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Elizabeth Simpson

Publications and source records attributed to Elizabeth Simpson.

At least 19 recordsLinked to original sources
PubMed2006

TCR-alpha CDR3 loop audition regulates positive selection.

How positive selection molds the T cell repertoire has been difficult to examine. In this study, we use TCR-beta-transgenic mice in which MHC shapes TCR-alpha use. Differential AV segment use is directly related to the constraints placed on the composition of the CDR3 loops. Where these constraints are low, efficient selection of alphabeta pairs follows. This mode of selection preferentially uses favored AV-AJ rearrangements and promotes diversity. Increased constraint on the alpha CDR3 loops leads to inefficient selection associated with uncommon recombination events and limited diversity. Further, the two modes of selection favor alternate sets of AJ segments. We discuss the relevance of these findings to the imprint of self-MHC restriction and peripheral T cell activation.

Animals↗
PubMed2006

Role of immunoproteasomes in cross-presentation.

The evidence that proteasomes are involved in the processing of cross-presented proteins is indirect and based on the in vitro use of proteasome inhibitors. It remains, therefore, unclear whether cross-presentation of MHC class I peptide epitopes can occur entirely within phagolysosomes or whether it requires proteasome degradation. To address this question, we studied in vivo cross-presentation of an immunoproteasome-dependent epitope. First, we demonstrated that generation of the immunodominant HY Uty(246-254) epitope is LMP7 dependent, resulting in the lack of rejection of male LMP7-deficient (LMP7(-/-)) skin grafts by female LMP7(-/-) mice. Second, we ruled out an altered Uty(246-254)-specific T cell repertoire in LMP7(-/-) female mice and demonstrated efficient Uty(246-254) presentation by re-expressing LMP7 in male LMP7(-/-) cells. Finally, we observed that LMP7 expression significantly enhanced cross-priming of Uty(246-254)-specific T cells in vivo. The observations that male skin grafts are not rejected by LMP7(-/-) female mice and that presentation of a proteasome-dependent peptide is not efficiently rescued by alternative cross-presentation pathways provide strong evidence that proteasomes play an important role in cross-priming events.

Animals↗
PubMed2006

Transplant tolerance: models, concepts and facts.

Despite extensive research, our understanding of immunological tolerance to self-antigens is incomplete, and the goal of achieving tolerance to allogeneic transplanted tissue remains elusive. Currently, it is generally believed that the blockade of T cell co-stimulation offers considerable potential for achieving tolerance in the clinical setting. However, the recent finding that CD154-specific antibody may act through the depletion of activated T cells rather than co-stimulation blockade alone highlights the need for a re-evaluation of published data and the role of co-stimulation blockade in transplant tolerance. Activated T cells are programmed to die unless they receive sufficient survival signals in the form of inflammatory and lymphotropic cytokines produced by activated antigen-presenting cells or the T cells themselves. In conditions where the threshold for surviving activation is not reached, for example when a small number of responder T cells are activated in the absence of substantial injury or inflammation, the ensuing death of all activated T cells can result in deletional tolerance. Therefore, we propose that tolerance represents a failure of T cells to survive activation and develop into memory cells. This concept is likely to apply in the transplant setting, where the strength of the alloresponse depends on both the number/phenotype of the recipients' alloreactive T cells and immunogenicity of the transplanted tissue. Hence, in some rodent donor-recipient strain combinations that instigate a weak alloresponse, many treatments that only modestly decrease the alloresponse can achieve tolerance. In contrast, clinical transplantation is characterised by a strong alloresponse and highly immunogenic allografts, and thus, most treatments fail to control allograft rejection, and tolerance is difficult to achieve.

Animals↗
PubMed2006

A historical perspective on immunological privilege.

Intimations of immunological privilege in sites of the body such as the eye and the brain go back in the literature more than a century, to reports of experiments using outbred animals and tumor transplants. The starting points of this review, however, are publications stemming from the transplantation of normal tissues and, as far as possible, the use of inbred animals, exploring the way in which interplay between genetic differences of different degree, from single minor histocompatibility antigens to full-house major histocompatibility complex mismatches, has been reported to affect the 'take' of grafts in putatively privileged sites. While these sites traditionally included the brain, the eye, the pregnancy, and the endocrine tissues such as thyroid, parathyroid, adrenal, and islets of Langerhans, from readings of the literature, it is clear that the eye and the pregnancy have claims to being in the strongest positions of privilege. Even then, the position is precarious, with stirrings of the adaptive immune system poised to attack. Various regulatory mechanisms have now moved center stage and will undoubtedly form a significant part in subsequent chapters in this volume. Perhaps surprisingly, as investigations on these mechanisms have advanced, there is evidence for the convergence of those mechanisms controlling both induced tolerance and immunological privilege.

