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Kennedy Institute of Rheumatology, London, United Kingdom; and
Department of Surgery, University of Limburg, Maastricht, The Netherlands
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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has been recognized to play an important role. Here we
investigate the feasibility and therapeutic efficacy of prolonged
blockade of TNF- activity through the adenovirus-mediated gene
delivery of a dimeric chimeric human p55 TNFR-IgG fusion protein and
compare it to protein therapy in established CIA. A single i.v.
administration of the replication-deficient adenovirus yielded
microgram serum levels of the chimeric fusion protein and ameliorated
CIA for 10 days. Subsequently, benefit was lost and a rebound to
greater inflammatory activity was observed despite the continual
presence of bioactive TNFR fusion protein. A similar trend was also
observed in mice injected directly with comparable amounts of a human
TNFR-IgG fusion protein, whereas the administration of a control
adenovirus-encoding ß-galactosidase or of a control human IgG1
protein did not significantly affect the disease course. The mechanisms
of the rebound of CIA were investigated, and augmented Ab
response to collagen type II and TNFR were identified as potential
causes. Our results confirm the feasibility of adenovirus-mediated gene
delivery of cytokine inhibitors in animal models of autoimmune diseases
for investigational purposes and highlight the importance of
prolonged studies. Further investigations are needed to optimize ways
of exploiting the potential of adenoviral gene therapy in
RA. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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regulates the production of other
proinflammatory cytokines such as IL-1, IL-6, IL-8, and GM-CSF
(1, 2) and therefore could be a potential target for
therapy. This concept has been supported by studies in an animal model
of RA, collagen-induced arthritis (CIA), where anti-TNF- Abs
given after onset of clinical symptoms significantly inhibit disease
progression (3, 4). The important role of TNF- in RA
was finally established in clinical trials where anti-TNF- mAbs
administered to patients with long-standing active RA were found to be
beneficial (5, 6, 7, 8). More recently, the p75 TNFR Ig fusion
protein was found to be effective in RA (9) and, to a
lesser extent, also the p55 TNFR Ig fusion protein (10, 11).
The definition of TNF- as a therapeutic target has led to a search
for other efficient means of blocking its activity. Low-molecular mass
chemicals that specifically block TNF- activity have not been
identified; however, drugs such as SB 203580, which blocks p38
mitogen-activated protein kinase (12), and
phosphodiesterase type IV inhibitors such as rolipram (13)
have been shown to reduce the production of TNF- and other
cytokines. Another possible approach is gene therapy, which has the
potential to become an effective therapeutic option if certain problems
can be overcome, chief among them being the availability of effective
vectors for gene delivery. Two viral systems have dominated the
literature in this field. Retroviruses were the first to be used,
which, as they only infect dividing cells, are used in ex vivo
procedures, where proliferating cells are cultured, infected, and
selected in vitro, then reimplanted containing the gene of interest
(14, 15). Adenoviruses, a more recent entrant to the
field, are efficient at transferring the gene of interest, can infect a
wide range of dividing and nondividing cells, and can generate large
amounts of proteins over extended periods of time (16).
The adenoviruses used in gene therapy are replication deficient due to
deletion of the E1 early transcriptional region and can be produced and
purified in large quantities. There is no insertion into host DNA,
therefore no risk of insertional mutagenesis (16).
However, there are problems with the use of adenoviruses for gene
therapy. As several studies have shown, adenoviruses are immunogenic
and also the cells expressing the gene product can become immunogenic,
leading to an immune response against the producing cells and cessation
of gene expression (17, 18). Nevertheless,
immunosuppressive therapy with a variety of agents can reduce the
immune response to adenoviruses, thus prolonging gene expression
(19, 20).
CIA is induced in DBA/1 mice by intradermal injection of native
collagen type II (CII) in CFA and has some important similarities to
human arthritis. For example, in both RA and CIA strong genetic
associations, mapping to MHC class II, and the histological appearance
of the erosions of cartilage and bone are similar in both diseases
(21). Most important, similar cytokines to those found in
RA are produced during the disease process. This was shown in situ by
immunohistology (22), by synovial dissection
(23), and especially by therapeutic studies with mouse
CIA, like human RA, being ameliorated by anti-TNF- Ab treatment
(4, 24). In the light of the clinical success of TNF-
blockade, by means of Abs or soluble TNFR, we have investigated the
feasibility and efficacy of adenoviral gene delivery of the 55-kDa TNFR
Ig fusion protein as a therapeutic strategy against CIA.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The recombinant adenovirus vectors used in this study, based on human adenovirus type 5, have been rendered replication deficient by deleting the E1a and E1b regions of the viral genome; each vector contains an expression cassette with the CMV early promoter, the pUC 19 polylinker, SV40 splice, and poly(A) signal sequences. The adenovirus encoding the human 55-kDa TNFR-mouse IgG1 fusion protein (AdTNFR; kindly donated by Drs. B. Beutler and J. Kolls, University of Texas, Southwestern Medical Center, Dallas, Texas), was constructed as previously described (25, 26). A control adenovirus encoding the Escherichia coli ß-galactosidase (Adßgal) was generously donated by Dr. M. Wood (University of Oxford, Oxford, U.K.).
