Paradoxical inhibition of T-cell function in response to CTLA-4 blockade; heterogeneity within the human T-cell population

The association between PD-1 gene polymorphisms and susceptibility to multiple sclerosis

Programmed cell death 1 (PD-1) is an immune checkpoint and has been reported to be associated with several autoimmune diseases. We aimed to investigate the association between human PD-1 gene (PDCD1) polymorphisms and multiple sclerosis (MS). This case-control study was conducted on 229 MS patients and 246 healthy controls. Genotyping of rs36084323 (PD-1.1 G/A), rs11568821 (PD-1.3 G/A) and rs2227981 (PD-1.5 C/T) polymorphisms was performed by PCR-RFLP technique. The frequency difference of PD-1.1 genotypes and alleles (-536 G/A) between patients and healthy controls was not significant. Regarding PD-1.3, the AA + AG genotype was found to be relatively higher in the control group. Concerning PD-1.5 (+7785 C/T), the frequency of T allele carriers (TT + CT) was relatively higher in MS patients, which was marginally insignificant (p = .07). PD-1 gene polymorphisms may be associated with MS; however, accurate conclusions require further studies with a larger number of samples.

Onset of Pyoderma Gangrenosum in Patients on Biologic Therapies: A Systematic Review

OBJECTIVE

To summarize clinical outcomes of paradoxical pyoderma gangrenosum (PG) onset in patients on biologic therapy.

METHODS

The authors conducted MEDLINE and EMBASE searches using PRISMA guidelines to include 57 patients (23 reports).

RESULTS

Of the included patients, 71.9% (n = 41/57) noted PG onset after initiating rituximab, 21.1% (n = 12/57) noted tumor necrosis factor α (TNF-α) inhibitors, 5.3% (n = 3/57) reported interleukin 17A inhibitors, and 1.8% (n = 1/57) reported cytotoxic T-lymphocyte-associated protein 4 antibodies. The majority of patients (94.3%) discontinued biologic use. The most common medications used to resolve rituximab-associated PG were intravenous immunoglobulins, oral corticosteroids, and antibiotics, with an average resolution time of 3.3 months. Complete resolution of PG in TNF-α-associated cases occurred within an average of 2.2 months after switching to another TNF-α inhibitor (n = 1), an interleukin 12/23 inhibitor (n = 2), or treatment with systemic corticosteroids and cyclosporine (n = 3), systemic corticosteroids alone (n = 1), or cyclosporine alone (n = 1).

CONCLUSIONS

Further investigations are warranted to determine whether PG onset is associated with underlying comorbidities, the use of biologic agents, or a synergistic effect. Nevertheless, PG may develop in patients on rituximab or TNF-α inhibitors, suggesting the need to monitor and treat such adverse effects.

T cell costimulation, checkpoint inhibitors and anti-tumor therapy

The hallmarks of the adaptive immune response are specificity and memory. The cellular response is mediated by T cells which express cell surface T cell receptors (TCRs) that recognize peptide antigens in complex with major histocompatibility complex (MHC) molecules on antigen presenting cells (APCs). However, binding of cognate TCRs with MHC-peptide complexes alone (signal 1) does not trigger optimal T cell activation. In addition to signal 1, the binding of positive and negative costimulatory receptors to their ligands modulates T cell activation. This complex signaling network prevents aberrant activation of T cells. CD28 is the main positive costimulatory receptor on naı¨ve T cells; upon activation, CTLA4 is induced but reduces T cell activation. Further studies led to the identification of additional negative costimulatory receptors known as checkpoints, e.g. PD1. This review chronicles the basic studies in T cell costimulation that led to the discovery of checkpoint inhibitors, i.e. antibodies to negative costimulatory receptors (e.g. CTLA4 and PD1) which reduce tumor growth. This discovery has been recognized with the award of the 2018 Nobel prize in Physiology/Medicine. This review highlights the structural and functional roles of costimulatory receptors, the mechanisms by which checkpoint inhibitors work, the challenges encountered and future prospects.

Cytotoxic T-Lymphocyte-Associated Antigen 4 (CTLA-4)- and Programmed Death 1 (PD-1)-Mediated Regulation of Monofunctional and Dual Functional CD4+ and CD8+ T-Cell Responses in a Chronic Helminth Infection

Chronic helminth infections are known to be associated with the modulation of antigen-specific T-cell responses. Strongyloides stercoralis infection is characterized by the downmodulation of antigen-specific Th1 and Th17 responses and the upregulation of Th2 and Th9 responses. Immune homeostasis is partially maintained by negative regulators of T-cell activation, cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and programmed death 1 (PD-1), which dampen effector responses during chronic infections. However, their roles in S. stercoralis infection are yet to be defined. Therefore, we sought to determine the role of CTLA-4 and PD-1 in regulating CD4⁺ and CD8⁺ T-cell responses and examined the frequencies of monofunctional and dual functional Th1/T cytotoxic type 1 (Tc1), Th17/Tc17, Th2/Tc2, and Th9/Tc9 cells in S. stercoralis infection in 15 infected individuals stimulated with parasite antigen following CTLA-4 or PD-1 blockade. Our data reveal that CTLA-4 or PD-1 blockade results in significantly enhanced frequencies of monofunctional and dual functional Th1/Tc1 and Th17/Tc17 cells and, in contrast, diminishes the frequencies of monofunctional and dual functional Th2/Tc2 and Th9/Tc9 cells with parasite antigen stimulation in whole-blood cultures. Thus, we demonstrate that CTLA-4 and PD-1 limit the induction of particular T-cell subsets in S. stercoralis infection, which suggests the importance of CTLA-4 and PD-1 in immune modulation in a chronic helminth infection.

Association between rs3087243 and rs231775 polymorphism within the cytotoxic T-lymphocyte antigen 4 gene and Graves' disease: a case/control study combined with meta-analyses

We conducted a case/control study to assess the impact of SNP rs3087243 and rs231775 within the CTLA4 gene, on the susceptibility to Graves' disease (GD) in a Chinese Han dataset (271 cases and 298 controls). The frequency of G allele for rs3087243 and rs231775 was observed to be significantly higher in subjects with GD than in control subjects (p = 0.005 and p = 0.000, respectively). After logistic regression analysis, a significant association was detected between SNP rs3087243 and GD in the additive and recessive models. Similarly, association for the SNP rs231775 could also be detected in the additive model, dominant model and recessive model. A meta-analysis, including 27 published datasets along with the current dataset, was performed to further confirm the association. Consistent with our case/control results, rs3087243 and rs231775 showed a significant association with GD in all genetic models. Of note, ethnic stratification revealed that these two SNPs were associated with susceptibility to GD in populations of both Asian and European descent. In conclusion, our data support that the rs3087243 and rs231775 polymorphisms within the CTLA4 gene confer genetic susceptibility to GD.

