Biomedical subjects

Robert I Lechler

Publications and source records attributed to Robert I Lechler.

At least 19 recordsLinked to original sources

PubMed2007

Physiologic and aberrant regulation of memory T-cell trafficking by the costimulatory molecule CD28.

Productive T-cell immunity requires both the activation and the migration of specific T cells to the antigenic tissue. The costimulatory molecule CD28 plays an essential role in the initiation of T-cell-mediated immunity. We investigated the possibility that CD28 may also regulate migration of primed T cells to target tissue. In vitro, CD28-mediated signals enhanced T-cell transendothelial migration, integrin clustering, and integrin-mediated migration. In vivo, T cells bearing a mutation in the CD28 cytoplasmic domain, which abrogates PI3K activation, displayed normal clonal expansion but defective localization to antigenic sites following antigenic rechallenge. Importantly, antibody-mediated CD28 stimulation led to unregulated memory T-cell migration to extra-lymphoid tissue, which occurred independently of T-cell receptor (TCR)-derived signals and homing-receptor expression. Finally, we provide evidence that CD28- and CTLA-4-mediated signals exert opposite effects on T-cell trafficking in vivo. These findings highlight a novel physiologic function of CD28 that has crucial implications for the therapeutic manipulation of this and other costimulatory molecules.

Amino Acid Substitution↗

PubMed2007

From current immunosuppressive strategies to clinical tolerance of allografts.

In order to prevent allograft rejection, most current immunosuppressive drugs nonspecifically target T-cell activation, clonal expansion or differentiation into effector cells. Experimental models have shown that it is possible to exploit the central and peripheral mechanisms that normally maintain immune homeostasis and tolerance to self-antigens, in order to induce tolerance to alloantigens. Central tolerance results from intrathymic deletion of T cells with high avidity for thymically expressed antigens. Peripheral tolerance to nonself-molecules can be achieved by various mechanisms including deletion of activated/effector T cells, anergy induction and active regulation of effector T cells. In this article, we briefly discuss the pathways of allorecognition and their relevance to current immunosuppressive strategies and to the induction of transplantation tolerance (through haematopoietic mixed chimerism, depleting protocols, costimulatory blockade and regulatory T cells). We then review the prospect of clinical applicability of these protocols in solid organ transplantation.

Humans↗

PubMed2006

Generation and expansion of human CD4+ CD25+ regulatory T cells with indirect allospecificity: Potential reagents to promote donor-specific transplantation tolerance.

BACKGROUND: Harnessing naturally arising CD4+ CD25+ regulatory T cells (Tregs) for potential adoptive cell therapy is hampered by their innate autoreactivity and their limited number. METHODS: CD4+ CD25+ Tregs were purified from peripheral blood of human leukocyte antigen (HLA) DR1*0101+ A2- individuals, and stimulated with autologous monocyte-derived dendritic cells (DCs). RESULTS: Here we show that CD4+ CD25+ Tregs specific for an HLA A2 (103-120) peptide can be selected from the peripheral blood CD4+ CD25+ T cell population of a healthy individual and detected using a tetramer comprised of HLA DRB1*0101 and the A2 peptide. The selected cells can be expanded substantially (i.e., a 1600-fold increase over a two-week period) by T-cell receptor (TCR) stimulation and high-doses of interleukin-2 (IL-2). The CD4+ CD25+Tregs with indirect allospecificity for the A2 peptide showed more potent antigen-specific suppression than polyclonal CD4+ CD25+ Tregs. CONCLUSIONS: These data may pave the way for clinical studies using CD4+ CD25+ Tregs with indirect allospecificity as therapeutic reagents for the induction of donor-specific transplantation tolerance.

Animals↗

PubMed2006

Galectin-1: a key effector of regulation mediated by CD4+CD25+ T cells.

The naturally occurring population of dedicated regulatory T cells that coexpress CD4 and CD25 is known to play a key role in the maintenance of peripheral T-cell tolerance; however, their mechanism of action has remained obscure. Here we report that a member of the family of beta-galactoside-binding proteins, galectin-1, is overexpressed in regulatory T cells, and that expression is increased after activation. Most importantly, blockade of galectin-1 binding significantly reduced the inhibitory effects of human and mouse CD4+CD25+ T cells. Reduced regulatory activity was observed in CD4+CD25+ T cells obtained from galectin-1-homozygous null mutant mice. These results suggest that galectin-1 is a key effector of the regulation mediated by these cells.

