas-Decamp 6 , P. Peters 6 , R. Lin 2 ,
E.D. Anton 1 , S. Zolla-Pazner 3 , D. Corti 4 , A. Wallace 6 , S. Wang 6 ,
X. Kong 5 , S. Lu 6 , P.R. Clapham 6
1 Monogram Biosciences, San Francisco, CA, USA; 2 University
of Massachusetts, Amherst, MA, USA; 3 New York University
Langone School of Medicine, New York, NY, USA; 4 Humabs
Biomed SA, Bellinzona, Switzerland; 5 New York University
School of Medicine, New York, NY, USA; 6 University of
Massachusetts Medical School, Worcester, MA, USA
Background: HIV-1 R5 viruses vary extensively in their capacity
to infect macrophages. R5 viruses that confer efficient infection
of macrophages are able to exploit low levels of CD4 for infection
and they predominate in brain tissue where macrophages are a
major target for infection. HIV-1 R5 variants that are transmitted
are generally non-macrophage-tropic. Here, we investigated the
sensitivity of macrophage-tropic and non-macrophage-tropic R5
envelopes to neutralizing antibodies.
Methods: Env+ pseudovirion neutralization assays were carried
out using HeLa TZM-bl cells. Envelope capture ELISAs assessed
monoclonal antibody binding to monomeric gp120.
Results: We observed striking differences in the sensitivity of
Env+ pseudovirions to soluble CD4 compared to neutralizing
monoclonal antibodies that target the CD4 binding site.
Macrophage-tropic R5 envelopes were sensitive to sCD4, while
non-macrophage-tropic envelopes were significantly more
resistant. In contrast, all envelopes were sensitive to VRC01
regardless of tropism, while mab b12 conferred an intermediate
neutralization pattern with all the macrophage-tropic and about
half of the non-macrophage-tropic envelopes sensitive.
Conclusion: CD4, b12 and VRC01 share binding specificities on the
outer domain of gp120. However, these reagents differ in their
ability to induce conformational changes on the trimeric envelope
and in specificity for residues on the V1V2 loop stem and β20-21
junction that are targets for CD4 in recruiting the bridging sheet.
These different binding specificities of CD4, b12 and VRC01 likely
explain the striking differences in envelope sensitivity to inhibition
by these reagents. However, they also provide an insight into the
envelope mechanisms that control macrophage-tropism. We
present a model where the efficiency of bridging sheet recruitment
by CD4 is a major determinant of HIV-1 R5 envelope sensitivity to
soluble CD4 and macrophage tropism.
165
POSTERS