Minimal Information about MHC Multimers (MIAMM).

With the goal of improving the reproducibility and annotatability of MHC multimer reagent data, we present the establishment of a new data standard: Minimal Information about MHC Multimers (https://miamm.lji.org/). Multimers are engineered reagents composed of a ligand and a MHC, which can be represented in a standardized format using ontology terminology. We provide an online Web site to host the details of the standard, as well as a validation tool to assist with the adoption of the standard. We hope that this publication will bring increased awareness of Minimal Information about MHC Multimers and drive acceptance, ultimately improving the quality and documentation of multimer data in the scientific literature.

MHC-I peptide binding activity assessed by exchange after cleavage of peptide covalently linked to ß2-microglobulin.

A common approach to measuring binding constants involves combining receptor and ligand and measuring the distribution of bound and free states after equilibration. For class I major histocompatibility (MHC-I) proteins, which bind short peptides for presentation to T cells, this approach is precluded by instability of peptide-free protein. Here we develop a method wherein a weakly-binding peptide covalently attached to the N-terminus of the MHC-I ß2m subunit is released from the peptide binding site after proteolytic cleavage of the linker. The resultant protein is able to bind added peptide. A direct binding assay and method for estimation of peptide binding constant (Kd) are described, in which fluorescence polarization is used to follow peptide binding. A competition binding assay and method for estimation of inhibitor binding constant (Ki) using the same principle also are also described. The method uses a cubic equation to relate observed binding to probe concentration, probe Kd, inhibitor concentration, and inhibitor Ki under general reaction conditions without assumptions relating to relative binding affinities or concentrations. We also delineate advantages of this approach compared to the Cheng-Prusoff and Munson-Rodbard approaches for estimation of Ki using competition binding data.

miRNA92a targets KLF2 and the phosphatase PTEN signaling to promote human T follicular helper precursors in T1D islet autoimmunity.

Aberrant immune activation mediated by T effector cell populations is pivotal in the onset of autoimmunity in type 1 diabetes (T1D). T follicular helper (TFH) cells are essential in the induction of high-affinity antibodies, and their precursor memory compartment circulates in the blood. The role of TFH precursors in the onset of islet autoimmunity and signaling pathways regulating their differentiation is incompletely understood. Here, we provide direct evidence that during onset of islet autoimmunity, the insulin-specific target T-cell population is enriched with a C-X-C chemokine receptor type 5 (CXCR5)+CD4+ TFH precursor phenotype. During onset of islet autoimmunity, the frequency of TFH precursors was controlled by high expression of microRNA92a (miRNA92a). miRNA92a-mediated TFH precursor induction was regulated by phosphatase and tension homolog (PTEN) - phosphoinositol-3-kinase (PI3K) signaling involving PTEN and forkhead box protein O1 (Foxo1), supporting autoantibody generation and triggering the onset of islet autoimmunity. Moreover, we identify Krueppel-like factor 2 (KLF2) as a target of miRNA92a in regulating human TFH precursor induction. Importantly, a miRNA92a antagomir completely blocked induction of human TFH precursors in vitro. More importantly, in vivo application of a miRNA92a antagomir to nonobese diabetic (NOD) mice with ongoing islet autoimmunity resulted in a significant reduction of TFH precursors in peripheral blood and pancreatic lymph nodes. Moreover, miRNA92a antagomir application reduced immune infiltration and activation in pancreata of NOD mice as well as humanized NOD Scid IL2 receptor gamma chain knockout (NSG) human leucocyte antigen (HLA)-DQ8 transgenic animals. We therefore propose that miRNA92a and the PTEN-PI3K-KLF2 signaling network could function as targets for innovative precision medicines to reduce T1D islet autoimmunity.

SARS-CoV-2 infection establishes a stable and age-independent CD8+ T cell response against a dominant nucleocapsid epitope using restricted T cell receptors.

