Anti-CD40
antibodies are in clinical development in patients with metastatic
melanoma, a
cancer that has been reported earlier to express CD40. The antitumor activity of anti-CD40
antibodies may be mediated by direct cytotoxic effects on CD40-positive
melanoma cells or indirectly through modulation of host cells. In these studies, biopsies of patients with primary and metastatic
melanoma, short-term cultures, and established
melanoma cell lines were analyzed for CD40 expression using a combination of methods including immunohistochemistry, flow cytometry, and gene expression profiling, and the cytotoxic effects of the anti-CD40 antibody
CP-870,893 on
melanoma cell lines were tested using cell viability assays. CD40 was expressed at a higher frequency in metastatic
melanoma lesions compared with primary
melanomas. There was a variable expression of CD40 in synchronous and metachronous
melanoma metastases. Expression of CD40 was present in slightly over half of a large panel of short-term primary
melanoma cultures, with a wide range of expression levels by flow cytometry. Similar results were obtained in established
melanoma cell lines when analyzed at the
mRNA level or by
surface protein staining. In approximately one-third of cell lines, the expression of CD40 could be up-regulated with a
histone deacetylase inhibitor. Treatment with increasing concentrations of
CP-870,893 had no antitumor activity against either CD40-positive or negative
melanoma cell lines. In conclusion, approximately one-third to one-half of
melanomas expresses CD40 at variable levels. Direct exposure to a CD40-activating antibody does not lead to antitumor activity in
melanoma cell lines, suggesting that the antitumor effects of these
antibodies in the clinic may be indirectly mediated.