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Clin Transl Immunology. 2019 Dec 25;8(12):e1100. doi: 10.1002/cti2.1100. eCollection 2019.

Accumulation of CD103+ CD8+ T cells in a cutaneous melanoma micrometastasis.

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Peter MacCallum Cancer Centre Melbourne VIC Australia.
Department of Microbiology & Immunology The University of Melbourne at the Peter Doherty Institute for Infection & Immunity Melbourne VIC Australia.
Sir Peter MacCallum Department of Oncology The University of Melbourne Parkville VIC Australia.
Telethon Kids Institute University of Western Australia Perth WA Australia.
Olivia Newton-John Cancer Research Institute Heidelberg VIC Australia.
Department of Surgery University of Melbourne Melbourne VIC Australia.



The immune system can halt cancer progression by suppressing outgrowth of clinically occult micrometastases in a state of cancer-immune equilibrium. Cutaneous melanoma provides a unique opportunity to study the immune contexture of such lesions, as miniscule skin metastases are accessible to clinical inspection and diagnostic biopsy.


Here, we analysed by multiplex immunofluorescence microscopy samples from a melanoma patient presenting with an overt and an occult in-transit metastasis (ITM), the latter of which appeared as a small erythematous papule.


Microarchitecture and immune composition in the two lesions were vastly different. CD4+ and CD8+ T cells accumulated around the margin of the overt SOX10+ Melan A+ ITM but were largely excluded from the tumor centre. By contrast, the occult micrometastasis contained only few SOX10+ Melan A- melanoma cells which were scattered within a dense infiltrate of T cells, including a prominent population of CD103+ CD8+ T cells resembling tissue-resident memory T (TRM) cells. Notably, almost every single melanoma cell in the micrometastasis was in close proximity to these TRM-like cells.


Such results support the emerging concept that CD103+ CD8+ TRM cells are key mediators of cancer surveillance and imply an important function of these cells in controlling clinically occult micrometastases in humans.


melanoma; micrometastasis; tissue‐resident memory T cells

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