CD28 and cytomegalovirus infection: In the present study, we studied 10 polymorphisms in patients with liver transplant of PD-1 gene (PD1.1 A/G, PD1.3 A/G, PD1.9 C/T), ICOS (693 A/G, 1720 C/T), CTLA-4 gene (318 C/T, 1722 T/C, 1661 A/G, 49 A/G), and CD28 (IVS3+17 C/T) and their association with CMV infection.