Large-Scale HLA Tetramer Tracking of T Cells during Dengue Infection Reveals Broad Acute Activation and Differentiation into Two Memory Cell Fates
T cells play important multifaceted roles during dengue infection, and understanding their responses is important for defining correlates of protective immunity and identifying effective vaccine antigens. Using mass cytometry and a highly multiplexed peptide-HLA (human leukocyte antigen) tetramer staining strategy, we probed T cells from dengue patients-a total of 430 dengue and control candidate epitopes-together with key markers of activation, trafficking, and differentiation. During acute disease, dengue-specific CD8+ T cells expressed a distinct profile of activation and trafficking receptors that distinguished them from non-dengue-specific T cells. During convalescence, dengue-specific T cells differentiated into two major cell fates, CD57+ CD127–-resembling terminally differentiated senescent memory cells and CD127+ CD57–-resembling proliferation-capable memory cells. Validation in an independent cohort showed that these subsets remained at elevated frequencies up to one year after infection. These analyses aid our understanding of the generation of T cell memory in dengue infection or vaccination.
Multifactorial heterogeneity of virus-specific T cells and association with the progression of human chronic hepatitis B infection
Associations between chronic antigen stimulation, T cell dysfunction, and the expression of various inhibitory receptors are well characterized in several mouse and human systems. During chronic hepatitis B virus (HBV) infection (CHB), T cell responses are blunted with low frequencies of virus-specific T cells observed, making these parameters difficult to study. Here, using mass cytometry and a highly multiplexed combinatorial peptide–major histocompatibility complex (pMHC) tetramer strategy that allows for the detection of rare antigen-specific T cells, we simultaneously probed 484 unique HLA-A*1101–restricted epitopes spanning the entire HBV genome on T cells from patients at various stages of CHB. Numerous HBV-specific T cell populations were detected, validated, and profiled. T cells specific for two epitopes (HBVpol387 and HBVcore169) displayed differing and complex heterogeneities that were associated with the disease progression, and the expression of inhibitory receptors on these cells was not linearly related with their extent of T cell dysfunction. For HBVcore169-specific CD8+ T cells, we found cellular markers associated with long-term memory, polyfunctionality, and the presence of several previously unidentified public TCR clones that correlated with viral control. Using high-dimensional trajectory analysis of these cellular phenotypes, a pseudo-time metric was constructed that fit with the status of viral infection in corresponding patients. This was validated in a longitudinal cohort of patients undergoing antiviral therapy. Our study uncovers complex relationships of inhibitory receptors between the profiles of antigen-specific T cells and the status of CHB with implications for new strategies of therapeutic intervention.
Late-differentiated effector neoantigen-specific CD8+ T cells are enriched in peripheral blood of non-small cell lung carcinoma patients responding to atezolizumab treatment
There is strong evidence that immunotherapy-mediated tumor rejection can be driven by tumor-specific CD8+ T cells reinvigorated to recognize neoantigens derived from tumor somatic mutations. Thus, the frequencies or characteristics of tumor-reactive, mutation-specific CD8+ T cells could be used as biomarkers of an anti-tumor response. However, such neoantigen-specific T cells are difficult to reliably identify due to their low frequency in peripheral blood and wide range of potential epitope specificities.
Dimensionality reduction for visualizing single-cell data using UMAP
Advances in single-cell technologies have enabled high-resolution dissection of tissue composition. Several tools for dimensionality reduction are available to analyze the large number of parameters generated in single-cell studies. Recently, a nonlinear dimensionality-reduction technique, uniform manifold approximation and projection (UMAP), was developed for the analysis of any type of high-dimensional data. Here we apply it to biological data, using three well-characterized mass cytometry and single-cell RNA sequencing datasets. Comparing the performance of UMAP with five other tools, we find that UMAP provides the fastest run times, highest reproducibility and the most meaningful organization of cell clusters. The work highlights the use of UMAP for improved visualization and interpretation of single-cell data.
Bystander CD8+ T cells are abundant and phenotypically distinct in human tumour infiltrates
Various forms of immunotherapy, such as checkpoint blockade immunotherapy, are proving to be effective at restoring T cell-mediated immune responses that can lead to marked and sustained clinical responses, but only in some patients and cancer types1,2,3,4. Patients and tumours may respond unpredictably to immunotherapy partly owing to heterogeneity of the immune composition and phenotypic profiles of tumour-infiltrating lymphocytes (TILs) within individual tumours and between patients5,6. Although there is evidence that tumour-mutation-derived neoantigen-specific T cells play a role in tumour control2,4,7,8,9,10, in most cases the antigen specificities of phenotypically diverse tumour-infiltrating T cells are largely unknown. Here we show that human lung and colorectal cancer CD8+ TILs can not only be specific for tumour antigens (for example, neoantigens), but also recognize a wide range of epitopes unrelated to cancer (such as those from Epstein–Barr virus, human cytomegalovirus or influenza virus). We found that these bystander CD8+ TILs have diverse phenotypes that overlap with tumour-specific cells, but lack CD39 expression. In colorectal and lung tumours, the absence of CD39 in CD8+ TILs defines populations that lack hallmarks of chronic antigen stimulation at the tumour site, supporting their classification as bystanders. Expression of CD39 varied markedly between patients, with some patients having predominantly CD39− CD8+ TILs. Furthermore, frequencies of CD39 expression among CD8+ TILs correlated with several important clinical parameters, such as the mutation status of lung tumour epidermal growth factor receptors. Our results demonstrate that not all tumour-infiltrating T cells are specific for tumour antigens, and suggest that measuring CD39 expression could be a straightforward way to quantify or isolate bystander T cells.