Triggering a second T cell receptor on diabetogenic T cells can prevent induction of diabetes

TCR-engineered T cells: a model of inducible TCR expression to dissect the interrelationship between two TCRs

TCR gene modified T cells for adoptive therapy simultaneously express the Tg TCR and the endogenous TCR, which might lead to mispaired TCRs with harmful unknown specificity and to a reduced function of TCR-Tg T cells. We generated dual TCR T cells in two settings in which either TCR was constitutively expressed by a retroviral promoter while the second TCR expression was regulable by a Tet-on system. Constitutively expressed TCR molecules were reduced on the cell surface depending on the induced TCR expression leading to strongly hampered function. Besides that, using fluorescence resonance energy transfer we detected mispaired TCR dimers and different pairing behaviors of individual TCR chains with a mutual influence on TCR chain expression. The loss of function and mispairing could not be avoided by changing the TCR expression level or by introduction of an additional cysteine bridge. However, in polyclonal T cells, optimized TCR formats (cysteineization, codon optimization) enhanced correct pairing and function. We conclude from our data that (i) the level of mispairing depends on the individual TCRs and is not reduced by increasing the level of one TCR, and (ii) modifications (cysteineization, codon optimization) improve correct pairing but do not completely exclude mispairing (cysteineization).

Promotion and prevention of autoimmune disease by CD8+ T cells

Until recently, little was known about the importance of CD8+ T effectors in promoting and preventing autoimmune disease development. CD8+ T cells can oppose or promote autoimmune disease through activities as suppressor cells and as cytotoxic effectors. Studies in several distinct autoimmune models and data from patient samples are beginning to establish the importance of CD8+ T cells in these diseases and to define the mechanisms by which these cells influence autoimmunity. CD8+ effectors can promote disease via dysregulated secretion of inflammatory cytokines, skewed differentiation profiles and inappropriate apoptosis induction of target cells, and work to block disease by eliminating self-reactive cells and self-antigen sources, or as regulatory T cells. Defining the often major contribution of CD8+ T cells to autoimmune disease and identifying the mechanisms by which they alter the pathogenesis of disease is a rapidly expanding area of study and will add valuable information to our understanding of the kinetics, pathology and biology of autoimmune disease.

Incomplete TCR-β allelic exclusion accelerates spontaneous autoimmune arthritis in K/BxN TCR transgenic mice

Allelic exclusion of antigen receptor loci is a fundamental mechanism of immunological self-tolerance. Incomplete allelic exclusion leads to dual T-cell receptor (TCR) expression and can allow developing autoreactive αβ T lymphocytes to escape clonal deletion. Because allelic exclusion at the TCR-β locus is more stringent than at the TCR-α locus, dual TCR-β expression has not been considered a likely contributor to autoimmunity. We show here that incomplete TCR-β allelic exclusion permits developing thymocytes bearing the autoreactive, transgene-encoded KRN TCR to be positively selected more efficiently, thereby accelerating the onset of spontaneous autoimmune arthritis. Our findings highlight dual TCR-β expression as a mechanism that can enhance the maturation of autoreactive pathogenic T cells and lead to more rapid development of autoimmune disease.

T cells expressing two different T cell receptors form a heterogeneous population containing autoreactive clones

During T cell development both alleles of the T cell receptor (TCR) alpha locus are rearranged. As a result, a sizeable proportion of T cells can express two distinct TCRs, but the functional significance of this phenomenon remains controversial. Studies on transgenic mice with two TCRs have focused on the risk of immunopathology that such cells may pose, while some have suggested that most dual-specific T cells are nonfunctional or even protective. We tracked the fate and TCR repertoire of single- and dual-specific T cells within a normal polyclonal population undergoing lymphopenia-induced proliferation, a setting which has been shown to cause immunopathology and autoimmunity. After the expansion the repertoire of dual-specific T cells had become highly biased, with both prominent clonal expansions and the complete disappearance of other clones. Our results suggest that the normal repertoire of dual-specific T cells contains both nonfunctional cells and a small, 5% fraction of clones which display a much higher than average affinity to antigens normally tolerated as harmless. This heterogeneity may also help in reconciling some of the earlier, conflicting results.

