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*
Department of Immune Regulation, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121; and
Hopital Necker, Paris, France
| Abstract |
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| Introduction |
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One problem in the previous studies in NOD mice was that autoaggressive
lymphocytes and their Ag specificities were difficult to precisely
define, quantify, and track (26). We therefore elected to
evaluate this intervention in the RIP-LCMV model for T1D. These
transgenic mice express a defined protein from lymphocytic
choriomeningitis virus (LCMV) (i.e., the gp) as target
autoantigen under control of the rat insulin promoter (RIP)
(27, 28, 29). In these RIP-LCMV-gp mice, the expression of the
transgene, which is restricted to the
cells, does not lead
spontaneously to islet destruction or infiltration (indifference or
ignorance). Only upon LCMV infection self-tolerance is broken and T1D
rapidly develops within 1014 days in over 95% of such mice
(27, 28, 29). Destruction of islet cells is initiated by virus
(self) Ag-specific T lymphocytes that attack
cells via perforin and
inflammatory cytokines (mainly IFN-
) (30).
CD8+ T cells play a major role in this effector
phase since their in vivo depletion prevents disease, whereas depletion
of CD4+ T cells does not (28).
The model offers four main advantages for our present goal: first, the time of initiation of autoimmunity can be chosen experimentally, and therefore the issue of timing of CD3 Ab therapy in relation to the autoimmune process can be addressed. Second, autoaggressive (LCMV-specific) T cells can be precisely tracked and quantified in RIP-LCMV mice because the primary autoantigen is known and most target epitopes have been mapped (31, 32). Third, one may analyze the effect of CD3 Ab treatment in a T1D model, in which it has been well demonstrated that CD8+ T lymphocytes play a major effector role (28, 30). Finally, this model provides a unique opportunity to evaluate the fate of the LCMV viral infection to which the host is exposed at the time of the CD3 Ab treatment. This is of major importance in the context of the presently ongoing clinical application of this strategy in patients presenting with recent onset T1D.
We report in this work that complete prevention of diabetes occurs when non-FcR-binding CD3 Ab is given from days 8 to 12 after LCMV infection, which is right before onset of diabetes in untreated control animals. Long-term diabetes protection is also obtained when giving the Ab earlier (days 05 after infection), but in this case, surprisingly, with a transient disease appearance and its secondary regression. Similar regression is observed when giving the Ab at the very onset of overt diabetes (days 1520 after infection). Importantly, in mice treated with non-FcR-binding CD3, these significant protective effects were obtained without impeding viral clearance.
| Materials and Methods |
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RIP-gp H-2b transgenic mice were described previously and express the LCMV-gp only in their islets, but not any other organs (28). These mice have been backcrossed to the C57BL/6 background for over 12 generations and develop diabetes independent of CD4 lymphocytes. The presence of the RIP-gp construct was determined by slot-blot hybridization or PCR using gene-specific probes or primer sets, respectively, as described previously (27, 28, 33).
Virus stocks consisted of LCMV strain ARMSTRONG (ARM; clone 53b) and Pichinde and vaccinia viruses. LCMV was plaque purified three times on Vero cells, and stocks were prepared by a single passage on BHK-21 cells. A dose of 105 PFU in 0.2 ml PBS was routinely given i.p. to induce diabetes.
Abs and immunization schedules
The hybridoma-producing 145 2C11 (hamster Ig anti-murine CD3) was obtained from J. A. Bluestone (34). The purified endotoxin-free Ab used for in vivo treatment was produced by CellTech (Berkshire, U.K.). Anti-CD3 F(ab')2 was prepared by conventional pepsin digestion of the entire Ab molecule (2-h digestion at 37°C in pH 3 buffer, pepsin at 2% (w/v) final concentration). Digested CD3-F(ab')2 were purified using a Sepharose CL-4-B protein A (Pharmacia, Piscataway, NJ) affinity chromatography column, followed by an UltroGel AcA54 column (Pharmacia). Ab to systemically block IL-4 was generated from the 11B11 hybridoma (BD PharMingen, San Diego, CA). Both Abs were resuspended at a final concentration of 1 mg/ml, and 100 µg was injected in 100 µl i.v. into the tail vein. For CD3-F(ab')2, injections were either given before or after LCMV infection of RIP-LCMV-gp mice daily on 5 consecutive days. For the IL-4 Ab, injections (500 µg i.v.) were administered every other day for 2 wk following LCMV infection of RIP-gp mice. The precise immunization schedules are indicated in the legend for each figure or table, respectively.
