Anti-CD8 antibodies can trigger CD8+ T cell effector function in the absence of TCR engagement and improve peptide-MHCI tetramer staining

Signaling via a CD28/CD40 chimeric costimulatory antigen receptor (CoStAR™), targeting folate receptor alpha, enhances T cell activity and augments tumor reactivity of tumor infiltrating lymphocytes

Transfer of autologous tumor infiltrating lymphocytes (TIL) to patients with refractory melanoma has shown clinical efficacy in a number of trials. However, extending the clinical benefit to patients with other cancers poses a challenge. Inefficient costimulation in the tumor microenvironment can lead to T cell anergy and exhaustion resulting in poor anti-tumor activity. Here, we describe a chimeric costimulatory antigen receptor (CoStAR) comprised of FRα-specific scFv linked to CD28 and CD40 intracellular signaling domains. CoStAR signaling alone does not activate T cells, while the combination of TCR and CoStAR signaling enhances T cell activity resulting in less differentiated T cells, and augmentation of T cell effector functions, including cytokine secretion and cytotoxicity. CoStAR activity resulted in superior T cell proliferation, even in the absence of exogenous IL-2. Using an in vivo transplantable tumor model, CoStAR was shown to improve T cell survival after transfer, enhanced control of tumor growth, and improved host survival. CoStAR could be reliably engineered into TIL from multiple tumor indications and augmented TIL activity against autologous tumor targets both in vitro and in vivo. CoStAR thus represents a general approach to improving TIL therapy with synthetic costimulation.

High-affinity CD8 variants enhance the sensitivity of pMHCI antigen recognition via low-affinity TCRs

CD8+ T cell-mediated recognition of peptide-major histocompatibility complex class I (pMHCI) molecules involves cooperative binding of the T cell receptor (TCR), which confers antigen specificity, and the CD8 coreceptor, which stabilizes the TCR/pMHCI complex. Earlier work has shown that the sensitivity of antigen recognition can be regulated in vitro by altering the strength of the pMHCI/CD8 interaction. Here, we characterized two CD8 variants with moderately enhanced affinities for pMHCI, aiming to boost antigen sensitivity without inducing non-specific activation. Expression of these CD8 variants in model systems preferentially enhanced pMHCI antigen recognition in the context of low-affinity TCRs. A similar effect was observed using primary CD4+ T cells transduced with cancer-targeting TCRs. The introduction of high-affinity CD8 variants also enhanced the functional sensitivity of primary CD8+ T cells expressing cancer-targeting TCRs, but comparable results were obtained using exogenous wild-type CD8. Specificity was retained in every case, with no evidence of reactivity in the absence of cognate antigen. Collectively, these findings highlight a generically applicable mechanism to enhance the sensitivity of low-affinity pMHCI antigen recognition, which could augment the therapeutic efficacy of clinically relevant TCRs.

Nasal administration of anti-CD3 monoclonal antibody modulates effector CD8+ T cell function and induces a regulatory response in T cells in human subjects

Background

Parenteral anti-CD3 Mab (OKT3) has been used to treat transplant rejection and parental administration of a humanized anti-CD3 Mab (Teplizumab) showed positive effects in diabetes. Nasal administration of anti-CD3 Mab has not been carried out in humans. Nasal anti-CD3 Mab suppresses autoimmune diseases and central nervous system (CNS) inflammation in animal models. We investigated the safety and immune effects of a fully humanized, previously uncharacterized nasal anti-CD3 Mab (Foralumab) in humans and its in vitro stimulatory properties.

Methods

In vitro, Foralumab were compared to UCHT1 anti-human CD3 mAb. For human administration, 27 healthy volunteers (9 per group) received nasal Foralumab or placebo at a dose of 10ug, 50ug, or 250ug daily for 5 days. Safety was assessed and immune parameters measured on day 1 (pre-treatment), 7, 14, and 30 by FACS and by scRNAseq.

Results

In vitro, Foralumab preferentially induced CD8+ T cell stimulation, reduced CD4+ T cell proliferation and lowered expression of IFNg, IL-17 and TNFa. Foralumab induced LAP, TIGIT, and KLRG1 immune checkpoint molecules on CD8+ and CD4+ T cells in a mechanism independent of CD8 T cells. In vivo, nasal Foralumab did not modulate CD3 from the T cell surface at any dose. Immune effects were primarily observed at the 50ug dose and consisted of reduction of CD8+ effector memory cells, an increase in naive CD8+ and CD4+ T cells, and reduced CD8+ T cell granzyme B and perforin expression. Differentially expressed genes observed by scRNAseq in CD8+ and CD4+ populations promoted survival and were anti-inflammatory. In the CD8+ TEMRA population there was induction of TIGIT, TGFB1 and KIR3DL2, indicative of a regulatory phenotype. In the memory CD4+ population, there was induction of CTLA4, KLRG1, and TGFB whereas there was an induction of TGF-B1 in naïve CD4+ T cells. In monocytes, there was induction of genes (HLA-DP, HLA-DQ) that promote a less inflammatory immune response. No side effects were observed, and no subjects developed human anti-mouse antibodies.

