Abstract P4-06-30: Adipose PD-L1 modulates checkpoint blockade immunotherapy efficacy in breast cancer

Programmed death-ligand 1 (PD-L1) and its receptor programmed cell death protein 1 (PD-1) play important roles in modulating antitumor immune response and are targeted by checkpoint blockade immunotherapy. While PD-L1 expression in both tumor and host cells is associated with antitumor therapeutic efficacy, the exact contribution of PD-L1 in various tissue and cell compartments to antitumor immune response remains to be elucidated. Here we show that PD-L1 expression is markedly elevated in human and mouse mature adipocytes compared to their preadipocyte counterparts. When co-cultured with mouse splenocytes in vitro, adipocytes prevent anti-PD-L1 antibody from activating CD8+T cells. Genetic ablation of adipose PD-L1 obliterates the inhibitory effect of adipocytes on anti-PD-L1 antibody. Conversely, enforced PD-L1 expression in preadipocytes confers the antibody-inhibitory activity. GW9662, a pharmacologic inhibitor of peroxisome proliferator-activated receptor γ (PPARγ) in adipogenesis, selectively reduces PD-L1 expression in mouse adipose tissue. The same PPARγ antagonist also enhances the antitumor efficacy of checkpoint blockade antibodies for treating multiple mammary tumors. Our findings provide a previously unappreciated approach to bolster anticancer immunotherapy efficacy and suggest a mechanism for the role of adipose tissue in breast cancer progression.

Citation Format: Wu B, Sun X, Gupta HB, Yuan B, Ge F, Li J, Hu Y, Curiel TJ, Li R. Adipose PD-L1 modulates checkpoint blockade immunotherapy efficacy in breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-06-30.

Rapamycin Prevents Surgery-Induced Immune Dysfunction in Patients with Bladder Cancer

The mechanistic target of rapamycin (mTOR) integrates environmental inputs to regulate cellular growth and metabolism in tumors. However, mTOR also regulates T-cell differentiation and activation, rendering applications of mTOR inhibitors toward treating cancer complex. Preclinical data support distinct biphasic effects of rapamycin, with higher doses directly suppressing tumor cell growth and lower doses enhancing T-cell immunity. To address the translational relevance of these findings, the effects of the mTOR complex 1 (mTORC1) inhibitor, rapamycin, on tumor and T cells were monitored in patients undergoing cystectomy for bladder cancer. MB49 syngeneic murine bladder cancer models were tested to gain mechanistic insights. Surgery-induced T-cell exhaustion in humans and mice and was associated with increased pulmonary metastasis and decreased PD-L1 antibody efficacy in mouse bladder cancer. At 3 mg orally daily, rapamycin concentrations were 2-fold higher in bladder tissues than in blood. Rapamycin significantly inhibited tumor mTORC1, shown by decreased rpS6 phosphorylation in treated versus control patients (P = 0.008). Rapamycin reduced surgery-induced T-cell exhaustion in patients, evidenced by a significant decrease in the prevalence of dysfunctional programmed death-1 (PD-1)-expressing T cells. Grade 3 to 4 adverse event rates were similar between groups, but rapamycin-treated patients had a higher rate of wound complications versus controls. In conclusion, surgery promoted bladder cancer metastasis and decreased the efficacy of postoperative bladder cancer immunotherapy. Low-dose (3 mg daily) oral rapamycin has favorable pharmacodynamic and immune modulating activity in surgical patients and has the potential to decrease surgery-induced immune dysfunction.

Oncogenic BRAFV600E Governs Regulatory T-cell Recruitment during Melanoma Tumorigenesis

Regulatory T cells (Treg) are critical mediators of immunosuppression in established tumors, although little is known about their role in restraining immunosurveillance during tumorigenesis. Here, we employ an inducible autochthonous model of melanoma to investigate the earliest Treg and CD8 effector T-cell responses during oncogene-driven tumorigenesis. Induction of oncogenic BRAFV600E and loss of Pten in melanocytes led to localized accumulation of FoxP3+ Tregs, but not CD8 T cells, within 1 week of detectable increases in melanocyte differentiation antigen expression. Melanoma tumorigenesis elicited early expansion of shared tumor/self-antigen-specific, thymically derived Tregs in draining lymph nodes, and induced their subsequent recruitment to sites of tumorigenesis in the skin. Lymph node egress of tumor-activated Tregs was required for their C-C chemokine receptor 4 (Ccr4)-dependent homing to nascent tumor sites. Notably, BRAFV600E signaling controlled expression of Ccr4-cognate chemokines and governed recruitment of Tregs to tumor-induced skin sites. BRAFV600E expression alone in melanocytes resulted in nevus formation and associated Treg recruitment, indicating that BRAFV600E signaling is sufficient to recruit Tregs. Treg depletion liberated immunosurveillance, evidenced by CD8 T-cell responses against the tumor/self-antigen gp100, which was concurrent with the formation of microscopic neoplasia. These studies establish a novel role for BRAFV600E as a tumor cell-intrinsic mediator of immune evasion and underscore the critical early role of Treg-mediated suppression during autochthonous tumorigenesis.Significance: This work provides new insights into the mechanisms by which oncogenic pathways impact immune regulation in the nascent tumor microenvironment. Cancer Res; 78(17); 5038-49. ©2018 AACR.

