Periodic Reporting for period 2 - ANIMATE (Adaptive Immunity in Human Atherosclerosis: Understanding its Cellular Basis to Define Novel Immunomodulatory Therapies)
Reporting period: 2021-07-01 to 2022-12-31
Cardiovascular disease (CVD) and its complications, myocardial infarction (MI) and stroke, represent the leading cause of mortality worldwide and cause an estimated 17.9 million deaths annually (~31% of all worldwide death cases). The most common underlying pathology for CVD is atherosclerosis, a chronic disease of the wall of medium-sized and large arteries that leads to the build-up of lipid- and leukocyte-rich atherosclerotic plaques. The continuous growth of atherosclerotic plaques eventually restricts the blood flow, which may cause a total occlusion of the vessel. Atherosclerosis is accompanied by an inflammatory and autoimmune response with immune cells (CD4+ T-helper cells) that falsely respond to endogenous proteins in the body (self-antigens), including ApoB-100 (ApoB), the main protein in low-density lipoprotein (LDL) cholesterol particles. The existence and function of such self-reactive CD4+ T cells remains elusive. For instance, it is not clear whether these are anti-inflammatory and protect from atherosclerosis or pro-inflammatory and pathogenic. In this project, the autoimmune response carried out by T-helper cells will be comprehensively studied by state-of-the-art cellular and molecular tools in mice and humans. Insights of this research will be used to identify novel immunomodulatory strategies to therapeutically stabilize the population of protective ApoB-specific T-helper cells, or to prevent their transformation into pathogenic T cell phenotypes by vaccination. In clinical association studies, a direct correlation of autoimmunity and clinical atherosclerosis will be tested. This project will decipher traits of protective immunity in atherosclerosis and help to build the conceptual framework to define novel therapeutic strategies for patients in the future.
In the last 30 months, we have found that T cells that respond to ApoB are protecting against early atherosclerosis. In fact, these cells exist in most healthy people. Most of these cells can be identified as T-regulatory cells, which are known to dampen immune responses. Thus, autoimmunity against ApoB is protective first. However, during atherosclerosis, this beneficial function is lost. We identified a loss of the important transcription factor FoxP3 as one of the important causes of this switch from protective to pathogenic phenotypes. The response of these atheroprotective cells may be boosted (at an early time-point) by vaccination with ApoB-peptide, but in the natural course of disease it is lost and replaced by a pathogenic phenotype. These findings indicate a potential paradigm shift in T cell biology in atherosclerosis and therefore represents an important breakthrough. That T cells are important for human atherosclerosis was shown by using a novel tool for quantified gene expression in single cells (single cell RNA-sequencing). Applying this tool to human atherosclerotic plaques, obtained after surgery, we showed that mouse atherosclerosis and human atherosclerosis are completely different from a cellular perspective: While mouse atherosclerosis is myeloid cell dominated (monocytes, macrophages), more than 60% of all leukocytes in human plaques are T cells. T cells from human tissue are also more activated than in the mouse. These data advance the field because they show that mouse models, which are most often used in atherosclerosis studies, are only of poor translatable value to investigate immunity, which has not directly been proven so far. We also showed that antibodies against ApoB-peptides correlate to clinical disease states in humans at high risk for atherosclerosis. These findings propose that adaptive immunity is one of the drivers of clinical disease in humans.
Our observation that peptide vaccination can boost protective parts of this response that are lost in older patients, open a new field for novel therapies in the future. We will optimize therapeutic strategies that may be tested in first clinical studies in humans after the completion of this project. We also seek for novel cellular biomarkers that may predict atherosclerotic disease earlier than available routine tests in the clinic. This is particularly important because some people still develop considerable degree of atherosclerosis despite not apparent classical risk factors. We would also like to answer the question whether these people have an overwhelmingly activated immune system. Together with precise mechanistic studies in mouse models that help to clarify how immune cells drive this disease, ANIMATE will considerably refine the classical view of the role of T cells in atherosclerosis.