Butyrophilins: Dynamic Regulators of Protective T Cell Immunity in Cancer.

The efficacy of current immunotherapies remains limited in many solid epithelial malignancies. Recent investigations into the biology of butyrophilin (BTN) and butyrophilin-like (BTNL) molecules, however, suggest these molecules are potent immunosuppressors of antigen-specific protective T cell activity in tumor beds. BTN and BTNL molecules also associate with each other dynamically on cellular surfaces in specific contexts, which modulates their biology. At least in the case of BTN3A1, this dynamism drives the immunosuppression of αß T cells or the activation of Vγ9Vδ2 T cells. Clearly, there is much to learn regarding the biology of BTN and BTNL molecules in the context of cancer, where they may represent intriguing immunotherapeutic targets that could potentially synergize with the current class of immune modulators in cancer. Here, we discuss our current understanding of BTN and BTNL biology, with a particular focus on BTN3A1, and potential therapeutic implications for cancer.

Olfactory Receptor OR2H1 Is an Effective Target for CAR T Cells in Human Epithelial Tumors.

Although chimeric antigen receptor (CAR)-expressing T cells have proven success in hematologic malignancies, their effectiveness in solid tumors has been largely unsuccessful thus far. We found that some olfactory receptors are expressed in a variety of solid tumors of different histologic subtypes, with a limited pattern of expression in normal tissues. Quantification of OR2H1 expression by qRT-PCR and Western blot analysis of 17 normal tissues, 82 ovarian cancers of various histologies, eight non-small cell lung cancers (NSCLCs), and 17 breast cancers demonstrated widespread OR2H1 expression in solid epithelial tumors with expression in normal human tissues limited to the testis. CAR T cells recognizing the extracellular domain of the olfactory receptor OR2H1 were generated with a targeting motif identified through the screening of a phage display library and demonstrated OR2H1-specific cytotoxic killing in vitro and in vivo, using tumor cells with spontaneous expression of variable OR2H1 levels. Importantly, recombinant OR2H1 IgG generated with the VH/VL sequences of the CAR construct specifically detected OR2H1 protein signal in 60 human lung cancers, 40 ovarian carcinomas, and 73 cholangiocarcinomas, at positivity rates comparable with mRNA expression and without OR2H1 staining in 58 normal tissues. CRISPR/Cas9-mediated ablation of OR2H1 confirmed targeting specificity of the CAR and the tumor-promoting role of OR2H1 in glucose metabolism. Therefore, T cells redirected against OR2H1-expressing tumor cells represent a promising therapy against a broad range of epithelial cancers, likely with an admissible toxicity profile.

Ovarian cancer immunogenicity is governed by a narrow subset of progenitor tissue-resident memory T cells.

Despite repeated associations between T cell infiltration and outcome, human ovarian cancer remains poorly responsive to immunotherapy. We report that the hallmarks of tumor recognition in ovarian cancer-infiltrating T cells are primarily restricted to tissue-resident memory (TRM) cells. Single-cell RNA/TCR/ATAC sequencing of 83,454 CD3+CD8+CD103+CD69+ TRM cells and immunohistochemistry of 122 high-grade serous ovarian cancers shows that only progenitor (TCF1low) tissue-resident T cells (TRMstem cells), but not recirculating TCF1+ T cells, predict ovarian cancer outcome. TRMstem cells arise from transitional recirculating T cells, which depends on antigen affinity/persistence, resulting in oligoclonal, trogocytic, effector lymphocytes that eventually become exhausted. Therefore, ovarian cancer is indeed an immunogenic disease, but that depends on ∼13% of CD8+ tumor-infiltrating T cells (∼3% of CD8+ clonotypes), which are primed against high-affinity antigens and maintain waves of effector TRM-like cells. Our results define the signature of relevant tumor-reactive T cells in human ovarian cancer, which could be applicable to other tumors with unideal mutational burden.

TGF-ß-mediated silencing of genomic organizer SATB1 promotes Tfh cell differentiation and formation of intra-tumoral tertiary lymphoid structures.

