DPP4 and infection: However, neither the innate nor the adaptive immune response is affected by the DPP-4 inhibitors being used clinically (128), and reassuringly, there is no evidence for any increased risk of infections in the pooled safety analyses (119–123) or in the CV safety outcome trials (125–127), in line with the view that the catalytic activity of DPP-4 is not necessary for the co-stimulatory role of CD26 in T-cell activation.