Impaired function of CTLA-4 in the lungs of patients with chronic beryllium disease contributes to persistent inflammation

Chronic beryllium disease (CBD) is an occupational lung disorder characterized by granulomatous inflammation and the accumulation of beryllium-responsive CD4(+) T cells in the lung. These differentiated effector memory T cells secrete IL-2, IFN-γ, and TNF-α upon in vitro activation. Beryllium-responsive CD4(+) T cells in the lung are CD28 independent and have increased expression of the coinhibitory receptor, programmed death 1, resulting in Ag-specific T cells that proliferate poorly yet retain the ability to express Th1-type cytokines. To further investigate the role of coinhibitory receptors in the beryllium-induced immune response, we examined the expression of CTLA-4 in blood and bronchoalveolar lavage cells from subjects with CBD. CTLA-4 expression was elevated on CD4(+) T cells from the lungs of study subjects compared with blood. Furthermore, CTLA-4 expression was greatest in the beryllium-responsive subset of CD4(+) T cells that retained the ability to proliferate and express IL-2. Functional assays show that the induction of CTLA-4 signaling in blood cells inhibited beryllium-induced T cell proliferation while having no effect on the proliferative capacity of beryllium-responsive CD4(+) T cells in the lung. Collectively, our findings suggest a dysfunctional CTLA-4 pathway in the lung and its potential contribution to the persistent inflammatory response that characterizes CBD.

IgG Fab fragments forming bivalent complexes by a conformational mechanism that is reversible by osmolytes

Generated by proteolytic cleavage of immunoglobulin, Fab fragments possess great promise as blocking reagents, able to bind receptors or other targets without inducing cross-linking. However, aggregation of Fab preparations is a common occurrence, which generates intrinsic stimulatory capacity and thwarts signal blockade strategies. Using a panel of biochemical approaches, including size exclusion chromatography, SDS-PAGE, mass spectrometry, and cell stimulation followed by flow cytometry, we have measured the oligomerization and acquisition of stimulatory capacity that occurs in four monoclonal IgG Fabs specific for TCR/CD3. Unexpectedly, we observed that all Fabs spontaneously formed complexes that were precisely bivalent, and these bivalent complexes possessed most of the stimulatory activity of each Fab preparation. Fabs composing bivalent complexes were more susceptible to proteolysis than monovalent Fabs, indicating a difference in conformation between the Fabs involved in these two different states of valency. Because osmolytes represent a class of compounds that stabilize protein folding and conformation, we sought to determine the extent to which the amino acid osmolyte l-proline might impact bivalent Fab complexation. We found that l-proline (i) inhibited the adoption of the conformation associated with bivalent complexation, (ii) preserved Fab monovalency, (iii) reversed the conformation of preformed bivalent Fabs to that of monovalent Fabs, and (iv) separated a significant percentage of preformed bivalent complexes into monovalent species. Thus, Fab fragments can adopt a conformation that is compatible with folding or packing of a bivalent complex in a process that can be inhibited by osmolytes.

Therapeutic approaches to multiple sclerosis: an update on failed, interrupted, or inconclusive trials of immunomodulatory treatment strategies

Multiple sclerosis (MS) continues to be a therapeutic challenge, and much effort is being made to develop new and more effective immune therapies. Particularly in the past decade, neuroimmunologic research has delivered new and highly effective therapeutic options, as seen in the growing number of immunotherapeutic agents and biologics in development. However, numerous promising clinical trials have failed to show efficacy or have had to be halted prematurely because of unexpected adverse events. Some others have shown results that are of unknown significance with regard to a reliable assessment of true efficacy versus safety. For example, studies of the highly innovative monoclonal antibodies that selectively target immunologic effector molecules have not only revealed the impressive efficacy of such treatments, they have also raised serious concerns about the safety profiles of these antibodies. These results add a new dimension to the estimation of risk-benefit ratios regarding acute or long-term adverse effects. Therapeutic approaches that have previously failed in MS have indicated that there are discrepancies between theoretical expectations and practical outcomes of different compounds. Learning from these defeats helps to optimize future study designs and to reduce the risks to patients. This review summarizes trials on MS treatments since 2001 that failed or were interrupted, attempts to analyze the underlying reasons for failure, and discusses the implications for our current view of MS pathogenesis, clinical practice, and design of future studies. In order to maintain clarity, this review focuses on anti-inflammatory therapies and does not include studies on already approved and effective disease-modifying therapies, albeit used in distinct administration routes or under different paradigms. Neuroprotective and alternative treatment strategies are presented elsewhere.

Autologous MUC1-specific Th1 effector cell immunotherapy induces differential levels of systemic TReg cell subpopulations that result in increased ovarian cancer patient survival

Adoptive T cell immunotherapy using autologous lymphocytes is a viable treatment for patients with cancer and requires participation of Ag-specific CD4 and CD8 T cells. Here, we assessed the immunotherapeutic effects of autologous MUC1 peptide-stimulated CD4(+) effector cells following adoptive transfer in patients with ovarian cancer. Using MUC1 peptide and IL-2 for ex vivo CD4(+)/Th1 effector cell generation, we show that three monthly treatment cycles of peripheral blood T cell restimulation and intraperitoneal re-infusion selectively modulated endogenous T cell-mediated immune responses that correlated with diminished serum CA125 tumor marker levels and enhanced patient survival. One patient remains disease-free, another patient survived long-term for nearly 16 months with recurrent disease and two patients expired within 3-5 months following final infusion. Although PBL from all patients showed elevated MUC1 cytolytic activity following therapy, such responses did not correlate with therapeutic efficacy. Long-term survivors showed elevated levels of systemic memory (CD45RO) and naïve (CD45RA) CD3/CD4/CD25(+) T cells when compared to that of pre-treatment levels and similarly treated short-term survivors. Such cells co-expressed different levels of Foxp3 and CTLA-4 that resulted in progressively lower systemic Foxp3/CTLA-4 memory T cell ratios that further correlated with disease-free survival. Lastly, these patients showed elevated levels of MUC1-specific T cells expressing the CCR5 and CCR1 chemokine receptors and the chemokine CCL4 associated with Th1 cell differentiation/memory. We suggest that effective immunotherapy with autologous MUC1-stimulated CD4(+) effector cells induces differential levels of systemic "Ag-experienced" and "Ag-inexperienced" CD4/CD25(+) TReg cell subpopulations that influence long-term tumor immunity in ovarian cancer patients.

Autoimmunity risk alleles in costimulation pathways

SUMMARY

The basis for susceptibility to common autoimmune diseases is a complex interplay between multiple genetic and environmental risk factors. We have now entered a new generation of genetic study designs which has not only furthered our understanding of the individual mechanisms involved in the common human autoimmune diseases but also has pointed towards common pathways. In this review we focus on costimulatory mechanisms with the most convincing association results in large collections of patients and control subjects. These include the genes encoding cytotoxic T-lymphocyte antigen-4, CD58, CD40, inducible T-cell costimulator ligand, CD244, CD226, tumor necrosis factor (TNF) (ligand) superfamily member 4, TNF superfamily member 15, and programmed cell death 1. The unbiased genome-wide association scans suggest that indeed immune related genes underlie the pathogenesis of human autoimmune disease with common involvement of costimulatory pathways. The identification of allelic variants associated with disease risk followed by understanding their functional outcomes and affected pathways provides a rationale approach for drug design.