Viruses were propagated in the 293 human embryonic kidney carcinoma
cell line routinely cultured in DMEM (BioWhittaker, Verviers, Belgium)
containing 5% FCS (Life Technologies, Paisley, U.K.), 2 mM
L-glutamine (Flow Laboratories, Irvine, U.K.), and 100 U/ml
penicillin/streptomycin (Life Technologies) in 5%
CO2 at 37°C. When 
80% confluent, culture
medium was replaced with DMEM 2% FCS plus live virus at a multiplicity
of 10. After 48 h, most of the cells rounded up and began to
detach from the plastic; they were harvested and virus was released by
three freeze/thaw cycles then purified by two rounds of cesium chloride
(Boehringer Mannheim, Lewes, East Sussex, U.K.) density gradient
centrifugation as previously described (27). Banded virus
was recovered, spin-dialyzed over Sepharose CL6B (Pharmacia, Uppsala,
Sweden), filtered, and stored at -80°C in 10% glycerol (BDH
Chemicals, Poole, U.K.) before use. To titer the final preparation, an
aliquot of virus was serially diluted and assayed for its ability to
form plaques on 293 cell monolayers (27).
Animal studies
The induction and assessment of CIA was performed as previously described (4). Briefly, male DBA/1 mice, 8–10 wk old, were immunized intradermally with 100 µg of bovine CII emulsified in CFA (Difco Laboratories, West Molesey, U.K.). The onset of arthritis was considered to be the day that erythema and/or swelling were first observed, and arthritic mice were given a daily clinical score per limb from 0 to 3, with 0 = normal, 1 = slight erythema and swelling, 2 = pronounced edematous swelling, and 3 = joint deformity with ankylosis, resulting in a maximum score of 12 per animal. Paw swelling was assessed using calipers (Kroeplin, Schluchlem, Germany) to measure the thickness of each affected hind paw.
Treatment protocol
Adenoviral vectors (2 x 107 and 2 x 108 pfu in 100 µl of isotonic saline) were injected into the tail vein i.v. once at the disease onset (day 1), and mice were monitored for disease activity up to day 21. Unimmunized DBA/1 mice were also injected i.v. with the higher dose of the virus as controls, monitored for 21 days, and showed no signs of illness. All animals that received recombinant adenovirus survived until sacrifice. Postmortem examination of the gross morphology of their liver, which is the target organ of adenovirus i.v. inoculation, showed no signs of pathology.
Human 55-kDa TNFR-human IgG1 fusion protein (p55-Sf2) was produced at
Centocor (a gift of Dr. B. Scallon and J. Ghrayeb, Malvern, PA). It is
a dimer of the extracellular domain of the human 55-TNFR where each
TNFR is fused to a partial J sequence that is attached to the whole of
the constant region of the human IgG1 H chain (28). Two
hundred micrograms were administered i.p. in 200 µl of saline on days
1, 3, 5, 7, 11, 13, and 15 after the onset of disease. As control, an
IgG1 with the same human IgG1
backbone used for the fusion construct
but without the TNFR moieties, also produced at Centocor, was given
i.p. following the same regimen.
A murine chimeric rat anti-mouse TNF Ab (murine IgG1 clone cV1q) (provided by Dr. B. Scallon and J. Ghrayeb, Centocor), was also injected i.p. at a dose of 500 µg, three times per week, for 3 wk.
Murine CTLA4-Ig, (a gift from Dr. Glenn Larsen, Genetics Institute, Boston, MA) was administered (50 µg/i.p.) at the onset of arthritis, which was 24 h before the AdTNFR i.v. injection. Controls received the same dose of CTLA4-Ig and isotonic saline alone i.v. 24 h later. Blood samples were obtained from all treated and control mice on day 3, 10, and 21, and the serum was stored at -80°C until use.
Soluble TNFR assay
Soluble p55 human TNFR was assayed in diluted serum samples by ELISA as previously described (29). Monoclonal anti-human p55 TNFR was used as capture Ab, and polyclonal rabbit IgG anti-p55 TNFR Ab conjugated to biotin was used as the detection Ab. Streptavidin-HRP conjugates were used to detect the biotinylated Abs followed by a chromogenic substrate of tetramethylbenzidine dihydrochloride (Kirkegaard and Perry, Gaithersburg, MD). Absorption was measured at 450 nm, and results were expressed as the mean of triplicate samples.
