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William S. Rowe Division of Rheumatology, Childrens Hospital Medical Center, Cincinnati, OH 45229
| Abstract |
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secretion
in response to stimulation with type II collagen, but only vIL-10
reduced the synovial mRNA levels of the proinflammatory cytokines
IL-1ß, TNF-
, and IL-6. These findings demonstrate that vIL-10 and
sTNFR-Ig act synergistically in suppressing CIA and suggest that gene
transfer offers a potential therapeutic modality for the treatment of
arthritis. | Introduction |
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, and IL-1ß, are found in the synovium and play
a major role in the progression of joint destruction (1, 2). Agents that inhibit secretion of these cytokines, or that
can block their binding to cell surface receptors, are increasingly
being viewed as potential therapeutic agents that might provide
increased specificity compared with traditional drugs. Delivery of these biologic agents represents particular challenges, including the production of sufficient quantities of purified material suitable for administration to humans. Gene transfer has been suggested as a more efficient means of delivery of these agents. In addition, it might allow one to achieve steady levels of the product, as opposed to the peaks and troughs associated with intermittent protein administration.
Two protein products of particular interest as therapeutic candidates for arthritis include soluble TNF receptor (sTNFR) and IL-10, both of which have undergone clinical studies in RA. These two products act on different components of the inflammatory process. sTNFR directly blocks the tissue destructive effects of TNF, whereas IL-10 indirectly inhibits inflammation by inhibiting T cell proliferation and secretion of proinflammatory cytokines by monocytes.
TNF is found in large quantities in the RA synovium and synovial fluid (1, 2). TNF induces the release of PGE2 and collagenase by synovial cells, contributes to fibrosis, and facilitates inflammatory cell infiltration by promoting adhesion of neutrophils and lymphocytes to endothelial cells. It can also induce downstream events such as up-regulation of IL-1 and IL-6 secretion and up-regulation of T cell-proliferative responses. A divalent p75 sTNFR-Ig fusion protein (Etanercept; Immunex, Seattle, WA) has shown dramatic efficacy at reducing inflammation in patients with RA (3) and has recently been approved by the Food and Drug Administration for use in RA and juvenile rheumatoid arthritis.
IL-10 is also being studied in clinical trials for RA. IL-10 is a product of Th2 cells, B cells, and macrophages that has mixed immunosuppressive and immunostimulatory properties. It suppresses the production of proinflammatory cytokines by Th1 cells (4, 5) and monocytes (4, 5, 6, 7). IL-10 can inhibit collagen-induced arthritis (CIA) (8, 9, 10) and is elevated in serum and synovial fluid of patients with RA (7, 11), where its overall effect on the inflammatory process is still debated. Elevated IL-10 levels correlated with rheumatoid factor titers and spontaneous IgM-rheumatoid factor production (11). These immunostimulatory effects may exacerbate disease and bear on its potential efficacy as a therapeutic agent.
Murine IL-10 and human IL-10 cDNA sequences exhibit a strong homology to an open reading frame in the EBV (human herpes virus 4) BamHI C fragment rightward reading frame 1 (BCRF1), termed viral IL-10 (vIL-10) (12, 13). The human and vIL-10 mature protein sequences are 84% identical, with most of their divergence found in the NH2-terminal 20 amino acids. vIL-10 shares many of the immunosuppressive properties of human IL-10 and murine IL-10, but lacks their immunostimulatory properties (14, 15). Recently, we and others have demonstrated that gene transfer of vIL-10 inhibits CIA (16, 17, 18) and can block invasion of cartilage by RA synoviocytes (19, 20). This may be a result of its ability to inhibit the T cell-proliferative response to type II collagen (CII) and to decrease mRNA levels of IL-1ß in CIA synovium (16).
Although the antiarthritic properties of vIL-10 and sTNFR-Ig have been extensively studied, neither of them alone can entirely suppress established disease. Given the complexity and redundancy of the inflammatory milieu in the joint, it is unlikely that a single target can achieve complete inhibition of inflammation. The therapeutic effects of simultaneous administration of vIL-10 and sTNFR-Ig has not previously been evaluated. Simultaneous delivery of two or more genes is possible using adenoviral vectors, providing a convenient method for studying the effects of combination therapy for arthritis. To determine whether vIL-10 and sTNFR-Ig can act synergistically in autoimmune arthritis, CIA was induced in mice and the effects of gene transfer of vIL-10 and sTNFR-Ig were determined.
| Materials and Methods |
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Male DBA/1J mice, 610 wk of age, were purchased from The Jackson Laboratory (Bar Harbor, ME), and housed under Institutional Animal Care and Use Committee-approved conditions in the animal resource facility at Childrens Hospital Research Foundation (Cincinnati, OH).
