Oral Abstract Session 01 - Global HIV Vaccine Enterprise

POSTERS
Posters
Topic 12: Vaccine Concepts and Design
P12.15
A Novel HIV Vaccine Targets the 12 Protease
Cleavage Sites
M. Luo 1 , D. Tang 1 , R. Capina 1 , X. Yuan 1 , C. Prego 2 , J.C. Pinto 2 ,
M. Alonso 2 , C. Barry 1 , R. Pilon 1 , C. Daniuk 1 , J. Tuff 1 , S. Pillet 1 ,
D. La 1 , T. Bielawny 1 , C. Czarnecki 1 , P. Lacap 1 , H. Peters 1 ,
G. Wong 1 , M. Kimani 3 , C. Wachihi 3 , J. Kimani 3 , T.B. Ball 1 ,
P. Sandstrom 1 , G. Kobinger 1 , F.A. Plummer 1
1 National Microbiology Laboratory, Winnipeg, Canada;
2 University of Santiago de Compostela, Santiago de
Compostela, Spain; 3 University of Nairobi, Nairobi, Kenya
Background: The protease of HIV-1 is a small 99-amino acid
aspartic enzyme mediating the cleavage of Gag, Gag-Pol and
Nef precursor polyproteins. The process is highly specific,
temporally regulated and essential for the production of
infectious virions. A total of 12 proteolytic reactions are required
to generate a viable virion. Therefore, a vaccine targeting the 12
protease cleavage sites(PCS) could be effective. The PCS of HIV-
1 are highly conserved among major subtypes, direct immune
responses against these sites would yield several advantages.
First, the immune response could destroy the virus before its
establishment in the host. Second, the vaccine could force the
virus to accumulate mutations eliminating the normal function
of the HIV protease. Third, restricting the immune responses to
these sites can avoid distracting immune responses that often
generate unwanted inflammatory responses, induce excess
immune activation, and attract more targets for HIV-1 infection,
establishment and spread.
Methods: We have conducted a pilot study to investigate the
feasibility and effectiveness of this approach. The recombinant
VSV-peptides were used to immunize cynomolgus macaques
and nanopackaged peptides were used to boost the immune
response to the 12 PCS of SIVmac239. The controls and
immunized macaques were repeatedly challenged intrarectally
with an increased dosage of SIVmac239.
Results: Results showed that antibody and T cell responses
to the 12 PCS can protect macaques against higher dosage of
SIVmac239 challenge (p=0.0005, R=0.8005) and the vaccine
group maintains significantly higher CD4+ counts (p=0.0002)
than the controls weeks after being infected. Population
coverage analysis showed that this approach can be applied to
>95% populations in the world.
Conclusion: A vaccine targets the 12 protease cleavage sites is a
viable approach for HIV prevention and treatment.
248
AIDS Vaccine 2012
P12.16
A Minimal T-Cell Immunogen Designed to
Cover HIV-1 Specificities Associated with
Control Is Immunogenic in Mice and Breaks CTL
Immunodominance
B. Mothe 1 , A. Llano 1 , M. Rosati 2 , S. Perez-Alvarez 1 , V. Kulkarni 2 ,
B. Chowdhury 2 , C. Alicea 2 , R.K. Beach 2 , N.Y. Sardesai 3 ,
G.N. Pavlakis 2 , B.K. Felber 2 , C. Brander 4
1 IrsiCaixa AIDS Research Institute-HIVACAT, Barcelona, Spain;
2 NCI-Frederick, Frederick, MD, USA; 3 Inovio Biomedical Corp.,
Blue Bell, PA, USA; 4 IrsiCaixa AIDS Research Institute-HIVACAT,
ICREA, Barcelona, Spain
Background: Few T-cell immunogen vaccine designs exist that
are based on large human immunogenicity data and which
avoid inducing responses to mutable epitopes that may serve
as immunodominant decoys. We have developed and tested
a rationally designed T cell immunogen sequence which
overcomes these limitations and which is currently undergoing
pre-clinical testing.
Methods: 250 HIV-1 clade B infected individuals were screened
for T cell responses to the entire HIV proteome. This yielded
26 regions in HIV-1 Gag, Pol, Vif and Nef proteins that were i)
preferentially targeted by individuals with low viral loads, ii)
more conserved and iii) elicited responses of higher functional
avidity and broader cross-reactivity than responses to other, lessbeneficial
regions. The ‘beneficial’ segments were linked by triple
alanines, translated into an expression-optimized nucleotide
sequence and cloned into a CMV plasmid harboring a GM-CSF
signal peptide. Immunogenicity was evaluated in C57BL/6 mice
two weeks after a second DNA vaccination. Cellular immune
responses were characterized using intracellular cytokine staining
and IFN-γ ELISPOT using overlapping peptide pools covering the
segments included in the T-cell immunogen.
Results: Vaccination with 20 μg of DNA generated both CD4 and
CD8 IFN-γ+ responses to the immunogen sequence. The T-cell
immunogen elicited a more balanced, broad T cell response to
all protein components (Gag, Pol, Vif and Nef) contained in the
immunogen than immunizations using plasmids encoding for the
entire Gag, Pol, Nef, Tat and Vif proteins, which induced a strong
Gag dominance.
Conclusion: Despite lower in vitro expression, the DNA vaccine
was strongly immunogenic in C57BL/6 mice, induced broad
CD4 and CD8 T cell responses and was able to break the
immunodominance of responses to targets that do not emerge
as particularly beneficial in large cohort screenings. Experiments
in humanized BLT mice are currently ongoing to map induced
responses in the context of different HLA genotypes.