Extensive flow cytometric immunophenotyping of human PBMC incorporating detection of chemokine receptors, cytokines and tetramers

Characterization of immune cells is essential to advance our understanding of immunology and flow cytometry is an important tool in this context. Addressing both cellular phenotype and antigen-specific functional responses of the same cells is valuable to achieve a more integrated understanding of immune cell behavior and maximizes information obtained from precious samples. Until recently, panel size was limiting, resulting in panels generally focused on either deep immunophenotyping or functional readouts. Ongoing developments in the field of (spectral) flow cytometry have made panels of 30⁺ markers more accessible, opening up possibilities for advanced integrated analyses. Here, we optimized immune phenotyping by co-detection of markers covering chemokine receptors, cytokines and specific T cell/peptide tetramer interaction using a 32-color panel. Such panels enable integrated analysis of cellular phenotypes and markers assessing the quality of immune responses and will contribute to our understanding of the immune system.

Thermal-exchange HLA-E multimers reveal specificity in HLA-E and NKG2A/CD94 complex interactions

There is growing interest in HLA-E-restricted T-cell responses as a possible novel, highly conserved, vaccination targets in the context of infectious and malignant diseases. The developing field of HLA multimers for the detection and study of peptide-specific T cells has allowed the in-depth study of TCR repertoires and molecular requirements for efficient antigen presentation and T-cell activation. In this study, we developed a method for efficient peptide thermal exchange on HLA-E monomers and multimers allowing the high-throughput production of HLA-E multimers. We optimized the thermal-mediated peptide exchange, and flow cytometry staining conditions for the detection of TCR and NKG2A/CD94 receptors, showing that this novel approach can be used for high-throughput identification and analysis of HLA-E-binding peptides which could be involved in T-cell and NK cell-mediated immune responses. Importantly, our analysis of NKG2A/CD94 interaction in the presence of modified peptides led to new molecular insights governing the interaction of HLA-E with this receptor. In particular, our results reveal that interactions of HLA-E with NKG2A/CD94 and the TCR involve different residues. Altogether, we present a novel HLA-E multimer technology based on thermal-mediated peptide exchange allowing us to investigate the molecular requirements for HLA-E/peptide interaction with its receptors.

Identification of HLA-E Binding Mycobacterium tuberculosis-Derived Epitopes through Improved Prediction Models

Tuberculosis (TB) remains one of the deadliest infectious diseases worldwide, posing great social and economic burden to affected countries. Novel vaccine approaches are needed to increase protective immunity against the causative agent Mycobacterium tuberculosis (Mtb) and to reduce the development of active TB disease in latently infected individuals. Donor-unrestricted T cell responses represent such novel potential vaccine targets. HLA-E-restricted T cell responses have been shown to play an important role in protection against TB and other infections, and recent studies have demonstrated that these cells can be primed in vitro. However, the identification of novel pathogen-derived HLA-E binding peptides presented by infected target cells has been limited by the lack of accurate prediction algorithms for HLA-E binding. In this study, we developed an improved HLA-E binding peptide prediction algorithm and implemented it to identify (to our knowledge) novel Mtb-derived peptides with capacity to induce CD8+ T cell activation and that were recognized by specific HLA-E-restricted T cells in Mycobacterium-exposed humans. Altogether, we present a novel algorithm for the identification of pathogen- or self-derived HLA-E-presented peptides.

Immunisation with the BCG and DTPw vaccines induces different programs of trained immunity in mice

In addition to providing pathogen-specific immunity, vaccines can also confer nonspecific effects (NSEs) on mortality and morbidity unrelated to the targeted disease. Immunisation with live vaccines, such as the BCG vaccine, has generally been associated with significantly reduced all-cause infant mortality. In contrast, some inactivated vaccines, such as the diphtheria, tetanus, whole-cell pertussis (DTPw) vaccine, have been controversially associated with increased all-cause mortality especially in female infants in high-mortality settings. The NSEs associated with BCG have been attributed, in part, to the induction of trained immunity, an epigenetic and metabolic reprograming of innate immune cells, increasing their responsiveness to subsequent microbial encounters. Whether non-live vaccines such as DTPw induce trained immunity is currently poorly understood. Here, we report that immunisation of mice with DTPw induced a unique program of trained immunity in comparison to BCG immunised mice. Altered monocyte and DC cytokine responses were evident in DTPw immunised mice even months after vaccination. Furthermore, splenic cDCs from DTPw immunised mice had altered chromatin accessibility at loci involved in immunity and metabolism, suggesting that these changes were epigenetically mediated. Interestingly, changing the order in which the BCG and DTPw vaccines were co-administered to mice altered subsequent trained immune responses. Given these differences in trained immunity, we also assessed whether administration of these vaccines altered susceptibility to sepsis in two different mouse models. Immunisation with either BCG or a DTPw-containing vaccine prior to the induction of sepsis did not significantly alter survival. Further studies are now needed to more fully investigate the potential consequences of DTPw induced trained immunity in different contexts and to assess whether other non-live vaccines also induce similar changes.