Tumor-intrinsic PD-L1 Research Articles

Tumor-Intrinsic PD-L1 Signaling in Cancer Initiation, Development and Treatment: Beyond Immune Evasion.

Although the role of PD-L1 in suppressing the anti-tumor immune response is extensively documented, recent discoveries indicate a distinct tumor-intrinsic role for PD-L1 in modulating epithelial-to-mesenchymal transition (EMT), cancer stem cell (CSC)-like phenotype, metastasis and resistance to therapy. In this review, we will focus on the newly discovered functions of PD-L1 in the regulation of cancer development, describe underlying molecular mechanisms responsible for PD-L1 upregulation and discuss current insights into novel components of PD-L1 signaling. Furthermore, we summarize our current understanding of the link between PD-L1 signaling and the EMT program as well as the CSC state. Tumor cell-intrinsic PD-L1 clearly contributes to cancer stemness, EMT, tumor invasion and chemoresistance in multiple tumor types. Conversely, activation of OCT4 signaling and upregulation of EMT inducer ZEB1 induce PD-L1 expression in cancer cells, thereby suggesting a possible immune evasion mechanism employed by cancer stem cells during metastasis. Our meta-analysis demonstrated that PD-L1 is co-amplified along with MYC, SOX2, N-cadherin and SNAI1 in the TCGA endometrial and ovarian cancer datasets. Further identification of immune-independent PD-L1 functions and characterization of crucial signaling events upstream or downstream of PD-L1 in diverse cancer types and specific cancer subtypes, would provide additional targets and new therapeutic approaches.

Antigen-Presenting Cell-Intrinsic PD-1 Neutralizes PD-L1 in cis to Attenuate PD-1 Signaling in T Cells

SUMMARYThe PD-1 pathway, consisting of the co-inhibitory receptor PD-1 on T cells and its ligand (PD-L1) on antigen-presenting cells (APCs), is a major mechanism of tumor immune evasion. PD-1 and PD-L1 blockade antibodies have produced remarkable clinical activities against a subset of cancers. Binding between T cell-intrinsic PD-1 and APC-intrinsic PD-L1 triggers inhibitory signaling to attenuate the T cell response. Here, we report that PD-1 is co-expressed with PD-L1 on tumor cells and tumor-infiltrating APCs. Using reconstitution and cell culture assays, we demonstrate that the co-expressed PD-1 binds to PD-L1 in cis. Such interaction inhibits the ability of PD-L1 to bind T cell-intrinsic PD-1 in trans and, in turn, represses canonical PD-L1/PD-1 inhibitory signaling. Selective blockade of tumor-intrinsic PD-1 frees up tumor-intrinsic PD-L1 to inhibit T cell signaling and cytotoxicity. Our study uncovers another dimension of PD-1 regulation, with important therapeutic implications.

Abstract 3696: Tumor-intrinsic PD-L1 alters tumor chemokines, NK cell trafficking and function, and renders distant PD-L1 null tumors responsive to αPD-L1