Conclusion

These findings demonstrate that nasal Foralumab is safe and immunologically active in humans and presents a new avenue for the treatment of autoimmune and CNS diseases.

CD8 agonism functionally activates memory T cells and enhances anti-tumor immunity

Memory CD8⁺ T cells mature after antigen clearance and ultimately express CD8 protein at levels higher than those detected in effector CD8⁺ T cells. However, it is not clear whether engagement of CD8 in the absence of antigenic stimulation will result in the functional activation of T cells. Here, we found that CD8 antibody-mediated activation of memory CD8⁺ T cells triggered T cell receptor (TCR) downstream signaling, enhanced T cell-mediated cytotoxicity, and promoted effector cytokine production in a glucose- and glutamine-dependent manner. Furthermore, pretreatment of memory CD8⁺ T cells with an agonistic anti-CD8 antibody enhanced their tumoricidal activity in vitro and in vivo. From these studies, we conclude that CD8 agonism activates glucose and glutamine metabolism in memory T cells and enhances the efficacy of memory T cell-based cancer immunotherapy.

Prothymosin Alpha: A Novel Contributor to Estradiol Receptor Alpha-Mediated CD8+ T-Cell Pathogenic Responses and Recognition of Type 1 Collagen in Rheumatic Heart Valve Disease

BACKGROUND

Rheumatic heart valve disease (RHVD) is a leading cause of cardiovascular death in low- and middle-income countries and affects predominantly women. The underlying mechanisms of chronic valvular damage remain unexplored and regulators of sex predisposition are unknown.

METHODS

Proteomics analysis of human heart valves (nondiseased aortic valves, nondiseased mitral valves [NDMVs], valves from patients with rheumatic aortic valve disease, and valves from patients with rheumatic mitral valve disease; n=30) followed by system biology analysis identified ProTα (prothymosin alpha) as a protein associated with RHVD. Histology, multiparameter flow cytometry, and enzyme-linked immunosorbent assay confirmed the expression of ProTα. In vitro experiments using peripheral mononuclear cells and valvular interstitial cells were performed using multiparameter flow cytometry and quantitative polymerase chain reaction. In silico analysis of the RHVD and Streptococcuspyogenes proteomes were used to identify mimic epitopes.

RESULTS

A comparison of NDMV and nondiseased aortic valve proteomes established the baseline differences between nondiseased aortic and mitral valves. Thirteen unique proteins were enriched in NDMVs. Comparison of NDMVs versus valves from patients with rheumatic mitral valve disease and nondiseased aortic valves versus valves from patients with rheumatic aortic valve disease identified 213 proteins enriched in rheumatic valves. The expression of the 13 NDMV-enriched proteins was evaluated across the 213 proteins enriched in diseased valves, resulting in the discovery of ProTα common to valves from patients with rheumatic mitral valve disease and valves from patients with rheumatic aortic valve disease. ProTα plasma levels were significantly higher in patients with RHVD than in healthy individuals. Immunoreactive ProTα colocalized with CD8⁺ T cells in RHVD. Expression of ProTα and estrogen receptor alpha correlated strongly in circulating CD8⁺ T cells from patients with RHVD. Recombinant ProTα induced expression of the lytic proteins perforin and granzyme B by CD8⁺ T cells as well as higher estrogen receptor alpha expression. In addition, recombinant ProTα increased human leukocyte antigen class I levels in valvular interstitial cells. Treatment of CD8⁺ T cells with specific estrogen receptor alpha antagonist reduced the cytotoxic potential promoted by ProTα. In silico analysis of RHVD and Spyogenes proteomes revealed molecular mimicry between human type 1 collagen epitope and bacterial collagen-like protein, which induced CD8⁺ T-cell activation in vitro.

CONCLUSIONS

ProTα-dependent CD8⁺ T-cell cytotoxicity was associated with estrogen receptor alpha activity, implicating ProTα as a potential regulator of sex predisposition in RHVD. ProTα facilitated recognition of type 1 collagen mimic epitopes by CD8⁺ T cells, suggesting mechanisms provoking autoimmunity.

CD8 coreceptor-mediated focusing can reorder the agonist hierarchy of peptide ligands recognized via the T cell receptor

CD8⁺ T cells are inherently cross-reactive and recognize numerous peptide antigens in the context of a given major histocompatibility complex class I (MHCI) molecule via the clonotypically expressed T cell receptor (TCR). The lineally expressed coreceptor CD8 interacts coordinately with MHCI at a distinct and largely invariant site to slow the TCR/peptide-MHCI (pMHCI) dissociation rate and enhance antigen sensitivity. However, this biological effect is not necessarily uniform, and theoretical models suggest that antigen sensitivity can be modulated in a differential manner by CD8. We used two intrinsically controlled systems to determine how the relationship between the TCR/pMHCI interaction and the pMHCI/CD8 interaction affects the functional sensitivity of antigen recognition. Our data show that modulation of the pMHCI/CD8 interaction can reorder the agonist hierarchy of peptide ligands across a spectrum of affinities for the TCR.

