The T immune cell responses in the lymph nodes, rather than in the blood, predict the efficacy of live attenuated simian immunodeficiency virus (SIV) vaccines, reports a study published online this week in Nature Medicine. These findings may be applicable to HIV vaccine development.
Live attenuated SIV vaccines can completely protect rhesus macaques from wild type SIV infection, but they are not sufficiently safe to use as a template for HIV vaccines in humans. Nevertheless, understanding the rhesus monkey’s immune responses to SIV vaccines’ protective efficacy is crucial to building a better understanding for HIV vaccine development.
Vaccine-induced protection against viruses is frequently associated with antibody responses or cellular responses in the blood. However, Louis Picker and colleagues found that SIV-specific T cell responses in the lymph node correlated with protection conferred by the live attenuated SIV vaccines. Moreover, persistent replication of the attenuated viruses in follicular helper T cells in the lymph nodes was associated with the protective T cell responses. This suggests that persistent antigen in lymphoid tissues may be required to elicit effector responses of a sufficient magnitude to control infection by the wildtype virus. The authors believe that eliciting effector memory responses in the tissues that first encounter the virus may similarly be necessary to achieve vaccine mediated control of HIV.