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T cell-mediated immunity has the ability to produce durable anti-melanoma responses resulting in improved survival of patients with advanced melanoma. Antigen presentation is a key determinant of T cell responses. Gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of multiple melanoma antigens to CD4+ T cells. However, GILT expression in melanoma has not been defined. We evaluated GILT and MHC class II expression in human primary and metastatic melanomas and nevi using immunohistochemistry. GILT staining in melanocytes was observed in 70% of primary and 58% of metastatic melanomas versus 0% of nevi. When present, the GILT staining intensity in melanocytes was typically faint. Both GILT and MHC class II expression were increased in melanocytes of primary and metastatic melanomas compared with nevi. GILT staining in antigen presenting cells was detected in 100% of primary and metastatic melanomas versus 31% of nevi and was typically intense. GILT expression was increased in antigen presenting cells of primary and metastatic melanomas compared to nevi, whereas MHC class II had equivalent high expression in antigen presenting cells of all melanocytic lesions. GILT staining in keratinocytes was detected in 67% of primary melanomas versus 14% of nevi and 6% of metastatic melanomas. GILT, but not MHC class II, expression was increased in keratinocytes of primary melanomas compared to nevi and metastases. GILT expression is anticipated to result in improved presentation of melanoma antigens and more effective anti-melanoma T cell responses. GILT expression may be a biomarker of immune recognition of melanoma.

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