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Programmed death-ligand 1 (PD-L1), a critical immune checkpoint ligand, is commonly overexpressed on the surface of many tumor types including lung and prostate cancer. PD-L1 can exert cancer-promoting activity through either suppressing T cell-mediated immune response or activating tumor-intrinsic signaling. Here, we demonstrated that β-tocotrienol (β-T3), an isomer of vitamin E, effectively inhibited PD-L1 expression both in vitro and in vivo , which was mechanistically associated inactivating JAK2/STAT3 pathway. Down-regulating PD-L1 expression by β-T3 led to enhanced immune response and inactivation of PD-L1-induced tumor-intrinsic signaling, which in turn contributed to its anticancer activity. This study uncovered a novel mechanism involved in the anticancer effect of β-T3. • ∗β-tocotrienol inhibits PD-L1 expression both in vitro and in vivo. • ∗β-tocotrienol mitigates PD-L1-mediated immune suppression. • ∗β-tocotrienol suppresses PD-L1-meidtated tumor-intrinsic signaling. • ∗β-tocotrienol inhibits tumor growth in vivo associated with enhanced immune response. [ABSTRACT FROM AUTHOR]

This study explored the effect of low-dose radiation on the expression of immune checkpoint molecules in lung cancer cells and its mechanism, as well as the antitumour effect of combined low-dose radiation and immune checkpoint inhibitors. Western blot analysis was used to assess the expression of the immune checkpoint molecules CD47, PD-L1, FGL-1 and CD155 in lung cancer cells after radiation. Western blotting was also used to explore changes in the JAK2/STAT3 pathway. CD8+ T lymphocyte infiltration in tumour tissues were assessed by immunohistochemistry in a mouse model. The inhibitory effect of low-dose radiation combined with PD-L1 or CD47 inhibitors on tumor growth was evaluated by measuring tumor volume. In response to low-dose irradiation, the expression of CD47 and PD-L1 in A549 and LLC cells was increased, the expression of p-JAK2 and p-STAT3 was also increased. AG490-mediated inhibition of the JAK2/STAT3 pathway before irradiation significantly reduced the expression of p-JAK2 and p-STAT3 in lung cancer cells, in the meantime, expression of CD47 and PD-L1 was also reduced. Conventional dose exposure exhibited the same trend. PD-L1 and CD47 protein levels increased after low-dose irradiation in an LLC tumour-bearing mouse model. Low-dose irradiation combined with PD-L1 or CD47 inhibitor treatment reduced levels of PD-L1 or CD47 in tumour tissues, increased the proportion of CD8+ T lymphocytes, and significantly inhibited tumour growth. Both low-dose and regular-dose irradiation upregulate expression of the immune checkpoint molecules CD47 and PD-L1 in lung cancer cells, and the mechanism may be related to the JAK2/STAT3 pathway. Furthermore, low-dose irradiation combined with PD-L1 or CD47 inhibitors significantly inhibits tumour growth. • Low dose irradiation can cause the upregulation of PD-L1 and CD47. • Irradiation may regulate the expression of CD47 and PD-L1 through the JAK2/STAT3 pathway. • Irradiation combined with PD-L1/CD47 inhibitor increased the infiltration of CD8-positive T cells. • Low dose irradiation combined with PD-L1/CD47 inhibitor enhanced the inhibition of tumor. [ABSTRACT FROM AUTHOR]