Background: Cancer immunotherapy with NKT cells is a potential new treatment strategy for advanced head and neck cancer. NKT cell therapy is promising due to its unique anti-tumor activity and higher degree of safety compared to current therapies. Radiotherapy is indispensable as a standard treatment for advanced head and neck cancer. To elucidate the possibility of using NKT cells as an adjuvant immunotherapy with radiotherapy, we examined the effect of radiotherapy on NKT cells in patients with head and neck cancer.
Methods: The number, IFN-gamma production and proliferation capacity of NKT cells were analyzed before and after 50 Gy radiation therapy in 12 patients with stage IV head and neck squamous cell carcinoma. The cytotoxic activity of NKT cells was examined in vitro.
Results: The number of NKT cells in the blood varied widely between patients. After radiation therapy, the population of CD3 T cells decreased significantly, while the NKT cell population remained stable. The number of NKT cells was the same after radiation therapy as before. IFN-gamma production from NKT cells collected just after radiotherapy was impaired after stimulation with exogenous ligand, but the proliferative responses of these NKT cells was enhanced in comparison to those collected before radiation therapy. Furthermore, the proliferated NKT cells displayed a significant level of anti-tumor activity.
Conclusion: NKT cells are relatively resistant to radiation and might therefore be suitable for adjuvant immunotherapy to eradicate remnant cancer cells in patients who have undergone radiation therapy.