Melanoma is an immunogenic cancer with a high response rate to immune checkpoint inhibitors (ICIs). It harbors a high mutation burden compared with other cancers and, as a result, has abundant tumor-infiltrating lymphocytes (TILs) within its microenvironment. However, understanding the complex interplay between the stroma, tumor cells, and distinct TIL subsets remains a substantial challenge in immune oncology. To properly study this interplay, quantifying spatial relationships of multiple cell types within the tumor microenvironment is crucial. To address this, we used cytometry time-of-flight (CyTOF) imaging mass cytometry (IMC) to simultaneously quantify the expression of 35 protein markers, characterizing the microenvironment of 5 benign nevi and 67 melanomas. We profiled more than 220,000 individual cells to identify melanoma, lymphocyte subsets, macrophage/monocyte, and stromal cell populations, allowing for in-depth spatial quantification of the melanoma microenvironment. We found that within pretreatment melanomas, the abundance of proliferating antigen-experienced cytotoxic T cells (CD8 ⁺ CD45RO ⁺ Ki67 ⁺ ) and the proximity of antigen-experienced cytotoxic T cells to melanoma cells were associated with positive response to ICIs. Our study highlights the potential of multiplexed single-cell technology to quantify spatial cell-cell interactions within the tumor microenvironment to understand immune therapy responses.

Zika virus (ZIKV) is an emerging arbovirus of the Flaviviridae family. Although ZIKV infection is typically mild and self-limiting in healthy adults, infection has been associated with neurological symptoms such as Guillain-Barré syndrome, and a causal link has been established between fetal microcephaly and ZIKV infection during pregnancy. These risks, and the magnitude of the ongoing ZIKV pandemic, have created an urgent need for the development of animal models to study the immune response to ZIKV infection. Previous animal models have primarily focused on pathogenesis in immunocompromised mice. In this study, we provide a model of ZIKV infection in wild-type immunocompetent C57BL/6 mice, and have provided an analysis of the immune response to infection. We evaluated the activation of several innate immune cell types, and studied the kinetics, phenotype, and functionality of T cell responses to ZIKV infection. Our results demonstrate that ZIKV infection is mild in wild-type immunocompetent C57BL/6 mice, resulting in minimal morbidity. Our data establish that at the peak of the adaptive response, antigen-experienced CD4⁺ T cells polarize to a Th1 phenotype, and antigen-experienced CD8⁺ T cells exhibit an activated effector phenotype, producing both effector cytokines and cytolytic molecules. Furthermore, we have identified a novel ZIKV CD8⁺ T cell epitope in the envelope protein that is recognized by the majority of responding cells. Our model provides an important reference point that will help dissect the impact of polymorphisms in the circulating ZIKV strains on the immune response and ZIKV pathogenesis. In addition, the identification of a ZIKV epitope will allow for the design of tetramers to study epitope-specific T cell responses, and will have important implications for the design and development of ZIKV vaccine strategies. Zika virus (ZIKV) is a mosquito-borne human pathogen of the Flaviviridae family. Most notably, it is responsible for an ongoing epidemic in the Americas, and has been causally linked to birth defects such as fetal microcephaly. These factors have led to an urgent need for small animal models, which may be used to study ZIKV infection, pathogenesis, and the antiviral immune response. To date, the majority of mouse models developed have used mice that lack a competent immune system. These models are excellent for characterizing infection and the pathogenesis of the virus, but are unable to provide a comprehensive analysis of the immune response to ZIKV infection, which will be useful for the design of effective vaccine strategies. Herein, we demonstrate that ZIKV is able to infect wild-type immunocompetent C57BL/6 mice, resulting in activation of the innate immune response and induction of an antiviral T cell response. We have also identified a novel epitope recognized by CD8⁺ T cells within the ZIKV envelope protein. Our model provides an important reference point regarding the T cell response to ZIKV infection, which will be useful in comparative analyses and will have implications in the design and development of effective vaccines.

