WNT signaling modulates PD-L1 expression in the stem cell compartment of triple-negative breast cancer

Abstract

Triple-negative breast cancers (TNBCs) are characterized by a poor prognosis and lack of targeted treatments, and thus, new therapeutic strategies are urgently needed. Inhibitors against programmed death-1 (PD-1)/PD-1 ligand (PD-L1) have shown significant efficacy in various solid cancers, but their activity against TNBCs remains limited. Here, we report that human TNBCs molecularly stratified for high levels of PD-L1 (PD-L1High) showed significantly enriched expression of immune and cancer stemness pathways compared with those with low PD-L1 expression (PD-L1Low). In addition, the PD-L1High cases were significantly associated with a high stemness score (SSHigh) signature. TNBC cell lines gated for aldehyde dehydrogenase (ALDH) and CD44 stemness markers exhibited increased levels of PD-L1 versus their ALDH-negative and CD44Low counterparts, and PD-L1High cells generated significantly more mammospheres than PD-L1Low cells. Murine mammary SCA-1-positive tumor cells with PD-L1High expression generated tumors in vivo with higher efficacy than PD-L1Low cells. Furthermore, treatment of TNBC cells with selective WNT inhibitors or activators downregulated or upregulated PD-L1 expression, respectively, implying a functional cross-talk between WNT activity and PD-L1 expression. Remarkably, human TNBC samples contained tumor elements co-expressing PD-L1 with ALDH1A1 and/or CD44v6. Additionally, both PD-L1-/SCA1-positive and ALDH1A1-positive tumor elements were found in close contact with CD3-, and PD-1-positive T cells in murine and human tumor samples. Overall, our study suggests that PD-L1-positive tumor elements with a stemness phenotype may participate in the complex dynamics of TNBC-related immune evasion, which might be targeted through WNT signaling inhibition.

Cancer Stem Cells: Devil or Savior—Looking behind the Scenes of Immunotherapy Failure

“…In agreement with another group [50], we recently showed that the activation of the WNT signaling pathway increased PD-L1 expression on the plasma membrane of triple-negative breast CSCs (TNBCSCs) [42]. We also provided the first evidence that PD-L1+ TNBCSCs interact with tumorinfiltrating CD8+ and PD-1+ immune cells, thus halting antitumor immune responses [42].…”

“…Specifically, the The recent introduction of monoclonal antibodies (mAbs) targeting the PD-1/PD-L1 signaling axis in cancer therapy significantly improved the survival of patients with different advanced and aggressive tumor types, including melanoma, non-small-cell lung cancer, and kidney carcinoma [49]. In agreement with another group [50], we recently showed that the activation of the WNT signaling pathway increased PD-L1 expression on the plasma membrane of triple-negative breast CSCs (TNBCSCs) [42]. We also provided the first evidence that PD-L1+ TNBCSCs interact with tumor-infiltrating CD8+ and PD-1+ immune cells, thus halting antitumor immune responses [42].…”

“…CD200 overexpression has been reported in the CSCs of human papillomavirus (HPV)-positive and HPV-negative head and neck squamous cell carcinomas, thus pointing out its candidacy as a potentially actionable CSC marker [39] and paving the way for new therapeutic approaches targeting this immunomodulation-associated protein [40]. PD-L1, an immune checkpoint protein known to trigger a protumorigenic immunophenotype, was also found to be upregulated on the plasma membrane of melanoma as well as ovarian, breast, colon, and lung CSCs [41][42][43][44]. In particular, PD-L1 binding to its receptor (PD-1) on the T cell plasma membrane inhibits the production of immunostimulating cytokines (i.e., IFN-γ and IL-2) [45,46], dampens the T cell-mediated immune response [47], and promotes the expansion of immunosuppressive regulatory T (T-reg) cells [48].…”

PD-L1 is overexpressed on breast cancer stem cells through notch3/mTOR axis

“…While writing this manuscript, Castagnoli et al 30 and Hsu et al 31 reported a role for Wnt signaling in regulating PD-L1 expression on breast CSCs. We did not see such an effect of the Wnt pathway on PD-L1 expression in our model of CSCs when we used the inhibitor ICG-001, which is supposed to block the Wnt pathway downstream by preventing the CBP/ β-catenin activation.…”

Targeted inhibition of Wnt signaling with a bacterial toxin fragment suppresses breast cancer tumor-initiating/chemo-resistant cells

“…In our study, it is likely that cisplatin treatment leads to an epithelial cell fate change toward a mesenchymal state (24), which may represent a dedifferentiation process that involves Wnt signaling. Lastly, Wnt signaling has been shown to contribute to immune invasion as well as systemic inflammation in the tumor microenvironment that drives cancer metastasis (42)(43)(44)(45). Whether TcdB FBD may provide a synergistic effect with immunotherapy such as PD-1/PD-L1 antibodies remains to be explored.…”