New perspectives on immunointervention in autoimmune diseases

Immunology Today, Vol 1I, No 11 1990

asking for grant applications for research on NIM At that time there was only one NINCDS-funded laboratory actively pursuing the subject. Today, together with other Institutes of the NIl-i and with the National Institute of Mental Health, more than 200 grants are funded to study N!M and NIMrelated research! We are in the midst

of a revolution in basic biomedical sciences, which inevitably will lead [o a corresponding revolution in clinical medicine and, even more impo~ antly, in preventive medicine.

The currently available treatments for autoimmune diseases were not developed with a clear knowledge of the mechanisms involved in the primum movens of the disease process, namely the activation of autoreactive T cells. A new generation of immunosuppressive agents that are potentially useful in the prevention and/or treatment of autoimmunity is being fostered by recent progress in the understand/ng of antigen presentation to T cells. In this article, contributed by the chairpersons of a recent workshop on the subject*, the potential of new therapeutic approaches targeting the major histocompatibility complex (MHC), T-cell receptor (TCR), CD4/CD8 and CD3 molecules, adhesion molecules, cytokine5 and cytokine receptors are considered.

New perspectiveson immunointerventionin autoimmune diseases

The immunologist's view of the re...... ,5,,,p between ~,, and non-seif has progressively changed over the years. Recognition of self antigens by the immune system was once considered to be invariably harmful and to lead directly to autoaggression and disease. This concept was later modified by observations showing tha~ autoreactive clones, in both T- and B-cell compartments, are present in normal individuals, and a distinction between autoreactivity and autoimmune disease began to emerge. It is now thought that recognition of self MHC molecules by T cells during and after T-cell development is the driving force shaping the available T-cell repertoire. The edge between phydological and pathological autoreactivity is subtle, as exemplified by the presence of low-affinity, nonpathological rheumatoid factors (RF) during normal immune respcnses *Theworkshopon New Perspectivesfor ImmunoA interventionin r,utoimmune Diseaseswas he!d in CalaMoresca,Sardinia,Italyon 10-15June1990as partof themeetingAllergy'90,andwasorganizedby L.AdoriniandE.Serca~.

References

1 Spector, N.H. (1987)in Encyclopedia ofNeuroscience (Adelman, G., ed.), pp 798-799, Birkhauser 2 Luk'yaneko,V.I (1961), :~d. Nauk SSSR.Uspeki 5ovrem. Biol. 51, 170-187

Novera Herbert Spector is at the Division of 3 Spector, N.H. in Psychoimmunologie Fundamental Neurosciences, NINDS, N/H, (Ka-_-chka,W.P. and Aschauer, H., eds), Betnesda, MD 20892, USA. Georg ThiemeVerlag (in press)

from Lucia 0 Ad0rini, Vincenz0Bamaba,C0nstantinBona, Franc0Celada,AntonioLammve(r ia, Eli Smarz, Ni:01eSudu-F and HarlmutWekede (for example afte: vaccination) and high-affinity RF in rheumatoid arthritis. Implementation of appropriate treatments (Fig. 1) to prevent and cure autoimmune diseases depends on an understanding of the mechanisms that tilt the immune system over the edge. Such an understanding should allow the development of selective immunointervention strategies that overcome the limitations intrinsic to counteracting the effects of autoimmunity with non-specific treatments, rather than specifically preventng the causes. Non-~pec;ific immunointervention

Only non-specific treatments are presrntly available for autoimmune diseases and, although they have diverse mec'.lanisms of action, they share the fundamental drawback of not distinguishing between physiological and pathological immune responses. Thus these treatments should be used as a last resort, during acute exacerbations when the undesired response mu.t be blocked regardless of the damage caused to physiological defence mechanisms. One example of non-specific immunointe~vention is the administration of monoclonal antibodies (mAbs) directed to monomorphic components (CD3) of the TCR complex. These rnAbs are currently used to overcome acute allograft rejection, and in this they are effective, at least for a limited period. However, this approach may not be applicable to

