CD8A and typhoid fever: The presence of both CD4+ helper T-cells and classical class Ia and non-classical HLA-E-restricted S. Typhi-specific CD8+ T-cells have been observed in individuals with typhoid fever or immunized with Ty21a and other attenuated leading typhoid vaccine candidates, including CVD 908-htrA and CVD 909 (51, 82–85, 88, 92, 114, 122, 123, 152, 172).