NK Cells in Cancer: Mechanisms of Dysfunction and Therapeutic Potential

Natural killer cells (NK) are innate lymphocytes endowed with the ability to recognize and kill cancer cells. Consequently, adoptive transfer of autologous or allogeneic NK cells represents a novel opportunity in cancer treatment that is currently under clinical investigation. However, cancer renders NK cells dysfunctional, thus restraining the efficacy of cell therapies. Importantly, extensive effort has been employed to investigate the mechanisms that restrain NK cell anti-tumor function, and the results have offered forthcoming solutions to improve the efficiency of NK cell-based therapies. The present review will introduce the origin and features of NK cells, summarize the mechanisms of action and causes of dysfunction of NK cells in cancer, and frame NK cells in the tumoral microenvironment and in the context of immunotherapies. Finally, we will discuss therapeutic potential and current limitations of NK cell adoptive transfer in tumors.

Macrophages and bone metastasis

In the prostate bone metastasis microenvironment, macrophages activate a cascade that involves Activin A, the extracellular matrix, and SRC kinase and drives resistance to anti-androgen therapy. These findings (Li et al., 2023. J. Exp. Med.https://doi.org/10.1084/jem.20221007) have broad implications, including metastasis diversity in different tissue milieus and the interplay between hormones and immunity.

Multimodal single-cell profiling of intrahepatic cholangiocarcinoma defines hyperactivated Tregs as a potential therapeutic target

BACKGROUND & AIMS

The landscape and function of the immune infiltrate of intrahepatic cholangiocarcinoma (iCCA), a rare, yet aggressive tumor of the biliary tract, remains poorly characterized, limiting development of successful immunotherapies. Herein, we aimed to define the molecular characteristics of tumor-infiltrating leukocytes with a special focus on CD4+ regulatory T cells (Tregs).

METHODS

We used high-dimensional single-cell technologies to characterize the T-cell and myeloid compartments of iCCA tissues, comparing these with their tumor-free peritumoral and circulating counterparts. We further used genomics and cellular assays to define the iCCA-specific role of a novel transcription factor, mesenchyme homeobox 1 (MEOX1), in Treg biology.

RESULTS

We found poor infiltration of putative tumor-specific CD39+ CD8+ T cells accompanied by abundant infiltration of hyperactivated CD4+ Tregs. Single-cell RNA-sequencing identified an altered network of transcription factors in iCCA-infiltrating compared to peritumoral T cells, suggesting reduced effector functions by tumor-infiltrating CD8+ T cells and enhanced immunosuppression by CD4+ Tregs. Specifically, we found that expression of MEOX1 was highly enriched in tumor-infiltrating Tregs, and demonstrated that MEOX1 overexpression is sufficient to reprogram circulating Tregs to acquire the transcriptional and epigenetic landscape of tumor-infiltrating Tregs. Accordingly, enrichment of the MEOX1-dependent gene program in Tregs was strongly associated with poor prognosis in a large cohort of patients with iCCA.

CONCLUSIONS

We observed abundant infiltration of hyperactivated CD4+ Tregs in iCCA tumors along with reduced CD8+ T-cell effector functions. Interfering with hyperactivated Tregs should be explored as an approach to enhance antitumor immunity in iCCA.

LAY SUMMARY

Immune cells have the potential to slow or halt the progression of tumors. However, some tumors, such as intrahepatic cholangiocarcinoma, are associated with very limited immune responses (and infiltration of cancer-targeting immune cells). Herein, we show that a specific population of regulatory T cells (a type of immune cell that actually suppresses the immune response) are hyperactivated in intrahepatic cholangiocarcinoma. Targeting these cells could enable cancer-targeting immune cells to act more effectively and should be looked at as a potential therapeutic approach to this aggressive cancer type.

Lipid-loaded macrophages as new therapeutic target in cancer

Macrophages are main players of the innate immune system. They show great heterogeneity and play diverse functions that include support to development, sustenance of tissue homeostasis and defense against infections. Dysfunctional macrophages have been described in multiple pathologies including cancer. Indeed tumor-associated macrophages (TAMs) are abundant in most tumors and sustain cancer growth, promote invasion and mediate immune evasion. Importantly, lipid metabolism influences macrophage activation and lipid accumulation confers pathogenic features on macrophages. Notably, a subset of lipid-loaded macrophages has been recently identified in many tumor types. Lipid-loaded TAMs support tumor growth and progression and exert immune-suppressive activities. In this review, we describe the role of lipid metabolism in macrophage activation in physiology and pathology and we discuss the impact of lipid accumulation in macrophages in the context of cancer.

