Generation of SARS-CoV-2 S1 Spike Glycoprotein Putative Antigenic Epitopes in Vitro by Intracellular Aminopeptidases

Large libraries of single-chain trimer peptide-MHCs enable antigen-specific CD8+ T cell discovery and analysis

The discovery and characterization of antigen-specific CD8+ T cell clonotypes typically involves the labor-intensive synthesis and construction of peptide-MHC tetramers. We adapt single-chain trimer (SCT) technologies into a high throughput platform for pMHC library generation, showing that hundreds can be rapidly prepared across multiple Class I HLA alleles. We use this platform to explore the impact of peptide and SCT template mutations on protein expression yield, thermal stability, and functionality. SCT libraries were an efficient tool for identifying T cells recognizing commonly reported viral epitopes. We then construct SCT libraries to capture SARS-CoV-2 specific CD8+ T cells from COVID-19 participants and healthy donors. The immunogenicity of these epitopes is validated by functional assays of T cells with cloned TCRs captured using SCT libraries. These technologies should enable the rapid analyses of peptide-based T cell responses across several contexts, including autoimmunity, cancer, or infectious disease.

Impact of ACE and Endoplasmic Reticulum Aminopeptidases Polymorphisms on COVID-19 Outcome

Background: COVID-19 outcomes display multiple unexpected varieties, ranging from unnoticed symptomless infection to death, without any previous alarm or known aggravating factors. Aim: To appraise the impact of ACErs4291(A/T) and ERAP1rs26618(T/C) human polymorphisms on the outcome of COVID-19. Subjects and methods: In total, 240 individuals were enrolled in the study (80 with severe manifestations, 80 with mild manifestations, and 80 healthy persons). ACErs4291(A/T) and ERAP1rs26618(T/C) genotyping was performed using RT-PCR. Results: The frequency of the ACErs4291AA genotype was higher among the severe COVID-19 group than others (p < 0.001). The ERAP1rs26618TT genotype frequency was higher among the severe COVID-19 group in comparison with the mild group (p < 0.001) and non-infected controls (p = 0.0006). The frequency of the ACErs4291A allele was higher among severe COVID-19 than mild and non-infected groups (64.4% vs. 37.5%, and 34.4%, respectively), and the ERAP1rs26618T allele was also higher in the severe group (67.5% vs. 39.4%, and 49.4%). There was a statistically significant association between severe COVID-19 and ACErs4291A or ERAP1rs26618T alleles. The coexistence of ACErs4291A and ERAP1rs26618T alleles in the same individual increase the severity of the COVID-19 risk by seven times [OR (95%CI) (LL−UL) = 7.058 (3.752−13.277), p < 0.001). A logistic regression analysis revealed that age, male gender, non-vaccination, ACErs4291A, and ERAP1rs26618T alleles are independent risk factors for severe COVID-19. Conclusions: Persons carrying ACErs4291A and/or ERAP1rs26618T alleles are at higher risk of developing severe COVID-19.

SARS-CoV-2 Envelope-mediated Golgi pH dysregulation interferes with ERAAP retention in cells

Endoplasmic reticulum (ER) aminopeptidase associated with antigen processing (ERAAP) trims peptide precursors in the ER for presentation by major histocompatibility (MHC)-I molecules to surveying CD8+ T-cells. This function allows ERAAP to regulate the nature and quality of the peptide repertoire and, accordingly, the resulting immune responses. We recently showed that infection with murine cytomegalovirus leads to a dramatic loss of ERAAP levels in infected cells. In mice, this loss is associated with the activation of QFL T-cells, a subset of T-cells that monitor ERAAP integrity and eliminate cells experiencing ERAAP dysfunction. In this study, we aimed to identify host factors that regulate ERAAP expression level and determine whether these could be manipulated during viral infections. We performed a CRISPR knockout screen and identified ERp44 as a factor promoting ERAAP retention in the ER. ERp44's interaction with ERAAP is dependent on the pH gradient between the ER and Golgi. We hypothesized that viruses that disrupt the pH of the secretory pathway interfere with ERAAP retention. Here, we demonstrate that expression of the Envelope (E) protein from Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) leads to Golgi pH neutralization and consequently decrease of ERAAP intracellular levels. Furthermore, SARS-CoV-2-induced ERAAP loss correlates with its release into the extracellular environment. ERAAP's reliance on ERp44 and a functioning ER/Golgi pH gradient for proper localization and function led us to propose that ERAAP serves as a sensor of disturbances in the secretory pathway during infection and disease.

