Oral Abstract Session 01 - Global HIV Vaccine Enterprise

Topic 12: Vaccine Concepts and Design
P12.33
Immunogenic Selection of HIV-1 MPER Epitopes for
Improved Vaccine Design
L. Wieczorek 1 , M. Rao 2 , K. Peachman 1 , N. Steers 1 , M. Marovich 2 ,
N. Michael 2 , V. Polonis 2 , V. Rao 3
1 Henry M. Jackson Foundation, Silver Spring, MD, USA; 2 Walter
Reed Army Institute of Research, Silver Spring, MD, USA;
3 Catholic University of America, Washington, DC, USA
Background: The goal of this study was to design structural
mimics of HIV-1 epitopes that have the potential to induce
broadly neutralizing antibodies (bnAbs). The structure of the
gp41 membrane proximal external region (MPER), targeted
by three bnAbs, requires further definition. Experiments were
designed to select epitopes with enhanced binding to MPER
bnAbs, to identify neutralization-competent MPER structures,
and to determine if selected MPER epitopes can broaden the
immune response as potential vaccines.
Methods: MPER epitopes were selected by biopanning with
phage-displayed peptide libraries against bnAbs 4E10, 2F5 and
Z13. Epitopes were screened in competition binding assays
where M13-displayed epitopes competed with envelope
peptides or infectious HIV-1 for antibody binding. In vivo
response to MPER was assessed by M13 immunoprecipitation
and neutralization competition assays using HIV-positive
plasma, and immunogenicity of select epitopes was assessed
in BALB/c mice.
Results: Forty-six unique 4E10 epitopes were identified,
representing both MPER homologous and non-homologous
sequences. Fourteen epitopes, capable of competing with MPER
peptide and HIV-1 for 4E10 binding, bound HIV-positive IgG. Of
these, five epitopes absorbed MPER-specific neutralizing activity
in HIV-positive patient plasma. Mouse immunization with the
selected neutralization-competent MPER epitopes elicited HIV-1
specific cellular and humoral immune responses and boosted the
neutralizing activity of a gp145 Env subunit vaccine.
Conclusion: This study demonstrates the diversity of epitope
recognition by 4E10 and the unique response to MPER in vivo.
The M13-displayed, neutralization-competent structures of
the 4E10 epitopes have the potential to elicit and boost HIV-
1 neutralizing antibody production in mice. Phage-displayed
epitopes can rapidly and inexpensively be selected to provide
epitope-specific depth and variation to HIV-1 vaccine designs
without requiring modification to major vaccine components.
P12.34
AIDS Vaccine 2012
Posters
Antigenicity and Immunogenicity of a Novel, Acute
HIV-1 Tanzanian Subtype C gp145 Envelope Protein
for Clinical Development
V. Polonis 1 , L. Wieczorek 2 , V. Kalyanaraman 3 , G. Matyas 1 ,
S. Whitney 3 , C. Williams 4 , S. Tovanabutra 2 , E. Sanders-Buell 2 ,
M. Wesberry 2 , C. Ochsenbauer 5 , A. Chenine 2 , M. Rao 1 , T. Tong 2 ,
C. Alving 1 , H. Cheng 6 , S. Zolla-Pazner 4 , N. Michael 1 , T. VanCott 3 ,
M. Marovich 1
1 Walter Reed Institute of Research, DIV Retrovirology, Silver
Spring, MD, USA; 2 Henry M. Jackson Foundation, Silver Spring,
MD, USA; 3 Advanced Biosciences Laboratories, Inc, Rockville,
MD, USA; 4 New York University School of Medicine, New
York, NY, USA; 5 University of Alabama, Birmingham, AL, USA;
6 University of California, Davis, CA, USA
Background: Eliciting broadly reactive neutralizing antibodies
remains a challenge in HIV-1 vaccine development, complicated
by variations in envelope (Env) subtype and structure, and by
the assays used for product down-selection. Since a majority of
new HIV-1 infections are subtype C and considering the novel
properties of C Envs, a C Env (CO6980v0c22) from an acutely
infected Tanzanian was developed as a candidate HIV vaccine.
Methods: The CO6980v0c22 Env sequence was codon optimized
and a stable CHO cell line expressing gp145 was established.
Purified gp145 was adjuvanted in alum or lipid A-liposomes,
injected into New Zealand white rabbits (4/group; 25 ug at
weeks 0, 4, and 8), or BALB/c mice (5/group; 10 ug in liposomes
at weeks 0, 3, 6, 8). Antibody titers were assessed by ELISA and
neutralizing antibodies were measured against pseudoviruses
in TZM-bl cells or against infectious molecular clones (IMC) in a
PBMC assay.
Results: Secreted gp145 is a novel subunit with the full MPER
extended by three lysines. Unlike some gp140 subunits, the
4E10 neutralizing monoclonal antibody (mAb) binds to gp145.
IgG1b12 binds weakly, VRC01 binds potently, as does the
V2-specific 697D mAb; the gp145 also binds to alpha4beta7
receptor, as demonstrated by flow cytometry. At week 10 postimmunization,
rabbit sera showed strong binding antibody
titers to several Env antigens, including the clade B V1V2gp70
scaffold protein. While neutralization of the HIV-2 MPERscaffold
pseudovirus was negative, cross-clade neutralization
was observed in both rabbits and mice, against Tier 1 subtype
B and C pseudoviruses, and against Tier 1 and Tier 2 IMC. Using
EGS cross-linking, it appears that the majority of the gp145
multimers are trimeric; this is currently under investigation
using electron microscopy techniques.
Conclusion: These data indicate essential immunogenic features
of a novel acute C HIV-1 Env that warrants further testing for
potential clinical development.
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POSTERS