Pathological Tau transmission initiated by binding lymphocyte-activation gene 3

The spread of prion-like protein aggregates is believed to be a common driver of pathogenesis in many neurodegenerative diseases. Accumulated tangles of filamentous Tau protein are considered pathogenic lesions of Alzheimer's disease (AD) and related Tauopathies, including progressive supranuclear palsy, and corticobasal degeneration. Tau pathologies in these illnesses exhibits a clear progressive and hierarchical spreading pattern that correlates with disease severity1,2. Clinical observation combined with complementary experimental studies3,4 have shown that Tau preformed fibrils (PFF) are prion-like seeds that propagate pathology by entering cells and templating misfolding and aggregation of endogenous Tau. While several receptors of Tau are known, they are not specific to the fibrillar form of Tau. Moreover, the underlying cellular mechanisms of Tau PFF spreading remains poorly understood. Here, we show that the lymphocyte-activation gene 3 (Lag3) is a cell surface receptor that binds to PFF, but not monomer, of Tau. Deletion of Lag3 or inhibition of Lag3 in primary cortical neurons significantly reduces the internalization of Tau PFF and subsequent Tau propagation and neuron-to-neuron transmission. Propagation of Tau pathology and behavioral deficits induced by injection of Tau PFF in the hippocampus and overlying cortex are attenuated in mice lacking Lag3 selectively in neurons. Our results identify neuronal Lag3 as a receptor of pathologic Tau in the brain, and for AD and related Tauopathies a therapeutic target.

Molecular Pathways and Mechanisms of LAG3 in Cancer Therapy

Immunotherapy targeting coinhibitory receptors has been highly successful in treating a wide variety of malignancies; however, only a subset of patients exhibits durable responses. The first FDA-approved immunotherapeutics targeting coinhibitory receptors PD1 and CTLA4, alone or in combination, significantly improved survival but were also accompanied by substantial toxicity in combination. The third FDA-approved immune checkpoint inhibitor targets LAG3, a coinhibitory receptor expressed on activated CD4+ and CD8+ T cells, especially in settings of long-term antigenic stimulation, such as chronic viral infection or cancer. Mechanistically, LAG3 expression limits both the expansion of activated T cells and the size of the memory pool, suggesting that LAG3 may be a promising target for immunotherapy. Importantly, the mechanism(s) by which LAG3 contributes to CD8+ T-cell exhaustion may be distinct from those governed by PD1, indicating that the combination of anti-LAG3 and anti-PD1 may synergistically enhance antitumor immunity. Clinical studies evaluating the role of anti-LAG3 in combination with anti-PD1 are underway, and recent phase III trial results in metastatic melanoma demonstrate both the efficacy and safety of this combination. Further ongoing clinical trials are evaluating this combination across multiple tumor types and the adjuvant setting, with accompanying translational and biomarker-focused studies designed to elucidate the molecular pathways that lead to improved antitumor T-cell responses following dual blockade of PD1 and LAG3. Overall, LAG3 plays an important role in limiting T-cell activation and has now become part of the repertoire of combinatorial immunotherapeutics available for the treatment of metastatic melanoma.

Abstract PD1-08: Esr1 mutant breast cancers show elevated basal cytokeratins and immune activation

Estrogen receptor alpha (ER/ESR1) is mutated in 30-40% of endocrine resistant ER-positive (ER+) breast cancer. ESR1 mutations cause ligand-independent growth and increased metastasis in vivo and in vitro. Despite the distinct clinical features and changes in therapeutic response associated with ESR1 mutations, there are no data about their potential role in intrinsic subtype switching.Applying five different luminal and basal gene set pairs derived from cell lines and tumors, ESR1 mutant cell models and clinical samples showed a significant enrichment of basal subtype markers. Among them, the six basal cytokeratins (BCKs) were the most enriched genes (KRT5/6A/6B/14/16/17) uniquely in ESR1 mutant cells but not other endocrine resistant cell models. BCKs were observed to heterogeneously express in a minor cell subpopulation in ESR1 mutant cell models and clinical specimens. ER ChIP-seq showed the mutant-specific induction of BCKs was independent of ER binding and instead selectively expressed in clones with low ER expression. In contrast, BCKs are associated with chromatin reprogramming centered around a progesterone receptor-orchestrated 154 kb insulated neighborhood at the KRT14/16/17 genomic region. Stronger CTCF binding was detected at the bases of chromatin loop in ESR1 mutant cells. Knockdown of progesterone receptor but not glucocorticoid receptor drastically blocked the induction of KRT14/16/17 in ESR1 mutant cells. Unexpectedly, high BCK expression in ER+ primary breast cancer is associated with good prognosis, and these tumors show enriched activation of a number of immune pathways, a distinctive feature shared with ESR1 mutant tumors. While the BCK-associated immune activation is not related to tumor mutation burdens, S100A8 and S100A9 were identified as the most highly induced immune mediators shared between high-BCKs ER+ and ESR1 mutant tumors, which was further validated in the plasma samples of a cohort of 18 patients with ER+ metastases (11 WT vs 7 mutant). Finally, single-cell RNA-seq analysis in an ER+ bone metastasis case inferred the involvement of S100A8 and S100A9 in paracrine crosstalk between epithelial and stromal cells, particularly macrophages and fibroblasts through TLR4 signaling. Collectively, these observations demonstrate that ESR1 mutant tumors gain basal features with induction of basal cytokeratins via epigenetic mechanisms in rare subpopulation of cells. This is associated with increased immune activation, encouraging additional studies of immune therapeutic vulnerabilities in ESR1 mutant tumors.

Citation Format: Zheqi Li, Yang Wu, Olivia Mcginn, Amir Bahreini, Nolan M. Priedigkeit, Kai Ding, Sayali Onkar, Carol A. Sartorius, Lori Miller, Margaret Rosenzweig, Nikhil Wagle, Jennifer K. Richer, William J. Muller, Laki Buluwela, Simak Ali, Dario A.A. Vignali, Yusi Fang, Li Zhu, George C. Tseng, Jason Gertz, Jennifer M. Atkinson, Adrian V. Lee, Steffi Oesterreich. Esr1 mutant breast cancers show elevated basal cytokeratins and immune activation [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD1-08.

Abstract PO-083: Utilizing spatial transcriptomics to elucidate tertiary lymphoid structure heterogeneity in human cancer

Blockade of the inhibitory PD1 pathway on CD8+ and CD4+ tumor infiltrating lymphocytes (TILs) has revolutionized standard of care for cancer patients. However, these approaches only benefit approximately 20% of cancer patients, thus a more comprehensive understanding of the immune response is paramount for the development of new therapeutic approaches and enhancement of the anti-tumor immune response. The presence of tertiary lymphoid structures (TLS) correlates with enhanced anti-tumor immunity and improved prognosis in several solid tumors. These ectopic lymphoid aggregates can exhibit features like secondary lymphoid organs (SLOs), including high endothelial venules, a T cell zone with mature dendritic cells (DCs), and a germinal center (GC) with follicular DCs and B cells, that facilitate the induction of immune responses in situ. Furthermore, the presence of TLS correlate with superior responses to immunotherapy and mature, GC-containing TLS correlate with increased T cell function in human tumors. However, current immunotherapies do not target TLS despite their predominance in the tumor microenvironment (TME) and key role in the adaptive immune response. Developing therapies that adequately induce TLS is limited by a lack of objective, bioinformatic analyses to elucidate the cellular and locational heterogeneity of TLS. TLS differences in composition are thought to define maturation levels i.e. early TLS have B and T cell aggregates but lack follicular DC and GC appear as the TLS mature. However, cellular composition is just one aspect of TLS heterogeneity. To successfully increase mature TLS in cancer patients for maximal humoral immunity, we must first understand the complete transcriptomic and proteomic profile of TLS in cancer patients. We have utilized the innovative Nanostring GeoMx platform to spatially interrogate the transcriptomics and proteomics associated with TLS. By pairing this technology with high level multispectral immunofluorescence via the Vectra Polaris system, we can link TLS heterogeneity to TLS position within the tumor. Further, we can analyze the complete activation profile of B and T cells to understand how TLS heterogeneity affects lymphocyte function. Our data have indicated that TLS can be linked to increased CD8+ T cell infiltrate and function. In fact, when mature TLS are not present, CD8+ T cell and Treg interactions increase, ultimately creating a more immunosuppressive TME. Lastly, utilizing a novel, robust bioinformatic pipeline, we have identified new genes that will aid in an objective definition of TLS. Specifically, CD27 is increased within TLS that are proximal to the tumor compared to those in the normal adjacent tissue. These studies will revolutionize the way in which TLS are defined within the TME, ultimately offering comprehensive gene and protein analysis of TLS that includes spatial geography of the structures and an unbiased, objective definition of TLS for future clinical utility and immunotherapeutic targeting.

