Oral Abstract Session 01 - Global HIV Vaccine Enterprise

POSTERS
Posters
Topic 3: B Cell Immunology and Antibody Functions
P03.31
Structural Comparison of Somatically Related PG9
and PG16 in Complex with Their Epitope Reveals
Differences in Glycan Recognition
M. Pancera 1 , J.S. McLellan 1 , S. Shahzad-ul-Hussan 1 , N. Doria-
Rose 1 , B. Zhang 1 , Y. Yang 1 , D.R. Burton 1 , W.C. Koff 1 , C.A.
Bewley 1 , P.D. Kwong 1
1 NIH/NIAID/VRC, Bethesda, MD, USA
Background: The somatically related antibodies, PG9 and PG16,
neutralize 70-80% of HIV-1 isolates and bind a glycosylated
epitope in the V1/V2 domain of HIV-1 gp120. Mutations in
V1/V2, and sometimes V3 depending on the HIV-1 strain,
affect neutralization and a glycan on Asn160 is required for
neutralization. Both antibodies also preferentially bind the native
trimer over monomeric gp120, especially PG16. The structure of
PG9 in complex with its epitope, a scaffolded V1/V2 from HIV-1
strain ZM109, was recently solved and showed that PG9 targets a
site of vulnerability comprising 2 glycans and a β-strand.
Methods: To understand the differences in binding properties
from these two somatically related antibodies, we first assessed
their binding to monomeric gp120 and scaffolded V1/V2 proteins
with different glycan types (oligomannose, hybrid, and complex).
In order for PG16 to bind the scaffolded V1/V2, the protein had to
be expressed in mammalian cells in the presence of swainsonine,
which inhibits glycan maturation past the hybrid state. A stable
complex could be obtained between PG16 and a scaffolded V1/
V2 domain from ZM109, and this complex was crystallized.
Results: Although the structure of PG16 bound to scaffolded V1/
V2 resembled that of PG9, some differences were seen: 1) PG16
binding to the β-strand is weaker than PG9 with fewer charged
interactions, 2) PG16 interacts with a hybrid glycan at position
N173. The difference in binding recognition of PG9 and PG16
to monomeric gp120 depends on the type of glycans present.
PG16 binds the protein portion of V1/V2 weaker than PG9 and
this might explain the higher affinity of PG9 for the monomer.
PG16 has evolved a second glycan site to compensate for weaker
peptide interaction.
Conclusion: The results show the importance of polyclonal
response in infected individual to combat HIV-1, and in this case,
to differential glycosylation.
132
AIDS Vaccine 2012
P03.32
Neutralizing and Non-Neutralizing Antibody
Responses in HIV-1 Subtype C Chronically Infected
Patients with Divergent Rates of Disease Progression
D. Archary 1 , R. Rong 2 , M.L. Gordon 1 , S. Boliar 3 , E.S. Gray 4 ,
A. Dugast 5 , T. Hermanus 6 , P.J. Goulder 7 , H.M. Coovadia 8 ,
L. Morris 6 , G. Alter 5 , C.A. Derdeyn 3 , T. Ndung’u 1
1 University of KwaZulu-Natal, Durban, South Africa; 2 Jiaotong-
Liverpool University, Suzhou, China, China; 3 Emory University,
Atlanta, GA, USA; 4 University of Western Australia, Australia;
5 Ragon Institute, Boston, MA, USA; 6 National Institute for
Communicable Diseases, Johannesburg, South Africa; 7 Oxford
University, United Kingdom (Great Britain); 8 University of
KwaZulu Natal, Durban, South Africa
Background: Development of an efficacious HIV-1 vaccine able
to elicit the production of broadly neutralizing antibodies (nAbs),
capable of retaining potent activity against a diverse panel of viral
isolates remains a significant challenge. The evolutionary forces
that shape envelope and ensuing nAb and non-neutralizing
antibodies in HIV-1 subtype C are incompletely understood and
these two parameters have been rarely studied concurrently.
Methods: We characterized patterns of virus-specific nAbs
and non-neutralizing antibodies in four slow progressors and
four progressors with chronic HIV-1 subtype C infection, over
a median of 21 months. Single cycle neutralization assays was
performed. In addition, the binding affinities of HIV-specific
immunoglobulins (IgGs) and the affinities of the IgGs to various
Fcγ receptors (FcγRs) were assessed.
Results: NAbs evolved significantly in progressors (p=0.003) from
study entry to study exit. NAb IC50 titers significantly correlated
with amino acid lengths for V1-V2 (p=0.04), C3-V5 (p=0.03) and
V1-V5 (p=0.04). Both groups displayed preferential heterologous
activity against the subtype C panel. Both groups displayed
preferential heterologous activity against the subtype C panel.
There were no significant differences in breadth of responses
between the groups for either subtype A or C. Neutralization
breadth and titers to subtype B reference strains was significantly
higher in progressors compared to slow progressors (both
p