Ann Rheum Dis 1999;58:(Suppl I) I107–I113
`
`I107
`
`Immunomodulation by thalidomide and
`thalidomide analogues
`
`Laura G Corral, Gilla Kaplan
`
`Tumour necrosis factor ♡ (TNF♡), a key
`cytokine involved in the host
`immune re-
`sponse, also contributes to the pathogenesis of
`both infectious and autoimmune diseases. To
`ameliorate the pathology resulting from TNF♡
`in these clinical settings, strategies for the inhi-
`bition of this cytokine have been developed.
`Our previous work has shown that the drug
`thalidomide is a partial inhibitor of TNF♡ pro-
`duction in vivo. For example, when leprosy
`patients suVering from erythema nodosum
`leprosum (ENL) are treated with thalidomide,
`the increased serum TNF♡ concentrations
`characteristic of this syndrome are reduced,
`with a concomitant improvement in clinical
`symptoms. Similarly, we have found that in
`patients with tuberculosis, with or without HIV
`infection, short-term thalidomide treatment
`reduces plasma TNF♡ levels in association
`with an accelerated weight gain. In vitro, we
`have also shown that thalidomide partially
`inhibits TNF♡ produced by human peripheral
`blood mononuclear cells (PBMC) responding
`to stimulation with lipopolysaccharide (LPS).
`Recently, we found that thalidomide can also
`act as a costimulatory signal
`for T cell
`activation in vitro resulting in increased
`production of interleukin 2 (IL2) and inter-
`feron ♤ (IFN♤). We also observed a bi-
`directional eVect on IL12 production: IL12
`production is inhibited by thalidomide when
`PBMC are stimulated with LPS, however,
`IL12 production is increased in the presence of
`the drug when cells are stimulated via the T cell
`receptor. The latter eVect is associated with
`upregulation of T cell CD40 ligand (CD40L)
`expression. Thus, in addition to its monocyte
`inhibitory activity, thalidomide exerts a co-
`stimulatory or adjuvant eVect on T cell
`responses. This combination of eVects may
`contribute to the immunomodulating proper-
`ties of the drug.
`To obtain drugs with increased anti-TNF♡
`activity that have reduced or absent toxicities,
`novel TNF♡ inhibitors were designed using
`thalidomide as template. These thalidomide
`analogues were found to be up to 50 000 times
`more active than thalidomide. The compounds
`comprise two diVerent types of TNF♡ inhibi-
`tors. One class of compounds, shown to be
`potent phosphodiesterase 4 (PDE4) inhibitors,
`are selective TNF♡ inhibitors in LPS stimu-
`lated PBMC and have either no eVect or a sup-
`pressive eVect on T cell activation. The other
`class of compounds also inhibit TNF♡ produc-
`tion, but do not inhibit PDE4 enzyme. These
`compounds are also potent inhibitors of several
`LPS induced monocyte inflammatory cy-
`tokines. Also, the latter compounds markedly
`
`stimulate the anti-inflammatory cytokine IL10.
`Similarly to thalidomide, these drugs that do
`not inhibit PDE4 act as costimulators of T cells
`but are much more potent than the parent
`drug. The distinct immunomodulatory activity
`of these new TNF♡ inhibitors may potentially
`allow them to be used in the clinic for the
`treatment of a wide variety of immunopatho-
`logical disorders of diVerent aetiologies.
`
`TNF♡ is a key player in the immune
`response
`TNF♡ is a pleiotropic cytokine produced
`primarily by monocytes and macrophages, but
`also by lymphocytes and NK cells. TNF♡ plays
`a central part in the host immune response to
`viral, parasitic, fungal and bacterial infections.
`The importance of TNF♡ and TNF♡ signal-
`ling through its receptors in the host immune
`response to disease has become clearer as a
`result of a number of seminal studies. For
`example, mice genetically deficient in TNF♡
`have a significantly reduced humoral immune
`response to adenovirus infection.1 In Leishma-
`nia major infection, TNF♡ signalling is impor-
`tant for protection as mice lacking TNF♡ p55
`receptor (TNFR-p55) show delayed elimina-
`tion of the parasites compared with controls
`and the lesions formed failed to resolve.2 Mice
`deficient in TNFR-p55 are also significantly
`impaired in their ability to clear infection with
`Candida albicans and readily succumb to the
`infection. TNF♡ signalling is also crucial in
`resisting Streptococcus pneumoniae infections in
`mice.3 In addition, TNF♡ is essential
`for
`protection
`against murine
`tuberculosis.