Adenovirus constructs
Three recombinant E1a/E3-deleted replication-defective
adenovirus type 5 vectors were used in this study. Ad(vIL-10) encodes
the BCRF1 cDNA under the control of the elongation factor-1
promoter, the 4F2 heavy chain enhancer, and the bovine growth hormone
polyadenylation site. Ad(BglII), which was used as a
control, lacks the BCRF1 cDNA, the elongation factor-1
promoter, the
4F2 heavy chain enhancer, and the bovine growth hormone polyadenylation
site, but is otherwise identical to Ad(vIL-10). These constructs were
generously provided by J. A. Bluestone and J. M. Leiden
(University of Chicago, Chicago, IL). Ad(sTNFR-Ig) encodes a divalent
human p55 sTNFR-Ig/murine IgG1 fusion protein under control of the CMV
promoter (21) and was generously provided by B. Beutler
(University of Texas, Southwestern, Dallas, TX). Recombinant
adenoviruses were produced and propagated in 293 cells and purified by
cesium chloride density centrifugation as described previously
(22, 23). Viruses were plaque purified three times before
the production of seed stocks, and their identities were confirmed by
restriction endonuclease and DNA sequence analysis. Viral titers
(particles/ml) were determined by A260
x 1012 following lysis of viral stocks in 0.1%
SDS, 10 mM Tris-HCl (pH 7.4), and 1 mM EDTA at 56°C for 10
min.
Treatment protocols
Arthritis was induced with bovine CII (Elastin Products, Owensville, MO) as described previously (24). Mice were injected intradermally with 100 µg of CII in CFA at the base of the tail on days 0 and 21. Adenovirus was administered on day 20 in 100 µl of buffer containing 10 mM Tris (pH 7.4), 1 mM MgCl2, 10% (v/v) glycerol by i.v. injection as described previously (16). Mice were divided into four groups: control group, 2 x 1010 particles of the control vector Ad(BglII); sTNFR-Ig group, 1010 particles of Ad(sTNFR-Ig) plus 1010 particles of Ad(BglII); vIL-10 group, 1010 particles of Ad(vIL-10) plus 1010 particles of Ad(BglII); and sTNFR-Ig/vIL-10 group, 1010 particles of Ad(vIL-10) plus 1010 particles of Ad(sTNFR-Ig). Mice were evaluated several times a week for arthritis using an established macroscopic scoring system (25) ranging from 0 to 4 (0, no detectable arthritis; 1, swelling and/or redness of paw or one digit; 2, two joints involved; 3, three or four joints involved; and 4, severe arthritis of the entire paw and digits). The arthritic index for each mouse was calculated by adding the four scores of the individual paws. At various time points, serum samples were collected and kept at -20°C for further analysis. Paws were frozen in liquid nitrogen immediately after harvesting and kept at -80°C for mRNA analysis.
vIL-10 measurement
Titers of vIL-10 were determined by ELISA. ELISA plates were coated overnight at 4°C with 1 µg/ml of the rat anti-mouse IL-10 mAb, JES39D7 (PharMingen, San Diego CA), washed (PBS-Tween 20), and blocked by overnight incubation at 4°C with 100 µl of PBS containing 1% BSA. After washing, 50-µl aliquots of the serum samples were added to duplicate wells and incubated at 4°C overnight. After washing, 100 µl of a 1 µg/ml dilution of the biotin-conjugated rat anti-viral IL-10 mAb, JES3-6B11 (PharMingen), was added to each well and incubated at room temperature for 1 h. Plates were washed and developed with peroxidase substrate system 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (Kirkegaard & Perry Laboratories, Gaithersburg MD). The plates were read at 410 nm on a kinetic microplate reader (Molecular Devices, Menlo Park, CA). OD readings for the duplicate wells were averaged and subtracted from readings of control serum. The absolute concentration of vIL-10 in serum was calculated using a standard curve generated with dilutions of purified vIL-10.
