T cells have pivotal roles in the immune response that drives atherosclerosis in patients with coronary artery disease (CAD). Of note, a peculiar subset of T cells, the CD4 + CD28null T lymphocytes, expand significantly in patients with acute coronary syndrome (ACS), while in stable angina (SA) their frequency is not significantly different from healthy subjects. CD4 + CD28null T cells are highly inflammatory and cytotoxic in spite of lacking the costimulatory receptor CD28, which is crucial for optimal function of T lymphocytes. The mechanisms that govern the function of CD4 + CD28null T cells are not known. The aim of this study was to investigate the expression and function of alternative costimulatory receptors in CD4 + CD28null T cells in CAD patients.Methods
The expression of alternative costimulatory receptors ICOS, CTLA-4, PD-1, OX40 and 4-1BB was quantified in CD4 + CD28null and conventional CD4 + CD28 + T cells from peripheral blood of ACS (n=24) and SA (n=24) patients. Furthermore, the inflammatory and cytotoxic function of CD4 + CD28null T cells was analysed. In addition, human atherosclerotic plaques from carotid endarterectomy were studied for the presence of CD4 + CD28null T cells and the expression of costimulatory receptors and ligands.Results
We found that in ACS patients, levels of costimulatory receptors OX40 and 4-1BB were significantly higher in circulating CD4 + CD28null T cells compared to conventional CD4 + CD28 + T lymphocytes. Of note, this alteration was specific to ACS as CD4 + CD28null T cells from SA patients showed similar OX40 and 4-1BB levels to their conventional counterparts. Furthermore, we showed that CD4 + CD28null T cells constitute an important proportion of CD4 + T lymphocytes in atherosclerotic plaques and express high levels of OX40 and 4-1BB. The ligands for OX40 and 4-1BB were present in atherosclerotic plaques and also expressed on monocytes in the peripheral circulation. Importantly, blockade of the alternative costimulatory receptors OX40 and 4-1BB reduced the ability of CD4 + CD28null T cells to produce inflammatory cytokines (IFN-gamma and TNF-alpha) and to release cytotoxic molecules like perforin.Conclusions
Costimulatory pathways are altered in CD4 + CD28null T cells from ACS patients. We show that the inflammatory and cytotoxic function of CD4 + CD28null T cells can be inhibited by blocking OX40 and 4-1BB costimulatory receptors. Modulation of costimulatory pathways will allow specific targeting of this cell subset and may improve the survival of ACS patients.