Estimates of serum TNFR-Ig concentrations were calculated with
reference to a recombinant truncated human p55 TNFR standard with a
molecular mass of 25–30 kDa. The results are expressed as µg/ml
of p55 TNFR equivalents, although comparable OD readings were
obtained with the recombinant TNFR-Ig fusion protein subsequently
provided (Centocor).
Bioassay of TNF inhibitory activity
To verify that the TNFR IgG1 present in serum was bioactive,
TNF- inhibitory levels were tested in serum samples of treated mice.
Inhibition of TNF- cytotoxicity on the TNF-sensitive murine
fibrosarcoma cell line WEHI 164 was assessed (30).
Briefly, 2 x 104 WEHI cells/well were
seeded in 96-well plates in 100 µl DMEM supplemented with 5% FCS, 2
mM L-glutamine, and 100 U/ml penicillin/streptomycin and
were adhered overnight in 5% CO2 at 37°C.
Serum samples were serially diluted in separate wells in 100 µl DMEM
and incubated with recombinant murine TNF- (Dr. A. Meager, National
Institute of Biological Standards and Controls, Potters Bar, U.K.) at a
concentration of 10 pg/ml, which generates 60% cytotoxicity and is
within the linear region of the dose-response curve, to allow the
soluble TNFR-IgG1 present to bind and neutralize TNF-. After 1
h, they were added to the WEHI cells cultured with actinomycin D at a
final concentration of 0.5 µg/ml. Cells were incubated overnight,
then 10 µl of MTT at 5 mg/ml in PBS were added, followed by another
overnight incubation at 37°C. Viable cells were quantitated by
solubilizing formazan crystals with 100 µl of 10% SDS in 0.01 M HCl
per well. OD was assessed at 540 nm using a Multiskan (Labsystems,
Helsinki, Finland).
Proliferation assay
Inguinal and popliteal lymph nodes were aseptically removed from AdTNFR-treated and control arthritic mice on day 10 or 21 after start of treatment. Then, 5 x 105 cells were cultured in 0.2 ml of DMEM supplemented with 2% heat-inactivated FCS in a 96-well flat-bottom plate. Increasing concentrations of UV-inactivated AdTNFR or denatured bovine CII, 50 µg/ml, or medium alone were added and incubated at 37°C in 5% CO2 for 72 h. Cells were pulsed with 1 µCi/well of [3H]thymidine (Amersham International, Little Chalfont, U.K.) and incubated for a further 24 h. Cultures were then harvested onto glass fiber filters with a semiautomated cell harvester (Titertek 550; Flow Laboratories). Cellular DNA synthesis was assessed by [3H]thymidine incorporation by a liquid scintillation spectrometer (LKB Instruments, Bromma, Sweden). Results are expressed as arithmetic mean cpm of triplicate cultures ± SEM.
Ab determinations
Anti-CII Ab levels were tested in individual sera using a standard ELISA. Microtiter plates were coated with 2 µg/ml of CII dissolved in TBS overnight at 4°C (31). After blocking for 1 h with 2% BSA, dilutions of sera from 1/50 to 1/6400 were applied to the wells. For isotype quantitation, sheep anti-mouse IgG1 and IgG2a linked to alkaline phosphatase (The Binding Site, Birmingham, U.K.) were used at a dilution of 1:5000. The plates were developed using p-nitrophenyl phosphate (Sigma, St. Louis, MO) as substrate, and OD was assessed at 405 nm. Anti-CII IgG2b Abs were quantitated using sheep anti-mouse IgG2b conjugated to peroxidase at a dilution of 1:10,000 (The Binding Site), tetramethylbenzidine dihydrochloride (Kirkegaard and Perry) was used as substrate, and OD was assessed at 450 nm. Each plate included a standard curve of a positive serum used to define arbitrary units of total IgG, IgG1, IgG2a, and IgG2b anti-CII Abs.
Anti-murine TNFR Abs (total IgG) were also measured by ELISA. Briefly, plates were coated with 1 µg/ml of nonpurified (culture supernatant) murine 55-kDa TNFR overnight at 4°C. After blocking for 2 h with 2% BSA, sera diluted 1:50 were added in duplicates and incubated at room temperature for 1 h. Anti-mouse total IgG linked to alkaline phosphatase (The Binding Site) diluted 1:5000 was then added for 1 h, and plates were developed using p-nitrophenyl phosphate (Sigma). Absorbance was assessed at 450 nm, and results were expressed in OD per individual serum tested.