Preclinical Evaluation of 89Zr-Df-IAB22M2C PET as an Imaging Biomarker for the Development of the GUCY2C-CD3 Bispecific PF-07062119 as a T Cell Engaging Therapy

Purpose

A sensitive and specific imaging biomarker to monitor immune activation and quantify pharmacodynamic responses would be useful for development of immunomodulating anti-cancer agents. PF-07062119 is a T cell engaging bispecific antibody that binds to CD3 and guanylyl cyclase C, a protein that is over-expressed by colorectal cancers. Here, we used ⁸⁹Zr-Df-IAB22M2C (⁸⁹Zr-Df-Crefmirlimab), a human CD8-specific minibody to monitor CD8+ T cell infiltration into tumors by positron emission tomography. We investigated the ability of ⁸⁹Zr-Df-IAB22M2C to track anti-tumor activity induced by PF-07062119 in a human CRC adoptive transfer mouse model (with injected activated/expanded human T cells), as well as the correlation of tumor radiotracer uptake with CD8+ immunohistochemical staining.

Procedures

NOD SCID gamma mice bearing human CRC LS1034 tumors were treated with four different doses of PF-07062119, or a non-targeted CD3 BsAb control, and imaged with ⁸⁹Zr-Df-IAB22M2C PET at days 4 and 9. Following PET/CT imaging, mice were euthanized and dissected for ex vivo distribution analysis of ⁸⁹Zr-Df-IAB22M2C in tissues on days 4 and 9, with additional data collected on day 6 (supplementary). Data were analyzed and reported as standard uptake value and %ID/g for in vivo imaging and ex vivo tissue distribution. In addition, tumor tissues were evaluated by immunohistochemistry for CD8+ T cells.

Results

The results demonstrated substantial mean uptake of ⁸⁹Zr-Df-IAB22M2C (%ID/g) in PF-07062119-treated tumors, with significant increases in comparison to non-targeted BsAb-treated controls, as well as PF-07062119 dose-dependent responses over time of treatment. A moderate correlation was observed between tumor tissue radioactivity uptake and CD8+ cell density, demonstrating the value of the imaging agent for non-invasive assessment of intra-tumoral CD8+ T cells and the mechanism of action for PF-07062119.

Conclusion

Immune-imaging technologies for quantitative cellular measures would be a valuable biomarker in immunotherapeutic clinical development. We demonstrated a qualification of ⁸⁹Zr-IAB22M2C PET to evaluate PD responses (mice) to a novel immunotherapeutic.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-021-01621-0.

MHC multimer: A Molecular Toolbox for Immunologists

The advent of the major histocompatibility complex (MHC) multimer technology has led to a breakthrough in the quantification and analysis of antigen-specific T cells. In particular, this technology has dramatically advanced the measurement and analysis of CD8 T cells and is being applied more widely. In addition, the scope of application of MHC multimer technology is gradually expanding to other T cells such as CD4 T cells, natural killer T cells, and mucosal-associated invariant T cells. MHC multimer technology acts by complementing the T-cell receptor-MHC/peptide complex affinity, which is relatively low compared to antigen-antibody affinity, through a multivalent interaction. The application of MHC multimer technology has expanded to include various functions such as quantification and analysis of antigen-specific T cells, cell sorting, depletion, stimulation to replace antigen-presenting cells, and single-cell classification through DNA barcodes. This review aims to provide the latest knowledge of MHC multimer technology, which is constantly evolving, broaden understanding of this technology, and promote its widespread use.

Methamphetamine facilitates pulmonary and splenic tissue injury and reduces T cell infiltration in C57BL/6 mice after antigenic challenge

Methamphetamine (METH) is a strong addictive central nervous system stimulant. METH abuse can alter biological processes and immune functions necessary for host defense. The acquisition and transmission of HIV, hepatitis, and other communicable diseases are possible serious infectious consequences of METH use. METH also accumulates extensively in major organs. Despite METH being a major public health and safety problem globally, there are limited studies addressing the impact of this popular recreational psychostimulant on tissue adaptive immune responses after exposure to T cell dependent [ovalbumin (OVA)] and independent [lipopolysaccharide (LPS)] antigens. We hypothesized that METH administration causes pulmonary and splenic tissue alterations and reduces T cell responses to OVA and LPS in vivo, suggesting the increased susceptibility of users to infection. Using a murine model of METH administration, we showed that METH causes tissue injury, apoptosis, and alters helper and cytotoxic T cell recruitment in antigen challenged mice. METH also reduces the expression and distribution of CD3 and CD28 molecules on the surface of human Jurkat T cells. In addition, METH decreases the production of IL-2 in these T-like cells, suggesting a negative impact on T lymphocyte activation and proliferation. Our findings demonstrate the pleotropic effects of METH on cell-mediated immunity. These alterations have notable implications on tissue homeostasis and the capacity of the host to respond to infection.