Lipid-loaded tumor-associated macrophages sustain tumor growth and invasiveness in prostate cancer

Tumor-associated macrophages (TAMs) are correlated with the progression of prostatic adenocarcinoma (PCa). The mechanistic basis of this correlation and therapeutic strategies to target TAMs in PCa remain poorly defined. Here, single-cell RNA sequencing was used to profile the transcriptional landscape of TAMs in human PCa, leading to identification of a subset of macrophages characterized by dysregulation in transcriptional pathways associated with lipid metabolism. This subset of TAMs correlates positively with PCa progression and shorter disease-free survival and is characterized by an accumulation of lipids that is dependent on Marco. Mechanistically, cancer cell–derived IL-1β enhances Marco expression on macrophages, and reciprocally, cancer cell migration is promoted by CCL6 released by lipid-loaded TAMs. Moreover, administration of a high-fat diet to tumor-bearing mice raises the abundance of lipid-loaded TAMs. Finally, targeting lipid accumulation by Marco blockade hinders tumor growth and invasiveness and improves the efficacy of chemotherapy in models of PCa, pointing to combinatorial strategies that may influence patient outcomes.

Neutrophil diversity and plasticity in tumour progression and therapy

Neutrophils play a key role in defence against infection and in the activation and regulation of innate and adaptive immunity. In cancer, tumour-associated neutrophils (TANs) have emerged as an important component of the tumour microenvironment. Here, they can exert dual functions. TANs can be part of tumour-promoting inflammation by driving angiogenesis, extracellular matrix remodelling, metastasis and immunosuppression. Conversely, neutrophils can also mediate antitumour responses by direct killing of tumour cells and by participating in cellular networks that mediate antitumour resistance. Neutrophil diversity and plasticity underlie the dual potential of TANs in the tumour microenvironment. Myeloid checkpoints as well as the tumour and tissue contexture shape neutrophil function in response to conventional therapies and immunotherapy. We surmise that neutrophils can provide tools to tailor current immunotherapy strategies and pave the way to myeloid cell-centred therapeutic strategies, which would be complementary to current approaches.

Re-education of Tumor-Associated Macrophages by CXCR2 Blockade Drives Senescence and Tumor Inhibition in Advanced Prostate Cancer

Tumor-associated macrophages (TAMs) represent a major component of the tumor microenvironment supporting tumorigenesis. TAMs re-education has been proposed as a strategy to promote tumor inhibition. However, whether this approach may work in prostate cancer is unknown. Here we find that Pten-null prostate tumors are strongly infiltrated by TAMs expressing C-X-C chemokine receptor type 2 (CXCR2), and activation of this receptor through CXCL2 polarizes macrophages toward an anti-inflammatory phenotype. Notably, pharmacological blockade of CXCR2 receptor by a selective antagonist promoted the re-education of TAMs toward a pro-inflammatory phenotype. Strikingly, CXCR2 knockout monocytes infused in Pten^pc−/−; Trp53^pc−/− mice differentiated in tumor necrosis factor alpha (TNF-α)-releasing pro-inflammatory macrophages, leading to senescence and tumor inhibition. Mechanistically, PTEN-deficient tumor cells are vulnerable to TNF-α-induced senescence, because of an increase of TNFR1. Our results identify TAMs as targets in prostate cancer and describe a therapeutic strategy based on CXCR2 blockade to harness anti-tumorigenic potential of macrophages against this disease.

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CXCR2 blockade drives re-education of tumor-associated macrophages (TAMs)

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Infusion of CXCR2-KO monocytes in tumor-bearing mice blocks tumor progression

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PTEN deletion sensitizes tumor cells to TNF-α-induced senescence and growth arrest

High-dimensional single cell-based immune profiling of the tumor immune microenvironment in prostate cancer

