Phenotypic and functional characterisation of tumour-infiltrating lymphocytes derived from thyroid tumours

The natural history of thyroid tumours and the hyper-reactivity of the immune system in patients with thyroid cancer suggest that immune surveillance may play a role in the control of this disease. A study was therefore undertaken to analyse the phenotypic and functional features of tumour-infiltrating lymphocytes (TILs) derived from thyroid tumours. In a series of experiments, it was found that, in contrast to TILs derived from patients with melanoma or renal cell carcinoma, thyroid TILs could be efficiently expanded in vitro only in the presence of allogeneic EBV transformed B (B. EBV) cells. Indeed, only one of the seven thyroid-derived TILs grew in vitro without feeder cells, whereas all 16 thyroid-derived TILs could be expanded in the presence of allogeneic B. EBV feeder cells. Phenotypic analysis of these TILs revealed a frequent in vitro expansion of an unusual T cell population that expressed both the CD4 and CD8 markers. Indeed, it was demonstrated that in five of 14 TILs in short-term culture (< day 23) and four of 11 TILs in long-term culture (> day 40), a lymphocyte population that coexpressed CD4 and CD8 antigen accounted for more than 15% of the total TIL population. This double-positive T cell population was not observed in TILs derived from melanoma or renal cell carcinoma. Thyroid-derived TILs also displayed an intense cytolytic activity against NK-sensitive tumour targets with 10 of 11 TILs exhibiting significant cytotoxicity towards the NK-sensitive K562 cell line. Six of 11 TILs were also cytotoxic towards autologous tumour, but when cold target inhibition with K562 was performed with three cultures, unlabelled K562 completely inhibited lysis of autologous tumour cells. A significant expansion of CD3+CD56+ T cells in the different TIL populations may explain this high level of NK-like cytotoxicity. In conclusion, TILs derived from thyroid tumours could be efficiently expanded in vitro under certain culture conditions. Different strategies must be explored to enhance their specific tumour autologous specificity, however, before they can be used in immunotherapy protocols.