Astrocytic regulation of human monocytic/microglial activation

Recent reports have described reduced immunological responsiveness and stimulatory capacity among monocytes/microglia that infiltrate malignant human gliomas. Herein, we demonstrate that culture of ex vivo human monocytes or primary human microglia with tumor cells isolated from glioblastoma multiforme (GBM) specimens renders them tolerogenic, capable of suppressing the function of ex vivo monocytes in the absence of tumor cells or their soluble factors. We demonstrate that the tolerance induced in monocytes/microglia by GBM tumor cells is not associated with interference with the signaling cascade associated with TLR- or CD40-induced monocyte activation. Rather, these tumor cells appear to up-regulate pathways that antagonize positive signaling pathways, including but not limited to STAT3 and STAT5. Finally, we demonstrate that the tolerogenic properties of GBM tumor cells amplify properties inherent to nontransformed astrocytes. Future studies that identify all of the molecular mechanisms by which astrocytes and malignant gliomas suppress monocyte/microglial function will have dual therapeutic benefits: suppressing these pathways may benefit patients with astrocytic tumors, while enhancing them may benefit patients with autoimmune processes within the CNS, such as multiple sclerosis.

Intracellular concentrations of Ca(2+) modulate the strength of signal and alter the outcomes of cytotoxic T-lymphocyte antigen-4 (CD152)-CD80/CD86 interactions in CD4(+) T lymphocytes

The costimulatory receptors CD28 and cytotoxic T-lymphocyte antigen (CTLA)-4 and their ligands, CD80 and CD86, are expressed on T lymphocytes; however, their functional roles during T cell-T cell interactions are not well known. The consequences of blocking CTLA-4-CD80/CD86 interactions on purified mouse CD4(+) T cells were studied in the context of the strength of signal (SOS). CD4(+) T cells were activated with phorbol 12-myristate 13-acetate (PMA) and different concentrations of a Ca(2+) ionophore, Ionomycin (I), or a sarcoplasmic Ca(2+) ATPase inhibitor, Thapsigargin (TG). Increasing concentrations of I or TG increased the amount of interleukin (IL)-2, reflecting the conversion of a low to a high SOS. During activation with PMA and low amounts of I, intracellular concentrations of calcium ([Ca(2+)](i)) were greatly reduced upon CTLA-4-CD80/CD86 blockade. Further experiments demonstrated that CTLA-4-CD80/CD86 interactions reduced cell cycling upon activation with PMA and high amounts of I or TG (high SOS) but the opposite occurred with PMA and low amounts of I or TG (low SOS). These results were confirmed by surface T-cell receptor (TCR)-CD3 signalling using a low SOS, for example soluble anti-CD3, or a high SOS, for example plate-bound anti-CD3. Also, CTLA-4-CD80/CD86 interactions enhanced the generation of reactive oxygen species (ROS). Studies with catalase revealed that H(2)O(2) was required for IL-2 production and cell cycle progression during activation with a low SOS. However, the high amounts of ROS produced during activation with a high SOS reduced cell cycle progression. Taken together, these results indicate that [Ca(2+)](i) and ROS play important roles in the modulation of T-cell responses by CTLA-4-CD80/CD86 interactions.

Lack of B7 expression, not human leukocyte antigen expression, facilitates immune evasion by human malignant gliomas

OBJECTIVE

Lack of human leukocyte antigens and costimulatory molecules have been suggested as mechanisms by which human malignant gliomas avoid immune recognition and elimination.

METHODS

Using quantitative multiparameter flow cytometric analysis, tumor cells from patients with glioblastoma multiforme (n = 18) were examined ex vivo for the expression of human leukocyte antigen Class I and II molecules and the costimulatory molecules B7-1 and B7-2. They were compared with reactive astrocytes from peritumoral brain metastases (n = 7), and astrocytes removed during nontumor surgery (n = 5).

RESULTS

In contrast to the vast majority of solid peripheral human tumors, these results demonstrate that glioblastoma multiforme frequently express both human leukocyte antigen Class I and II molecules. Like most solid peripheral tumors, glioblastoma multiforme tumor cells express few or no B7 costimulatory molecules. Functional assays using heterogeneous ex vivo tumor preparations or pure populations of ex vivo tumor cells and microglia obtained using fluorescence-activated cell sorting indicate that CD4+ T-cells are activated by tumor cells only in the presence of exogenous B7 costimulation (provided by addition of soluble agonist anti-CD28 monoclonal antibody).

CONCLUSION

Thus, in contrast to many solid peripheral tumors, failure to present tumor antigens is not a likely impediment to immunotherapeutic strategies against malignant gliomas. Rather, immunotherapeutic strategies need to overcome low levels of B7 costimulation.

Up-Regulation of Gene Related to Anergy in Lymphocytes Is Associated with Notch-Mediated Human T Cell Suppression

A growing body of literature indicates that the Notch pathway can influence the activation and differentiation of peripheral murine T cells, though comparatively little is known about the effects of Notch signaling in human T cells. In the present report we demonstrate that Jagged-1-induced Notch signaling (using immobilized Jagged-1 fusion protein) during stimulation of purified human CD4+ and CD8+ T cells potently inhibits T cell proliferation and effector function, including both Th1- and Th2-associated cytokines. Inhibition of T cell activation is not due to apoptosis or disruption of proximal TCR signaling, but is associated with up-regulation of GRAIL (gene related to anergy in lymphocytes) in CD4+ T cells, with modest effects on other E3 ubiquitin ligases such as c-Cbl and Itch. When evaluated for its effects on CD4+ T cell differentiation, Jagged-1-mediated signaling inhibits T cell cytokine secretion with no significant effect on proliferative responses. Collectively, these data demonstrate that Notch signaling in human T cells induced by Jagged-1 promotes a novel form of T cell hyporesponsiveness that differs from anergy, whereby primary T cell proliferation and cytokine secretion are potently inhibited, and effector function but not proliferative capacity are ameliorated upon secondary stimulation.

A molecular perspective of CTLA-4 function

Within the paradigm of the two-signal model of lymphocyte activation, the interest in costimulation has witnessed a remarkable emergence in the past few years with the discovery of a large array of molecules that can serve this role, including some with an inhibitory function. Interest has been further enhanced by the realization of these molecules' potential as targets to modulate clinical immune responses. Although the therapeutic translation of mechanistic knowledge in costimulatory molecules has been relatively straightforward, the capacity to target their inhibitory counterparts has remained limited. This limited capacity is particularly apparent in the case of the cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), a major negative regulator of T cell responses. Because there have been several previous comprehensive reviews on the function of this molecule, we focus here on the physiological implications of its structural features. Such an exercise may ultimately help us to design immunotherapeutic agents that target CTLA-4.