T-cell promiscuity in autoimmune diabetes

OBJECTIVE

It is well established that the primary mediators of beta-cell destruction in type 1 diabetes are T-cells. Nevertheless, the molecular basis for recognition of beta-cell-specific epitopes by pathogenic T-cells remains ill defined; we seek to further explore this issue.

RESEARCH DESIGN AND METHODS

To determine the properties of beta-cell-specific T-cell receptors (TCRs), we characterized the fine specificity, functional and relative binding avidity/affinity, and diabetogenicity of a panel of GAD65-specific CD4(+) T-cell clones established from unimmunized 4- and 14-week-old NOD female mice.

RESULTS

The majority of GAD65-specific CD4(+) T-cells isolated from 4- and 14-week-old NOD female mice were specific for peptides spanning amino acids 217-236 (p217) and 290-309 (p290). Surprisingly, 31% of the T-cell clones prepared from 14-week-old but not younger NOD mice were stimulated with both p217 and p290. These promiscuous T-cell clones recognized the two epitopes when naturally processed and presented, and this dual specificity was mediated by a single TCR. Furthermore, promiscuous T-cell clones demonstrated increased functional avidity and relative TCR binding affinity, which correlated with enhanced islet infiltration on adoptive transfer compared with that of monospecific T-cell clones.

CONCLUSIONS

These results indicate that promiscuous recognition contributes to the development of GAD65-specific CD4(+) T-cell clones in NOD mice. Furthermore, these findings suggest that T-cell promiscuity reflects a novel form of T-cell avidity maturation.

Dual T cell receptor expressing CD8+ T cells with tumor- and self-specificity can inhibit tumor growth without causing severe autoimmunity

The engineering of Ag-specific T cells by expression of TCR genes is a convenient method for adoptive T cell immunotherapy. A potential problem is the TCR gene transfer into self-reactive T cells that survived tolerance mechanisms. We have developed an experimental system with T cells that express two TCRs with defined Ag-specificities, one recognizing a tumor-specific Ag (LCMV-gp(33)), the other recognizing a self-Ag in the pancreas (OVA). By using tumor cells expressing high and low amounts of Ag and mice expressing high and low levels of self-Ag in the pancreas (RIP-OVA-Hi and RIP-OVA-Lo), we show that 1) tumor rejection requires high amount of tumor Ag, 2) severe autoimmunity requires high amount of self-Ag, and 3) if Ag expression on tumor cells is sufficient and low in the pancreas, successful adoptive T cell therapy can be obtained in the absence of severe autoimmunity. These results are shown with T cells from dual TCR transgenic mice or T cells that were redirected by TCR gene transfer. Our data demonstrate that the approach of adoptively transferring TCR redirected T cells can be effective without severe side effects, even when high numbers of T cells with self-reactivity were transferred.

Most human thymic and peripheral-blood CD4+CD25+ regulatory T cells express 2 T-cell receptors

Lack of allelic exclusion in the T-cell receptor (TCR) α locus gives rise to 2 different TCRs in 10% to 30% of all mature T cells, but the significance of such dual specificity remains controversial. Here we show that human CD4+CD25+ regulatory T (Treg) cells express 2 distinct Vα chains and thus 2 TCRs at least 3 times as often as other T cells. Extrapolating from flow cytometric analysis using Vα2-, Vα12-, and Vα24-specific monoclonal antibodies (mAbs), we estimated that between 50% and 99% of the CD25+ Treg cells were dual specific, as compared with about 20% of their CD25– counterparts. Moreover, both TCRs were equally capable of transmitting signals upon ligation. Cells with 2 TCRs also expressed more FOXP3, the Treg-cell lineage specification factor, than cells with a single TCR. Our findings suggest that expression of 2 TCRs favors differentiation to the Treg-cell lineage in humans and raise the question of the potential functional consequences of dual specificity.

