Expression of MAGE antigens and analysis of the inflammatory T-cell infiltrate in human seminoma

The MAGE gene family encodes antigens that are recognized by cytotoxic T-ce lls. The expression of MAGE antigens has been linked to tumor stage, and MA GE peptides are under investigation as possible vaccines. Seminomas are tum ors that are typically accompanied by a heavy inflammatory infiltrate, but have not been studied with regard to their MAGE antigen expression and its correlation with the inflammatory infiltrate. We investigated, therefore, M AGE protein expression, the amount of cytotoxic T-cells, clonality of the l ymphocytic infiltrate, apoptotic activity and occurrence of necrosis. Speci mens of 27 patients with classical seminoma were examined by immunohistoche mistry for CD4, CD8, CD56, CD45R0, beta (2)-microglobulin and HLA-DR. MAGE expression was detected with the monoclonal antibody 57B, reactive with MAG E-1, -3, -4, -6 and -12. Clonality of the inflammatory infiltrate was exami ned by multiplex polymerase chain reaction (PCR) analysis of the T-cell rec eptor rearrangement. Apoptotic cells were detected by DNA nick-end labeling of fragmented DNA, and the apoptotic index was determined semi-quantitativ ely. Expression of 57B was found in 19 (70%) of 27 seminomas. In all cases, more than 70% of T-cells expressed CD45R0. In four cases, a predominant in filtration of CD8-positive cytotoxic T-cells (CD4/CD8 ratio < 1) was presen t. However, 15 seminomas showed a CD4/CD8 ratio > 1. In all cases, infiltra tion of CD56-positive natural killer cells was only focal. HLA-DR expressio n was not detectable in tumor tissue; beta (2)-microglobulin was only focal in three cases. Analysis of the T-cell clonality revealed a polyclonal pop ulation. The apoptotic index was not significantly different in 57B-positiv e seminomas (4.15%) compared with 57B negative seminomas (3.80%). Also, no correlation between the 57B expression and the occurrence of necrosis was f ound. MAGE antigens are homogeneously expressed in most seminomas, but thei r presence does not appear to represent a dominant epitope responsible for the lymphocytic infiltrate.