sTNFR-Ig measurement
Titers of sTNFR-Ig were measured by assaying TNF inhibitory
activity as described previously (21). Briefly, samples
were serially diluted and 1 µl of each dilution was incubated at
37°C in separate wells of a 96-well plate with murine TNF-
at a
final concentration of 1 ng/ml in the presence of 100 µg/ml
cycloheximide. After 1 h, 7 x 104
SKMEL-109 cells (sensitive to lysis in the presence of TNF-
) were
added to each well, and the incubation was continued overnight. The
plates were then washed, stained with crystal violet, washed again, and
surviving cells were quantitated by solubilizing the stain in 50%
acetic acid and measuring OD at 490 nm. One neutralizing unit was
defined as the quantity of inhibitor required to neutralize 150 pg of
murine TNF-
. Control sera did not contain any TNF-neutralizing
activity.
Anti-CII Ab measurement
The titers of anti-CII Abs in the serum samples were determined by ELISA as described previously (25). All samples were measured in duplicate. Peroxidase-labeled goat anti-mouse IgG and IgM (Kirkegaard & Perry Laboratories) was used to measure CII-specific total Ig. IgG1 and IgG2a were measured using biotinylated rat anti-mouse IgG1 or IgG2a (PharMingen), followed by streptavidin-peroxidase. Plates were developed with peroxidase substrate system 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (Kirkegaard & Perry Laboratories). The plates were read at 410 nm as described above. OD readings for the duplicate wells were averaged. A serum sample from one of the control mice was tested at various dilutions and used as a standard to generate a curve from which relative titers of the other serum samples were calculated.
In vitro T cell function
A total of 5 x 105 spleen cells/well
were plated in triplicate at 37°C in 96-well flat-bottom microtiter
plates in DMEM containing 0.5% normal DBA/1 mouse serum in the
presence of heat-denatured (56°C for 10 min) CII. For IFN-
assays,
supernatants were harvested after 24 h. For proliferation assays,
cells were incubated for 72 h, followed by addition of 1 µCi of
[3H]TdR for an additional 18 h. Cells were
harvested and [3H]TdR incorporation per well
was measured and averaged for each triplicate. Background counts from
unstimulated cells were subtracted from each group. IFN-
was
measured by ELISA, as described previously (25), using
anti-IFN-
mAbs R46A2 and biotin-labeled XMG1.2 (PharMingen).
mRNA analysis
Paws were homogenized with a Tissue Tearor (Biospec Products, Bartlesville, OK) and RNA was extracted with RNASTAT 60 (Tel-Test, Friendswood, TX). RNase protection assays (RPA) were performed as described previously (26) on 2 µg of RNA utilizing the Riboquant MultiProbe RNase Protection Assay System (PharMingen) following the manufacturers instructions. Each commercial kit contained a set of cytokine/chemokine templates as well as a template for the housekeeping gene GAPDH. The mRNA level of each cytokine was expressed as the ratio of the phosphor imager units (storm 860 and Image Quart software; Molecular Dynamics, Sunnyvale, CA) of the cytokine to those of GAPDH from the same RNA sample.
Statistical analysis
2 with 1 df was used to test
categorical data for statistical significance. All comparisons were
performed between treated and control mice. Intergroup differences were
compared either by the Mann-Whitney U test if the data were
nonparametric (arthritic index) or by the two-tailed independent
t test if the data were parametric (disease incidence).
Comparisons of more than two means were done using the one-way ANOVA.
If the F ratio was significant by ANOVA, Tukeys honest
significant difference multiple comparison test was used for pairwise
comparisons. Uncorrected p values <0.05 were considered to
be statistically significant.
| Results |
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We and others have previously reported that vIL-10 gene transfer
can inhibit CIA when given before disease onset (16, 17, 18).
However, the treatment does not completely prevent CIA or have a
significant effect on established disease. To determine whether TNF
blockade can act synergistically with vIL-10, mice were treated with
adenoviral vectors encoding each cytokine, either alone or in
combination. Mice were immunized with CII on days 0 and 21. On day 20,
mice received i.v. injections of one of the following combinations of
adenovirus: the control vector Ad(BglII), Ad(sTNFR-Ig) plus
Ad(BglII), Ad(vIL-10) plus Ad(BglII), or
Ad(vIL-10) plus Ad(sTNFR-Ig). Significant synergism was observed with
the combination of vIL-10 and sTNFR-Ig on both the incidence and
severity of disease (Fig. 1
). As we have
previously reported (16), vIL-10 alone reduced disease
severity; however, the combination of vIL-10 and sTNFR-Ig was more
effective. sTNFR-Ig alone had no effect on either the incidence or
severity of CIA.