Histopathology
Arthritic hind paws (the first affected hind paw of each mouse) were removed postmortem on the 21st day after onset of clinical symptoms and of treatment, fixed in 10% buffered formalin, and decalcified in 5.5% EDTA in buffered formalin. Paws were then embedded in paraffin, sectioned, and stained with hematoxylin and eosin or saffranin O. Microscopic evaluation of arthritic paws was performed by an observer in a blinded fashion. The severity of arthritis in the distal interphalangeal joints, proximal interphalangeal joints, and metatarsophalangeal joints was classified as normal, mild, moderate, or severe based on the following criteria: normal = no damage; mild = minimal synovitis, cartilage loss, and bone erosions limited to discrete foci; moderate = synovitis and erosions present but intact joint architecture; and severe = extensive erosions and disrupted joint architecture.
Statistical analysis
For statistical analysis of macroscopic data, the Mann-Whitney U test of significance was applied using a Minitab statistical software package (Minitab, State College, PA). Differences were considered statistically significant when p < 0.05.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The i.v. administration of 2 x 107 and
2 x 108 pfu of AdTNFR on the day of
arthritis onset (day 1) resulted in a dose-dependent improvement of
erythema and paw swelling. The higher dose yielded a statistically
significant amelioration of clinical score from day 5 to day 10
(p < 0.02 by Mann-Whitney analysis), compared
with control mice given saline. After day 10, the benefit was lost, and
a significant deterioration in the AdTNFR treated mice was observed by
day 15 (p = 0.038), which continued until the
end of the experiment on day 21 (p = 0.0004).
The lower dose of AdTNFR (2 x 107 pfu) also
showed amelioration of the disease during the first 10 days, although
it was never statistically significant. Similar to the high-dose
regime, the disease activity also significantly increased on day 18
(p = 0.001) through day 21 (Fig. 1
).
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), indicating that the
initial amelioration of the disease observed with AdTNFR was due to the
viral delivery of the TNFR fusion protein and not to the adenovirus
itself, with the higher dose of AdTNFR administered being more
effective. The progression of arthritis was also studied in terms of
change in number of arthritic limbs over the 21-day disease course. A
trend toward reduced recruitment of affected limbs on day 10 was
observed in the groups of mice given AdTNFR; by day 21, those mice
showed a higher number of limbs affected than controls.
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Expression and bioactivity of the TNFR fusion protein
Mice injected with 2 x 108 pfu of
AdTNFR and controls were serially bled 3 days, 10 days, and 21 days
after the onset of arthritis. Sera were then assayed for the
presence of the human 55-kDa TNFR fusion protein by ELISA
(32). The dimeric protein encoded by the adenovirus was
already present at high concentrations on day 3, with the highest level
(in the range of 100 µg ml-1) reached on day
10. Thereafter, levels of TNFR remained high but started to decline on
day 21 after disease onset (Fig. 3).
Control mice that received either saline or Adßgal virus did not show
detectable levels of human TNFR at any time.
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), a biological assay on the TNF-sensitive murine
fibrosarcoma cell line WEHI 164 was performed to test whether the
fusion protein produced by the adenoviral construct was still bioactive
or whether it had been neutralized or degraded. For this purpose, serum
samples at day 3 and 21 from both the AdTNFR- and the Adßgal-treated
mice were serially diluted, preincubated for 1 h with 10 pg/ml of
recombinant murine TNF to allow binding to the receptor present, then
added to the WEHI cell culture and tested for inhibition of TNF
cytotoxicity. The data showed that while incubation with 10 pg/ml of
murine TNF- alone resulted in 60% cytotoxicity, preincubation
with sera from the AdTNFR treated mice reduced the TNF cytotoxic effect
to 20% on day 3 and 45% on day 21 (p <
0.05). The reduced degree of TNF inhibition observed on day 21 implied
that the virally encoded TNFR was still present, even if at lower
concentration, and bioactive at both time points. Thus, a lack of
bioactive TNFR was not the mechanism of augmented disease from day
15. CTLA4-Ig prevents the development of arthritis yet does not prevent its late exacerbation in AdTNFR-treated mice
In our laboratory, it has previously been shown that the i.p.