CD80 cytoplasmic domain controls localization of CD28, CTLA-4, and protein kinase Ctheta in the immunological synapse

The binding of costimulatory ligand CD80 to CD28 or CTLA-4 on T cells plays an important role in the regulation of the T cell response. We have examined the role of the cytoplasmic domain of CD80 in murine T cell costimulation and its organization in the immunological synapse (IS). Removal of CD80 cytoplasmic tail decreased its effectiveness in costimulating T cell proliferative response and early IL-2 production in response to agonist MHC-peptide complexes. Immunofluorescent study showed a decreased tailless CD80 accumulation in the IS of naive T cells. The two forms of CD80 accumulated differently at the IS; the tailless CD80 was colocalized with the TCR whereas the full-length CD80 was segregated from the TCR. In addition, we showed that CD80, CD28, and protein kinase Ctheta colocalized in the presence or absence of the CD80 cytoplasmic tail. Thus, the cytoplasmic tail of CD80 regulates its spatial localization at the IS and that of its receptors and T cell signaling molecules such as protein kinase Ctheta, and thereby facilitates full T cell activation.

A PD-1 polymorphism is associated with disease progression in multiple sclerosis

T cells are considered to play a pivotal role in orchestrating the self-reactive immune responses in multiple sclerosis (MS). Programmed death 1 (PD-1) is a member of the B7/CD28 superfamily of costimulatory molecules exerting inhibitory functions on T cells. Recently, an intronic 7146G/A polymorphism within the PD-1 gene was described and suggested to be associated with autoimmunity. We investigated whether this genetic polymorphism is a genetic modifier for risk and progression of MS. Blood samples from 939 German MS patients (mean age, 39 years; range, 13-71; 566 patients [60%] with relapsing-remitting MS, 279 (30%) with secondary, and 94 (10%) with primary progressive MS) and 272 healthy white controls were tested. Genotyping was performed by polymerase chain reaction and restriction enzyme digestion; results were confirmed by automatic sequencing. A significant association of the mutated allele with a progressive disease course was detected (44% 7146G vs 56% 7146A, chi(2) p = 0.002). Consequences of the PD-1 mutation for T-cell function were assessed ex vivo in some patients using microsphere-stimulated peripheral blood lymphocytes and purified CD4 cells. Importantly, PD-1-mediated inhibition of T-cell cytokine secretion (interferon-gamma) is impaired in patients carrying the PD-1 polymorphism. In conclusion, our data suggest that PD-1 polymorphism is a genetic modifier of the progression of MS, possibly through inducing a partial defect in PD-1-mediated inhibition of T-cell activation.

Human CTLA4 knock-in mice unravel the quantitative link between tumor immunity and autoimmunity induced by anti-CTLA-4 antibodies

Although results from preclinical studies in animal models have proven the concept for use of anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) antibodies in cancer immunotherapy, 2 major obstacles have hindered their successful application for human cancer therapy. First, the lack of in vitro correlates of the antitumor effect of the antibodies makes it difficult to screen for the most efficacious antibody by in vitro analysis. Second, significant autoimmune side effects have been observed in a recent clinical trial. In order to address these 2 issues, we have generated human CTLA4 gene knock-in mice and used them to compare a panel of anti-human CTLA-4 antibodies for their ability to induce tumor rejection and autoimmunity. Surprisingly, while all antibodies induced protection against cancer and demonstrated some autoimmune side effects, the antibody that induced the strongest protection also induced the least autoimmune side effects. These results demonstrate that autoimmune disease does not quantitatively correlate with cancer immunity. Our approach may be generally applicable to the development of human therapeutic antibodies.

CT60 single nucleotide polymorphisms of the cytotoxic T-lymphocyte-associated antigen-4 gene region is associated with Graves' disease in an Italian population

Graves' disease (GD) is an autoimmune and polygenic disorder. Several studies have shown that human leukocyte antigen (HLA) class II and the cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) gene are involved in the genetic susceptibility. We performed a case control study on 150 patients with GD and 301 controls, matched for age and gender, to verify the association of three polymorphisms located in CTLA-4 region (A49G, [AT](n)-3'UTR, and CT60) and of HLA-DRB1 and DQB1 loci with the disease in an Italian population. The prevalence of patients with GD carrying the G allele of CT60 was significantly higher compared to control subjects (p = 0.02, odds ratio [OR] = 1.82). The allelic frequency of the G allele of CT60 was also significantly higher in patients with GD (p = 0.02). The G allele frequency of A49G in patients was significantly higher compared to control subjects (p = 0.04). The 280 allele phenotype frequency of (AT)(n)-3'UTR was also significantly higher in patients (p = 0.04). The G allele of A49G, the G allele of CT60, and the 280 allele of (AT)(n)-3'UTR microsatellite were significantly increased in patients with GD with thyroid-associated ophthalmopathy (TAO) compared to controls (p = 0.04, p = 0.03, and p = 0.02, respectively), however, we did not find any significant difference between TAO and non-TAO patients. We also found the HLA-DRB1*03 allele to be associated with GD; interestingly, the association of the CTLA-4 markers was independent from the HLA DRB1*03 status. These results highlight the role of the CTLA-4 locus, in addition to HLA, in the susceptibility to GD. Inside the CTLA-4 region, CT60 appears to be the most associated polymorphism to GD, however, further studies are needed to identify the etiologic variant.

Anti–human CTLA-4 monoclonal antibody promotes T-cell expansion and immunity in a hu-PBL-SCID model: a new method for preclinical screening of costimulatory monoclonal antibodies

When adopting basic principles learned in mice to clinical application in humans, it is often difficult to distinguish whether a “translation” fails because of an invalid target in the human disease or because the therapeutic agents are not optimal for the human target. It is, therefore, desirable to develop preclinical models to optimize therapies for human targets using in vivo settings. Although anti–mouse CTLA-4 antibodies are known to enhance immune responses in vivo, their effect on T-cell activation in vitro ranges from enhancement to inhibition. Here we use the hu-PBL-SCID mouse model of Epstein-Barr virus (EBV)–associated lymphoma development to screen a panel of anti–human CTLA-4 monoclonal antibodies (mAbs) for their effect on human lymphocytes in an in vivo “humanized” environment. We report significant heterogeneity of anti–human CTLA-4 mAbs in enhancing the expansion of human T cells in mice, and this heterogeneity cannot be attributed to immunoglobulin isotypes or affinity for CTLA-4. These data validate the development of additional screening tools, such as the one described, to further characterize functional activity of antihuman antibodies before proceeding with clinical translation to human studies.

