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Journal of Virology, October 1999, p. 8720-8731, Vol. 73, No. 10
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Mosaic Structure of the Human Immunodeficiency
Virus Type 1 Genome Infecting Lymphoid Cells and the Brain: Evidence
for Frequent In Vivo Recombination Events in the Evolution of
Regional Populations
A.
Morris,1
M.
Marsden,1
K.
Halcrow,1
E. S.
Hughes,1
R. P.
Brettle,2
J. E.
Bell,3 and
P.
Simmonds1,*
Department of Medical Microbiology,
University of Edinburgh, Edinburgh EH8 9AG,1 and
Regional Infectious Diseases Unit, Western General
Hospital,2 and Department of
Neuropathology, University of Edinburgh, Western General
Hospital,3 Edinburgh EH4 2XU, United Kingdom
Received 16 December 1998/Accepted 7 July 1999
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ABSTRACT |
In addition to immunodeficiency, human immunodeficiency virus type
1 (HIV-1) can cause cognitive impairment and dementia through direct
infection of the brain. To investigate the adaptive process and timing
of HIV-1 entry into the central nervous system, we carried out an
extensive genetic characterization of variants amplified from different
regions of the brain and determined their relatedness to those in
lymphoid tissue. HIV-1 genomes infecting different regions of the brain
of one study subject with HIV encephalitis (HIVE) had a mosaic
structure, being assembled from different combinations of
evolutionarily distinct lineages in p17gag,
pol, individual hypervariable regions of gp120 (V1/V2, V3,
V4, and V5), and gp41/nef. Similar discordant phylogenetic
relationships were observed between p17gag and
V3 sequences of brain and lymphoid tissue from three other individuals
with HIVE. The observation that different parts of the genome of HIV
infecting a particular tissue can have different evolutionary histories
necessarily limits the conclusions that can be drawn from previous
studies of the compartmentalization of distinct HIV populations in
different tissues, as these have been generally restricted to sequence
comparisons of single subgenomic regions. The complexity of viral
populations in the brain produced by recombination could provide a
powerful adaptive mechanism for the spread of virus with new
phenotypes, such as antiviral resistance or escape from cytotoxic
T-cell recognition into existing tissue-adapted virus populations.
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INTRODUCTION |
Isolates of human immunodeficiency
virus (HIV) show great heterogeneity in their kinetics of replication,
coreceptor usage, cellular tropism, and cytopathic effects. Differences
in these properties have been hypothesized to underlie in vivo
differences in pathogenicity, which in turn may influence the rate of
disease progression in HIV-infected individuals (1, 2, 5, 9, 11,
16, 19, 20, 28, 40, 44). Differences in phenotype may also
underlie differences in in vivo cellular tropism, which would
substantiate the hypothesis that the different populations of HIV
infecting lymphoid tissue, brain, and other tissues may have originated
through an adaptive process following primary infection. Difficulties
in recovering HIV from nonlymphoid tissues have to date prevented
extensive analysis of their biological properties, although the
existence of consistent sequence differences in the envelope gene from
those recovered from lymphoid tissues provides indirect evidence for
specific cellular tropisms (3, 13, 14, 17, 22, 26, 27, 30, 31,
34-36, 42). However, an alternative hypothesis proposes that
differences in the rate of virus turnover in different cell types may
lead to the observed population differences, given the rapid temporal
change in HIV populations over time in peripheral blood mononuclear
cells, in lymph nodes (LN), and among HIV variants recovered from the
gastrointestinal tract (27, 45, 46).
To investigate whether differences in V3 and elsewhere in the HIV
genome reflect tissue adaptation, or whether they arise simply though
limited spatial or temporal sampling, we have compared nucleotide
sequences in different regions of the HIV type 1 (HIV-1) genome from
lymphoid tissue with autopsy samples from anatomically separated parts
of the brains of four study subjects with HIV encephalitis (HIVE). We
also determined whether sequences in p17gag,
pol, and different regions of the env gene
(V1/V2, V3, V4, V5, and gp41/nef) between different brain samples and
those from lymphoid tissue provided equivalent evidence for
tissue-specific compartmentalization of HIV-1.
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MATERIALS AND METHODS |
Study subjects.
Frozen samples of LN or spleen and from
several anatomically distinct regions of the brain from four
individuals with HIV giant cell encephalitis were stored at autopsy
(risk group, CD4 counts, and brain pathology are summarized in Table
1). Subject NA129 had received zidovudine
monotherapy for 17 months up to approximately 1 year before death; ddC
was used for 1 month, finishing 3 months before death. The other study
subjects had received minimal antiviral treatment: for NA234, a single
course of zidovudine for a duration of 1 month at 1 year before death;
for NA021, zidovudine intermittently over 1 year at 5 years before
death and zidovudine-ddC for 1 month at 1 year before death; for NA173,
zidovudine for 4 months at 2 years before death and then for 1 month at
1 year before death. None of the study subjects showed evidence for
genotypic resistance to zidovudine or other antiviral agents
(42a).
Pathology examination.
The brains were examined
pathologically as previously described (4). Assessment of
pathology findings was undertaken blind to the PCR analysis and
validated by three independent observers.
DNA extraction and amplification.
DNA was extracted from the
brain, LN, and spleen and quantified as previously described
(15). Total DNA was quantified spectroscopically, while HIV
proviral DNA was semiquantitated by amplification, using the
p17gag primers, of serial 10-fold dilutions of
DNA, with the last positive dilution used to indicate the minimum
proviral load in the sample. Samples were used for sequence comparison
only if proviral frequencies were >100 copies/106 cells,
and this excluded analysis of left parietal (LP) and both cerebellum
samples from NA234. Low levels were detected in two atrophied LN
samples from NA128, and lymphoid sequences were therefore obtained from
the spleen. For nucleotide sequencing, 1-µg aliquots of extracted DNA
were amplified as previously described (39) or amplified
after dilution to an endpoint (see below).
