Resident cutaneous memory T-cells: A clinical review of their role in chronic inflammatory dermatoses and potential as therapeutic targets.

Resident memory T-cells (T-RMs) remain in epithelial barrier tissues after antigen exposure and the initial effector phase. These T-RMs provide effective antimicrobial and anticancer immunity, however pathogenic T-RMs have been shown to mediate various chronic inflammatory disorders in a variety of tissue types. In the skin, T-RMs are referred to as resident cutaneous memory T-cells (cT-RMs). Understanding the mechanisms leading to the development and establishment of these cT-RMs populations may allow for targeted treatments providing durable responses in chronic immune-mediated skin diseases, even after cessation. In this Review, we summarise the evidence on cT-RMs as drivers of chronic inflammatory dermatoses including psoriasis, vitiligo, atopic dermatitis, cutaneous lupus erythematosus and alopecia areata, among others. Data from in-vitro, animal model, and ex-vivo human studies are presented - with a focus on the potential for cT-RMs to trigger acute disease flares as well as recurrent disease by establishing an immune 'memory' in the skin. Furthermore, available data on the potential for existing and novel treatments to affect the development or survival of cT-RMs in the skin are synthesised. These suggest a dynamic and rapidly growing area in the field of dermatology; however we also discuss areas in need of greater research to allow for optimal treatment selection for long-term disease control.