CTL assays and precursor analysis
CTL activity was measured in a 5- to 6-h in vitro 51Cr release assay. Briefly, to judge CTL recognition and lysis, syngeneic or allogeneic target cells were either infected with LCMV-ARM (multiplicity of infection = 1), or with recombinant vaccinia virus expressing the full-length LCMV-ARM gp or nucleoprotein (NP) (multiplicity of infection = 3). Uninfected target cells coated with LCMV peptides gp aa 3341, 276286 or NP aa 396404, or NP aa 118127 were also used as targets. Epitopes gp aa 3341, gp aa 276286, and NP aa 396404 of LCMV are all H-2b (Db) restricted for CTL recognition, while NP aa 118127 is restricted by the Ld haplotype. Assays used splenic lymphocytes at E:T ratios of 50:1, 25:1, and 12.5:1, or CTL clones and secondary CTL lines at ratios of 10:1, 5:1, 2.5:1, and 1:1. To determine CTL activity after secondary stimulation, spleen cells harvested from mice 30120 days after primary inoculation with 1 x 105 PFU LCMV i.p. were incubated with MHC-matched, irradiated, LCMV-infected, or peptide-coated macrophages in the presence of T cell growth factor containing IL-2 and irradiated syngeneic spleen feeder cells for 512 days. MC57 (H-2KbDb) and BALB/Cl7 (H-2d) cells used as CTL targets were grown as reported. Precursor frequencies of LCMV-specific CTL were determined as described.
Histologic and immunochemical analysis of tissues
Tissues taken for histologic analysis were fixed in 10% zinc Formalin and stained with H&E. Immunochemical studies were conducted on 6- to 10-µm freshly frozen cryomicrotome sections for immunostaining of islets to detect expression of MHC class I and II, Db, insulin, CD4, CD8, B220, and F4/80. Primary Abs were applied for 1 h. These consisted of rat anti-mouse CD4 (clone RM 4-5), anti-CD8 (clone 53-6.7), anti-B220 (clone RA3 6B2), anti-F4/80 (clone A3-1), anti-MAC-1 (clone M 1/70), anti-MHC class I (clone M 1/42), and anti-class II (clone M5/114) (BD PharMingen, and Boehringer Mannheim, Indianapolis, IN). After washing in PBS, the secondary Ab (biotinylated goat anti-rat (or anti-mouse) IgG; Vector Laboratories, Burlingham, CA) was applied for 1 h. Color reaction was developed with sequential treatment using avidin-HRP conjugate (Boehringer Mannheim) and diaminobenzidine-hydrogen peroxide.
Blood glucose monitoring
Blood samples were obtained from the retroorbital plexus of mice, and plasma glucose concentration was determined using Accucheck III (Boehringer Mannheim). Mice with blood glucose values higher than 300 mg/dl were considered to be diabetic.
Cytokine assays: ELISPOTs
Quantitation of cytokines in cell cultures with LCMV Ag-specific or generalized (PMA/ionomycin) in vitro stimulation was performed in sandwich ELISPOT assays, as described elsewhere (35, 36). Briefly, 96-well plates were precoated overnight at 4°C with 2 µg/ml purified capture Abs. After washing and blocking with 10% FCS in PBS, serial dilutions of live cells were added and were incubated overnight in a humidified cell incubator at 37°C in the presence of Ag (LCMV peptides) and Ag presenting (irradiated splenocytes). Washing and a 1-h incubation with 1 µg/ml matched biotinylated detection Abs (BD PharMingen) overnight at 4°C were followed by a 30-min incubation with a streptavidin-peroxidase conjugate (1:1000; Boehringer Mannheim). For color reaction, H2O2-activated ABTS (Sigma-Aldrich, St. Louis, MO) solution in 0.1 M citric acid (pH 4.35) was added. Plates were quantified blinded by two different investigators under a cell counting microscope.
