Combination of monoclonal antibodies and DPP-IV inhibitors
in the treatment of type 1diabetes:A plausible treatment
modality?
Anil Dubala a ,?,Ankur Gupta b ,Malay K.Samanta a
a Department of Pharmaceutical Biotechnology,JSS College of Pharmacy,Ooty 643001,Tamilnadu,India b
Department of Pharmaceutical Analysis,Himalayan Pharmacy Institute,Majhitar,E.Sikkim,India
a r t i c l e i n f o Article history:
Received 30October 2013Accepted 14April 2014
a b s t r a c t
Regulatory T cells (Tregs)are crucial for the maintenance of immunological tolerance.Type 1diabetes (T1D)occurs when the immune-regulatory mechanism fails.In fact,T1D is reversed by islet transplanta-tion but is associated with hostile effects of persistent immune suppression.T1D is believed to be depen-dent on the activation of type-1helper T (Th1)cells.Immune tolerance is liable for the activation of the Th1cells.The important role of Th1cells in pathology of T1D entails the depletion of CD4+T cells,which initiated the use of monoclonal antibodies (mAbs)against CD4+T cells to interfere with induction of T1D.Prevention of autoimmunity is not only a step forward for the treatment of T1D,but could also restore the b -cell mass.Glucagon-like peptide (GLP)-1stimulates b -cell proliferation and also has anti-apoptotic effects on them.However,the potential use of GLP-1as a possible method to restore pancreatic b -cells is limited due to rapid degradation by dipeptidyl peptidase (DPP)-IV.We hypothesize that treatment with combination of CD4mAbs and DPP-IV inhibitors could prevent/reverse T1D.CD4mAbs have the ability to induce immune tolerance,thereby arresting further progression of T1D;DPP-IV inhibitors have the capa-bility to regenerate the b -cell mass.Consequently,the combination of CD4mAbs and DPP-IV inhibitor could avoid or at least minimize the constraints of intensive subcutaneous insulin therapy.We presume that if this hypothesis proves correct,it may become one of the plausible therapeutic options for T1D.
ó2014Elsevier Ltd.All rights reserved.
Introduction
T cells originate from hematopoietic stem cells in the bone mar-row.The development of a T cell is shaped through positive and negative selection [1].Low af?nity interactions with self-antigens present on major histocompatibility complex (MHC)peptides pro-voke positive selection,whereas high af?nity interactions provoke negative selection.T cells that strongly interact with the self-antigen are deleted by negative selection through apoptotic signals in the thymus,which is a major mechanism of central tolerance.T lymphocytes,include specialized subsets of regulatory T cells (Tregs)that are crucial for the maintenance of immunological tolerance [2].Their major role is to shut down T cell-mediated immunity towards the end of an immune reaction and suppress auto-reactive T cells that escaped the process of negative selection in the thymus.Destruction of b -cells via autoimmune processes occur,when immune-regulatory mechanism fails,allowing auto reactive T cell clones to in?ltrate the pancreas,thereby selectively destroying the b -cells in the islets of Langerhans [3,4].
In general,Type 1diabetes (T1D)develops in the young popula-tion.Restoration of insulin secretion and normalization of glucose levels are essential to lead a healthy life.Exogenous administration of insulin is quintessential and a widely used treatment for T1D.Though the discovery of insulin transformed T1D treatment,it made this a fatal and devitalizing disease.Exogenous administra-tion of insulin in the instance of T1D is passive in nature that does not deal with the cause of the disease.Successful results using insulin therapy remains inadequate.
In fact,T1D is reversed by islet transplantation;nevertheless,it is associated with the surgical morbidity and hostile effects of per-sistent immune suppression [5].The body often destroys trans-planted islet cells owing to MHC of host identifying the graft tissue as foreign antigens and attacking them.Ergo,the main chal-lenge in a successful transplantation is to ?nd tissue types as sim-ilar as possible for both host and donor.However,availability of human islets from cadaveric pancreata is meager and dearth of islet source resulted in the quest for methods of generation of islet cells in vitro and in vivo .
The discovery of antibodies has had an enormous impact on the ?eld of immunology.In recent years,mainstream research has been focused on the pathological signi?cance of immune tolerance in T1D.Monoclonal antibodies (mAbs)are a breakthrough for
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0306-9877/ó2014Elsevier Ltd.All rights reserved.
?Corresponding author:Tel.:+919677448929.
