CTLA4 and viral infectious disease: This study demonstrates that, after control of the viral infection, CD4+ T cells downregulate inhibitory receptors like PD-1 and CTLA-4 and differentiate into long-lived memory cells, whereas persisting viremia continue to activate T cell responses, as well as PD-1 and CTLA-4 expression, and block T cell differentiation until the cells disappear from the circulation [86].