Oral Abstract Session 01 - Global HIV Vaccine Enterprise

Topic 3: B Cell Immunology and Antibody Functions
P03.57 LB
Antibody responses to V2 loop Are Induced by
CRF01_A E and not Clade B Envelopes
N. Karasavvas 1 , C. Karnasuta 1 , S. Madnote 1 , D. Arworn 1 ,
F. Sinangil 2 , S. Rerks-Ngarm 1 , R.J. O’Connell 1 , S. Nitayaphan 1 ,
V. Ngauy 1 , J.H. Kim 1 , N.L. Michael 1 , M.S. de Souza 1
1 AFRIMS, Bangkok, Thailand; 2 Global Solutions for Infectious
Diseases, South San Francisco, CA, USA
Background: The RV144 vaccine trial of canarypox vCP1521
(ALVAC-HIV) prime and bivalent HIV-1 envelop gp120 protein
subtype B/CRF01_AE boost (AIDSVAX B/E) demonstrated a
significant effect in preventing HIV-1 infection. A case-control
analysis suggested that variable loops 1 and 2 (V2) of gp120 may
have contributed to protection against HIV-1 acquisition. Two
other vaccine trials using gp120 only– VAX003 (AIDSVAX B/E) and
VAX004 (AIDSVAX B/B) failed to show protection
Methods: Binding antibody responses induced by the RV144,
VAX003 and VAX004 vaccine regimens were compared using
ELISA. Recombinant gp120 envelope proteins MN (subtype B),
92TH023 (CRF01_AE), A244 (CRF01_AE) and cyclic V2 peptides
were used as capture antigens
Results: After two protein injections, VAX004 had the highest
geometric mean titers (GMT) against MN (25,600), VAX003
against A244 (21,378) and RV144 against 92TH023 (6,263).
Antibody responses against V2 (CRF01_AE) were detected in
plasma samples from RV144 and VAX003 with GMTs of 972 and
1100, respectively. However, VAX004 failed to generate antibodies
against CRF01_AE V2. None of the three vaccines generated
antibodies against MN V2 after two protein immunizations.
Compared to VAX004, VAX003 had higher antibody responses
against all three recombinant proteins: 2-fold (MN), 4-fold
(A244) and 4-fold (92TH023) when two additional protein
injections were administered. Two additional protein
inoculations in the VAX trials failed to increase antibody titers
against, CRF01_AE V2, but generated a small response against
MN V2 (GMT, 76) in VAX003
Conclusion: Antibody responses against V2 were induced by
CRF01_A E recombinant proteins as there were no responses
induced by the AIDSVAX B/B vaccine regimen. Repeated protein
immunization increased the magnitude of responses against
recombinant proteins in VAX003 but failed to increase titers
against CRF01_AE V2. If antibodies against V2 are protective
against HIV-1 acquisition, designing antigens with greater V2
antigenicity would be critical
P03.58 LB
AIDS Vaccine 2012
Posters
Partial Germline Reversions Can Increase VRC07
Potency and Breadth
R.S. Rudicell 1 , I. Georgiev 1 , Z. Yang 1 , S. O’Dell 1 , Y. Kwon 1 , J. Zhu 1 ,
X. Wu 1 , P.D. Kwong 1 , J.R. Mascola 1 , G.J. Nabel 1
1 Vaccine Research Center, NIAID, NIH, Bethesda, MD, MD, USA
Background: VRC01 and related antibodies target the CD4
binding site (CD4bs), are broadly neutralizing and highly potent,
and have undergone high levels of somatic hypermutation.
To optimize such antibodies for passive immunization and
to further understand antibody development, we reverted
three CD4bs antibodies towards their putative germlines and
analyzed the effects on breadth and potency. Interestingly, we
also identified key germline reversion mutations that increased
neutralization potential.
Methods: Structure/function-based analyses were used to
design partially reverted heavy and light chains based on the
clonally-related antibodies VRC01, NIH45-46, and VRC07.
Mature CDRs were maintained and framework regions were
back-mutated. The antibodies were expressed, purified, and
tested for binding to gp120 by ELISA. Neutralization against a
panel of tier 2 HIV-1 pseudotyped viruses was determined for
select antibodies.
Results: The heavy chains of VRC01, NIH45-46, and VRC07 are
42%, 41%, and 44% somatically mutated from their germline
precursor, while the light chains are 29% (VRC01/07) and 27%
(NIH45-46) somatically mutated. We began by reverting over
half of the heavy chain somatic mutations and over one-third
of the light chain somatic mutations to their germline residue
identities. An iterative design approach was used, and we
systematically re-introduced mature residues to the partial
germline reversions. Most mutants retained the ability to bind
gp120 and neutralize diverse HIV-1 pseudoviruses, albeit with
lower breadth and/or potency than their mature counterparts.
Additionally, we found 3 partial-germline reversion mutations
that increased VRC07 potency.
Conclusion: Here, we showed that in most cases mature
framework regions in addition to mature CDRs were required
for highest neutralization potency and breadth. However, three
framework germline reversion mutations increased potency 2-3
fold. These partial reversions are being combined with other
mutations, including those that modulate Fc effector function,
to optimize the antibody function for passive transfer in NHPs
and humans.
145
POSTERS