Due to their ability to rapidly proliferate and produce effector cytokines, memory CD8⁺ T cells increase protection following reexposure to a pathogen. However, low inflammatory immunizations do not provide memory CD8⁺ T cells with a proliferation advantage over naive CD8⁺ T cells, suggesting that cell-extrinsic factors enhance memory CD8⁺ T cell proliferation in vivo. Herein, we demonstrate that inflammatory signals are critical for the rapid proliferation of memory CD8⁺ T cells following infection. Using murine models of viral infection and antigen exposure, we found that type I IFN–driven expression of IL-15 in response to viral infection prepares memory CD8⁺ T cells for rapid division independently of antigen reexposure by transiently inducing cell-cycle progression via a pathway dependent on mTOR complex-1 (mTORC1). Moreover, exposure to IL-15 allowed more rapid division of memory CD8⁺ T cells following antigen encounter and enhanced their protective capacity against viral infection. Together, these data reveal that inflammatory IL-15 promotes optimal responses by memory CD8⁺ T cells.

Recent data illustrate a key role for the transcriptional regulator bric-a-brac, tramtrack, and broad complex and cap’n’collar homology (Bach)2 in orchestrating T cell differentiation and function. Although Bach2 has a well-described role in B cell differentiation, emerging data show that Bach2 is a prototypical member of a novel class of transcription factors that regulates transcriptional activity in T cells at super-enhancers, or regions of high transcriptional activity. Accumulating data demonstrate specific roles for Bach2 in favoring regulatory T cell generation, restraining effector T cell differentiation, and potentiating memory T cell development. Evidence suggests that Bach2 regulates various facets of T cell function by repressing other key transcriptional regulators such as B lymphocyte–induced maturation protein 1. In this review, we examine our present understanding of the role of Bach2 in T cell function and highlight the growing evidence that this transcriptional repressor functions as a key regulator involved in maintenance of T cell quiescence, T cell subset differentiation, and memory T cell generation.

Within the microscopic world, there is an ongoing war between the host and foreign invaders, and the battlefield is the immune system. When a pathogen encounters innate immune cells, such as dendritic cells (DCs), it is quickly recognized as foreign. The DCs provide alarm signals in the form of inflammatory cytokines, degrade the pathogen, and present pathogen-derived peptides to adaptive immune cells, including CD8 + T cells. The primary function of CD8 + (or cytotoxic) T cells is to recognize and kill infected cells. They are critical soldiers of the immune system, but before carrying out their function, they must receive 3 signals to become appropriately activated. A naïve CD8 + T cell must have T-cell receptor (TCR) engagement by peptide: major histocompatibility complex (MHC) complexes from the antigen-presenting cell (signal 1) [1-5], ligation of costimulatory receptors (signal 2) [4, 6-11], and receive specific cytokine signals (signal 3), which are required for optimal cell accumulation, proliferation, and function [9, 12-15]. After integrating the proper signals, the newly activated antigen-specific CD8 + T cells undergo clonal expansion [16-18] and develop into "effectors" that have acquired the capacity to kill pathogen-infected host cells [1, 12, 19-22]. Following clonal expansion, 90%-95% of the pathogen-specific effector CD8 + T-cell population numerically contracts via apoptosis [18, 23, 24], and the remaining 5%-10% of cells constitute a long-lived memory CD8 + T-cell pool that provides enhanced protection from secondary infection (Fig 1A) [18, 23, 25, 26]. The development of the long-lived memory CD8 + T-cell pool is not a stochastic event, and the cells that seed this population can be identified among effector T cells early following infection. Thus, effector CD8 + T cells can be broadly divided into the following 2 subsets: memory precursor effector cells (MPECs), which will predominantly become long-lived memory CD8 + T cells and short-lived effector cells (SLECs), which are mostly lost during contraction after the T-cell response [27]. The establishment of a pool of memory CD8 + T cells is the goal of T-cell vaccination strategies, and understanding how to modulate their function is critical for vaccine development and immunotherapies. CD8 + T-cell battalion: How the host benefits from pathogeninduced inflammation Following infection, inflammatory cytokines (i.e., signal 3) are induced to counter the invading pathogen and to alarm the immune system. Pathogen-induced inflammatory cytokines impact several aspects of memory CD8 + T-cell biology. In addition to serving as signal 3 during the activation of naïve T cells, inflammatory cytokines regulate the antigen sensitivity, proliferation, and trafficking of both effector and established memory T-cell populations, giving the