CTLA4 and xeroderma pigmentosum: Relative to those of the healthy control subjects, the median plasma levels of the XP patients tested (n=15) were significantly elevated, with the median fold increases of CTLA-4, PD-1, PD-L1, LAG-3 and TIM-3 being 3.7-, 2.1-, 4.6-, 1.98- and 2.47-fold (P=0.032-P=0.0001), respectively.