Flow cytometry
Staining of cell surface Ag and intracellular Ags was performed
as described previously (36). For staining of
intracellular cytokines, cells were stimulated for 510 h by either of
the following methods using PE-conjugated anti-cytokine Abs
(PE-IFN-
, 18115A; PE-TNF-
, 18135A; PE-IL-2, 18005A;
PE-IL-4, 18035A): Polyclonal stimulation was provided by 5 ng/ml PMA
and 500 ng/ml ionomycin (Sigma-Aldrich) or, alternatively, plate-bound
CD3 and soluble CD28 Ab (37). Virus-specific stimulation
was provided by addition of 10-6 M LCMV-gp3342
peptide in the presence of 50 U/ml human rIL-2. All stimulation
cultures contained 1 µg/ml brefeldin A (B7651; Sigma-Aldrich) to
block protein transport into post-Golgi compartments and allow
cytokines to accumulate within cells. In some experiments,
LCMV-infected, irradiated peritoneal exudate cells provided Ag-specific
stimulation, and brefeldin A was added for 510 h after transfer to
fresh peritoneal exudate cells. Negative controls were stained with
cytokine-specific PE-conjugated Abs preincubated for 30 min at 4°C
with an excess of recombinant cytokine. Cells were acquired and
analyzed on a FACSort or FACSCalibur flow cytometer (BD Biosciences,
San Jose, CA) using CellQuest software.
RNA analysis/RNase protection assays
Whole pancreata were harvested on days 2, 7, 17, and 21 after
LCMV infection and immediately homogenized in 2 ml of
Tri-reagent (Molecular Research Center, Cincinnati, OH) using a
Polytron homogenizer. Total RNA was extracted with chloroform, followed
by isopropanol precipitation and washing with ethanol. Twenty
micrograms of total pancreatic RNA was used for hybridization with a
[32P]UTP-labeled multitemplate set containing
specific probes for IFN-
and TNF-
provided by a commercial kit
(Riboquant, mCK-3b; BD PharMingen). The RNase protection assay was
conducted according to the manufacturers guidelines. The resulting
analytical acrylamide gel was scanned using a STORM-860 PhosphorImager
System (Molecular Dynamics, Sunnyvale, CA), and the intensity of bands
corresponding to protected mRNAs was quantified using the ImageQuant
image analysis software (Molecular Dynamics) (38).
Viruses
Virus stocks consisted of LCMV-ARM (clone 53b), Pichinde virus, and vaccinia virus/LCMV gp and NP recombinants that expressed LCMV-gp aa 1398 and LCMV-NP aa 1558 (39). Virus was plaque purified three times on Vero cells, and virus stock was prepared by a single passage on BHK-21 cells. Stocks of recombinant vaccinia viruses were prepared by infection of 143 thymidine kinase- cells in media containing bromodeoxyuridine (39).
Adaptive transfers
For adaptive transfers, splenocytes from each donor mouse were obtained by gently pressing the spleens through a mesh and lysing the RBCs, as described previously (28). One donor spleen was used per recipient, and splenocytes were injected i.p. in 1 ml of PBS at day 12 post-LCMV infection. CD8 depletion was conducted before transfer using magnetic bead technology (33, 37).
| Results |
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The natural course of diabetes in LCMV virus-infected RIP-LCMV-gp
mice evolves in three phases (30). First, activation of
APCs, production of chemokines such as IFN-
-inducible
protein, and secretion of IFN-
occurs between days 2 and 5
after viral infection and is directly due to the presence of LCMV in
the pancreas. Second, the specific autoimmune process is initiated on
day 7 after LCMV infection, reflected in the arrival of autoaggressive
(anti-LCMV) lymphocytes in pancreas and islets. Finally,
destruction of most
cells is seen between days 10 and 18 after LCMV
infection and is mediated by inflammatory cytokines secreted from
islet-infiltrating lymphocytes (30).
Thus, it appeared important to assess the ability of CD3 Ab to affect
diabetes development when applied during each of these stages. Groups
of 810 RP-LCMV-gp mice were treated for 5 days daily with 100 µg of
CD3-F(ab')2 as shown in Fig. 1
. When the Ab was given in the first
phase, long-term protection from diabetes was observed. However,
diabetes initially appeared with the same incidence and rate seen in
untreated controls. Interestingly, the Ab induced regression of
established diabetes that took place 710 days after cessation of Ab
administration. Thus, early administration of the Ab during diabetes
pathogenesis did not induce primary prevention, but modified the late
course of the disease (Fig. 1
). In contrast, when administered during
the second phase, the Ab completely prevented diabetes development, and
only 10% of the mice developed diabetes transiently 23 wk after LCMV
infection (Fig. 1
). Finally, late administration (day 1520) of
CD3-F(ab')2 to recently diabetic RIP-gp mice
resulted in reversion from diabetes, and 75% of the animals were
permanently protected. Thus, CD3 has the ability to not only protect
RIP-LCMV-gp mice from diabetes, but also to reverse clinical disease in
this mouse strain, which we had never observed previously with any of
the clinical interventions we evaluated.