Adipose PD-L1 Modulates PD-1/PD-L1 Checkpoint Blockade Immunotherapy Efficacy in Breast Cancer

Programmed death-ligand 1 (PD-L1) and its receptor programmed cell death protein 1 (PD-1) modulate antitumor immunity and are major targets of checkpoint blockade immunotherapy. However, clinical trials of anti-PD-L1 and anti-PD-1 antibodies in breast cancer demonstrate only modest efficacy. Furthermore, specific PD-L1 contributions in various tissue and cell compartments to antitumor immunity remain incompletely elucidated. Here we show that PD-L1 expression is markedly elevated in mature adipocytes versus preadipocytes. Adipocyte PD-L1 prevents anti-PD-L1 antibody from activating important antitumor functions of CD8+ T cells in vitro. Adipocyte PD-L1 ablation obliterates, whereas forced preadipocyte PD-L1 expression confers, these inhibitory effects. Pharmacologic inhibition of adipogenesis selectively reduces PD-L1 expression in mouse adipose tissue and enhances the antitumor efficacy of anti-PD-L1 or anti-PD-1 antibodies in syngeneic mammary tumor models. Our findings provide a previously unappreciated approach to bolster anticancer immunotherapy efficacy and suggest a mechanism for the role of adipose tissue in breast cancer progression.

Tumor cell-intrinsic programmed death protein 1 expression and induction in human cancer cell lines

The programmed death protein 1 (PD-1) and ligand (PD-L1) axis inhibits T cell activation and reduces anti-tumor immunity. Most studies of the PD-1/PD-L1 axis test extrinsic, immune-dependent effects. However, tumor cell-intrinsic PD-L1 regulates immune-independent tumor mTOR signals, autophagy, and tumor initiating cell generation. Melanoma cell-intrinsic PD-1 regulates melanoma growth and mTOR. We tested PD-1 expression and induction in multiple human tumor cell lines. We detected PD-1 in human cell lines in vitro from ES2 ovarian cancer, VMM122 melanoma, and RT4 bladder cancer by flow cytometry, Western blot and RT-PCR. All lines were negative for the other PD-L1 receptor, CD80, by flow cytometry. Incubating lines with IFNα or IFNγ for 48 hours further augmented PD-1 expression as detected by flow, Western blot and RT-PCR. αPD-1 antibody (50 μg/ml) reduced proliferation of RT4 bladder cancer cells in vitro, demonstrating a direct PD-1 signal effect in these cells, and αPD-L1 similarly reduced in vitro proliferation. Interestingly, anti-PD-1 effects on reducing proliferation were similar: 41.5% reduction; p<0.0001. We used CRISPR/Cas9 to generate PD-L1KO RT4 cells. αPD-L1 did not reduce in vitro proliferation as expected, but unexpectedly, αPD-1 also had no anti-proliferative effect on PD-L1KO RT4 cells, suggesting a PD-L1/PD-1 interaction. In murine B16 melanoma, we generated PD-L1KO and PD-1KO cells using CRISPR/Cas9. Cell-intrinsic PD-L1 and PD-1 downregulate chemokine production. Among chemokines analyzed, PD-L1 suppressed CCL2 and CCL5, PD-1 suppressed CCL4 and CCL7, and both suppressed CCL3 and CXCL2. Understanding intrinsic PD-1 and PD-L1 effects on tumor cells can be exploited to improve cancer immunotherapy

Cell-intrinsic and spatially divergent tumor programmed death ligand 1 (PD-L1) signals modify local and systemic anti-tumor immunity through novel chemokine effects