The human T-cell receptor repertoire in health and disease and potential for omics integration

The adaptive immune system arose 600 million years ago in a cold-blooded fish. Over countless generations, our antecedents tuned the function of the T-cell receptor (TCR). The TCR system is arguably the most complex known to science. The TCR evolved hypervariability to fight the hypervariability of pathogens and cancers that look to consume our resources. This review describes the genetics and architecture of the human TCR and highlights surprising new discoveries over the past years that have disproved very old dogmas. The standardization of TCR sequencing data is discussed in preparation for big data bioinformatics and predictive analysis. We next catalogue new signatures and phenomenon discovered by TCR next generation sequencing (NGS) in health and disease and work that remain to be done in this space. Finally, we discuss how TCR NGS can add to immunodiagnostics and integrate with other omics platforms for both a deeper understanding of TCR biology and its use in the clinical setting.

CD8-Specific Designed Ankyrin Repeat Proteins Improve Selective Gene Delivery into Human and Primate T Lymphocytes

Adoptive T cell immunotherapy in combination with gene therapy is a promising treatment concept for chronic infections and cancer. Recently, receptor-targeted lentiviral vectors (LVs) were shown to enable selective gene transfer into particular types of lymphocytes both in vitro and in vivo. This approach might facilitate the genetic engineering of a patient's own T lymphocytes, possibly even shifting this concept from personalized medicine to an off-the shelf therapy in future. Here, we describe novel high-affinity binders for CD8 consisting of designed ankyrin repeat proteins (DARPins), which were selected to bind to the CD8 receptor of human and nonhuman primate (NHP) cells. These binders were identified by ribosome display screening of DARPin libraries using recombinant human CD8 followed by receptor binding analysis on primary lymphocytes. CD8-targeted LVs (CD8-LVs) were then generated that delivered genes exclusively and specifically to human and NHP T lymphocytes by using the same targeting domain. These CD8-LVs were as specific for human T lymphocytes as their single-chain variable fragment-based counterpart, but they could be produced to higher titers. Moreover, they were superior in transducing cytotoxic T cells both in vitro and in vivo when equal particle numbers were applied. Since the here described CD8-LVs transduced primary T lymphocytes from NHP and human donors equally well, they offer the opportunity for preclinical studies in different animal models including large animals such as NHPs without the need for modifications in vector design.

A class of γδ T cell receptors recognize the underside of the antigen-presenting molecule MR1

T cell receptors (TCRs) recognize antigens presented by major histocompatibility complex (MHC) and MHC class I-like molecules. We describe a diverse population of human γδ T cells isolated from peripheral blood and tissues that exhibit autoreactivity to the monomorphic MHC-related protein 1 (MR1). The crystal structure of a γδTCR-MR1-antigen complex starkly contrasts with all other TCR-MHC and TCR-MHC-I-like complex structures. Namely, the γδTCR binds underneath the MR1 antigen-binding cleft, where contacts are dominated by the MR1 α3 domain. A similar pattern of reactivity was observed for diverse MR1-restricted γδTCRs from multiple individuals. Accordingly, we simultaneously report MR1 as a ligand for human γδ T cells and redefine the parameters for TCR recognition.

Simultaneous Analysis of HCV-Specific CD4+ and CD8+ T Cells by Multicolor Flow Cytometry

CD4 T cell responses are key to effective control of HCV infection. However, their precise mechanisms of action and the molecular programs leading to effective T help versus CD4 T cell failure remain elusive. Direct visualization of HCV-specific CD4 T cells using HLA class II tetramers holds the promise to better define the function and phenotype of these cells and to isolate them for further molecular analysis. Here we describe how to utilize peptide-MHC (pMHC) class II tetramers in multicolor flow cytometry to define the expression of molecules on the surface and within HCV-specific CD4 T cells, how to analyze HCV-specific CD4 and CD8 T cells in the same tube, and how to sort live HCV-specific CD4 T cells as single cells or T cell populations for further analysis by RNAseq or other methods.

Expression and characterization of soluble epitope-defined major histocompatibility complex (MHC) from stable eukaryotic cell lines

MHC class I-specific reagents such as fluorescently-labeled multimers (e.g., tetramers) have greatly advanced the understanding of CD8+ T cells under normal and diseased states. However, recombinant MHC class I components (comprising MHC class I heavy chain and β2 microglobulin) are usually produced in bacteria following a lengthy purification protocol that requires additional non-covalent folding steps with exogenous peptide for complete molecular assembly. We have provided an alternative and rapid approach to generating soluble and fully-folded MHC class I molecules in eukaryotic cell lines (such as CHO cells) using a Sleeping Beauty transposon system. Importantly, this method culminates in generating stable cell lines that reliably secrete epitope-defined MHC class I molecules into the tissue media for convenient purification and eventual biotinylation/multimerization. Additionally, MHC class I components are covalently linked, providing the opportunity to produce a diverse set of CD8+ T cell-specific reagents bearing peptides with various affinities to MHC class I.

