Clarke B

Bio: Clarke B is an academic researcher from Wellcome Trust. The author has contributed to research in topics: Virus & Simian immunodeficiency virus. The author has an hindex of 1, co-authored 1 publications receiving 234 citations.

Increased Immune Response Elicited by DNA Vaccination with a Synthetic gp120 Sequence with Optimized Codon Usage

Abstract: DNA vaccination elicits humoral and cellular immune responses and has been shown to confer protection against several viral, bacterial, and parasitic pathogens. Here we report that optimized codon usage of an injected DNA sequence considerably increases both humoral and cellular immune responses. We recently generated a synthetic human immunodeficiency virus type 1 gp120 sequence in which most wild-type codons were replaced with codons from highly expressed human genes (syngp120). In vitro expression of syngp120 is considerably increased in comparison to that of the respective wild-type sequence. In BALB/c mice, DNA immunization with syngp120 resulted in significantly increased antibody titers and cytotoxic T-lymphocyte reactivity, suggesting a direct correlation between expression levels and the immune response. Moreover, syngp120 is characterized by rev-independent expression and a low risk of recombination with viral sequences. Thus, synthetic genes with optimized codon usage represent a novel strategy to increase the efficacy and safety of DNA vaccination.

Live attenuated, multiply deleted simian immunodeficiency virus causes AIDS in infant and adult macaques

Abstract: A substantial risk in using live attenuated, multiply deleted viruses as vaccines against AIDS is their potential to induce AIDS. A mutant of the simian immunodeficiency virus (SIV) with large deletions in nef and vpr and in the negative regulatory element induced AIDS in six of eight infant macaques vaccinated orally or intravenously. Early signs of immune dysfunction were seen in the remaining two offspring. Prolonged follow-up of sixteen vaccinated adult macaques also showed resurgence of chronic viremia in four animals: two of these developed early signs of disease and one died of AIDS. We conclude that this multiply deleted SIV is pathogenic and that human AIDS vaccines built on similar prototypes may cause AIDS.

Vaccine protection by a triple deletion mutant of simian immunodeficiency virus.

Abstract: Twelve rhesus monkeys were vaccinated with SIVmac316 delta nef (lacking nef sequences), and 12 were vaccinated with SIVmac239 delta3 (lacking nef, vpr, and upstream sequences in U3). SIVmac316 and SIVmac239 differ by only eight amino acids in the envelope; these changes render SIVmac316 highly competent for replication in macrophages. Seventeen of the animals developed persistent infections with the vaccine viruses. Seven of the 24 vaccinated animals, however, developed infections that were apparently transient in nature. Six of these seven yielded virus from peripheral blood when tested at weeks 2 and/or 3, three of the seven had transient antibody responses, but none of the seven had persisting antibody responses. The 24 monkeys were challenged in groups of four with 10 rhesus monkey infectious doses of wild-type, pathogenic SIVmac251 at weeks 8, 20, and 79 following receipt of vaccine. None of the seven with apparently transient infections with vaccine virus were protected upon subsequent challenge. Analysis of cell-associated viral loads, CD4+ cell counts, and viral gene sequences present in peripheral blood in the remainder of the monkeys following challenge allowed a number of conclusions. (i) There was a trend toward increased protection with length of time of vaccination. (ii) Solid vaccine protection was achieved by 79 weeks with the highly attenuated SIV239 delta3. (iii) Solid long-term protection was achieved in at least two animals in the absence of complete sterilizing immunity. (iv) Genetic backbone appeared to influence protective capacity; animals vaccinated with SIV239 delta3 were better protected than animals receiving SIV316 delta nef. This better protection correlated with increased levels of the replicating vaccine strain. (v) The titer of virus-neutralizing activity in serum on the day of challenge correlated with protection when measured against a primary stock of SIVmac251 but not when measured against a laboratory-passaged stock. The level of binding antibodies to whole virus by enzyme-linked immunosorbent assay also correlated with protection.

Simian immunodeficiency virus DNA vaccine trial in macaques.

Abstract: An experimental vaccine consisting of five DNA plasmids expressing different combinations and forms of simian immunodeficiency virus-macaque (SIVmac) proteins has been evaluated for the ability to protect against a highly pathogenic uncloned SIVmac251 challenge. One vaccine plasmid encoded nonreplicating SIVmac239 virus particles. The other four plasmids encoded secreted forms of the envelope glycoproteins of two T-cell-tropic relatives (SIVmac239 and SIVmac251) and one monocyte/macrophage-tropic relative (SIVmac316) of the uncloned challenge virus. Rhesus macaques were inoculated with DNA at 1 and 3, 11 and 13, and 21 and 23 weeks. Four macaques were inoculated intravenously, intramuscularly, and by gene gun inoculations. Three received only gene gun inoculations. Two control monkeys were inoculated with control plasmids by all three routes of inoculation. Neutralizing antibody titers of 1:216 to 1:768 were present in all of the vaccinated monkeys after the second cluster of inoculations. These titers were transient, were not boosted by the third cluster of inoculations, and had fallen to 1:24 to 1:72 by the time of challenge. Cytotoxic T-cell activity for Env was also raised in all of the vaccinated animals. The temporal appearance of cytotoxic T cells was similar to that of antibody. However, while antibody responses fell with time, cytotoxic T-cell responses persisted. The SIVmac251 challenge was administered intravenously at 2 weeks following the last immunization. The DNA immunizations did not prevent infection or protect against CD4+ cell loss. Long-term chronic levels of infection were similar in the vaccinated and control animals, with 1 in 10,000 to 1 in 100,000 peripheral blood cells carrying infectious virus. However, viral loads were reduced to the chronic level over a shorter period of time in the vaccinated groups (6 weeks) than in the control group (12 weeks). Thus, the DNA vaccine raised both neutralizing antibody and cytotoxic T-lymphocyte responses and provided some attenuation of the acute phase of infection, but it did not prevent the loss of CD4+ cells.