Interferon-beta enhances monocyte and dendritic cell expression of B7-H1 (PD-L1), a strong inhibitor of autologous T-cell activation: relevance for the immune modulatory effect in multiple sclerosis

Antigen-presenting cells (APC) are considered to play a critical role in promoting the (re)activation of potentially autoreactive T cells in multiple sclerosis (MS), an inflammatory demyelinating disorder of the central nervous system (CNS). B7-H1 (PD-L1) is a novel member of the B7 family proteins which exert costimulatory and immune regulatory functions. Here we characterize the expression and functional activity of B7-H1 expressed on monocytes and dendritic cells (DC) of healthy donors and MS patients. B7-H1 is constitutively expressed on monocytes and differentially matured DC, but not on B cells. IFN-beta, the principle immune modulatory agent used for the treatment of MS, strongly enhances B7-H1 expression on monocytes and semi-matured DC, but not B cells, in vitro. Importantly, B7-H1 expressed on APC strongly inhibits autologous CD4 T-cell activation. Neutralization of B7-H1 on monocytes or differentially matured monocyte-derived DC markedly increases the secretion of the pro-inflammatory cytokines, IFN-gamma and IL-2, T-cell proliferation, and the expression of T-cell activation markers. B7-H1 exhibits strong inhibitory effects when expressed on monocytes, immature or semi-mature DC, but less so when expressed on fully matured DC. B7-H1-dependent immune inhibition is in part mediated by CD4/CD25+ regulatory T cells. There is no difference in the baseline expression levels of monocytic B7-H1 between untreated MS patients and healthy donors. However, both groups show a significant concentration-dependent up-regulation of B7-H1 mRNA and protein in response to IFN-beta in vitro. Serial measurements of B7-H1 mRNA in MS patients before and 6 months after initiation of IFN-beta therapy corroborated the relevance of these results in vivo: Nine of nine patients showed a significant increase in B7-H1 mRNA levels after 6 months of IFN-beta therapy (median 1.04 vs. 8.78; p<0.05, two-sided t-test). Accordingly, protein expression of B7-H1 on monocytes was up-regulated after 24 h of IFN-beta application. In summary, B7-H1 expressed on APC acts as a strong inhibitor of autologous CD4 T-cell activation and may thus contribute to the maintenance of peripheral immune tolerance. IFN-beta up-regulates B7-H1 in vitro and in MS patients in vivo and might represent a novel mechanism how IFN-beta acts as a negative modulator on APC T-cell interactions in the periphery.

The initiation of the autoimmune response in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). Most evidence supports the autoimmune pathogenesis of the disease. According to this hypothesis, the activation of autoreactive T-cells is a central event in the development of autoimmune response in MS. We examined molecular events involved in the initiation of autoimmune response in MS. Recent studies in our laboratory have reported an unexpectedly high degree of T-cell receptor (TCR) degeneracy and molecular mimicry as a frequent phenomenon that might play a role in the initiation of autoimmune response in MS. This paper provides insights into the physiologic and pathologic role of autoreactive T-cells, and characterizes structurally and functionally the specific targets for new therapies of MS.

Diversity of Clonal T Cell Proliferation Is Mediated by Differential Expression of CD152 (CTLA-4) on the Cell Surface of Activated Individual T Lymphocytes

Inhibitory effects of CD152 (CTLA-4) engagement during T cell activation have been described. To date, such effects could only be correlated to CD152 expression at the population level because expression of CD152 on the cell surface is too low to be assessed by conventional immunofluorescence on the single cell level. In this study, we use magnetofluorescent liposomes for the immunofluorescent detection of surface CD152-expressing CD4(+) T cells and show that, despite the fact that nearly all cells express intracellular CD152, only a fraction of 12% of activated T cells expresses surface CD152 at any given time point. Surface CD152(+) T cells appear with similar kinetics after primary or secondary activation in vitro. However, the frequency of surface CD152(+) T cells 48 h postactivation is 2-fold higher during secondary activation. Surface expression of CD152 is independent of the proliferative history of an activated T cell. Instruction of T cells for surface expression of CD152 rather depends on the time elapsed since the onset of activation, with a maximum at 48 h, and requires less than 12 h of Ag exposure. CD152(-) T cells, when isolated by cell sorting and restimulated, continue to proliferate. CD152 blockade has no effect on their proliferation. Isolated surface CD152(+) T cells do not proliferate upon restimulation unless CD152 is blocked. CD152 thus acts directly and autonomously on individual activated and proliferating T lymphocytes. Due to its heterogeneous expression on the cell surface of activated Th cells, CD152 might diversify the T cell response.

Duplication of primate and rodent B7-H3 immunoglobulin V- and C-like domains: divergent history of functional redundancy and exon loss

B7-H3 is a novel protein structurally related to the B7 family of ligands by the presence of a single set of immunoglobulin-V-like and immunoglobulin-C-like (VC) domains. By multiplex PCR, the dominantly expressed form of human B7-H3 was found to be a splice variant containing tandemly duplicated VC domains (VCVC). In contrast, mouse B7-H3 cDNA contained only one single VC form due to an exon structure corresponding to V-(pseudoexon C)-(pseudoexon V)-C. Comparisons of human, monkey, mouse, and hamster genomic B7-H3 reveal that primates, but not rodents, exhibited a higher degree of intramolecular sequence similarity between VC duplications than between molecules. Both VC and VCVC forms of human B7-H3 inhibited CD4(+) T cell proliferation and downregulated cytokine production upon TCR activation. These results suggest independent, but convergent, paths of B7-H3 active domain duplication followed by divergent histories of exon degeneration in rodents and exon maintenance by humans.

The genetics of autoimmune endocrine disease

The common autoimmune endocrinopathies result from an interaction between environmental factors and genetic predisposition. Several chromosomal gene regions have been shown to contribute to more than one disease, supporting the clinical observation that the autoimmune endocrine diseases cluster within individuals and families. Genetic studies have implicated the major histocompatability complex (MHC)-human leucocyte antigen (HLA) genes on chromosome 6p21, although this chromosomal region does not explain all of the genetic contribution to the various disorders. Non-MHC-HLA genes, including disease-specific loci, are beginning to be identified and the publication of the draft sequence of the human genome will undoubtedly expediate future discoveries. Combined with the establishment of large cohorts of subjects with disease and the development of technology capable of performing high-throughput genotyping, genetic studies are likely to impact on the future treatment and prevention of the common autoimmune endocrine diseases.

Disease-modifying therapies in multiple sclerosis: an update on recent and ongoing trials and future strategies

Multiple sclerosis (MS) is the prototype inflammatory autoimmune disorder of the central nervous system and the most common cause of neurological disability in young adults exhibiting considerable clinical, radiological and pathological heterogeneity. Novel insights in the immunopathological processes, advances in biotechnology, development of powerful magnetic resonance imaging technologies together with improvements in clinical trial design led to a variety of evaluable therapeutic approaches. Therapy has changed dramatically over the past decade, yielding significant progress for the treatment of relapsing-remitting and secondary progressive MS. A substantial number of pivotal and preliminary reports continue to demonstrate encouraging new evidence that advances are being made in the care of MS patients. This review summarises recent progress with currently available disease-modifying therapies and - on the basis of present immunopathogenetic concepts - outlines ongoing studies as well as future treatment strategies.