PD-L1, expressed on many tumors, inhibits anti-tumor T cells by programmed death (PD)-1 engagement. Tumor PD-L1 predicts anti-PD-L1 treatment outcomes through incompletely understood mechanisms. We used naturally PD-L1+ murine B16 melanoma (ctrl) and made PD-L1KO B16 by CRISPR/Cas9. PD-L1KO B16 grew faster when ctrl B16 was on the opposite flank (trans). By contrast, ctrl B16 grew slower when trans to PD-L1KO B16. Anti-PD-L1 slowed ctrl but not PD-L1KO B16 tumors as expected. However, when PD-L1KO was trans to ctrl αPD-L1 now also slowed PD-L1KO growth. Anti-PD-L1 increased CD3+ T cell infiltration into ctrl and PD-L1KO tumors similarly in vivo, but increased natural killer (NK) cell numbers and functions (e.g., CD107a, IFN-g) in PD-L1KO tumors > ctrl. CD4+ and CD8+ T cells chemotaxed to PD-L1KO slightly > ctrl, but NK cells migrated 2-fold more to PD-L1KO vs ctrl. PD-L1KO tumors produced more CCL2 than ctrl in vitro and in vivo, and this CCL2 induced CCR2+ NK chemotaxis in vitro. Both NK cells and T cells were required for optimal trans responses to anti-PD-L1 treatment in vivo. In wild type mice, anti-CCL2 reduced growth of trans PD-L1KO tumors > ctrl, and reduced anti-PD-L1 efficacy against PD-L1KO> ctrl tumors. In CCR2KO mice, anti-PD-L1 efficacy was retained against trans ctrl B16, but abolished against PD-L1KO trans tumors. PD-L1 also regulated other chemokines recruiting receptor+ cells, with similar effects seen in MB49 bladder cancer and 4T1 breast cancer cells. Thus, tumor PD-L1 alters immune infiltrates and anti-PD-L1 efficacy through novel chemokine effects. Our models help understand anti-PD-L1 (and likely anti-PD-1) responses based on tumor PD-L1 expression and can define ways to improve immunotherapy for PD-L1 null tumors.

Surface and cytoplasmic PD-L1 regulate distinct cell-intrinsic signaling and functional outcomes

We reported that PD-L1 regulates tumor cell-intrinsic mTOR, autophagy and tumor initiating cell (TIC) generation. We found significant cytoplasmic PD-L1 in various mouse and human tumor cell lines by Western, flow cytometry and confocal. To assess subcellular localized PD-L1 effects, we CRISPR knocked out PD-L1 (KO) from mouse B16 melanoma cells and re-expressed PD-L1 only on surface (surfKI; Display vector) or cytoplasm (cytoKI; PcDNA vector). KO cells proliferated slowly vs ctrl in vitro, partially restored by surfKI and cytoKI. KO suppressed mTORC1 (p70S6K), which was reversed by cytoKI but not surfKI. Rapamycin (mTORC1 inhibitor) reduced surfKI and KO proliferation equally, but both > cytoKI (57% vs 88%, p<0.0001). AZD8055 (mTORC1/2 inhibitor) effects were similar. In WT mice surfKI grew faster (p <0.0001) than KO and cytoKI. SurfKI grew similar to total KI when injected into immunocompromised NSG mice, whereas cytoKIgrew slower than either (p<0.01). CytoKI and surfKI partially restored TIC numbers in vitro. We similarly generated PD-L1KO, cytoKI and surfKI cells in human ES2 ovarian cancer cells and found similar growth, rapamycin and AZD8055 effects thus far. Thus, surface and cytoplasmic PD-L1 contribute distinctly to tumor-intrinsic signals and pathogenesis. Current works tests PD-1/PD-L1 cooperation and PD-L1 cytoplasmic tail effects. Understanding specific cell-intrinsic PD-L1 signals affords novel biology insights and suggests new treatments and drug discovery.

Priming with percutaneous bacillus Calmette-Guerin (BCG) prior to intravesical BCG treatment safely improves BCG-specific response in patients with bladder cancer

Bacillus Calmette-Guérin (BCG) is the gold standard immunologic agent for patients with high-grade non-muscle invasive bladder cancer (NMIBC). Nevertheless, responses to BCG are heterogeneous and limited options exist when BCG therapy fails. Preclinical data in animal models of bladder cancer (BC) suggests that priming with percutaneous BCG vaccine prior to intravesical BCG instillation can enhance BCG-specific immunity and improve outcome. To study the safety, immunogenicity and preliminary efficacy of this approach, we administered percutaneous BCG 21 days prior to intravesical BCG instillation in “prime patients” with NMIBC (n=13) in a prospective single-arm clinical trial. Immune responses and clinical outcomes were monitored and compared to a contemporaneous cohort of “control patients” (n=9) receiving intravesical BCG without prior percutaneous BCG. Priming was well tolerated and no grade ≥3 adverse events were observed. Compared to control, prime patients had improvement in both local and systemic measures of BCG-specific immunity, scored by increased post-BCG urinary IL-8 and IL-17A and increased circulating CD4, CD8, and γδ T cell proliferation and effector function in response to BCG. Furthermore, ex vivo cytotoxicity of circulating NK and γδ T cells against RT4 BC was significantly increased in prime patient after BCG treatment and was mediated in part by NKG2D, suggesting an important role of innate effector immune mechanisms underlying BCG’s antitumor activity. Remarkably, no prime patients progressed whereas 3 out of 9 control patients progressed to muscle-invasive disease and underwent cystectomy. Thus, BCG priming safely enhances BCG-specific immunity and could improve outcome for patients with NMIBC.