Malaria-specific transgenic CD4+ T cells protect immunodeficient mice from lethal infection and demonstrate requirement for a protective threshold of antibody production for parasite clearance

T cells are important in the immune response to malaria, both for their cytokines and their help for antibody production. To look at the relative importance of these roles, a T-cell receptor (TCR) transgenic mouse has been generated carrying a TCR specific for an epitope of the merozoite surface protein 1 (MSP-1) of the malaria parasite, Plasmodium chabaudi. In adoptive transfer experiments, malaria-specific CD4+ T cells expand and produce interferon γ (IFN-γ) early in infection, but the population contracts quickly despite prolonged persistence of the parasite. MSP-1-specific CD4+ cells can protect immunodeficient mice from lethal infection; however, the parasite is only completely cleared in the presence of B cells showing that T helper cells are critical. Levels of malaria-specific antibody and the speed of their production clearly correlate with the time of resolution of infection, indicating that a critical threshold of antibody production is required for parasite clearance. Furthermore, T cells specific for a shed portion of MSP-1 are able to provide help for antibody to the protective region, which remains bound to the infected erythrocyte, suggesting that MSP-1 has all of the components necessary for a good vaccine. (Blood. 2005;106:1676-1684)

Induction of Peripheral Tolerance in Dual TCR T Cells: an Evidence for Non-dominant Signaling by One TCR

Recently, the existence of T cells with dual T cell receptor (TCR) in the immune system is generally accepted, while it has been controversial whether signals through one TCR would affect the functions of the other. In this study T cells expressing two different TCR were obtained from cross-hybrids of LCMV and AND TCR transgenic mice specific for the gp33 and peptide fragment of PCC (fPCC), respectively. Peptide stimulation demonstrated that the dual TCR T cells functioned independently in an antigen-specific manner. To examine whether the tolerance targeted for the one TCR affects the responsiveness of the other, the cross-hybrids were treated with gp33. Although T cells from F1 mice were rendered anergenic to gp33, no functional changes to fPCC were observed in terms of cellular proliferation and IL-2 secretion, suggesting that the dual TCR T cells remained reactive to fPCC. We therefore propose that signaling through the TCR is receptor-specific and 'negative dominance' of one TCR by tolerance induction is not applicable in this dual TCR system.

Retroviral transduction of peptide stimulated t cells can generate dual t cell receptor-expressing (bifunctional) t cells reactive with two defined antigens

BACKGROUND: Tumors and viruses have developed many mechanisms to evade the immune system, including down-regulation of target antigens and MHC molecules. These immune escape mechanisms may be able to be circumvented by adoptively transferring T cells engineered to express two different T cell receptors, each specific for a different antigen or MHC restriction molecule. METHODS: PBMC from the blood of normal healthy donors were stimulated for three days with an antigenic peptide from cytomegalovirus (CMV) pp65. These CMV reactive cultures were transduced with a encoding the TIL 5 T cell receptor (TCR) that mediates recognition of the dominant epitope of the melanoma antigen MART-1. Following selection for transduced cells, the cultures were evaluated for recognition of CMV pp65 and MART-1 expressing targets. RESULTS: We were able to rapidly create bifunctional T cells capable of recognizing both CMV pp65 and MART-1 using a combination of HLA-A2 tetramer staining and intracellular staining for interferon-gamma. These bifunctional T cells were sensitive to very low levels of antigen, recognize MART-1+ tumor cells, and maintained their bifunctionality for over 40 days in culture. CONCLUSION: Bifunctional T cells can be engineered by transducing short term peptide stimulated T cell cultures. These bifunctional T cells may be more effective in treating patients with cancer or chronic virus infections because they would reduce the possibility of disease progression due to antigen and/or MHC loss variants.