CTLA-4 in filarial infections: implications for a role in diminished T cell reactivity

To determine the role that CTLA-4 might play in mediating the diminished parasite Ag-specific T cell responsiveness that is characteristically seen in filaria-infected patients, several study populations and methods were used. First, quantitative assessment of mRNA expression determined that PBMC from uninfected adolescents exposed in utero to microfilarial (Mf) Ag demonstrated a strong up-regulation of CTLA-4 to the Mf stage of the parasite in contrast to that observed in cells from children born of uninfected mothers (p = 0.005). Next, the frequency of CTLA-4 expression was examined using flow cytometry in cells from filaria-infected and -uninfected individuals ex vivo. Individuals born in filarial endemic regions of the world (with long-standing infections) had greater percentages of CD4(+)CTLA-4(+) cells than did expatriate infected or uninfected individuals (p = 0.005 and 0.05, respectively); in addition, Mf(+) patients demonstrated higher frequencies of CD4(+)CTLA-4(+) and CD8(+)CTLA-4(+) cells (p = 0.027 and 0.037, respectively) than did Mf(-) infected individuals. Of interest, the greatest intensity of CTLA-4 expression occurred in CD4(+)CD25(+) cells, a population purported to include suppressor cells. Finally, in vitro blocking of CTLA-4 expression in PBMC from filaria-infected individuals induced a mean increase of 44% in IL-5 production to Mf Ag, whereas there was a concurrent mean decrease of 42% in IFN-gamma production, suggesting that CTLA-4 also acts to alter the Th1/Th2 balance in filaria-infected individuals. Together, these data indicate a significant role for CTLA-4 in regulating the host response to filarial infections and that factors such as length of exposure and patency are important codeterminants.

CTLA4 is associated with susceptibility to multiple sclerosis

We comprehensively screened CTLA4 for novel genetic variations in patients with MS. We studied genetic variations by association methods in a population-based sample of 122 sporadic patients with MS and 244 age-, gender- and ethnicity-matched controls, and by linkage and family-based association methods in 395 individuals from 59 American multiplex pedigrees with 141 affected individuals. Being homozygous for AT(8) (common) allele of the 3'(514) microsatellite (OR: 1.69; CI: 0.99-2.86) and for the common 5'(318)*C/E1(49)*A/3'(514*AT(8) haplotype (OR: 1.96; CI: 1.13-3.39) was associated with increased susceptibility to MS in Olmsted County. The genotype frequencies of other individual polymorphisms were not significantly different between cases and controls. A pooled analysis of association studies revealed an odds ratio of 1.28 (95% CI: 1.01-1.63; p=0.043) for 5'(-318)*C homozygotes and 1.28 (95% CI: 1.08-1.51; p=0.005) for the 3'(514)*AT(8) allele. We did not detect linkage with MS susceptibility in multiplex families. We did not find a strong association with age at onset, disease course or severity. CTLA-4 is associated with susceptibility to MS.

B7-CTLA4 interaction promotes cognate destruction of tumor cells by cytotoxic T lymphocytes in vivo

Costimulatory molecules B7-1 and B7-2 (hereby collectively called B7) interact with CD28 and CTLA4 on T cells and promote antitumor immunity. The function of B7-CTLA4 interaction in antitumor CTL response remains controversial. Here we used CD28(-/-) and CD28(+/-) or CD28(+/+) transgenic mice that express the T-cell receptor specific for an unmutated tumor antigen, P1A, and for tumor cells expressing a CTLA4-specific B7 mutant to evaluate the function of CD28-B7 and CTLA4-B7 interactions in induction and effector phases of antitumor immunity. We report that B7-CD28 and B7-CTLA4 interactions promote tumor rejection. However, this is achieved by distinct mechanisms. B7-CD28 interaction enhances T-cell clonal expansion, though a role for this interaction in the effector phase cannot be ruled out. In contrast, B7-CTLA4 interaction enhances the CTL-mediated destruction of tumors, but not T-cell clonal expansion.

GAD65-reactive T cells are activated in patients with autoimmune type 1a diabetes

Insulin-dependent type 1 diabetes is an autoimmune disease mediated by T lymphocytes recognizing pancreatic islet cell antigens. Glutamic acid decarboxylase 65 (GAD65) appears to be an important autoantigen in the disease. However, T cells from both patients with type 1 diabetes and healthy subjects vigorously proliferate in response to GAD65 stimulation ex vivo, leading us to postulate that the critical event in the onset of human diabetes is the activation of autoreactive T cells. Thus, we investigated whether GAD65-reactive T cells in patients with diabetes functioned as previously activated memory T cells, no longer requiring a second, costimulatory signal for clonal expansion. We found that in patients with new-onset type 1 diabetes, GAD65-reactive T cells were strikingly less dependent on CD28 and B7-1 costimulation to enter into cell cycle and proliferate than were equivalent cells derived from healthy controls. We hypothesize that these autoreactive T cells have been activated in vivo and have differentiated into memory cells, suggesting a pathogenic role in type 1 diabetes. In addition, we observed different effects with selective blockade of either B7-1 or B7-2 molecules; B7-1 appears to deliver a negative signal by engaging CTLA-4, while B7-2 engagement of CD28 upregulates T cell proliferation and cytokine secretion.

CD4(+) and CD8(+) anergic T cells induced by interleukin-10-treated human dendritic cells display antigen-specific suppressor activity

Interleukin-10 (IL-10)-treated dendritic cells (DCs) induce an alloantigen- or peptide-specific anergy in various CD4(+) and CD8(+) T-cell populations. In the present study, we analyzed whether these anergic T cells are able to regulate antigen-specific immunity. Coculture experiments revealed that alloantigen-specific anergic CD4(+) and CD8(+) T cells suppressed proliferation of syngeneic T cells in a dose-dependent manner. The same effect was observed when the hemagglutinin-specific CD4(+) T-cell clone HA1.7 or tyrosinase-specific CD8(+) T cells were cocultured with anergic T cells of the same specificity. Anergic T cells did not induce an antigen-independent bystander inhibition. Suppression was dependent on cell-to-cell contact between anergic and responder T cells, required activation by antigen-loaded DCs, and was not mediated by supernatants of anergic T cells. Furthermore, anergic T cells displayed an increased extracellular and intracellular expression of cytotoxic T-lymphocyte antigen (CTLA)-4 molecules, and blocking of the CTLA-4 pathway restored the T-cell proliferation up to 70%, indicating an important role of the CTLA-4 molecule in the suppressor activity of anergic T cells. Taken together, our experiments demonstrate that anergic T cells induced by IL-10-treated DCs are able to suppress activation and function of T cells in an antigen-specific manner. Induction of anergic T cells might be exploited therapeutically for suppression of cellular immune responses in allergic or autoimmune diseases with identified (auto) antigens.

