Depressed T lymphocyte function in brain tumor patients: monocytes as suppressor cells

Depressed cellular immune function has been demonstrated in patients with a variety of lymphoreticular and nonlymphoreticular neoplasms, including patients harboring brain tumors. In the present study, peripheral T lymphocytes from more than fifty percent of patients with central nervous system tumors, both primary and metastatic, exhibited depressed incorporation of 3H-thymidine in response to phytohemagglutinin (PHA) when tests were performed in the absence of autologous serum. Increased numbers of monocytes were present within mononuclear cell suspensions from brain tumor patients, and most of the cell populations containing elevated monocytes also exhibited depressed responses to PHA. A role for monocytes as suppressor cells was suggested by the finding that partial reconstitution of T cell function could frequently be effected by adherent cell depletion. However, total reversal of the defect was rare and there was no relationship between monocytes and T cell dysfunction in some patients. The results suggest that while monocytes may be involved in the immune depression seen in some patients with a brain tumor, the complete explanation is as yet unknown.