Prevention of type I diabetes transfer by glutamic acid decarboxylase 65 peptide 206-220-specific T cells

Glutamic acid decarboxylase (GAD) 65 is one of the major pancreatic antigens targeted by self-reactive T cells in type I diabetes mellitus. T cells specific for GAD65 are among the first to enter inflamed islets and may be important for the initiation of autoimmune diabetes. However, we previously reported that nonobese diabetic (NOD) mice transgenic for a T cell antigen receptor (TCR) specific for one of the immunodominant epitopes of GAD65, peptide 286-300 (G286), are protected from insulitis and diabetes. To examine whether other GAD65-reactive T cells share this phenotype, we have generated TCR transgenic NOD mice for a second immunodominant epitope of GAD65, peptide 206-220 (G206). As in G286 mice, G206 mice do not develop islet inflammation or diabetes. When adoptively transferred along with diabetogenic T cells, activated G206 T cells significantly delayed the onset of diabetes in NOD.scid recipients. Both G206 and G286 T cells produce immunoregulatory cytokines IFN-gamma and IL-10 at low levels when activated by cognate antigens. These data suggest that GAD65-specific T cells may play a protective role in diabetes pathogenesis by regulating pathogenic T cell responses. A better understanding of the functions of autoreactive T cells in type I diabetes will be necessary for choosing desirable targets for immunotherapy.

Factors affecting the susceptibility of the mouse pituitary gland to CD8 T-cell-mediated autoimmunity

We have previously shown, in a transgenic mouse model, that the pituitary gland is susceptible to CD8 T-cell-mediated autoimmunity, triggered by a cell-specific model autoantigen, resulting in pan-anterior pituitary hypophysitis and dwarfism. In the present study, we now demonstrate that antigen dose, the T-cell precursor frequency, the degree of lymphopenia and the context of target antigen expression, are important parameters determining the time course and extent of the pathological consequences of CD8 T-cell-mediated autoimmunity. Furthermore, our data indicate that the pituitary gland is susceptible to CD8 autoimmunity following an inflammatory insult such as a viral infection. As lymphocytic hypophysitis may be manifest in other autoimmune conditions, and the pituitary gland may be susceptible to T-cell-mediated pathology after immunization with a virus expressing soluble pituitary antigen, it is important to consider that strategies based on vaccination against soluble pituitary gonadotrophins could have other unexpected endocrine consequences.

Expression of dual TCR on DO11.10 T cells allows for ovalbumin-induced oral tolerance to prevent T cell-mediated colitis directed against unrelated enteric bacterial antigens

The triggering Ag for inflammatory bowel disease and animal models of colitis is not known, but may include gut flora. Feeding OVA to DO11.10 mice with OVA-specific transgenic (Tg) TCR generates Ag-specific immunoregulatory CD4(+) T cells (Treg) cells. We examined the ability of oral Ag-induced Treg cells to suppress T cell-mediated colitis in mice. SCID-bg mice given DO11.10 CD4(+)CD45RB(high) T cells developed colitis, and cotransferring DO11.10 CD45RB(low)CD4(+) T cells prevented CD4(+)CD45RB(high) T cell-induced colitis in the absence of OVA. The induction and prevention of disease by DO11.10 CD4(+) T cell subsets were associated with an increase in endogenous TCRalpha chain expression on Tg T cells. Feeding OVA to SCID-bg mice reconstituted with DO11.10 CD4(+)CD45RB(high) attenuated the colitis in association with increased TGF-beta and IL-10 secretion, and decreased proliferative responses to both OVA and cecal bacteria Ag. OVA feeding also attenuated colitis in SCID-bg mice reconstituted with a mix of BALB/c and DO11.10 CD45RB(high) T cells, suggesting that OVA-induced Treg cells suppressed BALB/c effector cells. The expression of endogenous non-Tg TCR allowed for DO11.10-derived T cells to respond to enteric flora Ag. Furthermore, feeding OVA-induced Treg cells prevented colitis by inducing tolerance in both OVA-reactive and non-OVA-reactive T cells and by inducing Ag-nonspecific Treg cells. Such a mechanism might allow for Ag-nonspecific modulation of intestinal inflammation in inflammatory bowel disease.