The resolution of SARS-CoV-2 replication hinges on cell-mediated immunity, wherein CD8+ T cells play a vital role. Nonetheless, the characterization of the specificity and TCR composition of CD8+ T cells targeting non-spike protein of SARS-CoV-2 before and after infection remains incomplete. Here, we analyzed CD8+ T cells recognizing six epitopes from the SARS-CoV-2 nucleocapsid (N) protein and found that SARS-CoV-2 infection slightly increased the frequencies of N-recognizing CD8+ T cells but significantly enhanced activation-induced proliferation compared to that of the uninfected donors. The frequencies of N-specific CD8+ T cells and their proliferative response to stimulation did not decrease over one year. We identified the N222-230 peptide (LLLDRLNQL, referred to as LLL thereafter) as a dominant epitope that elicited the greatest proliferative response from both convalescent and uninfected donors. Single-cell sequencing of T cell receptors (TCR) from LLL-specific CD8+ T cells revealed highly restricted Vα gene usage (TRAV12-2) with limited CDR3α motifs, supported by structural characterization of the TCR-LLL-HLA-A2 complex. Lastly, transcriptome analysis of LLL-specific CD8+ T cells from donors who had expansion (expanders) or no expansion (non-expanders) after in vitro stimulation identified increased chromatin modification and innate immune functions of CD8+ T cells in non-expanders. These results suggests that SARS-CoV-2 infection induces LLL-specific CD8+ T cell responses with a restricted TCR repertoire.

Production of Class II MHC Proteins in Lentiviral Vector-Transduced HEK-293T Cells for Tetramer Staining Reagents.

Class II major histocompatibility complex peptide (MHC-IIp) multimers are precisely engineered reagents used to detect T cells specific for antigens from pathogens, tumors, and self-proteins. While the related Class I MHC/peptide (MHC-Ip) multimers are usually produced from subunits expressed in E. coli, most Class II MHC alleles cannot be produced in bacteria, and this has contributed to the perception that MHC-IIp reagents are harder to produce. Herein, we present a robust constitutive expression system for soluble biotinylated MHC-IIp proteins that uses stable lentiviral vector-transduced derivatives of HEK-293T cells. The expression design includes allele-specific peptide ligands tethered to the amino-terminus of the MHC-II ß chain via a protease-cleavable linker. Following cleavage of the linker, HLA-DM is used to catalyze efficient peptide exchange, enabling high-throughput production of many distinct MHC-IIp complexes from a single production cell line. Peptide exchange is monitored using either of two label-free methods, native isoelectric focusing gel electrophoresis or matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry of eluted peptides. Together, these methods produce MHC-IIp complexes that are highly homogeneous and that form the basis for excellent MHC-IIp multimer reagents. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Lentivirus production and expression line creation Support Protocol 1: Six-well assay for estimation of production cell line yield Support Protocol 2: Universal ELISA for quantifying proteins with fused leucine zippers and His-tags Basic Protocol 2: Cultures for production of Class II MHC proteins Basic Protocol 3: Purification of Class II MHC proteins by anti-leucine zipper affinity chromatography Alternate Protocol 1: IMAC purification of His-tagged Class II MHC Support Protocol 3: Protein concentration measurements and adjustments Support Protocol 4: Polishing purification by anion-exchange chromatography Support Protocol 5: Estimating biotinylation percentage by streptavidin precipitation Basic Protocol 4: Peptide exchange Basic Protocol 5: Analysis of peptide exchange by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry Alternate Protocol 2: Native isoelectric focusing to validate MHC-II peptide loading Basic Protocol 6: Multimerization Basic Protocol 7: Staining cells with Class II MHC tetramers.

Human skin is colonized by T cells that recognize CD1a independently of lipid.

