Oral Abstract Session 01 - Global HIV Vaccine Enterprise

ORAL ABSTRACT SESSIONS
86
Oral Abstract Sessions
Oral Abstract Session 11: Vaccine Immunogens / Delivery
OA11.01
HIV-1 Envelope Trimer Elicits Higher Neutralizing
Antibody Responses Than Monomeric gp120
J.M. Kovacs 1 , J.P. Nkolola 2 , H. Peng 3 , A. Cheung 4 , J. Perry 4 ,
C.A. Miller 4 , M.S. Seaman 4 , D. Barouch 2 , B. Chen 1
1 Harvard Medical School and Children’s Hospital Boston,
Boston, MA, USA; 2 Beth Israel Deaconess Medical Center and
Ragon Institute, Boston, MA, USA; 3 Children’s Hospital Boston,
Boston, MA, USA; 4 Beth Israel Deaconess Medical Center,
Boston, MA, USA
Background: HIV-1 envelope glycoprotein is the primary target
for HIV-1-specific antibodies. The native HIV-1 envelope spike on
the virion surface is a trimer, but trimeric gp140 and monomeric
gp120 are currently believed to induce comparable immune
responses. Indeed, most studies on the immunogenicity of HIV-1
envelope oligomers have revealed only marginal improvement
over monomers. We report here that stable and homogenous
envelope trimers with characteristics expected for the native
viral spikes are substantially superior at eliciting neutralizing
antibodies in guinea pigs.
Methods: Stable envelope gp140 trimer derived from clinical
isolate sequences were stabilized with the T4-fibritin C-terminal
trimerization tag and produced in stablely transfected 293T
cells. Characterization of Env trimers was performed by Western
blotting, size-exclusion chromatography (SEC), analytical-ultra
centrifugation (AUC), multi-angle light scattering (MALS) and
surface plasmon resonance (SPR). Guinea pigs were immunized
six times with 100 µg of protein trimer or monomer in CpG/
Emulsigen adjuvants. Antibody responses were determined by
ELISA and TZM.bl neutralizing antibody assays.
Results: Homogeneous trimer and monomer preparations
exhibited high purity as measured by SEC and SDS-PAGE. AUC
and MALS analyses revealed expected molecular weight for both
trimer and monomer. SPR analyses revealed expected binding
with CD4 and multiple broadly neutralizing antibodies. These
trimers have markedly different antigenic properties than those
of monomeric gp120s derived from the same sequences. They
induce potent, cross-clade neutralizing antibody responses
with titers substantially higher than those elicited by the
corresponding gp120 monomers for a diverse set of both tier 1
and tier 2 viruses.
Conclusion: We have demonstrated the importance of generating
high-quality envelope trimers for antigenic and immunogenic
studies; furthermore these results highlight the immunologic
differences between monomers and high-quality envelope
trimers, illustrating important implications for HIV-1 vaccine
development and immunogen selection in large clinical trials.
AIDS Vaccine 2012
OA11.02
Shaping Humoral Responses Against Mini-libraries
of HIV Env Antigens via Lipid Nanoparticle Vaccine
Delivery
M.C. Hanson 1 , J. Mata-Fink 1 , W. Abraham 1 , K.D. Wittrup 2 ,
D.J. Irvine 3
1 Massachusetts Institute of Technology, Cambridge, MA, USA;
2 Ragon Institute of MGH, MIT and Harvard, Boston, MA, USA;
3 Howard Hughes Medical Institute, Chevy Chase, MD, USA
Background: Humoral immune responses elicited by an HIV
vaccine would ideally be comprised of durable high titers of
broadly neutralizing antibodies. Importantly, recent studies of
broadly neutralizing antibodies isolated from infected patients
have suggested that high degrees of somatic hypermutation
(SHM) are a common feature of antibodies with high potency and
good breadth. Thus, a successful vaccine will likely require both
immunogens capable of focusing the humoral response against
conserved neutralizing epitopes and appropriate adjuvants/
delivery systems capable of promoting elevated SHM and lasting
responses against these epitopes.
Methods: We generated a small library of gp120 mutants
engineered to have diverse surface compositions but a conserved
CD4 binding pocket recognized by the broadly neutralizing
antibody VRC01. These gp120 mutants were linked to “stealth”
liposomes via 2KDa PEG linkers. These lipid nanoparticles were
simultaneously loaded with immunostimulatory adjuvant
molecules such as MPLA (TLR4 agonist) or CpG (TLR9 agonist)
to support differentiation of helper T-cells and promote avidity
maturation of the antibody response. Mice were immunized
repeatedly with stealth liposomes carrying unique gp120
mutants in each boost.
Results: Stealth liposomes carrying TLR4 agonists (TLRa)
promoted long-lived humoral responses against env antigens
superior to traditional adjuvants such as alum, montanide, or
soluble protein mixed with TLRa. Studies of liposome/antigen
trafficking in vivo suggest these enhanced responses reflect
efficient trafficking of these nanoparticle vectors to lymph nodes.
Notably, this heterologous immunization strategy elicited antigp120
sera focused almost exclusively on the CD4 binding site
and that competed with VRC01 for binding to gp120.
Conclusion: This approach of combined immunogen design with
effective multivalent, nanoparticle-based antigen delivery may
provide a strategy to promote strong and long-lived neutralizing
antibody responses against HIV.
This work was funded by the NIH (AI095109) and the Ragon
Institute of MGH, MIT, and Harvard. DJI is an investigator of the
Howard Hughes Medical Institute.