`TNFR-p55 deficient mice have been shown to
`be more susceptible to tuberculosis infection.
`When TNF♡ was neutralised in vivo by mono-
`clonal antibodies impaired protection against
`mycobacterial infection was observed.4 5 The
`data from both models also established that
`TNF♡ and the TNFR- p55 are essential for
`production of reactive nitrogen intermediates
`by macrophages early in infection.
`
`TNF♡ contributes to disease pathogenesis
`Although TNF♡ is crucial to the protective
`immune response, it also plays a part in the
`pathogenesis of both infectious and autoim-
`mune diseases. Increased concentrations of
`TNF♡ have been shown to trigger the lethal
`eVects of septic shock syndrome.6 TNF♡ has
`also been implicated in the development of
`cachexia, the state of malnutrition that compli-
`cates the course of chronic infections and many
`cancers.7 In rheumatoid arthritis, TNF♡ is a
`critical mediator of joint inflammation and
`therefore an important
`therapeutic target.
`
`Celgene Corporation,
`Warren, NJ, USA
`L G Corral
`
`Laboratory of Cellular
`Physiology and
`Immunology, The
`Rockefeller University,
`New York, NY, USA
`G Kaplan
`
`Correspondence to:
`Dr L G Corral, The
`Rockefeller University, 1230
`York Avenue, New York NY
`10021, USA.
`
`DR. REDDY’S LABS., INC. EX. 1016 PAGE 1
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`

`

`I108
`
`Corral, Kaplan
`
`Recently, it has been shown that treatment of
`patients with neutralising anti-TNF♡ antibod-
`ies produces a dramatic reduction in disease
`activity in this condition.8 Similarly, it has been
`shown that in inflammatory bowel disease,
`neutralisation of TNF♡ results in a profound
`amelioration of clinical symptoms.9 10 Reduc-
`tions in TNF♡ levels have also been linked with
`a significant reduction of clinical symptoms in
`leprosy patients with ENL, including fever,
`malaise, and arthritic and neuritic pain.11 In
`tuberculosis patients, reduction of TNF♡ levels
`was associated with accelerated weight gain.12
`
`Thalidomide inhibits TNF♡ production
`by monocytes
`The pathology associated with TNF♡ produc-
`tion is profound and in many diseases leads to
`significant morbidity and mortality. This has
`led to a concerted eVort to discover drugs that
`will down regulate the production of
`this
`cytokine. Agents conventionally used in these
`diseases may inhibit TNF♡ production, but are
`also often broadly immunosuppressive (for
`example, cyclosporin A and corticosteroids)
`and therefore associated with extensive side
`eVects.13 Drugs
`that are potentially more
`specific in inhibiting TNF♡ are under active
`investigation and development. Our previous
`work has shown that the drug thalidomide
`(♡-N-phthalimidiglutarimide) is a relatively
`selective inhibitor of TNF♡ production by
`human monocytes in vivo. This property of
`thalidomide was first described in leprosy
`patients with ENL, an acute inflammatory
`complication of lepromatous leprosy that is
`accompanied by increased serum TNF♡ levels.
