Effect of IFN-alpha on tumor-infiltrating mononuclear cells and regressive changes in metastatic malignant melanoma.

Interferon-alpha (INF-alpha) has a documented activity against metastatic melanoma. To what extent an antiproliferative effect or tumor cell modulation or immunomodulation contributes to this antitumor effect is still uncertain. The role of immune mechanisms in the control of malignant melanoma is suggested by several studies. Therefore, this investigation used monoclonal antibodies, anti-CD4, anti-CD8, and anti-CD11c, to study the occurrence and distribution of tumor-infiltrating mononuclear cells in 10 untreated and 26 IFN-alpha-treated patients with regional metastatic malignant melanoma. IFN-alpha was given for 1-3 weeks before resection of the metastases. The infiltration of mononuclear cells in the stroma and close to tumor cells was studied. The duration of IFN-alpha treatment was found to be of importance for the immunomodulatory effect. In patients treated for < or = 1 week, tumor-infiltrating mononuclear cells were still mainly localized in the stroma, similar to the situation in untreated patients. The differences in CD4+ cells close to the tumor cells, comparing untreated patients and patients with various durations of IFN-alpha treatment, were highly significant (p = 0.009). Thus, IFN-alpha treatment resulted in recruitment of CD4+ cells close to the tumor cells. IFN-alpha had only a weak effect on the recruitment of CD8+ and CD11c+ mononuclear cells close to the tumor cells. Regressive changes in metastases were also analyzed and correlated to duration of treatment. Some of the criteria used for histopathologic regression in primary melanoma (distorted histologic architecture, low tumor cell density, and fibrosis) were applied to analyze the effect of IFN-alpha in metastatic melanoma. The tumor cell density was found to be significantly reduced in metastases with marked tumor regression compared with metastases with no, or only minor, regressive changes (p < 0.005). A chi-square analysis for trend, comparing untreated patients and patients with various durations of IFN-alpha treatment, showed that regressive changes of the tumor increased significantly during IFN-alpha treatment (p = 0.02).