injection of CTLA4-Ig at the time of collagen immunization prevents the
development of CIA (31). This observation demonstrated the
importance of costimulation and Ag presentation to T cells in the
pathogenesis of CIA, even after disease onset. Therefore, to
investigate the pathogenetic mechanism leading to the late exacerbation
observed in our experiments with the AdTNFR treatment, we first
attempted to reduce T lymphocytes responses through the administration
of a suboptimal dose of murine CTLA4-Ig. Mice were given one dose of
CTLA4-Ig (50 µg) i.p. 24 h before the i.v. injection of 2
x 108 pfu of AdTNFR, or saline, and the disease
was monitored for 21 days. As shown in Fig. 4, animals that received this low dose of
CTLA4-Ig alone (n = 7) showed an improvement in disease
progression (p < 0.05) from day 6 to day 12
compared with controls. In contrast, pretreatment on day 1 with
CTLA4-Ig and subsequent injection on day 2 with the higher dose of the
virus resulted instead in a clinical profile identical with the group
treated with AdTNFR alone, with a statistically significant benefit
starting on day 5 (p = 0.03) until day 10,
followed by an exacerbation of inflammation by day 18
(p = 0.033). Therefore, despite the transient
immunosuppression clearly caused in the control mice by the low dose
CTLA4-Ig administered, no additive or synergistic effect was observed
when both immunosuppressive agents were injected together.
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The development of CIA is associated with high levels of both
cell-mediated and humoral immunity to collagen (33). To
determine whether AdTNFR treatment was affecting the specific T cell
responses to collagen and whether a difference between the early and
late phase of AdTNFR treatment could be detected, lymph node T cell
proliferation from AdTNFR-treated and arthritic controls, on day 10 and
21 of arthritis, was ascertained. In the same experiment, which is
representative of three, the specific proliferative response to the
virus in vitro was also monitored, and as an additional control a group
of naive DBA/1 mice injected with AdTNFR and lymph node cells was
assayed 10 days later. The results showed on day 10 a much higher
proliferation to CII in arthritic vs nonimmunized DBA/1 mice (Fig. 5A). The AdTNFR-injected
arthritic mice at day 10 also showed a degree of proliferation to the
virus at the dose of 60 pfu/ml (p = 0.05). At
both time points, all CIA immunized mice showed a statistically
significant proliferation to CII (p = 0.03),
regardless of the AdTNFR treatment (Fig. 5, A and
B). Our results suggest that the AdTNFR early clinical
amelioration and late exacerbation of CIA are not associated with
changes in the specific T cell response to CII.
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To rule out the possibility that the late exacerbation of CIA by
AdTNFR was due to adenoviral infection, the effect of injecting human
TNFR fusion protein was compared with the adenoviral delivery of a
similar protein (but with a murine IgG tail) on CIA. Because of the
high serum levels reached with AdTNFR, a large amount, 200 µg of
p55-Sf2 fusion protein, was administered i.p. on alternate days (Fig. 6A). The clinical response was
similar to that observed in animals that had received the higher dose
of the adenovirus construct, suggesting that the paradoxical late
disease-enhancing effect repeatedly observed was attributable to the
TNFR fusion protein alone and not to the viral vector. To further
investigate whether the human Ig portion present in our fusion protein
could somehow affect the late stage of CIA, 200 µg of a control human
IgG1 (of the same isotype used to make the fusion protein construct)
were injected at the same regimen in a following experiment. As shown
in Fig. 6B, the human IgG1 protein did not alter the disease
process, thus suggesting that the soluble 55-kDa human TNFR part of the
fusion protein, and not the human Ig portion of the molecule, affects
the late course of CIA.
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CIA development has been shown to be dependent on humoral immune
responses to CII, with the anti-collagen IgG2a isotype playing a
major pathogenic role (34, 35). Previous studies from our
laboratory on treatment of CIA for 10 days with p55-Sf2 did not show
differences in total serum anti-collagen Ab levels between treated
groups and controls (36). Therefore, we decided to
evaluate and compare the anti-collagen IgG isotype distribution
present in the AdTNFR-injected mice in the p55-Sf2-treated mice and in
same stage arthritic controls over a longer time period (Fig. 7). Our data showed that in the 21-day
CIA control group all anti-collagen IgG subclasses were present,
with IgG2a and IgG2b equally represented and higher than the IgG1
subset. Interestingly, both the AdTNFR- and the p55-Sf2-treated groups
had higher concentrations of all subclasses of anti-collagen Abs,
but their IgG2a/IgG1 ratio was comparable to the arthritic controls.
Therefore, although the response to collagen was quantitatively
increased in the TNFR-treated groups, it seems qualitatively comparable
with the late stage of CIA development.
