Introduction: Epstein-Barr virus (EBV) is a gamma herpesvirus that is found in the majority of the human population. Though commonly established as a life-long, asymptomatic infection, EBV has also been implicated in a number of human malignancies including Hodgkin's and Burkitt's lymphomas, nasopharyngeal carcinoma as well as post-transplant lymphoproliferative disease in immunosuppressed patients. While EBV displays restricted gene expression during different latency programs, the viral gene products that are frequently detected in EBV-associated tumors include Epstein-Barr virus Nuclear Antigen 1 (EBNA1), Latent Membrane Protein 1 (LMP1) and Latent Membrane Protein 2A (LMP2A). Our lab has previously described the generation and characterization of monoclonal antibodies with T cell receptor-like specificities (TCR-like mAbs) targeting EBV latent epitopes in association with HLA-A0201. These antibodies have been shown to bind to their targets with high specificities and affinities, and were capable of recognizing antigens displayed on human nasopharyngeal carcinoma biopsies, highlighting their immunotherapeutic potential for targeting EBV-associated tumors.

Methods: EBV is particularly capable of transforming resting B cells into latently infected, actively proliferating B lymphoblastoid cell lines (BLCL) in vitro. As a proof-of-concept, we first generated EBV BLCLs from HLA-A0201+ human peripheral blood mononuclear cells (PBMCs) and compared the ability of our TCR-like mAbs to detect their endogenous targets before and after establishment of the cell lines. The xenograft model involving the inoculation of EBV BLCL into immunodeficient mice resembles B cell lymphoma that develops in post-transplant, immunosuppressed patients. Hence to test the ability of our TCR-like mAbs to target the BLCLs in vivo, we next inoculated PBMC-derived BLCLs into immunodeficient NSG mice and administered weekly dosage of TCR-like mAbs. Mice were assessed for changes in weight, survival as well as end-point organs analysis.

Results: Here, we showed that endogenous EBV latent epitopes could be detected by our TCR-like mAbs on PBMC-derived BLCLs after EBV establishment of the cell line. Despite the inherent heterogeneities between different donors PBMC-derived BLCLs, several of the HLA-A0201+ BLCLs tested displayed similar binding activities with these TCR-like mAbs. In addition, BLCL-injected NSG mice that received weekly treatment of TCR-like mAbs displayed reduced tumor burden, splenomegaly and liver tumor spots in comparison to mice that received isotype antibody or PBS control. Importantly, BLCL-injected NSG mice that received the TCR-like mAb targeting the EBNA1 latent epitope exhibited delayed weight loss and survival advantage.

Conclusion: We have utilized TCR-like mAbs with specificities against EBV latent epitopes expressed on HLA-A0201 and showed that these antibodies could recognize endogenous targets on EBV transformed, PBMC-derived BLCLs. Furthermore, weekly administration of TCR-like mAbs into BLCL xenograft NSG mice resulted in an overall reduction of tumor load and improved survival in one of the three described antibodies. Taken together, our data provide preliminary evidence for the therapeutic usage of antibodies with TCR-like specificities for the targeting EBV transformed BLCL in vivo.

Citation Format: Junyun Lai, Wei Jian Tan, Chien Tei Too, Nalini Srinivasan, Lan Hiong Wong, Fatimah Mustafa, Soh Ha Chan, Jianzhu Chen, Paul Anthony MacAry. Targeting Epstein-Barr virus transformed B lymphoblastoid cells using antibodies with T cell receptor-like specificities. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B095.