Immune Microenvironment of Hair Follicles in Tumor Immunotherapy.

Although tumor immunotherapy has shown significant efficacy against solid tumors, it frequently causes cutaneous and follicular adverse events resulting from disruption of the hair follicle immune microenvironment. This microenvironment is maintained through careful regulation by immune cells and cytokine networks to support normal hair cycling. Immune checkpoint inhibitors disturb this balance by activating T cells, promoting macrophage polarization toward pro-inflammatory phenotypes, upregulating inflammatory cytokines such as tumor necrosis factor-alpha, and activating Toll-like receptor/nuclear factor-kappa B signaling pathways, ultimately leading to follicular toxicity including alopecia. Encompass relies mainly on topical corticosteroids and other immunomodulatory agents. A deeper understanding of these mechanisms is essential to identify key regulatory nodes for future targeted interventions.