|
Numbers of autoaggressive LCMV CTL were determined at 7 and 14
days post-LCMV infection in RIP-LCMV mice treated successfully with
FcR-binding CD3 and non-FcR-binding CD3-F(ab')2
(Table I
). In the first
experiment, autoaggressive LCMV-specific lytic CTL activities on day 7
post-LCMV infection were significantly reduced in
CD3-F(ab')2-treated mice (Table II
). For these studies, intact CD3 or
CD3-F(ab')2 were given early (days 0 through 5)
to complete one full treatment course before harvesting splenocytes for
CTL assays on day 7. LCMV-gp33-specific lytic CTL
killing was 55 ± 8% in untreated mice, 20 ± 6% in
CD3-F(ab')2-treated mice, and 4 ± 1% in
FcR-binding CD3-treated mice. Thus, both the intact FcR-binding CD3 and
the non-FcR-binding CD3-F(ab')2 statistically
significantly reduced LCMV CTL activities in RIP-gp mice, but
CD3-F(ab')2 treatment left some sufficient
residual CTL activity intact, whereas intact CD3 completely abolished
LCMV CTL, which fits with the lack of viral clearance observed in this
group.
|
|
(Tables I
(data not shown) by CD8 lymphocytes after Ag-nonspecific
stimulation with CD3/CD28 was reduced 3- to 4-fold, indicating that
overall systemic loss of inflammatory effector functions was most
likely responsible for the specific reduction of autoaggressive
(LCMV-responsive) lymphocytes (Tables INon-FcR-binding CD3-F(ab')2 Ab treatment does not impede viral clearance
Interestingly, despite this systemic reduction of antiviral CTL
and an immune deviation reflected by a Th1-Th2 shift in cytokine
production, the ability to clear LCMV infection was not impaired and
occurred on day 14 postinfection, in
CD3-F(ab')2-treated mice with a similar
efficiency as in untreated mice (Tables I
and II
). In addition, the
capacity to eliminate other viral infections was unaffected (clearance
of Pichinde and vaccinia viruses, as assessed plaque assays described
in Materials and Methods; data not shown). These
observations are of particular importance, because T cells
predominantly mediate clearance of these viruses. Thus, administration
of CD3-F(ab')2 appears to be a safe and effective
way to prevent autoimmunity by systemically modulating the immune
system to a sufficient, but not excessive degree, which is reflected in
the ability to still clear viral infections. In contrast, treatment
with intact FcR-binding CD3 Ab had major side effects in that it
severely affected viral clearance (Tables I
and II
) as well as
survival, as illustrated by the 75% mortality rate scored at 4 wk
following LCMV infection in FcR-binding CD3-treated RIP-LCMV-gp
mice.
Reduction of TNF-
, lymphotoxin (LT)
, and overall
lymphocyte numbers in spleens of CD3-F(ab')2-treated
RIP-LCMV-gp mice
We extended our cytokine analysis by performing RNase
protection analyses on spleens comparing
CD3-F(ab')2-treated and untreated control mice on
day 10 post-LCMV infection. The amounts of LT
and TNF-
were
significantly reduced, and overall expression of CD4, CD8, and TCR
was lowered as well (Fig. 2
). This
confirms our previous observations (Tables I
and II
) showing lack of
expansion of CD4 and CD8 lymphocytes in
CD3-F(ab')2-treated mice and reduction of their
inflammatory cytokines. It is interesting to note that no change in
IL-2 production was detected. In parallel, there was a lack of CD8
infiltration in islets of RIP-gp mice protected from diabetes after
receiving CD3-F(ab')2 treatment (Fig. 3
).
