Requirement for multiple lymphocyte subsets in protection by a live attenuated vaccine against retroviral infection

Infection by live attenuated retroviruses provides excellent protection fro m challenge with pathogenic viruses in several animal models, but little is known about which immune effecters are necessary for protection. We examin ed this using adoptive transfer experiments in the Friend virus mouse model . Transfers of immune spleen cells into naive mice conferred complete prote ction, and transfers of purified lymphocyte subsets demonstrated that this effect required complex immune responses involving CD4(+) and CD8(+) T cell s and also B cells. In addition, passive immunization experiments demonstra ted that antibodies alone reduced virus loads but did not prevent infection . These findings may have implications for retroviral vaccine design in gen eral.