Natural killer cell therapies

Natural killer (NK) cells are lymphocytes of the innate immune system. A key feature of NK cells is their ability to recognize a wide range of cells in distress, particularly tumour cells and cells infected with viruses. They combine both direct effector functions against their cellular targets and participate in the generation, shaping and maintenance of a multicellular immune response. As our understanding has deepened, several therapeutic strategies focused on NK cells have been conceived and are currently in various stages of development, from preclinical investigations to clinical trials. Here we explore in detail the complexity of NK cell biology in humans and highlight the role of these cells in cancer immunity. We also analyse the harnessing of NK cell immunity through immune checkpoint inhibitors, NK cell engagers, and infusions of preactivated or genetically modified, autologous or allogeneic NK cell products.

New immune cell engagers for cancer immunotherapy

There have been major advances in the immunotherapy of cancer in recent years, including the development of T cell engagers - antibodies engineered to redirect T cells to recognize and kill cancer cells - for the treatment of haematological malignancies. However, the field still faces several challenges to develop agents that are consistently effective in a majority of patients and cancer types, such as optimizing drug dose, overcoming treatment resistance and improving efficacy in solid tumours. A new generation of T cell-targeted molecules was developed to tackle these issues that are potentially more effective and safer. In addition, agents designed to engage the antitumour activities of other immune cells, including natural killer cells and myeloid cells, are showing promise and have the potential to treat a broader range of cancers.

On blood and tissue-resident natural killer cells

Conventional natural killer (cNK) cells patrol the organism via circulation and invade tissues in response to infection or inflammation. In this issue of Immunity, Torcellan et al. report that circulating cNK cells are recruited into infected skin and differentiate into long-lived tissue-resident NK cells capable of mediating an accelerated response upon reinfection.

Canonical IRE1 function needed to sustain vigorous natural killer cell proliferation during viral infection

The unfolded protein response (UPR) aims to restore ER homeostasis under conditions of high protein folding load, a function primarily serving secretory cells. Additional, non-canonical UPR functions have recently been unraveled in immune cells. We addressed the function of the inositol-requiring enzyme 1 (IRE1) signaling branch of the UPR in NK cells in homeostasis and microbial challenge. Cell-intrinsic compound deficiency of IRE1 and its downstream transcription factor XBP1 in NKp46+ NK cells, did not affect basal NK cell homeostasis, or overall outcome of viral MCMV infection. However, mixed bone marrow chimeras revealed a competitive advantage in the proliferation of IRE1-sufficient Ly49H+ NK cells after viral infection. CITE-Seq analysis confirmed strong induction of IRE1 early upon infection, concomitant with the activation of a canonical UPR signature. Therefore, we conclude that IRE1/XBP1 activation is required during vigorous NK cell proliferation early upon viral infection, as part of a canonical UPR response.

Germinal center-dependent and -independent immune responses of tumor-infiltrating B cells in human cancers

B cells play essential roles in immunity, mainly through the production of high affinity plasma cells (PCs) and memory B (Bmem) cells. The affinity maturation and differentiation of B cells rely on the integration of B-cell receptor (BCR) intrinsic and extrinsic signals provided by antigen binding and the microenvironment, respectively. In recent years, tumor infiltrating B (TIL-B) cells and PCs (TIL-PCs) have been revealed as important players in antitumor responses in human cancers, but their interplay and dynamics remain largely unknown. In lymphoid organs, B-cell responses involve both germinal center (GC)-dependent and GC-independent pathways for Bmem cell and PC production. Affinity maturation of BCR repertoires occurs in GC reactions with specific spatiotemporal dynamics of signal integration by B cells. In general, the reactivation of high-affinity Bmem cells by antigens triggers GC-independent production of large numbers of PC without BCR rediversification. Understanding B-cell dynamics in immune responses requires the integration of multiple tools and readouts such as single-cell phenotyping and RNA-seq, in situ analyses, BCR repertoire analysis, BCR specificity and affinity assays, and functional tests. Here, we review how those tools have recently been applied to study TIL-B cells and TIL-PC in different types of solid tumors. We assessed the published evidence for different models of TIL-B-cell dynamics involving GC-dependent or GC-independent local responses and the resulting production of antigen-specific PCs. Altogether, we highlight the need for more integrative B-cell immunology studies to rationally investigate TIL-B cells as a leverage for antitumor therapies.