Intratumoral CD56bright Natural Killer cells are associated with improved survival in bladder cancer

Antitumor immune responses are largely mediated by cytotoxic lymphocytes that recognize tumor-associated antigens presented in the context of a major histocompatibility complex class I molecule (MHC I). However, many tumors downregulate MHC I expression as a means of immune escape. Under these conditions, additional effector lymphocytes, such as natural killer cells (NK cells) which mediate non-MHC restricted cytotoxicity, provide antitumor defenses. Using flow cytometric analysis, we discovered that NK cells predominate among lymphocytes infiltrating human and carcinogen-induced mouse bladder cancer (BC). Using transcriptomics and clinical outcomes from the TCGA dataset we found that the presence of intratumoral NK cells is associated with increased survival after cystectomy, especially in low MHC class I expressing tumors. We validated this finding using a local BC cohort and determined that functional NK cells decline with increasing patient age. Using in vitro assays, we found that intratumoral NK cells from bladder tumors exhibit MHC class I dependent cytotoxicity against BC cells. Importantly, intratumoral CD56dim NK cells increase with higher pathologic stage and are less functional (cytotoxicity and cytokine secretion) than CD56bright counterparts. The presence of intratumoral CD56brightNK cells predicts improved patient survival independent of tumor stage. We conclude that intratumoral NK cells are functional and prognostically relevant in BC, but their presence and function is diminished with aging or tumor MHC class I. Intratumoral CD56bright NK cells are associated with better clinical outcomes whereas CD56dim NK cells are dysfunctional and associated with advanced BC.

Rapamycin prevents surgery-induced T cell exhaustion in patients with bladder cancer

The mechanistic target of rapamycin (mTOR) integrates environmental inputs to regulate cellular growth and metabolism in tumors. However, mTOR also regulates T cell differentiation and activation, rendering applications of mTOR inhibitors towards treating cancer complex. Recent preclinical data supports distinct biphasic effects of rapamycin with higher doses directly suppressing tumor cell growth and lower doses enhancing T cell immunity. We conducted a randomized controlled pre-surgical clinical trial to study the tumor and immune effects of low dose mTOR complex 1 inhibition with rapamycin for patients with invasive, non-metastatic bladder cancer. At 3 mg daily for four weeks, rapamycin significantly inhibited tumor mTORC1 (ribosomal protein S6 phosphorylation), and achieved high bladder tissue levels. Rapamycin also reduced surgery-mediated T cell exhaustion, evidenced by a significant decrease in the prevalence of dysfunctional programmed death-1 (PD-1) expressing circulating T cells without decreasing T cell proliferation or cytokine production. In mice challenged with MB49 orthotopic bladder tumors, a 2 cm surgical laparotomy reduces the efficacy of α-PD-L1 immunotherapy but efficacy can be partly restored with presurgical administration of rapamycin. These findings support favorable delivery, pharmacodynamic activity, and immune modulatory profile of low dose rapamycin in bladder cancer and identifies a novel role for mTOR inhibition in modulating surgery-induced immune dysfunction.

Cell-intrinsic PD-L1 and PD-1 signal effects in bladder cancer

PD-1/PD-L1 provides a mechanism of immune escape, the blockage of which has reinvigorated interest in the treatment of urothelial cancer. We recently reported on cell-intrinsic PD-L1 effects in melanoma and ovarian cancer, and considered that effects in bladder cancer cells could differ based on distinct mutational landscapes. Using CRISPER/Cas9 methodology, we knockout PD-L1 in the murine bladder cancer cell line MB49 and the human bladder caner cell line RT. We show here that cell-intrinsic MB49 and RT4 cells express PD-L1 and PD-1 that each mediate cell-intrinsic signals. PD-L1 knockout has little effect on cells proliferation in vitro, but significant difference could be found in tumor size when we used MB49 Ctrl or MB49 PD-L1KO cells to challenge C57B16 mice. αPD-L1 and αPD-1 antibodies reduced bladder cancer cell proliferation in vitro demonstrating direct signaling effects. Bladder cancer cell-intrinsic PD-L1 promoted mTORC1 and tumor initiating cell generation similar to melanoma and ovarian cancer cells. By contrast to melanoma and ovarian cancer cells, bladder cancer cell PD-L1 promoted autophagy and had little effect on in vivo immune-independent growth. Base one the functional role, PD-L1 knockout increased proliferation inhibition induced by Rapamycin in both mouse and human bladder cancer cells. Furthermore, we found intrinsic PD-L1 suppress cytokine production, including CXCL10. Corresponding with increased CXCL10 secretion, more CXCR3+ NK cells could be attracted by PD-L1KO cancer cells. Overall, our findings further illustrated the intrinsic role of PD-L1 in bladder cancer development and found PD-1 expression on human bladder cancer cells for the first time.