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), these were not
detected. Anti-mouse TNFR responses were also evaluated: total IgG Abs toward the murine 55-kDa TNFR were detected, but a degree of binding was also observed in all arthritic controls. Nevertheless, the difference between AdTNFR-treated and control groups (n = 7 per group) was statistically significant at day 10 (p = 0.01) in three separate experiments (data not shown). As most mAbs to p55 TNFR are agonistic, we attempted to ascertain if the sera from AdTNFR or control mice were agonistic and able to kill the TNF-sensitive cell line WEHI 164. Mouse serum at concentration >1% interfered with their adherence, and while some lysis was detected with sera from AdTNFR and p55 IgG immunised mice, this did not reach statistical significance.
Effect of prolonged TNF neutralization with anti-TNF- mAb
on CIA
To elucidate whether prolonged neutralization of TNF during the
course of CIA was responsible for the late exacerbation of disease
observed with the administration of the soluble p55 TNFR, we injected
i.p. a group of mice (n = 10) with 500 µg of a rat
anti-mouse TNF Ab (cV1q) three times a week for 3 wk. Control mice
(n = 10) received PBS. As shown in Fig. 8, blockade of TNF activity, in this
experiment, significantly suppressed CIA (p =
0.0007 on day 21), strongly arguing against a direct involvement of
prolonged TNF blockade per se in the rebound effect observed with the
TNFR fusion protein treatment.
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The histological analysis of the interphalangeal joints from
arthritic and Adßgal controls and from mice treated with 2 x
108 particles of AdTNFR was performed on day 21
after disease onset. Fig. 9 shows
photomicrographs taken from representative AdTNFR-treated and
control animals. Arthritic controls and mice that received the control
adenovirus Adßgal showed active chronic proliferative synovitis. The
synovial lining layer was villous, hyperplastic, and infiltrated by
neutrophils. The subintima contained a diffuse infiltrate of
neutrophils, lymphocytes, and plasma cells with fibroblasts in the
periphery. Pannus formation caused severe erosions of the articular
cartilage and the subchondral bone. Prominent neovascularization
associated with pannus was also observed. In some joints, pannus was
very extensive with expansion into the bone marrow space, and marrow
elements were replaced by granulation tissue. The cartilage showed
severe degenerative changes with fragmentation of the surface and many
necrotic chondrocytes (Fig. 9A). Paws removed from
AdTNFR-treated mice showed a delay in the disease progression. Joint
pathology was characterized by acute inflammation of the synovium,
including oedema and intense infiltration by neutrophils and
mononuclear cells. Acute synovitis was accompanied by hyperplasia of
synovial intima and accumulation within the joint space of polymorphs,
cell debris, and macrophages immersed in a fibrin web. Active ingrowth
of granulation tissue from the synovium, leading to the formation of
pannus that covered and eroded the articular cartilage and the
subchondral bone, was also observed. The surrounding tissue was
oedematous with the presence of mast cells. The distribution and local
accumulation of mast cells varied between specimens, but they were
mainly increased at sites of pannus invasion and in the fibrous
synovial tissue than in areas with active inflammatory cells infiltrate
(Fig. 9B).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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, in both RA and
Crohn’s disease, are some of the major achievements based on the
understanding of the roles of cytokines in disease pathogenesis.
Specific down-regulation of TNF- activity in both RA and CIA has
relied predominantly on two approaches using biological agents:
injection of neutralizing anti-TNF- mAbs (3, 4, 5, 6, 7, 8) and
administration of soluble TNFR fusion proteins (9, 37).
These reports have demonstrated consistent therapeutic efficacy, with
differences in experimental design, specific pharmacokinetics, and TNF
binding properties of the TNF neutralizing compounds presumably
accounting for the observed variations on clinical benefit. Effective control of autoimmune arthritis requires flexible, prolonged neutralization of proinflammatory mediators, and gene therapy offers several potentially unique advantages over previous protein therapies (38), thus we and others have taken an interest in this field. Replication-deficient adenoviruses have proven to be suitable vectors for delivering in vivo high amounts of a specific protein over extended periods of time (16), although limitations related to the host immune responses have been reported (38, 39).
The main goal of the present study was to assess whether blockade of
TNF- activity through adenovirus-mediated gene transfer of a soluble
TNFR is feasible and effective compared with protein therapy in a
chronic inflammatory disease model such as CIA. The TNF inhibitor we
used was an adenovirally encoded chimeric fusion protein consisting of
a dimeric mouse IgG1 H chain coupled to two human 55-kDa TNFR
extracellular domain (26). This particular adenovirus
construct was chosen for its demonstrated efficacy in blocking murine
TNF- activity in vivo (26, 40, 41) and because previous
studies performed in our laboratory (36) and by others
(42, 43) using a similar human fusion protein showed
amelioration of arthritis in the short-term experiments performed.