|
|
Since we had observed an increased systemic number of
IL-4-producing CD4 lymphocytes after CD3 administration (Tables I
and II
) in ELISPOT assays, we evaluated the possibility that active
regulatory cells had been induced. In these studies, 2 x
107 splenocytes were isolated on day 12 after
CD3-F(ab')2 treatment (days 8 through 12) of
RIP-LCMV-gp mice and transferred i.p. into synchronously infected, but
not CD3-treated RIP-gp recipients. No reduction of T1D was observed in
recipients of such transfers, and all mice developed T1D within 3 wk
post-LCMV infection (Fig. 4
). To exclude
the possibility that cotransfer of pathogenic CD8 lymphocytes would
inhibit the function of regulatory T cells, i.e.,
CD25high (24, 40) or
CD4+ IL-4+ T cells
(36, 41), we depleted CD8 lymphocytes in donor spleens
from CD3-F(ab')2-treated mice before injection
into syngeneic RIP-gp recipients, but no protection was observed (Fig. 4
). The lack of transferable protection fits with the finding that we
did not observe any changes in numbers of
CD25high lymphocytes (data not shown) and their
cytokine production (10% IFN-
positive), making the induction of
CD25+ regulatory cells less likely in the
RIP-LCMV model, although we had observed their generation in
CD3-F(ab')2-treated NOD mice (24)
(L. Chatenoud, unpublished observation). One must take into
account that the rapid onset RIP-GP model is less prone to immune
regulation (28), that CD25+
regulatory cells might only occur in high enough numbers in the
pancreatic draining node, and that induction of this type of regulation
requires more time before it can be assessed in transfer experiments.
Finally, it was possible that the systemic increase in IL-4 production
could still have a beneficial effect, despite the fact that immune
regulation could not be transferred, indicating that no significant
numbers of active regulatory lymphocytes were induced after
CD3-F(ab')2 treatment. However, systemic blockade
of IL-4 by injection of 11B11 Ab had no effect on the degree of
protection achieved by CD3-F(ab')2 treatment
(Fig. 4
).
|
Histological examination of RIP-GP transgenic mice that had
received CD3-F(ab')2 treatment after onset of
clinical signs of T1D (days 1520 after LCMV infection) revealed a
minor loss of infiltration in most islets (Fig. 3
). Thus, permanent
reversion from clinically apparent T1D occurs by preserving just enough
cell mass to maintain normoglycemia, as already observed in the NOD
model (12). Islets are not free of infiltration, but
insulitis (Table III
) remains
nonprogressive. This is clinically important, because it
demonstrates that this type of intervention is: 1) one of the
few treatments capable of reverting clinical T1D, and 2) effective in
doing so not only in the NOD, but also in another animal model for T1D,
the RIP-LCMV model. Importantly, overall immune competence remains
intact, which makes this strategy attractive for the use in humans at
high risk for T1D.
|
| Discussion |
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This observation is crucial from the therapeutic viewpoint and provides a major additional argument for the usage of non-FcR-binding CD3 Abs in the clinic. The clinical application of such Abs was already strongly driven by their lack of mitogenicity, explaining their inability to induce, upon first injection, the massive systemic cytokine release syndrome typically observed with intact FcR-binding CD3 Abs (15, 16, 21, 22, 23). Our present results show that nonmitogenic CD3 Abs also avoid the harmful consequences of this therapy on responses to viral infections even when these occur simultaneously in relation to the Ab treatment.
On the mechanistic side, intact FcR-binding CD3 may affect the
antiviral immune response through massive T cell depletion. It is in
fact well established that T cell depletion is more profound and
long-lasting following administration of intact CD3 Abs with a
functional Fc fragment as compared with non-FcR-binding CD3 (9, 12, 42). This fits well with the present data showing that
LCMV-specific CTLs are undetectable in mice treated with FcR-binding
CD3. Another nonmutually exclusive possibility is that the high
mortality occurring with intact FcR-binding CD3 is due to the cytokine
release syndrome that develops at the time of ongoing LCMV infection.
In this case, some antiviral immunity could persist for a prolonged
period of time (43). These data also provide an important
example for the differential threshold in terms of the frequency of T
lymphocytes required for induction of autoimmunity, which appears to be
higher than that required for antiviral immune competence. Indeed, our
earlier studies using an MHC class I-restricted blocking peptide had
defined that >1/5000 LCMV-specific T cells are needed to destroy
LCMV-GP transgenic
cells, but that this number is still sufficient
to eliminate the virus (44). Our present data support this
concept, since intact CD3 completely abrogates the LCMV-specific lytic
CTL activities and their IFN-
production, whereas
CD3-F(ab')2 leaves residual lytic CTL activity
and cytokine production intact. It is interesting to note that the
putative additional modes of action elicited by
CD3-F(ab')2 (i.e., antigenic modulation
(12, 45), systemic immune deviation, induction of
regulatory T cells (24)) appear to be important for
protection from diabetes, but do not severely affect clearance of viral
infections. In conclusion, it will be vital that immune-based
interventions with systemic activity respect this line between
abrogating the pathogenic response, yet retain a sufficient immune
capacity to warrant antiviral immune competence. Our experimental data
demonstrate that this is a real possibility.
