CD4 and head and neck squamous cell carcinoma: As opposed to assessment of immune cell proliferation, in which potent exogenous stimuli (IL-2 and lectin mitogens) were used, other functional outcomes that were assessed (expression/secretion of biologically active mediators, activation of CD3+ and CD8+ T cells, phenotypic polarization of CD4+ T cells) were solely influenced by soluble mediators present in the CM from HNSCC cells.