The immune checkpoint receptor PD-1 on T follicular helper (Tfh) cells promotes Tfh:B cell interactions and appropriate positioning within tissues. Here, we examined the impact of regulation of PD-1 expression by the genomic organizer SATB1 on Tfh cell differentiation. Vaccination of CD4CreSatb1f/f mice enriched for antigen-specific Tfh cells, and TGF-ß-mediated repression of SATB1 enhanced Tfh differentiation of human T cells. Mechanistically, high Icos expression in Satb1-/- CD4+ T cells promoted Tfh cell differentiation by preventing T follicular regulatory cell skewing and resulted in increased isotype-switched B cell responses in vivo. Ovarian tumors in CD4CreSatb1f/f mice accumulated tumor antigen-specific, LIGHT+CXCL13+IL-21+ Tfh cells and tertiary lymphoid structures (TLS). TLS formation decreased tumor growth in a CD4+ T cell and CXCL13-dependent manner. The transfer of Tfh cells, but not naive CD4+ T cells, induced TLS at tumor beds and decreased tumor growth. Thus, TGF-ß-mediated silencing of Satb1 licenses Tfh cell differentiation, providing insight into the genesis of TLS within tumors.

Cellular stress responses and metabolic reprogramming in cancer progression and dormancy.

Recurrent disease after prolonged cancer dormancy is a major cause of cancer associated mortality, yet many of the mechanisms that are engaged to initiate dormancy as well as later recurrence remain incompletely understood. It is known that cancer cells initiate adaptation mechanisms to adapt tightly regulated cellular processes to non-optimal growth environments; Recent investigations have begun to elucidate the contribution of these mechanisms to malignant progression, with intriguing studies now defining cellular stress as a key contributor to the development and maintenance of cancer dormancy. This review will focus on our current understanding of stress responses facilitating malignant cell adaptation and metabolic reprogramming to establish cancer dormancy.

IgA-Dominated Humoral Immune Responses Govern Patients' Outcome in Endometrial Cancer.

Recent studies suggest that B cells could play an important role in the tumor microenvironment. However, the role of humoral responses in endometrial cancer remains insufficiently investigated. Using a cohort of 107 patients with different histological subtypes of endometrial carcinoma, we evaluated the role of coordinated humoral and cellular adaptive immune responses in endometrial cancer. Concomitant accumulation of T, B, and plasma cells at tumor beds predicted better survival. However, only B-cell markers corresponded with prolonged survival specifically in high-grade endometrioid type and serous tumors. Immune protection was associated with class-switched IgA and, to a lesser extent, IgG. Expressions of polymeric immunoglobulin receptor (pIgR) by tumor cells and its occupancy by IgA were superior predictors of outcome and correlated with defects in methyl-directed DNA mismatch repair. Mechanistically, pIgR-dependent, antigen-independent IgA occupancy drove activation of inflammatory pathways associated with IFN and TNF signaling in tumor cells, along with apoptotic and endoplasmic reticulum stress pathways, while thwarting DNA repair mechanisms. Together, these findings suggest that coordinated humoral and cellular immune responses, characterized by IgA:pIgR interactions in tumor cells, determine the progression of human endometrial cancer as well as the potential for effective immunotherapies. SIGNIFICANCE: This study provides new insights into the crucial role of humoral immunity in human endometrial cancer, providing a rationale for designing novel immunotherapies against this prevalent malignancy. See related commentary by Osorio and Zamarin, p. 766.

IgA transcytosis and antigen recognition govern ovarian cancer immunity.

