JOURNAL OF VIROLOGY, Mar. 2005, p. 2956–2963
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Vol. 79, No. 5
Multiclade Human Immunodeficiency Virus Type 1 Envelope
Immunogens Elicit Broad Cellular and Humoral Immunity
in Rhesus Monkeys
Michael S. Seaman,1Ling Xu,2Kristin Beaudry,1Kristi L. Martin,1Margaret H. Beddall,1
Ayako Miura,1Anna Sambor,2Bimal K. Chakrabarti,2Yue Huang,2Robert Bailer,2
Richard A. Koup,2John R. Mascola,2Gary J. Nabel,2and Norman L. Letvin1,2*
Division of Viral Pathogenesis, Beth Israel Deaconess Medical Center, Harvard Medical School,
Boston, Massachusetts,1and Vaccine Research Center, National Institute of Allergy
and Infectious Diseases, National Institutes of Health, Bethesda, Maryland2
Received 2 August 2004/Accepted 12 October 2004
The development of a human immunodeficiency virus type 1 (HIV-1) vaccine that elicits potent cellular and
humoral immune responses recognizing divergent strains of HIV-1 will be critical for combating the global
AIDS epidemic. The present studies were initiated to examine the magnitude and breadth of envelope (Env)-
specific T-lymphocyte and antibody responses generated by vaccines containing either a single or multiple
genetically distant HIV-1 Env immunogens. Rhesus monkeys were immunized with DNA prime–recombinant
adenovirus boost vaccines encoding a Gag-Pol-Nef polyprotein in combination with either a single Env or a
mixture of clade-A, clade-B, and clade-C Envs. Monkeys receiving the multiclade Env immunization developed
robust immune responses to all vaccine antigens and, importantly, a greater breadth of Env recognition than
monkeys immunized with vaccines including a single Env immunogen. All groups of vaccinated monkeys
demonstrated equivalent immune protection following challenge with the pathogenic simian-human immuno-
deficiency virus 89.6P. These data suggest that a multicomponent vaccine encoding Env proteins from multiple
clades of HIV-1 can generate broad Env-specific T-lymphocyte and antibody responses without antigenic
interference. This study demonstrates that it is possible to generate protective immune responses by vaccina-
tion with genetically diverse isolates of HIV-1.
The extreme genetic diversity of the human immunodefi-
ciency virus type 1 (HIV-1) envelope (Env) poses a daunting
challenge for the creation of an effective AIDS vaccine (16).
While Env is the principal target for HIV-1-specific antibody
responses, it also serves as a potent T-cell immunogen (15). An
ideal HIV-1 vaccine should elicit potent cellular and humoral
immunity capable of recognizing a diversity of viral isolates
(19, 23). However, the extraordinary genetic variation of
HIV-1 Env worldwide may make it impossible to create an
effective vaccine using only a single Env gene product.
While many of the promising AIDS vaccine candidates cur-
rently under investigation in nonhuman primates and early-
phase human clinical trials utilize Env immunogens derived
from a single HIV-1 primary isolate (10), this approach has
significant limitations. Although these vaccines generate po-
tent cellular and humoral immune responses against HIV-1
Env, it is likely that the breadth of immunity elicited by a single
Env immunogen will not effectively confer protection against
divergent strains of HIV-1. It is, however, not feasible to un-
dertake the development of multiple country- or clade-specific
vaccines. Moreover, such region-specific vaccines would likely
not protect against unrelated strains that might be newly in-
troduced into a population.
One strategy for creating a single HIV-1 vaccine for world-
wide use is to employ representative immunogens from multi-
ple clades of HIV-1 in a single vaccine formulation (22). Such
a multiclade vaccine would contain Env immunogens relevant
to the majority of HIV-1 infections worldwide and could be
feasibly tested. However, it is not clear whether a multicom-
ponent vaccine encoding antigens from various clades of
HIV-1 would elicit antiviral immunity greater than or equal to
that of a vaccine employing a single Env immunogen, and
whether a complex mixture of immunogens would result in
antigenic interference and diminished immune protection (13).
The present studies utilized the simian-human immunode-
ficiency virus (SHIV)–rhesus monkey model to investigate the
breadth and magnitude of immunity elicited by a DNA prime–
recombinant adenovirus (rAd) boost vaccine containing Gag-
Pol-Nef and either single-clade or multiple-clade Env immu-
nogens. Our findings demonstrate that a multiclade Env
vaccine elicits potent cellular and humoral immune responses
with greater breadth than can be generated by immunizations
performed with a single Env immunogen.
MATERIALS AND METHODS
Immunizations and challenge of rhesus monkeys. Thirty adult Indian-origin
rhesus monkeys (Macaca mulatta) were maintained in a facility accredited by the
Association for the Assessment and Accreditation of Laboratory Animal Care in
accordance with the guidelines of the Institutional Animal Care and Use Com-
mittee for Harvard Medical School and the Guide for the Care and Use of
Laboratory Animals. Monkeys were divided into five groups of six animals each.
Each experimental group included two monkeys expressing the major histocom-
patibility complex class I allele Mamu-A?01.
Plasmid DNA and rAd vaccine vectors were constructed as previously de-
* Corresponding author. Mailing address: Beth Israel Deaconess
Medical Center, Division of Viral Pathogenesis, 330 Brookline Ave./
RE-113, Boston, MA 02215. Phone: (617) 667-2766. Fax: (617) 667-
8210. E-mail: firstname.lastname@example.org.
with a multiclade envelope HIV vaccine candidate. Submitted for publica-
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