Recombinant interferon-γ can induce the expression of HLA-DR and -DC on DR-negative melanoma cells and enhance the expression of HLA-ABC and tumor-associated antigens

Abstract

Recombinant interferon-γ (IFN-γ) induced the expression of HLA-DR when added to the culture medium of HLA-DR⁻ melanoma cell lines. In addition, IFN-γ induced the expression of another class II antigen, HLA-DC, on a HLA-DR⁺ and -DC⁻ melanoma cell line and to a lower level on a -DR and -DC⁻ melanoma line. IFN-γ also enhanced the expression of HLA-ABC and β₂-microglobulin, as well as HLA-DR on DR⁺ melanoma cells. In contrast, IFN-α gave no induction of expression of HLA-DR and DC on two DR⁻ melanoma lines, while it did enhance the expression of HLA-ABC and of β₂-microglobulin. The expression of 3 out of 6 melanoma-associated differentiation antigens was enhanced by IFN-γ treatment. The modulation of antigens by IFN-γ was both dose and time dependent. A minimum incubation time of 48 h was necessary for the appearance of HLA-DR on the two HLA-DR⁻ melanoma lines, whereas HLA-ABC and β₂-microglobulin were already increased after 24 h. A dose of 20 U/ml IFN-γ started to induce the expression of HLA-DR and DC on melanoma cells GLL-19 and Me-43 and a plateau of maximum antigen expression was reached with 100 U/ml. Analyses of IFN-γ-treated cells by flow micro-fluorometry showed a homogeneous distribution of increased staining intensity rather than the appearance of two cell populations. Immunoprecipitation experiments using detergent-solubilized ¹²⁵I-labeled membrane proteins of IFN-γ-treated melanoma cells and a monoclonal anti-HLA-DR antibody confirmed the presence of HLA-DR antigens. When IFN-γ-treated cells were cultured without IFN the induced or enhanced expression of HLA antigens was reversible. Eight days after removal of IFN, the HLA-DR level was reduced by more than 90% and the level of HLA-ABC and β₂-microglobulin by more than 50%. The demonstration of the ability of HLA-DR⁻ melanoma cells to express HLA-DR after IFN-γ treatment was extended to cells from other types of tumor such as gliomas, colon carcinomas and one cervical carcinoma cell line.