Revisiting the Experimental Methods for Human Skin T-Cell Analysis

Tissue-resident memory T cells exist in both the epidermis and the dermis in human skin. To analyze these cells, the skin needs to be incubated with dispase II to separate the two layers, that is, the epidermis and the dermis. The next step varies among researchers; the subsequent enzymatic digestion of the two layers is popular, whereas the spontaneous migration method can also be done. Scraping of these layers to yield skin T cells may reduce antigen modulation. This study aimed to determine each method's limitations. Dispase II incubation itself cleaves T-cell antigens. Therefore, further enzymatic digestion with collagenases strongly cleaves antigens. The scraping method yields skin T cells that are affected by dispase II as it is. However, skin T-cell yield is low. The spontaneous migration method recovers and/or upregulates antigens with T-cell activation and loses ∼20% of T cells in the floating sheets. However, there was no prominent bias regarding CD103 expression between emigrants and the remaining T cells in the sheets. There were 10⁴ and 10⁵ CD3⁺ T cells per 1 cm² of the epidermis and upper dermis, respectively. Collectively, each method has strengths and limitations to analyze both the epidermal and dermal T cells.