Molecular and immunological analysis of genetic prostate specific antigen (PSA) vaccine

Abstract

Nucleic acid immunization has been investigated as immunotherapy for infectious diseases as well as for treating speci®c types of cancers. In this approach, nucleic acid expression cassettes are directly inoculated into the host, whose transfected cells become the production source of novel and possibly immunologically foreign protein. We have developed a DNA vaccine construct which encodes for PSA by cloning a cDNA for PSA into a mammalian expression vector under control of a CMV promoter. We investigated and characterized the immunogenicity of PSA DNA expression cassettes in mice. PSA-speci®c immune responses induced in vivo by immunization were characterized by enzyme-linked immunosorbent assay (ELISA), T helper proliferation cytotoxic T lymphocyte (CTL), and¯ow cytometry assays. We observed a strong and persistent antibody response against PSA for at least 180 days following immunization. In addition, a signi®cant T helper cell proliferation was observed against PSA protein. Using synthetic peptides spanning the PSA open frame, we identi®ed four dominant T helper epitopes of PSA. Furthermore, immunization with PSA plasmid induced MHC Class I CD8+ T cell-restricted cytotoxic T lymphocyte response against tumor cell targets expressing PSA. The prostate represents a very speci®c functional organ critical for reproduction but not for the health and survival of the individual. Understanding the immunogenicity of PSA DNA immunization cassettes o ers insight into the possible use of this tumorassociated antigen as a target for immunotherapy. These results demonstrate the ability of the genetic PSA to serve as a speci®c immune target capable of generating both humoral and cellular immune responses in vivo.

Immunization with type 5 adenovirus recombinant for a tumor antigen in combination with recombinant canarypox virus (alvac) cytokine gene delivery induces destruction of established prostate tumors

“…PSA-DNA vaccination leads to the generation of T-cell responses to PSA in BALB/c mice, 8 and BALB/c mice vaccinated with PSA-expressing P815 tumor cells were protected against a subsequent challenge with a histocompatible PSA-expressing lung carcinoma, and vice versa. 9 When rhesus monkeys were immunized with a recombinant vaccinia vector expressing PSA, a brief IgM response to PSA as well as specific T-cell proliferation was detected.…”

Efficient transfer of PSA and PSMA cDNAs into DCs generates antibody and T cell antitumor responses in vivo

“…16 It has been shown that human cytotoxic T lymphocytes (CTLs) respond to peptides derived from PSA 17 and that intramuscular immunization of mice with plasmid DNA encoding PSA also leads to potent CTL responses to specific tumor cells. 18 Furthermore, a preponderance of antibody responses were found to be directed to PSA antigens when general mRNA from a prostate tumor line was used to transfect autologous DCs. 19 In sum, these studies indicate that PSA is a valid antigen for potential prostate cancer immunotherapy strategies.…”

Human Dendritic Cells Transfected with RNA Encoding Prostate-Specific Antigen Stimulate Prostate-Specific CTL Responses In Vitro

“…Although the efficacy of PSAspecific peptides pulsed onto DC to induce CTL has not been reported to date, a conceptually superior approach would entail the targeting of multiple class I and class II epitopes present on the PSA molecule, which are thought to further stabilize or maintain effective T cell responses in vivo (7,8).…”