Citation Format: Dongyan Liu, Xiang Li, Rajesh Acharya, Ernest M. Meyer, Shelley Reynolds, Ayana Ruffin, Robert L. Ferris, Dario A.A. Vignali, Riyue Bao, Tullia C. Bruno. Utilizing spatial transcriptomics to elucidate tertiary lymphoid structure heterogeneity in human cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-083.

Abstract PR06: Tumor-infiltrating B cells colocalize with CD4 T effector cells within tertiary lymphoid structures to present antigen and educate the antitumor immune response in human primary tumors

Despite the success of checkpoint blockade immunotherapies, i.e., anti-PD1, only 20% of patients produce a durable response to these treatments. Thus, a need exists to develop additional therapeutic strategies to treat these patients, which includes evaluation of other tumor-infiltrating immune cells that could further augment the CD8+ and CD4+ T-cell response. Tumor-infiltrating B cells (TIL-B) represent a possible target for immunotherapy due to their predominance in the tumor microenvironment and crucial role in the immune response. In fact, current evidence suggests an antitumor role for TIL-Bs. Specifically, detection of TIL-Bs within tertiary lymphoid structures (TLS) correlates with both increased survival in patients with solid tumors and enhanced response to anti-PD1 immunotherapy. We hypothesize that TIL-Bs help generate potent, long-term immune responses against cancer by presenting tumor antigens to CD4 TILs within TLS. Utilizing single-cell RNAseq and high-level flow cytometry, we observed increased numbers of activated TIL-Bs in the primary tumors of head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC) patients. We further assessed the location of TIL-Bs within the TME and determined that they predominantly sit adjacent to CD4+ tumor-infiltrating lymphocytes (TILs) within TLS. Thus, we generated an antigen presentation assay in vitro, and we observed increased CD4+ TIL responses when TIL-Bs presented autologous tumor antigens. Further, there was a differential impact on CD4+ TIL phenotype; specifically, if TIL-Bs were activated (CD27+), the CD4+ TILs were T helper (anti-tumor) CD4+ T cells and if the TIL-Bs were nonactivated (CD27-), the CD4+ TILs were T regulatory cells (protumor). These data suggest that TIL-Bs influence the phenotype and function of CD4+ TILs in patient tumors within TLS. Ultimately, results from this study will increase effective targeting of TIL-Bs within patient primary tumors.

Citation Format: Ayana T. Ruffin, Anthony R. Cillo, Sheryl Kunning, Robert L. Ferris, Dario A.A. Vignali, Tullia C. Bruno. Tumor-infiltrating B cells colocalize with CD4 T effector cells within tertiary lymphoid structures to present antigen and educate the antitumor immune response in human primary tumors [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr PR06.

Abstract IA17: Cellular interactions and regulatory mechanisms in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) arises through exposure to environment carcinogens or malignant transformation by human papilloma virus (HPV). Two studies will be discussed. First, we have performed transcriptional profiling of single cells from peripheral and intratumoral immune populations in HPV- and HPV+ HNSCC and healthy donors. We found a spectrum of transcriptional relationships from very similar to highly divergent between the tumor microenvironments (TME) in HPV- and HPV+ HNSCC. Our comprehensive survey of the TME in in HPV- and HPV+ HNSCC highlights the diversity of immune states and complexity of crosstalk between immune populations, and is a benchmark for analysis of the TME in human cancer. Second, many cancer patients do not develop a durable response to current standard of care immunotherapies despite substantial advances in targeting immune inhibitory receptors. A potentially important and unappreciated compounding issue, which may serve as a dominant resistance mechanism, is the inherent systemic immune dysfunction that is often associated with advanced cancer. Although this has been described for decades, primary mechanisms and drivers remain unknown. Lack of response to inhibitory receptor blockade therapy and increased disease burden has been associated with circulating, peripheral CD8+ T-cell exhaustion, which is defined by poor T-cell function linked to increased inhibitory receptor expression (PD1 or LAG3). Our recent studies have assessed if LAG3 and PD1 impact systemic T-cell function.

Citation Format: Dario A.A. Vignali. Cellular interactions and regulatory mechanisms in head and neck cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr IA17.

Abstract TMIM-063: TARGETING NEUROPILIN-1+ T REGULATORY CELLS IN PATIENTS WITH HIGH GRADE SEROUS OVARIAN CANCER DECREASES TREG-SPECIFIC SUPPRESSION OF CD8+ T CELLS

Regulatory T cells (Treg) are a subpopulation of CD4+ T cells that suppress autoimmune responses, but also prevent clearance of tumors and chronic viral infections. In high grades serous ovarian cancer, a higher frequency of tumor infiltrating (TIL) Treg are associated with poor prognosis, but mechanisms governing the suppressive activity of TIL Treg in this context are limited. Our group has recently described a signaling axis through neuropilin-1 (NRP1) on TIL Treg in murine models of cancer that promotes the survival and suppressive function of Treg. When NRP1 is specifically knocked out on murine TIL Treg, there is reduced tumor growth and increased survival similar to the complete knockout of TIL Tregs, however, without death from overt autoimmunity. Thus, NRP1 is a viable target to specifically reduce TIL Treg suppressive function in the tumor microenvironment (TME), ultimately leading to increased anti-tumor immunity without adverse events. Given the importance of NRP1+ TIL Treg in murine cancer models, we sought to understand the role of NRP1 on TIL Treg from patients with high grade serious ovarian cancer.

Surface and total NRP1 expression was assessed by flow cytometry on CD4+CD25+CD127loFOXP3+ Treg from healthy donor PBL and ovarian cancer TIL or ascites fluid. Total NRP1 was expressed on a median of 1.8% (interquartile range [IQR]: 0.69% to 4.8%) of Treg from healthy donors compared with a median of 66% (IQR: 28% to 90%; p<0.001) and 82% (IQR: 38% to 99%; p=0.004) of Treg from ovarian TIL and ascites, respectively. Surface NRP1 was detected on 0.1% (IQR: 0% to 1%) of Treg in PBL from healthy donors, compared with 11.1% (IQR: 1.1% to 60%; p=0.01) on ovarian TIL and 82% (IQR: 14% to 82%; p=0.0015) on ascites. Further, in comparing expression of NRP1 on Treg from benign ovarian disease and malignant ovarian tumors, there was a trend toward increased NRP1 expression on Tregs from malignant disease (median 9.3% versus 54.5%, respectively; p=0.044). Finally, NRP1+ TIL Treg isolated from primary tumors or ascites fluid were capable of suppressing CD8+ T cell proliferation in a dose-dependent manner and suppression was abrogated by addition of an anti-NRP1 antibody.

In summary, both surface and total NRP1 are expressed more frequently on Treg from TIL and ascites fluid compared to Treg from healthy donor PBL and NRP1+ Tregs in the TME are more suppressive compared to NRP1- Tregs. NRP1 is a viable target to reduce Treg suppressive function in ovarian cancer tumors, which can be immunologically ““cold””. This could ultimately lead to increased CD8+ T cell infiltration and function in these patient tumors, which could then increase responsiveness to anti-PD1 as it relies upon CD8 T cell infiltration to be effective.

Citation Format: Anthony R. Cillo, Christopher A. Chuckran, Mengting Liao, Francesmary Modugno, Robert Edwards, Lan Coffman, Dario A.A. Vignali, Tullia C. Bruno. TARGETING NEUROPILIN-1+ T REGULATORY CELLS IN PATIENTS WITH HIGH GRADE SEROUS OVARIAN CANCER DECREASES TREG-SPECIFIC SUPPRESSION OF CD8+ T CELLS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr TMIM-063.

Tumor infiltrating B cells co-localize with CD4 T effector cells within organized tertiary lymphoid structures to present antigen and educate the anti-tumor immune response in human primary tumors

Only 20% of cancer patients produce a durable response to current immunotherapies. Thus, a need exists to develop additional therapeutic strategies to treat these patients, which includes evaluation of other tumor infiltrating immune cells that could further augment the T cell response. Tumor infiltrating B cells (TIL-B) represent a possible target for immunotherapy due to their crucial role in the immune response. In fact, current data demonstrate that detection of TIL-Bs within tertiary lymphoid structures (TLS) correlate with increased survival in patients with solid tumors and enhanced response to anti-PD1 immunotherapy. We hypothesize that TIL-Bs help generate potent, long-term immune responses against cancer by presenting tumor antigens to CD4 TILs within TLS.

