Suppression of Cellular Immunity by Head and Neck Irradiation: Precipitating Factors and Reparative Mechanisms in an Experimental Model

• A model was developed in C3H mice to investigate the immunosuppressive effects of head and neck irradiation and to explore mechanisms for repair of the defects. Mice receiving 1200 rad (12 Gy) of head and neck irradiation showed significant depression of delayed-type hypersensitivity, peripheral blood lymphocyte counts, spleen cell counts, and spleen cell production of interleukin-2. Treatment with optimal dosages of thymosin alpha 1 (Tα-1) produced significant increases in all of these values, in some instances to levels higher than in the nonirradiated controls. In identical experiments with mice irradiated to a portal limited to the pelvic region, Tα-1 induced only partial remission of the abnormalities. The dose response of Tα-1 with head and neck irradiation showed a relatively limited dose range for immune restoration, a finding that warrants similar determinations in clinical trials with immunomodulating agents. The results suggest a potential clinical usefulness of Tα-1 and also interleukin-2 in restoring cellular immunity after irradiation for head and neck cancers. The model appears to be useful for investigating immunomodulating agents before they are clinically evaluated as adjuvants with head and neck irradiation regimens. ( Arch Otolaryngol Head Neck Surg 1986;112:1185-1190)