Control of acute myeloid leukemia by a trifunctional NKp46-CD16a-NK cell engager targeting CD123

CD123, the alpha chain of the IL-3 receptor, is an attractive target for acute myeloid leukemia (AML) treatment. However, cytotoxic antibodies or T cell engagers targeting CD123 had insufficient efficacy or safety in clinical trials. We show that expression of CD64, the high-affinity receptor for human IgG, on AML blasts confers resistance to anti-CD123 antibody-dependent cell cytotoxicity (ADCC) in vitro. We engineer a trifunctional natural killer cell engager (NKCE) that targets CD123 on AML blasts and NKp46 and CD16a on NK cells (CD123-NKCE). CD123-NKCE has potent antitumor activity against primary AML blasts regardless of CD64 expression and induces NK cell activation and cytokine secretion only in the presence of AML cells. Its antitumor activity in a mouse CD123+ tumor model exceeds that of the benchmark ADCC-enhanced antibody. In nonhuman primates, it had prolonged pharmacodynamic effects, depleting CD123+ cells for more than 10 days with no signs of toxicity and very low inflammatory cytokine induction over a large dose range. These results support clinical development of CD123-NKCE.

Myc controls NK cell development, IL-15-driven expansion, and translational machinery

MYC is a pleiotropic transcription factor involved in cancer, cell proliferation, and metabolism. Its regulation and function in NK cells, which are innate cytotoxic lymphocytes important to control viral infections and cancer, remain poorly defined. Here, we show that mice deficient for Myc in NK cells presented a severe reduction in these lymphocytes. Myc was required for NK cell development and expansion in response to the key cytokine IL-15, which induced Myc through transcriptional and posttranslational mechanisms. Mechanistically, Myc ablation in vivo largely impacted NK cells' ribosomagenesis, reducing their translation and expansion capacities. Similar results were obtained by inhibiting MYC in human NK cells. Impairing translation by pharmacological intervention phenocopied the consequences of deleting or blocking MYC in vitro. Notably, mice lacking Myc in NK cells exhibited defective anticancer immunity, which reflected their decreased numbers of mature NK cells exerting suboptimal cytotoxic functions. These results indicate that MYC is a central node in NK cells, connecting IL-15 to translational fitness, expansion, and anticancer immunity.

Natural killer cells and type 1 innate lymphoid cells in cancer

Innate lymphoid cells (ILCs) are a group of innate lymphocytes that do not express RAG-dependent rearranged antigen-specific cell surface receptors. ILCs are classified into five groups according to their developmental trajectory and cytokine production profile. They encompass NK cells, which are cytotoxic, helper-like ILCs 1-3, which functionally mirror CD4⁺ T helper (Th) type 1, Th2 and Th17 cells respectively, and lymphoid tissue inducer (LTi) cells. NK cell development depends on Eomes (eomesodermin), whereas the ILC1 program is regulated principally by the transcription factor T-bet (T-box transcription factor Tbx21), that of ILC2 is regulated by GATA3 (GATA-binding protein 3) and that of ILC3 is regulated by RORγt (RAR-related orphan receptor γ). NK cells were discovered close to fifty years ago, but ILC1s were first described only about fifteen years ago. Within the ILC family, NK and ILC1s share many similarities, as witnessed by their cell surface phenotype which largely overlap. NK cells and ILC1s have been reported to respond to tissue inflammation and intracellular pathogens. Several studies have reported an antitumorigenic role for NK cells in both humans and mice, but data for ILC1s are both scarce and contradictory. In this review, we will first describe the different NK cell and ILC1 subsets, their effector functions and development. We will then discuss their role in cancer and the effects of the tumor microenvironment on their metabolism.

NKG2A blocks the anti-metastatic functions of natural killer cells

Pancreatic ductal adenocarcinoma (PDAC)-derived liver metastasis represents a major unmet medical need. Liu et al. show that circulating tumor cells (CTCs) from the hepatic portal vein (HPV), and not from primary or metastatic sites, are protected from natural killer (NK) cells through the NKG2A/HLA-E axis. Interfering with this pathway unleashes NK cells and prevents PDAC metastasis.