(~ 1990. ElsevierScience Publishers Ltd. UK. 0167--49191901502.00

autoimmune diseases, since sustained administration ot anti-CD3 antibodies would probably induce severe sioe effects. A somewhat more selective approach relies on the elimination of T cells expressing intedeukir. 2 (IL-2) receptors, using either anti-lL-2 receptor antibodies (in the native form or as immunotoxins) or IL-2-toxin conjugates. This approach is more selective than anti-CD3 treatment, since it removes activated lymphocytcs only, sparing nen-actiwted ones. I-cell activation could also be hindered via inhibition of cytokine gene transcription, in particul:: iL-2 gene transcription, by drugs such as cyclosporine A. Results from clinical trials indicate that cyclosporine A is indeed effective in some, but not all, autoimmune diseases. In addition, understanding the mechanisms 9f signal transduction via T-cell-specific kinases, phosphatases and G proteins may reveal possibilities for designing drugs to selectively inhibit T-cell functions. Another possibility is the use of antibodies directed against accessory molecules involved in T-cell activation. Accessory molecules expressed by T cells include CD4, CD8, lymphocyte function associated antigen 1 (LFA-1) and CD2, which bind respectively to MHC dass II, MHC class I, intercellular cell adhesion molecule 1 (ICAM-1) and LFA-3 on antigen-presenting cells (APCs). Monoc!ona! antibodies directed against integrins, such as LFA-1, may 383

Immunology Today, Vol. I 1, No. 11 1990

- evjs a . d lrea/ures ryT cell(Ts) / IL-2-toxin ~

T

~IL-2R f / / k-T-x , /

Activation by CR-id, ag (xCD4 ,I,

/I~~~.~

~

Inhibition

of aene transcrilotion

:~Uncoupling ~ of signal

~

transduction/

, Peptide

APC /~MIHcP'~ =t, (xT M l ~ Autoreactive / / \ ~CD3~Tcell .~

j Competition for ag presentation

Tolerance~ induction

r:lg. 1. Possibleattack po,nts for immunointervention in autoimmune diseases. Effective treatment may be .obtainea by interfering with . ~ f i c mechanismsor by a y/nergisticcombination of approaches.

not have a therapeutic application in chronic au~.oimmune diseases; they would probably induce an iatrogenic leukocyte adhesior, deficiency syndrome, similar to the inherited syndrome that is often fatal in childhood and is caused by a mutation of the I~ subunit common to LFA-1 and other integrins. Monodona! antibodies to CD4 and CD8 not only inhibit T-cell activation, in v/tro and in vivo, but also allow the induction of tolerar, ce to antigens introduced during the course of mAbmediated immunosuppression. In experimental models, induction of antigen-specific tolerance, for example ~o xenogeneic Ig or to pancreatic islet cell allografts, by injection of anti-CD4 antibodies has been clearly demonstrated. If applicable to autoantigens inducing autoimmune diseases, this could represent an interesting approach to re-establishing tolerance to self. Moreover, anti-CD4 mAbs have been effective in preventing and/or reversing experimental autoimmune diseases such as systemic lupus erythematosus (SLE), experimental allergic encephalomyelitis (EAE), insulindependent diabetes mellitus (IDDM) and rheum~t.~id arthritis (RA)-Iike syndromes. Preliminary results indi384

cate that treatment of RA patients with anti-CD4 mAbs depletes CD4÷ cells and reouces clinical symptoms. Although the long-term efficacy of this therapy has yet to be evaluated, in the short-term it appears to be devoid of acute side effects.

MHCblockade A striking characteristic of human autoimmune diseases is the increased frequency of certain HLA class II alleles in affected individuals. As demonstrated in RA, IDDM and pemphigus vulgaris, alleles positively associated with autoimmune diseasesshare amino acid residues in the hypervariable HLA regions involved in peptide binding. Therefore, it is probable that disease-associated HLA class II molecules have the capacity to bind autoantigen and present it to T cells, thereby inducing and maintaining (under appropriate environmental conditionsL the autoimmune disease. Blocking the antigen-presenting activity of disease-associated HLA class II molecules could thus interfere with disease. One possible approach to preventing activation of class-II-restricted autoreactive T cells is the administration of anti-MHC-class-II antibodies. This approach has been used