Animals↗
PubMed2005

Identification of the immunodominant HY H2-D(k) epitope and evaluation of the role of direct and indirect antigen presentation in HY responses.

Minor histocompatibility Ags derive from self-proteins and provoke allograft rejection and graft-vs-host disease in MHC-matched donor-recipient combinations. In this study, we define the HYD(k) epitope of the HY minor histocompatibility Ag as the 8mer peptide RRLRKTLL derived from the Smcy gene. Using HY tetramers, the response to this peptide was found to be immunodominant among the four characterized MHC class I-restricted HY epitopes (HYD(k)Smcy (defined here), HYK(k)Smcy, HYD(b)Uty, and HYD(b)Smcy). Indirect presentation stimulated a robust primary HYD(k)Smcy response. Indirect presentation and priming of HY-specific CD8+ T cells is also operative in the presence of a full MHC mismatch. To determine whether the indirect route of Ag presentation is required for HY priming, female parent into F1 (H2bxk) female recipient bone marrow chimeras were immunized with male cells of the other parental haplotype, limiting presentation to the direct pathway. The dominant H2b HY response (HYD(b)Uty) was dependent on indirect presentation. However, the dominant H2k HY response (HYD(k)Smcy) could be stimulated efficiently by the direct pathway. In contrast, secondary expansion of both HYD(k)Smcy and HYD(b)Uty-specific CD8+ T cells was effective only when Ag was presented by the direct route. Transgenic overproduction of Smcy mRNA within the immunizing cells resulted in a corresponding increase in the HYD(k)Smcy, HYD(b)Smcy, and HYK(k)Smcy-specific CD8+ T cell responses when presented via the direct pathway but did not enhance indirect presentation demonstrating the independent regulation of MHC class I-peptide occupancy in the two Ag-processing pathways.

Animals↗
PubMed2005

Engraftment of allogeneic hematopoietic stem cells requires both inhibition of host-versus-graft responses and 'space' for homeostatic expansion.

BACKGROUND: The establishment of host-versus-graft (HvG) tolerance is the primary aim of reduced intensity conditioning (RIC) regimens for allogeneic stem cell transplantation (SCT). It remains to be clarified to what extent recipient myeloablation is fundamental in the establishment of donor chimerism. METHODS: We have addressed this question in a murine model of RIC SCT in which the donor-recipient combination produces HvG against the male specific minor histocompatibility antigen HY. In this system engraftment can be monitored by RT-PCR and HvG effectors enumerated by tetramer analysis. RESULTS: We demonstrate that the dose of irradiation influences donor hemopoietic engraftment and affects generation of anti-donor specific T cells. Chimeric recipients do not mount a HvG immune response, becoming selectively tolerant, as demonstrated by the long term acceptance of skin grafts of donor but not third party origin. However, HvG tolerance is not sufficient to secure engraftment since, even in the absence of HvG, partial myeloablation was still required. The "space" produced by myeloablation and the consequent potential for donor cell expansion could also affect HvG tolerance, since its induction is severely impaired when donor hematopoietic cells have reduced proliferative capacity. CONCLUSIONS: We conclude that both some degree of myeloablation and HvG tolerance are required for successful engraftment, and that the capacity of donor cells to proliferate influences the induction of HvG tolerance.

Animals↗
PubMed2005

Regulatory T cells, derived from naïve CD4+CD25- T cells by in vitro Foxp3 gene transfer, can induce transplantation tolerance.