Most ovarian cancers are infiltrated by prognostically relevant activated T cells1-3, yet exhibit low response rates to immune checkpoint inhibitors4. Memory B cell and plasma cell infiltrates have previously been associated with better outcomes in ovarian cancer5,6, but the nature and functional relevance of these responses are controversial. Here, using 3 independent cohorts that in total comprise 534 patients with high-grade serous ovarian cancer, we show that robust, protective humoral responses are dominated by the production of polyclonal IgA, which binds to polymeric IgA receptors that are universally expressed on ovarian cancer cells. Notably, tumour B-cell-derived IgA redirects myeloid cells against extracellular oncogenic drivers, which causes tumour cell death. In addition, IgA transcytosis through malignant epithelial cells elicits transcriptional changes that antagonize the RAS pathway and sensitize tumour cells to cytolytic killing by T cells, which also contributes to hindering malignant progression. Thus, tumour-antigen-specific and -antigen-independent IgA responses antagonize the growth of ovarian cancer by governing coordinated tumour cell, T cell and B cell responses. These findings provide a platform for identifying targets that are spontaneously recognized by intratumoural B-cell-derived antibodies, and suggest that immunotherapies that augment B cell responses may be more effective than approaches that focus on T cells, particularly for malignancies that are resistant to checkpoint inhibitors.

Methyltransferase inhibitors restore SATB1 protective activity against cutaneous T cell lymphoma in mice.

Cutaneous T cell lymphoma (CTCL) has a poorly understood etiology and no known cure. Using conditional knockout mice, we found that ablation of the genomic organizer special AT-rich sequence-binding protein 1 (Satb1) caused malignant transformation of mature, skin-homing, Notch-activated CD4+ and CD8+ T cells into progressively fatal lymphoma. Mechanistically, Satb1 restrained Stat5 phosphorylation and the expression of skin-homing chemokine receptors in mature T cells. Notably, methyltransferase-dependent epigenetic repression of SATB1 was universally found in human Sézary syndrome, but not in other peripheral T cell malignancies. H3K27 and H3K9 trimethylation occluded the SATB1 promoter in Sézary cells, while inhibition of SUV39H1/2 methyltransferases (unlike EZH2 inhibition) restored protective SATB1 expression and selectively abrogated the growth of primary Sézary cells more effectively than romidepsin. Therefore, inhibition of methyltransferases that silence SATB1 could address an unmet need for patients with mycosis fungoides/Sézary syndrome, a set of incurable diseases.

BTN3A1 governs antitumor responses by coordinating αß and γδ T cells.

Gamma delta (γδ) T cells infiltrate most human tumors, but current immunotherapies fail to exploit their in situ major histocompatibility complex-independent tumoricidal potential. Activation of γδ T cells can be elicited by butyrophilin and butyrophilin-like molecules that are structurally similar to the immunosuppressive B7 family members, yet how they regulate and coordinate αß and γδ T cell responses remains unknown. Here, we report that the butyrophilin BTN3A1 inhibits tumor-reactive αß T cell receptor activation by preventing segregation of N-glycosylated CD45 from the immune synapse. Notably, CD277-specific antibodies elicit coordinated restoration of αß T cell effector activity and BTN2A1-dependent γδ lymphocyte cytotoxicity against BTN3A1+ cancer cells, abrogating malignant progression. Targeting BTN3A1 therefore orchestrates cooperative killing of established tumors by αß and γδ T cells and may present a treatment strategy for tumors resistant to existing immunotherapies.

The Unfolded Protein Response Mediator PERK Governs Myeloid Cell-Driven Immunosuppression in Tumors through Inhibition of STING Signaling.

The primary mechanisms supporting immunoregulatory polarization of myeloid cells upon infiltration into tumors remain largely unexplored. Elucidation of these signals could enable better strategies to restore protective anti-tumor immunity. Here, we investigated the role of the intrinsic activation of the PKR-like endoplasmic reticulum (ER) kinase (PERK) in the immunoinhibitory actions of tumor-associated myeloid-derived suppressor cells (tumor-MDSCs). PERK signaling increased in tumor-MDSCs, and its deletion transformed MDSCs into myeloid cells that activated CD8+ T cell-mediated immunity against cancer. Tumor-MDSCs lacking PERK exhibited disrupted NRF2-driven antioxidant capacity and impaired mitochondrial respiratory homeostasis. Moreover, reduced NRF2 signaling in PERK-deficient MDSCs elicited cytosolic mitochondrial DNA elevation and, consequently, STING-dependent expression of anti-tumor type I interferon. Reactivation of NRF2 signaling, conditional deletion of STING, or blockade of type I interferon receptor I restored the immunoinhibitory potential of PERK-ablated MDSCs. Our findings demonstrate the pivotal role of PERK in tumor-MDSC functionality and unveil strategies to reprogram immunosuppressive myelopoiesis in tumors to boost cancer immunotherapy.