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One trivial explanation for the observed synergism between vIL-10 and sTNFR-Ig was that sTNFR-Ig might prolong the expression of the vIL-10-encoding virus by inhibiting either the anti-adenovirus or the anti-vIL10 immune response. However, the simultaneous administration of Ad(vIL-10) and Ad(sTNFR-Ig) neither raised the serum level of vIL-10 nor prolonged its half-life (data not shown).
To determine the reasons for the ineffectiveness of sTNFR-Ig alone on
CIA as well as potential mechanisms of synergy with vIL-10, the
synovial tissues of treated mice were analyzed for proinflammatory
cytokine mRNA. We have previously demonstrated that vIL-10 reduces mRNA
levels of the proinflammatory cytokine IL-1ß in the paws of mice with
CIA (16). To determine the effects of sTNFR-Ig on mRNA
levels of proinflammatory cytokines, paws of treated mice were removed
on day 32 and mRNA levels were quantitated by RPA. vIL-10, but not
sTNFR-Ig, significantly reduced synovial mRNA levels of IL-1ß,
TNF-
, and IL-6 (Fig. 4
). The
combination of sTNFR-Ig and vIL-10 had an additive effect,
but this was not statistically significant.
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To determine the effects of vIL-10 and sTNFR-Ig on autoimmune
responses, humoral and cellular responses to CII were analyzed. To
determine the effects on the humoral immune response to CII, mice were
bled on days 32 and 57 and sera were analyzed for Abs to CII. Ab levels
varied between mice, but no significant differences were observed
between the groups in circulating titers of total IgG, IgG1, or IgG2a
anti-CII Abs (Fig. 5
). There was,
however, a trend toward decreased total Ig and IgG2a in the mice
receiving Ad(vIL-10) plus Ad(sTNFR-Ig).
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We have previously demonstrated that the anti-CII T cell
response is inhibited following vIL-10 gene transfer (16).
To determine the influence of sTNFR-Ig on T cell responses, DBA/1 mice
were immunized with CII on days 0 and 21. Adenovirus was injected on
day 20. Three spleens per group were removed on day 33 and cultured
with CII. Both vIL-10 and sTNFR-Ig, as well as the combination,
completely inhibited IFN-
secretion in response to CII (Fig. 6
). Proliferation was significantly
reduced by vIL-10 and the combination of vIL-10 and sTNFR-Ig, but not
by sTNFR-Ig alone.
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| Discussion |
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Because neither of these proteins completely inhibits disease, the present study investigated the effects on arthritis of simultaneous administration of sTNFR-Ig and vIL-10 by i.v. gene delivery. Following i.v. injection of adenovirus, transgenes are expressed predominantly in the liver (27, 28), although we have also recently observed low-level expression in the joints (S. Watanabe and R. Hirsch, manuscript in preparation). Given the large number of inflammatory mediators in the arthritic synovium, achieving disease remission by blocking a single early mediator in the inflammatory cascade is probably unrealistic. Therefore, the observed synergism between vIL-10 and sTNFR-Ig is of potential therapeutic interest and suggests that strategies that target multiple proinflammatory pathways may be more effective than targeting a single effector molecule. These findings are reminiscent of the synergism recently observed between the identical sTNFR-Ig-encoding adenoviral construct and IL-1 receptor antagonist in a rabbit model of arthritis (29).
The mechanism of the synergism observed with vIL-10 plus sTNFR-Ig is
not entirely clear. One possibility is that vIL-10 alone is so
effective at down-regulating the production of proinflammatory
cytokines in the joint that the potential additive effect of sTNFR-Ig
is difficult to measure, although it may be biologically significant.
There was a trend toward greater inhibition of IL-6, IL-1
, and
TNF-
with the combination treatment, and, at least for IL-6, the
level of significance was substantially greater for the combination
(p = 0.007) as compared with vIL-10 alone
(p = 0.021). Also, a trend toward decreased
IgG2a anti-CII Abs was observed with combination treatment on day
32, suggesting a shift toward a protective Th2 response.
