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Journal of Virology, September 2005, p. 11529-11532, Vol. 79, No. 17
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.17.11529-11532.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Reversion In Vivo after Inoculation of a Molecular Proviral DNA Clone of Simian Immunodeficiency Virus with a Cytotoxic-T-Lymphocyte Escape Mutation
Masahiro Kobayashi,1
Hiroko Igarashi,1
Akiko Takeda,1
Moriaki Kato,1,2 and
Tetsuro Matano1,3*
Department of Microbiology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan,1
Department of Urology, School of Medicine, The University of Kyorin, Tokyo 181-8611, Japan,2
AIDS Research Center, National Institute of Infectious Diseases, Tokyo 162-8640, Japan3
Received 2 April 2005/
Accepted 1 June 2005

ABSTRACT
Vaccine-based control of the replication of a simian immunodeficiency
virus (SIV), SIVmac239, in macaques has recently been shown.
In the process of the control, a mutant virus escaping from
epitope-specific cytotoxic-T-lymphocyte (CTL) responses was
rapidly selected and contained. In this study, we show that
the wild-type virus appeared and became predominant in the absence
of the epitope-specific CTL after inoculation of naive macaques
with a molecular clone DNA of the CTL escape mutant SIV. This
is the first report describing reversion in vivo from an inoculated,
molecular proviral DNA clone of immunodeficiency virus with
a CTL escape mutation.

TEXT
Virus-specific CD8
+ cytotoxic-T-lymphocyte (CTL) responses are
crucial for the control of immunodeficiency virus infection.
The importance of CTL has been indicated by temporal association
of CTL appearance with the resolution of primary viremia in
human immunodeficiency virus type 1-infected humans (
4,
13)
and by monoclonal anti-CD8 antibody-mediated CD8 depletion experiments
with macaque AIDS models (
10,
15,
23). Therefore, AIDS vaccine
studies have been making efforts to develop methods efficiently
eliciting virus-specific CTL responses (
18). However, viral
escape from CTL recognition can lead to viral evasion from immune
control and has frequently been observed in immunodeficiency
virus infection (
1,
5,
8,
19,
21,
22). Under strong immune pressure
exerted by CTL, viruses are often forced to mutate, with viral
fitness costs, to escape from the CTL responses (
7,
9,
11,
17,
20,
24). Some CTL escape mutant viruses with lower viral fitness
require additional compensatory mutations to restore their replicative
competence (
6,
11,
20). It is important to evaluate replicative
ability of CTL escape mutants in vivo.
Recently, CTL-based control of replication of a pathogenic simian immunodeficiency virus (SIV), SIVmac239 (12), has been shown in a preclinical vaccine trial using non-Indian rhesus macaques (17). In that study, macaques vaccinated with a DNA priming followed by a Gag-expressing Sendai virus vector-booster were challenged intravenously with SIVmac239. Five of eight vaccinees controlled viral replication and had undetectable levels of plasma viremia after 5 weeks of infection. All of the five macaques showed rapid selection of CTL escape mutations in gag, indicating that vaccine-induced CTL contained replication of the wild-type challenge virus. Among the five, three vaccinees that share a major histocompatibility complex class I (MHC-I) haplotype, 90-120-Ia, showed high levels of Gag206-216 (IINEEAADWDL) epitope-specific CTL responses and rapid selection of a mutant escaping from the CTL. The replicative ability of the virus with the CTL escape mutation, Gag216S, leading to a substitution from leucine (L) to serine (S) at the 216th amino acid (aa) in Gag was diminished compared to the wild type. In the present study, we have observed replication of this mutant SIV, SIVmac239Gag216S, in the absence of Gag206-216-specific CTL responses after its inoculation into naive macaques. All the animal experiments in this study were performed in accordance with the guidelines for laboratory animals of the National Institute of Infectious Diseases.
First, two cynomolgus macaques (Macaca fascicularis), C99049 and C99058, were coinoculated intramuscularly with 5 mg of the wild-type SIVmac239 molecular clone DNA (pBRmac239) and 5 mg of the mutant SIVmac239Gag216S molecular clone DNA (pBRmac239Gag216S) (17). We extracted RNA from plasma and quantitated plasma SIV RNA levels as described previously (17); both that of the wild type and that of the mutant are detectable in this assay. In both of the animals, plasma viremia was observed after the inoculation (Fig. 1A). Both the wild type and mutant viral genomes were detected at comparable levels by sequencing of a gag gene fragment amplified by reverse transcription and nested PCR from plasma RNA at week 1, but the mutant was poorly detected and the wild type was dominant at weeks 2 and 3. We then subcloned the amplified fragments into plasmids for sequencing and counted the numbers of clones carrying the wild-type (Gag216L) or the mutant (Gag216S) sequence at the region encoding the 216th aa in Gag. It revealed that the wild-type SIV became dominant 2 or 3 weeks after the inoculation (Fig. 1B). This result indicates that the replicative ability of this CTL escape mutant virus was diminished compared to that of the wild type, confirming the previous results obtained with rhesus macaques (17). After euthanasia of macaques at week 3, we extracted genomic DNA, by using the DNeasy kit (QIAGEN K.K., Tokyo, Japan), from the submandibular lymph node (LN), the mesenchymal LN, and the inguinal LN and subcloned proviral gag gene fragments amplified by nested PCR from the DNA into plasmids for sequencing. The mutant Gag216S was detected in most of the LNs, but the wild-type sequence was dominant in the proviral genomes in all the LNs (Fig. 1C).
Second, two cynomolgus macaques, C87072 and C87134, were inoculated
intramuscularly with 5 mg of the mutant SIVmac239Gag216S molecular
clone DNA alone. Plasma viremia was maintained until euthanasia
of macaques at week 12 (C87072) or week 10 (C87134) after the
inoculation (Fig.
2A). We subcloned viral
gag gene fragments
amplified from plasma RNA and found the wild-type Gag216L sequence
at week 5, although it was undetectable at week 4 in both of
the animals (Fig.
2B). In macaque C87072, 9 of 10 viral
gag clones showed the wild-type Gag216L sequence at week 7 (Fig.
2B), and most of the proviral
gag clones were the wild type
in the submandibular LN, the mesenchymal LN, and the inguinal
LN at week 12 (Fig.
2C). In macaque C87134, the ratio of wild-type
to total viral
gag clones was 3/11 at week 8 but 12/21 at week
10 (Fig.
2B). The wild-type Gag216L sequence was detected but
was not predominant in the proviral
gag clones from the LNs
at week 10 (Fig.
2C). These results indicate that the mutant
SIVmac239Gag216S proliferated in all the LNs but was outgrown
by the wild-type virus.
We further examined virus-specific CD8
+ T-cell responses in
macaques by flow cytometric analysis of antigen-specific interferon-
(IFN-