Exosomes Produced by Mesenchymal Stem Cells Drive Differentiation of Myeloid Cells into Immunosuppressive M2-Polarized Macrophages in Breast Cancer.

Tumor-associated macrophages are major contributors to malignant progression and resistance to immunotherapy, but the mechanisms governing their differentiation from immature myeloid precursors remain incompletely understood. In this study, we demonstrate that exosomes secreted by human and mouse tumor-educated mesenchymal stem cells (MSCs) drive accelerated breast cancer progression by inducing differentiation of monocytic myeloid-derived suppressor cells into highly immunosuppressive M2-polarized macrophages at tumor beds. Mechanistically, MSC-derived exosomes but not exosomes from tumor cells contain TGF-ß, C1q, and semaphorins, which promote myeloid tolerogenic activity by driving PD-L1 overexpression in both immature myelomonocytic precursors and committed CD206+ macrophages and by inducing differentiation of MHC class II+ macrophages with enhanced l-Arginase activity and IL-10 secretion at tumor beds. Accordingly, administration of tumor-associated murine MSC-derived exosomes accelerates tumor growth by dampening antitumor immunity, and macrophage depletion eliminates exosome-dependent differences in malignant progression. Our results unveil a new role for MSC-derived exosomes in the differentiation of myeloid-derived suppressor cells into macrophages, which governs malignant growth.

IL-33 delays metastatic peritoneal cancer progression inducing an allergic microenvironment.

Ovarian cancer is frequently diagnosed as peritoneal carcinomatosis. Unlike other tumor locations, the peritoneal cavity is commonly exposed to gut-breaching and ascending genital microorganisms and has a unique immune environment. IL-33 is a local cytokine that can activate innate and adaptive immunity. We studied the effectiveness of local IL-33 delivery in the treatment of cancer that has metastasized to the peritoneal cavity. Direct peritoneal administration of IL-33 delayed the progression of metastatic peritoneal cancer. Prolongation in survival was not associated with a direct effect of IL-33 on tumor cells, but with major changes in the immune microenvironment of the tumor. IL-33 promoted a significant increase in the leukocyte compartment of the tumor immunoenvironment and an allergic cytokine profile. We observed a substantial increase in the number of activated CD4+ T-cells accompanied by peritoneal eosinophil infiltration, B-cell activation and activation of peritoneal macrophages which displayed tumoricidal capacity. Depletion of CD4+ cells, eosinophils or macrophages reduced the anti-tumor effects of IL-33 but none of these alone were sufficient to completely abrogate its positive benefit. In conclusion, local administration of IL-33 generates an allergic tumor environment resulting in a novel approach for treatment of metastatic peritoneal malignancies, such as advanced ovarian cancer.

IRE1α-XBP1 controls T cell function in ovarian cancer by regulating mitochondrial activity.