E-mail address:anildubala@https://www.doczj.com/doc/059012976.html, (A.Dubala).
immune based therapies.They could induce tolerance/protective immunity either by targeting the regulatory immune responses or eliminating antigen reactive clones,which can avert autoim-mune diabetes.
Prevention of autoimmunity is not only a step forward for the treatment of T1D but could also restore b-cell mass.Glucagon-like peptide(GLP)-1is produced from intestinal L cells and has been shown to stimulate b-cell proliferation,neogenesis,and also has anti-apoptotic effects on b-cells[6,7].However,the potential use of GLP-1as a possible method to regenerate pancreatic b-cells is limited due to its rapid degradation by dipeptidyl peptidase (DPP)-IV[8].To conquer this,GLP-1agonists and DPP-IV inhibitors have been investigated for the treatment of diabetes[9]. Discussion
Normally,a balance exists between type1helper T(Th1)cells that selectively interfere with lymphocyte activation,namely anti-T cell antibodies,which can induce/restore self tolerance to well de?ned b-cell antigens enmeshed as prospective targets is at the focal point of research in T1D.
In T1D,antigen-speci?c immunotherapy is an enviable intent that induces immune tolerance.The primary auto-antigen that is very likely to initiate T1D is insulin peptide B:9–23.Peptide therapy i.e.,a peptide vaccine utilizing B:9–23or a derivative of B:9–23,came into view as an interesting approach for the treat-ment of autoimmune diabetes[15].Studies had shown that immu-nization with insulin peptide B:9–23alone may be insuf?cient to reverse disease or induce long-term tolerance;however,it requires combination with an appropriate immune modulator that can enhance Treg function[16,17].The majority of pathogenic CD4+T cells recognize insulin B:9–23peptide-MHC-II complex only when the insulin peptide is bound in register3(R3)[18].Intervention with mAb287blocks binding of IAg7-B:10–23R3tetramers associ-ated with T cells and inhibits T-cell responses to soluble B:9–23
strategy of our hypotheses,Schematic representation of(a)pancreatic b-cells autoimmune destruction.The CD4+T cells secrete may activate b-cell speci?c pre-cytotoxic T cells(CD8+T cell)to differentiate into effector T cells.IFN-c released by CD4
substantial amounts of b-cell cytotoxic cytokines.Cytokines and granzymes/perforin,which are toxic to b-cells released from
induce the destruction of pancreatic b-cells.Oxygen free radicals secreted from activated macrophages can also kill b-cells, entailed depletion of CD4+T cells,which initiated the use of CD4mAbs against CD4+T cells that interfere with induction of T1D,and GLP-1half-life which in turn may augment the b-cells mass through cAMP/PK-A/CREB pathway.
2 A.Dubala et al./Medical Hypotheses83(2014)1–5
combined effect,that is decrease in effector CD4and/or CD8T cells and induction of Tregs[20].Pescovitz and colleagues carried out a double blind study involved87newly diagnosed T1D patients,ran-domly allocated to receive four infusions of anti-CD20mAb(ritux-imab)or placebo on days1,8,15,and22.The results demonstrated the partial preservation of b-cell function over a period of1year in patients with T1D[21].As the effects of B cell depletion on disease associated T cell responses were not known,efforts were initiated to minimize this ambiguity.Herold et al.[22]compared T cell subset distributions and auto-reactivity pro?les in rituximab recip-ients that had positive C-peptide responses with those unrespon-sive to treatment from the rituximab trial(NCT00279305)[21].B cell depletion with rituximab impacted with an increase in proliferative cellular immune responses to diabetes antigens and attenuated b-cell loss[22].The mechanism underlying this effect is not clear,owing to the fact that eventually disease and disease progression are T cell dependent[22].