Animals↗

PubMed2006

Chronic exposure to Helicobacter pylori impairs dendritic cell function and inhibits Th1 development.

Helicobacter pylori causes chronic gastric infection that affects the majority of the world's population. Despite generating an inflammatory response, the immune system usually fails to clear the infection. Since dendritic cells (DCs) play a pivotal role in shaping the immune response, we investigated the effects of H. pylori on DC function. We have demonstrated that H. pylori increased the expression of activation markers on DCs while upregulating the inhibitory B7 family molecule, PD-L1. Functionally, H. pylori-treated DCs resulted in the production of interleukin-10 (IL-10) and IL-23 but not of alpha interferon (IFN-alpha). While very little or no IL-12 was produced to H. pylori alone, simultaneous ligation of CD40 on DCs induced IL-12 release. We also demonstrated that DCs treated with H. pylori-induced IFN-gamma production by allogeneic naive T cells. However, stimulation of DCs with H. pylori for an extended period of time impaired their ability to produce cytokines after CD40 ligation and limited their ability to promote IFN-gamma release, suggesting that the DCs had become exhausted by the prolonged stimulation. The effect of chronic infection with H. pylori on DC function was further investigated by focusing on DC development. Demonstrating that monocytes differentiated into DCs in the presence of H. pylori exhibited an exhausted phenotype with an impaired ability to produce IL-12 and a downregulation of CD1a. Our results raise the possibility that in chronic H. pylori infection DCs become exhausted after prolonged antigen exposure leading to suboptimal Th1 development. This effect may contribute to persistence of H. pylori infection.

Antigens, CD↗

PubMed2006

In vitro-expanded donor alloantigen-specific CD4+CD25+ regulatory T cells promote experimental transplantation tolerance.

CD4+CD25+ regulatory T (Treg) cells play a critical role in the induction and maintenance of peripheral immune tolerance. In experimental transplantation models in which tolerance was induced, donor-specific Treg cells could be identified that were capable of transferring the tolerant state to naive animals. Furthermore, these cells appeared to have indirect allospecificity for donor antigens. Here we show that in vivo alloresponses can be regulated by donor alloantigen-specific Treg cells selected and expanded in vitro. Using autologous dendritic cells pulsed with an allopeptide from H2-Kb, we generated and expanded T-cell lines from purified Treg cells of CBA mice (H2k). Compared with fresh Treg cells, the cell lines maintained their characteristic phenotype, suppressive function, and homing capacities in vivo. When cotransferred with naive CD4+CD25- effector T cells after thymectomy and T-cell depletion in CBA mice that received CBK (H2k+Kb) skin grafts, the expanded Treg cells preferentially accumulated in the graft-draining lymph nodes and within the graft while preventing CBK but not third-party B10.A (H2k+Dd) skin graft rejection. In wild-type CBA, these donor-specific Treg cells significantly delayed CBK skin graft rejection without any other immunosuppression. Taken together, these data suggest that in vitro-generated tailored Treg cells could be considered a therapeutic tool to promote donor-specific transplant tolerance.

Animals↗

PubMed2006

In-vitro generation and characterisation of murine CD4+CD25+ regulatory T cells with indirect allospecificity.

Naturally arising CD4(+)CD25(+) regulatory T cells play a pivotal role in the prevention of autoimmunity and in the induction of donor-specific transplantation tolerance. Harnessing regulatory cells for potential adoptive cell therapy is hampered by their lack of antigen-specificity and their limited numbers. Here we describe the generation and expansion of murine CD4(+)CD25(+) T cells with antigen-specificity for an K(d) peptide as potential reagents for adoptive cell therapy in promoting donor-specific transplantation tolerance. Using bone marrow-derived autologous dendritic cells pulsed with the K(d) peptide, we generated T cell lines from purified CD4(+)CD25(+) T cells from C56BL/6 mice. The T cell lines expressed high level of CD25 and low level of CD45RB and CD69. They maintained the expression of CD62L, GITR, CTLA-4 and more importantly FoxP3. The CD4(+)CD25(+) T cell lines were anergic after TCR stimulation and produced little cytokine such as IL-2 and IFN-gamma. Importantly, they were more potent than freshly isolated CD4(+)CD25(+) T cells in suppressing proliferation and cytokine secretion by effector CD4(+) T cells. Furthermore, the CD4(+)CD25(+) T cell lines could be expanded to large cell numbers and maintained in culture up to 1 year. The K(d)-specific CD4(+)CD25(+) T cell lines will be invaluable in devising a strategy for the induction of cardiac transplantation tolerance in wild-type B6 mice carrying a full mismatch BALB/c heart.