Programmed cell death ligand 1 (PD-L1) regulates tumor initiating cell (TIC) generation by controlling the stemness gene Oct4 through mTORC1

TIC mediate tumor formation, drug resistance and relapse. We reported that PD-L1 promotes tumor mTORC1, and TIC number and functions. Knocking down PD-L1 reduced expression of stemness genes Oct4 and Nanog and the mTORC1 signaling component Raptor in B16 melanoma and ID8agg ovarian cancer (OC) cells. To understand how PD-L1 controls stemness, we treated control and PD-L1 KO (KO) B16 cells with rapamycin (mTORC1 inhibitor), PI3K inhibitor wortmannin, Notch inhibitor Compound E, and c-Myc inhibitor JQ1. Only rapamycin affected control and KO CD133+CD44+CD24+ TIC differentially (50% reduced TIC in control versus 0% in KO, p=0.0075). We over-expressed Oct4 in B16 but failed to get clones, so over-expressed it in ID8agg PD-L1lo cells (KI) and found that TICs (CD44+CD24+) had improved proliferation and 2-fold more TIC than PD-L1lo cells (p=0.015, p=0.018). We sorted ID8agg, PD-L1lo and KI TIC and cultured them in stem cell medium. KI TICs formed four-fold bigger spheres than PD-L1lo TIC (p<0.0001), consistent with improved self-renewal. The KI spheres were also 1.5-fold larger than those of ID8agg (p=0.032). ID8agg, PD-L1lo and KI cells were then treated with rapamycin. KI TIC were resistant to rapamycin treatment (3 fold reduction in control, 2.9 fold in PD-L1lo versus none in KI), suggesting that PD-L1 drives stemness through mTORC1 driven Oct4 expression. Thus, PD-L1 regulates stemness genes through mTORC1.

A randomized control trial to establish the feasibility and safety of rapamycin treatment in an older human cohort: Immunological, physical performance, and cognitive effects

Inhibition of the mechanistic target of rapamycin (mTOR) pathway by rapamycin (RAPA), an FDA-approved immunosuppressive drug used as a clinical therapy to prevent solid organ allograft rejection, enhances longevity in mice. Importantly, RAPA was efficacious even when initiated in relatively old animals, suggesting that mTOR inhibition could potentially slow the progression of aging-associated pathologies in older humans (Harrison et al., 2009; Miller et al., 2011). However, the safety and tolerability of RAPA in older human subjects have not yet been demonstrated. Towards this end, we undertook a placebo-controlled pilot study in 25 generally healthy older adults (aged 70-95 years); subjects were randomized to receive either 1 mg RAPA or placebo daily. Although three subjects withdrew, 11 RAPA and 14 controls completed at least 8 weeks of treatment and were included in the analysis. We monitored for changes that would indicate detrimental effects of RAPA treatment on metabolism, including both standard clinical laboratory assays (CBC, CMP, HbA1c) and oral glucose tolerance tests (OGTTs). We also monitored parameters typically associated with aging that could potentially be modified by RAPA; these included cognitive function which was assessed by three different tools: Executive Interview-25 (EXIT25); Saint Louis University Mental Status Exam (SLUMS); and Texas Assessment of Processing Speed (TAPS). In addition, physical performance was measured by handgrip strength and 40-foot timed walks. Lastly, changes in general parameters of healthy immune aging, including serum pro-inflammatory cytokine levels and blood cell subsets, were assessed. Five subjects reported potential adverse side effects; in the RAPA group, these were limited to facial rash (1 subject), stomatitis (1 subject) and gastrointestinal issues (2 subjects) whereas placebo treated subjects only reported stomatitis (1 subject). Although no other adverse events were reported, statistically significant decrements in several erythrocyte parameters including hemoglobin (HgB) and hematocrit (Hct) as well as in red blood cell count (RBC), red blood cell distribution width (RDW), mean corpuscular volume (MCV), and mean corpuscular hemoglobin (MCH) were observed in the RAPA-treatment group. None of these changes manifested clinically significant effects during the short duration of this study. Similarly, no changes were noted in any other clinical laboratory, cognitive, physical performance, or self-perceived health status measure over the study period. Immune parameters were largely unchanged as well, possibly due to the advanced ages of the cohort (70-93 years; mean age 80.5). RAPA-associated increases in a myeloid cell subset and in T_REGS were detected, but changes in most other PBMC cell subsets were not statistically significant. Importantly, the OGTTs revealed no RAPA-induced change in blood glucose concentration, insulin secretion, and insulin sensitivity. Thus, based on the results of our pilot study, it appears that short-term RAPA treatment can be used safely in older persons who are otherwise healthy; a trial with a larger sample size and longer treatment duration is warranted.

Tyrosine phosphorylation regulates ERβ ubiquitination, protein turnover, and inhibition of breast cancer

Unlike estrogen receptor α (ERα) that predominantly promotes hormone-dependent breast tumor growth, ERβ exhibits antitumor effects in a variety of cancer types. We recently identified a phosphotyrosine residue in ERβ, but not ERα, that dictates ERβ transcriptional activity and antitumor function. We show here that this ER isotype-specific phosphotyrosine switch is important for regulating ERβ activity in cell proliferation, migration, and invasion. At the mechanistic level, phosphorylated ERβ, which recruits transcriptional coactivator p300, is in turn targeted by p300 for ubiquitination and proteasome-dependent protein turnover. Furthermore, ERβ-specific agonists such as S-equol enhance ERβ phosphorylation, suggesting a crosstalk between ligand- and posttranslational modification-dependent ERβ activation. Inhibition of xenograft tumor growth by S-equol is associated with reduced tumor Ki-67 expression and elevated ERβ tyrosine phosphorylation. Taken together, our data support the notion that phosphotyrosine-dependent ERβ signaling is an attractive target for anticancer treatment.