We observed increased numbers of activated TIL-Bs in the primary tumors of head and neck squamous cell carcinoma and non-small cell lung cancer patients. We further assessed the transcriptional signature and location of TIL-Bs within the TME and demonstrated that they are adjacent to Th1 and Tfh CD4+ tumor infiltrating lymphocytes (TILs) within organized, germinal center containing TLS. Further, we generated an antigen presentation assay in vitro, and we observed increased CD4+ TIL responses when TIL-Bs presented autologous tumor antigens. These data suggest that TIL-Bs influence the function of CD4+ TILs in patient tumors within TLS. Ultimately, results from this study will increase effective targeting of TIL-Bs within patient primary tumors.

Abstract A053: Activated B cells in human primary tumors present antigen and increase antitumor function of CD4 T-cells in tertiary lymphoid structures

Immunotherapy, specifically anti-PD1, has improved patient survival in a range of tumor types including head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC). Despite the success of anti-PD1 therapy, only 20% of patients produce a durable response to this treatment. Thus, a need exists to develop additional therapeutic strategies to treat these patients, which includes evaluation of other tumor-infiltrating immune cells that could further augment the CD8+ and CD4+ T-cell response. Tumor-infiltrating B cells (TIL-B) represent a possible target for immunotherapy due to their predominance in the tumor microenvironment (TME) and crucial role in the immune response. However, TIL-B function in cancer and in the context of immunotherapy has been understudied. In fact, conclusions on an anti- or protumor role for TIL-Bs in the TME is dependent on the study. However, in HNSCC and NSCLC patients, current evidence suggests an antitumor role for TIL-Bs. Specifically, detection of TIL-Bs within tertiary lymphoid structures (TLS) correlates with better prognosis. While TIL-Bs have been identified in HNSCC and NSCLC patients, their complete phenotypic signature and function in the TME has been understudied with no focus on their role as antigen presenting cells (APCs) and their influence on CD8+ and CD4+ tumor infiltrating lymphocytes (TILs). We hypothesize that TIL-Bs help generate potent, long-term immune responses against cancer by presenting tumor antigens to CD4 TILs within TLS.Using unmanipulated, primary human B cells from fresh tumor, we quantified and further characterized TIL-Bs in HNSCC and NSCLC utilizing single-cell RNAseq and multiparameter flow cytometry. We observed increased numbers of activated TIL-Bs in these primary tumors compared to other immune subsets, specifically CD27+ TIL-Bs. We further assessed the TIL-Bs by correlating phenotype of the TIL-B with its location in the TME, predominantly separating out differences between TIL-Bs within TLS and outside TLS. In addition, we generated a specific antigen presentation assay in vitro, and we observed three types of CD4+ TIL responses when TIL-Bs presented autologous tumor antigens. There were activated responder CD4+ TILs that proliferated when combined with TIL-Bs alone, which indicates stimulation with endogenous tumor antigens. There were antigen-associated responders that required exogenous autologous tumor lysate to elicit a CD4+ TIL response, and there were patient CD4 TILs that did not respond to antigen presentation by TIL-Bs. Within the activated and antigen-associated responders, the TIL-B phenotype influenced the CD4+ TIL phenotype; if the TIL-Bs were activated (CD27+), the CD4+ TILs were T helper (antitumor) CD4+ T-cells and if the TIL-Bs were non-activated (CD27-), the CD4+ TILs were T regulatory cells (protumor). These data suggest that TIL-Bs influence the phenotype and function of CD4+ TILs in patient tumors. In conclusion, activated TIL-Bs are increased in human primary tumors, they can present antigen to CD4+ TILs and influence their overall phenotype. Determining the complete activation signature of TIL-Bs in HNSCC and NSCLC patients will determine the extent of their antitumor function in these cancers. Comparison of TIL-Bs in HNSCC and NSCLC is important as there are not many unified studies on TIL-B function across tumor types. Further, because HNSCC has two etiologies (viral vs. carcinogen induced), we are able to better study the differential function of activated and nonactivated TIL-Bs in solid tumors. Ultimately, results from this study will help predict how to target TIL-B functions in future TIL-B-specific immunotherapies or in combination with current immunotherapies for HNSCC and NSCLC patients like blockade of the inhibitory receptor, PD-1.

Citation Format: Tullia C. Bruno, Ayana T. Ruffin, Anthony R. Cillo, Robert L. Ferris, Dario A.A. Vignali. Activated B cells in human primary tumors present antigen and increase antitumor function of CD4 T-cells in tertiary lymphoid structures [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A053.

TIM-1 signaling is required for maintenance and induction of regulatory B cells

Apart from their role in humoral immunity, B cells can exhibit IL-10-dependent regulatory activity (Bregs). These regulatory subpopulations have been shown to inhibit inflammation and allograft rejection. However, our understanding of Bregs has been hampered by their rarity, lack of a specific marker, and poor insight into their induction and maintenance. We previously demonstrated that T cell immunoglobulin mucin domain-1 (TIM-1) identifies over 70% of IL-10-producing B cells, irrespective of other markers. We now show that TIM-1 is the primary receptor responsible for Breg induction by apoptotic cells (ACs). However, B cells that express a mutant form of TIM-1 lacking the mucin domain (TIM-1(Δmucin) ) exhibit decreased phosphatidylserine binding and are unable to produce IL-10 in response to ACs or by specific ligation with anti-TIM-1. TIM-1(Δmucin) mice also exhibit accelerated allograft rejection, which appears to be due in part to their defect in both baseline and induced IL-10(+) Bregs, since a single transfer of WT TIM-1(+) B cells can restore long-term graft survival. These data suggest that TIM-1 signaling plays a direct role in Breg maintenance and induction both under physiological conditions (in response to ACs) and in response to therapy through TIM-1 ligation. Moreover, they directly demonstrate that the mucin domain regulates TIM-1 signaling.

Modulation of redox balance leaves murine diabetogenic TH1 T cells "LAG-3-ing" behind

Preventing activation of diabetogenic T cells is critical for delaying type 1 diabetes onset. The inhibitory molecule lymphocyte activation gene 3 (LAG-3) and metalloprotease tumor necrosis factor-α converting enzyme (TACE) work together to regulate TH1 responses. The aim of this study was to determine if regulating redox using a catalytic antioxidant (CA) could modulate TACE-mediated LAG-3 shedding to impede diabetogenic T-cell activation and progression to disease. A combination of in vitro experiments and in vivo analyses using NOD mouse strains was conducted to test the effect of redox modulation on LAG-3 shedding, TACE enzymatic function, and disease onset. Systemic treatment of NOD mice significantly delayed type 1 diabetes onset. Disease prevention correlated with decreased activation, proliferation, and effector function of diabetogenic T cells; reduced insulin-specific T-cell frequency; and enhanced LAG-3(+) cells. Redox modulation also affected TACE activation, diminishing LAG-3 cleavage. Furthermore, disease progression was monitored by measuring serum soluble LAG-3, which decreased in CA-treated mice. Therefore, affecting redox balance by CA treatment reduces the activation of diabetogenic T cells and impedes type 1 diabetes onset via decreasing T-cell effector function and LAG-3 cleavage. Moreover, soluble LAG-3 can serve as an early T-cell-specific biomarker for type 1 diabetes onset and immunomodulation.

Prevention of autoimmune diabetes by ectopic pancreatic β-cell expression of interleukin-35

Interleukin (IL)-35 is a newly identified inhibitory cytokine used by T regulatory cells to control T cell-driven immune responses. However, the therapeutic potential of native, biologically active IL-35 has not been fully examined. Expression of the heterodimeric IL-35 cytokine was targeted to β-cells via the rat insulin promoter (RIP) II. Autoimmune diabetes, insulitis, and the infiltrating cellular populations were analyzed. Ectopic expression of IL-35 by pancreatic β-cells led to substantial, long-term protection against autoimmune diabetes, despite limited intraislet IL-35 secretion. Nonobese diabetic RIP-IL35 transgenic mice exhibited decreased islet infiltration with substantial reductions in the number of CD4(+) and CD8(+) T cells, and frequency of glucose-6-phosphatase catalytic subunit-related protein-specific CD8(+) T cells. Although there were limited alterations in cytokine expression, the reduced T-cell numbers observed coincided with diminished T-cell proliferation and G1 arrest, hallmarks of IL-35 biological activity. These data present a proof of principle that IL-35 could be used as a potent inhibitor of autoimmune diabetes and implicate its potential therapeutic utility in the treatment of type 1 diabetes.

