Oral Abstract Session 01 - Global HIV Vaccine Enterprise

POSTERS
Posters
Topic 3: B Cell Immunology and Antibody Functions
P03.03
V5 Region in the HIV-1 Envelope Glycoprotein
Determines Viral Sensitivity to the Broadly
Neutralizing Monoclonal Antibody VRC01
D. Guo 1 , X. Shi 2 , K. Arledge 3 , D. Song 4 , L. Jiang 3 , L. Fu 3 ,
S. Zhang 5 , X. Wang 5 , L. Zhang 3
1 Institute of Pathogen Biology,Chinese Academy of Medical
Sciences, Beijing, China; 2 Comprehensive HIV/AIDS Research
Center, Tsinghua University, Beijing, China; 3 Comprehensive
HIV/AIDS Research Center, Tsinghua University, Beijing, China;
4 China Agricultural University, Beijing, China; 5 School of
Medicine, Tsinghua University, Beijing, China
Background: VRC01, a broadly neutralizing monoclonal antibody
(bnmAbs), is capable of neutralizing a diverse array of HIV-1
isolates through recognition of the loop D and the V5 regions
within the CD4 binding site on envelope glycoprotein gp120.
Nonetheless, resistant strains have been identified. Here, we
examined two closely related envelope clones derived at a single
time point from a CRF08_BC infected patient which displayed an
over 20-fold difference in VRC01 neutralization sensitivity.
Methods: A total of 15 chimeric envelope clones were generated
by interchanging the loop D and/or V5 regions between the
original envelopes or by single alanine substitutions within each
region. The resultant effects on VRC01 neutralization sensitivity
were subsequently studied in the context of pseudotyped viruses.
Results: Our results showed that interchanging the V5 region
between the two clones completely swapped their neutralization
sensitivity profiles, while exchanging the loop D region alone
had minimal impact. Mutagenesis analysis revealed that the
potential N-linked glycosylation site (PNGS) at position 460 in
the V5 region contributed to over 90% of observed resistance,
while other amino acid changes made no discernible differences.
Furthermore, changes in resistance were found to positively
correlate with VRC01 binding activity to the corresponding
envelope glycoprotein. None of the substitutions, however,
significantly altered binding and neutralization sensitivity to
bnmAb b12 or soluble CD4. Of note, a mutation that removed
the PNGS at position 463 in the V5 region increased resistance
to ibalizumab, a non-immunosuppressive monoclonal antibody
that binds CD4 and has been shown to inhibit entry of diverse
HIV-1 isolates.
Conclusion: In summary, our data indicates that amino acid
residues in the V5 region play a critical role in determining viral
sensitivity to VRC01. Increased length, glycosylation and long
side-chain of amino acids in the V5 region may collectively create
steric hindrance that lowers binding affinity, thereby increasing
resistance to VRC01 neutralization.
118
AIDS Vaccine 2012
P03.04
Comprehensive Mapping of SIVmac239 Envelope
Antigenic Determinants Recognized by Specific
Polyclonal Antibodies in Vaccinated and/or Infected
Macaques
J. Guo 1 , T. Zuo 2 , L. Zhang 2 , Z. Chen 1
1 AIDS Institute, LKS Faculty of Medicine, The University of
Hong Kong, Hong Kong, China; 2 AIDS Research Center, School
of Medicine, Tsinghua University, Beijing, China
Background: The RV144 trial has demonstrated a modest level
of protection against HIV infection, which was partially related
to binding antibodies targeting V2 loop. Along with several
broad HIV-neutralizing antibodies identified recently, it is of
great importance to understand the major differences between
vaccination and infection in eliciting humoral immune responses.
Methods: We adopted a robust mapping technique for a
quantitative measurement of antigenic determinants of entire
SIVmac239 envelope glycoprotein displayed on the surface of
the yeast as a combinatorial antigen library. Positive yeast clones
recognized by the immunized and/or infected serum were
identified and obtained by FACS followed by sequencing and
structural analysis.
Results: The finding of reactive determinants ranges from
30 to 240 amino acids, which allows some conformational
determinants being evaluated as a major technical improvement.
The antigen profile of the two types of vaccine-induced sera
before viral challenge shared two dominant domains that
concentrated at the V1V2 stem of gp120 and the ecto-domain of
gp41. Interestingly, using a FACS-based antibody binding assay,
there were no significant differences of titer and MFI of anti-
V1V2 antibodies between the two vaccination groups, suggested
a minimal role of these antibodies in controlling viral replication
post SIVmac239 challenge. A major distinct domain, however,
was identified near the V3 loop and the main CD4 binding region
which was significantly recognized by the immune serum of
the effective vaccination regimen but not of the non-effective
vaccination regimen or natural SIV infection. Unexpectedly, the
anti-V1/V2 antibody responses were shifted to the ecto-gp41
region when infected macaques developed AIDS.
Conclusion: We present a comprehensive analysis of antigenic
determinants recognized by specific antibody responses
generated by vaccination and/or SIVmac239 infection. Our
findings have significant implications to help understanding the
humoral immunity against neutralization-resistant SIVmac239
infection and simian AIDS, and to guide rational vaccine
immunogen identification and design.