Abstract Programmed death ligand (PD-L) 1 is expressed on many tumors and inhibits anti-tumor T cells through programmed death (PD)-1. Tumor PD-L1 predicts αPD-L1 treatment effects, but mechanism(s) for PD-L1- tumor response to αPD-L1 are unclear. Our studies suggest tumor-intrinsic PD-L1 signals and spatially varied PD-L1 expression may contribute to response deviation. We used PD-L1+ B16 melanoma (ctrl) and made PD-L1KO by CRISPR. αPD-L1 slowed ctrl but not PD-L1KO B16 growth in mice as expected, but PD-L1KO also responded to αPD-L1 if ctrl B16 was on the trans flank. αPD-L1 elicited similar CD3+ T cell infiltration into ctrl vs. PD-L1KO tumors, but without detectable B16-specific T cell increase. CD11b+ cell infiltration was similar in ctrl and PD-L1KO. Strikingly, NKp46+ and NK1.1+ natural killer (NK) cells infiltrated PD-L1KO > ctrl. NK cells increased significantly (~2-fold) after αPD-L1 in PD-L1KO vs. ctrl, along with NK effector functions (e.g., IFN-γ). Tumor PD-L1 altered tumor chemokines (e.g., CXCL12, CCL2) that could explain trafficking. CD4+ and CD8+ T cells chemotaxed to PD-L1KO slightly > ctrl (with slightly > PD-1+ T cells) in transwells, but NK cells migrated ~2-fold more to PD-L1KO vs. ctrl (with increased activation (e.g., PD-1, CD69), also seen in vivo). We observed that tumor β2 microglobulin (B2M) expression was suppressed by tumor PD-L1. Tumor PD-L1 alteration of immune infiltrates by altering chemokines is a novel mechanism for PD-L1 TIL control. These data also indicate that tumor PD-L1 blunts NK cell infiltration in B16 and reduces B2M, which could boost NK cell anti-tumor activity. These changes correlate with rescued αPD-L1 response of PD-L1KO B16. As αPD-L1 did not increase B16-specific T cells in PD-L1low, we hypothesize that rescue of αPD-L1 response is in part NK cell-mediated. Preliminary in vivo NK cell depletion + αPD-L1 experiments implicate a role for NK cells in PD-L1KO tumor response, but more work is needed to identify mechanisms. Effects extend beyond B16 as ctrl (PD-L1+) MB49 bladder cancer cells in trans elicited αPD-L1 response of PD-L1KO MB49 tumors. Mouse breast and ovarian cancers, and human ovarian and bladder cells exhibit similar PD-L1-intrinsic effects. Finally, αPD-L1 directly altered tumor cell chemokine production in vitro, suggesting additional, novel αPD-L1 treatment mechanisms requiring more study. Our models are useful to understand αPD-L1 (and likely αPD-1) responses based on tumor PD-L1 expression and will help define strategies to improve responses in PD-L1low tumors, and possibly poorly responsive PD-L1+ tumors. Citation Format: Curtis A. Clark, Harshita B. Gupta, Alvaro Padron, Deyi Zhang, Vincent Hurez, Mary Jo Turk, Rong Li, Tyler Curiel. Tumor-intrinsic PD-L1 alters tumor chemokines, NK cell trafficking and function, and renders distant PD-L1 null tumors responsive to αPD-L1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3696. doi:10.1158/1538-7445.AM2017-3696

Correction: Tumor-Intrinsic PD-L1 Signals Regulate Cell Growth, Pathogenesis, and Autophagy in Ovarian Cancer and Melanoma.

Correction: Tumor-Intrinsic PD-L1 Signals Regulate Cell Growth, Pathogenesis, and Autophagy in Ovarian Cancer and Melanoma.

PD-L1 Promotes Self-Renewal and Tumorigenicity of Malignant Melanoma Initiating Cells.

Recent studies have indicated that therapeutic antibodies targeting PD-L1 show remarkable efficacy in clinical trials in multiple tumors and that a melanoma cell-intrinsic PD-1: PD-L1 axis promotes tumor growth. However, few studies have shown tumor-intrinsic PD-L1 effects in malignant melanoma initiating cells (MMICs). Here, we aim to determine the possible regulatory effects of PD-L1 on MMICs. The ALDEFLUOR kit was used to identify ALDH+ MMICs. Flow cytometry was used to examine the expression of PD-L1 on ALDH+ MMICs. To determine the role of PD-L1 in MMICs self-renewal, we cultured melanoma cells with anti-PD-L1 and measured tumorsphere formation and apoptosis. In addition, the effects of anti-PD-L1 on tumorigenicity and residual ALDH+ MMICs in tumors were evaluated in vivo. We demonstrated that melanoma cell-intrinsic PD-L1 was expressed in ALDH+ MMICs. Blocking PD-L1 in melanoma cell lines impaired tumorsphere formation and induced the apoptosis of sphere cells. In addition, blocking PD-L1 inhibited tumor growth in vivo. We observed residual ALDH+ MMICs within the tumor. The results showed that blocking PD-L1 also significantly decreased the residual ALDH+ MMICs in the tumors. In conclusion, these results suggest a new mechanism underlying melanoma progression and PD-L1-targeted therapy, which is distinct from the immunomodulatory actions of PD-L1.

Tumor cell-intrinsic PD-L1 promotes tumor-initiating cell generation and functions in melanoma and ovarian cancer.