CD1a-autoreactive T cells contribute to skin disease, but the identity of immunodominant self-lipid antigens and their mode of recognition are not yet solved. In most models, MHC and CD1 proteins serve as display platforms for smaller antigens. Here, we showed that CD1a tetramers without added antigen stained large T cell pools in every subject tested, accounting for approximately 1% of skin T cells. The mechanism of tetramer binding to T cells did not require any defined antigen. Binding occurred with approximately 100 lipid ligands carried by CD1a proteins, but could be tuned upward or downward with certain natural self-lipids. TCR recognition mapped to the outer A' roof of CD1a at sites remote from the antigen exit portal, explaining how TCRs can bind CD1a rather than carried lipids. Thus, a major antigenic target of CD1a T cell autoreactivity in vivo is CD1a itself. Based on their high frequency and prevalence among donors, we conclude that CD1a-specific, lipid-independent T cells are a normal component of the human skin T cell repertoire. Bypassing the need to select antigens and effector molecules, CD1a tetramers represent a simple method to track such CD1a-specific T cells from tissues and in any clinical disease.

Synthesis, stabilization, and characterization of the MR1 ligand precursor 5-amino-6-D-ribitylaminouracil (5-A-RU).

Mucosal-associated invariant T (MAIT) cells are an abundant class of innate T cells restricted by the MHC I-related molecule MR1. MAIT cells can recognize bacterially-derived metabolic intermediates from the riboflavin pathway presented by MR1 and are postulated to play a role in innate antibacterial immunity through production of cytokines and direct bacterial killing. MR1 tetramers, typically stabilized by the adduct of 5-amino-6-D-ribitylaminouracil (5-A-RU) and methylglyoxal (MeG), are important tools for the study of MAIT cells. A long-standing problem with 5-A-RU is that it is unstable upon storage. Herein we report an efficient synthetic approach to the HCl salt of this ligand, which has improved stability during storage. We also show that synthetic 5-A-RU•HCl produced by this method may be used in protocols for the stimulation of human MAIT cells and production of both human and mouse MR1 tetramers for MAIT cell identification.

A miRNA181a/NFAT5 axis links impaired T cell tolerance induction with autoimmune type 1 diabetes.

Molecular checkpoints that trigger the onset of islet autoimmunity or progression to human type 1 diabetes (T1D) are incompletely understood. Using T cells from children at an early stage of islet autoimmunity without clinical T1D, we find that a microRNA181a (miRNA181a)-mediated increase in signal strength of stimulation and costimulation links nuclear factor of activated T cells 5 (NFAT5) with impaired tolerance induction and autoimmune activation. We show that enhancing miRNA181a activity increases NFAT5 expression while inhibiting FOXP3+ regulatory T cell (Treg) induction in vitro. Accordingly, Treg induction is improved using T cells from NFAT5 knockout (NFAT5ko) animals, whereas altering miRNA181a activity does not affect Treg induction in NFAT5ko T cells. Moreover, high costimulatory signals result in phosphoinositide 3-kinase (PI3K)-mediated NFAT5, which interferes with FoxP3+ Treg induction. Blocking miRNA181a or NFAT5 increases Treg induction in murine and humanized models and reduces murine islet autoimmunity in vivo. These findings suggest targeting miRNA181a and/or NFAT5 signaling for the development of innovative personalized medicines to limit islet autoimmunity.

Type 1 diabetes vaccine candidates promote human Foxp3(+)Treg induction in humanized mice.

