Metastatic melanomas express inhibitory low affinity fc gamma receptor and escape humoral immunity.

Our research, inspired by the pioneering works of Isaac Witz in the 1980s, established that 40% of human metastatic melanomas express ectopically inhibitory Fc gamma receptors (FcgammaRIIB), while they are detected on less than 5% of primary cutaneous melanoma and not on melanocytes. We demonstrated that these tumoral FcgammaRIIB act as decoy receptors that bind the Fc portion of antimelanoma IgG, which may prevent Fc recognition by the effector cells of the immune system and allow the metastatic melanoma to escape the humoral/natural immune response. The FcgammaRIIB is able to inhibit the ADCC (antibody dependent cell cytotoxicity) in vitro.

Selective expression of inhibitory Fcgamma receptor by metastatic melanoma impairs tumor susceptibility to IgG-dependent cellular response.

During melanoma progression, patients develop anti-tumor immunity including the production of anti-tumor antibodies. Although the strategies developed by malignant cells to escape anti-tumor cellular immunity have been extensively investigated, little is known about tumor resistance to humoral immunity. The main effect of IgG antibodies is to activate the immune response by binding to host Fc gamma receptors (FcgammaR) expressed by immune cells.

Modulation of tumor growth by inhibitory Fc(gamma) receptor expressed by human melanoma cells.

The efficacy of anti-tumor IgG reflects the balance between opposing signals mediated by activating and inhibitory Fc(gamma) receptors (Fc(gamma)Rs) expressed by effector cells. Here, we show that human malignant melanoma cells express the inhibitory low-affinity Fc(gamma) receptor Fc(gamma)RIIB1 in 40% of tested metastases. When melanoma cells were grafted in nude mice, a profound inhibition of Fc(gamma)RIIB1 tumor growth that required the intracytoplasmic region of the receptor was observed.