) induction as described previously (
16,
17). In brief,
peripheral blood mononuclear cells (PBMCs) were cocultured with
autologous herpesvirus papio-immortalized B lymphoblastoid cells
infected with a vesicular stomatitis virus G-pseudotyped SIV
for SIV-specific stimulation. Alternatively, PBMCs were cocultured
with B lymphoblastoid cells pulsed with the Gag
206-216-epitope
peptide for Gag
206-216-specific stimulation or a mixture of
the peptides with a 216S mutation corresponding to the 206th
through 220th aa and the 210th through 225th aa in Gag (Gag
206-220.216S
and Gag
210-225.216S peptides, respectively) for Gag
206-225.216S-specific
stimulation. PBMCs derived from macaques C99049 at week 3, C99058
at week 3, C87072 at week 12, and C87134 at week 10 were subjected
to this assay (Fig.
3). SIV-specific CD8
+ T-cell responses were
detected but Gag
206-216-specific IFN-

induction was undetectable,
confirming no Gag
206-216-specific CTL responses in any of four
animals. Gag
206-225.216S-specific CD8
+ T-cell responses were
also undetectable, indicating that the predominance of the wild-type
virus in these four macaques was not due to immune pressure
exerted by the mutant-specific CTL recognizing an epitope with
the mutant Gag216S sequence.
In the previous study (
17), the Gag216S mutant virus escaping
from Gag
206-216-specific CTL was rapidly selected in the vaccinees
possessing the MHC-I haplotype
90-
120-Ia after SIVmac239 challenge.
However, the CTL escape mutant with lower viral fitness was
rapidly contained and became undetectable in plasma after week
5 postchallenge. The present study shows that this mutant SIV,
which was rapidly contained in the vaccinees in the previous
study, can replicate and is unable to be rapidly contained in
naive macaques, leading to the appearance of the wild-type virus
in the absence of Gag
206-216-specific CTL responses. This suggests
the requirement of additional adaptive immune responses as well
as Gag
206-216-specific CTLs for containment of this CTL escape
mutant virus with lower viral fitness.
Viral adaptation by escape mutations under CTL pressure and reversion after transmission to MHC-I-mismatched hosts have been indicated in immunodeficiency virus infection (2, 3, 7, 14). It has recently been shown that reversion by de novo mutation can really occur after challenge of macaques with a cloned SIV with CTL escape mutations (7). In that study, preparation of the challenge virus stock from a molecular clone DNA of the mutant SIV required viral replication in vitro for more than a week. In the present study, to see the reversion by de novo mutation only in vivo by deleting the in vitro replication process for virus stock preparation, we directly inoculated macaques with a molecular clone DNA of the mutant SIV. Our results show that the reversion by de novo mutation can really occur and be detected in 5 weeks after inoculation of the mutant molecular clone DNA. Thus, this is the first report describing the reversion in vivo from an inoculated, molecular proviral DNA clone of immunodeficiency virus with a CTL escape mutation.

ACKNOWLEDGMENTS
This work was supported by a grant from the Ministry of Education,
Culture, Sports, Science, and Technology, grants from the Japan
Health Sciences Foundation, and grants from the Ministry of
Health, Labor, and Welfare in Japan.
We thank T. Kodama and R. C. Desrosiers for providing SIVmac239 molecular clone DNA, Y. Ami, F. Ono, K. Komatsuzaki, A. Hiyaoka, H. Ogawa, K. Hanari, K. Oto, H. Oto, H. Akari, and K. Terao for assistance in the animal experiments, and K. Mori, N. Yamamoto, T. Sata, T. Kurata, Y. Nagai, and A. Nomoto for their help.

FOOTNOTES
* Corresponding author. Mailing address: Department of Microbiology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Phone: 81-3-5841-3407. Fax: 81-3-5841-3374. E-mail:
matano{at}m.u-tokyo.ac.jp.


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Journal of Virology, September 2005, p. 11529-11532, Vol. 79, No. 17
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.17.11529-11532.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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