Memory T cell subsets, migration patterns, and tissue residence

Using epigenetics to define vaccine-induced memory T cells

Memory T cells generated from acute infection or vaccination have the potential to provide the host with life-long immunity against re-infection. Protection by memory T cells is achieved through their acquired ability to persist at anatomical sites of the primary infection as well as maintaining a heightened ability to recall effector functions. The maintenance of CD8 and CD4 T cell function in a state of readiness is key to life-long immunity and manifest through changes in transcriptional regulation. Yet, the ability to identify poised transcriptional programs at the maintenance stage of the response is lacking from most transcriptional profiling studies of memory T cells. Epigenetic profiling allows for the assessment of transcriptionally poised (promoters that are readily accessible for transcription) states of antigen-specific T cells without manipulation of the activation state of the cell. Here we review recent studies that have examined epigenetic programs of effector and memory T cell subsets. These reports demonstrate that acquisition of epigenetic programs during memory T cell differentiation to acute and chronic infections is coupled to, and potentially regulate, the cell's recall response. We discuss the usefulness of epigenetic profiling in characterizing T cell differentiation state and function for preclinical evaluation of vaccines and the current methodologies for single locus versus genome-wide epigenetic profiling.

Human dendritic cell subsets in vaccination

Owing to their properties, dendritic cells (DCs) are often called 'nature's adjuvants' and thus have become the natural targets for antigen delivery. DCs provide an essential link between the innate and the adaptive immune responses. DCs are at the center of the immune system owing to their ability to control both tolerance and immunity. DCs are thus key targets for both preventive and therapeutic vaccination. Herein, we will discuss recent progresses in our understanding of DC subsets physiology as it applies to vaccination.

Memory NK cells: why do they reside in the liver?

Immune memory is the hallmark of adaptive immunity. However, recent studies have shown that natural killer (NK) cells, key components of the innate immune system, also mediate memory responses in mice and humans. Strikingly, memory NK cells were liver-resident in some models, raising the question as to whether the liver is a special organ for the acquisition of NK cell memory. Here, we review the characteristics of NK cell memory by summarizing recent progress and discuss how the liver may generate both the initiation and the recall phase of memory. We propose that the liver may have unique precursors for memory NK cells, which are developmentally distinct from NK cells derived from bone marrow.

CD8+ effector T cells at the fetal-maternal interface, balancing fetal tolerance and antiviral immunity

During pregnancy CD8+ effector T cells need optimal immune regulation to prevent a detrimental response to allogeneic fetal cells while providing immune protection to infections. A significant proportion of (prospective) mothers carry naïve or memory CD8+ T cells with a TCR that can directly bind to paternal MHC molecules. In addition, a high percentage of pregnant women develop specific T cell responses to fetal minor histocompatibility antigens (mHags). Under normal conditions, fetal-maternal MHC and mHag mismatches lead to elevated lymphocyte activation but do not induce pregnancy failure. Furthermore, viral infections alter the maternal CD8+ T cell response by changing the CD8+ T cell repertoire and increasing the influx of CD8+ T cells to decidual tissue. The normally high T cell activation threshold at the fetal-maternal interface may prevent efficient clearance of viral infections. Conversely, the increased inflammatory response due to viral infections may break fetal-maternal tolerance and lead to pregnancy complications. The aim of this review is to discuss the recent studies of CD8+ T cells in pregnancy, identify potential mechanisms for antigen-specific immune recognition of fetal extravillous trophoblast (EVT) cells by CD8+ T cells, and discuss the impact of viral infections and virus-specific CD8+ T cells during pregnancy.

High-dimensional analysis of human CD8(+) T cell phenotype, function, and antigen specificity

Antigen-specific T cells are critical initiators and orchestrators of the adaptive immune response. Categorizing antigen-specific T cell subsets is not a simple task given the diversity of these cells and the large number of parameters that can be considered. Here, we focus on human CD8(+) T cells and discuss the utility of high-dimensional mass cytometric analysis techniques for the concurrent identification and characterization of antigen-specific T cells involved in immunological homeostasis and disease. We first provide an overview of previously identified T cell subsets. We then discuss the segregation of antigen-specific T cells based on protein expression through surface and/or intracellular staining, on functional capacity through measurement expression of cytokines or other inducible markers, and on the antigen-specificity of the cell assessed using peptide-major histocompatibility complex multimers. High-dimensional mass cytometry enables a deeper and more integrated view of all three aspects of antigen-specific T cell diversity than do traditional techniques. Use of mass cytometry for precise measurement of the status of antigen-specific immune responses should result in better prediction of vaccine efficacy and disease outcomes.