As tumor PD-L1 provides signals to anti-tumor PD-1+ T cells that blunt their functions, αPD-1 and αPD-L1 antibodies have been developed as anti-cancer immunotherapies based on interrupting this signaling axis. However, tumor cell-intrinsic PD-L1 signals also regulate immune-independent tumor cell proliferation and mTOR signals, among other important effects. Tumor-initiating cells (TICs) generate carcinomas, resist treatments and promote relapse. We show here that in murine B16 melanoma and ID8agg ovarian carcinoma cells, TICs express more PD-L1 versus non-TICs. Silencing PD-L1 in B16 and ID8agg cells by shRNA (‘PD-L1lo’) reduced TIC numbers, the canonical TIC genes nanog and pou5f1 (oct4), and functions as assessed by tumorosphere development, immune-dependent and immune-independent tumorigenesis, and serial transplantability in vivo. Strikingly, tumor PD-L1 sensitized TIC to interferon-γ and rapamycin in vitro. Cell-intrinsic PD-L1 similarly drove functional TIC generation, canonical TIC gene expression and sensitivity to interferon-γ and rapamycin in human ES2 ovarian cancer cells. Thus, tumor-intrinsic PD-L1 signals promote TIC generation and virulence, possibly by promoting canonical TIC gene expression, suggesting that PD-L1 has novel signaling effects on cancer pathogenesis and treatment responses.

Tumor-Intrinsic PD-L1 Signals Regulate Cell Growth, Pathogenesis, and Autophagy in Ovarian Cancer and Melanoma.

PD-L1 antibodies produce efficacious clinical responses in diverse human cancers, but the basis for their effects remains unclear, leaving a gap in the understanding of how to rationally leverage therapeutic activity. PD-L1 is widely expressed in tumor cells, but its contributions to tumor pathogenicity are incompletely understood. In this study, we evaluated the hypothesis that PD-L1 exerts tumor cell-intrinsic signals that are critical for pathogenesis. Using RNAi methodology, we attenuated PD-L1 in the murine ovarian cell line ID8agg and the melanoma cell line B16 (termed PD-L1lo cells), which express basal PD-L1. We observed that PD-L1lo cells proliferated more weakly than control cells in vitro As expected, PD-L1lo cells formed tumors in immunocompetent mice relatively more slowly, but unexpectedly, they also formed tumors more slowly in immunodeficient NSG mice. RNA sequencing analysis identified a number of genes involved in autophagy and mTOR signaling that were affected by PD-L1 expression. In support of a functional role, PD-L1 attenuation augmented autophagy and blunted the ability of autophagy inhibitors to limit proliferation in vitro and in vivo in NSG mice. PD-L1 attenuation also reduced mTORC1 activity and augmented the antiproliferative effects of the mTORC1 inhibitor rapamycin. PD-L1lo cells were also relatively deficient in metastasis to the lung, and we found that anti-PD-L1 administration could block tumor cell growth and metastasis in NSG mice. This therapeutic effect was observed with B16 cells but not ID8agg cells, illustrating tumor- or compartmental-specific effects in the therapeutic setting. Overall, our findings extend understanding of PD-L1 functions, illustrate nonimmune effects of anti-PD-L1 immunotherapy, and suggest broader uses for PD-L1 as a biomarker for assessing cancer therapeutic responses. Cancer Res; 76(23); 6964-74. ©2016 AACR.

PD-L1 is highly expressed in Enzalutamide resistant prostate cancer.

Efficacy of Enzalutamide (ENZ) in castration resistant prostate cancer (CRPC) patients is short-lived. Immunotherapy like T cell checkpoint blockade may improve patient survival. However, when and where checkpoint molecules are expressed in CRPC and whether immune evasion is a mechanism of ENZ resistance remains unclear. Thus, we investigated whether clinically relevant immunotherapy targets, specifically PD-L1/2 , PD-1 and CTLA-4, are upregulated in ENZ resistant (ENZR) patients and in a pre-clinical model of ENZ resistance. We show for the first time that patients progressing on ENZ had significantly increased PD-L1/2+ dendritic cells (DC) in blood compared to those naïve or responding to treatment, and a high frequency of PD-1+T cells. These data supported our pre-clinical results, in which we found significantly increased circulating PD-L1/2+ DCs in mice bearing ENZR tumors compared to CRPC, and ENZR tumors expressed significantly increased levels of tumor-intrinsic PD-L1. Importantly, the expression of PD-L1 on ENZR cells, or the ability to modulate PD-L1/2+ DC frequency, was unique to ENZR cell lines and xenografts that did not show classical activation of the androgen receptor. Overall, our results suggest that ENZ resistance is associated with the strong expression of anti-PD-1 therapy targets in circulating immune cells both in patients and in a pre-clinical model that is non-AR driven. Further evaluation of the contribution of tumor vs. immune cell PD-L1 expression in progression of CRPC to anti-androgen resistance and the utility of monitoring circulating cell PD-L1 pathway activity in CRPC patients to predict responsiveness to checkpoint immunotherapy, is warranted.