Loss of epigenetic modification driven by the Foxp3 transcription factor leads to regulatory T cell insufficiency

Regulatory T (Treg) cells, driven by the Foxp3 transcription factor, are responsible for limiting autoimmunity and chronic inflammation. We showed that a well-characterized Foxp3(gfp) reporter mouse, which expresses an N-terminal GFP-Foxp3 fusion protein, is a hypomorph that causes profoundly accelerated autoimmune diabetes on a NOD background. Although natural Treg cell development and in vitro function are not markedly altered in Foxp3(gfp) NOD and C57BL/6 mice, Treg cell function in inflammatory environments was perturbed and TGF-β-induced Treg cell development was reduced. Foxp3(gfp) was unable to interact with the histone acetyltransferase Tip60, the histone deacetylase HDAC7, and the Ikaros family zinc finger 4, Eos, which led to reduced Foxp3 acetylation and enhanced K48-linked polyubiquitylation. Collectively this results in an altered transcriptional landscape and reduced Foxp3-mediated gene repression, notably at the hallmark IL-2 promoter. Loss of controlled Foxp3-driven epigenetic modification leads to Treg cell insufficiency that enables autoimmunity in susceptible environments.

The development and function of regulatory T cells

Regulatory T cells (Tregs) are a critical subset of T cells that mediate peripheral tolerance. There are two types of Tregs: natural Tregs, which develop in the thymus, and induced Tregs, which are derived from naive CD4(+) T cells in the periphery. Tregs utilize a variety of mechanisms to suppress the immune response. While Tregs are critical for the peripheral maintenance of potential autoreactive T cells, they can also be detrimental by preventing effective anti-tumor responses and sterilizing immunity against pathogens. In this review, we will discuss the development of natural and induced Tregs as well as the role of Tregs in a variety of disease settings and the mechanisms they utilize for suppression.

On the dynamics of TCR:CD3 complex cell surface expression and downmodulation

TCR downmodulation following ligation by MHC:peptide complexes is considered to be a pivotal event in T cell activation. Here, we analyzed the dynamics of TCR:CD3 cell surface expression on resting and antigen-activated T cells. We show that the TCR:CD3 complex is very stable and is rapidly internalized and recycled in resting T cells. Surprisingly, the internalization rate is not increased following TCR ligation by MHC:peptide complexes, despite significant TCR downmodulation, suggesting that constitutive internalization rather than ligation-induced downmodulation serves as the force that drives serial ligation. Furthermore, TCR downmodulation is mediated by the intracellular retention of ligated complexes and degradation by lysosomes and proteasomes. Thus, our data demonstrate that ligation induces TCR downmodulation by preventing recycling rather than inducing internalization.

Multiplexed particle-based flow cytometric assays

Several methods have been developed to quantify soluble analytes in biological fluids and tissue culture samples, including bioassays, ELISA, RPA and PCR. However, each of these techniques possesses one or more significant limitations; ELISA will only measure one analyte as a time; PCR does not detect native protein. The recent development of particle-based flow cytometric assays has raised hopes that many of these limitations can be overcome. The technology utilizes microspheres as the solid support for a conventional immunoassay, affinity assay or DNA hybridization assay which are subsequently analyzed on a flow cytometer. Several multiplexed bead systems are currently marketed by different vendors. We have used the Luminex FlowMetrix system which consists of 64 different bead sets manufactured with uniform, distinct proportions of red and orange fluorescent dyes (detected by FL2/FL3 on a FACScan). Each bead set forms the basis of an individual assay using a green fluorescent reporter dye (FL1). This system facilitates the development of multiplexed assays that simultaneously measure many different analytes in a small sample volume. They can also be developed into rapid, 'no wash' assays that can be completed in <2 h. This review traces the historical association between microspheres and flow cytometry, the development and use of particle-based flow cytometric assays, how they compare with current assays and potential future developments of this very exciting technology.

Simultaneous quantitation of 15 cytokines using a multiplexed flow cytometric assay

Several methods have been developed to quantify cytokines and chemokines in biological fluids and tissue culture samples, including bioassays, enzyme-linked immunosorbent assay (ELISA), intracellular staining, ribonuclease protection assay (RPA) and polymerase chain reaction (PCR). However, each of these techniques possesses one or more significant limitations. Here, we describe a new multiplexed assay, using the FlowMetrix system, that can quantify multiple cytokines simultaneously in a small sample volume. This assay was found to be more accurate, sensitive and reproducible than the conventional microtitre ELISA procedure. Furthermore, the time and cost involved are comparable to, or less than, the ELISA. A key feature of the FlowMetrix assay is its ability to multiplex: here, we show that this assay can accurately quantitate 15 cytokines in a 100 microl sample volume while the same analysis by ELISA requires 1.5 ml (100 microl for each cytokine assay). By using this Flow Metrix assay, we could demonstrate that only T helper 1 (T(H)1)-deviated cells produce detectable levels of interleukin (IL)-2, while only T(H)2-deviated cells produce significant amounts of IL-4. Six other cytokines were produced by both T cell subsets, with the T(H)1 population producing more IL-3, granulocyte-monocyte colony stimulating factor (GM-CSF) and interferon (IFN)-gamma, and the T(H)2 population producing more IL-5, IL-10, and IL-13. Seven other cytokines were not produced in detectable amounts. This assay should prove to be a powerful tool in the quantitation of cytokines, or any other soluble product for which antibody pairs are available. It will also provide a more complete picture of the plethora of cytokines secreted during an immune response.

Differential CD3 zeta phosphorylation is not required for the induction of T cell antagonism by altered peptide ligands

T cells recognize foreign Ags in the form of short peptides bound to MHC molecules. Ligation of the TCR:CD3 complex gives rise to the generation of two tyrosine-phosphorylated forms of the CD3 zeta-chain, pp21 and pp23. Replacement of residues in MHC-bound peptides that alter its recognition by the TCR can generate altered peptide ligands (APL) that antagonize T cell responses to the original agonist peptide, leading to altered T cell function and anergy. This biological process has been linked to differential CD3zeta phosphorylation and generation of only the pp21 phospho-species. Here, we show that T cells expressing CD3zeta mutants, which cannot be phosphorylated, exhibit a 5-fold reduction in IL-2 production and a 30-fold reduction in sensitivity following stimulation with an agonist peptide. However, these T cells are still strongly antagonized by APL. These data demonstrate that: 1) the threshold required for an APL to block a response is much lower than for an agonist peptide to induce a response, 2) CD3zeta is required for full agonist but not antagonist responses, and 3) differential CD3zeta phosphorylation is not a prerequisite for T cell antagonism.

Profound enhancement of T cell activation mediated by the interaction between the TCR and the D3 domain of CD4

CD4 plays an important role in the activation and development of CD4+ T cells. This is mediated via its bivalent interaction with MHC class II molecules and the TCR:CD3 complex through p56lck. Recent studies have implicated a third site of interaction between the membrane-proximal extracellular domains of CD4 and the TCR. Due to these multiple interactions, direct evidence for the functional importance of this extracellular association has remained elusive. Furthermore, the residues that mediate this interaction are unknown. In this study, we analyzed the function of 61 CD4 mutants. Alanine substitution of just 2 residues, either Q114/F182 or F182/F201, which are partially buried and located close to the D2/D3 interface, completely abrogated CD4 function. Direct evidence for the functional importance of TCR:CD4.D3 interaction was obtained using an anti-CD3fos:anti-CD4jun-bispecific Ab. Surprisingly, it induced strong T cell activation in hybridomas transfected with cytoplasmic-tailless CD4, despite the lack of association with either p56lck or MHC class II molecules. However, this effect was completely abrogated with the CD4 mutants Q114A/F182A or F182A/F201A. These data demonstrate that TCR:CD4.D3 interaction can have a profound effect on T cell activation and obviates the need for receptor oligomerization.

Immunoregulation of Th cells by naturally processed peptide antagonists

Th cells recognize protein Ags as short peptides bound to MHC class II molecules. Altered peptide ligands can antagonize (inhibit) T cell responses to stimulatory peptides. Peptides generated by APC may contain peptide flanking residues (PFR), which lie outside the minimal binding epitope and can be recognized by the TCR. Our data show that PFR-dependent T cells were found to be potently antagonized by peptides that lack PFR and responded poorly to native protein or the immunogenic epitope delivered by a recombinant influenza virus. These data provide the first evidence that Ag processing generates both stimulatory and antagonist peptides from a single immunogenic epitope, an observation that may have important implications for T cell immunoregulation and autoimmunity.