Amplified DNA was either sequenced directly by cycle sequencing
(Amersham) or cloned into pGEM, using poly(T) overhangs (pGEM-T Vector
system; Promega). Miniprepped DNA from clones was sequenced by using a
Sequenase version 2.0 kit (U.S. Biochemical) according to the
manufacturer's protocol.
Nucleotide sequencing.
For samples with evidence of sequence
heterogeneity, amplified DNA was cloned and approximately 10 clones
were sequenced. Sequences from other samples without evidence for
heterogeneity (no detectable multiple bands at any position on a
sequencing gel lane) or length polymorphism analysis (23)
were directly sequenced. The sequence data set for the
p17gag region of NA234 was assembled from cloned
sequences from each of the brain regions and extended from positions
405 to 795 in the HIVLAI genomic sequence (GenBank
accession no. K02013). Sequences in the pol region of NA234
were directly sequenced from amplified DNA and compared between bases
2189 and 2842, using the PCR primers used for detection of antiviral
resistance mutations (43); there was no evidence for
intrasample sequence heterogeneity. Sequences in the V1/V2 region from
NA234 were amplified by using primers as previously described
(23). Amplified DNA was homogeneous by length polymorphism
analysis, and nucleotide sequences from regions other than LN, left
frontal (LF), and right frontal (RF) were obtained by direct sequencing
of amplified DNA. Sequences in V3 and V4/V5 were amplified by using
primers as previously described (38). Length polymorphisms
in the V4/V5 region in some brain samples from NA234 necessitated
multiple clones to be sequenced. Sequences from each tissue were
amplified in the gp41/nef region by using outer primers
5'-AGGGCTGCTATTAACAAGAGATGG-3' and
5'-GTAGCTGCTGTATTGCTACTTGTG-3' and inner primers
5'-AGGTCTTCAGACCTGGAGGAGG-3' and
5'-TATTGCTACTTGTGATTGCTCCATG-3' (5' base positions 7166, 8541, 7215, and 8531, respectively). Direct sequencing was carried out on the amplified DNA from the 3' end by using the antisense inner primer, while an internal primer (5'-TGAGGGGACAGATAGGGTTATAGA-3', position of 5' base 8287 in HIVLAI genome) was used
to sequence the 5' end.
Sequences were aligned and distances were estimated with the Simmonic
2000 Sequence Editor package. Synonymous and nonsynonymous
distances
and standard errors were estimated by the method of
Nei and Gojobori
(
33). Phylogenetic analysis was carried out
with the MEGA
program (
29). The nucleotide sequences from
p17
gag and V3 amplified from each of the study
subjects were compared
with each other and with a range of standard
HIV-1 variants. Each
set of sequences from the four study subjects was
monophyletic
in both genomic regions and distinct from those of the
published
sequences of subtype B: HIVSF2 (
K02007), HIVRF (
M17451),
HIVOYI (
M26727), HIVLAI (
K02013), HIVJRFL (
M74978), HIVYU2
(
M93258),
HIVCAM1 (
D10112), HIVNY5CG (
M38431), HIVHAN
(
U43131), HIVWMJ22
(
M12507), and HIVSFAAA (
M65024). This
comparison provided no evidence
for coinfection with more than
one epidemiologically unrelated HIV
strains or for intersample
or exogenous laboratory
contamination.
Nucleotide sequence accession numbers.
Nucleotide sequences
obtained in this study have been submitted to GenBank and assigned
accession no. AF174692 through AF175123.
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RESULTS |
Sequence relationships in different regions of the HIV-1
genome.
Autopsy samples were obtained from multiple regions of the
brain and from LN of an individual (NA234) with autopsy evidence of
HIVE. The p17gag region was amplified by nested
PCR and cloned from samples with virus loads of greater than 100 proviral copies/106 cells. These nucleotide sequences
formed two distinct evolutionary lineages, each with bootstrap support
of 
80%. Sequences from LN, brain stem, right parietal (RP) and LF
regions (lineage A) showed a closer sequence relationship to each other
than to variants obtained from elsewhere in the brain (lineage B) (Fig.
1). At synonymous sites, the mean
pairwise Jukes-Cantor (J-C) distances were 0.057 (mean standard error
±0.026) among members of lineage A and 0.055 (±0.024) for lineage B,
almost nonoverlapping with the range of pairwise distances observed
between the two lineages (mean synonymous distance 0.109 ± 0.038). On the basis of the previously established mean rate of
sequence change in this region of gag (0.6 to 0.7% per site
per year [24, 25]), these distances suggest a time of
divergence between lineages A and B of around 8.4 ± 2.9 years,
compared with a likely duration of HIV infection of around 10 years in
this study subject.
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FIG. 1.
Phylogenetic analysis of the
p17gag region amplified from different regions
of the brain and from lymphoid tissue of NA234. Divergence between
nucleotide sequences was estimated from J-C distances (scale indicated
below tree), and the tree was constructed from the distance matrix by
the neighbor-joining method. The robustness of groupings was indicated
by bootstrap resampling of 100 data sets, with values of 75%
indicated on branches; lineages are indicated by single letters. The
tree was rooted by using the sequence of HIVLAI (accession
no. K02013) as an outgroup.
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In contrast to LN sequences, those from other regions of the brain were
relatively homogeneous, apart from those from the
RP region, which
formed at least three separate clusters within
lineage A, and a single
sequence from the LF region, which grouped
in lineage B instead of
lineage A. Sequences in lineage B, comprising
exclusively brain-derived
variants, clustered by tissue origin,
with a tendency for variants
recovered from adjacent tissues to
be more similar to each other (e.g.,
left occipital [LO) and right
occipital [RO] regions) than to
variants from virus with greater
physical separation (e.g., occipital
region to RF region). Most
regional variants in lineage B had common
ancestors distinct from
any variants found in lymphoid tissue, and more
recent times of
divergence than that between lineages A and B can be
inferred.