Tumours evade immune control by creating hostile microenvironments that perturb T cell metabolism and effector function1-4. However, it remains unclear how intra-tumoral T cells integrate and interpret metabolic stress signals. Here we report that ovarian cancer-an aggressive malignancy that is refractory to standard treatments and current immunotherapies5-8-induces endoplasmic reticulum stress and activates the IRE1α-XBP1 arm of the unfolded protein response9,10 in T cells to control their mitochondrial respiration and anti-tumour function. In T cells isolated from specimens collected from patients with ovarian cancer, upregulation of XBP1 was associated with decreased infiltration of T cells into tumours and with reduced IFNG mRNA expression. Malignant ascites fluid obtained from patients with ovarian cancer inhibited glucose uptake and caused N-linked protein glycosylation defects in T cells, which triggered IRE1α-XBP1 activation that suppressed mitochondrial activity and IFNγ production. Mechanistically, induction of XBP1 regulated the abundance of glutamine carriers and thus limited the influx of glutamine that is necessary to sustain mitochondrial respiration in T cells under glucose-deprived conditions. Restoring N-linked protein glycosylation, abrogating IRE1α-XBP1 activation or enforcing expression of glutamine transporters enhanced mitochondrial respiration in human T cells exposed to ovarian cancer ascites. XBP1-deficient T cells in the metastatic ovarian cancer milieu exhibited global transcriptional reprogramming and improved effector capacity. Accordingly, mice that bear ovarian cancer and lack XBP1 selectively in T cells demonstrate superior anti-tumour immunity, delayed malignant progression and increased overall survival. Controlling endoplasmic reticulum stress or targeting IRE1α-XBP1 signalling may help to restore the metabolic fitness and anti-tumour capacity of T cells in cancer hosts.

Gr1-/low CD11b-/low MHCII+ myeloid cells boost T cell anti-tumor efficacy.

Conventional APCs that express MHC class II (MHCII) and co-stimulatory molecules include dendritic cells (DCs) and macrophages. Beyond these conventional APCs, immune stimulatory cells have been more recently shown to extend to a class of atypical APCs, composed of mast cells, basophils, and eosinophils. Here, we describe a unique type of APC, Gr1-/low CD11b-/low cells with a granularity and size characteristic of myeloid cells and with the ability to present Ag for crosspresentation. These cells constitutively express MHCII and the costimulatory molecules, CD80, CD86, and CD40. They do not express pan markers of myeloid DCs (CD11c), plasmacytoid DCs (Ly6C), or macrophages (F4/80), and their frequency is inversely correlated with myeloid-derived suppressor cells (MDSCs) in tumor-bearing mice. Among splenocytes, they are more abundant than DCs and macrophages, and they exhibit antitumor immune stimulatory function at a steady state without further activation, ex vivo. They are also found within the tumor bed where they retain their immune stimulatory function. Our findings suggest the use of these novel APCs in additional preclinical studies to further investigate their utility in APC-based cancer immunotherapies.

Autophagy-deficient breast cancer shows early tumor recurrence and escape from dormancy.

Breast cancer patients who initially respond to cancer therapies often succumb to distant recurrence of the disease. It is not clear why people with the same type of breast cancer respond to treatments differently; some escape from dormancy and relapse earlier than others. In addition, some tumor clones respond to immunotherapy while others do not. We investigated how autophagy plays a role in accelerating or delaying recurrence of neu-overexpressing mouse mammary carcinoma (MMC) following adriamycin (ADR) treatment, and in affecting response to immunotherapy. We explored two strategies: 1) transient blockade of autophagy with chloroquine (CQ), which blocks fusion of autophagosomes and lysosomes during ADR treatment, and 2) permanent inhibition of autophagy by a stable knockdown of ATG5 (ATG5KD), which inhibits the formation of autophagosomes in MMC during and after ADR treatment. We found that while CQ prolonged tumor dormancy, but that stable knockdown of autophagy resulted in early escape from dormancy and recurrence. Interestingly, ATG5KD MMC contained an increased frequency of ADR-induced polyploid-like cells and rendered MMC resistant to immunotherapy. On the other hand, a transient blockade of autophagy did not affect the sensitivity of MMC to immunotherapy. Our observations suggest that while chemotherapy-induced autophagy may facilitate tumor relapse, cell-intrinsic autophagy delays tumor relapse, in part, by inhibiting the formation of polyploid-like tumor dormancy.

Frontline Science: Microbiota reconstitution restores intestinal integrity after cisplatin therapy.

