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To overcome the hurdles of immunotherapy, we investigated whether calcipotriol, a synthetic vitamin D analog, could overcome the immune evasion of glioblastoma multiforme (GBM) by modulating immune responses and the immunosuppressive tumor microenvironment. Administration of calcipotriol considerably reduced tumor growth. Both in vivo and in vitro studies revealed that CD8+T and natural killer (NK) cell gene signatures were enriched and activated, producing high levels of IFN-γ and granzyme B. In contrast, regulatory T cells (Treg) were significantly reduced in the calcipotriol-treated group. The expression of CD127, the receptor for thymic stromal lymphopoietin (TSLP), is elevated in CD4+T cells and potentially supports T-cell priming. Depleting CD4+T cells, but not NK or CD8+T cells, completely abrogated the antitumor efficacy of calcipotriol. These data highlight that the calcipotriol/TSLP/CD4+T axis can activate CD8+T and NK cells with a concomitant reduction in the number of Tregs in GBM. Therefore, calcipotriol can be a novel therapeutic modality to overcome the immune resistance of GBM by converting immunologically "cold" tumors into "hot" tumors. DATA AVAILABILITY: Data are available upon reasonable request. The RNA-seq dataset comparing the transcriptomes of control and calcipotriol-treated GL261 tumors is available from the corresponding author upon request., Competing Interests: Conflict of interest statement All authors declare that they have no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)