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Background: Genetic lesions that drive prostate cancer (PCa) development are able to modify the immune response and tumor infiltrating immune subsets, resulting in tumor progression. We investigated the profile of the immune microenvironment in PCa by high dimensional single cell analysis. Methods: We conducted an immune profiling study based on integrated RNA single cell sequencing and multiparametric flow cytometry in order to dissect the immune landscape of PCa. CD45+ immune cells infiltrating tumoral and adjacent non tumoral tissues were isolated from patients with PCa who underwent software assisted fusion biopsy, based on MRI, and/or radical prostatectomy, and analyzed by single cell sequencing. The primary endpoint was to evaluate the effectiveness of single cell RNA sequencing on CD45+ cell sorted from tumoral and adjacent non-tumoral tissues. Secondary endpoint was the identification of tumor-driven immune changes in prostatic lesions. Results: The cohort consisted of 3 patients who underwent radical prostatectomy (RP) and 45 patients with positive prostate biopsy; the negative control was checked by pathological assessment. In patients who underwent RP the gene expression analysis identified a modulation in the abundance of several immune subsets infiltrating the tumoral tissue, when compared with the non tumoral, evident for Tumor associated macrophages (TAMs), Natural Killer cells (NK) and T regulatory cells. We then implemented a 22 parameters flow cytometry panel that we tested on fresh prostatic tissue and peripheral blood from positive PCa biopsies. We identified a subset of tumor infiltrating macrophages showing an altered gene expression profile when compared with macrophages infiltrating the non-tumoral tissue. Importantly we derived a genetic signature from this subset of tumoral TAMs that resulted to be associated with cancer progression. Conclusions: Our findings support the effectiveness of single cell RNA sequencing in the dissection of the immune landscape in PCa and identified immune changes in patients when comparing neoplastic tissue with non tumoral areas. Such data may be useful for understanding the role of immune system in PCa carcinogenesis.

Publisher Correction: Compartmentalized activities of the pyruvate dehydrogenase complex sustain lipogenesis in prostate cancer

In the HTML version of this article initially published, the name of author Diletta Di Mitri was miscoded in the XML such that Di was included as part of the given name instead of the family name. The error has been corrected in the HTML version of the article.

IL-23 secreted by myeloid cells drives castration-resistant prostate cancer

Patients with prostate cancer frequently show resistance to androgen-deprivation therapy, a condition known as castration-resistant prostate cancer (CRPC). Acquiring a better understanding of the mechanisms that control the development of CRPC remains an unmet clinical need. The well-established dependency of cancer cells on the tumour microenvironment indicates that the microenvironment might control the emergence of CRPC. Here we identify IL-23 produced by myeloid-derived suppressor cells (MDSCs) as a driver of CRPC in mice and patients with CRPC. Mechanistically, IL-23 secreted by MDSCs can activate the androgen receptor pathway in prostate tumour cells, promoting cell survival and proliferation in androgen-deprived conditions. Intra-tumour MDSC infiltration and IL-23 concentration are increased in blood and tumour samples from patients with CRPC. Antibody-mediated inactivation of IL-23 restored sensitivity to androgen-deprivation therapy in mice. Taken together, these results reveal that MDSCs promote CRPC by acting in a non-cell autonomous manner. Treatments that block IL-23 can oppose MDSC-mediated resistance to castration in prostate cancer and synergize with standard therapies.

Compartmentalized activities of the pyruvate dehydrogenase complex sustain lipogenesis in prostate cancer

The mechanisms by which mitochondrial metabolism supports cancer anabolism are still unclear. Here, we unexpectedly find that genetic and pharmacological inactivation of Pyruvate Dehydrogenase A1 (PDHA1), a subunit of pyruvate dehydrogenase complex (PDC) inhibits prostate cancer development in different mouse and human xenograft tumour models by affecting lipid biosynthesis. Mechanistically, we show that in prostate cancer, PDC localizes in both mitochondria and nucleus. While nuclear PDC controls the expression of Sterol regulatory element-binding transcription factor (SREBF) target genes by mediating histone acetylation, mitochondrial PDC provides cytosolic citrate for lipid synthesis in a coordinated effort to sustain anabolism. In line with these evidence, we find that PDHA1 and the PDC activator, Pyruvate dehydrogenase phosphatase 1 (PDP1), are frequently amplified and overexpressed at both gene and protein level in prostate tumours. Taken together, these findings demonstrate that both mitochondrial and nuclear PDC sustain prostate tumourigenesis by controlling lipid biosynthesis thereby pointing at this complex as a novel target for cancer therapy.

Non-Cell-Autonomous Regulation of Cellular Senescence in Cancer

Cellular senescence is a permanent growth arrest that is broadly recognized to act as a barrier against tumorigenesis. Senescence is predominant in premalignant tumors, and senescence escape is thought to be required for tumor progression. Importantly, evidences indicate that cell-autonomous mechanisms, such as genetic alterations or therapeutic interventions targeting specific genetic pathways, can affect the senescence response in cancer. Nevertheless, new findings have emerged in the last few years that indicate a fundamental role for the tumor microenvironment in the regulation of cellular senescence. Indeed, cytokines belonging to the senescent secretome, as well as tumor-infiltrating immune subsets, have been described to modulate the senescence response in tumors. Such evidence demonstrates that senescence initiation also relies on non-cell-autonomous mechanisms, which are discussed in the present review.