Tissue-specific transcriptional profiles and heterogeneity of natural killer cells and group 1 innate lymphoid cells

Natural killer (NK) cells and type 1 innate lymphoid cells (ILC1s) are populations of non-T, non-B lymphocytes in peripheral tissues. Although NK and ILC1 subsets have been described, their identification and characteristics remain unclear. We performed single-cell RNA sequencing and CITE-seq to explore NK and ILC1 heterogeneity between tissues. We observed that although NK1 and NK2 subsets are conserved in spleen and liver, ILC1s are heterogeneous across tissues. We identified sets of genes expressed by related subsets or characterizing unique ILC1 populations in each organ. The syndecan-4 appeared as a marker discriminating murine ILC1 from NK cells across organs. Finally, we revealed that the expressions of EOMES, GZMA, IRF8, JAK1, NKG7, PLEK, PRF1, and ZEB2 define NK cells and that IL7R, LTB, and RGS1 differentiate ILC1s from NK cells in mice and humans. Our data constitute an important resource to improve our understanding of NK-ILC1 origin, phenotype, and biology.

Antitumor immunity induced by antibody-based natural killer cell engager therapeutics armed with not-alpha IL-2 variant

Harnessing innate immunity is emerging as a promising therapeutic approach in cancer. We report here the design of tetraspecific molecules engaging natural killer (NK) cell-activating receptors NKp46 and CD16a, the β-chain of the interleukin-2 receptor (IL-2R), and a tumor-associated antigen (TAA). In vitro, these tetraspecific antibody-based natural killer cell engager therapeutics (ANKETs) induce a preferential activation and proliferation of NK cells, and the binding to the targeted TAA triggers NK cell cytotoxicity and cytokine and chemokine production. In vivo, tetraspecific ANKETs induce NK cell proliferation and their accumulation at the tumor bed, as well as the control of local and disseminated tumors. Treatment of non-human primates with CD20-directed tetraspecific ANKET leads to CD20⁺ circulating B cell depletion, with minimal systemic cytokine release and no sign of toxicity. Tetraspecific ANKETs, thus, constitute a technological platform for harnessing NK cells as next-generation cancer immunotherapies.

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Tetraspecific ANKETs constitute a technological platform to harness NK cells in cancer

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Tetraspecific ANKETs target NKp46, CD16a, IL-2Rβ, and a tumor antigen

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Tetraspecific ANKETs stimulate NK cell proliferation, activation, and antitumor functions

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In vivo, tetraspecific ANKETs promote NK cell tumor accumulation and antitumor activity

Bringing natural killer cells to the clinic

Cancer is a leading cause of mortality worldwide, with around 10 million deaths every year. Despite huge advances due to immunotherapy, the majority of cancer patients present primary or secondary resistance to these treatments. In this Found in Translation, we focus on the approaches developed to harness the anti-tumor function of NK cells, suggesting promising strategies to complete the therapeutic arsenal of cancer immunotherapies.

Role of the ITAM-Bearing Receptors Expressed by Natural Killer Cells in Cancer

Natural Killer (NK) cells are innate lymphoid cells (ILCs) capable of recognizing and directly killing tumor cells. They also secrete cytokines and chemokines, which participate in the shaping of the adaptive response. NK cells identify tumor cells and are activated through a net positive signal from inhibitory and activating receptors. Several activating NK cell receptors are coupled to adaptor molecules containing an immunoreceptor tyrosine-based activation motif (ITAM). These receptors include CD16 and the natural cytotoxic receptors NKp46, NKp44, NKp30 in humans. The powerful antitumor NK cell response triggered by these activating receptors has made them attractive targets for exploitation in immunotherapy. In this review, we will discuss the different activating receptors associated with ITAM-bearing cell surface receptors expressed on NK cells, their modulations in the tumor context and the various therapeutic tools developed to boost NK cell responses in cancer patients.