Variants within lineage B may therefore have originated from
the
spread of HIV within the brain rather than from multiple seeding
from the peripheral circulation and thus differ in origin from
brain-derived variants in lineage A (LF and RP). To confirm the
separate groupings of LF and RF sequences, DNAs extracted from
these
tissues and from LN were separately analyzed by limiting
dilution as
previously described (
39). Sequences obtained were
similar
or identical to those obtained by cloning of PCR products
(data not
shown).
In marked contrast to the relationships observed in
p17
gag, LF and RF sequences from both V1/V2 and
V3 regions in gp120 grouped
together in a distinct lineage from those
of LN sequences (bootstrap
support
80%) (Fig.
2A and B), demonstrating that variants
from
LF and RF regions shared a common ancestor distinct from that
of
variants in the LN region. The probability of this discordant
phylogeny
arising through sampling was <0.0001 (Fisher's exact
test). To
investigate the robustness of the difference in branching
order in
p17
gag and V3, a user-defined tree of
p17
gag sequences with the branching order of V3
was created by using
RETREE in the PHYLIP package (
18). With
the Hasegawa-Kishino-Yano
test, a p17
gag tree
with the V3 branching order was significantly less likely
than the most
likely tree calculated by using maximum likelihood
(DNAML;
P = 0.018).
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FIG. 2.
Comparison of sequences from LF and RF regions of the
brain of NA234 with those of the LN region in V1/V2 (A), V3 (B), V4
(C), and V5 (D) hypervariable regions (outgroup, symbols, and bootstrap
method as for Fig. 1).
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In the V4/V5 region, sequence relationships were more complex and also
discordant from those observed both for p17
gag
and for V1/V2 or V3 (Fig.
2C,
2D,
3C, and
3D). Variants from
the LN region formed three lineages (A, B, and C),
with a fourth
lineage comprising variants from the LF and RF regions
(lineage
D). However, approximately half of the LF variants grouped
with
lineage C. Similar sequence relationships were observed for the
V5
region, with three main lineages comprising LN (A), LN and
LF (B), and
LF and RF (C). Because V4 and V5 sequences were amplified
in the same
PCR fragment, it was also possible to observe different
combinations of
lineages between the two regions (Fig.
3D). For
example, V4 sequences
of 12 LF clones were in lineage C in V4
and in lineage B in V5 (i.e.,
CB), while 9 clones were DC and
7 were CC. Similar reassortments were
observed in LN sequences
(one AA, two AB, one BB, and three BC).
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FIG. 3.
(A) Distribution of phylogenetic groupings in different
regions of the genome of HIV-1 variants infecting NA234. Letters refer
to bootstrap-supported groupings identified by phylogenetic analysis
(Fig. 1, 2, and 3); vertical bars indicate discontinuities in groupings
that require the minimum number of recombination events. The sequence
conservation and monophylogeny of the pol region originated
either through recombination or from a lower rate of sequence change
compared with the rest of the genome; sequence relationships are
indicated with an interrupted line to indicate this uncertainty. Three
samples contained sequences distributed in more than one clade in V4
and V5, in the combinations tabulated in LN (B), CP (C), and LF (D)
regions of the brain.
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To investigate further the tissue distribution of variants in different
genomic regions, we obtained sequences from the
pol,
V1/V2,
V3, and gp41/
nef regions of variants recovered from other
parts of the brain (Fig.
4). The most
conserved region was the
pol region, in which sequences from
different regions of the brain
did not display any significant
phylogenetic groupings. The mean
pairwise distance between
pol sequences from different samples
was 0.013 (0.048 at
synonymous sites), lower than observed between
variants within either
lineage A or lineage B in the p17
gag region.
Either there was a lower rate of sequence change at synonymous
sites in
this part of the genome or the
pol region of the genome
originated after the diversification of p17
gag,
implying the existence of recombination between the
pol
region
and more variable regions of the genome.
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FIG. 4.
Comparison of inferred amino acid sequences of variants
from different regions of the brain of NA234 in V1/V2 (A), V3 (B), V4
(C), V5 (D), and gp41 (E) /nef, using LN variants as reference
sequences. Horizontal lines divide primary bootstrap-supported (75%
of data sets) phylogenetic groupings of nucleotide sequences. Each
number in the third column indicates the number of clones used to
create the indicated consensus sequence. c, consensus sequence obtained
by direct sequencing of PCR product. Symbols: ·, sequence identity
with LN sequence; -, gap introduced to presence sequence alignment;
*, termination codon. Sequences are numbered by their positions in
the HIVLAI gp120 (A to D) or nef (E) sequence.
BS, brain stem.
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In V1/V2, we observed four bootstrap-supported lineages, differing from
each other by distances of 0.022 to 0.076, compared
with distances of 0 to 0.008 within lineages. The distribution
of sequences from different
regions of brain did not match the
distribution of sequences into the
two lineages in p17
gag (Fig.
3 and
4). For
example, sequences from LN (A in p17
gag) and
choroid plexus (CP) (B in p17
gag) regions were
found in the same lineage in V1/V2, while sequences
from LF and RP
regions, which grouped with the LN sequence in
p17
gag, were on three separate lineages in V1/V2
(A, C, and
D).
Similar complexity was observed among sequences from V3, V4, V5, and
gp41/
nef, with variants from the CP showing the greatest
diversity in V3, V4, and V5. A subpopulation of CP variants grouped
with those found in lymphoid tissue (e.g., lineages C in V3, B
in V4
and V5, and A in gp41), but as described above for LN and
LF, there
were inconsistent relationships in the V4 and V5 regions
(Fig.
3C),
with all four combinations of lineages B and C in V4
and A and B in V5
being observed. Overall, no consistent relationship
between lineages
was observed among the other samples collected
from the brain (Fig.
