Antigen and transforming growth factor Beta receptors contribute to long term functional and phenotypic heterogeneity of memory CD8 T cells

Persistent Antigen Harbored by Alveolar Macrophages Enhances the Maintenance of Lung-Resident Memory CD8+ T Cells

Lung tissue-resident memory T cells are crucial mediators of cellular immunity against respiratory viruses; however, their gradual decline hinders the development of T cell-based vaccines against respiratory pathogens. Recently, studies using adenovirus (Ad)-based vaccine vectors have shown that the number of protective lung-resident CD8+ TRMs can be maintained long term. In this article, we show that immunization of mice with a replication-deficient Ad serotype 5 expressing influenza (A/Puerto Rico/8/34) nucleoprotein (AdNP) generates a long-lived lung TRM pool that is transcriptionally indistinct from those generated during a primary influenza infection. In addition, we demonstrate that CD4+ T cells contribute to the long-term maintenance of AdNP-induced CD8+ TRMs. Using a lineage tracing approach, we identify alveolar macrophages as a cell source of persistent NP Ag after immunization with AdNP. Importantly, depletion of alveolar macrophages after AdNP immunization resulted in significantly reduced numbers of NP-specific CD8+ TRMs in the lungs and airways. Combined, our results provide further insight to the mechanisms governing the enhanced longevity of Ag-specific CD8+ lung TRMs observed after immunization with recombinant Ad.

Zymosan by-passes the requirement for pulmonary antigen encounter in lung tissue-resident memory CD8+ T cell development

Tissue-resident memory T cells (Trm) in the lung provide a frontline defence against respiratory pathogens. Vaccination models that lodge CD8⁺ Trm populations in the lung have been developed, all of which incorporate the local delivery of antigen plus adjuvant into the airways; a necessary approach as local cognate antigen recognition is required for optimal lung Trm development. Although pulmonary delivery of antigen is important for lung Trm development, the impact the co-administered adjuvant has on Trm differentiation is unclear. We show that while altering the adjuvant co-administered with the pulmonary delivered antigen does not impact the size of the lung Trm population, a particular adjuvant, zymosan, when administered into the airways without antigen can drive effector CD8⁺ T cells to differentiate into lung Trm. Zymosan signalling via dectin-1 receptor was sufficient to promote antigen-independent lung Trm development. When combined with an injectable influenza vaccination regime, intranasal zymosan delivery significantly boosted the size of the influenza virus-specific lung Trm population. Our results highlight that eliciting the appropriate local inflammatory milieu can by-pass the requirement for local antigen recognition in lung Trm development and emphasises that the appropriate selection of adjuvant can greatly improve vaccines that aim to elicit pulmonary Trm.

Antibody-targeted vaccination to lung dendritic cells generates tissue-resident memory CD8 T cells that are highly protective against influenza virus infection

Influenza virus gains entry into the body by inhalation and initiates its replication cycle within the lung. The early stage of infection, while the virus is confined to the lung mucosa, provides the ideal window of opportunity for an effective immune response to control the infection. Tissue-resident memory (Trm) CD8 T cells, located in a variety of tissues including the lung, are ideally situated to act during this window and stall the infection. The factors involved in the differentiation of lung Trm cells remain poorly defined. We demonstrate that recognition of antigen presented locally by dendritic cells (DCs) and transforming growth factor-β (TGFβ) signaling are both required. We exploited this knowledge to develop an antibody-targeted vaccination approach to generate lung Trm cells. Delivering antigen exclusively to respiratory DCs results in the development of lung CD8 Trm cells that are highly protective against lethal influenza challenge. Our results describe an effective vaccination strategy that protects against influenza virus infection.

Every breath you take: the impact of environment on resident memory CD8 T cells in the lung

Resident memory T cells (T_RM) are broadly defined as a population of T cells, which persist in non-lymphoid sites long-term, do not re-enter the circulation, and are distinct from central memory T cells (T_CM) and circulating effector memory T cells (T_EM). Recent studies have described populations of T_RM cells in the skin, gut, lungs, and nervous tissue. However, it is becoming increasingly clear that the specific environment in which the T_RM reside can further refine their phenotypical and functional properties. Here, we focus on the T_RM cells that develop following respiratory infection and reside in the lungs and the lung airways. Specifically, we will review recent studies that have described some of the requirements for establishment of T_RM cells in these tissues, and the defining characteristics of T_RM in the lungs and lung airways. With continual bombardment of the respiratory tract by both pathogenic and environmental antigens, dynamic fluctuations in the local milieu including homeostatic resources and niche restrictions can impact T_RM longevity. Beyond a comprehensive characterization of lung T_RM cells, special attention will be placed on studies, which have defined how the microenvironment of the lung influences memory T cell survival at this site. As memory T cell populations in the lung airways are requisite for protection yet wane numerically over time, developing a comprehensive picture of factors which may influence T_RM development and persistence at these sites is important for improving T cell-based vaccine design.