Science - 06.12.2019

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A generalized HIV vaccine design strategy for priming

of broadly neutralizing antibody responses

Jon M. Steichen, Ying-Cing Lin, Colin Havenar-Daughton, Simone Pecetta, Gabriel Ozorowski,
Jordan R. Willis
, Laura Toy, Devin Sok, Alessia Liguori, Sven Kratochvil, Jonathan L. Torres,
Oleksandr Kalyuzhniy, Eleonora Melzi, Daniel W. Kulp, Sebastian Raemisch, Xiaozhen Hu,
Steffen M. Bernard, Erik Georgeson, Nicole Phelps, Yumiko Adachi, Michael Kubitz, Elise Landais,
Jeffrey Umotoy, Amanda Robinson, Bryan Briney, Ian A. Wilson, Dennis R. Burton,
Andrew B. Ward, Shane Crotty†, Facundo D. Batista†, William R. Schief†

people each year, making development of an
HIV vaccine a global health priority. Nearly
all licensed vaccines protect by inducing anti-
bodies, but highly variable pathogens such as
HIV and influenza virus have eluded tradi-
tional vaccine strategies. The discoveries of
broadly neutralizing antibodies
(bnAbs) that bind to conserved epi-
topes on the surface proteins of these
viruses have inspired vaccine design
strategies to induce bnAbs. Antibodies
are produced by B cells, and highly
effective antibodies like bnAbs acquire
affinity-enhancing mutations when a
bnAb-precursor B cell mutates and
matures from the original naïve B cell
(or germline) state. Among several
new vaccine strategies, germline-
targeting vaccine design aims to
induce bnAbs by first stimulating
bnAb-precursor B cells and then
shepherding B cell affinity matura-
tion with a series of rationally de-
signed boosting immunogens. A key
rationale for this strategy is that
germline-reverted forms ofbnAbs—
precursors with all recognizable
amino acid mutations reverted to
germline—typically have no detect-
able affinity for HIV envelope (Env).
Thus, for a vaccine to initiate bnAb
induction, a germline-targeting prim-
ing immunogen with appreciable
affinity for bnAb precursors must be

RATIONALE:Most HIV bnAbs (and
most antibodies to any patho-
gen) bind to their target by using
their heavy chain complementarity-
determining region 3 (HCDR3) as a
major binding determinant. Hence,
an optimal HIV vaccine that induces
multiple bnAbs, and a general solu-
tion to germline-targeting vaccine
design that could be applied broadly

to other pathogens, will need to work with
HCDR3-dependent antibodies. However, the
need to design germline-targeting immu-
nogens to initiate HCDR3-dependent bnAb
responses faces major technical challenges. Al-
though each B cell expresses a single unique
antibody, different B cells produce diverse

antibodies encoded by different combinations
of antibody genes, with the greatest antibody
genetic diversity encoded in the HCDR3 por-
tion of the molecule. The exceptional diversity
in the human B cell repertoire makes any sin-
gle HCDR3 sequence an impractical vaccine
target. Rather, a pool of precursors sharing a
set of bnAb-associated genetic features must
be identified and targeted. Thus, owing to
the enormous diversity of human antibodies,
a germline-targeting im-
munogen should have af-
finity for diverse bnAb
precursors in order to suc-
ceed in diverse vaccine

RESULTS:Herein we report a solution to the
above challenges. Using the strongly HCDR3-
dependent bnAb BG18 that binds a conserved
site on HIV Env as a high-value target and a
proof of principle, we demonstrate a method
to identify pools of potential bnAb precursors
in an ultradeep human antibody sequence
database, guided by key genetic fea-
tures that enable bnAb structural
recognition of the antigen. We then
use a representative set of those
potential bnAb precursors as design
targets to guide our engineering of
HIV Env immunogens that bind to
diverse potential bnAb precursors.
Lastly, we provide critical preclini-
cal validation of immunogen design
by assessing these immunogens for
(i) their ability to select rare poten-
tial bnAb-precursor naïve B cells from
the blood of healthy human donors,
(ii) their modes of binding to bnAb
precursors, and (iii) their capacity
to prime rare bnAb-precursor B cells
with physiologically relevant affin-
ities in a mouse model.

CONCLUSION:Overall, we demon-
strate a new approach to defining
diverse precursors for a target anti-
body and designing vaccine immu-
nogens that take advantage of that
information. The approach lays out
a generalizable pathway for the de-
velopment and preclinical validation
of germline-targeting immunogens
to stimulate precursors for HCDR3-
dependent antibodies.


Steichenet al.,Science 366 , 1216 (2019) 6 December 2019 1of1

The list of author affiliations is available in the
full article online.
*These authors contributed equally to this work.
†Corresponding author. Email: schief@scripps.
edu (W.R.S.); [email protected]
(F.D.B.); [email protected] (S.C.)
Cite this article as J. M. Steichenet al.,
Science 366 , eaax4380 (2019). DOI: 10.1126/

Use immunogen as bait
to isolate potential
bnAb precursors from
human B cells

Design immunogen
for breadth of
reactivity to diverse

Structural validation
of precursor binding

B cell

Target antibody

Priming of rare
precursors in vivo

Using bioinformatics,
identify diverse potential
precursors for target
antibody in ultradeep
human antibody
sequence database

Determine key
genetic features of
target antibody that
enable structural
engagement of


General strategy for germline-targeting vaccine design.Four key steps
are defined here for design and validation of germline-targeting immunogens:
structural and genetic understanding of target antibody-antigen
interaction, identification of diverse antibody precursors, design
of an immunogen to bind diverse precursors, and preclinical immunogen
validation by isolating human B cell binders, assessing structural interaction
with precursors, and stimulating responses in transgenic mice.


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