In a 4NQO-induced ABX+CRS mouse model, we found that Kyn treatment led to the exhaustion of CD8+ T cells derived from splenic lymphocytes, as evidenced by the increase expression of immune inhibitory receptors (IRs: programmed cell death receptor 1 (PD-1); lymphocyte activating 3 (LAG-3) and T-cell immunoglobulin and mucin-domain containing-3 (TIM-3)) and the reduced release of the effector cytokines interferon-γ (IFN-γ) and tumour necrosis factor (TNF) (figure 7A). This evidence concerns the gene PDCD1 and congenital rubella syndrome.