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

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