EXPRESSION OF THE COSTIMULATORY MOLECULE B7 ON MELANOMA-CELLS

The induction of T-cell responses against tumor cells is believed to d epend on both recognition of antigen and receipt of co-stimulatory sig nals from interaction of ligands such as B7 with its receptors CD28 or CTLA-4 on T cells. In the present study the expression of B7 on cultu red human melanoma cells was studied at the mRNA level by reverse PCR analysis and surface expression by flow cytometric analysis with monoc lonal antibodies (MAbs). PCR analysis revealed mRNA for B7 in 3 of 6 ( 50%) cultured primary melanoma and 8 of 19 (42%) cultures of metastati c melanoma. Analysis of B7 expression by flow cytometry using the BBI MAb revealed low levels of expression in 3 of 10 melanoma that had mRN A for B7. In 2 of the latter (but not 4 other PCR(+) lines) expression could be increased by culture in GM-CSF, IL-2, IFN-gamma and IFN-alph a 2. Our results indicate that although mRNA for B7 is present in 40-5 0% of melanoma cell lines, expression at the protein level is at low o r undetectable levels in the majority of the cell lines. Expression of B7 protein was also not detected in studies on tissue sections from 1 1 primary and 9 metastatic melanomas. (C) 1994 Wiley-Liss, Inc.