BACKGROUND: Regulatory T (Treg) cells, generated in vitro by Foxp3 gene transfer into naive CD4+25- T cells, have been shown to inhibit the development of inflammation and autoimmune disease, but it is not known whether they are able to prevent allograft rejection. This study investigated whether Treg cells generated from naive CD4+ T cells by Foxp3 gene transfer could induce transplantation tolerance. METHODS: HY-specific, T-cell receptor (TCR)-transgenic CD4+25- T cells were retrovirally transduced with the Foxp3 gene. The phenotype, function, and cytokine profiles of the transduced cells were examined in vitro by fluorescence-activated cell sorter, T-cell proliferation assays, enzyme-linked immunosorbent assay, and intracellular cytokine staining. Adoptive transfer and skin grafting experiments were conducted to assess whether Foxp3-transduced HY-specific T cells could prevent the rejection of syngeneic male grafts. RESULTS: CD4+25- T cells retrovirally transduced with Foxp3 express a panel of cell surface and intracellular molecules closely associated with Treg activity. This Treg phenotype was stable during in vitro culture with some further maturation. In vitro, Foxp3-transduced cells were functionally anergic and suppressive T cells. In vivo adoptive transfer of Foxp3-transduced HY-specific TCR-transgenic CD4+ T cells protected male skin grafts from rejection by syngeneic females. Retroviral transduction of the Foxp3 gene into non-TCR-transgenic CD4+25- T cells, however, had no influence on male skin graft rejection. CONCLUSION: This study provides the first evidence that Foxp3-transduced T cells can control the rejection of an allogeneic transplant and suggests that T-cell Foxp3 gene transfer may have therapeutic value in clinical transplantation.

Animals↗
PubMed2005

Thymocyte-thymocyte interaction for efficient positive selection and maturation of CD4 T cells.

Despite numerous reports on MHC class II expression by T cells from a wide spectrum of mammalian species including humans, the biological relevance of this phenomenon has never been tested with appropriately designed animal models. To address this issue, we developed mouse models in which immature thymocytes are the only positively selecting antigen-presenting cells in the thymus. In these mice, CD4+ T cells were generated with the appropriate maturation phenotype and showed a diverse repertoire of TCR Vbetas. The CD4+ T cells were functionally competent, mediating effective allogeneic responses that involved polyclonal TCR Vbetas. These results suggest that the thymocyte-thymocyte (T-T) interaction operates as an independent pathway for CD4+ T cell selection in the thymi of species with MHC II-positive thymocytes. This T-T interaction appears to be the basis for the generation of donor MHC-restricted CD4+ T cells in xenogeneic hosts.

Animals↗
PubMed2005

Mixed-haplotype MHC class II molecules select functional CD4+ T cells.

MHC class II molecules are formed from polymorphic alpha and beta chains. While pairing of chains is most efficient within class II isotypes and haplotypes, limited pairing and surface expression of mixed-haplotype and -isotype class II molecules is common. The function of such molecules in antigen presentation has been established by the unique restriction of responses in F1 mice. However, it has not been established whether mixed class II molecules are able to mediate selection of functional T cells and how the reduced avidity of the TCR/MHC interaction influences the repertoire. In this report we have addressed these issues through the production of mice expressing solely mixed-haplotype class II molecules. The mixed class II molecules promote selection of a small CD4+ T cell repertoire with modified TCR use. The selected CD4+ T cells are functional in vivo and in vitro.

Amino Acid Sequence↗
PubMed2004

Induction of unresponsiveness limits tumor protection by adoptively transferred MDM2-specific cytotoxic T lymphocytes.

There is evidence showing that high avidity CTLs can be more effective than low avidity CTLs for adoptive tumor immunotherapy. Because many T cell-recognized tumor antigens are nonmutated self-proteins, tolerance mechanisms are likely to render high avidity T cells unresponsive or cause T cell elimination by clonal deletion. We recently used the allo-restricted strategy to circumvent immunologic tolerance to a ubiquitously expressed tumor-associated protein, MDM2, and raised high avidity CTLs in humans and in mice. In this study, we investigated whether high avidity MDM2-specific CTLs can mediate tumor protection without causing damage to normal tissues in mice. Although the CTLs prolonged survival of tumor-bearing mice without causing damage to normal tissues, tumor protection was incomplete. We show that tumor growth occurred despite the continued presence of MDM2-specific CTLs and the continued susceptibility of tumor cells to CTL killing. However, analysis of the CTLs revealed that they had been rendered unresponsive in vivo because they did not produce interferon gamma in response to antigen-specific stimulation. These experiments suggest that induction of unresponsiveness may be an important mechanism limiting the efficacy of adoptive CTL therapy.