Another impressive feature of the data we present is the ability of
non-FcR-binding CD3 to not only protect RIP-LCMV-GP mice from diabetes,
but also to reverse established disease in this mouse strain, which we
had never observed previously with any of the clinical interventions we
evaluated. The natural course of the disease in RIP-LCMV-GP mice is
rather acute, most
cells being eliminated as soon as 18 days after
LCMV infection. The acuteness of the disease in this model relies on
the characteristics of the major effector population, i.e., mostly
LCMV-specific high-affinity CD8 T cells that colonize the periphery
because of lack of expression of the transgene in the thymus (28, 30). Indeed, this is clearly demonstrated through studies in
another transgenic line of mice, RIP-LCMV-NP, that express the
transgene (the NP of LCMV) in both the
cells and the thymus.
Accordingly, LCMV infection triggers a slow onset T1D in these mice
that appears within 16 mo depending on the hosts MHC background
(27, 28, 46). In this model, high affinity autoreactive
CD8 T cells are deleted in the thymus, and the autoimmune process is
dependent on low affinity autoreactive CD8 that escapes selection, and
on a major CD4 component that plays an important modulatory role
(28, 33). Thus, in preclinical terms and focusing on
disease kinetics, the RIP-LCMV-NP model, as the NOD model, displays
more similarities with slow onset adulthood diabetes. In contrast,
RIP-LCMV-GP mice may represent a better model for rapid onset T1D
typical of childhood.
The finding that the non-FcR-binding CD3 Ab can reverse disease when
given to overtly diabetic RIP-LCMV mice was unexpected. However, it
fits well with the notion, supported by in vitro and in vivo data from
the NOD model, that the physical destruction of
cells is to a large
extent preceded by a phase of reversible T cell-mediated inflammation
that results in a significant impairment in their capacity to release
insulin in response to conventional stimulations. Thus, heavily
infiltrated pancreatic islets from old, but still nondiabetic female
NOD fail to release insulin upon stimulation with high glucose
concentrations when examined immediately after the isolation. However,
this inhibition of
cell function is fully reversible upon clearing
of the immune cell infiltrate after culturing the islets for 7 days in
vitro (47). Moreover, Sreenan et al. (48)
showed that at the time of diabetes onset there is a significant
residual
cell mass of
30%, and that in old nondiabetic NOD
female mice the in vivo insulin secretion is reduced to a greater
degree than the actual
cell mass (48). Thus, the
diabetes regression we observed strongly indicates that in the
RIP-LCMV-GP model as well as in the NOD, a large component of the
diabetogenic effect of aggressive infiltrating T lymphocytes is due to
an inflammation that impairs
cell function. This may be effectively
reversed using agents such as CD3 Abs that are effective at rapidly and
completely clearing the insulitis (9, 12).
The results obtained when the Ab was administered in the early, first phase (day 05) appear more paradoxical, since such treatment proved to be unable to prevent diabetes onset, but finally led to disease regression similar to that obtained after late Ab administration. In such early treated mice, one cannot invoke a solely antiinflammatory effect, as suggested above for mice treated late, since diabetes regression occurred 6 days after the end of CD3 Ab treatment. It is more tempting in this setting to suspect an additional immunoregulatory mechanism.
