CD28 and granulomatosis with polyangiitis: Alterations of the peripheral T-cell compartment have been reported in GPA such as the expansion of circulating effector memory T-cells (TEM) including Th1-type CD4+ and CD8+ T-cell populations lacking costimulatory CD28 expression (CD28−), Th17 and Th22 cells, IL-21-producing cells, and CD4+CD8+ double-positive cells.