3),
and apart from LO and RO regions, each
region of the brain contained a
different combination of phylogenetically
distinct subgenomic
fragments.
Tissue-specific grouping.
Variants from different regions of
the brain of NA234 consistently grouped separately from those recovered
from LN in the V1/V2, V3, and gp41/nef subgenomic regions.
To investigate further the differentiation between lymphoid and
brain-derived variants, sequences from the
p17gag and V3 regions were obtained from 8 to 12 brain regions from three other individuals (NA021, NA173, and NA128)
and compared with those amplified from the corresponding LN or spleen
samples (Table 2; Fig.
5 and 6).
Sequences from each individual were monophyletic in both
p17gag and V3 upon comparison with each other
and with epidemiologically unlinked subtype B sequences (listed in
Materials and Methods).
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FIG. 5.
Comparison of inferred amino acid sequences of variants
from the V3 region of NA173 (A), NA021 (B), and NA128 (C), using the LN
or spleen (SPL) sequences as a reference. Horizontal lines divide
bootstrap-supported (75% of data sets) phylogenetic groupings of
nucleotide sequences (symbols and sequence numbering correspond to
those in Fig. 4). BS, brain stem.
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FIG. 6.
Phylogenetic analysis of p17gag
(column 1) and V3 sequences (column 2) of the four study subjects (A
through D). Sequences from each of the four subjects were monophyletic
in both genomic regions upon comparison with each other and the
sequences available from GenBank listed in Materials and Methods and
were used to root each clade. p17gag and V3
trees from different study subjects were plotted by using the indicated
scale of J-C distances. Sequences were derived from brain ( ), from
lymphoid tissue (LN or spleen [SPL]) ( ), or from CP ( ). All
bootstrap values of 75% are indicated on branches. Sequences from
NA234 were obtained from individual clones of amplified DNA instead of
by direct sequencing; single representative clones from each sample or
multiple clones for those containing sequences in more than one lineage
(i.e., LN and CP) have therefore been included. BS, brain stem; BG,
basal ganglia.
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In each of the three study subjects, p17
gag
sequences of variants infecting different regions of the brain and
lymphoid tissue
showed interrelationships different from those observed
in V3.
First, there was no correlation between sequence diversity
between
the two genomic regions (Table
2). For example,
p17
gag sequences from NA173 showed two- to
threefold-greater variability
between brain regions (mean J-C distance
of 0.035 ± 0.010) and
between brain and lymphoid tissue (mean J-C
distance of 0.04 ±
0.011) than the corresponding sequences from
NA128 (distances
of 0.012 ± 0.006 and 0.023 ± 0.008). In
contrast, sequences from
NA128 in the V3 region were more variable than
those from NA173
(0.035 ± 0.011 and 0.080 ± 0.018, compared
with mean distances
of 0.017 ± 0.008 and 0.031 ± 0.011 for
NA173).
Second, phylogenetic analysis of the p17
gag and
V3 sequences produced different groupings of variants (Fig.
6). For
example,
LN sequences from NA021 clustered separately from
brain-derived
variants in the V3 region but grouped with brain variants
in p17
gag. Conversely, LN sequences from NA173
were distinct from all but
one of the variants in
p17
gag but were undifferentiated from brain
variants in V3. In each
of the four study subjects, tissue specificity
depended on the
region being compared. A specific instance of
incompatible phylogeny
comparable to that observed for NA234 (see
above) was observed
in NA021, where LN sequences formed a bootstrap
supported lineage
in V3 distinct from the brain variants, while the
primary branching
order in p17
gag divided
sequences from the RT and RO brain regions from the rest
of the
sequences.
Sequence divergence and pathology appearance.
The severity of
HIVE varied between the study subjects (Table 1), ranging from
infrequent giant cells confined to perivascular regions (NA173) to
widespread pathology affecting both white and grey matter (NA128; Fig.
7). The extent and type of HIV-induced pathology correlated with the degree of V3 but not
p17gag sequence diversity between different
brain regions and in the extent to which V3 sequences from the brain
differed from those in lymphoid tissue. V3 sequences from NA173 (who
showed minimal HIV-related pathology) were largely undifferentiated
from those detected in LN, with only an alanine-arginine change
segregating by tissue (mean J-C distances listed in Table 2). At the
other extreme, the spleen-derived sequence from NA128 had a predicted syncytium-inducing phenotype and differed at multiple sites from the
nonsyncytium-inducing variants in the brain. In the
p17gag region, however, sequences from NA173
were the most variable, and those from NA128 were the least variable.
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FIG. 7.
Immunocytochemical detection of p24 antigen in
representative sections of cerebral white matter of two study subjects
with HIVE. (A) NA173. Immunopositive mononuclear and giant cells
(stained brown with diaminobenzidine) are confined to the perivascular
region. (B) NA128. Widely dispersed HIV-infected microglia in white
matter.
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DISCUSSION |
This study documents the extraordinary complexity of HIV
populations in vivo, findings which have several implications in understanding mechanisms of tissue adaptation and the timing of entry
of HIV into the central nervous system (CNS). The marked sequence
diversity of the p17gag region and the readily
identifiable clusters of sequences in the hypervariable regions of
env (V1/V2, V3, V4, and V5) of NA234 and other study
subjects provided evidence for recombination between different regions
of the genome. For example, variants infecting separate regions of the
brain of NA234 were assembled from two different
p17gag lineages and a limited number of distinct
hypervariable region lineages, often with different combinations within
same autopsy sample (e.g., the V4 and V5 sequences in the LN, CP, and
LF sequences [Fig. 3 to D]). In the other three study subjects, the
different degrees of variability and the discordant phylogenetic
groupings between p17gag and V3 regions indicate
a lack of genetic linkage between these two subgenomic regions and
further support the hypothesis of frequent recombination in vivo.