Abstract LB120: Comprehensive biomarkers analysis to explain resistances to PD1-L1 ICIs: The precision immuno-oncology for advanced non-small cell lung cancer (PIONeeR) trial

Background: Resistance to PD1/L1 immune checkpoint inhibitors (ICIs) in advanced NSCLC patients is observed in about 80% of individuals with no robust predictive biomarker yet. The PIONeeR trial (NCT03493581) aims to predict such resistances through a comprehensive multiparametric biomarkers analysis.

Methodology: Among the >300 advanced NSCLC patients (pts) recruited in PIONeeR, we focused on the first 137 ≥2nd line ECOG PS0-1 pts treated with single-agent nivolumab, pembrolizumab or atezolizumab. Tumor tissue was collected at baseline and pts were re-biopsied at 6 weeks, and blood-sampled every cycle throughout the 24 weeks post C1D1. Response to PD1/L1 ICIs was assessed by RECIST 1.1 every 6 weeks. Immune contexture was characterized in tumor & blood of each pt through FACS for circulating immune cell subtypes quantification and endothelial activation, blood soluble factors dosage, dual- & multiplex IHC/digital pathology to quantify immune cells infiltrating the tumor, WES for TMB & ICI plasma dosage, leading to 331 measured biomarkers in addition to routine clinical parameters. Multivariable (MV) logistic regression was used to examine the association of each biomarker (controlled by sex, age, smoking status, histological type & PDL1+ Tumor Cells) with the risk of Early Progression (EP), i.e. within 3.5 months of treatment. Multivariable Cox regression analysis was conducted for association with PFS and OS.

Results: Overall, the 137 pts were mainly male (64%), smokers (92%) and <70yrs (68%). Tumors were mainly non-squamous (79%) with >1% PDL1+ TC in 36% of the cases, and 21% of pts were still on treatment at data cut-off. Archived samples were available for 80% of pts at inclusion and re-biopsy was available in 52.9% of these cases. The median follow up was 19.8 months, 22.5% of pts did not progress at data cut-off while 62% presented EP. Tumor Cytotoxic T-cells density, especially PD1+ were lower in EP (MV OR=0.45, p=0.022); conversely, higher proportions of circulating cytotoxic T-cells and activated T-cells (HLA-DR+) were observed in EP (MV OR=3.8, p<0.001). Among other biomarkers, Tregs (MV OR=0.44, p=0.018), NK cell subsets (MV OR≤0.44, p<0.05), albumin (MV OR=0.4, p<0.01) and PDL1 TC % (MV OR=0.27, p<0.01) were decreased whereas alkaline phosphatase was increased (OR=3, p=0.018). >65% inter-pt variability was observed in plasma exposures for all ICIs, with 8-10% of pts displaying trough levels below the target engagement threshold. Data will be presented through unsupervised clustering algorithms & multi-modal supervised learning methods. Changes after 6 weeks of treatment will be analyzed to further investigate drugs mechanisms of action.

Conclusion: The PIONeeR trial provides with the 1st comprehensive biomarkers’ analysis to establish predictive models of resistance in advanced NSCLC pts treated with PD1/L1 ICIs and highlights how tumor and circulating biomarkers are complementary.

Citation Format: Laurent Greillier, Florence Monville, Vanina Leca, Frédéric Vely, Stephane Garcia, Joseph Ciccolini, Florence Sabatier, Gilbert Ferrani, Nawel Boudai, Lamia Ghezali, Marcellin Landri, Clémence Marin, Mourad Hamimed, Laurent Arnaud, Melanie Karlsen, Kevin Atsou, Sivan Bokobza, Pauline Fleury, Arnaud Boyer, Clarisse Audigier-Valette, Stéphanie Martinez, Hervé Pegliasco, Patrice Ray, Lionel Falchero, Antoine Serre, Nicolas Cloarec, Louisiane Lebas, Stephane Hominal, Patricia Barre, Sarah Zahi, Ahmed Frikha, Pierre Bory, Maryannick Le Ray, Lilian Laborde, Virginie Martin, Richard Malkoun, Marie Roumieux, Julien Mazieres, Maurice Perol, Eric Vivier, Sebastien Benzekry, Jacques Fieschi, Fabrice Barlesi. Comprehensive biomarkers analysis to explain resistances to PD1-L1 ICIs: The precision immuno-oncology for advanced non-small cell lung cancer (PIONeeR) trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB120.

