Controversies on the prognostic significance of tumor infiltrating leukocytes in solid human tumors.

We have performed immunophenotypical (IP) analyses of tumor infiltrating leukocytes (TIL) in both childhood brain tumors (medulloblastomas[MEDs]/primitive neuroectodermal tumors [PNETs] and astrocytomas [ASTRs]) and malignant melanomas (both primary and metastatic) employing a well-characterized library of monoclonal antibodies (MoABs) directed against leukocyte differentiation/activation associated antigens. The antigens were detected by an indirect, biotinstreptavidin conjugated alkaline phosphatase (AP) immunocytochemical technique. Our systematic cell-surface antigen expression profile analysis of 76 primary childhood brain tumors (34 MEDs/PNETs and 42 ASTRs) identified CD8+ CTL in 58/76 brain tumors. CD4+, MHC class II restricted helper lymphocytes were present in 65/76 brain tumors and represented 1-10% of the observed cells. Macrophages were present in 74/76 childhood brain tumor cases observed by us. Leukocyte common antigen (LCA) expression was demonstrated in all 76 brain tumors studied. MoAB UJ 308 detected the presence of premyelocytes and mature granulocytes in 60/76 brain tumors. They were localized perivascularly, within the tumor tissue, or close to necrotic regions. Natural killer (NK) cells were not defined in the childhood brain tumors observed in this study. The IP characteristics of the heterogeneous leukocytic infiltrate of 30 primary (PMs) and 10 metastatic melanomas (MMs) was also investigated by us. We established the presence of some type of melanoma infiltrating host's immunological effector cells in all 40 observed melanoma cases. More specifically, we found NK cells, macrophages and granulocytes in 30/30 PMs and 10/10 MMs. These effector cells represented the vast majority (> 80%) of the melanoma infiltrating immunocompetent cells. T lymphocytes were observed in 20/30 PMs and 6/10 MMs, but their numbers represented only between 5% to 10% of the heterogeneous leukocytic infiltrate. B cells were found in 22/30 PMs and 8/10 MMs, their numbers representing less than 5%. Presence of cells of the dendritic reticulum, involved in antigen presentation was not determined in any of the observed PMs and MMs. The notion that infiltration of the neoplastically transformed mass of cells by TIL is always a prognostically positive phenomenon has changed in recent years as research on extracellular matrix remodeling and angiogenesis have identified numerous secreted factors which are common to both neoplastically transformed cells and infiltrating leukocytes.