Biology Reference
In-Depth Information
studies demonstrated that antibodies induced by oligomeric Env
cross-reacted with HIV Env of other subtypes and neutralized both T
cell-adapted and some primary isolates of HIV-1.
130
To use the
trimeric Env as an immunogen to elicit functional antibody responses,
the first and foremost challenge is to stabilize Env in the trimeric con-
formation without compromising the structural integrity of the mol-
ecule. Several approaches have been tried with reasonable
success.
78,131-142
Yang
et al
. used GCN4-stabilized oligomers to
demonstrate that antibodies induced by oligomeric gp140 were more
effective at neutralizing heterologous primary isolates compared to
antibodies elicited by the corresponding monomeric gp120 pro-
tein.
143
Earl
et al
. made similar observations in rhesus macaques using
a trimeric Env protein from SIV.
135
Recently, we reported the purifi-
cation and characterization of stable trimeric Env protein from US4
(Subtype B R5 isolates).
140
We also purified and characterized trimeric
protein from SF162 and demonstrated that it elicited strong antibody
responses in rabbits that neutralized two out of six heterologous sub-
type-B primary isolates.
144
To further enhance the immunogenicity of
trimeric Env, we have introduced a partial deletion of the V2 loop and
expressed, purified, and characterized this novel Env immunogen.
139
Using biophysical, biochemical, and immunological techniques, we
demonstrated that the purified Env was a trimer, had nanomolar affin-
ity to CD4, and had critical neutralizing epitopes exposed and pre-
served on the trimer.
139
Deletion of the V2 loop qualitatively altered
the immunogenicity of the V3 and V1 loops and rendered the C5
region more immunogenic.
145
The V2 loop deletion in the context of
a trimer elicited strong antibodies in rabbits that neutralized five out
of six heterologous subtype-B primary isolates, and conferred partial
protection upon pathogenic challenge with SHIV
SF162P4
to rhesus
macaques immunized with this V2 loop deleted trimer in a DNA
prime and protein boost strategy.
146,147
These animals were followed
for more than three years without any sign of disease. In addition, we
demonstrated a reasonable correlation between the presence of
neutralizing antibodies at the time of challenge in the vaccinated
animals and the levels of plasma viremia during acute infection.
148
