Oral Abstract Session 01 - Global HIV Vaccine Enterprise

Symposium 03: New Env Immunogens
S03.01
Structural Basis For HIV-1 Trimeric Env Immunogen
Y. Mao 1
1 Dana-Farber Cancer Institute, Boston, MA, USA
The trimeric envelope glycoprotein complex of human
immunodeficiency virus (HIV-1) is a membrane-fusing machine
that mediates virus entry into host cells. Binding of the gp120
exterior envelope glycoprotein to CD4 and the chemokine
receptor on target cells triggers conformational changes that
allow the gp41 transmembrane envelope glycoprotein to
fuse the viral and cell membranes. We determined an atomic
structure of the fully glycosylated HIV-1 envelope trimer in its
unliganded, pre-fusion state, including the complete exterior
and transmembrane regions, by cryo-electron microscopy. The
atomic model reveals a dramatic conformational transition of
gp120 between its unliganded and CD4-bound states, a torus-like
fold of gp41 entirely different from its post-fusion conformation,
and a conserved topology of the glycan shield. The quaternary
structure of the trimer exhibits tensegrity that stores the free
energy fuelling virus entry. The structure provides insights into
virus-host interactions and represents an atomic reference for
vaccine immunogen design.
S03.02
Symposia Sessions
Pure Native Env Trimers On VLP Surfaces and in
Soluble Form
J.M. Binley 1
1 TPIMS, San Diego, CA, USA
We hypothesize that as the target of nAbs, the native Env trimer
is the most logical basis for a nAb vaccine. Two possible formats
to present native trimer are in situ in lipid membranes (e.g. VLPs)
or as a soluble recombinant. Different problems have limited
progress in both areas: 1) Although VLPs and other particle
based approaches present native trimer, they invariably also
express non-functional forms of Env. The problem here is that
non-functional Env is immunodominant and may interfere with
responses against the more antibody-resistant native trimer. 2)
Attempts to produce soluble trimers involve truncating gp160
before the transmembrane spanning domain (i.e. gp140). The
problem here has been inefficient gp120/gp41 maturation and
a failure of gp140 to assemble into stable trimers. Although
various innovative mutations have helped address these issues,
none have so far have resulted in trimers that fully recapitulate
the native complex. We have been working to solve these two
problems. Regarding the first problem, we have developed
pure native “trimer VLPs” in which junk Env is eliminated using
protease digests together with specific mutations that improve
trimer folding and stability. Ongoing immunogenicity trials in
rabbits will be presented. Regarding the second problem, we
have shown that soluble SOS mutant-based trimers but not WT
trimers can be extracted from lipid membranes and are stable
at 37°C for extended periods in certain buffers. These trimers
retain an ability to bind to PG9 and PG16 and other broad nAbs,
but do not bind to non-nAbs. We have generated a producer
cell line and are currently developing purification procedures to
yield mg quantities of trimer for structural and immunogenicity
purposes. These new pure trimer platforms provide new tools
for other research areas, including mapping broad HIV+ serum
neutralization and for accessing new neutralizing mAbs from
infected donors.
AIDS Vaccine 2012
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SYMPOSIA SESSIONS