Resistance to superinfection by a vigorously replicating, uncloned stock of simian immunodeficiency virus (SIVmac251) stimulates replication of a live attenuated virus vaccine (SIVmacC8).
Vaccination with live attenuated simian immunodeficiency virus (SIVmacC8) confers potent, reproducible protection against homologous wild-type virus challenge (SIVmacJ5). The ability of SIVmacC8 to confer resistance to superinfection with an uncloned ex vivo derivative of SIVmac251 (SIVmac32H/L28) was investigated. In naïve, Mauritian-derived cynomolgus macaques (Macaca fascicularis), SIVmac32H/L28 replicated to high peak titres (>10(8) SIV RNA copies ml(-1)), persisted at high levels and induced distinctive pathology in lymphoid tissues. In cynomolgus macaques vaccinated with SIVmacC8, no evidence of detectable superinfection was observed in 3/8 vaccinates following challenge 3 or 20 weeks later with SIVmac32H/L28. Analyses after SIVmac32H/L28 challenge revealed a significant reduction in viral RNA (P<0.001) and DNA levels between 20 week vaccinates and challenge controls. Amongst 3 week vaccinates, less potent protection was observed. However, analysis of env from breakthrough virus indicated >99% sequence similarity with the vaccine virus. Highly sensitive PCR assays that distinguish vaccine and challenge virus stocks demonstrated restimulation of replication of the vaccine virus SIVmacC8 in the face of potent protection against a vigorous, homologous challenge virus. Vaccine-induced antiviral neutralizing antibodies and anti-Nef CD8+ cytotoxic T cell responses did not correlate with the outcome of the challenge. Defining the mechanism of vaccine protection will need to account for the effective control of a genetically closely related challenge virus whilst remaining unable to suppress replication of the pre-existing vaccine virus. The role of innate and intrinsic anti-retroviral immunity in the protection conferred by live attenuated SIV vaccines warrants careful study.
Berry
Neil
N
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Stebbings
Richard
R
Division of Biotherapeutics, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Ferguson
Debbie
D
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Ham
Claire
C
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Alden
Jack
J
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Brown
Stuart
S
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Jenkins
Adrian
A
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Lines
Jenny
J
Division of Biotherapeutics, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Duffy
Laura
L
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Davis
Leanne
L
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Elsley
William
W
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Page
Mark
M
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Hull
Robin
R
Division of Biological Services, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Stott
Jim
J
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.
Almond
Neil
N
Division of Retrovirology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK.