Rationale Accurate knowledge of the cellular composition of the heart is essential to fully understand the changes that occur during pathogenesis and to devise strategies for tissue engineering and regeneration. Objective To examine the relative frequency of cardiac endothelial cells, hematopoietic-derived cells and fibroblasts in the mouse and human heart. Methods and Results Using a combination of genetic tools and cellular markers, we examined the occurrence of the most prominent cell types in the adult mouse heart. Immunohistochemistry revealed that endothelial cells constitute over 60%, hematopoietic-derived cells 5–10%, and fibroblasts under 20% of the non-myocytes in the heart. A refined cell isolation protocol and an improved flow cytometry approach provided an independent means of determining the relative abundance of non-myocytes. High dimensional analysis and unsupervised clustering of cell populations confirmed that endothelial cells are the most abundant cell population. Interestingly, fibroblast numbers are smaller than previously estimated, and two commonly assigned fibroblast markers, Sca-1 and CD90, underrepresent fibroblast numbers. We also describe an alternative fibroblast surface marker that more accurately identifies the resident cardiac fibroblast population. Conclusions This new perspective on the abundance of different cell types in the heart demonstrates that fibroblasts comprise a relatively minor population. By contrast, endothelial cells constitute the majority of non-cardiomyocytes and are likely to play a greater role in physiologic function and response to injury than previously appreciated.

Rationale Cardiac fibroblasts are critical to proper heart function through multiple interactions with the myocardial compartment but appreciation of their contribution has suffered from incomplete characterization and lack of cell-specific markers. Objective To generate an unbiased comparative gene expression profile of the cardiac fibroblast pool, identify and characterize the role of key genes in cardiac fibroblast function, and determine their contribution to myocardial development and regeneration. Methods and Results High-throughput cell surface and intracellular profiling of cardiac and tail fibroblasts identified canonical MSC and a surprising number of cardiogenic genes, some expressed at higher levels than in whole heart. Whilst genetically marked fibroblasts contributed heterogeneously to interstitial but not cardiomyocyte compartments in infarcted hearts, fibroblast-restricted depletion of one highly expressed cardiogenic marker, Tbx20, caused marked myocardial dysmorphology and perturbations in scar formation upon myocardial infarction. Conclusions The surprising transcriptional identity of cardiac fibroblasts, the adoption of cardiogenic gene programs and direct contribution to cardiac development and repair provokes alternative interpretations for studies on more specialized cardiac progenitors, offering a novel perspective for reinterpreting cardiac regenerative therapies.

Cardiac tissue macrophages (cTMs) are abundant in the murine heart but the extent to which the cTM phenotype changes with age is unknown. This study characterizes aging-dependent phenotypic changes in cTM subsets. Using the Cx3cr1GFP/+ mouse reporter line where GFP marks cTMs, and the tissue macrophage marker Mrc1, we show that two major cardiac tissue macrophage subsets, Mrc1−GFPhi and Mrc1+GFPhi cTMs, are present in the young (<10 week old) mouse heart, and a third subset, Mrc1+GFPlo, comprises ~50% of total Mrc1+ cTMs from 30 weeks of age. Immunostaining and functional assays show that Mrc1+ cTMs are the principal myeloid sentinels in the mouse heart and that they retain proliferative capacity throughout life. Gene expression profiles of the two Mrc1+ subsets also reveal that Mrc1+GFPlo cTMs have a decreased number of immune response genes (Cx3cr1, Lpar6, CD9, Cxcr4, Itga6 and Tgfβr1), and an increased number of fibrogenic genes (Ltc4s, Retnla, Fgfr1, Mmp9 and Ccl24), consistent with a potential role for cTMs in cardiac fibrosis. These findings identify early age-dependent gene expression changes in cTMs, with significant implications for cardiac tissue injury responses and aging-associated cardiac fibrosis.