Antigen presentation by keratinocytes directs autoimmune skin disease

The antigen-presenting cells that initiate and maintain MHC class II-associated organ-specific autoimmune diseases are poorly defined. We now describe a new T cell antigen receptor (TCR) transgenic (Tg) model of inflammatory skin disease in which keratinocytes activate and are the primary target of autoreactive CD4(+) T cells. We previously generated keratin 14 (K14)-A(beta)b mice expressing MHC class II only on thymic cortical epithelium. CD4(+) T cells from K14-A(beta)b mice fail to undergo negative selection and thus have significant autoreactivity. The TCR genes from an autoreactive K14-A(beta)b CD4 hybridoma were cloned to produce a TCR Tg mouse, 2-2-3. 2-2-3 TCR Tg cells are negatively selected in WT C57BL6 mice but not in 2-2-3K14-A(beta)b mice. Interestingly, a significant number of mice that express both the K14-A(beta)b transgene and the autoreactive 2-2-3 TCR spontaneously develop inflammatory skin disease with mononuclear infiltrates, induction of MHC class II expression on keratinocytes, and T helper 1 cytokines. Disease can be induced by skin inflammation but not solely by activation of T cells. Thus, cutaneous immunopathology can be directed through antigen presentation by tissue-resident keratinocytes to autoreactive TCR Tg CD4(+) cells.

Dual receptor T cells extend the immune repertoire for foreign antigens

Since the discovery of T cells that express two T cell receptors (TCRs), termed dual TCR cells, most studies have focused on their autoimmune potential, while their beneficial roles remained elusive. We identified, in normal mice, dual TCR cells that participated in the immune response to a foreign antigen. Unlike single TCR cells, dual TCR cells used the nonselected TCR to respond in the periphery, but relied on coexpression of a second TCR for intrathymic selection. We found that they were selected at low frequency in the naïve repertoire, but dominated the response to antigen through clonal expansion. Thus, dual TCR cells can extend the TCR repertoire for foreign antigens by rescuing functional TCRs that cannot be selected on single TCR cells; they can, therefore, benefit the immune system.

Presented antigen from damaged pancreatic beta cells activates autoreactive T cells in virus-mediated autoimmune diabetes

The induction of autoimmunity by viruses has been attributed to numerous mechanisms. In mice, coxsackievirus B4 (CB4) induces insulin-dependent diabetes mellitus (IDDM) resembling the final step of disease progression in humans. The immune response following the viral insult clearly precipitates IDDM. However, the molecular pathway between viral infection and the subsequent activation of T cells specific for islet antigen has not been elucidated. These T cells could become activated through exposure to sequestered antigens released by damaged beta cells, or they could have responded to factors secreted by the inflammatory response itself. To distinguish between these possibilities, we treated mice harboring a diabetogenic T cell repertoire with either the islet-damaging agent streptozotocin (STZ) or poly I:C, which nonspecifically activates T cells. Significantly, only treatment of mice with STZ resulted in IDDM and mimicked the effects observed following CB4 infection. Furthermore, antigen-presenting cells from STZ-treated mice were shown to directly activate autoreactive T cells and induce diabetes. Therefore, the primary role of CB4 in the precipitation of IDDM is to damage tissue, causing release and presentation of sequestered islet antigen. These events stimulate autoreactive T cells and thereby initiate disease.

