Myeloid progenitor cells mediate immune suppression in patients with head and neck cancers

Patients with squamous cell carcinomas of the head and neck (HNSCC) have pr ofound defects in their immune defenses. We have shown that among the mecha nisms that contribute to this immune dysfunction are immune inhibitory CD34 (+) progenitor cells,whose levels become elevated in the peripheral blood a nd within the tumor tissue. One goal of our studies is to overcome the immu ne inhibitory activities of tumor-induced CD34(+) progenitor cells by stimu lating their differentiation into cells, such as dendritic or monocytic cel ls, that can stimulate immune reactivity to autologous cancer. Results of i n vitro analyses with CD34(+) suppressor cells of HNSCC patients and of in vivo studies in animal tumor models have shown the capacity of tumor-induce d CD34(+) cells to differentiate into cells that phenotypically resemble mo nocytic or dendritic cells. Whether these cells can differentiate into dend ritic cells in HNSCC patients is currently being tested. Less clear is whet her the pathway by which the tumor-induced CD34(+) cells differentiate will result in cells having the full capacity to function as potent stimulators of immune reactivity to autologous tumor. (C) 1999 International Society f or Immunopharmacology. Published by Elsevier Science Ltd. All rights reserv ed.