Animals↗
PubMed2004

DNA fusion vaccines induce targeted epitope-specific CTLs against minor histocompatibility antigens from a normal or tolerized repertoire.

We have designed DNA fusion vaccines able to induce high levels of epitope-specific CD8(+) T cells, using linked CD4(+) T cell help. Such vaccines can activate effective immunity against tumor Ags. To model performance against minor histocompatibility (H) Ags important in allogeneic hemopoietic stem cell transplantation, responses against the H2D(b)-restricted Uty and Smcy male HY epitopes have been investigated. Vaccination of females induced high levels of tetramer-specific, IFN-gamma-producing CD8(+) T cells against each epitope. Vaccines incorporating a single epitope primed effector CTL able to kill male splenocytes in vitro and in vivo, and HY(Db)Uty-specific vaccination accelerated rejection of syngeneic male skin grafts. Priming against either epitope established long-term memory, expandable by injection of male cells. Expanded CD8(+) T cells remained specific for the priming HY epitope, with responses to the second suppressed. To investigate vaccine performance in a tolerized repertoire, male mice were vaccinated with the fusion constructs. Strikingly, this also generated epitope-specific IFN-gamma-producing CD8(+) T cells with cytotoxic function. However, numbers and avidity were lower than in vaccinated females, and vaccinated males failed to reject CFSE-labeled male splenocytes in vivo. Nevertheless, these findings indicate that DNA fusion vaccines can mobilize CD8(+) T cells against endogenous minor H Ags, even from a profoundly tolerized repertoire. In the transplantation setting, vaccination of donors could prime and expand specific T cells for in vivo transfer. For patients, vaccination could activate a potentially less tolerized repertoire against similar Ags that may be overexpressed by tumor cells, for focused immune attack.

Animals↗
PubMed2004

Transplantation tolerance induced by intranasal administration of HY peptides.

Induction of antigen-specific tolerance to transplantation antigens is desirable to control host-versus-graft and graft-versus-host reactions. Following molecular identification of a set of minor histocompatibility (H) antigens, we have used selected HY peptide epitopes for this purpose. Intranasal administration of individual major histocompatibility complex (MHC) class II-restricted HY peptides induces indefinite survival of syngeneic male skin grafts and allows engraftment of male bone marrow. Tolerance involves linked suppression to additional HY epitopes on test grafts. Long-term tolerance also requires suppression of emerging thymic emigrants. It does not involve deletion. HY peptide-specific CD4(+) and CD8(+) T cells expand on re-exposure to male antigen; these expansions are smaller in tolerant than control mice and fewer HY-specific cells from tolerant females secrete interferon gamma and interleukin 10 (IL-10). Significantly, CD4(+) cells from peptide-pretreated females fail to make IL-2 responses to cognate peptide, limiting expansion of the HY-specific CD8(+) populations that can cause graft rejection. Consistent with this, tolerance induction by HY peptide is abrogated by coadministration of lipopolysaccharide. IL-10 does not appear to be critically involved because tolerance is inducible in IL-10-deficient mice. Adoptive transfer of tolerance into naive neonatal recipients by splenocytes from long-term tolerant donors provides evidence for involvement of regulatory cells.

Administration, Intranasal↗
PubMed2004

Reminiscences of Sir Peter Medawar: in hope of antigen-specific transplantation tolerance.

Peter Medawar's career in medical research (he always described himself as a medical research scientist) began as a student of zoology in Oxford. He obtained a first class degree in 1936, aged 21, and undertook postgraduate studies with Florey. His work was anchored in a broad field; he was adept at addressing novel questions in the context of prior ideas and knowledge. His earlier interest in growth, driven as much by mathematics as biology, gave way to transplantation at the beginning of World War II, treatment of burns patients being the driver. He interpreted the results of grafting autologous and allogeneic human skin, observed clinically and microscopically, as immunological; he identified accelerated donor-specific reactions to subsequent grafts as 'second set', and described cell (lymphocyte) mediated infiltration of allo- but not auto-grafts following initial vascularization, both in the patient context and in experimental animals. He became intrigued by the consequences of hematopoietic chimerism, from which his landmark discoveries on the induction of transplantation tolerance derive. These results, his interpretation and dissemination of them, gave hope to transplant surgeons that donor-specific transplant tolerance would be achievable. Many immunosuppressive drugs later, we are now reapproaching this hope, from various angles.

