CD27 and infection: There was a slight shift of cells from the fully differentiated to the undifferentiated and intermediate subpopulations as defined by CD27 and CD28, indicating that differentiation may not be maintained at the same high levels as in the first year of infection, although the tendency of CD8 T-cells of chronically infected adults to retain a large differentiated subpopulation [6], [7] suggests that the populations of the Gambian infants will never approach their pre-infection levels of differentiation.