Death ligand expression profiles on multiple myeloma patient lymphocytes

Multiple Myeloma (MM), the second most common hematologic malignancy, is responsible for 2% of all cancer-related deaths. Like most of the cancer cases, MM patients also suffer from progressive immunodeficiency. Normally, ?immune-surveillance? mechanism, if not disturbed, is the default strategy of body to prevent expansion of tumor cells. One of the strategies immune system cells use in this process is the death-ligand mediated apoptosis induction. Myeloma cells have death receptors on their surface; yet, for induction of apoptosis through these receptors, death ligands should be present in the vicinity of the receptors. The main sources for death ligands are the cytotoxic lymphocytes of the immune system. Thus, we hypothesized that, one of the reasons why myeloma cells survive may be the absence of the death ligands, as those cells escape from apoptosis despite the death receptor expression on their surface. In order to test our hypothesis, we studied peripheral blood samples of MM patients to investigate surface FasL and TRAIL expression. Then we compared FasL and TRAIL surface expression patterns on MM patient peripheral blood lymphocytes with those of the healthy age/sex matched volunteers. Our results indicated reduced numbers of FasL and TRAIL proteins on CD3+, CD3+CD4+, CD3+CD8+ and CD3- lymphocytes of MM patients, although CD4+CD25+ cells did not exhibit a similar phenotype. Intriguingly, the positive/negative cell ratio was not statistically different between two groups. Thus, our results show that, although death ligand expressing lymphocyte numbers do not change between two groups, surface ligand expression on these positive cells gets downregulated. This, indeed, may represent a possible pathway used by myeloma cells to escape from the anti-tumor immunity.