to prevent experimental autoimmune diseases like EAE in mice and rats and IDDM in non-obese diabetic mice. To obtain a selective inhibition of T-cell responses restricted by the diseaseassociated HLA class II allele, allelespecific antibodies should be used. In general, the use of monoctonal antibodies in the therapy of autoimmune diseases is complicated by the immunogenicity of the antibody molecules - even after their chimerization or humanization -which may prevent long-term treatment. An alternative to inhibition of T-cell responses by anti-MHC-class-II antibodies is blockade of the MHCbinding site by peptidic competitors. The feasibility of preventing autoimmune diseases by in vivo peptide competition has recently been demonstrated, again in the EAE model: coinjection of competitor and encephalitogenic peptides prevents the clinical development of EAE, probably because the competitor inhibits binding of the encephalitogenic peptide to class, molecules. In one study, encephalitogenic and competitor peptides did not share sequence homology, suggesting that induction of T-cell anergy or suppression by the competitor peptide is not the mechanism of disease prevention. Thus, inhibition of r-cell activation by blocking the binding of antigenic peptides to class !! molecules can prevent the induction of experimental autoimmune diseases, and this could lead to the development of a new generation of immunosuppressive agents. Experiments using the mouse lysozyme (ML) sequence 46-62, which binds to I-Ak, as a prototype MHC blocker support the possibility of a therapeutic approach based on MHC blockade. ML 46-62 is, for the mouse, a non-immunogenic self p=ptide. Therefore, inhibition of T-cell activation by coinjection ol antigen and ML 46-62 does not appear to result from direct TCR blockade, from induction of tolerance, or from antigen-specific suppression by the competitor. Coinjection of hen eggwhite lysozyme (HEL) and ML 46-62 into BIO.A(4R) mice (which express only I-Ak class II molecules), inhibits both T-cell proliferation to HEL and the anti-HEL antibody response, even when the mice had already been primed with antigen. MHC-selective inhibition can be achieved not only by coinjection of antigen and

Immunology Today, Vol. 11, No. 11 7990

ne s competitor in complete Freund's adjuvant (CFA) but also by parenteral administration of soluble peptide competitors under conditions in which the competitor is not immunogenic. In most human autoimmune diseases the autoantigen is probably an endogenous cellular antigen so it is important to ascertain whether an exogenous competitor can inhibit the T-cell activation induced by the endogenous antigen. Antigenpresenting cells transfected with the HEL gene constitutively present HEL peptides to class-II-restricted T cells, and the presentation of endogenous antigen can be efficiently inhibited by an exogenous competitor; this suggests a lack of compartmentalization between endogenous and exogenous peptides in the interaction with MHC class II molecules. When considered together these results indicate that MHC blockade is a practical approach to the "herapy of HLA-hnked autoimmune diseases. Although it is only partially selective, since all T-cell responses restricted by the blocked HLA allele are inhibited, its reversibility could be exploited to avoid undesirable side effects.

[e tures-

Idiotypes The repertoire of T- and B-cell populations contains precursors that can recognize idiotypes of the recep-

and they decrease in the remission phase coincident with an incredsed production of anti-idiotypic antibodies; this suggests that antiidiotypic therapy may accelerate remission or prevent relapse. This treatment has the greatest chance of success when the pathogenic antibodies are mono- or oligoclonal (as in myasthenia gravis (M,:), autoimmune haemolyuc anemia, thrombocytopenia and pemphigus) or when they bear a predominant idiotype. Epibodies, initially described in rheumatoid arthritis, have also been observed in MG, SLE and tubulointerstitial nephritis. Little is known about the pathogenic role of these anti-idiotypic antibodies but they could be viewed as superantibodies that establish high connectivity between clones specific for self and non-self antigens. Some experimental systems have described a relationship between anti-idiotypes carrying the internal image of antigen (Ab213)and idiotypic species found on autoimmune B cells. Such immunog:-aic internal image antibodies are probabiy rare, since they shot, ld bear an immunogenic r-cell determinant in addition to B-cell determinants. If such an unusual Ab213 were responsible for autoaggression, T-cell therapy directed against the TCR or other sur-

d~seasecan also confer specific resistance to it, after simple manipulations such as irradiation, fixation or high pressure treatment. Such treatments ablate the pathogenTc potential while preserving the immunogenic function of the lines. This strategy relies on two properties of autoimmune T cells in exp,.arl'ental animal models. First, potentio,y autoaggressive T-cell clones have been demonstrated in the T-cell repertoire of normal individuals, and in the hea!thy organism these clones are controlled by suppressive mechanisms, probably involving regulatory T cells specific fgr TCR variable region determinants of pathogenic clones. Second, at least an some autoimmune models, the pathogenic T cells use an unexpectedly restricted repertoire of TCR V elements. For example, in the PL/J mouse and in the Lewis rat, encephalitogenic T-cell clones use Vp8.2 chains almost exclusively, although the encephalitogenic epitope recognized by the relevant T cells is different. T-cell vaccination has been performed using two different approaches. In the 'traditional' vaccination protocol, att~:nuated pathogenic T cells that b,~':e been preactivated are transfen~d~ ~=:,citing clonotype-specific regulatory T cells that can prevent disease induction.