Large libraries of single-chain trimer peptide-MHCs enable rapid antigen-specific CD8+ T cell discovery and analysis

CD8 + cytotoxic T cell responses against viral infection represent a major element of the adaptive immune response. We describe the development of a peptide antigen - major histompatibility complex (pMHC) library representing the full SARS-CoV-2 viral proteome, and comprised of 634 pMHC multimers representing the A*02.01, A*24.02, and B*07.02 HLA alleles, as well as specific antigens associated with the cytomegalovirus (CMV). These libraries were used to capture non-expanded CD8 + T cells from blood samples collected from 64 infected individuals, and then analyzed using single cell RNA-seq. The discovery and characterization of antigen-specific CD8 ⁺ T cell clonotypes typically involves the labor-intensive synthesis and construction of peptide-MHC tetramers. We adapted single-chain trimer (SCT) technologies into a high throughput platform for pMHC library generation, showing that hundreds can be rapidly prepared across multiple Class I HLA alleles. We used this platform to explore the impact of peptide and SCT template mutations on protein expression yield, thermal stability, and functionality. SCT libraries were an efficient tool for identifying T cells recognizing commonly reported viral epitopes. We then constructed SCT libraries designed to capture SARS-CoV-2 specific CD8 ⁺ T cells from COVID-19 participants and healthy donors. The immunogenicity of these epitopes was validated by functional assays of T cells with cloned TCRs captured using SCT libraries. These technologies should enable the rapid analyses of peptide-based T cell responses across several contexts, including autoimmunity, cancer, or infectious disease.

Bioinformatic Analysis of B- and T-cell Epitopes from SARS-CoV-2 Structural Proteins and their Potential Cross-reactivity with Emerging Variants and other Human Coronaviruses

BACKGROUND

The mutations in SARS-CoV-2 variants of concern (VOC) facilitate the virus' escape from the neutralizing antibodies induced by vaccines. However, the protection from hospitalization and death is not significantly diminished. Both vaccine boosters and infection improve immune responses and provide protection, suggesting that conserved and/or cross-reactive epitopes could be involved. While several important T- and B-cell epitopes have been identified, mainly in the S protein, the M and N proteins and their potential cross-reactive epitopes with other coronaviruses remain largely unexplored.

AIMS

To identify and map new potential B- and T-cell epitopes within the SARS-CoV-2 S, M and N proteins, as well as cross-reactive epitopes with human coronaviruses.

METHODS

Different bioinformatics tools were used to: i) Identify new and compile previously-reported B-and T-cell epitopes from SARS-CoV-2 S, M and N proteins; ii) Determine the mutations in S protein from VOC that affect B- and T-cell epitopes, and; iii) Identify cross-reactive epitopes with coronaviruses relevant to human health.

RESULTS

New, potential B- and T-cell epitopes from S, M and N proteins as well as cross-reactive epitopes with other coronaviruses were found and mapped within the proteins' structures.

CONCLUSION

Numerous potential B- and T-cell epitopes were found in S, M and N proteins, some of which are conserved between coronaviruses. VOCs present mutations within important epitopes in the S protein; however, a significant number of other epitopes remain unchanged. The epitopes identified here may contribute to augmenting the protective response to SARS-CoV-2 and its variants induced by infection and/or vaccination, and may also be used for the rational design of novel broad-spectrum coronavirus vaccines.

Discovery of the First Selective Nanomolar Inhibitors of ERAP2 by Kinetic Target-Guided Synthesis

Endoplasmic reticulum aminopeptidase 2 (ERAP2) is a key enzyme involved in the trimming of antigenic peptides presented by Major Histocompatibility Complex class I. It is a target of growing interest for the treatment of autoimmune diseases and in cancer immunotherapy. However, the discovery of potent and selective ERAP2 inhibitors is highly challenging. Herein, we have used kinetic target-guided synthesis (KTGS) to identify such inhibitors. Co-crystallization experiments revealed the binding mode of three different inhibitors with increasing potency and selectivity over related enzymes. Selected analogues engage ERAP2 in cells and inhibit antigen presentation in a cellular context. 4 d (BDM88951) displays favorable in vitro ADME properties and in vivo exposure. In summary, KTGS allowed the discovery of the first nanomolar and selective highly promising ERAP2 inhibitors that pave the way of the exploration of the biological roles of this enzyme and provide lead compounds for drug discovery efforts.

