Augmentation of leukocyte infiltration in murine tumors expressing B-cell derived but not nasopharyngeal carcinoma derived EBV membrane protein LMP1

The Epstein-Barr virus (EBV) encoded latent membrane protein of B cell orig in, B-LMP1 (B95-8 prototype) and nasopharyngeal carcinoma (NPC) derived C-L MP1 (CAO prototype) were transfected individually in S6C adenocarcinoma cel ls of ACA (H-2f) origin. We have shown previously that inoculation of B-LMP 1 expressing S6C cells led to tumor rejection in preimmunized, immunocompet ent syngeneic ACA mice, whereas the C-LMP1 transfectants were not immunogen ic. Furthermore, B-LMP1 but not C-LMP1 expressing S6C cells grew with necro sis and extensive skin damage in non-immunized mice. A study was carried ou t to determine whether the in vivo growth pattern of S6C cells expressing t wo different LMP1 isolates could be correlated to any immunomodulatory mech anism. An increased infiltration of CD45+ leukocytes was found in B-LMP1 ex pressing S6C tumors originating in non-immunized, syngeneic ACA mice. The C -LMP1 expressors, vector transfectants and untransfected parental tumors ha d significantly lower number of infiltrating leukocytes. The immunoaccessor y molecules ICAM-1, B7-1 and MHC Class I and It expression was unaltered in both B- and C-LMP1 transfectants. The data suggest that B-LMP1 but not C-L MP1 induce anti-tumor immune response. J. Med. Virol. 60:417-424, 2000. (C) 2000 Wiley-Liss, Inc.