Influence of specimen age and use of different negative controls in determination of intracytoplasmic levels of cytokines after whole-blood culture assay

Intracytoplasmic detection of cytokines by flow cytometry has become a powerful tool in the characterization of cytokine-producing cells. However, it is not known to what extent specimen age and the use of various negative controls may influence the amount of cytokine-positive cells. We therefore compared different times of storage and the use of several negative controls in the determination of intracytoplasmic levels of cytokines. There was a substantial decline of interleukin-2- and gamma interferon-positive lymphocytes after 20 h and especially after 48 h of storage. The precision of intracytoplasmic interleukin-6 determination decreases after long-term storage compared to 2 h of storage, whereas the amount of interleukin-8-positive monocytes remained rather stable. Therefore, we recommend performing the analysis as fast as possible after the blood sample is drawn. Under consideration of isotype-matched antibodies and nonstimulated cells as negative controls instead of the purified antibody-blocking control, strikingly higher amounts of interleukin-2-, gamma interferon, interleukin-6-, and interleukin-8-positive cells were found. For a meaningful interpretation of data these differences have to be kept in mind. Further studies should evaluate the exact specificity of these controls.

Dual effect of CD85/leukocyte Ig-like receptor-1/Ig-like transcript 2 and CD152 (CTLA-4) on cytokine production by antigen-stimulated human T cells

The functional outcome of a T cell response to Ag is the result of a balance between coactivation and inhibitory signals. In this study we have investigated the effects of the CD85/leukocyte Ig-like receptor (LIR)-1/Ig-like transcript (ILT) 2 and of CD152 (CTLA-4) inhibitory receptors on the modulation of cell-mediated immune responses to specific Ags, both at the effector and at the resting/memory cell level. Proliferation and cytokine production of CD4+ T lymphocytes stimulated by recall Ags have been evaluated. Cross-linking of CD85/LIR-1/ILT2 or CD152 molecules on cultured T cells using specific mAb and goat anti-mouse antiserum inhibits Ag-specific T cell proliferation. This inhibition is always paralleled by increased production of cytokines that down-regulate immune responses, e.g., IL-10 and TGF-beta. In contrast, the production of cytokines that support T cell expansion and function (e.g., IL-2, IFN-gamma, and IL-13) is significantly decreased. A long-term effect of CD85/LIR-1/ILT2 and of CD152 occurs during Ag-specific T cell activation and expansion. T cells, primed in the presence of anti-CD85/LIR-1/ILT2 and anti-CD152 blocking mAb (but in the absence of cross-linking), proliferate at higher rates and produce higher amounts of IL-2, IFN-gamma, and IL-13, in comparison with T cells stimulated with the Ag alone. We also show that the inhibitory receptors exert a similar effect during Ag activation of specific CD4+ effector T cells. Ag-specific polyclonal CD4+ T cell lines exhibit increased proliferation and IL-2, IFN-gamma, and IL-13 production when the CD85/LIR-1/ILT2 receptor is blocked by specific mAb. In contrast, cross-linking of this receptor down-regulates Ag-specific CD4+ T cell proliferation and increases IL-10 and TGF-beta production.

CD4+CD28- costimulation-independent T cells in multiple sclerosis

Multiple lines of evidence suggest that CD4+ lymphocytes initiate autoimmune responses against myelin antigens in multiple sclerosis (MS). The increased frequency of activated myelin-specific cells in MS patients indicates that the activation of autoreactive cells represents a central event in the pathogenesis of the disease. We identified a CD4+ subpopulation that is characterized phenotypically by the persistent absence of surface CD28 expression and functionally by CD28-independent activation and Th1 cytokine secretion. Owing to their costimulation-independent activation and their expression of a full agonist signaling activation pattern, CD4+CD28- cells have the potential to initiate autoimmune responses in the central nervous system, a compartment devoid of professional antigen presenting cells. Long-term memory CD4+CD28- cells produce high amounts of IFN-gamma and maximally upregulate IFN-gamma and IL-12Rbeta2 chain expression in the absence of costimulation. They exhibit prominent growth characteristics and increased survival after activation, likely related to their persistent lack of CTLA-4 surface expression. The CD4+CD28- population is expanded in a subgroup of MS patients. Myelin basic protein-specific cells detected in this cell subset may play an important role in the inflammatory response within the central nervous system.

Signaling through CD28 and CTLA-4 controls two distinct forms of T cell anergy

Primary T cell proliferative responses to TCR ligation plus CD28 costimulation are surprisingly heterogeneous. Many cells that enter G1 fail to progress further through the cell cycle, and some of these cells subsequently fail to divide upon restimulation, even in the presence of IL-2. Such IL-2-refractory anergy is distinct from the IL-2-reversible anergy induced by TCR occupancy in the absence of CD28 costimulation. Here, we focus on the contributions of cell cycle progression and costimulatory (CD28/CTLA-4) signals in the regulation of anergy. We show that CD28 costimulation is not sufficient for anergy avoidance and that activated T cells must progress through the cell cycle in order to escape anergy. Induction of this "division-arrest" form of anergy requires CTLA-4 signaling during the primary response. Also, cell division per se is not sufficient for anergy avoidance: the few T cells that undergo multiple rounds of cell division during overt CD28 costimulatory blockade do not escape the ultimate induction of clonal anergy. Anergy avoidance by primary T cells is thus a multistep process: in order to participate in a productive immune response, an individual T cell activated through its antigen receptor must receive CD28 costimulation and progress through the cell cycle. Anergy may be induced either through a combination of CTLA-4 signaling and the failure of cell cycle progression, or through a proliferation-independent mechanism in which TCR ligation occurs in the absence of CD28.

Role of CD47 in the induction of human naive T cell anergy

We recently reported that CD47 ligation inhibited IL-2 release by umbilical cord blood mononuclear cells activated in the presence of IL-12, but not IL-4, preventing the induction of IL-12Rbeta(2) expression and the acquisition of Th1, but not the Th2 phenotype. Here we show that in the absence of exogenous cytokine at priming, CD47 ligation of umbilical cord blood mononuclear cells promotes the development of hyporesponsive T cells. Naive cells were treated with CD47 mAb for 3 days, expanded in IL-2 for 9-12 days, and restimulated by CD3 and CD28 coengagement. Effector T cells generated under these conditions were considered to be anergic because they produced a reduced amount of IL-2 at the single-cell level and displayed an impaired capacity 1) to proliferate, 2) to secrete Th1/Th2 cytokines, and 3) to respond to IL-2, IL-4, or IL-12. Moreover, CD47 mAb strongly suppressed IL-2 production and IL-2Ralpha expression in primary cultures and IL-2 response of activated naive T cells. Induction of anergy by CD47 mAb was IL-10 independent, whereas inclusion of IL-2 and IL-4, but not IL-7, at priming fully restored T cell activation. Furthermore, CD28 costimulation prevented induction of anergy. Thus, CD47 may represent a potential target to induce anergy and prevent undesired Th0/Th1 responses such as graft vs host diseases, allograft rejection, or autoimmune diseases.