Animals↗

PubMed2006

Knockdown of mouse VCAM-1 by vector-based siRNA.

Graft rejection is critically dependent on the recruitment of leukocytes via adhesion molecules on the endothelium, and inhibition of these interactions can prolong graft survival. We have therefore developed an approach using siRNA to inhibit the expression of VCAM-1 in endothelial cells. We transfected siRNA constructs into murine corneal and vascular endothelium and looked at expression of VCAM-1 and other surface molecules by flow cytometry. Adhesion assays (both static and under flow) were used to determine the effect of VCAM-1 inhibition. The activation of cellular stress responses was assessed by RT-PCR. Constructs encoding siRNA can block expression of VCAM-1 in both corneal and vascular endothelial cells (in the latter case after cytokine stimulation). Inhibition of VCAM-1 expression reduced the ability of T cells to adhere to endothelium. However, there were non-specific effects of siRNA expression, including upregulation of (Programmed Death Ligand 1) PDL1 and decreased cell growth. Analysis of stress pathways showed that the endothelial cells transfected with siRNA had upregulated molecules associated with cell stress. While these data are supportive of a potential therapeutic role for siRNA constructs in blocking the expression of adhesion molecules, they also highlight potential non-specific effects of siRNA that must be carefully considered in any application of this technology.

Animals↗

PubMed2006

Regulatory T cells and transplantation tolerance.

In the past decade, several types of regulatory T cells (Tregs) have been identified to play a pivotal role in the control of autoimmunity and transplantation tolerance in rodents and in human beings, including innate regulatory NKT cells and gammadelta T cells, naturally occurring FoxP3 expressing CD4(+)CD25(+) T cells, and in-vitro induced Tregs including interleuking-10 (IL-10)-secreting Tr1 CD4(+) T cells, TGF-beta-producing Th3 CD4(+) T cells, anergic CD4(+) T cells, CD8(+)CD28(-) and CD3(+)CD4(-)CD8(-) T cells. Recent studies have shown that innate and adaptive Tregs may be linked and act in concert to mediate immunosuppression. As our understanding of regulatory T cell populations has substantially advanced, compelling evidence support the prospect that in-vitro expanded, patient-tailored Tregs with indirect anti-donor allospecificity could be potential reagents as adoptive cell therapy for individualized medicine to promote clinical transplantation tolerance.

Animals↗

PubMed2006

In vitro expanded alloantigen-specific CD4+CD25+ regulatory T cell treatment for the induction of donor-specific transplantation tolerance.

The key goal in clinical transplantation is the induction of donor-specific transplantation tolerance to minimise the morbidity and mortality associated with long-term immunosuppression. Naturally occurring CD4(+)CD25(+) regulatory T cells (Tregs) expressing forkhead transcript factor FoxP3 play a crucial role in the prevention of autoimmunity, and appear to mediate transplantation tolerance, and these cells can have indirect allospecificity for donor antigens. Here we show that self-reactive human CD4(+)CD25(+) Tregs can be subverted into allopeptide-specific cells in vitro and be expanded to large cell numbers, and that similar in vitro expanded murine CD4(+)CD25(+) Tregs with indirect allospecificity were capable of inducing donor-specific experimental transplantation tolerance. These data provide a platform for clinical studies using CD4(+)CD25(+) Tregs with indirect allospecificity as potential reagents for the induction of donor-specific transplantation tolerance.

Adoptive Transfer↗

PubMed2006

A novel pathway of antigen presentation by dendritic and endothelial cells: Implications for allorecognition and infectious diseases.