T cell receptor recognition of MHC class II-bound peptide flanking residues enhances immunogenicity and results in altered TCR V region usage

Naturally processed MHC class II-bound peptides possess ragged NH2 and COOH termini. It is not known whether these peptide flanking residues (PFRs), which lie outside the MHC anchor residues, are recognized by the TCR or influence immunogenicity. Here we analyzed T cell responses to the COOH-terminal PFR of the H-2A(k) immunodominant epitope of hen egg lysozyme (HEL) 52-61. Surprisingly, the majority of T cells were completely dependent on, and specific for, the COOH-terminal PFR of the immunogen. In addition, there were striking correlations between TCR V beta usage and PFR dependence. We hypothesize that the V alpha CDR1 region recognizes NH2-terminal PFRs, while the V beta CDR1 region recognizes COOH-terminal PFRs. Last, peptides containing PFRs were considerably more immunogenic and mediated a greater recall response to the HEL protein. These results demonstrate that PFRs, which are a unique characteristic of peptides bound to MHC class II molecules, can have a profound effect on TCR recognition and T cell function. These data may have important implications for peptide-based immunotherapy and vaccine development.

TCR-mediated adhesion of T cell hybridomas to planar bilayers containing purified MHC class II/peptide complexes and receptor shedding during detachment

T cell recognition of foreign Ag/MHC class II complexes is sensitive down to approximately 100 complexes per cell or approximately 0.2 complexes/micron2. To better understand the physical basis of the recognition stage of Ag presentation, we examined adhesion of the lysozyme- specific T cell hybridoma, 3A9, to artificial bilayers containing covalent MHC class II/peptide complexes or adhesion molecules. Adhesion of 3A9 cells required a superphysiologic density of the MHC class II/peptide complex and was partly dependent on CD4; cells adhered but did not crawl. No adhesion was observed to bilayers containing MHC class II molecules without the lysozyme peptide. Activated 3A9 cells adhered and crawled on bilayers containing ICAM-1. The physical strength of contacts was tested with fluid shear. 3A9 cells adherent to bilayers containing MHC class II/peptide complexes shed their contact, which remained on the substrate and contained TCR. In contrast, 3A9 cells peeled from the ICAM-1 bilayer, and held firmly on LFA-1 bilayers; in a manner dependent on filamentous actin. When ICAM-1 and the MHC/peptide complexes were combined, the 3A9 cells adhered tightly and spread, but did not crawl, on the bilayers and TCR clustered at the center of the contact area. Physiologically, the TCR is unlikely to directly initiate adhesion. TCR clusters formed with the assistance of adhesion mechanisms may have to be shed to allow de-adhesion, and this may contribute to TCR down-regulation.

TCR-mediated adhesion of T cell hybridomas to planar bilayers containing purified MHC class II/peptide complexes and receptor shedding during detachment

T cell recognition of foreign Ag/MHC class II complexes is sensitive down to approximately 100 complexes per cell or approximately 0.2 complexes/micron2. To better understand the physical basis of the recognition stage of Ag presentation, we examined adhesion of the lysozyme- specific T cell hybridoma, 3A9, to artificial bilayers containing covalent MHC class II/peptide complexes or adhesion molecules. Adhesion of 3A9 cells required a superphysiologic density of the MHC class II/peptide complex and was partly dependent on CD4; cells adhered but did not crawl. No adhesion was observed to bilayers containing MHC class II molecules without the lysozyme peptide. Activated 3A9 cells adhered and crawled on bilayers containing ICAM-1. The physical strength of contacts was tested with fluid shear. 3A9 cells adherent to bilayers containing MHC class II/peptide complexes shed their contact, which remained on the substrate and contained TCR. In contrast, 3A9 cells peeled from the ICAM-1 bilayer, and held firmly on LFA-1 bilayers; in a manner dependent on filamentous actin. When ICAM-1 and the MHC/peptide complexes were combined, the 3A9 cells adhered tightly and spread, but did not crawl, on the bilayers and TCR clustered at the center of the contact area. Physiologically, the TCR is unlikely to directly initiate adhesion. TCR clusters formed with the assistance of adhesion mechanisms may have to be shed to allow de-adhesion, and this may contribute to TCR down-regulation.

Requirement for Stat4 in interleukin-12-mediated responses of natural killer and T cells

Signal transducers and activators of transcription (STATs) are activated by tyrosine phosphorylation in response to cytokines and mediate many of their functional responses. Stat4 was initially cloned as a result of its homology with Stat1 (refs 4, 5) and is widely expressed, although it is only tyrosine-phosphorylated after stimulation of T cells with interleukin (IL)-12 (refs 6,7). IL-12 is required for the T-cell-independent induction of the cytokine interferon (IFN)-gamma, a key step in the initial suppression of bacterial and parasitic infections. IL-12 is also important for the development of a Th1 response, which is critical for effective host defence against intracellular pathogens. To determine the function of Stat4 and its role in IL-12 signalling, we have produced mice that lack Stat4 by gene targeting. The mice were viable and fertile, with no detectable defects in haematopoiesis. However, all IL-12 functions tested were disrupted, including the induction of IFN-gamma, mitogenesis, enhancement of natural killer cytolytic function and Th1 differentiation.

The two membrane proximal domains of CD4 interact with the T cell receptor

During T cell activation, CD4 is intimately involved in colocalizing the T cell receptor (TCR) with its specific peptide ligand bound to class II molecules of the major histocompatibility complex (MHC). Previously, the COOH-terminal residues, Trp62/63, which flank the immunodominant epitope of hen egg lysozyme (HEL 52-61), were shown to have a profound effect on TCR recognition. CD4 maintains the fidelity of this interaction when short peptides are used. To determine which portion of CD4 was responsible for this effect, a series of CD4 mutants were made and transfected into CD4 loss variants of two HEL 52-61-specific T cell hybridomas. Surprisingly, some CD4 mutants that failed to interact with MHC class II molecules (D2 domain mutant) or with p56kk (cytoplasmic-tailless mutant) restored responsiveness. Nevertheless, a significant reduction in association between cytoplasmic-tailless CD4 and the TCR, as determined by fluorescence resonance energy transfer, was observed. Thus, neither colocalization of CD4 and the TCR nor signal transduction via CD4 was solely responsible for the functional restoration of these T cell hybridomas by wild-type CD4. However, substitution of the two membrane proximal domains of murine CD4 (D3 and D4) with domains from human CD4 or intercellular adhesion molecule 1 not only abrogated its ability to restore function, but also substantially reduced its ability to associate with the TCR. Furthermore, the mouse/human CD4 chimera had a potent dominant negative effect on T cell function in the presence of equimolar concentrations of wild-type CD4. These data suggest that the D3/D4 domains of CD4 may interact directly or indirectly with the TCR-CD3 complex and influence the signal transduction processes. Given the striking structural differences between CD4 and CD8 in this region, these data define a novel and unique function for CD4.

Lack of IL-4-induced Th2 response and IgE class switching in mice with disrupted Stat6 gene

Signal transducers and activators of transcription (Stats) are activated by tyrosine phosphorylation in response to cytokines, and are thought to mediate many of their functional responses. Stat6 is activated in response to interleukin (IL)-4 and may contribute to various functions including mitogenesis, T-helper cell differentiation and immunoglobulin isotype switching. To evaluate the role of Stat6, we generated Stat6-null mice (Stat6 -/-) by gene disruption in embryonic stem cells. The mice were viable, indicating the lack of a non-redundant function in normal development. Although naive lymphoid cell development was normal, Stat6 -/- mice were deficient in IL-4-mediated functions including Th2 helper T-cell differentiation, expression of cell surface markers, and immunoglobulin class switching to IgE. In contrast, IL-4-mediated proliferation was only partly affected.

The interaction between CD4 and MHC class II molecules and its effect on T cell function

During T cell activation, CD4 and CD8 form a 'bridge' between the T cell receptor (TCR) and major histocompatibility complex (MHC) class II and class I molecules, respectively. Due to this intimate association, CD4 and CD8 are now termed co-receptors and considered an integral part of this multimolecular complex. In addition, interest in CD4 has been heightened by the discovery that it is, in part, the receptor for HIV. Although CD4 and CD8 appear to perform similar immune functions, they are structurally diverse suggesting that their mode of interaction with the TCR and MHC molecules may differ. This review will focus primarily on a series of studies which have attempted to map the residues which mediate CD4:MHC class II interaction. These data will be evaluated in light of our current understanding of CD8:MHC class I, and CD4:TCR interactions. In addition, a model to explain the structural and functional differences between CD4 and CD8 will be presented. Finally, the potential effect of these multiple interactions on T cell function will be discussed.