Abstract 2346: Targeting the tumor immune response for pro-senescence therapy in prostate cancer

Cellular senescence is a stable growth arrest that constrains cell cycle progression in case proliferation becomes aberrant, thus limiting tumorigenesis. Oncogenic mutations and loss of tumor suppressor genes that cause uncontrolled cell-cycle progression are required events in tumor development. Nevertheless, many of these genetic alterations retain an intrinsic tumor-suppressive potential that gives rise to oncogene-induced senescence and tumor suppressor loss-induced senescence. Interestingly, many evidences support the idea that a strong interplay occurs between senescence, cancer cells, and tumor infiltrating immune populations, thus opening at the possibility to tune such interplay for cancer treatment. Indeed, tumor infiltrating T helper 1 cells can drive senescence in cancers in a cytokine-induced manner, by secreting IFNγ and TNFα in the tumor microenvironment. In addition, we recently described a model where Pten loss induced senescence is hindered in prostate tumor by non-cell-autonomous mechanisms. Our study support a model where tumor-infiltrating CD11b+Gr-1+ myeloid cells paracrinally triggers tumor senescence evasion in the prostate of Pten null mice, eventually promoting tumor progression. These findings we’ll be discussed. Interestingly, we will present new evidences from our lab indicating that M1 macrophages are polarized to the M2 phenotype in both Pten pc-/- and that treatments that interfere with the M1-M2 polarization and switch the skewing to the M1 polarization profile can induce senescence in Pten; Trp53pc-/- invasive prostate cancer tumours thereby arresting tumour progression. These findings open at the possibility that M1 directly control senescence in tumor cells. Finally, we have identified a gene expression signature that distinguishes myeloid infiltration in tumors and can be used as a predictive marker for tumor progression in prostate cancer patients. These evidences we’ll be also discussed.

Citation Format: Diletta Di Mitri, JingJing Chen, Andrea Alimonti. Targeting the tumor immune response for pro-senescence therapy in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2346. doi:10.1158/1538-7445.AM2015-2346

The p38 mitogen-activated protein kinase cascade modulates T helper type 17 differentiation and functionality in multiple sclerosis

The p38 mitogen-activated protein kinase cascade is required for the induction of a T helper type 17 (Th17) -mediated autoimmune response, which underlies the development and progression of several autoimmune diseases, such as experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis (MS). However, the contribution of p38 phosphorylation to human Th cell differentiation has not been clarified. Here we demonstrate that the p38 signalling pathway is implicated in the generation of Th17 lymphocytes from human CD4(+)  CD27(+)  CD45RA(+) naive T cells, both in healthy donors and in patients affected by the relapsing-remitting form of MS. Our data also indicate that p38 activation is essential for interleukin-17 release from central memory lymphocytes and committed Th17 cell clones. Furthermore, CD4(+) T cells isolated from individuals with relapsing-remitting MS display an altered responsiveness of the p38 cascade, resulting in increased p38 phosphorylation upon stimulation. These findings suggest that the p38 signalling pathway, by modulating the Th17 differentiation and response, is involved in the pathogenesis of MS, and open new perspectives for the use of p38 inhibitors in the treatment of Th17-mediated autoimmune diseases.

Tumor-infiltrating myeloid cells drive senescence evasion and chemoresistance in tumors

The present study supports a model in which Pten loss-induced senescence is hindered in prostate tumor cells by non cell-autonomous mechanisms. Indeed, paracrine signaling by tumor-infiltrating CD11b⁺Gr-1⁺ myeloid cells triggers senescence evasion in prostate lesions of Pten-null mice, eventually promoting tumor progression.

Molecular Pathways: Targeting Tumor-Infiltrating Myeloid-Derived Suppressor Cells for Cancer Therapy

Tumor-infiltrating myeloid-derived suppressor cells (MDSC) are a heterogeneous and immunosuppressive cell subset that blocks the proliferation and the activity of both T and natural killer (NK) cells and promotes tumor vasculogenesis and progression. Recent evidences demonstrate that the recruitment of MDSCs in tumors also blocks senescence induced by chemotherapy promoting chemoresistance. Hence, the need of novel therapeutic approaches that can efficiently target MDSC recruitment and function in cancer. Among them, novel combinatorial treatments of chemotherapy and immunotherapy or treatments that induce depletion of MDSCs in peripheral sites should be taken in consideration.