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Mutations in the gene are a main cause of congenital heart disease. Several studies have addressed the phenotypic consequences of disrupting the gene locus, although animal models to date failed to recapitulate the full spectrum of the human disease. Here, we describe a new point mutation murine model, akin to its human counterpart disease-generating mutation. Our model fully reproduces the morphological and physiological clinical presentations of the disease and reveals an understudied aspect of-driven pathology, a primary right ventricular dysfunction. We further describe the molecular consequences of disrupting the transcriptional network regulated by in the heart and show that-dependent perturbation of the Wnt signaling pathway promotes heart dysfunction through alteration of cardiomyocyte metabolism. Our data provide mechanistic insights on how regulates heart function and metabolism, a link in the study of congenital heart disease, and confirms that our models are the first murine genetic models to our knowledge to present all spectra of clinically relevant adult congenital heart disease phenotypes generated by mutations in patients.

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e14607 Background: Concerns have been raised over administration of influenza vaccination concurrent with immune checkpoint inhibitor therapy, specifically, implication in induction of Guillain-Barre syndrome. The aim of this study is to assess the safety and efficacy of influenza vaccination in patients undergoing anti-PD1 therapy. Methods: This is a prospective observational study evaluating the safety and efficacy of Afluria (Seqirus) in patients receiving anti-PD1 therapy. Antibody titers against common influenza A and B antigens were measured by a semi-quantitative ELISA on days 0, 45 and 90+ post vaccine administration to confirm anti-PD1 therapy did not interfere with anti-influenza humoral responses. Influenza infection, confirmed by rapid antigen testing, and influenza-related hospitalizations were reported among vaccinated patients. Safety was assessed using the FDA toxicity grading scale for clinical trials. Results: The acute humoral responses and subsequent IgG responses of the 28 patients included in this study are as follows in the table. IgM responses at 45 days to both influenza A and B common antigens were statistically significant (all P<0.05*). IgG response to common influenza B antigens was increased at day 45 ( P=0.001*). One of 28 patients contracted influenza B infection, confirmed by rapid antigen testing. There were no influenza-related hospitalizations. One patient had a grade 2 local adverse event (AE). A second patient had both a grade 2 local and a grade 2 systemic AE (myalgia). No grade 3/4 local or systemic AEs were reported. Conclusions: Administration of influenza vaccination concurrent with anti-PD1 therapy appeared safe in our study. No grade 3/4 local or systemic AEs were noted. Anti-PD1 therapy did not adversely affect anti-influenza humoral responses. Our data demonstrate that the increase in IgM reactivity to common influenza A and B antigens appears to be an immediate reaction to revaccination. Seroprotection can be inferred by documented infection in only one patient and absence of influenza related-hospitalizations. [Table: see text]

Background: The umbilical artery (UA) Doppler pulsatility index is used clinically to detect elevated feto-placental vascular resistance. However, this metric is confounded by variation in fetal cardiac function and is only moderately predictive of placental pathology. Our group developed a novel ultrasound methodology that measures wave reflections in the UA, thereby isolating a component of the Doppler signal that is specific to the placenta. The present study examined whether wave reflections in the UA are predictive of placental vascular pathology. Methods: Standard clinical Doppler ultrasound of the UAs was performed in 241 pregnant women. Of these, 40 women met narrowly defined preset criteria for the control group, 36 had maternal vascular malperfusion (MVM) and 16 had fetal vascular malperfusion (FVM). Using a computational procedure, the Doppler waveforms were decomposed into a pair of forward and backward propagating waves. Findings: Compared to controls, wave reflections were significantly elevated in women with either MVM (p<0.0001) or FVM pathology (p = 0.02). In contrast, the umbilical and uterine artery pulsatility indices were only elevated in the MVM group (p<0.0001) and there were no differences between women with FVM and the controls. Interpretation: The measurement of wave reflections in the UA, combined with standard clinical ultrasound parameters, has the potential to improve the diagnostic performance of UA Doppler to detect placental vascular pathology. Identifying women with FVM pathology is particularly challenging prenatally and future investigations will determine if women at risk of this specific placental disease could benefit from this novel diagnostic technique.