Amino acid residues that flank core peptide epitopes and the extracellular domains of CD4 modulate differential signaling through the T cell receptor

Hen egg lysozyme 52-61-specific CD4+ T cells responded by interleukin 2 (IL-2) secretion to any peptide containing this epitope regardless of length of NH2- and COOH-terminal composition. However, CD4- variants could only respond to peptides containing the two COOH-terminal tryptophans at positions 62 and 63. Substitutions at these positions defined patterns of reactivity that were specific for individual T cells inferring a T cell receptor (TCR)-based phenomenon. Thus, the fine specificity of major histocompatibility complex (MHC)-peptide recognition by the TCR was dramatically affected by CD4 and the COOH-terminal peptide composition. Peptides that failed to induce IL-2 secretion in the CD4- variants nevertheless induced strong tyrosine phosphorylation of CD3 zeta. Thus, whereas the TCR still recognized and bound to the MHC class II-peptide complex resulting in protein phosphorylation, this interaction failed to induce effective signal transduction manifested by IL-2 secretion. This provides a clear example of differential signaling mediated by peptides known to be naturally processed. In addition, the external domains of CD4, rather than its cytoplasmic tail, were critical in aiding TCR recognition of all peptides derived from a single epitope. These data suggest that the nested flanking residues, which are present on MHC class II but not class I bound peptides, are functionally relevant.

Interactions of CD4 with MHC class II molecules, T cell receptors and p56lck

CD4 and CD8 are members of the immunoglobulin supergene family of proteins, and function as co-receptors with the T cell receptor (TCR) in binding MHC class II or class I molecules, respectively. Within this multimeric complex, CD4 interacts with three distinct ligands. CD4 interacts through its D1 and D2 domains with MHC class II proteins, through its D3 and D4 domains with T cell receptors, and through its cytoplasmic tail with p56lck, a src-related, protein tyrosine kinase. Each of these interactions is important in the function of CD4 and will be discussed in turn.

Specificity and promiscuity among naturally processed peptides bound to HLA-DR alleles

Naturally processed peptides were acid extracted from immunoaffinity-purified HLA-DR2, DR3, DR4, DR7, and DR8. Using the complementary techniques of mass spectrometry and Edman microsequencing, > 200 unique peptide masses were identified from each allele, ranging from 1,200 to 4,000 daltons (10-34 residues in length), and a total of 201 peptide sequences were obtained. These peptides were derived from 66 different source proteins and represented sets nested at both the amino- and carboxy-terminal ends with an average length of 15-18 amino acids. Strikingly, most of the peptides (> 85%) were derived from endogenous proteins that intersect the endocytic/class II pathway, even though class II molecules are thought to function mainly in the presentation of exogenous foreign peptide antigens. The predominant endogenous peptides were derived from major histocompatibility complex-related molecules. A few peptides derived from exogenous bovine serum proteins were also bound to every allele. Four prominent promiscuous self-peptide sets (capable of binding to multiple HLA-DR alleles) as well as 84 allele-specific peptide sets were identified. Binding experiments confirmed that the promiscuous peptides have high affinity for the binding groove of all HLA-DR alleles examined. A potential physiologic role for these endogenous self-peptides as immunomodulators of the cellular immune response is discussed.

Minute quantities of a single immunodominant foreign epitope are presented as large nested sets by major histocompatibility complex class II molecules

The processing and presentation of immunogenetic peptides is an obligate event in the generation of an immune response. However, the degree of complexity with which an immunogenic foreign epitope is presented is still unclear. This question was addressed by analyzing the naturally processed peptides generated from exogenously-derived hen egg white lysozyme (HEL) bound to the murine major histocompatibility complex (MHC) class II molecule, H-2Ak. Using reversed-phase chromatography (RPC), T cell hybridomas and mass spectrometry, 16 peptides were identified that contain the minimal MHC binding epitope 52-61. These peptides exhibited substantial N- and C-terminal extensions and ranged from 13-28 amino acids in length. In contrast, MHC class I molecules present peptides of 8-11 residues and each foreign epitope appears to be represented by only a single peptide. The data here also show that only approximately 0.8% of the total bound peptide was derived from this single HEL epitope. These findings provide direct evidence that relatively small amounts of processed peptide are required to stimulate an effective T cell response.

Predominant naturally processed peptides bound to HLA-DR1 are derived from MHC-related molecules and are heterogeneous in size

Peptides bound to class I molecules are 8-10 amino acids long, and possess a binding motif representative of peptides that bind to a given class I allele. In the only published study of naturally processed peptides bound to class II molecules (mouse I-Ab and I-Eb), these peptides were longer (13-17 amino acids) and had heterogenous carboxy terminals but precise amino-terminal truncations. Here we report the characterization of acid-eluted peptides bound to HLA-DR1 by high-performance liquid chromatography, mass spectrometry and microsequencing analyses. The relative molecular masses of the peptides varied between 1,602 and 2,996 (13-25 residues), the most abundant individual M(r) values being between 1,700 and 1,800, corresponding to an average peptide length of 15 residues. Complete sequence data were obtained for twenty peptides derived from five epitopes, of which all but one were from self proteins. These peptides represented sets nested at both the N- and C-terminal ends. Binding experiments confirmed that all of the isolated peptides had high affinity for the groove of DR1. Alignment of the peptides bound to HLA-DR1 and the sequences of 35 known HLA-DR1-binding peptides revealed a putative motif. Although peptides bound to class II molecules may have some related features (due to the nonpolymorphic HLA-DR alpha-chain), accounting for degenerate binding to different alleles, particular amino acids in the HLA-DR beta-chains presumably define allelic specificity of peptide binding.

Does CD4 help to maintain the fidelity of T cell receptor specificity?

During antigen presentation, a close association between CD4 and the T cell receptor (TCR) occurs as a result of interacting with the same major histocompatibility complex class II molecule. The potential consequences of such an intimate interaction on TCR specificity was addressed using CD4 loss variants of four different murine T cell hybridomas specific for the immunodominant hen egg lysozyme (HEL) peptide 46-61. While all the CD4+ and CD4- variants tested possessed comparable surface expression of TCR, CD3, CD2 and LFA-1, and responded similarly to immobilized anti-TCR and anti-CD3 monoclonal antibodies, they differed dramatically in their responses to either the naturally processed HEL antigen, synthetic peptide 46-61 or staphylococcal enterotoxin superantigens. While one hybridoma was comparatively unaffected by the loss of CD4, another lost its responsiveness to antigen and peptide completely while retaining reactivity to SE. In contrast, two other hybridomas still responded to antigen but lost reactivity to synthetic peptide and SE. These data could not be readily explained on the basis of affinity or signal transduction requirements alone, and thus suggest that the intimate association of CD4 with the TCR may result in a subtle modulation of its fine specificity for some but not all T cells.

Species-specific binding of CD4 to the beta 2 domain of major histocompatibility complex class II molecules

Exon-shuffled constructs between mouse (IA beta b) and human (DR3 beta) class II beta chains were made to study the interaction sites between CD4 and major histocompatibility complex (MHC) class II molecules, and to determine whether a species barrier is involved. The overall structure and the peptide binding groove appeared to be unaffected by the exon shuffling procedure as determined by monoclonal antibody and peptide binding assays, respectively. While purified CD4+ BALB/c T cells responded strongly in a mixed leukocyte reaction to transfectants expressing the whole IA molecule, the response to IA molecules containing a DR beta 2 domain was substantially reduced. In addition, the presence of an IA beta 2 domain in DR failed to restore the weak xenoreactivity to the whole DR molecule. Similar observations were made with murine HEL-specific, IA alpha k beta b-restricted T cell hybridomas which responded significantly stronger to the whole compared with the exon-shuffled IA molecules. The involvement of CD4 in these differential responses was confirmed by the observation that CD4 loss variants responded to both molecules comparably, and transfection of CD4 into these cells restored the parental phenotype. In contrast, CD4 loss variants transfected with human CD4 responded equally to both the whole and the exon-shuffled molecules. Taken together, these data imply the existence of a partial species barrier, and suggest that CD4 interacts with the beta 2 domain of MHC class II molecules, probably in addition to other contact sites. Models for the interaction of CD4 with MHC class II molecules are presented.

