CMV Modulation of the Immune System in ANCA-associated Vasculitis

Infection is the commonest cause of death in patients with ANCA-associated vasculitis (AAV). The investigators have shown that the expansion of CD4+CD28- T-cells present in patients with AAV is driven by CMV and this expansion is associated with increased infection risk. It is suggested that these cells are driven by CMV reactivation and express markers of T-cell exhaustion with reduced cytokine production and inhibitory receptor expression. However the phenotype of CMV-specific T cells in those with extreme expansions of CD4+CD28- T-cells has not been explored. The investigators aim to investigate the phenotype of CMV-specific T-cells comparing those patients with extreme expansions of CD4+CD28- T-cells to those with smaller expansions and relate this to CMV reactivation. The investigators will monitor CMV reactivation in urine and blood monthly by qPCR. This will be correlated with the expansion of CD4+CD28- T-cells and the phenotype of these cells, specifically looking at cytokine production and inhibitory receptor expression. The investigators will identify CMV-specific T-cells by MHC class II tetramers or by stimulating with CMV lysate. The investigators will proceed to undertake a randomised controlled trial with valaciclovir or no treatment to investigate whether the reduction of CMV reactivation improves the phenotype of CD4+CD28- T-cells in these patients.