Oral Abstract Session 01 - Global HIV Vaccine Enterprise

Topic 12: Vaccine Concepts and Design
P12.37
Yeast Surface Display of HIV Env Protein Variants for
the Discovery of Novel Vaccine Immunogens
S. Grimm 1 , M. Ackerman 1
1 Dartmouth College, Lebanon, NH, USA
Background: The discovery of broadly neutralizing antibodies
(bnAbs) such as 4E10, pg9 and VRC01 binding to the HIV env spike
has electrified the field and shows that, in principle, the human
immune system is capable of producing protective antibodies
against HIV. All current vaccination strategies have however
failed to elicit such bnAbs, leaving room for novel approaches to
address this problem.
Protein engineering techniques such as yeast surface display
have proven potential for the discovery and affinity maturation
of monoclonal antibodies. Antibody libraries are presented
on yeast cells and flow cytometric sorting is used to identify
antibody variants with improved properties. As antibodies,
also HIV env spikes are posttranslationally modified in the
secretory pathway and composed of disulphide bond-containing
glycoproteins. We here investigated whether HIV spike protein
variants can be displayed or secreted from surface of the yeast
strain S. cerevisiae.
Methods: A panel of HIV env spike protein-encoding genes
was inserted in vectors allowing for the display or secretion of
the encoded proteins in S. cerevisiae. The displayed protein
variants were analyzed for binding to either bnAbs or pooled HIV
immunoglobulin from the serum of infected individuals (HIVIg)
using flow cytometry. The secreted protein variants were tested
for binding activities on an Octet biosensor.
Results: We found that HIV env spike protein variants can be
displayed or secreted from the yeast strain S. cerevisiae. Both
displayed and secreted variants showed binding to bnAbs and HIVIg.
Conclusion: This study suggests that yeast surface display is
as a viable option for the engineering of HIV env spike protein
variants and may become a valuable tool for the discovery of
novel vaccine immunogens.
P12.38
AIDS Vaccine 2012
Posters
Development of Candidate HIV Vaccines Using VSV
Vectors to Express Membrane-Anchored MPER
Immunogen
M. Yuan 1 , A. Wilson 1 , M. Kemelman 1 , M. Panis 1 , I. Lorenz 1 ,
C. Jurgens 1 , M.J. Chiuchiolo 1 , R. King 1 , M. Caulfield 1 , C.L. Parks 1
1 International AIDS Vaccine Initiative, Brooklyn, NY, USA
Background: The HIV-neutralizing activity of monoclonal
antibodies 2F5, 4E10, and Z13 have shown that the membraneproximal
external region (MPER) of HIV Env is an important
vaccine target, but development of an immunogen that elicits
similar virus-neutralizing antibody responses against the MPER
from a wide range of subtypes has been difficult to achieve. It has
been proposed that a MPER immunogen must be membraneassociated
to adopt the conformation needed to elicit broadly
neutralizing antibodies, and accordingly, we have developed
Vesicular Stomatitis Virus(VSV) Vectors that express membraneanchored
MPER epitopes.
Methods: Replication-competent and single-cycle VSV vectors
have been developed that express a truncated VSV G protein
(G-Stem) in which the natural G ectodomain is replaced with
MPER sequence (GStemMPER). The nucleotide sequence of
GStemMPER has been optimized by computer based algorithms
to ensure genetic stability. Several VSV vector modifications are
also introduced for directing immune responses towards MPER
rather than G. Those strategies include relocation of GStemMPER
and VSV G glycoprotein to achieve maximal MPER expression
while minimize the anti-vector immunity, incorporation of
different VSV G serotypes and pseudotyping single- cycle VSV
vectors with various types of glycoproteins.
Results: Western blot analysis confirmed expression of MPER
epitopes. Assessment by FACS showed the cell surface MPER
being recognized by 2F5 and 4E10 monoclonal antibodies.
Immunoprecipitation study further proved incorporation of
MPER into viral particles.
Conclusion: Multiple VSV-GStemMPER vectors are being
evaluated in small animal studies to compare their
immunogenicity and whether the membrane-anchored form of
the MPER immunogen elicits humoral responses with a broad
range of HIV neutralizing activity.
259
POSTERS