History, 20th Century↗
PubMed2004

Immunotherapy and gene therapy.

The Immunotherapy and Gene Therapy meeting of the Academy of Medical Sciences reviewed the state-of-the-art and translational prospects for therapeutic interventions aimed at killing tumor cells, correcting genetic defects and developing vaccines for chronic infections. Crucial basic science concepts and information about dendritic cells, the structure and function of T-cell receptors, and manipulation of the immune response by cytokine antagonists and peptides were presented. This information underpins vaccine design and delivery, as well as attempts to immunomodulate autoimmune disease. Results from studies using anticancer DNA vaccines, which include appropriate signals for both the innate and adaptive immune response, were presented in several talks. The vaccines incorporated helper epitopes and cancer target epitopes such as immunoglobulin idiotypes (for lymphomas and myelomas), melanoma-associated antigens (for melanoma and other solid tumors) and minor histocompatibility antigens (for leukemia). The results of using vaccines employing similar principles and designed to reduce viral load in HIV/AIDS patients were also presented. The introduction of suicide genes incorporating the bacterial enzyme nitroreductase gene (ntr) targeted at tumor cells prior to administration of the prodrug CB-1954, converted by ntr into a toxic alkylating agent, was discussed against the background of clinical trials and improved suicide gene design. The introduction into hematopoietic stem cells of missing genes for the common gamma-chain, deficiency of which causes severe combined immunodeficiency (SCID), used similar retroviral transduction. The outcome of treating six SCID patients in the UK, and ten in France was successful immune reconstitution in the majority of patients, but in two of the French cases a complication of lymphoproliferative disease due to insertional mutagenesis was observed. The adoptive transfer of T-cells specific for minor histocompatibility antigens (for leukemia), cytomegalovirus (CMV; for CMV infection following stem cell transplantation) and selected Epstein-Barr virus-encoded antigens (for nasopharyngeal carcinoma) were discussed in relation to the source of specifically primed T-cells or the possibility of transducing recipient T-cells with high-affinity, antigen-specific T-cell receptor genes.

Animals↗
PubMed2003

Cognate recognition of the endothelium induces HY-specific CD8+ T-lymphocyte transendothelial migration (diapedesis) in vivo.

The physiologic significance of MHC-peptide complex presentation by endothelial cells (ECs) to trafficking T lymphocytes remains unresolved. On the basis of our observation that cognate recognition of ECs enhanced transendothelial migration of antigen-specific T lymphocytes in vitro, we have proposed that by displaying antigenic peptides from the underlying tissue, ECs promote the recruitment of antigen-specific T cells. In this study, we have tested this hypothesis by comparing the trafficking of HY-specific T lymphocytes into antigenic and nonantigenic tissue using in vivo models of T-cell recruitment. Up-regulated expression of H2 molecules presenting endogenous antigen in the peritoneal mesothelium and vessels led to the local recruitment of HY-specific T cells in male, but not female, mice. Intravital microscopy experiments analyzing EC-HY-specific T-cell interactions in the cremasteric vascular bed revealed that cognate recognition of the endothelium results in enhanced diapedesis of T cells into the tissue, while not affecting rolling and adhesion. Our results are consistent with the hypothesis that, under inflammatory conditions, antigen presentation by the endothelium contributes to the development and specificity of T-cell-mediated inflammation by favoring the selective migration of antigen-specific T cells.

Animals↗
PubMed2003

Fc-dependent depletion of activated T cells occurs through CD40L-specific antibody rather than costimulation blockade.

Although the underlying mechanisms are not well understood, it is generally believed that antigen recognition by T cells in the absence of costimulation may alter the immune response, leading to anergy or tolerance. Further support for this concept comes from animal models of autoimmunity and transplantation, where treatments based on costimulation blockade, in particular CD40 ligand (CD40L)-specific antibodies, have been highly effective. We investigated the mechanisms of action of an antibody to CD40L and provide evidence that its effects are dependent on the constant (Fc) region. Prolongation of graft survival is dependent on both complement- and Fc receptor-mediated mechanisms in a major histocompatibility complex (MHC)-mismatched skin transplant model. These data suggest that antibodies to CD40L act through selective depletion of activated T cells, rather than exerting immune modulation by costimulation blockade as currently postulated. This finding opens new avenues for treatment of immune disorders based on selective targeting of activated T cells.

Animals↗