CD4+CD25high regulatory cells in human peripheral blood

Thymectomy in mice on neonatal day 3 leads to the development of multiorgan autoimmune disease due to loss of a CD(+)CD25(+) T cell regulatory population in their peripheral lymphoid tissues. Here, we report the identification of a CD4(+) population of regulatory T cells in the circulation of humans expressing high levels of CD25 that exhibit in vitro characteristics identical with those of the CD4(+)CD25(+) regulatory cells isolated in mice. With TCR cross-linking, CD4(+)CD25(high) cells did not proliferate but instead totally inhibited proliferation and cytokine secretion by activated CD4(+)CD25(-) responder T cells in a contact-dependent manner. The CD4(+)CD25(high) regulatory T cells expressed high levels of CD45RO but not CD45RA, akin to the expression of CD45RB(low) on murine CD4(+)CD25(+) regulatory cells. Increasing the strength of signal by providing either costimulation with CD28 cross-linking or the addition of IL-2 to a maximal anti-CD3 stimulus resulted in a modest induction of proliferation and the loss of observable suppression in cocultures of CD4(+)CD25(high) regulatory cells and CD4(+)CD25(-) responder cells. Whereas higher ratios of CD4(+)CD25(high) T cells are required to suppress proliferation if the PD-L1 receptor is blocked, regulatory cell function is shown to persist in the absence of the PD-1/PD-L1 or CTLA-4/B7 pathway. Thus, regulatory CD4 T cells expressing high levels of the IL-2 receptor are present in humans, providing the opportunity to determine whether alterations of these populations of T cells are involved in the induction of human autoimmune disorders.

Association of CTLA-4 but not CD28 gene polymorphisms with systemic lupus erythematosus in the Japanese population

OBJECTIVE

Systemic lupus erythematosus (SLE) in a multisystem autoimmune disorder characterized by multiorgan pathology and autoantibodies against a variety of autoantigens. The CD28 and CTLA-4 genes might be candidate genes for SLE, because costimulation signals from CD80/CD86 to CD28/CTLA-4 have been suggested to play an important role in the activation or inactivation of T lymphocytes.

METHODS

We investigated three polymorphic regions within the CTLA-4 gene, a C/T base exchange in the promoter region -318 (CTLA-4 -318C/T), an A/G substitution in the exon 1 position 49 (CTLA-4 49A/G), an (AT)(n) repeat polymorphism in the 3' untranslated region of exon 4 [CTLA-4 3' (AT)(n)], and a CD28 gene polymorphism, a T/C substitution in the intron 3 position +17 (CD28 IVS3+17T/C), in SLE patients and controls.

RESULTS

SLE patients had significantly higher frequencies of the CTLA-4 49G allele (P=0.003) and of the CTLA-4 (AT)(n) 106 bp allele (P=0.0008) than controls. We also found a strong linkage disequilibrium between the A allele of CTLA-4 49A/G and the 86 bp allele of CTLA-4 3' (AT)(n). On the contrary, no association was found between SLE and CTLA-4 -318C/T or CD28 IVS3 +17T/C.

CONCLUSION

We conclude that the CTLA-4 gene appears to play a significant role in the development of SLE in the Japanese population.

CTLA-4 blockade enhances the CTL responses to the p53 self-tumor antigen

p53 is an attractive target for cancer immunotherapy because it is overexpressed in a high proportion of many different types of tumors. However, it is also expressed in normal tissues and acts as a toleragen in vivo. Previously, detailed examination of the repertoire specific for the murine p53(261-269) epitope in conventional and p53-deficient mice demonstrated that because of expression of p53, the CD8(+) T cells that respond to this epitope express low-affinity TCRs. It has been reported that tolerance to tumor Ags can be broken by in vivo administration of anti-CTLA-4 mAb. With the goal of overriding tolerance and achieving optimal activation of p53-specific CTL, the current study has assessed the effect of anti-CTLA-4 mAb on the p53-specific repertoire. It was found that blockade of CTLA-4 engagement at the time of antigenic stimulation induced a vigorous amplification of the CTL responses to p53 as well as proportionate expansion of the memory T cell pool. This effect was dependent on the presence of CD4(+) T cell help and correlated with an enhancement of helper function. However, anti-CTLA-4 treatment did not enhance the avidity of the resultant p53-specific CTL populations and, therefore, could not reverse this important consequence of tolerance.

Analysis of the expression of critical activation/interaction markers on peripheral blood T cells in B-cell chronic lymphocytic leukaemia: evidence of immune dysregulation

B-cell chronic lymphocytic leukaemia (B-CLL) is characterized by an accumulation of clonal malignant B cells. The intrinsic characteristics that permit this accumulation have been extensively studied and described. However, it is possible that proliferation and survival of this malignant clone is facilitated by a disruption in the interaction between B and T cells that normally regulate the immune system. In this study, using flow cytometry and cell culture techniques, marked abnormalities of the expression of certain key activation and interaction molecules on the peripheral blood T cells of patients with B-CLL were demonstrated. In particular, on comparison with normal controls, there was a marked reduction in the number of circulating T cells expressing CD25 (interleukin 2 receptor) (P = 0.007), CD28 (P = 0.01) and CD152 (CTLA-4) (P = 0.001). There was also a reduction in the number of circulating T cells expressing CD4 (P = 0.03), CD5 (P = 0.05) and CD11a (P = 0.01). There was no difference in the number expressing T-cell receptor alphabeta (P = 0.1), CD8 (P = 0.4), CD54 (P = 0.4) and CD154 (P = 0.5), and the only marker expressed on a greater number of circulating T cells in B-CLL patients was HLA-DR (P = 0.05). These results suggest that there is a profound T-cell dysregulation that may contribute to the survival of the malignant B cells in patients with B-CLL and to the related autoimmune phenomena of the disease.

Induction of hyporesponsiveness and impaired T lymphocyte activation by the CD31 receptor:ligand pathway in T cells

CD31 is a member of the Ig superfamily expressed on various cell types of the vasculature, including a certain subpopulation of T lymphocytes. Previous reports suggest that interaction of CD31 with its heterophilic ligand on T cells (T cell CD31 ligand) plays a regulatory role in T lymphocyte activation. Here we demonstrate that a soluble rCD31-receptorglobulin (CD31Rg) specifically down-regulated the proliferation of human peripheral blood CD31(-) T lymphocytes stimulated via CD3 and CD28 mAbs. Notably, engagement of the T cell CD31 ligand by CD31Rg during primary stimulation also induced a prolonged unresponsive state in T cells. Retroviral transduction of CD31 into CD31(-) Th clones resulted in a significant inhibition of their proliferative capacity. When cocultured with purified CD31(-) T lymphocytes, irradiated CD31-transduced Th clones counterregulated the CD3/CD28-mediated activation of these cells. Furthermore, primary stimulation in the presence of CD31-transduced Th clones induced a comparable state of hyporesponsiveness in the T cell responders as the soluble CD31Rg. Thus, by counterregulating the activation of cognate T lymphocytes, CD31-expressing T cells might contribute to the establishment and maintenance of peripheral tolerance.