¢,UIJ

ICIt..t~

Tk ........ l_a.--_. i ll~)~ l~yUldl.Uly

IUI

GIIILI~JEll

~'AI~/I~'~I.~EIJ

U.y

I allU

u

cells. Anti-idiotypic (i.e. idiotypespecific) receptors of T and B cells can be classified into four categories: (1) Ab2oL, antigen non-inhibitable antiidiotypes recognizing a frameworkassociated idiotype, (2) Ab2~/, antigen-inhibitable anti-idiotypes recognizing a paratope-associated idiotype, (3) Ab213, anti-icliotypes carrying the internal image of antigen, where the idiotype mimics a foreign or a self antigen, and (4) Ab2~, or epibody, anti-idiotypes recognizing both idiotype and antigen. Each of these four types of antiidiotypes could, in principle, be used for immunointervention in autoimmune diseases. B-cell idiotypes

Ab2oL and ~b2~/, when administered in small amounts or transferred vi~ the placenta, have a stimulatory effect, but when injected in large amounts cause idiotype suppression. Idiotypic anti-DNA antibodies are present at high concentratbns during the florid phase of SLE

IIICIII~.I~'I~)

UI

LIIt~

llUi~'l

I

LUll

"r I

----ii-L~II")

L--L .... U~lldV~

I:LA IIKI~

inducing Ab213 could be added to anti-idiotypic suppressor cells, but treatments directed against the B-cell there is no formal proof that they idiotype. recognize peptide sequences from the TCR of the pathogenic T cells. An T-cell idiotypes alternative approach, based on active Anti-idiotypic treatment can also immunization of rats with synthetic be envisaged in autoimmune dis- peptide sequences of TCR compeases where T cells directly mediate lementarity determining regions the pathogenic events. Indeed, anti- from encephalitogenic T-cell clones, idiotypic antibodies recognizing the has recently raised much interest. ImTCR idiotype expressed by autoreac- munization of encephalitogenic T tive T cells mediating EAE have been cells with TCR peptides can prevent shown to prevent the disease in- EAE induction in the Lewis rat, acduced by injection of myelin basic tivating regulatory T cells that can protein (MBP~ in CFA. Anti-TCR idio- prevent the expansion of or neutraltypes may downregulate the TCR or, ize MBP-specific CD4 ÷ encephaif antibodies are conjugated to toxins, litogenic T cells. Are these strategies realistic for may delete the autoreactive T-cell clones mediating autoimmune dis- treatment of human autoimmune eases. This treatment can be success- diseases? Preliminary T-cei; vacciful only if the pathogenic T cells nation trials, reinfusing activated, express a restricted repertoire of TCR autologous T cells .nto multiple sclerosis (MS) patients, have shown the V genes. relative safety of the approach. How:ever, practical application will deT-cell vaccination This term is used to describe the pend on the cellular and molecular observation that autoaggressive organization of the human T-cell T-cell lines mediating an autoimmune response against autoantigens. At 385

-news a ,d ire,

t.res

present, studies o~ human MBPs,-~,.i~ic T cells from MS patients are controversial: some studies report a restricted TCR V gene usage and others a high degree of variability in the TCR repertoire of MBP-sp~iflc T cells. Io clarify this issue iz is important to distinguish pathogenic from autoreactive but not autoaggressive T cells, sir~.e this could reveal dominant TCR usage by pathogenic clones. If the TCR repertoire of pathogenic T cells uses many V region families, then vaccination protocols with cells or peptides will have to be tailored for each individual paiient which would limk the large-scale applicability of this approach.

Induction of autoantigen-spedlic

toleranceor suppression Of all of the possible modes of

therapy (Fig. 1), induction of suppression or tolerance specific for the autoantigen is likely to be the most effective a~d have the fewest side effects, since induction of peripheral tolerance or suppression should inactivate only the autoreactive T cells. Candidate autoantigens are being identqfied in autoimmune conditions (eg. human MBP in MS, thyroid peroxidase in Graves' disease), rendering approaches based on inhibition of autoreactive T cells via induction of specific peripheral tolerance and/or suppression more attractive. With respect to tolerance, a major point that must be borne in mind is the dominance of the determinant within the autoantigen. Obviously, it is necessary to induce tolerance to the dominant determinant inducing pathogenic, autoreactive T cells and, if this is not sufficient, to other, sub-

L__

ImmunologyTodayDiary Are you planning a meeting? Please send details to our Editorial Office for inclusion in our comprehensive Diary of courses and conferences.

