Cloning and sequencing of the cynomolgus monkey prostate specific antigen cDNA.

BACKGROUND: Prostate-specific antigen (PSA) is an invaluable tumor marker for the detection of early prostate cancer, and can be a target for active immunotherapy of prostate cancer. We wanted to assess the usefulness of the cynomolgus monkey (Macaca fascicularis) as a relevant animal model to evaluate PSA-specific therapies. METHODS: RNA was isolated from the prostate of cynomolgus monkeys, and PSA gene products were amplified by reverse transcriptase-polymerase chain reaction using primers from conserved regions of human and rhesus monkey (Macaca mulatta) PSA genes. These amplified products were then sequenced. RESULTS: The cynomolgus PSA amino acid sequence is 89.7% identical to the human PSA gene, and 99.2% identical to the rhesus PSA amino acid sequence. Like the human and rhesus PSA genes, an open-reading frame of 261 amino acids was identified for the cynomolgus gene. Expression of the cynomolgus PSA gene appears to be restricted to the prostate, as it is in humans. CONCLUSIONS: The high identity between human and cynomolgus PSA sequences suggests that the cynomolgus monkey should be studied further for its potential as a large animal model to evaluate PSA-specific therapies.

Interleukin-18 enhances Th1 immunity and tumor protection of a DNA vaccine.

DNA vaccines show efficacy in many preclinical models, but these results have not yet translated to consistent clinical efficacy. Co-administration of molecularly encoded adjuvants is one approach that may enable DNA vaccines to achieve enhanced immune response induction in humans. Interleukin-18 (IL-18) is a Th1-type cytokine that has been shown to augment the activity of DNA vaccines in some preclinical models. A prostate-specific antigen (PSA) DNA vaccine was tested in a mouse tumor model system to explore the impact of co-administration of a pIL-18 plasmid. Low doses of the pPSA vaccine were not capable of inducing tumor protection, but when pIL-18 was co-administered, complete tumor protection was observed in all mice. Tumor protection was mediated by both CD4(+) and CD8(+) T cells. Detailed analysis of the immune response in mice immunized with either pPSA or pPSA/pIL-18 demonstrated that pIL-18 skewed the PSA-specific immune response toward Th1. More importantly, stronger CD4(+) and CD8(+) T cell responses developed in the pPSA/pIL-18-immunized mice, with faster kinetics. These results suggest that IL-18 is a powerful adjuvant molecule that can enhance the development of antigen-specific immunity and vaccine efficacy.

Induction of Th1-type immunity and tumor protection with a prostate-specific antigen DNA vaccine.

Prostate specific antigen (PSA) is a serum marker that is widely used in the detection and monitoring of prostate cancer. Though PSA is a self-antigen, T cell responses to PSA epitopes have been detected in healthy men and prostate cancer patients, suggesting it may be used as a target for active immunotherapy of prostate cancer. A PSA DNA vaccine (pPSA) was evaluated in mice and monkeys for its ability to induce antigen-specific immune responses. Mice immunized intradermally with pPSA demonstrated strong PSA-specific humoral and cellular immunity. The anti-PSA immune responses were skewed toward Th1, as shown by high IFNgamma and IL-2 production. The immune response was sufficient to protect mice from challenge with PSA-expressing tumor cells. Tumor protection was durable in the absence of additional vaccination, as demonstrated by protection of vaccinated mice from tumor rechallenge. Furthermore, pPSA vaccination induced PSA-specific antibody titers in male cynomolgus monkeys, which express a closely related PSA gene. These results demonstrate that vaccination with pPSA may be able to break tolerance and can induce an immune response that mediates tumor protection.