Conditionally-live attenuated SIV upregulates global T effector memory cell frequency under replication permissive conditions

Abstract

BackgroundLive attenuated SIV induces potent protection against superinfection with virulent virus; however the mechanism of this vaccine effect is poorly understood. Such knowledge is important for the development of clinically acceptable vaccine modalities against HIV.ResultsUsing a novel, doxycycline dependent, replication-competent live-attenuated SIVmac239Δnef (SIV-rtTAΔnef), we show that under replication-permissive conditions SIV-rtTAΔnef is fully viable. Twelve rhesus macaques were infected with a peak plasma vRNA on average two log10 lower than in 6 macaques infected with unconditionally replication-competent SIVΔnef. Consistent with the attenuated phenotype of the viruses the majority of animals displayed low or undetectable levels of viraemia by 42-84 days after infection. Next, comparison of circulating T cells before and after chronic infection with parental SIVΔnef revealed a profound global polarisation toward CD28-CCR7- T-effector memory 2 (TEM2) cells within CD95+CD4+ and CD95+CD8+ populations. Critically, a similar effect was seen in the CD95+ CD4+ population and to somewhat lesser extent in the CD95+ CD8+ population of SIV-rtTAΔnef chronically infected macaques that were maintained on doxycycline, but was not seen in animals from which doxycycline had been withdrawn. The proportions of gut-homing T-central memory (TCM) and TEM defined by the expression of α4β7 and CD95 and differential expression of CD28 were increased in CD4 and CD8 cells under replication competent conditions and gut-homing CD4 TCM were also significantly increased under non-permissive conditions. TEM2 polarisation was seen in the small intestines of animals under replication permissive conditions but the effect was less pronounced than in the circulation. Intracellular cytokine staining of circulating SIV-specific T cells for IL-2, IFN-γ, TNF-α and IL-17 showed that the extent of polyfunctionality in CD4 and CD8 T cells was associated with replication permissivity; however, signature patterns of cytokine combinations were not distinguishable between groups of macaques.ConclusionTaken together our results show that the global T memory cell compartment is profoundly skewed towards a mature effector phenotype by attenuated SIV. Results with the replication-conditional mutant suggest that maintenance of this effect, that may be important in vaccine design, might require persistence of replicating virus.

Role of Occult and Post-acute Phase Replication in Protective Immunity Induced with a Novel Live Attenuated SIV Vaccine

“…Total SIV gag vRNA profiles are shown for Groups A-C as a continuum of vaccination and wild-type challenge profiles (Fig 1C). As previously reported [26], the SIVrtTA vaccinates displayed a transient peak in plasma vRNA kinetics which is characteristic for attenuated SIVmac239Δ nef with two exceptions: E65 (Group A) and E70 (Group B). These animals exhibited a persisting shoulder of ~ 10 2 vRNA copies/ml to ~100 days post-vaccination.…”

“…We have previously reported that under replication permissive conditions, during the period when live attenuated virus RNA was essentially below the limit of detection in plasma, the global circulating T effector memory (T EM ) cell frequency was upregulated [26]. Hence, we were interested to determine if this effect was associated with the degree of protection from superinfection.…”

“…The development of SIVrtTA with potential to be temporally modulated for replication in vivo provides a novel tool to further dissect the processes of protection elicited by live attenuated SIV. Previously, we reported this novel virus to replicate in vivo and being fully infectious in rhesus macaques, with the ability to disseminate to lymphoid tissues and elicit a range of immunological responses including reversible changes in the frequency of memory T cell subsets dependent upon the withdrawal of dox [26]. …”

“…In the study reported here we have sought to influence occult phase persisting turnover of live attenuated SIV using a novel approach: the conditionally live attenuated SIVmac239Δ nef vaccine (SIVrtTA) that in vitro is absolutely dependent on the presence of doxycycline (dox) to replicate [24, 25]. Previously, we have shown that SIVrtTA is infectious in Indian rhesus macaques and induced reversible up-regulation of the frequency of global circulating T EM [26]. …”

Simian Immunodeficiency Virus Infection and Mucosal Immunity

“…Other studies are exploring the links between immunity to HERV antigens, HERV antigen reactivation, and HIV and SIV infection, and preliminary experiments are showing strong correlates of protection using HERV antigen immunization to protect against SIV and HIV using a "cross-clade" immunogenicity approach (Jones et al, 2012). Other methodologies being explored include conditionally replicating SHIVs that can be "turned on" or "off" with antibiotics or other substrates that allow closer examinations of the effective immune responses associated with antigen persistence, yet better control of attenuated vaccines that may limit their potential for pathogenicity (Manoussaka et al, 2013).…”