To date, recombination has been most easily identified between
different subtypes of HIV-1; for example, variants of HIV-1 from
Thailand contain gag sequences resembling those of subtype A
but distinct from subtype A in the env gene (7),
while other viruses appear to have been generated by multiple
recombination events (e.g., HIV-1MAL [10,
37] and subtype I [21]). Recombination has
also been observed upon infection with different strains of HIV-1,
either experimentally in a chimpanzee exposed to the laboratory isolates HIVLAI and HIV-1SF2 (47) or
possibly through multiple exposure to two or more sources of HIV
infection in a blood recipient and an injecting drug user (12,
49). We have now demonstrated that recombination also occurs
within an infected individual between variants descended in each case
from the original infecting strain. The finding that different parts of
the HIV genome can have different evolutionary histories severely
limits the concept of tissue specificity of variants of HIV in vivo,
particularly if these conclusions are based on a single subgenomic
region. For example, the brain-specific and frequently monophyletic
nature of HIV sequences in the pol region (virodemes) of
variants infecting antiviral agent-treated individuals (48)
may not be reflected elsewhere in the genome. Indeed, sequence
relationships in the env gene may differ substantially from
pol, as variation in the former region is more likely to confer phenotypic differences in cellular tropism. The existence of
recombination provides an explanation for discordant phylogenies between p17gag, V1/V2, and V3 that we observed
between brain (in the LF region) and LN sequences in three previous
subjects (14, 23, 24). While sequences in V3 were tissue
specific, sequences in the p17gag and V1/V2
regions were diverse, and some evolutionary lineages were common to
variants recovered from brain, lung, and LN. Our observations support
the hypothesis that recombination may accompany the acquisition of
antiviral resistance, as exemplified by the appearance of
zidovudine-resistant mutants in the peripheral circulation which
occurred without evidence for a comparable bottlenecking in
env (6); V3 sequences showed no reduction in
diversity during the process of population replacement in
pol region.
The diversity of V3 sequences in different brain regions of the four
study subjects was similar to a previous comparison of variants
infecting different brain regions (mean pairwise distance between brain
regions, 0.021 [8], excluding sequences from the LF
region that were highly divergent in sequence and failed to group
phylogenetically with sequences derived from other regions of the
brain). The LF sequences may have originated from exogenous contamination of the PCR, or corresponded to an epidemiologically unlinked isolate in a case of mixed infection. In either case, the
observed degree of sequence divergence was unlikely to have originated
from sequence change over the course of infection within the study subject.
Greater degrees of sequence complexity may also originate from the
presence of different infected cell types in a tissue sample. HIV
sequences amplified from the choroid plexus of NA234 showed the
greatest diversity in the env region, containing variants corresponding to those from lymphoid tissue and brain, consistent with
the presence of virus from blood-derived cells and brain parenchyma.
The proximity of these different cell types in the CP may provide an
opportunity for recombination of HIV to occur, as well as a site of
entry of HIV into the CNS. Without biological characterization of the
variants found in the CP or elsewhere in the brain, it remains unclear
whether recombinant genomes have been selected or represent random
samplings of phenotypically identical viruses. However, the multiple
recombination events observed in this study would provide a powerful
mechanism for adaptation, providing, for example, an effective method
for the spread of antiviral agent resistance or cytotoxic T-cell escape mutants into the CNS. Recombination between these latter determinants and env could produce new virus populations that retain
their neuroadapted phenotype.
The differing sequence relationships between brain-derived and lymphoid
variants from the four study subjects suggests that entry of HIV-1 into
the CNS can occur at different times. The current consensus view that
entry occurs early during HIV infection is supported by the observation
that HIV RNA sequences can be detected in cerebrospinal fluid
throughout the course of infection and by the detection of low levels
of HIV proviral sequences in brains of asymptomatic individuals
(4, 15, 41). Early entry is also supported by the extensive
sequence diversity in the p17gag region of
variants recovered from the brain, such as between lineages A and B
observed in NA234 in this study, which implies several years of
divergent evolution (24). However, the relevance of early
entry into the CNS in the development of late stage HIVE remains
unclear, since active virus replication has not been demonstrated immunocytochemically during early infection (4), and brains show little evidence of pathology apart from the presence of
infiltrating CD8 lymphocytes in perivascular areas.
Evidence for a contribution of late-entering variants to HIVE is
provided by NA173, who showed a distinctive pathology appearance of
HIV-expressing infiltrating macrophages confined to the perivascular regions (Table 1; Fig. 7A). The hypothesis of recent entry of HIV-infected cells into the brain parenchyma was supported by the
observation of close sequence similarity in the V3 region of
brain-derived variants with those obtained from lymphoid cells. This
late-entry picture contrasted strongly with the distribution of HIV
infection in NA128, in which HIV was widely dispersed in white (Fig.
7B) and grey matter, while V3 sequences were distinct between spleen
and brain and heterogeneous within brain (Table 2; Fig. 5C). This
correlation was, however, not supported by sequence comparisons in the
p17gag region, where sequence diversity was
greatest in NA173 and least in NA128.
Indeed, to understand the adaptive significance of the sequence
differences in different parts of the genome, it will in the future be
necessary to analyze functionally the contribution of each genomic
region to the phenotype of the virus. In particular, it will be
important to determine the phenotypic significance of recombination
between the p17gag and env regions,
particularly as variants with different combinations of lineages in the
two regions were associated with distinct pathology appearances.
Understanding what contributes to neurotropism will illuminate the
selective pressures (if any) that produce the recombinant viruses
observed in this study. The lack of genetic linkage in the HIV genome
resulting from recombination greatly enhances its ability to adapt to
several simultaneously acting selection pressures, as indicated by the
rapid emergence in vitro of dual antiviral agent-resistant mutants
(32).
| |
ACKNOWLEDGMENTS |
We are grateful to Francis Brannan for preparation of the
sections for immunocytochemistry and for the provision of frozen samples from the MRC Edinburgh Brain Bank. We also greatly appreciate the critical review and discussion contributed by Donald Smith.