Optimized Peptide-MHC Multimer Protocols for Detection and Isolation of Autoimmune T-Cells

Peptide–MHC (pMHC) multimers have become the “gold standard” for the detection and isolation of antigen-specific T-cells but recent evidence shows that normal use of these reagents can miss fully functional T-cells that bear T-cell receptors (TCRs) with low affinity for cognate antigen. This issue is particularly pronounced for anticancer and autoimmune T-cells as self-reactive T-cell populations are enriched for low-affinity TCRs due to the removal of cells with higher affinity receptors by immune tolerance mechanisms. Here, we stained a wide variety of self-reactive human T-cells using regular pMHC staining and an optimized technique that included: (i) protein kinase inhibitor (PKI), to prevent TCR triggering and internalization, and (ii) anti-fluorochrome antibody, to reduce reagent dissociation during washing steps. Lymphocytes derived from the peripheral blood of type 1 diabetes patients were stained with pMHC multimers made with epitopes from preproinsulin (PPI), insulin-β chain, glutamic acid decarboxylase 65 (GAD65), or glucose-6-phospate catalytic subunit-related protein (IGRP) presented by disease-risk allelles HLA A*02:01 or HLA*24:02. Samples from ankylosing spondylitis patients were stained with a multimerized epitope from vasoactive intestinal polypeptide receptor 1 (VIPR1) presented by HLA B*27:05. Optimized procedures stained an average of 40.5-fold (p = 0.01, range between 1.4 and 198) more cells than could be detected without the inclusion of PKI and cross-linking anti-fluorochrome antibody. Higher order pMHC dextramers recovered more cells than pMHC tetramers in parallel assays, and standard staining protocols with pMHC tetramers routinely recovered less cells than functional assays. HLA A*02:01-restricted PPI-specific and HLA B*27:05-restricted VIPR1-specific T-cell clones generated using the optimized procedure could not be stained by standard pMHC tetramer staining. However, these clones responded well to exogenously supplied peptide and endogenously processed and presented epitopes. We also showed that anti-fluorochrome antibody-conjugated magnetic beads enhanced staining of self-reactive T-cells that could not be stained using standard protocols, thus enabling rapid ex vivo isolation of autoimmune T-cells. We, therefore, conclude that regular pMHC tetramer staining is generally unsuitable for recovering self-reactive T-cells from clinical samples and recommend the use of the optimized protocols described herein.

Humoral and cellular immune response induced by antigenic protein of Sarcoptes scabiei var. caprae

Aim:

Scabies is one of the most important diseases in goats and caused by a complex hypersensitivity process that involves both humoral and cell-mediated immune responses. This phenomenon shows that the variety of Sarcoptes scabiei has different characteristics of specific antigenic protein or different immune-dominant. This research aims to detect the humoral and cellular immune response of rabbits which were immunized with the protein of S. scabiei var. caprae.

Materials and Methods:

This research was done as follows, identification and collection of Sarcoptes scabiei var caprae from goat infected with scabies, separation of protein antigen from S. scabiei mites with ultrasonic sonicator, measurement of protein content with spectrophotometry, rabbit injection with 500 μg dose of antigen protein which was repeated 5 times (5x booster) every 2 weeks. Measurement of IgG titer using indirect ELISA, whereas to detect the expression of cellular immune response (TLR-9, CD4, and CD8) using Direct Immunofluorescence assay.

Results:

Based on the statistical analysis, it showed that there was a significant enhancement (p<0.05) for optical density value or antibody titer and cellular immune response was shown by TLR-9, CD4, and CD8 expression in rabbit T lymphocytes which appear yellow to green fluorescent color using fluorescence microscope. The amount of fluorescence T lymphocytes showed a significant difference (p<0.05) between the control and various boosters.

Conclusion:

Antigenic protein of S. scabiei var. caprae contains ligands, which are involved in the pathogen-associated molecular pattern that has an ability to induce humoral and cellular immune response in rabbit. Specifically, that TLR-9 is not only involved in innate immunity but also in adaptive immunity and can be used as alternative adjuvant development research.

Peptide-MHC Class I Tetramers Can Fail To Detect Relevant Functional T Cell Clonotypes and Underestimate Antigen-Reactive T Cell Populations

Peptide-MHC (pMHC) multimers, usually used as streptavidin-based tetramers, have transformed the study of Ag-specific T cells by allowing direct detection, phenotyping, and enumeration within polyclonal T cell populations. These reagents are now a standard part of the immunology toolkit and have been used in many thousands of published studies. Unfortunately, the TCR-affinity threshold required for staining with standard pMHC multimer protocols is higher than that required for efficient T cell activation. This discrepancy makes it possible for pMHC multimer staining to miss fully functional T cells, especially where low-affinity TCRs predominate, such as in MHC class II–restricted responses or those directed against self-antigens. Several recent, somewhat alarming, reports indicate that pMHC staining might fail to detect the majority of functional T cells and have prompted suggestions that T cell immunology has become biased toward the type of cells amenable to detection with multimeric pMHC. We use several viral- and tumor-specific pMHC reagents to compare populations of human T cells stained by standard pMHC protocols and optimized protocols that we have developed. Our results confirm that optimized protocols recover greater populations of T cells that include fully functional T cell clonotypes that cannot be stained by regular pMHC-staining protocols. These results highlight the importance of using optimized procedures that include the use of protein kinase inhibitor and Ab cross-linking during staining to maximize the recovery of Ag-specific T cells and serve to further highlight that many previous quantifications of T cell responses with pMHC reagents are likely to have considerably underestimated the size of the relevant populations.