Due to their cytotoxic activities, many anticancer drugs cause extensive damage to the intestinal mucosa and have antibiotic activities. Here, we show that cisplatin induces significant changes in the repertoire of intestinal commensal bacteria that exacerbate mucosal damage. Restoration of the microbiota through fecal-pellet gavage drives healing of cisplatin-induced intestinal damage. Bacterial translocation to the blood stream is correspondingly abrogated, resulting in a significant reduction in systemic inflammation, as evidenced by decreased serum IL-6 and reduced mobilization of granulocytes. Mechanistically, reversal of dysbiosis in response to fecal gavage results in the production of protective mucins and mobilization of CD11b+ myeloid cells to the intestinal mucosa, which promotes angiogenesis. Administration of Ruminococcus gnavus, a bacterial strain selectively depleted by cisplatin treatment, could only partially restore the integrity of the intestinal mucosa and reduce systemic inflammation, without measurable increases in the accumulation of mucin proteins. Together, our results indicate that reconstitution of the full repertoire of intestinal bacteria altered by cisplatin treatment accelerates healing of the intestinal epithelium and ameliorates systemic inflammation. Therefore, fecal microbiota transplant could paradoxically prevent life-threatening bacteremia in cancer patients treated with chemotherapy.

IFN-γ orchestrates tumor elimination, tumor dormancy, tumor escape, and progression.

Tumor immunoediting consisting of three phases of elimination, equilibrium or dormancy, and escape has been supported by preclinical and clinical data. A comprehensive understanding of the molecular mechanisms by which antitumor immune responses regulate these three phases are important for developing highly tailored immunotherapeutics that can control cancer. To this end, IFN-γ produced by Th1 cells, cytotoxic T cells, NK cells, and NKT cells is a pleiotropic cytokine that is involved in all three phases of tumor immunoediting, as well as during inflammation-mediated tumorigenesis processes. This essay presents a review of literature and suggests that overcoming tumor escape is feasible by driving tumor cells into a state of quiescent but not indolent dormancy in order for IFN-γ-producing tumor-specific T cells to prevent tumor relapse.

Conditioning neoadjuvant therapies for improved immunotherapy of cancer.

Recent advances in the treatment of melanoma and non-small cell lung cancer (NSCLC) by combining conventional therapies with anti-PD1/PD-L1 immunotherapies, have renewed interests in immunotherapy of cancer. The emerging concept of conventional cancer therapies combined with immunotherapy differs from the classical concept in that it is not simply taking advantage of their additive anti-tumor effects, but it is to use certain therapeutic regimens to condition the tumor microenvironment for optimal response to immunotherapy. To this end, low dose immunogenic chemotherapies, epigenetic modulators and inhibitors of cell cycle progression are potential candidates for rendering tumors highly responsive to immunotherapy. Next generation immunotherapeutics are therefore predicted to be highly effective against cancer, when they are used following appropriate immune modulatory compounds or targeted delivery of tumor cell cycle inhibitors using nanotechnology.

SATB1 Expression Governs Epigenetic Repression of PD-1 in Tumor-Reactive T Cells.

Despite the importance of programmed cell death-1 (PD-1) in inhibiting T cell effector activity, the mechanisms regulating its expression remain poorly defined. We found that the chromatin organizer special AT-rich sequence-binding protein-1 (Satb1) restrains PD-1 expression induced upon T cell activation by recruiting a nucleosome remodeling deacetylase (NuRD) complex to Pdcd1 regulatory regions. Satb1 deficienct T cells exhibited a 40-fold increase in PD-1 expression. Tumor-derived transforming growth factor ß (Tgf-ß) decreased Satb1 expression through binding of Smad proteins to the Satb1 promoter. Smad proteins also competed with the Satb1-NuRD complex for binding to Pdcd1 enhancers, releasing Pdcd1 expression from Satb1-mediated repression, Satb1-deficient tumor-reactive T cells lost effector activity more rapidly than wild-type lymphocytes at tumor beds expressing PD-1 ligand (CD274), and these differences were abrogated by sustained CD274 blockade. Our findings suggest that Satb1 functions to prevent premature T cell exhaustion by regulating Pdcd1 expression upon T cell activation. Dysregulation of this pathway in tumor-infiltrating T cells results in diminished anti-tumor immunity.