Immune tolerance is executed partly by Foxp3(+)regulatory T (Treg) cells, which suppress autoreactive T cells. In autoimmune type 1 diabetes (T1D) impaired tolerance promotes destruction of insulin-producing ß-cells. The development of autoantigen-specific vaccination strategies for Foxp3(+)Treg-induction and prevention of islet autoimmunity in patients is still in its infancy. Here, using human haematopoietic stem cell-engrafted NSG-HLA-DQ8 transgenic mice, we provide direct evidence for human autoantigen-specific Foxp3(+)Treg-induction in vivo. We identify HLA-DQ8-restricted insulin-specific CD4(+)T cells and demonstrate efficient human insulin-specific Foxp3(+)Treg-induction upon subimmunogenic vaccination with strong agonistic insulin mimetopes in vivo. Induced human Tregs are stable, show increased expression of Treg signature genes such as Foxp3, CTLA4, IL-2Rα and TIGIT and can efficiently suppress effector T cells. Such Foxp3(+)Treg-induction does not trigger any effector T cells. These T1D vaccine candidates could therefore represent an expedient improvement in the challenge to induce human Foxp3(+)Tregs and to develop novel precision medicines for prevention of islet autoimmunity in children at risk of T1D.

The yeast gene COQ5 is differentially regulated by Mig1p, Rtg3p and Hap2p.

Ubiquinone (CoQ) is an important component of the electron transport chain and serves to regenerate cellular anti-oxidants. In Saccharomyces cerevisiae, expression of the COQ5 gene, encoding for a C-methyltransferase involved in CoQ synthesis, is transcriptionally regulated by carbon source. We have identified three transcription factors involved in this regulation. Mig1p repressed COQ5 expression on dextrose, while Rtg1p/Rtg3p heterodimers up-regulated COQ5 expression on oleic acid. Hap2p modulated the response to oleic acid but did not have an effect in other nonfermentable carbon sources such as glycerol. These results suggest that the regulation of COQ5 gene expression by carbon source is multifactorial and involves the interaction of various transcription factors.

The regulation of COQ5 gene expression by energy source.

The degree of severity of cardiomyopathy is inversely correlated with tissue levels of coenzyme Q (Q), suggesting that Q synthesis may impact the progression of the disease. It has been suggested that Q functions as an endogenously synthesized anti-oxidant, in addition to regenerating the potent anti-oxidants, vitamins E and C. However, very little is known about the mechanisms that regulate Q synthesis. Using the simple eukaryote Saccharomyces cerevisiae as a model, experiments have been designed to investigate the regulation of Q synthesis at the genetic level. To investigate the regulation of COQ5 gene expression by energy source, mRNA content was evaluated in yeast cells treated with dextrose, glycerol or oleic acid. After 1.5 h, more COQ5 mRNA is produced by oleic acid treated cells than by glycerol treated. Experiments performed using COQ5 promoter deletion/reporter constructs demonstrate a specific response to oleic acid. Additional promoter deletion analysis demonstrates that a non-fermentable carbon source element is also present, responding to both glycerol and oleic acid. The specific oleic acid response appears to be regulated by the Rtg family of transcription factors. This family of proteins is required for oleic acid-induced expression of genes of beta-oxidation and peroxisomal proliferation, and plays an important role in co-ordinating mitochondrial/peroxisomal/nuclear communication in response to oleic acid, as well as defects in cellular respiration.

CD8 T cell competition for dendritic cells in vivo is an early event in activation.

T cell responses against an antigen are often focused on a small fraction of potentially immunogenic determinants, a phenomenon known as immunodominance. Immunodominance can be established at several stages of antigen presentation, including antigen processing, binding of peptides to MHC, and competition between T cells for dendritic cells (DCs). The mechanism of this T cell competition is unclear, but may include competition for physical access to DCs, competition for limiting soluble DC-derived factors, or a suppressive effect of one T cell population on the other(s). To model DC-specific T cell competition, normal mice were injected with one or two T cell receptor transgenic CD8 T cell populations, each with high affinity for different peptides presented by different class I MHC complexes. These mice were immunized with DCs pulsed with peptides that are recognized by the transferred T cells. Competition was detectable when both T cell populations were transferred and their target peptides were present on the same DCs. The competition resulted in fewer cells entering the response, but had no effect on the level of activation of the cells that did respond. The effect was evident very early in the response, and in fact the competing T cells needed to be present in the first 5 h of the response for competition to occur. Thus, some aspect of DCs other than peptide/MHC complexes is limiting in the earliest stages of the CD8 T cell response. These results have implications for the design of multivalent vaccines.