Processing of an endogenous protein can generate MHC class II-restricted T cell determinants distinct from those derived from exogenous antigen

Class II MHC molecules on the surface of an APC present immunogenic peptides derived mainly from exogenous proteins to CD4+ T cells. During its transport to the cell surface, class II molecules intersect the endocytic pathway where they acquire peptides derived from endocytosed proteins. However, class II-restricted presentation of endogenously derived peptides can also occur. The current studies were undertaken to examine the ability of different types of APC to generate and present four different T cell determinants derived from an endogenous, nonsecreted, truncated form of hen-egg white lysozyme (HEL[1-80]-Kk). This was compared with the ability of these APC to generate the same determinants from exogenous HEL. All the peptides derived from endogenous HEL[1-80]-Kk tested, were presented by B cells to HEL-specific T cell hybridomas with an efficiency similar to presentation of the same determinants from exogenous HEL. In contrast, an I-Ak-bearing rat fibroblast was unable to generate the HEL peptide 25-43 from exogenous HEL, but could efficiently produce it from endogenous HEL[1-80]-Kk. The results indicate first, that peptides derived from an endogenous Ag can be presented by MHC class II molecules with an efficiency comparable to that of the presentation of the exogenous Ag. Second, that Ag-presenting B cells can generate the same repertoire of antigenic peptides from endogenous Ag as those generated from the exogenous protein. And third, that in contrast to B cells, certain "nonprofessional" APC can generate, from an endogenous protein, T cell determinants distinct from those generated after endocytosis of the exogenous protein. These results suggest that processing of exogenous and endogenous Ag by different APC take place in different intracellular compartments.

Processing of an endogenous protein can generate MHC class II-restricted T cell determinants distinct from those derived from exogenous antigen

Class II MHC molecules on the surface of an APC present immunogenic peptides derived mainly from exogenous proteins to CD4+ T cells. During its transport to the cell surface, class II molecules intersect the endocytic pathway where they acquire peptides derived from endocytosed proteins. However, class II-restricted presentation of endogenously derived peptides can also occur. The current studies were undertaken to examine the ability of different types of APC to generate and present four different T cell determinants derived from an endogenous, nonsecreted, truncated form of hen-egg white lysozyme (HEL[1-80]-Kk). This was compared with the ability of these APC to generate the same determinants from exogenous HEL. All the peptides derived from endogenous HEL[1-80]-Kk tested, were presented by B cells to HEL-specific T cell hybridomas with an efficiency similar to presentation of the same determinants from exogenous HEL. In contrast, an I-Ak-bearing rat fibroblast was unable to generate the HEL peptide 25-43 from exogenous HEL, but could efficiently produce it from endogenous HEL[1-80]-Kk. The results indicate first, that peptides derived from an endogenous Ag can be presented by MHC class II molecules with an efficiency comparable to that of the presentation of the exogenous Ag. Second, that Ag-presenting B cells can generate the same repertoire of antigenic peptides from endogenous Ag as those generated from the exogenous protein. And third, that in contrast to B cells, certain "nonprofessional" APC can generate, from an endogenous protein, T cell determinants distinct from those generated after endocytosis of the exogenous protein. These results suggest that processing of exogenous and endogenous Ag by different APC take place in different intracellular compartments.

Induction of immunity against Schistosoma mansoni by drug (Ro11-3128)-terminated infections: analysis of surface antigen recognition

As with 20 krad-irradiated infections in mice, the present study shows that the immunity induced by Ro11-3128 termination of unattenuated infections at the skin stage is species specific, not operating against S. japonicum. Treatment with the drug Ro15-5458, also effective at the skin stage, however, resulted in significantly lower levels of resistance than Ro11-3128. Sera from mice immunized by infection plus Ro11-3128 treatment on days 1 or 2 (Ro11S) coprecipitated essentially the same pattern of 125I-labelled surface antigens as the 20 krad vaccine serum (VMS), viz. Mr 38,000, 32,000, 23,000 and 15,000. However, recognition by Ro11S was markedly stronger. Sera from the infected and Ro15-5458-treated mice (Ro15S) failed to recognize the Mr 23,000 antigen and produced a weaker response than Ro11S or VMS against the Mr 38,000 or 32,000 antigens but a comparable response to VMS against the Mr 15,000 antigen. Ro11S and VMS also recognized the Mr 16,000 surface antigen seen by Western blotting but its recognition by Ro15S was weaker. Compared with sera from animals treated at the skin stage, sera from animals treated at the lung stage (day + 6) showed weaker recognition of the Mr 32,000 and 15,000 antigens and no recognition of the Mr 23,000 antigen. In contrast, sera from mice treated at 15 days recognized both the Mr 32,000 and 23,000 antigens but not the Mr 15,000 antigen. Mice treated at these times show progressively less immunity than at the skin stage. Infected but untreated animals only showed significant recognition of the Mr 32,000 antigen. Thus compared with infections treated with Ro11-3128 on days 1 or 2, treatment at later times or with the drug Ro15-5458 resulted in selective and differential absence or diminution of response against either the Mr 38,000, 32,000, 23,000, 16,000 or 15,000 antigens. In vitro, Ro11-3128, in contrast to Ro15-5458, caused multiple vesicle formation at the surface of skin stage schistosomula but this was progressively less pronounced with lung and liver stage worms. The vesicles were shown to express surface membrane antigens but were apparently not derived from the existing outer leaflet of the surface membrane. It is suggested that this altered antigen expression might explain the optimum immunity induced.

Antibody-dependent killing of Schistosoma mansoni schistosomula in vitro by starch-elicited murine macrophages. Critical role of the cell surface integrin Mac-1 in killing mediated by the anti-Mr 16,000 mAb B3A

Starch-elicited murine peritoneal macrophages were able to kill schistosomula in vitro in the presence of a variety of immune sera. Dose response experiments revealed the superior "quality" of serum from mice vaccinated four times with highly irradiated cercariae (4xVMS) in mediating killing at titers comparable to the other sera tested. B3A, a partially protective mAb (IgG3) that recognizes a Mr 16,000 schistosomular surface Ag, mediated higher levels of killing than any of the sera at comparable titers. In contrast, H12, a partially protective mAb (IgG2a; anti-Mr 32,000), and C1C9, a nonprotective McAb (IgG3; anti-Mr 38,000) failed to mediate killing. Two anti-Mac-1 alpha-chain mAb (5C6 and M1/70) mediated substantial dose-dependent blocking of 4xVMS and B3A-mediated macrophage killing. In contrast, a mAb to the Mac-1-associated beta-chain was less effective, whereas the mAb F4/80 did not significantly block killing despite being present on this macrophage population. Although whole 5C6 Ig was the most efficient at inhibiting B3A-mediated killing, 5C6 Fab fragments were still effective at concentrations as low as 0.5 microgram/ml (10 nM). On a molar basis 5C6 appeared to be more effective at blocking 4xVMS-mediated killing than M1/70, while only M1/70 was capable of inhibiting macrophage adherence to schistosomula. These findings, together with the observation that anti-alpha chain mAb were far more effective at blocking killing than the anti-beta-chain mAb, rules out the possibility that 5C6 is nonspecifically inhibiting B3A-FcR interaction. The data also imply a functional relationship between Mac-1 and FcRIII, the receptor for B3A, in macrophage killing.

Antibody-dependent killing of Schistosoma mansoni schistosomula in vitro by starch-elicited murine macrophages. Critical role of the cell surface integrin Mac-1 in killing mediated by the anti-Mr 16,000 mAb B3A

Starch-elicited murine peritoneal macrophages were able to kill schistosomula in vitro in the presence of a variety of immune sera. Dose response experiments revealed the superior "quality" of serum from mice vaccinated four times with highly irradiated cercariae (4xVMS) in mediating killing at titers comparable to the other sera tested. B3A, a partially protective mAb (IgG3) that recognizes a Mr 16,000 schistosomular surface Ag, mediated higher levels of killing than any of the sera at comparable titers. In contrast, H12, a partially protective mAb (IgG2a; anti-Mr 32,000), and C1C9, a nonprotective McAb (IgG3; anti-Mr 38,000) failed to mediate killing. Two anti-Mac-1 alpha-chain mAb (5C6 and M1/70) mediated substantial dose-dependent blocking of 4xVMS and B3A-mediated macrophage killing. In contrast, a mAb to the Mac-1-associated beta-chain was less effective, whereas the mAb F4/80 did not significantly block killing despite being present on this macrophage population. Although whole 5C6 Ig was the most efficient at inhibiting B3A-mediated killing, 5C6 Fab fragments were still effective at concentrations as low as 0.5 microgram/ml (10 nM). On a molar basis 5C6 appeared to be more effective at blocking 4xVMS-mediated killing than M1/70, while only M1/70 was capable of inhibiting macrophage adherence to schistosomula. These findings, together with the observation that anti-alpha chain mAb were far more effective at blocking killing than the anti-beta-chain mAb, rules out the possibility that 5C6 is nonspecifically inhibiting B3A-FcR interaction. The data also imply a functional relationship between Mac-1 and FcRIII, the receptor for B3A, in macrophage killing.