Tumor-extrinsic discoidin domain receptor 1 promotes mammary tumor growth by regulating adipose stromal interleukin 6 production in mice

Discoidin domain receptor 1 (DDR1) is a collagen receptor that mediates cell communication with the extracellular matrix (ECM). Aberrant expression and activity of DDR1 in tumor cells are known to promote tumor growth. Although elevated DDR1 levels in the stroma of breast tumors are associated with poor patient outcome, a causal role for tumor-extrinsic DDR1 in cancer promotion remains unclear. Here we report that murine mammary tumor cells transplanted to syngeneic recipient mice in which Ddr1 has been knocked out (KO) grow less robustly than in WT mice. We also found that the tumor-associated stroma in Ddr1-KO mice exhibits reduced collagen deposition compared with the WT controls, supporting a role for stromal DDR1 in ECM remodeling of the tumor microenvironment. Furthermore, the stromal-vascular fraction (SVF) of Ddr1 knockout adipose tissue, which contains committed adipose stem/progenitor cells and preadipocytes, was impaired in its ability to stimulate tumor cell migration and invasion. Cytokine array-based screening identified interleukin 6 (IL-6) as a cytokine secreted by the SVF in a DDR1-dependent manner. SVF-produced IL-6 is important for SVF-stimulated tumor cell invasion in vitro, and, using antibody-based neutralization, we show that tumor promotion by IL-6 in vivo requires DDR1. In conclusion, our work demonstrates a previously unrecognized function of DDR1 in promoting tumor growth.

Considerations for successful cancer immunotherapy in aged hosts

Improvements in understanding cancer immunopathogenesis have now led to unprecedented successes in immunotherapy to treat numerous cancers. Although aging is the most important risk factor for cancer, most pre-clinical cancer immunotherapy studies are undertaken in young hosts. This review covers age-related immune changes as they affect cancer immune surveillance, immunopathogenesis and immune therapy responses. Declining T cell function with age can impede efficacy of age-related cancer immunotherapies, but examples of successful approaches to breach this barrier have been reported. It is further recognized now that immune functions with age do not simply decline, but that they change in potentially detrimental ways. For example, detrimental immune cell populations can become predominant during aging (notably pro-inflammatory cells), the prevalence or function of suppressive cells can increase (notably myeloid derived suppressor cells), drugs can have age-specific effects on immune cells, and attributes of the aged microenvironment can impede or subvert immunity. Key advances in these and related areas will be reviewed as they pertain to cancer immunotherapy in the aged, and areas requiring additional study and some speculations on future research directions will be addressed. We prefer the term Age Related Immune Dysfunction (ARID) as most encompassing the totality of age-associated immune changes.

Abstract 5649: Cell-intrinsic PD-L1 directs tumor initiating cell fate and rapamycin and interferon-γ response

Tumor initiating cells (TIC) foster treatment resistance and tumor relapse. We show here that in mouse B16 (melanoma) and ID8agg (ovarian carcinoma), and human ovarian cancer ES2, PD-L1 knockdown (shRNA) reduced TIC numbers and functions. Data shown are from 2 PD-L1lo clones/cell type. Sorted, control CD44+CD133+CD24+ (B16), CD44+CD24+ (ID8agg) and ALDHhi (ES2) TIC formed 50-75% more and bigger spheres vs. PD-L1lo TIC in vitro, consistent with reduced TIC self-renewal in PD-L1lo. In vivo, PD-L1lo B16 and ID8agg TIC exhibited reduced tumorigenicity in wild type mice, consistent with poor TIC function, but immune effects could not be excluded. B16 and ES2 PD-L1lo TIC had significantly reduced tumorigenicity versus control TIC in immune deficient NSG mice consistent with cell-autonomous, immune-independent TIC promotion by PD-L1. In further confirmation, we found reduced serial transplantability of PD-L1lo B16 TIC in NSG mice. The canonical stemness genes nanog and pou5f1 (oct4) were significantly higher in control vs. PD-L1lo TIC for B16 and ID8agg. The canonical stemness gene SOX2 was significantly higher in control vs. PD-L1lo ES2 TIC. Altogether, these data validate effects in human cells, and are consistent with PD-L1 driving TIC through stemness gene control, although specific genes differed in distinct tumors (likely due to differing mutational landscapes). mTORC1 signaling linked to stemness (assessed by raptor) was lower but mTORC2 was unaffected (rictor) in PD-L1lo vs control TIC from all 3 tumors, suggesting mTORC1 control of PD-L1-mediated TIC generation. In support, the mTORC1 inhibitor rapamycin reduced control TIC significantly (>50% vs. untreated). Strikingly, rapamycin significantly increased PD-L1lo TIC in all 3 tumors, suggesting mTORC1 effects differ by tumor PD-L1 status. Interferon (IFN)-γ similarly reduced control TIC and augmented PD-L1lo TIC numbers, suggesting the novel concept that PD-L1 alters IFN-γ signals. PD-L1 sensitization of TIC to IFN-γ and rapamycin is the first example of a molecule enhancing TIC treatment response to our knowledge. We recently reported that αPD-L1 directly reduces B16 and ID8agg proliferation in vitro and in vivo (accession no. 27671674). Preliminary data now show that αPD-L1 (and αPD-1) directly reduce TIC proliferation, and these effects differ from non-TIC. We challenge the paradigm that tumor PD-L1 is primarily an immune escape molecule and that αPD-L1 works primarily to block T cell PD-1 interactions.