Shimizu et al.[23]revealed that both CD4+and CD8+T cells are of vital importance in the development of T1D.CD3is a part of the T cell receptor(TCR),thus it can be found on every T cell.Strategies were postulated by using treatment with monoclonal antibodies to CD3that interfere with pathogenic T-cell activation in T1D.Pre-clinical studies of CD3mAbs in NOD corroborated that they were effective and induced transient depletion,especially when Fc receptor nonbinding CD3antibodies were used(i.e.,in mouse, F[ab]2fragments or IgG3CD3antibodies,and in patients,human-ized Fc-mutated CD3antibodies)[24–29].CD3mAbs act on both pathogenic T cells and Tregs.The distinct effect of CD3mAbs cause unresponsiveness or predominantly kills the Th1cells,whereas Th2cells may be stimulated by them[30].In addition,CD3mAbs induce a population of Tregs that can prevent or lead to reversal of T1D[31,32].Belghith et al.[33]made efforts to understand the mechanism of CD3epsilon-speci?c antibodies involved in the supremacy of Tregs in NOD Cd28à/àmice.There are two main subgroups of CD4+CD25+Tregs:thymus-derived,naturally occur-ring CD4+CD25+Tregs and peripherally induced CD4+CD25+Foxp3+ Tregs[34].CD3mAbs instigate TGF-b activation,thereby inducing CD4+CD25+Foxp3+Tregs,which regain their functional capacity to regulate in?ammatory responses against destructive autoimmu-nity in T1D[33].Findings from previous studies elicit that CD4+CD25high Tregs act in a cytokine independent manner,there-fore suggesting another type of Treg being operational in the set-ting up of immune regulation[35].A subset of FoxP3+cells present within a CD4+CD25low lymphocyte subset suppressed T cell immunity in spontaneously diabetic NOD mice in a TGF-b-dependent manner.This distinct Treg subset was evident in NOD, but not normal mice,suggesting that NOD mice may generate these adaptive Tregs in an attempt to regulate ongoing autoimmu-nity[35].This result has led to clinical trials with humanized Fc-mutated anti-CD3mAbs in humans that interfere with patho-genic T-cell activation.The outcome of this study yielded favorable clinical effects,such as reduced insulin intake,and decline of C-peptide levels[29,36–38],which was further supported by recent clinical studies[39–42].
De?ciency in Tregs is a critical determinant of diabetes suscep-tibility[43].D’Alise et al.[44]reported the lack of a primary de?cit in Treg numbers in NOD mice,whether in prediabetic animals of any age or in those with recent-onset diabetes.The functional inef-?cacy in T1D was not rooted with NOD Tregs suppression but with effector conventional Th cells.Treg cell activation is antigen-spe-ci?c,which implies that suppressive activities of Treg cells are anti-gen-dependent[45].To substantiate this,D’Alise et al.executed a study in which conventional Th cells,rather than Tregs,responded more effectively to anti-CD3/28mAb stimulation in vitro or to a natural pancreatic antigen in vivo.This difference was independent of autoimmune in?ammation,did not map to the idd3region,and was not due to the overproduction of IL-21in NOD mice.Thus,the immune dysregulation in this T1D model was entrenched in the ability of effector T cells to be regulated[44].
The important role of conventional Th cells,particularly Th1 cells,in pathology of T1D entailed depletion of CD4+T cells,which initiated the use of depleting CD4mAbs against CD4+T cells,that interfere with induction of T1D(Fig.1b).Bulk elimination of T cells including Tregs involved in immune regulation,may subsequently result in immune suppression.In addition,depletion of target cells may not be essential in CD4mAb mediated immune regulation [46,47].Assessing this,Qin et al.and Hutchings et https://www.doczj.com/doc/059012976.html,ed non-depleting mAbs contrary to CD4mAbs,and reported that a short course of non-depleting mAbs enabled a rapid response on pro?-cient cells involved in autoimmune destruction of b-cells[46,47]. Adding to it,non-depleting CD4mAbs could alleviate the risk of immune suppression by interrupting the elimination of Tregs.
The ultimate goal of therapeutic intervention is to not only shut down the autoimmune responses hostile to b-cells,but also to enable the restoration of endogenous insulin secretion and nor-malization of glucose levels.Thus,?nding means to restore b-cell mass,by initiating their replication or regeneration from precursor cells is a major goal of current research.
It is a widely known fact that glucoincretin hormone GLP-1can act as a growth and differentiation factor for mature b-cells and their precursors[6–9].GLP-1receptor stimulation leads to the acti-vation of adenylate cyclase with the help of G-proteins.Activated adenylate cyclase forms cAMP,which in turn activates protein kinase(PK)-A and eventually translocates to the nucleus through the nucleus pore.These activated PK-A,phosphorylate the cAMP response element binding(CREB)protein.Phosphorylated CREB binds to a cAMP response element region(CRE),subsequently binding to CREB-binding protein(CBP),thereby coactivating it and allowing it to express various genes and proteins.Embracing this mechanism in the current content may pave the way to achieve the therapeutic goal of restoring functional b-cells through the mitogenic action of GLP-1on the b-cell[6].
