Induction of therapeutic antibodies by vaccination against external loops of tumor-associated viral latent membrane protein.

Some human herpesviruses (HHV) are etiological contributors to a wide range of malignant diseases. These HHV express latent membrane proteins (LMPs), which are type III membrane proteins consistently exposed at the cell surface in these malignancies. These LMPs have relatively large cytoplasmic domains but only short extracellular loops connecting transmembrane segments that are accessible at the surface of infected cells, but they do not elicit antibodies in the course of natural infection and tumorigenesis. We report here that conformational peptides mimicking two adjacent loops of the Epstein-Barr virus (EBV) LMP1 (2LS peptides) induce high-affinity antibodies with remarkable antitumor activities in mice. In active immunization experiments, LMP1-targeting 2LS vaccine conferred tumor protection in BALB/c mice. Moreover, this tumor protection is dependent upon a humoral anti-2LS immune response as demonstrated in DO11.10 (TCR-OVA) mice challenged with LMP1-expressing tumor and in SCID mice xenografted with human EBV-positive lymphoma cells. These data provide a proof of concept for 2LS immunization against short external loops of viral LMPs. This approach might possibly be extended to other infectious agents expressing type III membrane proteins.

Autoactivation of the Epstein-Barr virus oncogenic protein LMP1 during type II latency through opposite roles of the NF-kappaB and JNK signaling pathways.

Epstein-Barr virus (EBV) is associated with several human malignancies where it expresses limited subsets of latent proteins. Of the latent proteins, latent membrane protein 1 (LMP1) is a potent transforming protein that constitutively induces multiple cell signaling pathways and contributes to EBV-associated oncogenesis. Regulation of LMP1 expression has been extensively described during the type III latency of EBV. Nevertheless, in the majority of EBV-associated tumors, the virus is commonly found to display a type II latency program in which it is still unknown which viral or cellular protein is really involved in maintaining LMP1 expression. Here, we demonstrate that LMP1 activates its own promoter pLMP1 through the JNK signaling pathway emerging from the TES2 domain. Our results also reveal that this activation is tightly controlled by LMP1, since pLMP1 is inhibited by LMP1-activated NF-kappaB signaling pathway. By using our physiological models of EBV-infected cells displaying type II latency as well as lymphoblastoid cell lines expressing a type III latency, we also demonstrate that this balanced autoregulation of LMP1 is shared by both latency programs. Finally, we show that this autoactivation is the most important mechanism to maintain LMP1 expression during the type II latency program of EBV.