Because the viral transgene expression lasts for weeks
(16) as opposed to a serum half-life of hours when the
fusion protein is injected (44), an evaluation of its
effects on CIA for a prolonged time appeared clinically relevant. The
results obtained highlight some interesting and unexpected findings.
Firstly, the i.v. administration of AdTNFR yielded high serum levels of
the recombinant protein (in the range of 100 µg
ml-1) for the entire 21-day period of arthritis.
Clinical assessment of the mice revealed a dose-dependent decrease of
CIA severity for 10 days. This paralleled previous work with repeated
injections of the soluble TNFR fusion protein alone (36).
However, the clinical benefit was lost after day 10, despite the
continual presence of high levels of bioactive soluble TNFR, with a
subsequent inflammatory flare that persisted for the remaining period
of observation. The mechanisms of this paradoxical response was
analyzed in vivo through the administration of a control adenovirus or
repeated injections of a related TNFR fusion protein (human TNFR/human
IgG1) and of the control human IgG1 over a 21-day period. Our studies
showed absence of systemic inflammatory response to the Adßgal virus
or to the control human IgG1 protein, whereas a biphasic response was
observed again in the TNFR fusion protein-treated animals (see Fig. 6A). Thus, under the experimental conditions used, therapy
with the 55-kDa TNFR ameliorates the early acute phase of established
CIA but, if prolonged, causes exacerbation of the disease. There are
several possible mechanisms that could account for the exacerbation of
arthritis after day 10. One possibility is that TNF blockade is harmful
in the late stage of CIA or that prolonged blockade of TNF is harmful.
The first hypothesis seems unlikely in the context of arthritis as
previous studies performed in patients with long-standing RA using
either anti-TNF- mAbs or the 75-kDa TNFR fusion protein were
beneficial (5, 6, 9) even in the long-term (7, 45). However, because of potential differences between human RA
and murine CIA, direct comparison between the results of therapy in the
two diseases may not always be applicable. Furthermore, it has recently
been shown that mice deficient in TNF (TNF-/-)
fail to regulate and limit in vivo an inflammatory response
(46). A late florid inflammatory response developed in
TNF-/- mice injected with Corynebacterium
parvum at a time when the inflammatory lesions in the
TNF+/+ control mice had resolved. Indeed, in our
study, the histology of arthritic paws from AdTNFR-treated mice showed
on day 21 the massive leukocyte infiltration and synovitis usually
present in the early acute phase of CIA, whereas control animals showed
evidence of cartilage destruction and bone erosions with remodeling and
fibrosis. Thus, the prolonged blockade of TNF- achieved in our
experiments could be possibly interfering with the up-regulation of
homeostatic mechanisms such as the production of IL-10, TGFß, or
other mediators that are likely to be involved in limiting and
eventually reversing inflammation (24). To test this
hypothesis we injected mice with a chimeric mouse IgG1 rat Fab
anti-TNF- mAb, at plateau doses, 500 µg three times per week,
for 3 wk. This resulted in clinical benefit for the entire duration of
the experiment, and argues strongly against TNF- blockade, at the
incomplete level achievable with neutralizing mAbs or fusion proteins,
being intrinsically proinflammatory (see Table I). The results shown in Fig. 8 mimic
those obtained clinically, where long-term treatment showed a stable or
augmented benefit (45).
|
itself, if present
chronically, is capable of down-regulating T cell responses
(47). Hence, chronic anti-TNF- therapy could be
augmenting T cell responses, contributing to the late exacerbation of
arthritis. However, CTLA4-Ig, which is known to block costimulatory
signals between T cells and APC ameliorates CIA (31, 48, 49). This suppressed macroscopic inflammation in control animals
but did not affect the response to the AdTNFR treatment. This is
consistent with the in vitro results that T cell proliferative
responses to CII in AdTNFR-treated and control mice were comparable at
both early and late stage CIA (see Fig. 5). These results exclude a
direct T cell involvement in the exacerbation process observed in the
TNFR-treated group. In contrast, it was found that the humoral immune
responses to CII were augmented by TNFR treatment, either by adenovirus
product or protein (Fig. 7), and thus an alternative hypothesis for the
increase in inflammation could involve interference with B lymphocyte
regulatory mechanisms, leading to enhanced production of potentially
harmful anti-collagen Abs. It has been previously reported that
anti-CII Abs, of the IgG2a subclass in particular, exert a
pathogenetic role in CIA (34, 35), but whether the 2-fold
increase detected in our experiments is sufficient to augment