In the present study, vIL-10 was more effective than sTNFR-Ig at inhibiting murine CIA. This finding is supported by our own earlier studies (16) as well as those of others (17, 18) demonstrating that Ad(vIL-10) can either completely prevent or markedly delay disease onset. The effect of vIL-10 is lost as the serum titer drops secondary to development of anti-vIL-10 Abs (16). We cannot rule out the possibility that neutralizing anti-vIL-10 Abs might also neutralize protective endogenous murine IL-10. However, this possibility is unlikely, since neither murine IL-10 protein nor mRNA was detected in the sera or the joints of any of the mice, including the controls.
The effects of TNF blockade in murine CIA appear to be more complex.
TNF clearly plays a role in the acute phase of CIA, although it might
not be as critical a mediator as other cytokines. Analysis of paw mRNA
in early CIA demonstrates a preponderance of IL-2, IL-1ß, and IL-6,
with TNF-
being less dominant (26). Similarly, TNF-
protein is detected in CIA only during the first few days of arthritis
(30). The effects of TNF blockade appear to depend both on
the timing and duration of blockade as well as the neutralizing agent.
For instance, Abs to TNF have been found to either have no effect on
established disease (31) or to inhibit disease onset as
well as established disease (32). sTNFR also can inhibit
CIA. A divalent p75 sTNFR-Ig fusion protein inhibited disease onset as
well as established disease (33). A p55 divalent sTNFR-Ig
fusion protein similar to the one used in the present study inhibited
established disease in one study (34) and disease onset in
another study (35). The identical sTNFR-Ig-encoding
adenoviral construct used in the present study had a modest inhibitory
effect in rat CIA (36).
Our observation that sTNFR-Ig alone could not inhibit disease, despite
high TNF-neutralizing titers, correlated with the inability of sTNFR-Ig
to block up-regulation of proinflammatory gene products in the
synovium. These findings support the recent study of Quattrocchi et al.
(37) which utilized the identical p55 sTNFR-Ig-encoding
adenoviral vector. In that study, a modest inhibitory effect was
observed during the first 10 days of treatment followed by an
exacerbation of disease despite continued circulating sTNFR-Ig. This
inefficacy was not observed with anti-TNF mAb, raising the
intriguing possibility that sTNFR has additional effects beyond TNF
neutralization. Our own observations also suggest a mild exacerbation
of established disease after day 35, although this did not reach
statistical significance (see Fig. 2
). Quattrocchi et al.
(37) hypothesized that prolonged blockade of TNF is
harmful, perhaps by interfering with the up-regulation of homeostatic
mechanisms such as production of IL-10, TGF-ß, or other mediators
that are likely to be involved in limiting inflammation. Thus,
prolonged blockade of TNF before disease onset might augment T cell
responses, contributing to the observed lack of efficacy of sTNFR-Ig
when administered 710 days before disease onset.
Depending on the timing and dose, TNF can be either proinflammatory or anti-inflammatory. For instance, it has recently been shown that TNF knockout mice fail to regulate and limit an in vivo inflammatory response (38), and TNF can inhibit T cell responses and suppress autoimmunity in NZBXNZW and NOD mice (39). TNF is also capable of enhancing T cell responses (40). Thus, the inhibitory effects of sTNFR-Ig on the T cell response to CII is not unexpected. Clearly, the mechanisms of action of these mediators are complex and will require further investigation.
The present study supports earlier observations suggesting that adenoviral vectors can be used to simultaneously deliver multiple therapeutic genes with sufficient efficiency to control arthritis in animals. The observation that stable serum levels of sTNFR-Ig were achieved for over 40 days following gene transfer suggests that even "first-generation" adenoviral vectors, such as those used in the present study, can allow long-term transgene expression, depending on the half-life and immunogenicity of the gene product. Thus, with further modifications, such as removal of all viral genes to reduce the cytotoxic antiadenoviral response, such vectors might ultimately be useful in patients with chronic rheumatic diseases.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Raphael Hirsch, Division of Rheumatology, Childrens Hospital Medical Center, PAV 2-129, 3333 Burnet Avenue, Cincinnati, OH 45229. E-mail address: ![]()
3 Abbreviations used in this paper: RA, rheumatoid arthritis; sTNFR, soluble TNF receptor; CIA, collagen-induced arthritis; v, viral; CII, type II collagen; BCRF1, BamH1 C fragment rightward reading frame 1; RPA, RNase protection assay. ![]()
Received for publication June 30, 1999. Accepted for publication November 11, 1999.
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