Possible Involvement of Skin‐Resident Memory T Cells in Refractory Chronic Alopecia Areata

ABSTRACT Alopecia areata is a typical skin disease with unmet needs. So far, it has been understood that the main cause of the intractability of chronic cases is the decrease in inflammatory cell infiltration and falling into the telogen‐like phase. However, in some cases, even in long‐term chronic cases, inflammatory cell infiltration can be seen, so that we speculate that the long‐term persistence of these perifollicular cells may be the reason for the lack of improvement as skin resident memory T (T RM ) cells. To investigate the presence of T RM , nine treatment‐resistant chronic AA patients and 5 acute AA patients were employed for staining with CD69 and CD103 as markers for identifying skin T RM cells. This study revealed the number of CD8 + CD103 + T and CD69 + CD103 + T cells tended to increase with increasing disease duration and refractoriness. In one case of AA refractory to conventional treatment, an oral JAK inhibitor (JAKi) showed dramatic efficacy with a reduction in the number of infiltrating CD103 + cells, including CD8 + CD103 + T and CD69 + CD103 + T cells. These results suggest that refractory cases in the chronic phase tend to have more infiltrating skin T RM cells, and JAKi may be effective in the refractory cases of chronic AA.