To Be or Not to Be: The Case of Endoplasmic Reticulum Aminopeptidase 2

To be, or not to be, that is the question. (William Shakespeare, Hamlet)

Endoplasmic reticulum aminopeptidases 1 and 2 (ERAP1 and ERAP2, respectively) play a role in trimming peptides that are too long to be bound and presented by class I HLA (HLA-I) molecules to CD8⁺ T cells. They may also affect the HLA-I-presented peptide repertoire by overtrimming potential epitopes. Both enzymes may also be released from the cell to cleave cytokine receptors and regulate blood pressure. Both enzymes are polymorphic, which affects their expression, specificity, and activity, resulting in their role in diseases associated with HLA-I. In this brief review, we concentrate on ERAP2, less investigated because of its lack in laboratory mice and 25% of humans, as well as a lower polymorphism. ERAP2 was found to be associated with several diseases and to influence ERAP1 effects. It was discovered recently that the defective ERAP2 gene, not encoding functional aminopeptidase, may nevertheless, during viral infections, produce a truncated protein isoform of unknown function, possibly interfering with ERAP1 and full-length ERAP2 by heterodimer formation. The disease associations of ERAP2, alone or in combination with ERAP1, are reviewed.

Immunouniverse of SARS-CoV-2

SARS-CoV-2 virus has become a global health problem that has caused millions of deaths worldwide. The infection can present with multiple clinical features ranging from asymptomatic or mildly symptomatic patients to patients with severe or critical illness that can even lead to death. Although the immune system plays an important role in pathogen control, SARS-CoV-2 can drive dysregulation of this response and trigger severe immunopathology. Exploring the mechanisms of the immune response involved in host defense against SARS-CoV-2 allows us to understand its immunopathogenesis and possibly detect features that can be used as potential therapies to eliminate the virus. The main objective of this review on SARS-CoV-2 is to highlight the interaction between the virus and the immune response. We explore the function and action of the immune system, the expression of molecules at the site of infection that cause hyperinflammation and hypercoagulation disorders, the factors leading to the development of pneumonia and subsequent severe acute respiratory distress syndrome which is the leading cause of death in patients with COVID-19.

ERAP2 Is Associated With Immune Infiltration and Predicts Favorable Prognosis in SqCLC

Background

Immunotherapy has been proven effective among several human cancer types, including Squamous cell lung carcinoma (SqCLC). ERAP2 plays a pivotal role in peptide trimming of many immunological processes. However, the prognostic role of ERAP2 and its relationship with immune cell infiltration in SqCLC remains unclear.

Methods

The differential expression of ERAP2 was identified via GEO and TCGA databases. We calculated the impact of ERAP2 on clinical prognosis using the Kaplan-Meier plotter. TIMER was applied to evaluate the abundance of immune cells infiltration and immune markers. SqCLC tissue microarrays containing 190 patients were constructed, and we performed immunohistochemical staining for ERAP2, CD8, CD47, CD68, and PD-L1 to validate our findings in public data.

Results

In the GEO SqCLC database, ERAP2 was upregulated in patients with better survival (p=0.001). ERAP2 expression in SqCLC was significantly lower than that of matched normal samples (p<0.05) based on TCGA SqCLC data. Higher expression of ERAP2 was significantly associated with better survival in SqCLC patients from TCGA (p=0.007), KM-plotter (p=0.017), and our tissue microarrays (TMAs) (p=0.026). In univariate and multivariate Cox analysis of SqCLC TMAs, high ERAP2 expression was identified as an independent protective factor for SqCLC patients (Univariate Cox, HR=0.659, range 0.454-0.956, p<0.05. Multivariate Cox, HR=0.578, range 0.385-0.866, p<0.05). In TIMER, ERAP2 was positively correlated with several immune markers (CD274, p=1.27E-04; CD68, p=5.88E-08) and immune infiltrating cells (CD8⁺ T cell, p=4.09E-03; NK cell, p=1.00E-04). In our cohort, ERAP2 was significantly correlated with CD8⁺ tumor-infiltrating lymphocytes (TILs) (p=0.0029), and patients with higher ERAP2 expression had a higher percentage of PD-L1 positive patients (p=0.049) and a higher CD8⁺ TILs level (p=0.036).