inflammation in the manner observed here is not clear. Another possible mechanism of the inflammatory flare could be the presence of agonistic Abs to the p55 TNFR in mice injected with AdTNFR, which may cross-link the TNFR and hence mimic TNF action. Abs raised against the injected human 55-kDa TNFR may cross-react with its mouse homologue, because both receptors bind human TNF with high efficiency and hence must have similar conformations. We investigated whether Abs to mouse p55 TNFR were raised in the serum of mice treated with TNFR and detactable by ELISA. For the experiment, purified murine 55-kDa TNFR was not available, so we used a nonpurified preparation (culture supernatant) that yielded a degree of nonspecific binding also in control mice. The statistical analysis performed on individual sera from seven AdTNFR-treated mice and seven arthritic controls was consistently significant on samples obtained on day 10 just before relapse, but not significant on day 21 in three different experiments (data not shown). The IgG titer against TNFR is probably high, because we could detect Abs in the presence of high (40–100 µg ml-1) circulating levels of the virally encoded soluble human TNFR. In view of the very high serum levels of human TNFR encoded by the adenovirus, it did not make sense to attempt to detect Abs to the human TNFR. As it has been reported that Abs to the 55-kDa TNFR possess TNF-like activity in vitro due to their ability to cross-link the receptor molecules (50), we set up several assays to test this hypothesis in our system. The most direct was to evaluate whether sera from the AdTNFR mice were capable of lysing murine TNF-sensitive cell lines such as WEHI 164. Increased cytotoxicity was indeed observed, although the results were not statistically significant compared with controls (data not shown), probably due to the deleterious effects of mouse serum on WEHI 164 cells and the consequent large variations. However, in small compartments from which clearance is slow, as for example the mouse joint, concentrated levels of anti TNFR Abs could be highly cytotoxic or stimulatory. It is of interest that, whereas in mice, in acute studies as during sepsis, the human TNFR p55 Fc (lenercept Hoffmann-La Roche, Nutley, NJ) fusion protein is highly effective, more so than the TNFR p75 Fc fusion protein (51), the same is apparently not true in longer-term clinical studies in RA patients. There, the p75 TNFR Fc fusion protein (9) has been very effective, whereas the p55 TNFR Fc fusion protein has been less effective (10, 11). The latter protein has been reported to be immunogenic in 40% treated individuals and it is thus conceivable that its relative lack of effect could be due to agonistic Abs to the human cell-bound TNFR. Such agonistic Abs were recently detected in a subset of RA patients treated with a human TNFR55-IgG1 fusion protein (52). Thus, we think that this is the likeliest mechanism for the disease relapse.
It has also been reported that in certain circumstances soluble cytokine receptors (53) and the dimeric form of the 75-kDa TNFR fusion protein in particular (54, 55), while potent inhibitors of TNF action in vitro, may also stabilize the cytokine, thus prolonging its activity in vitro, but whether this also happens in vivo is unclear. However, worsening of certain disease states has indeed been reported for example in sepsis after p75 TNFR fusion protein treatment (56) and in multiple sclerosis with the p55 TNFR fusion protein, but the mechanisms of these clinical effects are not known (57).
In conclusion, the increasing number of biological activities attributed to TNF and its soluble receptors make it difficult to unravel protective or harmful effects in different disease states. Our findings highlight the feasibility of adenovirus-mediated gene transfer of cytokine inhibitors in vivo as a useful approach to study cytokine functions during the course of chronic inflammatory and immune-mediated diseases and point out a peculiar effect of an immunogenic soluble TNFR administration in the follow-up of CIA. These effects need to be understood before therapy with such agents can be contemplated in humans.
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Acknowledgments |
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Footnotes |
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2 Current address: National Institute Medical Research, London, U.K.
3 Current address: Austin Hospital Institute for Medical Research, Melbourne, Australia.
4 Address correspondence and reprint requests to Dr. Marc Feldmann, Kennedy Institute of Rheumatology, 1 Aspenlea Road, Hammersmith, London W6 8LH, U.K. E-mail address:
5 Abbreviations used in this paper: RA, rheumatoid arthritis; CIA, collagen-induced arthritis; AdTNFR, p55 TNFR adenovirus; Adßgal, ß-galactosidase adenovirus; CII, collagen type II.
Received for publication December 15, 1998. Accepted for publication April 26, 1999.
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References |
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, n = 9),
or saline alone (
, n = 10) were injected i.v.
into the tail vein. Mice were examined every other day for 21 days for
signs of joint inflammation and scored as previously described. Mean
clinical score presented as average clinical score per group ±
SEM. Statistically significant differences between treatments are
indicated (*, p < 0.02; **,
p < 0.001). A representative result from three
experiments is shown.
, n = 10),
with CTLA4-Ig 50 µg i.p. in saline (
,
n = 10). On day 2, one group of mice that received
CTLA4-Ig (
