The pattern of cytokine gene expression in freshly excised human metastatic melanoma suggests a state of reversible anergy of tumor‐infiltrating lymphocytes

Abstract

Expression of an extended panel of cytokine genes was investigated by reverse polymerase chain reaction (PCR) in 10 freshly excised melanoma metastases infiltrated by lymphocytes (TIL). cDNA encoding for CD3‐δ and tyrosinase could be amplified in all samples, confirming the presence of T lymphocytes and melanoma cells. Cytokine genes possibly transcribed by both cell types, such as GM‐CSF, IL‐6 and IL‐10 could be amplified from 5, 2 and 2 samples respectively. In contrast, IL‐β and TNF‐α mRNA were never detectable, IL‐1α, IL‐3 and IL‐7 mRNA could be observed only in one case each. Transcripts encoding for TGF‐β1 were observed in 8 samples, while TGF‐β2 and 3 mRNA were detectable in only 2 specimens. mRNA encoding for cytokine genes typically transcribed by antigen‐stimulated T lymphocytes, such as IL‐2, IL‐4 and IFN‐7 were rarely or never detectable (none, none and 1 of the samples respectively). In one case, where no cytokine gene transcription was detectable at the time of surgery, we addressed the question of the antigenicity of the tumor and of the functional competence of TIL. A primary tumor cell line was generated and cultured TIL were induced to transcribe IL‐2 and IFN‐γ genes by incubation with the autologous irradiated tumor cell line, but not with autologous EBV‐transformed cells. In these conditions, tumor‐specific cytotoxic T lymphocytes (CTL) could be generated only after 3 weekly re‐stimulations. In contrast, if autologous irradiated EBV‐transformed cells were added to the cultures, specific CTL could be detected after one single tumor stimulation. Thus, signs of active responsiveness in terms of lymphokine gene mRNA are seldom detectable in melanoma metastases. Tumor‐specific responses, however, including IL‐2 and IFN‐γ gene expression and generation of CTL can be produced in vitro from specimens in which no cytokine gene mRNA is detectable ex vivo.