Complete and durable prevention of disease was observed when the
non-FcR-binding CD3 was applied from days 8 to 12 after infection once
the autoimmune process is actively engaged, as assessed by the islet
invasion (30). A marked decrease in the cytotoxic and
cytokine (IFN-
and TNF-
)-producing capacity of LCMV-specific
autoaggressive CD8 lymphocytes was observed in treated as compared with
control mice. Given the key role of IFN-
as an effector mechanism in
the RIP-LCMV-GP model (by directly acting on
cells in synergy with
other cytokines and by sensitizing
cells to CTL lysis through
up-regulation of class I molecules (30)), its reduction
fits well with the observed prevention of type 1 diabetes. Moreover,
CD4 cells from treated mice displayed a typical Th2 immune deviation
with an excess of IL-4 production upon polyclonal stimulation. This
could have been of potential relevance to explain the therapeutic
effect, because immune intervention strategies such as autoantigen
(insulin) administration, which shift the intraislet infiltrate from a
Th1 to a Th2 phenotype (33), have a beneficial effect in
the RIP-LCMV model, and because destructive insulitis in the final
effector phase of T1D in RIP-LCMV mice is characterized by a
predominance of IFN-
over IL-4 (30, 49). However, the
CD3 Ab-induced protection was not abrogated by IL-4 Ab therapy.
Thus, taken together, our data indicate that non-FcR-binding CD3 Ab may act in two nonmutually exclusive ways: 1) A direct action on effector T cells by partially reducing their numbers (i.e., partial depletion, as already demonstrated in other models including the NOD mice (12)) and affecting their lytic as well as inflammatory functions; and 2) induction of an immunomodulatory effect.
These two effects have been shown to coexist in a chronological fashion
in the CD3-protected NOD mice (12, 24). It is interesting
that neither in RIP-LCMV nor in NOD mice immunomodulation appears to
involve Th2-type cells, since the Ab-induced protection was not
abrogated by IL-4 Ab therapy. In contrast, studies in the NOD mouse
model had demonstrated that protection from diabetes after CD3
F(ab')2 treatment can be transferred to NOD-SCID
recipients by mixing CD25+ or
CD62L+ regulatory cells with diabetogenic
lymphocytes in coadoptive transfers (24, 50, 51) (L.
Chatenoud, personal communication). These studies indicated the
induction of an active regulatory cell population among the
CD25+ lymphocytes of yet unknown Ag specificity.
It is possible that we were unable to find evidence for transferable
protection in our present investigation, because the numbers of
CD25+ are too low to be effective in direct
transfers or even CD8-depleted spleens (Fig. 4
). These studies do not
preclude the existence of a regulatory population that could affect
diabetes in a model with slower disease onset, but our data show that
down-modulation of a Th1 response can occur in the absence of
IL-4-producing immunoregulatory cells.
In conclusion, treatment with nonmitogenic
CD3-F(ab')2, but not with intact FcR-binding CD3,
appears to be a safe and efficacious way to prevent autoimmune
diabetes. We find that the main mechanism underlying this effect is
reduced expansion of overall inflammatory T lymphocytes, which results
in a drastic reduction of lytic activity as well as IFN-
and TNF-
generation by autoaggressive CD8 lymphocytes. Importantly, general
immune competence is not affected by this intervention, whereas intact
FcR-binding CD3 treatment abrogates the ability to clear LCMV
infection. We find no direct evidence for regulatory cells in our
RIP-LCMV model with rather rapid disease onset, and the protection from
T1D cannot be transferred. It will be advisable to quantify primarily
autoaggressive T cells during clinical trials that should be reduced in
all successfully treated individuals. Augmentation of certain
regulatory lymphocytes (CD25+ cells or IL-4
producers) might vary depending on the individual situation and
kinetics of disease. Finally, nonmitogenic CD3 appears to be one of the
few interventions capable of reverting clinical T1D, which occurs in
NOD as well as RIP-LCMV mouse transgenic lines. These observations open
new perspectives for the use of this intervention not only in patients
presenting with recent onset diabetes, but also in prediabetic subjects
and in recipients of islet allografts.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 Address correspondence and reprint requests to Dr. Matthias G. von Herrath, Department of Immune Regulation, La Jolla Institute for Allergy and Immunology, 10355 Science Center Drive, IR-3, San Diego, CA 92121. E-mail address: matthias{at}liai.org ![]()
3 Abbreviations used in this paper: T1D, type 1 diabetes; GP, glycoprotein; LCMV, lymphocytic choriomeningitis virus; LT, lymphotoxin; NOD, nonobese diabetic; NP, nucleoprotein; RIP, rat insulin promoter. ![]()
Received for publication August 30, 2001. Accepted for publication November 6, 2001.
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+CD4+ thymocytes expressing L-selectin mediate "active tolerance" in the nonobese diabetic mouse. J. Immunol. 161:2620.This article has been cited by other articles:
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