In vitro simian virus 40 large tumor antigen expression correlates with differential immune responses following DNA immunization

Abstract

Simian virus 40 (SV40) contains an essential protein, large tumor antigen (Tag), which assists in viral replication and causes cell transformation and immortalization. Our laboratory has examined plasmid DNA, expressing SV40 Tag under two different promoters, for use in potential cancer vaccination strategies. One plasmid, pSV3-neo, failed to induce SV40 Tag antibody, produced a weak cell-mediated response, and only partial protection in murine experimental tumor challenge systems. The second plasmid, pCMV-Tag, induced antibodies to SV40 Tag, produced a robust cell-mediated response, and invoked complete tumor immunity in vivo. The induction of CD4+ and CD8+ T cell responses following plasmid DNA immunization and tumor cell challenge reflected a type 1 cytokine secretion profile. Our hypothesis for this differential immune response is that pCMV-Tag exhibits a higher level of transgene expression due to a more efficient promoter. We determined that pCMV-Tag levels of SV40 Tag mRNA and protein expression were higher when compared to pSV3-neo. A threshold amount of SV40 Tag may be required to stimulate antibody production and provide complete systemic tumor immunity.

Role of the Innate Immune Response and Tumor Immunity Associated with Simian Virus 40 Large Tumor Antigen

“…Previous work from our laboratory has indicated a required initial role for SV40 Tag-specific antibody in achieving complete protection from mKSA tumor development when recombinant protein or plasmid DNA is utilized as a prophylactic vaccine (4,19,31).…”

“…SV40 Tag IgG antibody was detected in sera from immunized mice through indirect enzyme-linked immunosorbent assay (ELISA) as described by our laboratory (17,19). Briefly, 200 ng of recombinant SV40 Tag in boratebuffered saline (BBS) was used to coat 96-well microtiter plates overnight at 4°C.…”

Fcγ Receptors Play a Dominant Role in Protective Tumor Immunity against a Virus-Encoded Tumor-Specific Antigen in a Murine Model of Experimental Pulmonary Metastases

“…Activated Th2 CD4 ϩ T cells might also be functioning to maintain low levels of the inhibitory receptor Fc␥RIIB on effector cells, as shown by one investigation (29), resulting in the increased activities of Fc␥RI/III-expressing immunologic cell populations. Though CD8 ϩ T-cell function cannot be ruled out altogether in providing some level of tumor immunity, particularly when employing other active immunization modalities, such as plasmid DNA expressing SV40 Tag (2,19,25,26), our previous studies indicated that depletion of CD8 ϩ T cells during the course of rSV40 Tag immunization had no observable effect on the resultant tumor immunity (15). Therefore, we surmise that with regard to tumor immunity from mKSA challenge resulting from rSV40 Tag immunization, SV40 Tag specific antibody opsonizes the function of mKSA tumor cells and effector cells, such as macrophages and NK cells, via ADCC to mediate tumor lysis through expression of Fc␥RI/III.…”

CD4+T Lymphocytes Are Critical Mediators of Tumor Immunity to Simian Virus 40 Large Tumor Antigen Induced by Vaccination with Plasmid DNA

“…Studies performed with recombinant Tag (rTag) vaccination revealed a number of critical immune components that function within this system, including Tag-specific antibodies (25,29), natural killer (NK) cells (24,26), and CD8 ϩ T lymphocytes (26). Additionally, targeted depletion of CD4 ϩ T lymphocytes has demonstrated the importance of this cell population in the immune induction phase (22), presumably illustrating the helper function that these cells exert in the activation of other antitumor immune effectors.…”