To help readers, remember to include the deadline date for submission of abstracts.

386

Immunology Today, Vol 11, No. I 1 1990

dominant, determinants. In the case of MBP, although tolerance to the dominant determinant, as well as to the whole MBP molecule, was achieved at the lewl of T-cell proliferation by tolerogenic administration of the MBP peptide Ac-i-9, tolerant mice still developed EAE when injecteci with MBP in adjuvant. However, with a detailed knowledge of the determinant sLructure and hierarchy in a given MHC haplotype, peptide-induced tolerance to the autoantigen should be possible. Therapeutic application of the tolerance approach will also depend on the appropriate delivery of the tolerogen; intravenous or oral administration would probably be most suitable. The cycling of remission and relapse typical of most autoimmune diseases may reflect an underlying suppressive activity that can reestablish successful regulation. Approaches aimed at facilitating induction or re-induction of suppression to the autoantigen should therefore influence the natural course of the disease and avoid side effects. Antigen-specific suppression is still a phenomenon without a molecular explanation. Nevertheless, it has been repeatedly demonstrated that selected determinants of a given molecule can induce suppression that nullifi~s t h p r~,nr~nr,~ n f h ~ l n ~ r T folio . . . . . . . . . . . . . . . . .

IV

. . . . . . . . . . .

i~ "

•

~

"

Conclusions Based on the current ur derstanding of the immune system, the best therapeutic strategy for autoimmune diseases would be to re, ram ti~e immune system to avoid reactivity with S _ I J [ L . . _1~_~.:_ • L: -~ uy u,~,,,.guisf,ny it from I. I.O.1. I-:~I~I'~I . As an alte~native to this presently impractical approach, several options are available. Considering the proven efficacy in experimental models, the selectivity of action and lack of potential side effects, induction of tolerance or specific suppression to the autoantigen would appear to be the most suitable strategy, followed by deletion or inactivation of autoreactive, pathogenic T cells (using antiTCR idiotypes or T-cell vaccination), blockade of disease-associated HLA molecules, and non-selective treatments. The feasibility of clinical application is, unfortunately, in the reverse order, since some non-selective treatments are already available and MHC blockade is being developed, while deletion of autorea:ive T cells and induction of tolerance/suppression are being considered. It is likely that clinical development of these treatmants will proceed by successive generation of drugs, aiming at increasing selectivity and efficacy. When, and if, these immunotherapeutic agents become available, it will be possible to match a given autoimmune disease with

i'i'C: m ~ ¢ f

=nnrnnri~f~

+r~fry~n+

~

directed against other determinants and also to use a synergistic combiof the same molecule. Usually, it has been found that suppressor T-cell cr~)-inducing or helper T-cell (TH)inducing determinants are distinct and non-overlapping, although their sequence may be juxtaposed in the antigen molecule. In any case, specific suppression over an antigen bridge requires the presence of T~inducing and T.-inducing determinants on the same molecule, and it is probable that in many instances these determinants are distant enough to become separated during processing of the autoantigen. To implement antigen-specific suppressicr, effe~ively, Ts-inducing determinants should be grafted onto immunodominant TH-inducing epitopes recognized by pathogenic, autoreactive T cells. However futuristic this appr,ach may seem, it is intellectually ve.y appealing and its correct application may become a prevalent procedure for the treatment of autoimmune diseases in the next millennium.

nation of approaches (e.g. MHC blockade and antigen-induced tolerance) for a rational, effective prevention and therapy of autoimmune diseases.

Luciano Adorini is in Preclinical Research, Sandoz PharmaLtd, CH-4002, Basel, Switzerland; VincenzoCdrnabais in I Clinica Medica, Universita" 'La Sapienza" 00161 Roma, Italy; Constantin Bona is at the Dept of Microbiology, Mount Si,:ai School of Medicine, POB 1124, New York, NY 10029, USA;Franco Celadais at the Hospital for Joim Diseasesand Dept of PathologyNYU, New York, NY 10003, USA; Antonio Lanzavecchia is at the Basel Institute for Immunology, CH-4005, Basel, Switzerland; EliSercarzis at the Dept of Microbiolegy, UCLA,Los Angeles, CA 90024-1489, USA; Nicole Suciu-Focais at the Dept of Pathology, Columbia University, New York, NY 10032, USA; and Hartmut Wekerle ~sat the Dept of Neuroimmunology, Max Planck Institute for Psychiatry, D-8033 Ma~insried, Germany.