This study was supported by Medical Research Council Strategic Project
grant G9632414.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Medical Microbiology, University of Edinburgh, Teviot Place, Edinburgh EH8 9AG, United Kingdom. Phone: 44 131 650 3138. Fax: 44 131 650 6531. E-mail: Peter.Simmonds{at}ed.ac.uk.
| |
REFERENCES |
| 1.
|
Alkhatib, G.,
C. Combadiere,
C. C. Broder,
Y. Feng,
P. E. Kennedy,
P. M. Murphy, and E. A. Berger.
1996.
CC CKR5: a RANTES, MIP-1 alpha, MIP-1 beta receptor as a fusion cofactor for macrophage-tropic HIV-1.
Science
272:1955-1958[Abstract].
|
| 2.
|
Asjo, B.,
J. Albert,
A. Karlsson,
L. Morfeldt Manson,
G. Biberfeld,
K. Lidman, and E. M. Fenyo.
1986.
Replicative capacity of human immunodeficiency virus from patients with varying severity of HIV infection.
Lancet
ii:660-662.
|
| 3.
|
Ball, J. K.,
E. C. Holmes,
H. Whitwell, and U. Desselberger.
1994.
Genomic variation of human immunodeficiency virus type 1 (HIV-1) molecular analyses of HIV-1 in sequential blood samples and various organs obtained at autopsy.
J. Gen. Virol.
75:867-879.
|
| 4.
|
Bell, J. E.,
A. Busuttil,
J. W. Ironside,
S. Rebus,
Y. K. Donaldson,
P. Simmonds, and J. F. Peutherer.
1993.
Human immunodeficiency virus and the braininvestigation of virus load and neuropathologic changes in pre-AIDS subjects.
J. Infect. Dis.
168:818-824[Medline].
|
| 5.
|
Berson, J. F.,
D. Long,
B. J. Doranz,
J. Rucker,
F. R. Jirik, and R. W. Doms.
1996.
A seven-transmembrane domain receptor involved in fusion and entry of T-cell-tropic human immunodeficiency virus type 1 strains.
J. Virol.
70:6288-6295[Abstract].
|
| 6.
|
Brown, A. J. L., and A. Cleland.
1996.
Independent evolution of the env and pol genes of HIV-1 during zidovudine therapy.
AIDS
10:1067-1073[Medline].
|
| 7.
|
Carr, J. K.,
M. O. Salminen,
C. Koch,
D. Gotte,
A. W. Artenstein,
P. A. Hegerich,
D. St. Louis,
D. S. Burke, and F. E. McCutchan.
1996.
Full-length sequence and mosaic structure of a human immunodeficiency virus type 1 isolate from Thailand.
J. Virol.
70:5935-5943[Abstract].
|
| 8.
|
Chang, J.,
R. Jozwiak,
B. Wang,
T. Ng,
Y. C. Ge,
W. Bolton,
D. E. Dwyer,
C. Randle,
R. Osborn,
A. L. Cunningham, and N. K. Saksena.
1998.
Unique HIV type 1 V3 region sequences derived from six different regions of brain: region-specific evolution within host-determined quasispeciesshort communication.
AIDS Res. Hum. Retroviruses
14:25-30[Medline].
|
| 9.
|
Cheng-Mayer, C.,
D. Seto,
M. Tateno, and J. A. Levy.
1988.
Biological features of HIV-1 that correlate with virulence in the host.
Science
240:80-82[Abstract/Free Full Text].
|
| 10.
|
Cornelissen, M.,
G. Kampinga,
F. Zorgdrager, and J. Goudsmit.
1996.
Human immunodeficiency virus type 1 subtypes defined by env show high frequency of recombinant gag genes.
J. Virol.
70:8209-8212[Abstract].
|
| 11.
|
Deng, H. K.,
R. Liu,
W. Ellmeier,
S. Choe,
D. Unutmaz,
M. Burkhart,
P. Dimarzio,
S. Marmon,
R. E. Sutton,
C. M. Hill,
C. B. Davis,
S. C. Peiper,
T. J. Schall,
D. R. Littman, and N. R. Landau.
1996.
Identification of a major co-receptor for primary isolates of HIV-1.
Nature
381:661-666[Medline].
|
| 12.
|
Diaz, R. S.,
E. C. Sabino,
A. Mayer,
J. W. Mosley, and M. P. Busch.
1995.
Dual human immunodeficiency virus type 1 infection and recombination in a dually exposed transfusion recipient.
J. Virol.
69:3273-3281[Abstract].
|
| 13.
|
Di Stefano, M.,
S. Wilt,
F. Gray,
M. DuboisDalcq, and F. Chiodi.
1996.
HIV type 1 V3 sequences and the development of dementia during AIDS.
AIDS Res. Hum. Retroviruses
12:471-476[Medline].
|
| 14.
|
Donaldson, Y. K.,
J. E. Bell,
E. C. Holmes,
E. S. Hughes,
H. K. Brown, and P. Simmonds.
1994.
In vivo distribution and cytopathology of variants of human immunodeficiency virus type 1 showing restricted sequence variability in the V3 loop.
J. Virol.
68:5991-6005[Abstract/Free Full Text].
|
| 15.
|
Donaldson, Y. K.,
J. E. Bell,
J. W. Ironside,
R. P. Brettle,
J. R. Robertson,
A. Busuttil, and P. Simmonds.
1994.
Redistribution of HIV outside the lymphoid system with onset of AIDS.
Lancet
343:382-385.
|
| 16.
|
Dragic, T.,
V. Litwin,
G. P. Allaway,
S. R. Martin,
Y. X. Huang,
K. A. Nagashima,
C. Cayanan,
P. J. Maddon,
R. A. Koup,
J. P. Moore, and W. A. Paxton.
1996.
