DOCK2 Sets the Threshold for Entry into the Virtual Memory CD8+ T Cell Compartment by Negatively Regulating Tonic TCR Triggering

The transcriptional cofactor Tle3 reciprocally controls effector and central memory CD8+ T cell fates

Antigen-experienced CD8+ T cells form effector and central memory T cells (TEM and TCM cells, respectively); however, the mechanism(s) controlling their lineage plasticity remains incompletely understood. Here we show that the transcription cofactor Tle3 critically regulates TEM and TCM cell fates and lineage stability through dynamic redistribution in antigen-responding CD8+ T cell genome. Genetic ablation of Tle3 promoted CD8+ TCM cell formation at the expense of CD8+ TEM cells. Lineage tracing showed that Tle3-deficient CD8+ TEM cells underwent accelerated conversion into CD8+ TCM cells while retaining robust recall capacity. Tle3 acted as a coactivator for Tbet to increase chromatin opening at CD8+ TEM cell-characteristic sites and to activate CD8+ TEM cell signature gene transcription, while engaging Runx3 and Tcf1 to limit CD8+ TCM cell-characteristic molecular features. Thus, Tle3 integrated functions of multiple transcription factors to guard lineage fidelity of CD8+ TEM cells, and manipulation of Tle3 activity could favor CD8+ TCM cell production.

DOCK2-deficiency causes defects in anti-viral T cell responses and poor control of herpes simplex virus infection

The expanding number of rare immunodeficiency syndromes offers an opportunity to understand key genes that support immune defence against infectious diseases. However, patients with these diseases are by definition rare. In addition, any analysis is complicated by treatments and co-morbid infections requiring the use of mouse models for detailed investigations. Here we develop a mouse model of DOCK2 immunodeficiency and demonstrate that these mice have delayed clearance of herpes simplex virus type 1 (HSV-1) infections. Further, we found that they have a critical, cell intrinsic role of DOCK2 in the clonal expansion of anti-viral CD8+ T cells despite normal early activation of these cells. Finally, while the major deficiency is in clonal expansion, the ability of primed and expanded DOCK2-deficient CD8+ T cells to protect against HSV-1-infection is also compromised. These results provide a contributing cause for the frequent and devastating viral infections seen in DOCK2-deficient patients and improve our understanding of anti-viral CD8+ T cell immunity.

Pre-existing T Cell Memory to Novel Pathogens

Immunological experiences lead to the development of specific T and B cell memory, which readies the host for a later pathogen rechallenge. Currently, immunological memory is best understood as a linear process whereby memory responses are generated by and directed against the same pathogen. However, numerous studies have identified memory cells that target pathogens in unexposed individuals. How "pre-existing memory" forms and impacts the outcome of infection remains unclear. In this review, we discuss differences in the composition of baseline T cell repertoire in mice and humans, factors that influence pre-existing immune states, and recent literature on their functional significance. We summarize current knowledge on the roles of pre-existing T cells in homeostasis and perturbation and their impacts on health and disease.

Insights from DOCK2 in cell function and pathophysiology

Dedicator of cytokinesis 2 (DOCK2) can activate the downstream small G protein Rac and regulate cytoskeletal reorganization. DOCK2 is essential for critical physiological processes such as migration, activation, proliferation, and effects of immune cells, including lymphocytes, neutrophils, macrophages, and dendritic cells. For example, DOCK2 is involved in the development and activation of T and B lymphocytes by affecting synapse formation and inhibiting the development of the Th2 lineage by downregulating IL-4Rα surface expression. Not only that, DOCK2 may be a molecular target for controlling cardiac transplant rejection and Alzheimer’s disease (AD). Patients with defects in the DOCK2 gene also exhibit a variety of impaired cellular functions, such as chemotactic responses of lymphocytes and reactive oxygen species (ROS) production by neutrophils. To date, DOCK2 has been shown to be involved in the development of various diseases, including AD, pneumonia, myocarditis, colitis, tumors, etc. DOCK2 plays different roles in these diseases and the degree of inflammatory response has a different impact on the progression of disease. In this paper, we present a review of recent advances in the function of DOCK2 in various immune cells and its role in various diseases.

Functional heterogeneity and adaptation of naive T cells in response to tonic TCR signals

Mature CD4⁺ and CD8⁺ T cells constitutively experience weak T cell receptor (TCR) stimulation in response to self-antigens, termed tonic (or basal) signaling. How tonic TCR signal strength impacts T cell responses to foreign antigens is an active area of investigation. Such studies rely on surrogate markers of tonic signal strength, including CD5, Ly6C, and transgenic reporters of Nr4a genes. Recent research indicates that strong tonic TCR signal strength influences basal T cell metabolism, effector differentiation, and TCR signal transduction. T cells that experience the strongest tonic TCR signaling exhibit features of T cell activation and negative regulation. These data suggest a model whereby adaptation to tonic signaling has lasting effects that alter T cell activation and differentiation.

Signals for antigen-independent differentiation of memory CD8+ T cells

Conventional CD8+ memory T cells develop upon stimulation with foreign antigen and provide increased protection upon re-challenge. Over the past two decades, new subsets of CD8+ T cells have been identified that acquire memory features independently of antigen exposure. These antigen-inexperienced memory T cells (TAIM) are described under several names including innate memory, virtual memory, and memory phenotype. TAIM cells exhibit characteristics of conventional or true memory cells, including antigen-specific responses. In addition, they show responsiveness to innate stimuli and have been suggested to provide additional levels of protection toward infections and cancer. Here, we discuss the current understanding of TAIM cells, focusing on extrinsic and intrinsic molecular conditions that favor their development, their molecular definitions and immunological properties, as well as their transcriptional and epigenetic regulation.

DOCK2 contributes to endotoxemia-induced acute lung injury in mice by activating proinflammatory macrophages

Dedicator of cytokinesis 2 (DOCK2), an atypical Rac activator, has important anti-inflammatory properties in blepharitis, enteric bacterial infection and colitis. However, the roles of DOCK2 in macrophage activation and acute lung injury (ALI) are still poorly elucidated. In vitro studies demonstrated that DOCK2 was essential for the nucleotide-sensing Toll-like receptor (TLR) 4-mediated inflammatory response in macrophages. We also confirmed that exposure of macrophages to LPS induced Rac activation through a TLR4-independent, DOCK2-dependent mechanism. Phosphorylation of IκB kinase (IKK) β and nuclear translocation of transcription factor nuclear factor kappa B (NF-κB) were impaired in Ad-shDOCK2-expressing macrophages, resulting in a decreased inflammatory response. Similar results were obtained when EHop-016 (a Rac inhibitor) was used to treat uninfected macrophages. In summary, these data indicate that the DOCK2-Rac signaling pathway acts in parallel with TLR4 engagement to control IKKβ activation for inflammatory cytokine release. Next, we investigated whether pharmacological inhibition of DOCK2 protects against endotoxemia-induced lung injury in mice. Treatment with 4-[3'-(2″-chlorophenyl)-2'-propen-1'-ylidene]-1-phenyl-3,5-pyrazolidinedione (CPYPP), a small-molecule inhibitor of DOCK2, reduced the severity of lung injury, as indicated by decreases in the lung injury score and myeloperoxidase (MPO) activity. Moreover, CPYPP attenuated LPS-induced proinflammatory cytokine release in mice. Our studies suggest that inhibition of DOCK2 may suppress LPS-induced macrophage activation and that DOCK2 may be a novel target for treating endotoxemia-related ALI.