Dual TCR-expressing T lymphocytes in health and disease

The authors briefly review recent experimental advances in elucidating the role of dual T cell receptor (TCR)-expressing lymphocytes in the development of diseases with special emphasis on autoimmunity. Moreover, they summarize present knowledge about these cells concerning their proportion among peripheral blood mononuclear cells, their functionality, and their impact on allorecognition and memory both in humans and in mice. Finally, they describe disease-associated clonal expansions of dual TCR-expressing cells in humans, most of which have been observed in peripheral T cell malignancies. Other cases occurred in inflammatory bowel disease and in HIV infection. They propose that expression of two distinct TCR on malignant T lymphocytes might be much higher than is suggested by the few cases described so far, and that their presence might impinge on therapeutic immunization strategies which make use of the TCR itself as a target.

Autoreactive isotype-specific T cells determine B cell frequency

Suppressive activities involving T-B and T-T cell interactions are important to maintain immune system homeostasis. Negative control of IgG2ab+ B cells by anti-IgG2ab T cells derived from Igha mice has been well documented. Nevertheless the real contribution of anti-IgG2ab T cells, endogenously matured in Ighb mice, in controlling IgG2ab+ B cell function has never been investigated. We previously generated anti-IgG2ab TCR-transgenic mice and showed that transgenic T cells were not deleted in the thymus and that they were responsible for a complete and chronic IgG2ab suppression. Here we show that T cells expressing high density of anti-IgG2ab TCR were positively selected in the thymus with a higher efficiency in animals expressing IgG2ab, reached peripheral lymphoid organs and negatively controlled IgG2ab serum levels. Moreover, anti-IgG2ab T cells transgenic for the single TCR chain, thus undergoing normal rearrangements and normal processes of selection, also reached the periphery and suppressed IgG2ab. Interestingly, concentration of IgG2ab in serum inversely correlated with the peripheral frequency of Ig-specific T cells. Finally, T cells able to suppress IgG2ab were obtained from Ighb non-transgenic mice, indicating that anti-2ab T cells are naturally present in the periphery of Ighb animals. We propose that IgG2ab-specific T cells contribute to determine IgG2ab serum levels in Ighb mice.

Transfer of specificity for human immunodeficiency virus type 1 into primary human T lymphocytes by introduction of T-cell receptor genes

The introduction of genes encoding T-cell receptor (TCR) chains specific for human immunodeficiency virus into T cells of infected patients represents a means to quantitatively and qualitatively improve immunity to the virus. Our results demonstrate that the high level of TCR expression required for physiologic functioning can be reproducibly achieved with retroviral vectors encoding full-length unmodified TCR chains under the control of a strong internal constitutive phosphoglycerate kinase promoter.

Repertoire requirements of CD4+ T cells that prevent spontaneous autoimmune encephalomyelitis

Spontaneous experimental autoimmune encephalomyelitis arises in 100% of mice exclusively harboring myelin basic protein-specific T cells, and can be prevented by a single injection of CD4+ T cells obtained from normal donors. Given the powerful regulatory effect of the transferred T cells, we further investigated their properties, and, in particular, their repertoire requirements. Transfer of monoclonal OVA-specific CD4+ T cells did not confer protection from disease even when present at very high proportions (about 80% of total lymphocytes). Lack of protection was also evident after immunization of these animals with OVA, indicating that not just any postthymic CD4+ T cells has the potential to become regulatory. However, protection was conferred by cells bearing limited TCR diversity, including cells expressing a single Valpha4 TCR chain or cells lacking N nucleotides. We also investigated whether coexpression of the myelin basic protein-specific TCR with another TCR in a single cell would alter either pathogenesis or regulation. This was not the case, as myelin basic protein-specific/OVA-specific recombinase activating gene-1-/- double TCR transgenic mice still developed experimental autoimmune encephalomyelitis spontaneously even after immunization with OVA. Based on this evidence, we conclude that CD4+ T regulatory cells do not express canonical TCRs and that the altered signaling properties brought about by coexpression of two TCRs are not sufficient for the generation of regulatory T cells. Instead, our results indicate that regulatory T cells belong to a population displaying wide TCR diversity, but in which TCR specificity is central to their protective function.