The strongest CD8+ T cell responses ever recorded in humans occur as a result of infection by the Epstein-Barr Virus (EBV). Following a massive CD8+ T cell response during acute EBV infection, ∼5.5% of the total CD8+ T cell repertoire in blood is thereafter committed to the life-long suppression of viral replication. The key to this response is the EBV Latent Membrane Protein-1 (LMP1) which functions as a constitutively activated form of the CD40 receptor. LMP1 consists of an N-terminal domain that clusters in cell membranes and a C-terminal domain that engages the proteins of the CD40 signalosome. Studies to determine if LMP1 could be used for immunotherapy led to the following conclusions: (1) LMP1 mRNA directly activated human dendritic cells (DCs), showing its potential as an adjuvant for mRNA vaccines; (2) Adenovirus (Ad)-delivered LMP1 strongly enhanced vaccine-induced CD8+ T cell responses in mice, indicating that LMP1 may enhance Ad-based oncolytic therapies; (3) lentiviruses incorporating LMP1 became strong activators of DCs in vitro; and (4) DNA vaccines incorporating LMP1 protected mice from tumor challenge in a B16F10 melanoma metastasis model. These data show that the LMP1 nucleic acid sequence is a portable genetic adjuvant with broad applicability to tumor immunotherapy. In related studies, the membrane clustering N-terminal domain of LMP1 was fused to Interferon-beta Promoting Stimulator-1 (IPS-1, also called MAVS, VISA, or Cardif), a protein that requires membrane clustering to become activated. This fusion protein acts independently of cyclic dinucleotides (CDN) to activate downstream mediators of the STING pathway. Vaccination of mice with Ad expressing antigen plus LMP1-IPS-1 resulted in complete protection from challenge with Vaccinia-antigen virus (>1 million-fold protection). These data suggest that LMP1-IPS-1 combined with gene delivery technologies may supplant the need for small molecule CDNs for STING pathway activation in immuno-oncology.

Citation Format: Richard S. Kornbluth, Sachin Gupta, James M. Termini, Elizabeth Guirado, Geoffrey W. Stone. Immune activation by LMP1 CD40 pathway and LMP1-IPS-1 STING pathway activators [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B062.