Citation Format: Harshita B. Gupta, Curtis A. Clark, Bin Yuan, Gangadhara Sareddy, Srilakshmi Pandeswara, Alvaro S. Padron, Vincent Hurez, Jose-Conejo Garcia, Ratna Vadlamudi, Rong Li, Tyler J. Curiel. Cell-intrinsic PD-L1 directs tumor initiating cell fate and rapamycin and interferon-γ response [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 5649. doi:10.1158/1538-7445.AM2017-5649

Abstract 1608: CD122-selective IL-2/anti-IL-2 complexes reduce regulatory T cell function and promote CD8+ T cell polyfunctionality for durable ovarian cancer immunotherapy

The IL-2 receptor (IL-2R) is an attractive target for cancer immunotherapy as it controls both immune-suppressive regulatory T cells (Tregs) and anti-tumor T cells. We tested depleting Tregs as immunotherapy using anti-CD25 (high-affinity IL-2R subunit) antibodies (αCD25) in ID8agg mouse ovarian cancer (OC). αCD25 reduced ascites and Treg numbers but failed to reduce tumor burden, possibly because it depleted newly activated anti-tumor T cells in tumor-draining lymph nodes. Thus, αCD25 could be novel malignant ascites palliation, but has limited stand-alone efficacy. We then tested IL-2/anti-IL-2 complexes (IL-2c) that selectively stimulate medium-affinity (CD122/CD132) IL-2R thought to expand anti-tumor T cells preferentially, but with little Treg effects. In contrast to several single agents we tested that failed to treat ID8agg (e.g., αCD25, αPD-L1, IL-2 fusion toxin denileukin diftitox), IL-2c alone durably reduced ID8agg tumor burden despite lowering the tumor microenvironmental CD8+/Treg ratio. Thus, we hypothesized that IL-2c improved CD8+ function, reduced Treg function, or both. IL-2c increased polyfunctional IFN-γ+TNF-α+ anti-tumor T cells as expected, an effect that persists weeks after drug clearance. IL-2c also increased anti-tumor T cell CD25 expression that increased IL-2 sensitivity and STAT5 phosphorylation, a likely mechanism for increased polyfunctionality. Unexpectedly, IL-2c reduced the Treg functional mediators CD25, TIGIT and granzyme B, and reduced Treg suppressive function. Thus, favorable Treg modifications are a novel IL-2c mechanism of action. Adding αCD25 to IL-2c to deplete Tregs further unexpectedly worsened IL-2c efficacy in ID8agg and reduced effector memory T cells and polyfunctional T cells in the tumor microenvironment, suggesting a previously unappreciated role for CD25 in IL-2c therapy. Similar data were seen in B16 melanoma, suggesting αCD25 reduction of IL-2c efficacy is not tumor or compartment-specific (ID8agg is peritoneal and B16 is subcutaneous). αPD-L1, an ineffective monotherapy in ID8agg, combined with IL-2c to promote complete responses, suggesting potential for potent, novel combinatorial approaches. Our data suggest that antagonizing high affinity IL-2R (such as to deplete Tregs with αCD25) has limited cancer immunotherapy utility without more specific Treg targeting. In contrast, stimulating medium-affinity IL-2R with CD122-selective IL-2c has great translational promise by simultaneously improving beneficial anti-tumor T cells and reducing detrimental Treg function.