HIV-1 entry into CD4(+) cells is mediated by the chemokine receptor CC-CKR-5.
Nature
381:667-673[Medline].
|
| 17.
|
Epstein, L. G.,
C. Kuiken,
B. M. Blumberg,
S. Hartman,
L. R. Sharer,
M. Clement, and J. Goudsmit.
1991.
HIV-1 V3 domain variation in brain and spleen of children with AIDS: tissue-specific evolution within host-determined quasispecies.
Virology
180:583-590[Medline].
|
| 18.
|
Felsenstein, J.
1989.
PHYLIPphylogeny inference package (version 3.2).
Cladistics
5:164-166.
|
| 19.
|
Feng, Y.,
C. C. Broder,
P. E. Kennedy, and E. A. Berger.
1996.
HIV-1 entry cofactor: functional cDNA cloning of a seven-transmembrane, G protein-coupled receptor.
Science
272:872-877[Abstract].
|
| 20.
|
Fenyo, E. M.,
L. Morfeldt Manson,
F. Chiodi,
B. Lind,
A. von Gegerfelt,
J. Albert,
E. Olausson, and B. Asjo.
1988.
Distinct replicative and cytopathic characteristics of human immunodeficiency virus isolates.
J. Virol.
62:4414-4419[Abstract/Free Full Text].
|
| 21.
|
Gao, F.,
D. L. Robertson,
C. D. Carruthers,
Y. Y. Li,
E. Bailes,
L. G. Kostrikis,
M. O. Salminen,
F. Bibolletruche,
M. Peeters,
D. D. Ho,
G. M. Shaw,
P. M. Sharp, and B. H. Hahn.
1998.
An isolate of human immunodeficiency virus type 1 originally classified as subtype I represents a complex mosaic comprising three different group M subtypes (A, G, and I).
J. Virol.
72:10234-10241[Abstract/Free Full Text].
|
| 22.
|
Haggerty, S., and M. Stevenson.
1991.
Predominance of distinct viral genotypes in brain and lymph node compartments of HIV-infected individuals.
Viral Immunol.
4:123-131[Medline].
|
| 23.
|
Hughes, E. S.,
J. E. Bell, and P. Simmonds.
1997.
Investigation of population diversity of human immunodeficiency virus type 1 in vivo by nucleotide sequencing and length polymorphism analysis of the V1/V2 hypervariable region of env.
J. Gen. Virol.
78:2871-2882[Abstract].
|
| 24.
|
Hughes, E. S.,
J. E. Bell, and P. Simmonds.
1997.
Investigation of the dynamics of the spread of human immunodeficiency virus to brain and other tissues by evolutionary analysis of sequences from the p17gag and env genes.
J. Virol.
71:1272-1280[Abstract].
|
| 25.
|
Kasper, P.,
P. Simmonds,
K. E. Schneweis,
R. Kaiser,
B. Matz,
J. Oldenburg,
H. H. Brackmann, and E. C. Holmes.
1995.
The genetic diversification of the HIV type 1 gag p17 gene in patients infected from a common source.
AIDS Res. Hum. Retroviruses
11:1197-1201[Medline].
|
| 26.
|
Keys, B.,
J. Karis,
B. Fadeel,
A. Valentin,
G. Norkrans,
L. Hagberg, and F. Chiodi.
1993.
V3 sequences of paired HIV-1 isolates from blood and cerebrospinal fluid cluster according to host and show variation related to the clinical stage of disease.
Virology
196:475-483[Medline].
|
| 27.
|
Korber, B. T. M.,
K. J. Kunstman,
B. K. Patterson,
M. Furtado,
M. M. Mcevilly,
R. Levy, and S. M. Wolinsky.
1994.
Genetic differences between blood- and brain-derived viral sequences from human immunodeficiency virus type 1-infected patients: evidence of conserved elements in the V3 region of the envelope protein of brain-derived sequences.
J. Virol.
68:7467-7481[Abstract/Free Full Text].
|
| 28.
|
Kozak, S. L.,
E. J. Platt,
N. Madani,
F. E. Ferro,
K. Peden, and D. Kabat.
1997.
CD4, CXCR-4, and CCR-5 dependencies for infections by primary and laboratory-adapted isolates of human immunodeficiency virus type 1.
J. Virol.
71:873-882[Abstract].
|
| 29.
|
Kumar, S.,
K. Tamura, and M. Nei.
1993.
MEGA: Molecular Evolutionary Genetics Analysis, version 1.0.
The Pennsylvania State University, University Park, Pa.
|
| 30.
|
Li, Y. X.,
J. C. Kappes,
J. A. Conway,
R. W. Price,
G. M. Shaw, and B. H. Hahn.
1991.
Molecular characterization of human immunodeficiency virus type 1 cloned directly from uncultured human brain tissue: identification of replication-competent and -defective viral genomes.
J. Virol.
65:3973-3985[Abstract/Free Full Text].
|
| 31.
|
Liu, Z. Q.,
C. Wood,
J. A. Levy, and C. Cheng Mayer.
1990.
The viral envelope gene is involved in macrophage tropism of a human immunodeficiency virus type 1 strain isolated from brain tissue.
J. Virol.
64:6148-6153[Abstract/Free Full Text].
|
| 32.
|
Moutouh, L.,
J. Corbeil, and D. D. Richman.
1996.
Recombination leads to the rapid emergence of HIV-1 dually resistant mutants under selective drug pressure.
Proc. Natl. Acad. Sci. USA
93:6106-6111[Abstract/Free Full Text].
|
| 33.
|
Nei, M., and T. Gojobori.
1986.
Simple methods for estimating the numbers of synonymous and non-synonymous nucleotide substitutions.
Mol. Biol. Evol.
3:418-426[Abstract].
|
| 34.
|
Pang, S.,
H. V. Vinters,
T. Akashi,
W. A. O'Brien, and I. S. Chen.
1991.
