Terminally Differentiated CD4+ T Cells Promote Myocardial Inflammaging

The cardiovascular and immune systems undergo profound and intertwined alterations with aging. Recent studies have reported that an accumulation of memory and terminally differentiated T cells in elderly subjects can fuel myocardial aging and boost the progression of heart diseases. Nevertheless, it remains unclear whether the immunological senescence profile is sufficient to cause age-related cardiac deterioration or merely acts as an amplifier of previous tissue-intrinsic damage. Herein, we sought to decompose the causality in this cardio-immune crosstalk by studying young mice harboring a senescent-like expanded CD4+ T cell compartment. Thus, immunodeficient NSG-DR1 mice expressing HLA-DRB1*01:01 were transplanted with human CD4+ T cells purified from matching donors that rapidly engrafted and expanded in the recipients without causing xenograft reactions. In the donor subjects, the CD4+ T cell compartment was primarily composed of naïve cells defined as CCR7+CD45RO-. However, when transplanted into young lymphocyte-deficient mice, CD4+ T cells underwent homeostatic expansion, upregulated expression of PD-1 receptor and strongly shifted towards effector/memory (CCR7- CD45RO+) and terminally-differentiated phenotypes (CCR7-CD45RO-), as typically seen in elderly. Differentiated CD4+ T cells also infiltrated the myocardium of recipient mice at comparable levels to what is observed during physiological aging. In addition, young mice harboring an expanded CD4+ T cell compartment showed increased numbers of infiltrating monocytes, macrophages and dendritic cells in the heart. Bulk mRNA sequencing analyses further confirmed that expanding T-cells promote myocardial inflammaging, marked by a distinct age-related transcriptomic signature. Altogether, these data indicate that exaggerated CD4+ T-cell expansion and differentiation, a hallmark of the aging immune system, is sufficient to promote myocardial alterations compatible with inflammaging in juvenile healthy mice.

Myc overexpression enhances epicardial contribution to the developing heart and promotes extensive expansion of the cardiomyocyte population

Myc is an essential regulator of cell growth and proliferation. Myc overexpression promotes the homeostatic expansion of cardiomyocyte populations by cell competition, however whether this applies to other cardiac lineages remains unknown. The epicardium contributes signals and cells to the developing and adult injured heart and exploring strategies for modulating its activity is of great interest. Using inducible genetic mosaics, we overexpressed Myc in the epicardium and determined the differential expansion of Myc-overexpressing cells with respect to their wild type counterparts. Myc-overexpressing cells overcolonized all epicardial-derived lineages and showed increased ability to invade the myocardium and populate the vasculature. We also found massive colonization of the myocardium by Wt1Cre-derived Myc-overexpressing cells, with preservation of cardiac development. Detailed analyses showed that this contribution is unlikely to derive from Cre activity in early cardiomyocytes but does not either derive from established epicardial cells, suggesting that early precursors expressing Wt1Cre originate the recombined cardiomyocytes. Myc overexpression does not modify the initial distribution of Wt1Cre-recombined cardiomyocytes, indicating that it does not stimulate the incorporation of early expressing Wt1Cre lineages to the myocardium, but differentially expands this initial population. We propose that strategies using epicardial lineages for heart repair may benefit from promoting cell competitive ability.

Temporal fate mapping reveals age-linked heterogeneity in naive T lymphocytes in mice

Understanding how our T-cell compartments are maintained requires knowledge of their population dynamics, which are typically quantified over days to weeks using the administration of labels incorporated into the DNA of dividing cells. These studies present snapshots of homeostatic dynamics and have suggested that lymphocyte populations are heterogeneous with respect to rates of division and/or death, although resolving the details of such heterogeneity is problematic. Here we present a method of studying the population dynamics of T cells in mice over timescales of months to years that reveals heterogeneity in rates of division and death with respect to the age of the host at the time of thymic export. We use the transplant conditioning drug busulfan to ablate hematopoetic stem cells in young mice but leave the peripheral lymphocyte compartments intact. Following their reconstitution with congenically labeled (donor) bone marrow, we followed the dilution of peripheral host T cells by donor-derived lymphocytes for a year after treatment. Describing these kinetics with mathematical models, we estimate rates of thymic production, division and death of naive CD4 and CD8 T cells. Population-averaged estimates of mean lifetimes are consistent with earlier studies, but we find the strongest support for a model in which both naive T-cell pools contain kinetically distinct subpopulations of older host-derived cells with self-renewing capacity that are resistant to displacement by naive donor lymphocytes. We speculate that these incumbent cells are conditioned or selected for increased fitness through homeostatic expansion into the lymphopenic neonatal environment.