Dendritic cells (DCs) are the major antigen presenting cells capable of stimulating T cell responses following either organ transplantation or a viral infection. In the context of allorecognition, T cells can be activated following presentation of alloantigens by donor DCs (direct), as well as by recipient DCs presenting processed donor major histocompatibility complex (MHC) as peptides (indirect). We have recently described another mechanism by which alloreactive T cells are activated. Recipient DCs can acquire donor MHC through cell-to-cell contact and this acquired MHC can stimulate a T cell response (the semidirect pathway). Similarly, during a viral infection, DCs are capable of stimulating T cells directly, as occurs when infected DCs present processed viral antigens, or indirectly by a process known as cross-presentation. Although cross-presentation of exogenous antigen is an important mechanism for controlling infectious diseases, it is possible that peptide:MHC acquisition (the semidirect pathway) may also play a part in immunity against pathogens. In this review, we discuss the possible contributions of the semidirect pathway/MHC transfer in infectious disease.

Antigen Presentation↗

PubMed2006

Helicobacter pylori has stimulatory effects on naive T cells.

BACKGROUND: Despite an apparently active host response, Helicobacter pylori infection can persist for life. Unexpectedly, T cells from apparently uninfected individuals respond to H. pylori antigen by proliferating. Also, the T-cell proliferative response appears to be less in infected compared with uninfected individuals. MATERIALS AND METHODS: We have investigated the T-cell response of isolated human peripheral blood, naive, and memory CD4+ T cells to H. pylori antigen in infected and uninfected subjects. RESULTS: In agreement with previous findings, the peripheral blood proliferative response was higher in uninfected compared with infected subjects. Interestingly, there was a response in CD4+ CD45RO+ (memory) and CD4+CD45RA+ (naive) subsets. The RO/RA ratio of the response to H. pylori antigen was 0.8-2.1 in both H. pylori-positive and H. pylori-negative subjects, which was similar to that of a known superantigen (2.5 and 2.2 in Helicobacter-positive and -negative subjects, respectively) whereas the RO/RA response ratio to a recall antigen (tetanus toxoid) was 9.8 and 18.7 in Helicobacter-positive and -negative subjects, respectively. Mononuclear cells isolated from cord blood also responded to H. pylori antigen, whereas there was no response to tetanus toxoid. The cord blood response and CD4+ CD45RA+ cell response to H. pylori antigen were inhibited predominantly by anti-HLA-DR and to some extent by anti-HLA-DQ antibodies. Investigation of the response to five different recombinant H. pylori antigens identified two that produced a response in naive T cells. CONCLUSIONS: These data suggest that H. pylori possesses molecules that cause higher than expected proliferation of naive T cells.

Antibodies, Monoclonal↗

PubMed2006

CD4+CD25+ regulatory T cell therapy for the induction of donor-specific clinical transplantation tolerance.

Naturally occurring CD4+CD25+ regulatory T cells (Tregs) have been shown to play a key role in the control of autoimmunity. Interestingly, they are also capable of mediating transplantation tolerance and they can have indirect allospecificity for donor antigens. An increasing body of evidence in experimental studies has indicated that adoptive transfer of in vitro expanded CD4+CD25+ Tregs with indirect antidonor allospecificity can induce long-term donor-specific transplantation tolerance. Thus, adoptive cell therapy using patient-specific CD4+CD25+ Tregs as individualised medicine to promote clinical transplantation tolerance is promising.

Animals↗

PubMed2006

CD4+CD25+ regulatory T-cell therapy for allergy, autoimmune disease and transplant rejection.

Naturally occurring CD4+CD25+ regulatory T cells (Tregs) play a critical role in the control of periphery tolerance to self-antigens. Interestingly, they also control immune responses to allergens and transplant antigens. Recent studies in animal models have shown that adoptive transfer of CD4+CD25+ Tregs can prevent or even cure allergic and autoimmune diseases, and appear to induce transplantation tolerance. Thus, adoptive cell therapy using patient-specific CD4+CD25+ Tregs has been emerged as individualized medicine for the treatment of inflammatory disease including allergy, autoimmune disease and transplant rejection. Furthermore, strategies to activate and expand antigen-specific CD4+CD25+ Tregs in vivo using pharmacological agents may represent a novel avenue for drug development.

Animals↗

PubMed2005

Arvanil inhibits T lymphocyte activation and ameliorates autoimmune encephalomyelitis.

