Immunocharacteristics of testicular germ cell cancers – revelation of a new key network?

Human testicular germ cell tumours (TGCTs) are frequently characterised by an abundance of infiltrating immune cells, most previously identified as T cells and macrophages. The involvement of other immune cell subtypes, the differences in terms of immune cell recruitment and cytokine presence in TGCTs have not yet been investigated in detail. This study addresses the above listed caveats which harbour the potential of providing novel insights into the immunocharacteristics of TGCTs.
   
   Using immunohistochemistry on human testicular biopsy samples, B cells and dendritic cells were found to be uniquely present within cancer samples in comparison to other testicular inflammatory conditions. Using RT-qPCR, significantly increased levels of transcripts encoding proinflammatory (e.g. IL1b and TNFa), Th1-related (IL2 and IFNg) and B cell-supporting cytokines (IL6 and CXCL13) were found to be characteristic for testis cancer indicating the presence of an environment that might attract and/or maintain B cells at the tumour site. Moreover, this (proinflammatory) tumour microenvironment might most likely be involved in perpetuating local inflammation and thereby facilitating tumour cell growth and invasion, as known from other tumour entities.
   
   In contrast, despite visible immune cell infiltration in hypospermatogenesis samples, the cytokine microenvironment associated with both normal spermatogenesis and hypospermatogenesis was identified as being largely similar and characterised by the involvement of Th2-related cytokines (e.g. IL5 and IL13) suggesting that these cytokines might be involved in maintaining the testicular immune privilege.
   
   An in vitro model was subsequently developed to assess the interactions and particular contributions of each immune cells and testicular cancer cells to the tumour cytokine microenvironment. TCam-2 cells (a human seminoma-derived cell line) were cocultured with normal human peripheral blood mononuclear cells (PBMCs) to interrogate the consequences of their colocalistion for the cytokine microenvironment, using RT-qPCR and ELISA. The results illustrate that cytokine expression profiles of TCam-2 cells that were cocultured with PBMC via direct contact, are characterised by significantly increased mRNA levels of pro-inflammatory cytokines and Th1-related cytokines compared to monocultured controls, which highly resembles the ex vivo data. Interestingly, no changes in PBMC cytokine transcript levels post-coculture were detected; measurements of cytokine levels were unchanged after coculture, both with and without mitogen pre-stimulation (to increase the immunological activity and overcome the possible hypo-responsiveness of PBMCs).
   
   It was further demonstrated that TCam-2 cells naturally produce significantly higher levels of IL6 mRNA and protein compared to PBMC. This suggests a possible role of IL6 as a maintenance factor for testicular cancer cells.
   
   These novel results indicate a special involvement of B cells, dendritic cells and IL6 in testicular germ cell cancer. In this setting, IL6 might be necessary for maintaining or facilitating cancer cell proliferation and invasion. Moreover, increased IL6 levels could be a direct consequence of the presence of even few neoplastic cells. In line with this, IL6 has already been identified as a potent predictive or prognostic marker for other cancers, such as e.g. non-small cell lung cancer and gastriccancer. This study has thus substantially deepened the knowledge on the immunocharacteristics of human TGCTs.