Developmental dynamics of the neural crest-mesenchymal axis in creating the thymic microenvironment

The thymic stroma is composed of epithelial and nonepithelial cells providing separate microenvironments controlling homing, differentiation, and selection of hematopoietic precursor cells to functional T cells. Here, we explore at single-cell resolution the complex composition and dynamic changes of the nonepithelial stromal compartment across different developmental stages in the human and mouse thymus, and in an experimental model of the DiGeorge syndrome, the most common form of human thymic hypoplasia. The detected gene expression signatures identify previously unknown stromal subtypes and relate their individual molecular profiles to separate differentiation trajectories and functions, revealing an unprecedented heterogeneity of different cell types that emerge at discrete developmental stages and vary in their expression of key regulatory signaling circuits and extracellular matrix components. Together, these findings highlight the dynamic complexity of the nonepithelial thymus stroma and link this to separate instructive roles essential for normal thymus organogenesis and tissue maintenance.

Prognostic impact of neurohormonal inhibition in pulmonary arterial hypertension

Background

Experimental evidence points towards a hyperactivity of the sympathetic nervous system and renin-angiotensin-aldosterone system in the pathobiology of pulmonary arterial hypertension (PAH), raising the hypothesis that blockade of neurohormonal axis may have favorable effects in this context.

Purpose

To assess the use and prognostic impact of neurohormonal inhibitors (NEUi) in a single centre cohort of subjects with PAH.

Methods

We analysed retrospectively collected data from our register of right heart catheterizations (RHC) performed consecutively from January 1st 2005 until October 31st 2018. We selected patients with PAH and complete information about demographics, biochemical data and drug therapy at the time of RHC. Patients on beta-blocker, angiotensin-converting enzyme inhibitor (ACEi), angiotensin receptor blocker (ARB) or mineralocorticoid receptor antagonist (MRA) at the time of RHC were classified as NEUi users. Comparisons between NEUi recipients and non-recipients were drawn by chi-square or t-test, as appropriate. Death from any cause was assessed by Kaplan-Meier analysis.

Results

Complete data were available for 57 PAH patients. Mean pulmonary artery pressure, pulmonary artery wedge pressure, diastolic pressure gradient, pulmonary vascular resistance and cardiac index were 45.0±14.9 mmHg, 10.9±3.5 mmHg, 16.0±10.2 mmHg, 8.8±5.1 Wood units and 2.5±0.8 l/min/m2 respectively. Twenty-seven subjects (47.4%) were taking at least one NEUi when RHC was performed: 12 (21.1%) were on beta-blocker, 15 (26.3%) on ACEi/ARB and 6 (10.5%) on MRA. NEUi users were significantly older (67.6±11.9 vs. 58.3±15.2 years, p=0.039), had a higher body mass index (25.9±4.4 vs. 23.6±3.5, p=0.029), more frequently systemic arterial hypertension (74.1% vs. 40.0%, p=0.020), smoking habit (51.9% vs. 20.0%, p=0.025) and lower estimated glomerular filtration rate (58.7±22.7 vs. 73.7±24.7 ml/min/1.73 m2, p=0.022) than non-users. Moreover, 5 NEUi users (18.5%), but no NEUi non-users, had a history of coronary artery disease. Hemodynamic parameters were similar in NEUi recipients and non-recipients (p=NS). Seven patients (25.9%) died in the NEUi users group vs. 17 (56.7%) in the non-users one (p=0.038). Kaplan-Meier analysis confirmed that subjects not taking NEUi were more likely to die over the course of follow-up (Log-Rank p=0.020) (Figure 1).

Conclusions

Our data identify a subset of atypical PAH patients, with pre-capillary pulmonary hypertension and a comorbidity profile for left heart disease (LHD), in whom NEUi have shown to improve survival. A prognostic benefit of NEUi, due to their effects on cardiovascular comorbidities in this kind of patients, has been speculated. Future prospective studies are needed to identify the most appropriate treatment strategies for atypical forms of PAH, with subtle and probably covert LHD.

Figure 1. Kaplan-Meier survival curves

Funding Acknowledgement

Type of funding source: None

Keratinocyte growth factor impairs human thymic recovery from lymphopenia

BACKGROUND

The lymphocyte-depleting antibody alemtuzumab is a highly effective treatment of relapsing-remitting multiple sclerosis (RRMS); however 50% of patients develop novel autoimmunity post-treatment. Most at risk are individuals who reconstitute their T-cell pool by proliferating residual cells, rather than producing new T-cells in the thymus; raising the possibility that autoimmunity might be prevented by increasing thymopoiesis. Keratinocyte growth factor (palifermin) promotes thymopoiesis in non-human primates.

METHODS

Following a dose-tolerability sub-study, individuals with RRMS (duration ≤10 years; expanded disability status scale ≤5·0; with ≥2 relapses in the previous 2 years) were randomised to placebo or 180mcg/kg/day palifermin, given for 3 days immediately prior to and after each cycle of alemtuzumab, with repeat doses at M1 and M3. The interim primary endpoint was naïve CD4+ T-cell count at M6. Exploratory endpoints included: number of recent thymic-emigrants (RTEs) and signal-joint T-cell receptor excision circles (sjTRECs)/mL of blood. The trial primary endpoint was incidence of autoimmunity at M30.

FINDINGS

At M6, individuals receiving palifermin had fewer naïve CD4+T-cells (2.229x107/L vs. 7.733x107/L; p=0.007), RTEs (16% vs. 34%) and sjTRECs/mL (1100 vs. 3396), leading to protocol-defined termination of recruitment. No difference was observed in the rate of autoimmunity between the two groupsConclusion: In contrast to animal studies, palifermin reduced thymopoiesis in our patients. These results offer a note of caution to those using palifermin to promote thymopoiesis in other settings, particularly in the oncology/haematology setting where alemtuzumab is often used as part of the conditioning regime.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01712945Funding: MRC and Moulton Charitable Foundation.