HIV-1 env sequence variation in brain tissue of patients with AIDS-related neurologic disease.
J. Acquir. Immune. Defic. Syndr.
4:1082-1092.
|
| 35.
|
Power, C.,
J. C. Mcarthur,
R. T. Johnson,
D. E. Griffin,
J. D. Glass,
S. Perryman, and B. Chesebro.
1994.
Demented and nondemented patients with AIDS differ in brain-derived human immunodeficiency virus type 1 envelope sequences.
J. Virol.
68:4643-4649[Abstract/Free Full Text].
|
| 36.
|
Reddy, R. T.,
C. L. Achim,
D. A. Sirko,
S. Tehranchi,
F. G. Kraus,
F. Wong-Staal,
C. A. Wiley,
I. Grant,
J. H. Atkinson,
M. Kelly,
J. L. Chandler,
M. R. Wallace,
J. A. McCutchan,
S. A. Spector,
L. Thal,
R. K. Heaton,
J. Hesselink,
T. Jernigan,
E. Masliah,
I. Abramson,
N. Butters,
T. Patterson,
S. Zisook, and D. Jeste.
1996.
Sequence analysis of the V3 loop in brain and spleen of patients with HIV encephalitis.
AIDS Res. Hum. Retroviruses
12:477-482[Medline].
|
| 37.
|
Robertson, D. L.,
P. M. Sharp,
F. E. McCutchan, and B. H. Hahn.
1995.
Recombination of HIV-1.
Nature
374:124-126[Medline].
|
| 38.
|
Simmonds, P.,
P. Balfe,
C. A. Ludlam,
J. O. Bishop, and A. J. Leigh Brown.
1990.
Analysis of sequence diversity in hypervariable regions of the external glycoprotein of human immunodeficiency virus type 1.
J. Virol.
64:5840-5850[Abstract/Free Full Text].
|
| 39.
|
Simmonds, P.,
P. Balfe,
J. F. Peutherer,
C. A. Ludlam,
J. O. Bishop, and A. J. Leigh Brown.
1990.
Human immunodeficiency virus-infected individuals contain provirus in small numbers of peripheral mononuclear cells and at low copy numbers.
J. Virol.
64:864-872[Abstract/Free Full Text].
|
| 40.
|
Simmons, G.,
D. Wilkinson,
J. D. Reeves,
M. Dittmar,
S. Beddows,
J. Weber,
G. Carnegie,
U. Desselberger,
P. W. Gray,
R. A. Weiss, and P. R. Clapham.
1996.
Primary, syncytium-inducing human immunodeficiency virus type 1 isolates are dual-tropic and most can use either Lestr or CCR5 as coreceptors for virus entry.
J. Virol.
70:8355-8360[Abstract].
|
| 41.
|
Sinclair, E.,
F. Gray, and F. Scaravilli.
1992.
PCR detection of HIV proviral DNA in the brain of an asymptomatic HIV-positive patient.
J. Neurol.
239:469-471[Medline].
|
| 42.
|
Steuler, H.,
B. Storch Hagenlocher, and B. Wildemann.
1992.
Distinct populations of human immunodeficiency virus type 1 in blood and cerebrospinal fluid.
AIDS Res. Hum. Retroviruses
8:53-59[Medline].
|
| 42a.
| Strappe, P. Personal communication.
|
| 43.
|
Stuyver, L.,
A. Wyseur,
A. Rombout,
T. Scarcez,
C. Verhofstede,
D. Rimland,
R. F. Schinazi, and R. Rossau.
1997.
Line probe assay for rapid detection of drug-selected mutations in the human immunodeficiency virus type 1 reverse transcriptase gene.
Antimicrob. Agents Chemother.
41:284-291[Abstract].
|
| 44.
|
Tersmette, M.,
J. M. Lange,
R. E. de Goede,
F. de Wolf,
J. K. Eeftink Schattenkerk,
P. T. Schellekens,
R. A. Coutinho,
J. G. Huisman,
J. Goudsmit, and F. Miedema.
1989.
Association between biological properties of human immunodeficiency virus variants and risk for AIDS and AIDS mortality.
Lancet
i:983-985.
|
| 45.
|
Vanderhoek, L.,
C. J. A. Sol,
J. Maas,
V. V. Lukashov,
C. L. Kuiken, and J. Goudsmit.
1998.
Genetic differences between human immunodeficiency virus type 1 subpopulations in faeces and serum.
J. Gen. Virol.
79:259-267[Abstract].
|
| 46.
|
Vanderhoek, L.,
C. J. A. Sol,
F. Snijders,
J. F. W. Bartelsman,
R. Boom, and J. Goudsmit.
1996.
Human immunodeficiency virus type 1 RNA populations in faeces with higher homology to intestinal populations than to blood populations.
J. Gen. Virol.
77:2415-2425[Abstract/Free Full Text].
|
| 47.
|
Wei, Q., and P. N. Fultz.
1998.
Extensive diversification of human immunodeficiency virus type 1 subtype B strains during dual infection of a chimpanzee that progressed to AIDS.
J. Virol.
72:3005-3017[Abstract/Free Full Text].
|
| 48.
|
Wong, J. K.,
C. C. Ignacio,
F. Torriani,
D. Havlir,
N. J. S. Fitch, and D. D. Richman.
1997.
In vivo compartmentalization of human immunodeficiency virus: evidence from the examination of pol sequences from autopsy tissues.
J. Virol.
71:2059-2071[Abstract].
|
| 49.
|
Zhu, T. F.,
N. Wang,
A. Carr,
S. Wolinsky, and D. D. Ho.
1995.
Evidence for coinfection by multiple strains of human immunodeficiency virus type 1 subtype b in an acute seroconvertor.
J. Virol.
69:1324-1327[Abstract].
|
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Abstract
Introduction