Intracellular osteopontin regulates homeostasis and function of natural killer cells

Natural killer (NK) cells play an essential role in the immune response to infection and cancer. After infection or during homeostatic expansion NK cells express a developmental program that includes a contraction phase followed by the formation of long-lived mature memory-like cells. Although this NK cell response pattern is well established, the underlying mechanisms that ensure efficient transition to long-lived NK cells remain largely undefined. Here we report that deficient expression of intracellular osteopontin (OPN-i) by NK cells results in defective responses to IL-15 associated with a substantial increase in the NK cell contraction phase of homeostatic expansion, defective expression of the Eomes transcription factor, and diminished responses to metastatic tumors. The OPN-i–deficient phenotype is accompanied by increased NK cell apoptosis, impaired transition from immature to mature NK cells, and diminished ability to develop memory-like NK cells that respond to mouse cytomegalovirus. Gene pathway analysis of OPN-i–deficient NK cells suggests that the mechanistic target of rapamycin pathway may connect OPN-i to Eomes and T-bet expression by mature NK cells following up-regulation of OPN-i after IL-15 stimulation. Identification of OPN-i as an essential molecular component for maintenance of functional NK cell expansion provides insight into the NK cell response and may provide the basis for improved approaches to immunotherapy for infectious disease and cancer.

Forced miR-146a expression causes autoimmune lymphoproliferative syndrome in mice via downregulation of Fas in germinal center B cells

Key Points miR-146a may be involved in the pathogenesis of ALPS by targeting Fas. Sustained expression of miR-146a in B cells is the major factor leading to the enhanced homeostatic expansion of B and T cells.

A GM-CSF and IL-4 Fusion Cytokine Triggers Conversion of B-Cells to Tumoricidal Effectors

Abstract 1048 We have previously demonstrated that coupling of GMCSF at the N-terminus of common γ-chain interleukins IL2, IL15 and IL21 leads to meaningful gain-of function activity in interleukin-responsive lymphomyeloid cells. Considering the physiological and immunological importance of IL4 that is a member of γ-chain interleukins, we tested the bioactivity of a novel fusion cytokine consisting of a fusion between GM-CSF and IL-4 (GIFT4). We observed that GIFT4 leads to a pan-STAT hyper-phosphorylation response in resting splenic B-cells distinct from IL4 only and that treated B-cells up-regulated expression of MHCI/II, CD80 and CD86, secreted IL-12, IL-1a, IL-6, and substantial amounts of CCL3 and GM-CSF, akin to recently described innate response activator (IRA) B-cells (Science 335, 597, 2012). In vivo delivery of recombinant GIFT4 protein to normal mice leads to homeostatic expansion of splenic B cells and plasma cells as well as humoral hyper-responsiveness to antigenic challenge. We further showed that B16F0 melanoma cells engineered to secrete GIFT4 are immune-rejected in a B-cell dependent manner. The clinical effect was abolished when B16F0-GIFT4 cells were implanted in B-cell deficient μMT, CD4−/−, CD8−/− or FcγR−/− mice consistent with a pivotal for B cells, their T-cell helper function and antibody-dependent cell-mediated cytotoxicity for the observed melanoma-specific therapeutic effect. Thus, GIFT4 defines a novel engineered cytokine that mediates endogenous expansion of B-cells with potent immune helper and antigen-specific effector function. We propose that GIFT4 protein could serve as a novel immunotherapeutic agent and defines a previously unrecognized potential of B-cells as tumoricidal effectors. Disclosures: No relevant conflicts of interest to declare.