Conclusions

For the first time, our study demonstrates that higher expression of ERAP2 is tightly associated with the immuno-supportive microenvironment and can predict a favorable prognosis in SqCLC. Meanwhile, ERAP2 may be a promising immunotherapeutic target for patients with SqCLC.

HLA-B*15 predicts survival in Egyptian patients with COVID-19

Genetic differences among individuals could affect the clinical presentations and outcomes of COVID-19. Human Leukocyte Antigens are associated with COVID-19 susceptibility, severity, and prognosis. This study aimed to identify HLA-B and -C genotypes among 69 Egyptian patients with COVID-19 and correlate them with disease outcomes and other clinical and laboratory data. HLA-B and -C typing was performed using Luminex-based HLA typing kits. Forty patients (58%) had severe COVID-19; 55% of these patients died, without reported mortality in the moderate group. The alleles associated with severe COVID-19 were HLA-B*41, -B*42, -C*16, and -C*17, whereas HLA-B*15, -C*7, and -C*12 were significantly associated with protection against mortality. Regression analysis showed that HLA-B*15 was the only allele associated with predicted protection against mortality, where the likelihood of survival increased with HLA-B*15 (P < 0.001). Patient survival was less likely to occur with higher total leukocytic count, ferritin, and creatinine levels. This study provides interesting insights into the association between HLA class I alleles and protection from or severity of COVID-19 through immune response modulation. This is the first study to investigate this relationship in Egyptian patients. More studies are needed to understand how HLA class I alleles interact and affect Cytotoxic T lymphocytes and natural killer cell function.

Allotypic variation in antigen processing controls antigenic peptide generation from SARS-CoV-2 S1 spike glycoprotein

Population genetic variability in immune system genes can often underlie variability in immune responses to pathogens. Cytotoxic T-lymphocytes are emerging as critical determinants of both severe acute respiratory syndrome coronavirus 2 infection severity and long-term immunity, after either recovery or vaccination. A hallmark of coronavirus disease 2019 is its highly variable severity and breadth of immune responses between individuals. To address the underlying mechanisms behind this phenomenon, we analyzed the proteolytic processing of S1 spike glycoprotein precursor antigenic peptides across ten common allotypes of endoplasmic reticulum aminopeptidase 1 (ERAP1), a polymorphic intracellular enzyme that can regulate cytotoxic T-lymphocyte responses by generating or destroying antigenic peptides. We utilized a systematic proteomic approach that allows the concurrent analysis of hundreds of trimming reactions in parallel, thus better emulating antigen processing in the cell. While all ERAP1 allotypes were capable of producing optimal ligands for major histocompatibility complex class I molecules, including known severe acute respiratory syndrome coronavirus 2 epitopes, they presented significant differences in peptide sequences produced, suggesting allotype-dependent sequence biases. Allotype 10, previously suggested to be enzymatically deficient, was rather found to be functionally distinct from other allotypes. Our findings suggest that common ERAP1 allotypes can be a major source of heterogeneity in antigen processing and through this mechanism contribute to variable immune responses in coronavirus disease 2019.

Immunodominance complexity: lessons yet to be learned from dominant T cell responses to SARS-COV-2

Immunodominance is a complex and highly debated topic of T cell biology. The current SARS-CoV-2 pandemic has provided the opportunity to profile adaptive immune responses and determine molecular factors contributing to emerging responses towards immunodominant viral epitopes. Here, we discuss parameters that alter the dynamics of CD8 viral epitope processing, generation and T-cell responses, and how immunodominance counteracts viral immune escape mechanisms that develop in the context of emerging SARS-CoV-2 variants.

Antigen presentation in SARS-CoV-2 infection: the role of class I HLA and ERAP polymorphisms

Given the highly polymorphic nature of Human Leukocyte Antigen (HLA) molecules, it is not surprising that they function as key regulators of the host immune response to almost all invading pathogens, including SARS-CoV-2, the etiological agent responsible for the recent COVID-19 pandemic. Several correlations have already been established between the expression of a specific HLA allele/haplotype and susceptibility/progression of SARS-CoV-2 infection and new ones are continuously emerging. Protective and harmful HLA variants have been described in both mild and severe forms of the disease, but considering the huge amount of existing variants, the data gathered in such a brief span of time are to some extent confusing and contradictory. The aim of this mini-review is to provide a snap-shot of the main findings so far collected on the HLA-SARS-CoV-2 interaction, so as to partially untangle this intricate yarn. As key factors in the generation of antigenic peptides to be presented by HLA molecules, ERAP1 and ERAP2 role in SARS-CoV-2 infection will be revised as well.

