Brutons tyrosine kinase inhibition to suppress mast cell activation in atherosclerosis

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation

Aim

Acute cardiovascular diseases, such as myocardial infarction or stroke, are still a major cause of death in Western Society. The main underlying pathology of cardiovascular diseases is atherosclerosis, which is caused by the accumulation of lipids and inflammatory cells in the vessel wall, in so-called atherosclerotic plaques. Mast cells accumulate within these atherosclerotic plaques and activation of mast cells leads to the progression and destabilization of advanced plaques via the secretion of pro-inflammatory mediators and cytokines. Mast cells can be activated by various stimuli, of which crosslinking of the Fcε receptor I (FcεRI) with IgE-antigen complexes is best known. Bruton’s tyrosine kinase (BTK), a cytoplasmic nonreceptor tyrosine kinase, is involved in the downstream signaling of FcεRI-mediated mast cell activation and degranulation. Therefore, BTK might be an attractive target to interfere in the FcεRI-mediated mast cell activation pathway. In this study, we thus aimed to assess the effects of the BTK inhibitor ACP-196 on FcεRI-mediated mast cell activation, plaque progression and destabilization in an atherosclerotic mouse model.

Methods and Results

Male LDLr knockout mice, 7-11 weeks old, were treated with ACP-196 (25 mg/kg p.o., n=15) or control solvent (n=14) three times per week for eight weeks. During treatment, mice were fed a Western-type diet (WTD) to induce atherosclerotic plaque formation. During the experiment, plasma total cholesterol levels and body weight did not differ between the control and treatment group. After eight weeks, mice were sacrificed and hearts were isolated to determine atherosclerotic plaque size and stability in the aortic root by histology. Other immunological relevant tissues, such as aorta, spleen and mediastinal lymph nodes were harvested to examine mast cell activation status and other immune cells by flow cytometry. After eight weeks of ACP-196 treatment in LDLr knockout mice, a significant 59% reduction in the frequency of CD117+ FcεRI+ mast cells was observed in aortic plaques of ACP-196 treated mice (0.24±0.06%) compared to control mice (0.57±0.08%, p<0.05), while relative mast cell activation status was not affected. Additionally, ACP-196 treatment inhibited B cell maturation in the circulation, spleen, mediastinal lymph nodes and peritoneal cavity of LDLr knockout mice compared to control mice. However, these effects on immune cells did not translate into effects on atherosclerosis, as ACP-196 treatment (size:12.3±2%; collagen:14.5±1.9%) did not significantly affect atherosclerotic plaque size and collagen content when compared to control mice (size:11.5±1.4%; collagen: 13.6±1.5%).

Conclusions

Conclusively, these findings suggest that ACP-196 treatment leads to reduced migration of mast cells to the atherosclerotic plaques of LDLr knockout mice, but does not directly affect mast cell activation and initial atherosclerotic lesion development.

Virus specific CD8+ T-cells accumulate, but do not recognize antigen, in the atherosclerotic lesion

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): ERA CVD

Dutch Heart Foundation

Viral infections have been associated with the progression of atherosclerosis. CD8+ T-cells directed against common viruses, such as influenza and Epstein-Barr virus, have been detected inside of human atherosclerotic lesions. These virus specific CD8+ T-cells have been hypothesized to contribute to the development of atherosclerosis, however, their mechanism of action in the atherosclerotic lesion remains unclear. This study aimed to characterize the behavior of virus specific CD8+ T-cells in the atherosclerotic lesion.

The presence of virus specific CD8+ T-cells in atherosclerotic lesions was assessed by performing T-cell receptor (TCR)-β sequencing on human endarterectomy samples and patient matched blood samples (N=10). These TCRs were subsequently compared to known virus specific TCR sequences. Virus specific CD8+ T-cells seemed to accumulate in the atherosclerotic lesion (mean=3.5%), compared to patient matched blood samples (mean=2.0%) (p=0.053). Moreover, these virus specific CD8+ T-cells produced significantly more IFN-γ (p=0.0009) and Granzyme B (p=0.0038) in response to external stimuli, suggesting these T-cells may play a pro-inflammatory role in the pathogenesis of atherosclerosis.

To investigate if virus specific CD8+ T-cells can be stimulated in situ, the immunopeptidome of 51 pooled human plaques was determined and matched with various viral peptidomes. Only one peptide presented in the atherosclerotic lesions matched a viral peptidome, rendering almost all virus specific CD8+ T-cells in the lesion antigen non-specific.

In conclusion, virus specific CD8+ T-cells are enriched in atherosclerotic lesions and have an activated phenotype, compared to other plaque residing CD8+ T-cells. The absence of virus specific antigen presentation in the atherosclerotic lesion suggests that if these CD8+ T-cells contribute to inflammation, they do so in an antigen independent manner.

Granzyme B+ CD4+ T cells associate with an unstable plaque phenotype in advanced human atherosclerosis

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): The Dutch Heart Foundation

Cytotoxic CD4+ T cells have previously been found in peripheral blood of patients with coronary artery disease (1), however their occurrence in atherosclerotic plaques and their association with the pathophysiology of atherosclerosis has not been established.

Single-cell RNA sequencing was performed on human carotid atherosclerotic plaques of 18 patients to identify specific T cell populations (2). Next, human femoral and carotid atherosclerotic plaques (n=95) and matched blood samples (n=49) were analyzed by flow cytometry for the presence of CD4+GZMB+ T cells. Plaque morphology was assessed by Movat’s Pentachrome staining.

A distinct cytotoxic GZMB+ PRF1+ CD28- CD4+ T cell cluster was identified using single-cell RNA sequencing. Furthermore, flow cytometry analysis showed that the percentage of GZMB+CD4+ T cells was significantly elevated in plaque compared to blood (Blood: 12.17±2.0 vs. Plaque: 17.40±1.0; P=0.0002). Moreover, a significant positive correlation was observed between the percentage of GZMB+CD4+ T cells in blood versus plaque (P=0.031). In line with the proinflammatory character of these cells, we found a positive association of GZMB+CD4+ T cells (P=0.036) with necrotic core size, whereas no correlation was found with this subtype in the circulation.

In this study we have shown an enrichment of cytotoxic CD4+ T cells in atherosclerotic lesions, which positively correlate with necrotic core size. Future studies are aimed at elucidating the role of these cells in advanced atherosclerosis.