DNA methyltransferase inhibition upregulates MHC-I to potentiate cytotoxic T lymphocyte responses in breast cancer

Potentiating anti-tumor immunity by inducing tumor inflammation and T cell-mediated responses are a promising area of cancer therapy. Immunomodulatory agents that promote these effects function via a wide variety of mechanisms, including upregulation of antigen presentation pathways. Here, we show that major histocompatibility class-I (MHC-I) genes are methylated in human breast cancers, suppressing their expression. Treatment of breast cancer cell lines with a next-generation hypomethylating agent, guadecitabine, upregulates MHC-I expression in response to interferon-γ. In murine tumor models of breast cancer, guadecitabine upregulates MHC-I in tumor cells promoting recruitment of CD8+ T cells to the microenvironment. Finally, we show that MHC-I genes are upregulated in breast cancer patients treated with hypomethylating agents. Thus, the immunomodulatory effects of hypomethylating agents likely involve upregulation of class-I antigen presentation to potentiate CD8+ T cell responses. These strategies may be useful to potentiate anti-tumor immunity and responses to checkpoint inhibition in immune-refractory breast cancers.

Immunotherapy often fails as a single option treatment in cancer. Here, the authors show that targeting of DNA methyltransferases, such as DNMT1, can potentiate anti-tumor immunity and response to checkpoint inhibition by increasing MHC gene expression and the recruitment of CD8+ T cells.

Normalized Synergy Predicts That CD8 Co-Receptor Contribution to T Cell Receptor (TCR) and pMHC Binding Decreases As TCR Affinity Increases in Human Viral-Specific T Cells

The discovery of naturally occurring T cell receptors (TCRs) that confer specific, high-affinity recognition of pathogen and cancer-associated antigens remains a major goal in cellular immunotherapies. The contribution of the CD8 co-receptor to the interaction between the TCR and peptide-bound major histocompatibility complex (pMHC) has previously been correlated with the activation and responsiveness of CD8⁺ T cells. However, these studies have been limited to model systems of genetically engineered hybridoma TCRs or transgenic mouse TCRs against either a single epitope or an array of altered peptide ligands. CD8 contribution in a native human antigen-specific T cell response remains elusive. Here, using Hepatitis C Virus-specific precursor CTLs spanning a large range of TCR affinities, we discovered that the functional responsiveness of any given TCR correlated with the contribution of CD8 to TCR/pMHC binding. Furthermore, we found that CD8 contribution to TCR/pMHC binding in the two-dimensional (2D) system was more accurately reflected by normalized synergy (CD8 cooperation normalized by total TCR/pMHC bonds) rather than synergy (total CD8 cooperation) alone. While synergy showed an increasing trend with TCR affinity, normalized synergy was demonstrated to decrease with the increase of TCR affinity. Critically, normalized synergy was shown to correlate with CTL functionality and peptide sensitivity, corroborating three-dimensional (3D) analysis of CD8 contribution with respect to TCR affinity. In addition, we identified TCRs that were independent of CD8 for TCR/pMHC binding. Our results resolve the current discrepancy between 2D and 3D analysis on CD8 contribution to TCR/pMHC binding, and demonstrate that naturally occurring high-affinity TCRs are more capable of CD8-independent interactions that yield greater functional responsiveness even with CD8 blocking. Taken together, our data suggest that addition of the normalized synergy parameter to our previously established TCR discovery platform using 2D TCR affinity and sequence test would allow for selection of TCRs specific to any given antigen with the desirable attributes of high TCR affinity, CD8 co-receptor independence and functional superiority. Utilizing TCRs with less CD8 contribution could be beneficial for adoptive cell transfer immunotherapies using naturally occurring or genetically engineered T cells against viral or cancer-associated antigens.

Targeted suppression of autoreactive CD8+ T-cell activation using blocking anti-CD8 antibodies

CD8⁺ T-cells play a role in the pathogenesis of autoimmune diseases such as multiple sclerosis and type 1 diabetes. However, drugs that target the entire CD8⁺ T-cell population are not desirable because the associated lack of specificity can lead to unwanted consequences, most notably an enhanced susceptibility to infection. Here, we show that autoreactive CD8⁺ T-cells are highly dependent on CD8 for ligand-induced activation via the T-cell receptor (TCR). In contrast, pathogen-specific CD8⁺ T-cells are relatively CD8-independent. These generic differences relate to an intrinsic dichotomy that segregates self-derived and exogenous antigen-specific TCRs according to the monomeric interaction affinity with cognate peptide-major histocompatibility complex class I (pMHCI). As a consequence, “blocking” anti-CD8 antibodies can suppress autoreactive CD8⁺ T-cell activation in a relatively selective manner. These findings provide a rational basis for the development and in vivo assessment of novel therapeutic strategies that preferentially target disease-relevant autoimmune responses within the CD8⁺ T-cell compartment.

