EBV-gp350 Confers B-Cell Tropism to Tailored Exosomes and Is a Neo-Antigen in Normal and Malignant B Cells—A New Option for the Treatment of B-CLL

gp350, the major envelope protein of Epstein-Barr-Virus, confers B-cell tropism to the virus by interacting with the B lineage marker CD21. Here we utilize gp350 to generate tailored exosomes with an identical tropism. These exosomes can be used for the targeted co-transfer of functional proteins to normal and malignant human B cells. We demonstrate here the co-transfer of functional CD154 protein on tailored gp350+ exosomes to malignant B blasts from patients with B chronic lymphocytic leukemia (B-CLL), rendering B blasts immunogenic to tumor-reactive autologous T cells. Intriguingly, engulfment of gp350+ exosomes by B-CLL cells and presentation of gp350-derived peptides also re-stimulated EBV-specific T cells and redirected the strong antiviral cellular immune response in patients to leukemic B cells. In essence, we show that gp350 alone confers B-cell tropism to exosomes and that these exosomes can be further engineered to simultaneously trigger virus- and tumor-specific immune responses. The simultaneous exploitation of gp350 as a tropism molecule for tailored exosomes and as a neo-antigen in malignant B cells provides a novel attractive strategy for immunotherapy of B-CLL and other B-cell malignancies

INDUCTION OF THE LYTIC VIRAL CYCLE IN EPSTEIN-BARR-VIRUS CARRYING BURKITT-LYMPHOMA LINES IS ACCOMPANIED BY INCREASED EXPRESSION OF MAJOR HISTOCOMPATIBILITY COMPLEX-MOLECULES

Six Epstein Barr virus (EBV) genome-carrying Burkitt lymphoma (BL) cultures (P3HR-1, Raji, Akata, Daudi, Rael and Jijoye) were induced to enter the lytic cycle. Phorbol esther (TPA), n-butyrate, 5-azacytidine (5AzaC) or anti-IgG were used according to their known inducing capacity on these cell lines. Concomitantly with the appearance of the viral early antigens (EA) in a proportion of cells, the expression of major histocompatibility complex (MHC) class II antigens increased in the cultures. On P3HR-1 and Raji cells class I expression also increased. The enhancement of MHC expression correlated with the efficiency of induction and required only an early event of the viral lytic cycle. Treatment of 3 EBV-negative lymphoma lines (BJAB, Ramos and BL41) with TPA plus n-butyrate or 5AzaC did not influence MHC expression. Moreover, BL lines which carry the EBV genome after having been infected in vitro and which cannot be induced for the viral lytic cycle did not change MHC expression after treatment with the inducing agents. In mixed cultures the allo-stimulatory capacity of induced cells with elevated MHC expression was stronger compared to the untreated ones