Targeting CISH enhances natural cytotoxicity receptor signaling and reduces NK cell exhaustion to improve solid tumor immunity

Background

The success and limitations of current immunotherapies have pushed research toward the development of alternative approaches and the possibility to manipulate other cytotoxic immune cells such as natural killer (NK) cells. Here, we targeted an intracellular inhibiting protein ‘cytokine inducible SH2-containing protein’ (CISH) in NK cells to evaluate the impact on their functions and antitumor properties.

Methods

To further understand CISH functions in NK cells, we developed a conditional Cish-deficient mouse model in NK cells (Cish^fl/flNcr1^Ki/+). NK cells cytokine expression, signaling and cytotoxicity has been evaluated in vitro. Using intravenous injection of B16F10 melanoma cell line and EO711 triple negative breast cancer cell line, metastasis evaluation was performed. Then, orthotopic implantation of breast tumors was performed and tumor growth was followed using bioluminescence. Infiltration and phenotype of NK cells in the tumor was evaluated. Finally, we targeted CISH in human NK-92 or primary NK cells, using a technology combining the CRISPR(i)-dCas9 tool with a new lentiviral pseudotype. We then tested human NK cells functions.

Results

In Cish^fl/flNcr1^Ki/+ mice, we detected no developmental or homeostatic difference in NK cells. Global gene expression of Cish^fl/flNcr1^Ki/+ NK cells compared with Cish^+/+Ncr1^Ki/+ NK cells revealed upregulation of pathways and genes associated with NK cell cycling and activation. We show that CISH does not only regulate interleukin-15 (IL-15) signaling pathways but also natural cytotoxicity receptors (NCR) pathways, triggering CISH protein expression. Primed Cish^fl/flNcr1^Ki/+ NK cells display increased activation upon NCR stimulation. Cish^fl/flNcr1^Ki/+ NK cells display lower activation thresholds and Cish^fl/flNcr1^Ki/+ mice are more resistant to tumor metastasis and to primary breast cancer growth. CISH deletion favors NK cell accumulation to the primary tumor, optimizes NK cell killing properties and decreases TIGIT immune checkpoint receptor expression, limiting NK cell exhaustion. Finally, using CRISPRi, we then targeted CISH in human NK-92 or primary NK cells. In human NK cells, CISH deletion also favors NCR signaling and antitumor functions.

Conclusion

This study represents a crucial step in the mechanistic understanding and safety of Cish targeting to unleash NK cell antitumor function in solid tumors. Our results validate CISH as an emerging therapeutic target to enhance NK cell immunotherapy.

Exploiting Natural Killer Cell Engagers to Control Pediatric B-cell Precursor Acute Lymphoblastic Leukemia

Natural killer (NK) cells represent a promising cell type in antitumor immunotherapy for efficacy and safety, particularly in the treatment of hematologic malignancies. NK cells have been shown to exert antileukemia activity in the context of haploidentical hematopoietic stem cell transplantation (haplo-HSCT). Products have been developed to boost the activation of NK cells only when cross-linked by tumor cells, avoiding any off-target effect. Here, we tested the in vitro effect of different NK-cell engagers (NKCE), which trigger either NKp46 or NKp30 together with CD16A, and target either CD19 or CD20 to induce killing of pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Target cells were NALM-16 and MHH-CALL-4 cell lines and four primary leukemias, while effector cells were resting NK cells derived from healthy donors and pediatric patients with leukemia after αβT/B-depleted haplo-HSCT. The NK cell-resistant MHH-CALL-4 was efficiently killed using all NKCEs. Boosting of NK activity against MHH-CALL-4 was also evident by degranulation and IFNγ production. Because of the lack of CD20 and high expression of CD19 on primary BCP-ALL, we focused on NKCEs targeting CD19. NKp46- and NKp30-based NKCEs displayed similar potency at inducing NK-cell activity, even when challenged with primary BCP-ALL blasts. Their efficacy was shown also using NK cells derived from transplanted patients. NKCE-induced activation against BCP-ALL can override HLA-specific inhibitory interactions, although the strongest response was observed by the alloreactive NK-cell subset. These data support the therapeutic use of NKp46/CD16A/CD19-NKCE to fight refractory/relapsed leukemia in pretransplantation or posttransplantation settings.

