Unraveling the Complex Relationship Between Cancer Immunity and Autoimmunity: Lessons from Melanoma and Vitiligo
A relationship between melanoma and vitiligo, a skin disorder characterized by the loss of melanocytes, has been postulated for many decades. In some cases, vitiligo is almost certainly a manifestation of autoimmune-mediated destruction of melanocytes. Melanocytes and melanoma cells share melanocyte differentiation antigens. Based on a number of observations, de novo vitiligo developing in patients with melanoma has been regarded as a sign of good prognosis. The immune system tolerates or ignores differentiation antigens because these antigens are self-derived. Therefore, immune tolerance or ignorance must be overcome to prime naive T and B cells to induce cancer immunity and autoimmunity against melanocyte differentiation antigens. Mouse models of concurrent melanoma and autoimmune vitiligo have revealed strategies to overcome immune ignorance or tolerance to melanocyte differentiation antigens: immunization with self-antigens as altered self (e.g., orthologues or mutated versions), expression in viral vectors, passive immunization with antibodies or T cells, incorporating potent adjuvants into active immunization, and blockade or removal of a downregulatory mechanism. Extensive investigations into the mechanisms that lead to tumor immunity and autoimmunity elicited by certain differentiation antigens have further revealed a variety of distinct cellular and molecular requirements, which are redundant and alternative.