`Thalidomide treatment of patients with ENL
`was shown to induce a prompt reduction of
`TNF♡ serum levels with a concomitant abro-
`gation of clinical symptoms.11 Furthermore, in
`patients with tuberculosis, with or without
`concomitant HIV infection, thalidomide treat-
`ment was found to both decrease plasma
`TNF♡ protein levels as well as monocyte
`TNF♡ mRNA levels. This decrease was associ-
`ated with an accelerated weight gain.12 In a
`rabbit model of mycobacterial meningitis, tha-
`lidomide treatment combined with antibiotics
`produced a marked reduction in TNF♡ levels,
`leucocytosis, and brain disease.14 In addition,
`thalidomide inhibited TNF♡ serum levels in
`mice challenged with LPS thus partially
`protecting the animals from septic shock.15
`In vitro, we have found that thalidomide
`selectively reduces the production of TNF♡ by
`human monocytes cultured in the presence of
`both LPS and mycobacterial products.16 How-
`ever, this inhibition was only partial (50% to
`70%) possibly because of the instability of the
`drug in aqueous solutions.17 The mechanism
`by which thalidomide reduces TNF♡ produc-
`tion is still unclear. The drug seems to inhibit
`TNF♡ production by human monocytes in
`vitro in association with enhanced degradation
`of TNF♡ mRNA.18 It also inhibits the activa-
`tion of the nuclear factor ♭B (Nf♭B),19 20 a pro-
`moter for the transcription of TNF♡ as well as
`transcription of HIV-1.21 22
`
`Thalidomide has T cell costimulatory
`properties
`Recently, we reported that thalidomide also has
`a hitherto unappreciated immunomodulatory
`eVect: the drug was shown to costimulate
`human T cells in vitro, synergising with stimu-
`lation via the T cell receptor complex to
`increase IL2 mediated T cell proliferation and
`T cell IFN♤ production.23 Optimal T cell acti-
`vation requires two signals.24 The first signal or
`signal 1 is delivered by clustering of the T cell
`antigen-receptor-CD3 complex through en-
`gagement of specific foreign peptides bound to
`MHC molecules on the surface of an antigen
`presenting cell
`(APC). Signal 1 can be
`mimicked by crosslinking the T cell receptor
`(TCR) complexes with anti-CD3 antibodies.
`Signal 2 (or costimulation) is antigen inde-
`pendent and may be provided by cytokines or
`by surface ligands on the APC that interact
`with their receptors on the T cell. Costimula-
`tory signals are essential to induce maximal T
`cell proliferation and secretion of cytokines,
`including IL2, which ultimately drive T cell
`clonal expansion. As antigenic stimulation in
`the absence of costimulatory signals leads to T
`cell anergy or apoptosis, costimulation is criti-
`cally important in the induction and regulation
`of cellular immunity.
`Thalidomide appears to act as a costimulator
`to T cells that have received signal 1 via the
`TCR.23 In our experiments in vitro, stimulation
`of purified T cells with anti-CD3 antibodies, in
`the absence of signal 2, induced only minimal
`T cell proliferation. However, the addition of
`thalidomide to this cell culture system resulted
`in a concentration dependent
`increase in
`proliferative responses.23 25 The thalidomide
`mediated costimulation of T cell proliferation
`was accompanied by increases in IL2 and IFN♤
`production. It is noteworthy that in the absence
`of anti-CD3, there was no T cell proliferative
`response to thalidomide, indicating that the
`drug is not mitogenic in itself. It
`is also
`interesting to note that in these experiments,
`thalidomide did not inhibit TNF♡ production
`by purified T cells stimulated by anti-CD3
`antibodies. This is in contrast with the eVects
`of the drug on TNF♡ produced by monocytes.
`As already described above, thalidomide inhib-
`its monocyte TNF♡ production. The costimu-
`latory eVect of thalidomide was greater on the
`CD8+ T cells than on the CD4+ T cell
`subset.23
`In addition to its eVects on T cell prolifera-
`tion and T cell cytokine production, we
`observed that thalidomide induced the up-
`regulation of CD40L expression on activated T
`cells.25 26 CD40L/CD40 interaction occurs
`early in the sequence of signalling events
`between T cells and antigen presenting cells
`(APC). Signalling through CD40 has been
`shown to activate APC and to induce expres-
`sion of costimulatory molecules such as B7, as
`well as stimulating production of IL12.27 28
`Thus, CD40 signalling results in a stimulatory
`feedback mechanism in which the activated
`APC amplifies the T cell response.29 It has also
`been suggested that CD40L function is essen-
`
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`

`

`Immunomodulation by thalidomide and thalidomide analogues
`
`I109
`
`tial for the survival of CD8+ T cells and that in
`its absence these cells die or become anergic.30
`These studies show that in addition to its
`inhibitory eVect on the production of mono-
`cyte cytokines, thalidomide exerts a costimula-
`tory or adjuvant eVect on T cell responses. The
`immune modulating eVects of the drug in
`patients may thus be attributable to a balance
`between the inhibition of production of mono-
`including TNF♡, and the
`cyte cytokines,
`costimulation of T cell activity. The eVects of
`thalidomide in vivo in HIV infected patients
`seem to reflect the costimulatory activity of the
`drug.26 In a placebo controlled study to evalu-
`ate the eVects of in vivo immunomodulation
`with thalidomide, the drug was administered
`for
`four weeks to HIV infected patients.
