CD8A and infection: 15, 16 In addition, we recently found that immunization with ScaA, when combined with TSA56, not only provides protective immunity against lethal challenges with the homologous strain but also confers significant protection against heterologous strains in a mouse infection model.16 Recently, two other groups reported that CD8 T cells from infected mice protected naive mice from lethal challenges with O. tsutsugamushi.