The role of antibody affinity and titre in immunity to Schistosoma mansoni following vaccination with highly irradiated cercariae

Sera from rabbits and rats vaccinated with highly irradiated cercariae of Schistosoma mansoni (VRabS, VRatS) were found to be of substantially higher affinity than sera from CBA mice vaccinated four times (4 X CVMS), single sex sera (SSS) or chronic infection sera (CIS). In contrast, VRabS and SSS appeared to possess the highest titres of antibody, followed by CIS and VRatS, with 4 X CVMS displaying the lowest titre. Two mouse strains selectively bred for high-affinity (HA) or low-affinity (LA) antibody following vaccination were tested for their ability to resist a challenge infection. LA mice, which produce high titres of low-affinity antibody, manifested significantly more resistance than HA mice, which produce low titres of high-affinity antibody. Immunoprecipitation studies demonstrated that sera from vaccinated LA mice (LVMS) recognized 125I-labelled schistosomular surface antigens more intensely than sera from vaccinated HA mice (HVMS). However, peritoneal macrophages from HA and LA mice in the presence of HVMS, LVMS or 4 X CVMS, and naive macrophages activated in vitro with interferon-gamma (IFN-gamma)/lipopolysaccharide (LPS) mediated comparable levels of schistosomula killing in vitro. The experiments described here provide evidence that the titre of antibody rather than its affinity may be a more critical factor in the development of optimal immunity to S. mansoni.

Immunity to Schistosoma mansoni in vivo: contradiction or clarification?

In recent years controversy and contradiction have hindered the elucidation of the immune effector mechanisms that are most effective against Schistosoma mansoni - an essential goal for the development of an effective vaccine. However, recent in-vivo studies have clarified the relative contributions of such mechanisms to protection. Here, Dario Vignali and colleagues summarize current evidence that suggests that both antibody and CD4+ T cells, in cooperation with macrophages, are crucial for the development of an effective response. In addition, a model is presented that may account for some of the discrepancies observed and which could be used as a basis for future research.

A role for CD4+ but not CD8+ T cells in immunity to Schistosoma mansoni induced by 20 krad-irradiated and Ro 11-3128-terminated infections

The role of CD4+ (L3/T4+) and CD8+ (Lyt-2+) T cells in immunity to Schistosoma mansoni induced by 20 krad-irradiated and Ro 11-terminated infections in mice was investigated directly by in vivo depletion of these subsets with cytotoxic rat monoclonal antibodies (mAb). Effective physical depletion was demonstrated by flow cytometric analysis and immunohistochemical staining. Functional depletion of helper activity following anti-CD4 treatment was indicated by an abrogation of concanavalin A(Con A)-induced colony-stimulating factor (CSF) release, while anti-CD8 treatment had no effect in these assays. Pre-existing S. mansoni-specific antibody levels were unaffected by anti-CD4 and anti-CD8 treatment. In vivo depletion of CD4+ T cells resulted in a dramatic reduction in immunity induced by one (up to 100%) and two (up to 70%) vaccinations with 20 krad-irradiated cercariae and also of resistance induced by Ro 11-attenuated infections (up to 100%). Depletion of CD8+ T cells had no effect on resistance induced by any of the vaccination protocols investigated. A correlation was observed between resistance and T cell-induced, macrophage-mediated killing of schistosomula in vitro, both of which were abrogated following anti-CD4 treatment but were unaffected by CD8+ T-cell depletion. The possible role of CD4+ T cells in vivo and the implications for vaccine development are discussed.

Histological examination of the cellular reactions around schistosomula of Schistosoma mansoni in the lungs of sublethally irradiated and unirradiated, immune and control rats

Histopathological data on the cellular reactions (foci) around Schistosoma mansoni schistosomula in the lungs of both irradiated (750 rad) and unirradiated, passively immunized and normal rats were consistent with the idea that a significant proportion of immune-mediated attrition in passively immunized rats occurs in the lungs. In unirradiated rats, immune serum elicited an enhanced (i.e. larger) and accelerated (i.e. more rapidly developing) inflammatory cellular infiltration around lung-stage parasites when administered 5 days post-infection, when the parasites were already in the lungs. This demonstrated the antigenicity of lung-stage schistosomula and their potential as targets for immune attack. In irradiated rats, innate immunity was decreased as judged by an increase in the number of worms recovered by portal perfusion, and was accompanied by an overall decreased percentage of trapped parasites compared with unirradiated controls, suggesting that trapping in the lungs is involved in innate, as well as acquired immunity. In contrast to the results in unirradiated rats, passive transfer of immune serum into irradiated recipients did not result in larger lung foci than in the NRS-recipients. However, there was evidence of an accelerated response resulting in an essentially similar ratio of trapped parasites (VRS- compared with NRS-recipients) in irradiated rats, as compared with unirradiated rats, reflecting the similar levels of resistance manifested in both groups of rats. This also lent credence to the notion that it was the speed of immune recognition of the migrating schistosomula and the establishment of trapping foci that were of greater importance rather than the size of the enveloping granulomata.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on immunity to Schistosoma mansoni in vivo: whole-body irradiation has no effect on vaccine-induced resistance in mice

Actively immunized mice, whole-body irradiated with 650 or 525 rad., manifested comparable levels of resistance to Schistosoma mansoni compared with unirradiated, immunized mice in spite of a marked reduction in circulating leucocytes (greater than 90%) and platelets (greater than 85%), and despite an abrogation of delayed-type hypersensitivity (DTH) (Type IV) response to schistosomular antigens (as determined by footpad swelling, 24 h after injection of antigen). However, limited histopathological comparison of lung sections from irradiated and unirradiated mice 7 days post-challenge showed that cellular reactions ('foci') around parasites were essentially similar in size and cellular composition except that in irradiated mice, eosinophils were poorly represented both in the foci and in lung tissue in general. Neither presumed immune complex-mediated (Type III, Arthus reaction) hypersensitivity (as determined by footpad swelling, 5 h after injection of antigen) nor serum anti-schistosomulum extract antibody levels (as determined by ELISA) were affected. In addition, the pattern of 125I-labelled schistosomular surface antigens immunoprecipitated with serum from irradiated and unirradiated mice was essentially similar. These results are consistent with antibody playing an important role in vaccine-induced immunity in mice but suggest that radiosensitive T cell function and radiosensitive cells, such as platelets and polymorphonuclear cells, including eosinophils, may not be essential.

Comparison of the role of complement in immunity to Schistosoma mansoni in rats and mice

In vivo depletion of C3 with cobra venom factor (CoF) was used to demonstrate the participation of complement in the innate immunity to S. mansoni and in the acquired immunity of both actively and passively immunized rats. Complement was shown to play an important role in innate immunity, being more involved later in larval migration (Days 8-13 post-infection) than at earlier times (Days--1-3 and Days 3-8 post-infection). Furthermore, the specific component of immunity conferred by immune serum transferred at the lung-migration stage also required complement for optimal expression. This supports the notion that both innate and acquired immunity act not against the much studied early post-penetration stages, but primarily against the lung stages. Although decomplementation at earlier stages of parasite migration (up to 3 days post-infection) did cause some reduction of innate immunity, there was no evidence of any effect on the levels of resistance actively induced by exposure to irradiated cercariae. This suggests that, while complement may play a role in innate immunity during the skin-migration phase, specific complement-mediated attrition does not play a crucial role at this time. The situation was very different in the mouse model, since no involvement of complement in either innate or irradiated vaccine-induced immunity could be demonstrated within the first 15 days of infection. Thus, there appear to be phases in the parasite migration in rats, but not in mice, during which complement becomes a critical factor in both innate and acquired immunity to S. mansoni.

The influence of 7,12-dimethylbenzanthracene on natural killer (NK) cell function in rats

The administration to 2 strains of rat (Alderley Park and Sprague Dawley) of 40 (2 X 20) mg of 7,12-dimethylbenzanthracene (DMBA) on a single day caused a transient depression of NK cell function. The splenic natural cytotoxic capacity of both DMBA treated and control animals was augmented by inclusion within the assay of interferon (IFN) but IFN failed to restore carcinogen-treated splenocyte cytotoxicity to normal values. Splenocyte populations from DMBA treated animals exhibiting reduced cytotoxic activity possessed normal frequencies of target-binding lymphocytes suggesting that the impairment of reactivity was attributable to a defect in the post-recognitive stage of NK mediated lysis. Administration of DMBA was not associated with a reduction in spleen weight or cellularity or with an impairment of splenic lymphocyte responsiveness to phytohaemagglutinin (PHA) indicating that depressed NK cell function was not a result of general lymphotoxicity. These data confirm previous reports that administration of chemical carcinogens may be associated with a depression of NK cell function.