Despite,GLP-1being a feasible avenue to regenerate pancre-atic b-cells,DPP-IV invariably breaks it down.Previous reports suggest that a sustained treatment of exogenously administered GLP-1is required to in?uence b-cell regulation[8].DPP-IV inhibi-tion has come into view as an interesting preventive therapeutic approach.As the correlation between DPP-IV inhibition and b-cell neogenesis is well established[48],this effect is believed to be predominantly as a result of longevity of the incretin hormones including GLP-1and glucose-dependent insulinotropic polypeptide (GIP)(Fig.1c).Till date,a majority of studies performed on ani-mal models sought to reveal the role of DPP-IV inhibitors in the treatment of T1D[48,49].Results from these studies corroborate that inhibition of DPP-IV may ameliorate the b-cell mass and improve functional aftermath.Ellis et al.[50]for the?rst time evaluated the clinical ef?cacy of sitagliptin on glucose control and variability in adult patients with T1D.Sitagliptin signi?cantly improved overall glucose control including postprandial and24h glucose control,while signi?cantly reducing prandial insulin requirements in adult patients with T1D.These?ndings suggest that therapeutic potential of DPP-IV inhibitors may extend beyond glycemic control to include augmentation of b-cell mass and function.In addition,Kim et al.[51]studied the effects of sitagliptin(a DPP-IV inhibitor)on CD4+T cell migration in NOD mice as DPP-IV increases migration of splenic CD4+T cells via a pathway involving cAMP/PK-A/Ras-related C3botulinum toxin substrate1(Rac1)GTP binding activity.Results portrayed the inhibitory potential of sitagliptin towards the migration of splenic CD4+T cells.
A.Dubala et al./Medical Hypotheses83(2014)1–53
Hypothesis
Treatment with CD4mAbs conjugated sitagliptin-loaded poly-meric nanoparticulate drug delivery system,thereby selective depletion of CD4+T cells and restoration of the b-cell mass would be a new therapeutic approach for the correction of T1D. Implications of the hypothesis
Our hypothesis reinforced the certainty that T1D results from the autoimmune destruction of the b-cells by auto reactive T cells [1–4].Sherry et al.[52]divulged the ef?cacy of exendin-4in com-bination with CD3mAbs in NOD mice,which showed improved b-cell mass,and subsequent increase in insulin secretion.Earlier reports recommended the use of CD4mAbs as ef?cacious and less toxic immunosuppressive agents than CD3mAbs[5].Extension of the GLP-1half-life using long acting GLP-1analogues would be insuf?cient to regenerate b-cells for the control of T1D,unless these compounds are administered multiple times over each day. Polymeric nanoparticles have recently attracted great attention as potential drug delivery systems in view of their applications in the sustained release of drugs.Due to their nano size,the particles penetrate into small capillaries and are taken up within cells, allowing an ef?cient drug accumulation at the targeted sites in the body.The use of biodegradable materials for nanoparticles preparation allows sustained drug release at the targeted site over a period of days or even weeks[53].Hence,our investigation aspires to determine if extending the shelf life of GLP-1through sitagliptin loaded polymeric nanoparticles would regenerate pancreatic b-cells.In addition to this,CD4mAbs conjugated to sitagliptin loaded polymeric nanoparticles could provide better results,the reason being that CD4+T cells play a central role in T1D.CD4mAbs selectively deplete CD4+T cells,and at some extent sitagliptin has selective effects on subpopulation of T-cells that are involved in the autoimmunity[51].
In conclusion,CD4mAbs could arrest the autoimmunity in T1D and sitagliptin loaded polymeric nanoparticles could regenerate pancreatic b-cells.Altogether,antibody-drug conjugates could avoid or at least minimize the constraints of intensive subcutane-ous insulin therapy.Thus,consequential strategy of our hypothesis may be an ef?cacious approach for the treatment of T1D.The design of our hypothesis includes the development of CD4mAbs conjugated sitagliptin loaded polymeric nanoparticulate drug delivery system and evaluation of its ef?ciency in vivo;the feasibil-ity of our hypothesis is encompassed in this.
Con?ict of interest
None declared.
Acknowledgements
We thank Santhivardhan Chinni and Shashank M.for their assistance in manuscript preparation.The present hypothesis is supported by the DBT-NE(File No.:BT/521/NE/TBP/2013)Grant to M.K.S.
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