CD34+ immune suppressive cells in the peripheral blood of patients with head and neck cancer.

Patients with head and neck squamous cell carcinoma (HNSCC) have profound defects in their immune defenses. Using immunofluorescent staining and flow cytometric analysis, we found that most patients with HNSCC have increased levels of CD34+ cells within their peripheral blood. These circulating CD34+ cells contribute to the depressed functional competence of the peripheral blood T-lymphocytes. This was demonstrated by the increased level of proliferative responsiveness to interleukin-2 by the patients' peripheral blood T-cells after depletion of CD34+ cells. These results show the importance of CD34+ cells in contributing to the depression of T-lymphocyte function in patients with HNSCC and suggest that strategies designed to reduce the levels of circulating CD34+ cells may enhance the immune reactivity of the patients' circulating T-lymphocytes against the HNSCC.