Ubiquinone accumulates in the mitochondria of yeast mutated in the ubiquinone binding protein, Qcr8p.

In Saccharomyces cerevisiae, the trans-membrane helix of Qcr8p, the ubiquinone binding protein of complex III, contributes to the Q binding site. In wild-type cells, residue 62 of the helix is non-polar (proline). Substitution of proline 62 with a polar, uncharged residue does not impair the ability of the cells to respire, complex III assembly is unaffected, ubiquinone occupancy of the Q binding site is unchanged, and mitochondrial ubiquinone levels are in the wild-type range. Substitution with a +1 charged residue is associated with partial respiratory competence, impaired complex III assembly, and loss of cytochrome b. Although ubiquinone occupancy of the Q binding site is similar to wild-type, total mitochondrial ubiquinone doubled in these mutants. Mutants with a +2 charged substitution at position 62 are unable to respire. These results suggest that the accumulation of ubiquinone in the mitochondria may be a compensatory mechanism for impaired electron transport at cytochrome b.

Ubiquinone binding protein used for determination of coenzyme Q.

The conventional method of assaying for the ubiquinone (CoQ) content of biological samples is to partition CoQ into an organic phase and separate it from contaminants by high-performance liquid chromatography (HPLC). HPLC is an accurate method of quantifying CoQ content but is not ideal for routine clinical analyses. This paper describes the development of a rapid method for assaying the CoQ content of biological samples based on the binding of CoQ to a CoQ binding peptide. The 14-amino acid binding peptide was chemically synthesized, and conditions for immobilizing the peptide on microfuge tubes were established. CoQ could be selectively bound to the immobilized peptide, eluted, and determined spectrophotometrically. Limits of detection for the method were 0.25 to 5 nmol CoQ. To test biological samples, CoQ was isolated from cultures of Saccharomyces cerevisiae grown in oleic acid medium. The recovery of CoQ samples using the binding assay ranged from 99 to 102% of the values obtained with HPLC. The assay described here provides an inexpensive, rapid method for determining the CoQ content of large numbers of biological samples in a variety of laboratory settings.

Generation of monoclonal antibodies specific for human kallikrein 2 (hK2) using hK2-expressing tumors.

BACKGROUND: Human kallikrein 2 (hK2) and prostate-specific antigen (PSA) are serine proteases in the human kallikrein gene family that are 80% identical at the protein level. Like PSA, hK2 is expressed primarily in the prostate, making it an attractive bio-marker for prostate cancer development. In addition, its potent enzymatic activity may functionally affect the biology of prostate cancer. In order to further elucidate the possible roles of hK2 in prostate cancer, we have generated a panel of hK2-specific, non-PSA cross-reactive monoclonal antibodies. METHODS: A novel tumor-immunization strategy was used to produce monoclonal antibodies. Human hK2 cDNA was transfected into a BALB/c tumor cell line and used to immunize both BALB/c and PSA-expressing BALB/c.PSA transgenic mice. Because the BALB/c.PSA transgenic mouse showed a biased response towards hK2, a B cell fusion was performed using spleen cells from a transgenic mouse immunized in this fashion. RESULTS: A panel of monoclonal antibodies was produced and shown to be hK2-specific using newly developed hK2-specific sandwich ELISA and ELIspot assays. One of the monoclonal antibodies (6B7) was used to detect hK2 in human prostate by immunohistochemistry. Interestingly, two of the antibodies affected the function of hK2. The 1F8 antibody enhanced the enzymatic activity of hK2 whereas the 3C7 antibody inhibited its function. CONCLUSIONS: These hK2-specific antibodies illustrate a novel approach for constructing B-cell hybridomas and provide useful reagents to examine the role of hK2 in the biology and detection of prostate cancer.