`Thalidomide treatment did not aVect TNF♡
`levels in these patients. In contrast, thalidomide
`treatment
`resulted in significant
`immune
`stimulation. This was reflected by increases in
`DTH responses and increased plasma levels of
`T cell activation markers such as soluble IL2
`receptor (sIL2R) and soluble CD8 antigen. An
`earlier study of tuberculosis patients treated
`with thalidomide showed increased plasma
`levels of IFN♤ suggesting an immunostimula-
`tory eVect of the drug.12 Recently, patients suf-
`fering from sarcoidosis have shown consistent
`increases in sIL2R plasma levels after thalido-
`mide treatment (Oliver et al, manuscript in
`preparation). In the same study, thalidomide
`treatment increased the proliferation of sarcoid
`patient T cells in response to concanavalin A in
`vitro. These results
`strongly suggest
`that
`thalidomide directly stimulates T cells in vivo
`in patients, corresponding to the T cell
`costimulatory properties of the drug observed
`in vitro in T cells from normal donors,23 25 as
`well as in the T cells of HIV infected patients.26
`
`Thalidomide analogues are improved
`TNF♡ inhibitors
`In addition to being the drug of choice for the
`treatment of ENL,
`thalidomide has been
`shown to be useful in a number of clinical situ-
`ations including rheumatoid arthritis, HIV
`associated aphthous ulcers and chronic graft
`versus host disease.31–34 However, thalidomide
`is a potent teratogen and ingestion of the drug
`by a pregnant woman can lead to catastrophic
`
`birth defects.35 In addition, thalidomide treat-
`ment is often accompanied by a number of side
`eVects,
`including peripheral neuropathy.36
`Therefore, the use of thalidomide requires
`strict monitoring of all patients.37 Thus, there is
`a pressing need to develop drugs with increased
`TNF♡ inhibitory activity and reduced or
`absent toxicities. Towards this end, structural
`analogues of thalidomide have been designed
`and synthesised at Celgene Corporation (War-
`ren, New Jersey) and screened for inhibition of
`TNF♡ production. A large number of potent
`novel TNF♡ inhibitors were thus identified.
`Recently, some of
`these compounds were
`described.20 38–40 On a molar basis, the more
`potent of these thalidomide analogues were
`found to be up to 50 000-fold more potent
`than thalidomide at inhibiting TNF♡ produc-
`tion by human PBMC stimulated by LPS in
`vitro. Furthermore, we have shown that some
`of these compounds retain high activity in LPS
`stimulated human whole blood.40 In vivo,
`several of
`these new compounds
`showed
`improved activity in reducing LPS induced
`TNF♡ levels in mice17 and in inhibiting the
`development of adjuvant arthritis in rats.40a
`
`Thalidomide analogues comprise two
`distinct classes of molecules
`A group of thalidomide analogues, selected for
`their capacity to potently inhibit TNF♡ pro-
`duction by LPS stimulated PBMC, was further
`investigated (fig 1). When tested for their effect
`in vitro on LPS induced cytokines, diVerent
`patterns of cytokine modulation were shown.25
`One class of compounds, class I or ImiDs
`(Immunomodulatory Imide Drugs) showed
`not only potent inhibition of TNF♡ but also
`marked inhibition of LPS induced monocyte
`IL1♢ and IL12 production. LPS induced IL6
`was also inhibited by these drugs, albeit
`partially. These drugs were potent stimulators
`of LPS induced IL10, increasing IL10 levels by
`200–300%. In contrast, the other class of com-
`pounds, class II or SelCiDs (Selective Cytokine
`Inhibitory Drugs), while still potently inhibit-
`ing TNF♡ production, had a more modest
`inhibitory eVect on LPS induced IL1♢ and
`IL12, and did not inhibit IL6 even at high drug
`concentrations. In addition, SelCiDs produced
`a more modest IL10 stimulation (20–50%
`increases). In all of these characteristics, SelC-
`iDs were more similar to thalidomide than
`ImiDs.16 17
`the SelCiDs
`Further characterisation of
`showed that they are potent PDE4 inhibitors.39
`PDE4 is one of the major phosphodiesterase
`isoenzymes found in human myeloid and lym-
`phoid lineage cells.41 The enzyme plays a
`crucial part in regulating cellular activity by