Citation Format: Justin M. Drerup, Sri Lakshmi Pandeswara, Aijie Liu, Curtis A. Clark, Alvaro S. Padron, Wanjiao Chen, Vincent Hurez, Tyler J. Curiel. CD122-selective IL-2/anti-IL-2 complexes reduce regulatory T cell function and promote CD8+ T cell polyfunctionality for durable ovarian cancer immunotherapy [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 1608. doi:10.1158/1538-7445.AM2017-1608

Attenuation of RNA polymerase II pausing mitigates BRCA1-associated R-loop accumulation and tumorigenesis

Most BRCA1-associated breast tumours are basal-like yet originate from luminal progenitors. BRCA1 is best known for its functions in double-strand break repair and resolution of DNA replication stress. However, it is unclear whether loss of these ubiquitously important functions fully explains the cell lineage-specific tumorigenesis. In vitro studies implicate BRCA1 in elimination of R-loops, DNA-RNA hybrid structures involved in transcription and genetic instability. Here we show that R-loops accumulate preferentially in breast luminal epithelial cells, not in basal epithelial or stromal cells, of BRCA1 mutation carriers. Furthermore, R-loops are enriched at the 5' end of those genes with promoter-proximal RNA polymerase II (Pol II) pausing. Genetic ablation of Cobra1, which encodes a Pol II-pausing and BRCA1-binding protein, ameliorates R-loop accumulation and reduces tumorigenesis in Brca1-knockout mouse mammary epithelium. Our studies show that Pol II pausing is an important contributor to BRCA1-associated R-loop accumulation and breast cancer development.

Tumor cell-intrinsic CD274/PD-L1: A novel metabolic balancing act with clinical potential

Tumor expression of the immune co-signaling molecule CD274/PD-L1 was originally described as impeding antitumor immunity by direct engagement of its receptor, PDCD1/PD-1, on antitumor T cells. Melanoma-intrinsic PDCD1 was recently shown to promote tumor growth and MTOR signals in cooperation with tumor CD274, and sarcoma-intrinsic CD274 signaling promotes glucose metabolism to impede antitumor immunity. Our recent report shows that tumor cell-intrinsic CD274 promotes MTORC1 signaling in mouse melanoma and mouse and human ovarian cancer, inhibits autophagy and sensitizes some tumors to clinically available pharmacological autophagy inhibitors and confers resistance to MTOR inhibitors. Tumor CD274 could be a biomarker of autophagy or MTOR inhibitor response in selected tumors, and these inhibitors could improve anti-CD274 or anti-PDCD1 cancer immunotherapy. As we found that distinct tumor types exhibit this CD274-driven phenotype, it could be widely applicable.

Myeloid Cells That Impair Immunotherapy Are Restored in Melanomas with Acquired Resistance to BRAF Inhibitors

Acquired resistance to BRAFV600E inhibitors (BRAFi) in melanoma remains a common clinical obstacle, as is the case for any targeted drug therapy that can be developed given the plastic nature of cancers. Although there has been significant focus on the cancer cell-intrinsic properties of BRAFi resistance, the impact of BRAFi resistance on host immunity has not been explored. Here we provide preclinical evidence that resistance to BRAFi in an autochthonous mouse model of melanoma is associated with restoration of myeloid-derived suppressor cells (MDSC) in the tumor microenvironment, initially reduced by BRAFi treatment. In contrast to restoration of MDSCs, levels of T regulatory cells remained reduced in BRAFi-resistant tumors. Accordingly, tumor gene expression signatures specific for myeloid cell chemotaxis and homeostasis reappeared in BRAFi-resistant tumors. Notably, MDSC restoration relied upon MAPK pathway reactivation and downstream production of the myeloid attractant CCL2 in BRAFi-resistant melanoma cells. Strikingly, although combination checkpoint blockade (anti-CTLA-4 + anti-PD-1) was ineffective against BRAFi-resistant melanomas, the addition of MDSC depletion/blockade (anti-Gr-1 + CCR2 antagonist) prevented outgrowth of BRAFi-resistant tumors. Our results illustrate how extrinsic pathways of immunosuppression elaborated by melanoma cells dominate the tumor microenvironment and highlight the need to target extrinsic as well as intrinsic mechanisms of drug resistance. Cancer Res; 77(7); 1599-610. ©2017 AACR.

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-L1^lo’) 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.

Considerations for successful cancer immunotherapy in aged hosts

Immunotherapy is now experiencing unprecedented successes in treating various cancers based on new understandings of cancer immunopathogenesis. Nonetheless, although ageing is the biggest risk factor for cancer, the majority of cancer immunotherapy preclinical studies are conducted in young hosts. This review will explore age-related changes in immunity as they relate to cancer immune surveillance, immunopathogenesis and responses to immunotherapy. Although it is recognized that declining T cell function with age poses a great challenge to developing effective age-related cancer immunotherapies, examples of successful approaches to overcome this hurdle have been developed. Further, it is now recognized that immune functions do not simply decline with age, but rather change in ways than can be detrimental. For example, with age, specific immune cell populations with detrimental functions can become predominant (such as cells producing proinflammatory cytokines), suppressive cells can become more numerous or more suppressive (such as myeloid-derived suppressor cells), drugs can affect aged immune cells distinctly and the aged microenvironment is becoming recognized as a significant barrier to address. Key developments in these and other areas will be surveyed as they relate to cancer immunotherapy in aged hosts, and areas in need of more study will be assessed with some speculations for the future. We propose the term 'age-related immune dysfunction' (ARID) as best representative of age-associated changes in immunity.