Identification of human viral protein-derived ligands recognized by individual MHCI-restricted T-cell receptors

Evidence indicates that autoimmunity can be triggered by virus-specific CD8⁺ T cells that crossreact with self-derived peptide epitopes presented on the cell surface by major histocompatibility complex class I (MHCI) molecules. Identification of the associated viral pathogens is challenging because individual T-cell receptors can potentially recognize up to a million different peptides. Here, we generate peptide length-matched combinatorial peptide library (CPL) scan data for a panel of virus-specific CD8⁺ T-cell clones spanning different restriction elements and a range of epitope lengths. CPL scan data drove a protein database search limited to viruses that infect humans. Peptide sequences were ranked in order of likelihood of recognition. For all anti-viral CD8⁺ T-cell clones examined in this study, the index peptide was either the top-ranked sequence or ranked as one of the most likely sequences to be recognized. Thus, we demonstrate that anti-viral CD8⁺ T-cell clones are highly focused on their index peptide sequence and that ‘CPL-driven database searching' can be used to identify the inciting virus-derived epitope for a given CD8⁺ T-cell clone. Moreover, to augment access to CPL-driven database searching, we have created a publicly accessible webtool. Application of these methodologies in the clinical setting may clarify the role of viral pathogens in the etiology of autoimmune diseases.

More tricks with tetramers: a practical guide to staining T cells with peptide-MHC multimers

Analysis of antigen-specific T-cell populations by flow cytometry with peptide-MHC (pMHC) multimers is now commonplace. These reagents allow the tracking and phenotyping of T cells during infection, autoimmunity and cancer, and can be particularly revealing when used for monitoring therapeutic interventions. In 2009, we reviewed a number of 'tricks' that could be used to improve this powerful technology. More recent advances have demonstrated the potential benefits of using higher order multimers and of 'boosting' staining by inclusion of an antibody against the pMHC multimer. These developments now allow staining of T cells where the interaction between the pMHC and the T-cell receptor is over 20-fold weaker (K(D) > 1 mm) than could previously be achieved. Such improvements are particularly relevant when using pMHC multimers to stain anti-cancer or autoimmune T-cell populations, which tend to bear lower affinity T-cell receptors. Here, we update our previous work to include discussion of newer tricks that can produce substantially brighter staining even when using log-fold lower concentrations of pMHC multimer. We further provide a practical guide to using pMHC multimers that includes a description of several common pitfalls and how to circumvent them.

Antibody stabilization of peptide-MHC multimers reveals functional T cells bearing extremely low-affinity TCRs

Fluorochrome-conjugated peptide–MHC (pMHC) multimers are commonly used in combination with flow cytometry for direct ex vivo visualization and characterization of Ag-specific T cells, but these reagents can fail to stain cells when TCR affinity and/or TCR cell-surface density are low. pMHC multimer staining of tumor-specific, autoimmune, or MHC class II–restricted T cells can be particularly challenging, as these T cells tend to express relatively low-affinity TCRs. In this study, we attempted to improve staining using anti-fluorochrome unconjugated primary Abs followed by secondary staining with anti-Ab fluorochrome-conjugated Abs to amplify fluorescence intensity. Unexpectedly, we found that the simple addition of an anti-fluorochrome unconjugated Ab during staining resulted in considerably improved fluorescence intensity with both pMHC tetramers and dextramers and with PE-, allophycocyanin-, or FITC-based reagents. Importantly, when combined with protein kinase inhibitor treatment, Ab stabilization allowed pMHC tetramer staining of T cells even when the cognate TCR–pMHC affinity was extremely low (K_D >1 mM) and produced the best results that we have observed to date. We find that this inexpensive addition to pMHC multimer staining protocols also allows improved recovery of cells that have recently been exposed to Ag, improvements in the recovery of self-specific T cells from PBMCs or whole-blood samples, and the use of less reagent during staining. In summary, Ab stabilization of pMHC multimers during T cell staining extends the range of TCR affinities that can be detected, yields considerably enhanced staining intensities, and is compatible with using reduced amounts of these expensive reagents.

Cell type specific gene delivery by lentiviral vectors: New options in immunotherapy

Many cells of the immune system are defined by distinct surface markers, which can be used to restrict gene delivery exclusively to a cell type of choice. This article explains recent findings about a CD8-specific vector that enhances the killing of tumor cells in TCR-based gene transfer strategies.