`degrading the ubiquitous second messenger
`cAMP and maintaining it at low intracellular
`levels. Inhibition of PDE4 results in increased
`cAMP levels leading to the modulation of LPS
`induced cytokines
`including inhibition of
`TNF♡.42 Increasing intracellular cAMP levels
`have been shown to inhibit TNF♡ production
`in monocytes as well as in lymphocytes,41 43
`although it is not clear how this inhibition is
`
`SelCiDs
`
`CH3
`
`O
`
`O
`
`CH3
`
`O
`
`NH2
`
`NO
`
`CH3
`
`O
`
`O
`
`CH3
`
`O
`
`NH2
`
`O
`
`O
`
`N
`
`O
`
`N
`
`H2N
`
`Thalidomide
`
`N
`
`O
`
`OO
`
`N
`
`O
`
`O O
`
`N
`
`N
`
`O
`
`NH2
`
`N
`
`O
`
`O
`
`N
`
`O
`
`OO
`
`N
`
`O
`
`NH2
`
`IMiDs
`
`N
`
`O
`
`O O
`
`N
`H3C
`O
`
`NH2
`
`O
`Figure 1 Chemical structures of thalidomide and selected thalidomide analogues.
`
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`

`

`I110
`
`Corral, Kaplan
`
`regulated. Interestingly, the IMiDs and tha-
`lidomide were found not to inhibit PDE4.40
`In addition to the diVerential modulation of
`LPS induced monocyte cytokines, the two
`classes of compounds showed distinct eVects
`on T cell activation. SelCiDs,
`the PDE4
`inhibitors, had little eVect on T cell activation
`causing only a slight inhibition of T cell prolif-
`eration. This eVect was not unexpected as it is
`well established that increasing cAMP levels in
`T cells during the early phase of mitogen or
`antigen activation results in a decrease in
`proliferative potential.44 On the other hand,
`IMiDs, the non-PDE4 inhibitors, were potent
`costimulators of T cells and increased cell pro-
`liferation dramatically in a dose dependent
`manner.25 Similarly to thalidomide, these com-
`pounds had a greater costimulatory eVect on
`the CD8+ T cell subset than on the CD4+ T
`cell subset (Corral et al, unpublished observa-
`tion). IMiDs, when added to anti-CD3 stimu-
`lated T cells, also caused marked increases in
`the secretion of IL2 and IFN♤ and induced the
`up-regulation of CD40L expression on T
`cells.25 These findings show that in addition to
`their
`strong anti-inflammatory properties,
`IMiDs eYciently costimulate T cells with 100
`to 1000 times the potency of the parent drug.
`The molecular target of these co-stimulatory
`cytokine modulating drugs is as yet unknown.
`
`Thalidomide and IMiDs modulate
`cytokines diVerently according to cell
`type and stimulation pathway
`As described above, thalidomide has been
`shown to inhibit IL12 production by LPS
`stimulated monocytes in vitro.25 45 In vivo,
`however,
`thalidomide
`treatment of HIV
`infected26 and M tuberculosis infected patients
`induced increases
`in plasma IL12 levels
`(Bekker et al, submitted data). Thalidomide
`treatment also resulted in increases in plasma
`IL12 levels in patients with scleroderma and
`sarcoidosis (Oliver et al, manuscripts in prepa-
`ration). These dual and opposite eVects of tha-
`lidomide may be explained by the diVerential
`modulation of cytokines according to target
`cell
`type and specific pathways of cellular
`stimulation.
`IL12 is produced primarily by APC
`(monocytes/macrophages and dendritic cells)
`and is regulated by both T cell dependent and
`T cell
`independent pathways. LPS directly
`induces T cell independent IL12 production
`by APC, which is inhibited by thalidomide. In
`the T cell dependent pathway, on the other
`hand, the production of IL12 by the APC is
`
`induced primarily by the interaction of CD40
`on the surface of the APC with CD40L on the
`surface of activated T cells.28 46 When T cells
`were stimulated by anti-CD3, thalidomide and
`IMiDs treatment caused a significant stimula-
`tion of IL12 production.25 Thalidomide and
`IMiDs also induced an up-regulation of
`CD40L on the surface of T cells.25 26 Blockade
`of this pathway inhibits the production of IL12
`and abolishes
`the
`stimulatory
`eVect of
`thalidomide.26 Interestingly, in HIV infected
`patients, the consistent increases in plasma
`IL12 levels induced by thalidomide treatment
`lagged behind the increases in T cell activation
`markers.26 This observation suggested that
`IL12 production was augmented as a conse-
`quence of drug induced T cell activation.
