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During normal pregnancy, a state of systemic suppression of the maternal immune system seems to be present.

Summary Interferon alpha (IFN-a) has a documented activity against malignant melanoma with a response rate of only approximately 20%. It would therefore be of considerable importance if patients likely to respond could be identified. The degree of mononuclear cell infiltration in primary tumours has been reported to correlate with a favourable prognosis. This investigation used monoclonal antibodies, anti-CD4, -CD8 and -CD 1 lc, to identify subsets of tumour-infiltrating mononuclear cells in fine needle aspirates to study whether the presence of such cells correlates with the therapeutic effect of IFN-a. Twenty-one patients with systemic and 20 with regional metastatic malignant melanoma were studied before initiation of IFN-a treatment. A statistically significant correlation (P<0.001) was found between the occurrence of CD4+ lymphocytes in fine needle aspirates and the therapeutic benefit of IFN-a in patients with systemic disease. Ten out of 11 with moderate to high numbers of infiltrating CD4+ lymphocytes achieved tumour regression. In contrast, among patients with low numbers of these cells in metastatic lesions, nine out of ten had progressive disease. Similar results were found in patients with regional disease.

A large number of studies have indicated that specific immune reactivity plays a crucial role in the control of malignant melanoma. In this context, expression of MHC I, MHC II and B7 molecules by melanoma cells is seen as relevant for the immune response against the tumour. For a better understanding of the biological relevance of MHC II and B7 expression by tumour cells in metastatic melanoma, we studied the expression of these molecules in melanoma metastases in relation to the inflammatory response, regression of the tumour and survival from 27 patients treated with biochemotherapy (30 mg m À2 Cisplatin and 250 mg m À2 decarbazine (dimethyl-triazene-imidazole-carboxamide, DTIC) on days 1 -3 i.v., and 10 7 IU IFN-a2b 3 days a week s.c., q. 28d). In 19 out of 27 lesions studied, we found expression of MHC II by the tumour cells, while only in one out of 11 tumour biopsies obtained from untreated metastatic melanoma patients, MHC II expression was detected.

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