T cell recognition of Epstein-Barr virus associated lymphomas

Epstein-Barr virus, a lymphotropic herpesvirus of humans, has potent B cell growth transforming activity yet persists in the lymphoid tissues of most individuals as a lifelong asymptomatic infection. Virus induced B cell growth transformation in vitro is associated with the expression of a limited set of viral genes encoding six nuclear antigens (EBNA 1, 2, 3A, 3B, 3C and LP) and two latent membrane proteins (LMP 1, 2). Healthy virus carriers possess strong EBV specific CTL memory that can be reactivated in vitro. Here, we summarize experiments in which the antigenic specificities of these HLA class I restricted memory CTL responses have been mapped in a range of individuals with different HLA backgrounds. Of the known EBV latent proteins, EBNA 3A, 3B and 3C are frequently the dominant targets for such responses, but examples of responses directed against epitopes of EBNA 2, EBNA-LP or the LMP have been identified; by contrast, CTL responses against epitopes of EBNA 1 have not been observed. Epstein-Barr virus is associated with at least three malignancies of lymphoid origin--immunoblastic lymphomas of the immunosuppressed, endemic Burkitt's lymphoma and a subset of Hodgkin's disease. The immunoblastic lymphomas express the complete spectrum of EBV coded latent proteins and a cellular phenotype similar to that of in vitro transformed B lymphoblastoid cell lines; accordingly, they remain sensitive to EBV specific CTL recognition. Endemic BL cells are not recognized by such CTL, and at least three consistent features of this tumour could contribute to immune escape: (a) allele specific downregulation of HLA class I antigen expression, (b) absence/low expression of cellular adhesion molecules and (c) restriction of EBV latent protein expression to EBNA 1 only. The relative importance of these three features of the BL cell phenotype with regard to sensitivity to CTL recognition is re-interpreted in the light of recent results. Finally, the pattern of virus latent protein expression in EBV positive Hodgkin's disease is described, and the possibility of EBV specific CTL control against this tumour is discussed.