Both vaccination and challenge perturbed circulating T cell populations, but only the frequency of SIV-specific CD8 + polyfunctional T cells measured on the day of challenge was associated with protection. Moreover, some evidence of very low level breakthrough of vaccine virus replication was seen and protection was weaker than that obtained with SIVmac239Δ nef.

Protection appeared independent of doxycycline status at the time of virulent virus challenge suggesting that occult replication may not be absolutely necessary for persistence of immunity however, stronger protection was observed in monkeys vaccinated with SIVrtTA where vaccine replication persisted for longer after peak viraemia. To address whether this occult replication is critical to the generation of protective immunity we used a novel construct (SIVrtTA) based on the prototypic live attenuated SIVmac239Δ nef but which requires the presence of the antibiotic doxycycline to replicate. Following disappearance of vaccine virus from the peripheral circulation replication persists in lymphoid tissue. In non-human primates live-attenuated SIV induces a potent vaccine effect. Within the parameters of the study design, on-going occult-phase replication may not be absolutely required for protective immunity.ĭevelopment of an HIV vaccine remains a global health priority. Moreover, challenge virus-specific Nef CD8 + polyfunctional T cell responses and antigen were detected in tissues post mortem in completely-protected macaques indicating post-challenge control of infection. High frequencies of total circulating CD8 +T effector memory cells and a higher total frequency of SIV-specific CD8 + mono and polyfunctional T cells on the day of wild-type challenge were associated with complete protection but these parameters were not predictive of outcome when assessed 130 days after challenge. Mutations were identified in the LTR promoter region and rtTA gene that do not affect doxycycline-control but were associated with enhanced post-acute phase replication in protected vaccinates. Critically, the complete protection in two SIVrtTA vaccinates was associated with enhanced SIVrtTA replication in the immediate post-acute vaccination period but was independent of doxycycline status at the time of challenge. Six vaccinates, four SIVmac239Δ nef and two SIVrtTA vaccinates exhibited complete protection, defined by lack of wild-type viraemia post-challenge and virus-specific PCR analysis of tissues recovered post-mortem, whereas six SIVrtTA vaccinates were protected from high levels of viraemia. Unvaccinated challenge controls exhibited ~10 7 peak plasma viral RNA copies/ml persisting beyond the acute phase.

Doxycycline was withdrawn from 4 of 8 SIVrtTA vaccinates before challenge with wild-type virus. Indian rhesus macaques were vaccinated either with SIVrtTA or with SIVmac239Δ nef. In order to evaluate the role of persisting virus replication during occult phase immunisation in the live attenuated SIV vaccine model, a novel SIVmac239Δ nef variant (SIVrtTA) genetically engineered to replicate in the presence of doxycycline was evaluated for its ability to protect against wild-type SIVmac239.

30 day writing challenge ocult