Tumor infiltrating lymphocytes in squamous cell carcinoma of the head and neck: Mechanisms of enhancement using prostaglandin synthetase inhibitors

Previous studies have demonstrated clinical responses to indomethacin in squamous cell carcinoma of the head and neck suggesting a relationship between prostaglandin metabolism and tumor surveillance. We have extended these observations by investigating the populations of mononuclear leukocytes which infiltrated SCCHN before and after treating patients with indomethacin. To investigate these observations, human tumor infiltrating lymphocyte populations were studied before and after systemic indomethacin administration. Tissue samples were obtained from seven patients aged 51-67 years presenting with SCC (retromolar trigone, tongue, epiglottis and tonsillar lesions) before and after treatment with indomethacin (1 mg/kg dose PO TID) for 14 days. Immunohistochemical analysis using indirect immunofluorescence showed marked increases in tumor infiltrating lymphocyte populations following treatment. A seven-fold increase was observed in CD2 lymphocytes after two weeks of indomethacin. The number of CD4 and CD8 lymphocytes increased similiarly. CD56 lymphocytes rose eleven-fold as did CD11b/CD18 cells. (p<0.05 for all values). Two control patients were studied with no observable increase in lymphocytes on serial biopsies two weeks apart. Cultured human squamous cell carcinoma cells synthesized significant levels of prostaglandin E₂. The observations noted in these studies are consistent with the known inhibitory effect of tumor derived prostaglandin E₂ on interleukin-1 and interleukin-2 synthesis by activated immunocytes as well as other immune limiting effects. These findings, when considered together suggest clinical responses to indomethacin previously reported in squamous cell carcinoma of the head and neck may reflect an increase in immune response to the tumor brought about by inhibition of PGE₂ synthesis. Tumor tissues from head and neck cancer have been shown to have elevated local levels of immunosuppressive prostaglandin metabolites (Berlinger, 1984). Patients with squamous cell carcinoma of the head and neck (SCCHN) exhibit local, regional and systemic immunosuppression and demonstrate clinical responses to prostaglandin synthesis inhibitors (Panje, 1981). While little is known regarding specific modifiers of host immune response in improving the outcome of therapy for head and neck cancer, there is evidence to suggest that tumor associated prostaglandins attenuate host immune response in this malignancy. Immunomodulation with enhancement of host immune response may be possible through inhibition of tumor associated prostaglandins and may provide an important new therapeutic approach. It is essential to understand the pivotal role which prostaglandins play in regulating immune response in malignancy to optimize immunomodulatory therapy in the treatment approach to SCCHN. Studies in humans and animals demonstrate administration of a prostaglandin synthesis inhibitor causes regression of squamous cell carcinoma (Panje, 1981; Blitzer, 1983; Hial, 1976). These results suggest that inhibition of PG synthesis is linked to tumor regression. The extent to which tumor cell production of prostaglandin compounds contributes to suppression of tumor infiltrating leukocytes and the success of the effector cell system in dealing with malignancy is unknown. The variable clinical responses observed in patients bearing SCCHN and given prostaglandin synthesis inhibitors may be a result of comparative tumor differences in prostaglandin synthesis. Metabolism of [³H]-AA by similar SCCHN cell lines is observed to yield significantly different prostaglandin profiles (Cross, 1992a, see Figures 1 and 2). Principle prostaglandin products included prostaglandin E₂ (PGE₂) and 6-keto-prostaglandin-F_1a (6-keto-PGF_1a). The ratio [PGE₂]/[6-keto-PGF_1a] observed demonstrated a five-fold difference between the two cell lines over a ten hour timecourse. The supernatant prostaglandin concentration varied with cell line studied with maximum PGE₂ concentration in excess of 100 nmoles/1. This level approximates the level of PGE₂ required to provide immune limiting effects using in-vitro assays.