`The dichotomous nature of
`thalidomide
`cytokine modulation may explain the seem-
`ingly opposite eVects observed in diVerent
`clinical situations. When patients with Behçet’s
`syndrome are treated with thalidomide, healing
`of inflammatory aphthous ulcers occurs, but is
`sometimes accompanied by exacerbation of
`erythema nodosum.47 Similarly, the paradoxi-
`cal worsening of graft versus host disease48 and
`toxic epidermal necrolysis49 reported in clinical
`trials of thalidomide may be a manifestation of
`the unsuspected immune stimulatory eVect of
`this drug.
`
`Potential clinical applications of
`thalidomide and thalidomide analogues
`The thalidomide analogues discussed here
`seem to have retained diVerent properties of
`the parent drug (table 1). The distinct
`immunomodulatory activities of
`these two
`classes of drugs suggest they may have applica-
`tions in diVerent immunopathological disor-
`ders. SelCiDs, which inhibit PDE4, may be
`used in clinical situations in which PDE4 inhi-
`bition and selective TNF♡ inhibition are
`beneficial. Therapeutic increase of intracellular
`cAMP levels by PDE4 inhibitors has anti-
`inflammatory eVects, which may aVord conse-
`quent benefits in a variety of diseases such as
`asthma,50 atopic dermatitis51 and rheumatoid
`arthritis.52 Indeed, in an animal model of adju-
`vant arthritis,
`thalidomide derived PDE4
`inhibitors have shown eYcacy in suppressing
`the development of disease as measured by
`ankle swelling, hind limb radiographic changes
`and weight gain.40a The suppression of arthritis
`was accompanied by a reduction in TNF♡ and
`IL2 mRNA levels in the ankle joints of treated
`rats.
`
`Table 1 Immunomodulatory profiles of thalidomide and thalidomide analogues
`
`Thalidomide
`
`IMiDs
`
`SelCIDs
`
`Inhibits LPS induced inflammatory
`cytokines TNF♡ and IL12
`
`Strongly inhibit LPS induced inflammatory
`cytokines: TNF♡, IL1♢, IL6 and IL12
`
`Strongly inhibit LPS induced
`inflammatory cytokines TNF♡ and IL12
`
`Stimulates LPS induced
`anti-inflammatory cytokine IL10
`
`Strongly stimulate LPS induced
`anti-inflammatory cytokine IL10
`
`Stimulate LPS induced
`anti-inflammatory cytokine IL10
`
`Costimulates T cell activation
`
`Strongly costimulate T cell activation
`
`Inhibit or have no eVect on T cell
`activation
`
`Does not inhibit PDE4
`
`Do not inhibit PDE4
`
`Strongly inhibit PDE4
`
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`
`

`

`Immunomodulation by thalidomide and thalidomide analogues
`
`I111
`
`Other known selective PDE4 inhibitors,
`such as rolipram, have been reported to have
`dose limiting side eVects, such as nausea and
`vomiting, which limit the therapeutic use of
`these drugs.53 54 These side eVects may be pro-
`duced by the lack of specificity of
`these
`drugs—that is, the compounds inhibit one or
`more PDE isoenzymes in non-target tissues.
`For example, it is probable that the emetic
`activity of PDE4 inhibitors is attributable to an
`action of the drugs in the CNS.55 Intensive
`eVort is being directed towards identifying
`compounds with improved therapeutic ratios.
`Preliminary results with thalidomide derived
`PDE inhibitors indicate that these novel drugs
`are selective inhibitors of PDE4 and may be
`better tolerated than other PDE4 inhibitors, as
`they have not shown evidence of emesis in ani-
`mals. One of these drugs has been recently
`shown to be well tolerated in a small human
`safety trial in the United Kingdom (D Stirling,
`personal communication).
`The IMiDs, as
`thalidomide, are anti-
`inflammatory drugs that do not target PDE4.