This study examined the immunomodulatory effect of arvanil, a synthetic capsaicin-anandamide hybrid. Arvanil inhibits lymphocyte proliferation and IFN-gamma production. The phenotype of activated CD4+T cells treated with arvanil shows a down-regulation of T cell activation markers such as CD25, HLA-DR and CD134/OX40. Arvanil and anandamide do not induce apoptosis on CD4+T cells. Arvanil blocks the G1/S phase transition of the cell cycle in stimulated peripheral blood mononuclear cells, inducing activation of p21waf-1/cip-1 and phosphorylation of Akt/PKB. In vivo, arvanil ameliorates experimental autoimmune encephalomyelitis in the SJL/J mouse. Our findings have relevance for the use of arvanil and related compounds as a novel immunotherapeutic approach in the treatment of multiple sclerosis.

Animals↗

PubMed2005

Creation of tolerogenic human dendritic cells via intracellular CTLA4: a novel strategy with potential in clinical immunosuppression.

Activation of T lymphocytes requires the recognition of peptide-major histocompatibility complexes (MHCs) and costimulatory signals provided by antigen-presenting cells (APCs). It has been shown that T-cell activation without costimulation can lead to anergy. In this study, we developed a novel strategy to inhibit expression of B7 molecules (CD80/86) by transfecting APCs with a gene construct encoding a modified cytotoxic T lymphocyte antigen 4 (CTLA4) molecule (CTLA4-KDEL) that is targeted to the endoplasmic reticulum (ER). APCs expressing this construct failed to express CD80/86 on their surface, were unable to stimulate allogeneic and peptide-specific T-cell responses, and induced antigen-specific anergy of the responding T cells. Cells expressing CTLA4-KDEL do not up-regulate the indoleamine 2, 3-dioxygenase enzyme, unlike cells treated with soluble CTLA4-immunoglobin (Ig). This gene-based strategy to knock out surface receptors is an attractive alternative to using immature dendritic cells for preventing transplant rejection and treating of autoimmune diseases.

Antigens, CD↗

PubMed2005

Tolerant T cells display impaired trafficking ability.

Based on our previous observation that anergic T lymphocytes lose their migratory ability in vitro, we have proposed that anergic T cells are retained in the site where they have been generated to exert their regulatory function. In this study we have analyzed T lymphocyte trafficking and motility following the induction of tolerance in vivo. In a model of non-deletional negative vaccination to xenoantigens in which dendritic cells (DC) localize to specific lymphoid sites depending on the route of administration, tolerant T cells remained localized in the lymph nodes colonized by tolerogenic DC, while primed T cells could traffic efficiently. Using an oral tolerance model that enables the 'tracking' of ovalbumin-specific TCR-transgenic T cells, we confirmed that T cells lose the ability to migrate through syngeneic endothelial cell monolayers following tolerance induction in vivo. Finally, we show that tolerant T cells (both in vitro and ex vivo) can inhibit migration of responsive T cells in an antigen-independent manner. Thus, hyporesponsive T cells localize at the site of tolerance induction in vivo, where they exert their anti-inflammatory properties. In physiological terms, this effect is likely to render immunoregulation a more efficient and controllable event.

Animals↗

PubMed2005

Activated CD1d-restricted natural killer T cells secrete IL-2: innate help for CD4+CD25+ regulatory T cells?

CD4(+)CD25(+) and CD1d-restricted natural killer T (NKT) cells are thymus-derived self-reactive regulatory T cells that play a key role in the control of pathological immune responses. Little is known about functional cooperation between innate regulatory NKT cells and adaptive CD4(+)CD25(+) regulatory cells. Here we show that human CD4(+)Valpha24(+)Vbeta11(+) (CD4(+) NKT) cells isolated from peripheral blood by flow cytometric cell sorting secrete substantial amounts of IL-2 after stimulation with dendritic cells (DC) and alpha-Galactosylceramide. When cocultured with CD4(+)CD25(+) cells, CD4(+) NKT cells promoted moderate proliferation of CD4(+)CD25(+) cells. The proliferation of CD4(+)CD25(+) T cells was due to soluble IL-2 produced by activated CD4(+) NKT cells. The expanded CD4(+)CD25(+) cells remained anergic and retained their potent suppressive properties. These findings indicate that unlike conventional CD4(+) and CD8(+) T cells, which are susceptible to CD4(+)CD25(+) regulatory cell suppression, NKT cells promote CD4(+)CD25(+) regulatory cell proliferation. These data raise the possibility that NKT cells can function as helper cells to CD4(+)CD25(+) regulatory T cells, thereby providing a link between the two naturally occurring populations of regulatory T cells.

Antigens, CD1↗