T regulatory cells are markers of disease activity in multiple sclerosis patients

FoxP3⁺ Treg cells are believed to play a role in the occurrence of autoimmunity and in the determination of clinical recurrences. Contradictory reports are, however, available describing frequency and function of Treg cells during autoimmune diseases. We examined, by both polychromatic flow cytometry, and real-time RT-PCR, several Treg markers in peripheral blood mononuclear cells from patients with multiple sclerosis (MS), an autoimmune disease affecting the central nervous system. We found that Tregs, as defined by CD25, CD39, FoxP3, CTLA4, and GITR expression, were significantly decreased in stable MS patients as compared to healthy donors, but, surprisingly, restored to normal levels during an acute clinical attack. We conclude that Treg cells are not involved in causing clinical relapses, but rather react to inflammation in the attempt to restore homeostasis.

Cytomegalovirus infection induces the accumulation of short-lived, multifunctional CD4+CD45RA+CD27+ T cells: the potential involvement of interleukin-7 in this process

The relative roles that ageing and lifelong cytomegalovirus (CMV) infection have in shaping naive and memory CD4+ T-cell repertoires in healthy older people is unclear. Using multiple linear regression analysis we found that age itself is a stronger predictor than CMV seropositivity for the decrease in CD45RA+ CD27+ CD4+ T cells over time. In contrast, the increase in CD45RA⁻ CD27⁻ and CD45RA+ CD27⁻ CD4+ T cells is almost exclusively the result of CMV seropositivity, with age alone having no significant effect. Furthermore, the majority of the CD45RA⁻ CD27⁻ and CD45RA+ CD27⁻ CD4+ T cells in CMV-seropositive donors are specific for this virus. CD45RA+ CD27⁻ CD4+ T cells have significantly reduced CD28, interleukin-7 receptor α (IL-7Rα) and Bcl-2 expression, Akt (ser473) phosphorylation and reduced ability to survive after T-cell receptor activation compared with the other T-cell subsets in the same donors. Despite this, the CD45RA+ CD27⁻ subset is as multifunctional as the CD45RA⁻ D27+ and CD45RA⁻ CD27⁻ CD4+ T-cell subsets, indicating that they are not an exhausted population. In addition, CD45RA+ CD27⁻ CD4+ T cells have cytotoxic potential as they express high levels of granzyme B and perforin. CD4+ memory T cells re-expressing CD45RA can be generated from the CD45RA⁻ CD27+ population by the addition of IL-7 and during this process these cells down-regulated expression of IL-7R and Bcl-2 and so resemble their counterparts in vivo. Finally we showed that the proportion of CD45RA+ CD27⁻ CD4+ T cells of multiple specificities was significantly higher in the bone marrow than the blood of the same individuals, suggesting that this may be a site where these cells are generated.

Expression of ectonucleotidase CD39 by Foxp3+ Treg cells: hydrolysis of extracellular ATP and immune suppression

In the immune system, extracellular ATP functions as a "natural adjuvant" that exhibits multiple proinflammatory effects. It is released by damaged cells as an indicator of trauma and cell death but can be inactivated by CD39 (nucleoside triphosphate diphosphohydrolase-1 [NTPDase 1]), an ectoenzyme that degrades ATP to AMP. Here, we show that CD39 is expressed primarily by immune-suppressive Foxp3(+) regulatory T (Treg) cells. In mice, the enzyme is present on virtually all CD4(+)CD25(+) cells. CD39 expression is driven by the Treg-specific transcription factor Foxp3 and its catalytic activity is strongly enhanced by T-cell receptor (TCR) ligation. Activated Treg cells are therefore able to abrogate ATP-related effects such as P2 receptor-mediated cell toxicity and ATP-driven maturation of dendritic cells. Also, human Treg cells express CD39. In contrast to mice, CD39 expression in man is restricted to a subset of Foxp3(+) regulatory effector/memory-like T (T(REM)) cells. Notably, patients with the remitting/relapsing form of multiple sclerosis (MS) have strikingly reduced numbers of CD39(+) Treg cells in the blood. Thus, in humans CD39 is a marker of a Treg subset likely involved in the control of the inflammatory autoimmune disease.