`These compounds, in addition to their poten-
`tial use to decrease inflammation, could also be
`useful in clinical settings where there is a defect
`in T cell function, as in HIV disease. HIV
`infection is accompanied by deficiencies in the
`production of IL12 and in the up-regulation of
`CD40L.56 57 IL12 has been shown to restore
`HIV specific cell mediated immunity in vitro58
`and to increase HIV specific CTL responses in
`vitro59 and in vivo.60 Also, deficient
`IL12
`responses in HIV infected patients can be
`restored in vitro by CD40L and IFN♤,61 the
`same costimulatory factors induced by thalido-
`mide and IMiDs. Thus, these drugs may even-
`tually be used to restore or stimulate IL12 pro-
`duction in immune deficient patients.
`IL12 has also been shown to exhibit potent
`anti-tumour activity in murine tumour models
`through various mechanisms
`including the
`stimulation of natural killer cell activity,62 activa-
`tion of CD8+ cytotoxic T cells63 and increased
`IFN♤ mediated anti-angiogenesis.64 Thalido-
`mide has also recently been reported to exhibit
`anti-tumour activity through the inhibition of
`angiogenesis in vivo.65–68 However, this anti-
`angiogenic eVect does not seem to be mediated
`by TNF♡ inhibition. Although these studies did
`not determine the mechanism of thalidomide’s
`anti-angiogenic activity, it is conceivable that
`stimulation of IFN♤/IL12 levels may be at least
`partly responsible. One report indicates that
`thalidomide may have anti-angiogenic activity in
`multiple myeloma in humans.69
`In summary, our recent findings that thalido-
`mide and IMiDs preferentially costimulate
`CD8+ T cells and induce T cell dependent
`IL12 production suggest possible applications
`of
`these drugs
`in the
`control of viral
`infections70 71 or
`in boosting anti-tumour
`immunity.72 73 Also, there are anecdotal reports
`of the eYcacy of thalidomide in treating refrac-
`tory inflammatory bowel disease.74–76 Recently,
`preliminary findings were announced from a
`pilot study with patients with Crohn’s disease
`refractory to standard treatments (Annual
`Digestive Disease Meeting, May 1999, Or-
`
`lando, FL). In this study, two third of the
`patients experienced a significant improvement
`in their condition. This therapeutic eVect may
`be a combination of TNF♡ inhibition and
`CD8+ T cell stimulation.77 78
`
`Conclusions
`In several disease conditions such as septic
`shock, chronic infections and cancer, overpro-
`duction of TNF♡ is accompanied by severe
`toxicities. Thalidomide inhibits TNF♡ produc-
`tion in diVerent diseases without causing the
`immunosuppression often associated with
`standard agents such as glucocorticoids and
`cyclosporin A. Our results indicate that the
`immunomodulating eVects of thalidomide may
`occur via the inhibition of TNF♡ production
`and/or the stimulation of T cell responses,
`without the suppression of host immunity.
`Recent eVorts have concentrated on develop-
`ing TNF♡ inhibitors that are eYcient, safe and
`specific. The collaboration between Rockefeller
`University and Celgene Corporation scientists
`has led to the discovery of two diVerent classes
`of immunomodulators derived from thalido-
`mide and selected for their potent anti-TNF♡
`inhibitory activity. Preliminary results indicate
`that at least some of these new compounds are
`non-toxic and non-teratogenic.20 The two
`classes of thalidomide analogues, however, pos-
`sess distinct properties.
`IMiDs are potent
`inhibitors of monocyte inflammatory cytokine
`production and also are strong costimulators of
`T cell activity. SelCiDs, on the other hand, are
`potent PDE4 inhibitors and thus, more selective
`inhibitors of TNF♡. Unlike IMiDs,
`these
`compounds do not costimulate T cells but
`inhibit T cell activity. Thus, the two classes of
`compounds may prove to be useful in diVerent
`clinical
`settings according to their
`immu-
`nomodulatory properties. The thalidomide ana-
`logues are being used as investigational tools in
`animal disease models to define mechanisms of
`pathogenesis and to continue to elucidate the
`mechanisms of drug action.
`
`We thank Dr Victoria Freedman and Dr George Muller for
`helpful and patient review of this manuscript, Marguerite Nulty
`for typing the manuscript and Dr Patrick Haslett for critical dis-
`cussions during the preparation of this report.
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