The B subunit of E. coli helps control the in vivo growth of solid tumors expressing the Epstein-Barr virus latent membrane protein 2A

The latent membrane protein 2A (LMP2A), of Epstein Barr Virus (EBV), is expressed on a number of EBV-associated cancers and is a potential target for immunotherapeutic intervention and vaccination. The E. coli enterotoxin subunit B (EtxB), has previously been shown to enhance antigen processing and presentation of LMP2A leading to increased killing by LMP2A-specific cytotoxic T lymphocytes (CTLs) in vitro. To test the potential of EtxB to enhance CTL targeting of LMP2A expressed in solid tumors in vivo, we generated a murine tumor model (Renca-LMP2A), in which LMP2A is expressed as a transgenic neo-antigen on a renal carcinoma (Renca) cell line and forms solid tumors when injected s.c into BALB/c mice. The data clearly demonstrate that despite expression of LMP2A, Renca-LMP2A tumors do not trigger immune responses sufficient to control tumor growth in vivo. However, prior immunization with a recombinant vaccinia virus vector expressing LMP2A (Vac-LMP2A) led to significantly lower tumor growth rate in mice compared to un-immunized controls. Importantly, the rate of growth of Renca-LMP2A in mice previously immunized with Vac-LMP2A was significantly less compared with mice injected with vector-control transgenic Renca cells that do not express LPM2A (Renca-VC). Furthermore, we found that amongst Vac-LMP2A-immunized mice given Renca-LMP2A, daily injection of EtxB into the tumor site resulted in a significant delay in the onset of tumor growth and lower tumor volumes compared with Vac-LMP2A-immunized mice that were not treated with EtxB. Critically, the immunomodulatory effect caused by EtxB was significant; despite the progressive down-regulation of LMP2A and MHC class I expression by RencaLMP2A. Taken together these data clearly demonstrate the potential efficacy of using EtxB as a novel therapeutic agent in controlling the growth of EBV-associated tumors.