Comparison of peptide-major histocompatibility complex tetramers and dextramers for the identification of antigen-specific T cells

Fluorochrome-conjugated peptide-major histocompatibility complex (pMHC) multimers are widely used for flow cytometric visualization of antigen-specific T cells. The most common multimers, streptavidin-biotin-based 'tetramers', can be manufactured readily in the laboratory. Unfortunately, there are large differences between the threshold of T cell receptor (TCR) affinity required to capture pMHC tetramers from solution and that which is required for T cell activation. This disparity means that tetramers sometimes fail to stain antigen-specific T cells within a sample, an issue that is particularly problematic when staining tumour-specific, autoimmune or MHC class II-restricted T cells, which often display TCRs of low affinity for pMHC. Here, we compared optimized staining with tetramers and dextramers (dextran-based multimers), with the latter carrying greater numbers of both pMHC and fluorochrome per molecule. Most notably, we find that: (i) dextramers stain more brightly than tetramers; (ii) dextramers outperform tetramers when TCR-pMHC affinity is low; (iii) dextramers outperform tetramers with pMHC class II reagents where there is an absence of co-receptor stabilization; and (iv) dextramer sensitivity is enhanced further by specific protein kinase inhibition. Dextramers are compatible with current state-of-the-art flow cytometry platforms and will probably find particular utility in the fields of autoimmunity and cancer immunology.

The molecular determinants of CD8 co-receptor function

CD8(+) T cells respond to signals mediated through a specific interaction between the T-cell receptor (TCR) and a composite antigen in the form of an epitopic peptide bound between the polymorphic α1 and α2 helices of an MHC class I (MHCI) molecule. The CD8 glycoprotein 'co-receives' antigen by binding to an invariant region of the MHCI molecule and can enhance ligand recognition by up to 1 million-fold. In recent years, a number of structural and biophysical investigations have shed light on the role of the CD8 co-receptor during T-cell antigen recognition. Here, we provide a collated resource for these data, and discuss how the structural and biophysical parameters governing CD8 co-receptor function further our understanding of T-cell cross-reactivity and the productive engagement of low-affinity antigenic ligands.

T-cell receptor gene transfer exclusively to human CD8(+) cells enhances tumor cell killing

Transfer of tumor-specific T-cell receptor (TCR) genes into patient T cells is a promising strategy in cancer immunotherapy. We describe here a novel vector (CD8-LV) derived from lentivirus, which delivers genes exclusively and specifically to CD8(+) cells. CD8-LV mediated stable in vitro and in vivo reporter gene transfer as well as efficient transfer of genes encoding TCRs recognizing the melanoma antigen tyrosinase. Strikingly, T cells genetically modified with CD8-LV killed melanoma cells reproducibly more efficiently than CD8(+) cells transduced with a conventional lentiviral vector. Neither TCR expression levels, nor the rate of activation-induced death of transduced cells differed between both vector types. Instead, CD8-LV transduced cells showed increased granzyme B and perforin levels as well as an up-regulation of CD8 surface expression in a small subpopulation of cells. Thus, a possible mechanism for CD8-LV enhanced tumor cell killing may be based on activation of the effector functions of CD8(+) T cells by the vector particle displaying OKT8-derived CD8-scFv and an increase of the surface density of CD8, which functions as coreceptor for tumor-cell recognition. CD8-LV represents a powerful novel vector for TCR gene therapy and other applications in immunotherapy and basic research requiring CD8(+) cell-specific gene delivery.

Testing for HLA/peptide tetramer-binding to the T cell receptor complex on human T lymphocytes

HLA/peptide tetramers are frequently used for ex vivo monitoring of disease- or vaccine-induced T cell immune responses and for T cell epitope identification. However, when low-levels HLA/peptide tetramer-positive T cell populations are encountered, it is difficult to ascertain whether this represents a true T cell receptor (TCR)-mediated interaction or background signal. To address this issue, we have developed a method for both HLA class I and class II tetramer assays to confirm tetramer-binding to the TCR/CD3 complex. Preincubation of T cells with anti-CD3 mAb SPV-T3b and subsequent crosslinking interferes with the binding of HLA/peptide tetramers to the TCR/CD3 complex and thereby indicates to what extent HLA/peptide tetramer binds through interaction with TCR/CD3 complex. SPV-T3b pretreatment results in a 2- to 10-fold decrease in tetramer-binding intensity to antigen-specific CD8+ or CD4+ T cells, whereas background reactivity of HLA/peptide tetramers containing HIV-derived peptide in HIV-negative donors remained unchanged. SPV-T3b pretreatment forms a valuable tool to verify tetramer-based detection of antigen-specific T cells during the monitoring of immune responses in clinical studies.

The multiple roles of the CD8 coreceptor in T cell biology: opportunities for the selective modulation of self-reactive cytotoxic T cells

Short peptide fragments generated by intracellular protein cleavage are presented on the surface of most nucleated cells bound to highly polymorphic MHCI molecules. These pMHCI complexes constitute an interface that allows the immune system to identify and eradicate anomalous cells, such as those that harbor infectious agents, through the activation of CTLs. Molecular recognition of pMHCI complexes is mediated primarily by clonally distributed TCRs expressed on the surface of CTLs. The coreceptor CD8 contributes to this antigen-recognition process by binding to a largely invariant region of the MHCI molecule and by promoting intracellular signaling, the effects of which serve to enhance TCR stimuli triggered by cognate ligands. Recent investigations have shed light on the role of CD8 in the activation of MHCI-restricted, antigen-experienced T cells and in the processes of T cell selection and lineage commitment in the thymus. Here, we review these data and discuss their implications for the development of potential therapeutic strategies that selectively target pathogenic CTL responses erroneously directed against self-derived antigens.