ERAP1 and ERAP2 Enzymes: A Protective Shield for RAS against COVID-19?

Patients with coronavirus disease 2019 (COVID-19) have a wide variety of clinical outcomes ranging from asymptomatic to severe respiratory syndrome that can progress to life-threatening lung lesions. The identification of prognostic factors can help to improve the risk stratification of patients by promptly defining for each the most effective therapy to resolve the disease. The etiological agent causing COVID-19 is a new coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that enters cells via the ACE2 receptor. SARS-CoV-2 infection causes a reduction in ACE2 levels, leading to an imbalance in the renin-angiotensin system (RAS), and consequently, in blood pressure and systemic vascular resistance. ERAP1 and ERAP2 are two RAS regulators and key components of MHC class I antigen processing. Their polymorphisms have been associated with autoimmune and inflammatory conditions, hypertension, and cancer. Based on their involvement in the RAS, we believe that the dysfunctional status of ERAP1 and ERAP2 enzymes may exacerbate the effect of SARS-CoV-2 infection, aggravating the symptomatology and clinical outcome of the disease. In this review, we discuss this hypothesis.

Longitudinal high-throughput TCR repertoire profiling reveals the dynamics of T-cell memory formation after mild COVID-19 infection

COVID-19 is a global pandemic caused by the SARS-CoV-2 coronavirus. T cells play a key role in the adaptive antiviral immune response by killing infected cells and facilitating the selection of virus-specific antibodies. However, neither the dynamics and cross-reactivity of the SARS-CoV-2-specific T-cell response nor the diversity of resulting immune memory is well understood. In this study, we use longitudinal high-throughput T-cell receptor (TCR) sequencing to track changes in the T-cell repertoire following two mild cases of COVID-19. In both donors, we identified CD4+ and CD8+ T-cell clones with transient clonal expansion after infection. We describe characteristic motifs in TCR sequences of COVID-19-reactive clones and show preferential occurrence of these motifs in publicly available large dataset of repertoires from COVID-19 patients. We show that in both donors, the majority of infection-reactive clonotypes acquire memory phenotypes. Certain T-cell clones were detected in the memory fraction at the pre-infection time point, suggesting participation of pre-existing cross-reactive memory T cells in the immune response to SARS-CoV-2.

A New ERAP2/Iso3 Isoform Expression Is Triggered by Different Microbial Stimuli in Human Cells. Could It Play a Role in the Modulation of SARS-CoV-2 Infection?

Following influenza infection, rs2248374-G ERAP2 expressing cells may transcribe an alternative spliced isoform: ERAP2/Iso3. This variant, unlike ERAP2-wt, is unable to trim peptides to be loaded on MHC class I molecules, but it can still dimerize with both ERAP2-wt and ERAP1-wt, thus contributing to profiling an alternative cellular immune-peptidome. In order to verify if the expression of ERAP2/Iso3 may be induced by other pathogens, PBMCs and MDMs isolated from 20 healthy subjects were stimulated with flu, LPS, CMV, HIV-AT-2, SARS-CoV-2 antigens to analyze its mRNA and protein expression. In parallel, Calu3 cell lines and PBMCs were in vitro infected with growing doses of SARS-CoV-2 (0.5, 5, 1000 MOI) and HIV-1BAL (0.1, 1, and 10 ng p24 HIV-1Bal/1 × 106 PBMCs) viruses, respectively. Results showed that: (1) ERAP2/Iso3 mRNA expression can be prompted by many pathogens and it is coupled with the modulation of several determinants (cytokines, interferon-stimulated genes, activation/inhibition markers, antigen-presentation elements) orchestrating the anti-microbial immune response (Quantigene); (2) ERAP2/Iso3 mRNA is translated into a protein (western blot); (3) ERAP2/Iso3 mRNA expression is sensitive to SARS-CoV-2 and HIV-1 concentration. Considering the key role played by ERAPs in antigen processing and presentation, it is conceivable that these enzymes may be potential targets and modulators of the pathogenicity of infectious diseases and further analyses are needed to define the role played by the different isoforms.