Group 1 ILCs regulate T cell-mediated liver immunopathology by controlling local IL-2 availability

Group 1 innate lymphoid cells (ILCs), which comprise both natural killer (NK) cells and ILC1s, are important innate effectors that can also positively and negatively influence adaptive immune responses. The latter function is generally ascribed to the ability of NK cells to recognize and kill activated T cells. Here, we used multiphoton intravital microscopy in mouse models of hepatitis B to study the intrahepatic behavior of group 1 ILCs and their cross-talk with hepatitis B virus (HBV)-specific CD8⁺ T cells. We found that hepatocellular antigen recognition by effector CD8⁺ T cells triggered a prominent increase in the number of hepatic NK cells and ILC1s. Group 1 ILCs colocalized and engaged in prolonged interactions with effector CD8⁺ T cells undergoing hepatocellular antigen recognition; however, they did not induce T cell apoptosis. Rather, group 1 ILCs constrained CD8⁺ T cell proliferation by controlling local interleukin-2 (IL-2) availability. Accordingly, group 1 ILC depletion, or genetic removal of their IL-2 receptor a chain, considerably increased the number of intrahepatic HBV-specific effector CD8⁺ T cells and the attendant immunopathology. Together, these results reveal a role for group 1 ILCs in controlling T cell-mediated liver immunopathology by limiting local IL-2 concentration and have implications for the treatment of chronic HBV infection.

Abstract P051: Function of shp-1 and shp-2 phosphatases in T cell-mediated anti-tumor response

After exposure to chronic inflammatory stimuli, the immune system can switch from a functional state where it acts to reestablish homeostasis to a dysfunctional state. In the context of cancer, T cells that become exposed to continuous stimulation eventually reach a state of exhaustion, characterized by poor effector function and expression of inhibitory receptors, such as PD-1. Although PD-1 signaling inhibition leads to T cell reinvigoration and has been applied as an effective treatment versus a wide range of tumors, the signaling pathway downstream of this receptor is still poorly understood. Recent work from others and us challenged the notion that the phosphatase shp-2 is essential for activation of the molecular cascade downstream PD-1 receptor engagement. The shp-2 homologue (shp-1) has also been associated with PD-1 signaling in T cells and functional redundancy between these phosphatases might occur downstream of this receptor. Therefore, we investigated the effect of shp-1 and the combination of both (shp-1/2) downstream of PD-1 by knocking out these phosphatases in T cells in a mouse model. In vivo results after tumor engraftment suggest that shp-1 as well as shp-1/2 deletion in T cells are not sufficient to ameliorate tumor control. Furthermore, ablation of shp-1 and shp-1/2 impair the beneficial effects of the anti-PD1 treatment. In fact, deletion of both phosphatases leads to decrease CD8+ T cell presence in the tumor microenvironment and in vitro results show that these cells have impaired survival. This data implies that elimination or inhibition of shp-1/2 is not a suitable strategy for effective immunotherapeutic approaches as well as highlights the importance of further elucidating the mechanisms behind this important inhibitory pathway.

Citation Format: Pedro Ventura, Milica Gakovic, Berenice Fischer, Sarah Thomson, Hanif J Khameneh, Alessandro Zenobi, Giorgia Rota, Eric Vivier, Walter Birchmeier, Doreen Cantrell, Greta Guarda. Function of shp-1 and shp-2 phosphatases in T cell-mediated anti-tumor response [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P051.

Type 1 Innate Lymphoid Cells Limit the Antitumoral Immune Response

Natural killer (NK) cells are known to be able to kill established tumor cell lines, but important caveats remain regarding their roles in the detection and elimination of developing primary tumors. Using a genetic model of selective ILC1 and NK cell deficiency, we showed that these cells were dispensable for tumor immunosurveillance and immunoediting in the MCA-induced carcinogenesis model. However, we were able to generate primary cell lines derived from MCA-induced tumors with graded sensitivity to NK1.1⁺ cells (including NK cells and ILC1). This differential sensitivity was associated neither with a modulation of intratumoral NK cell frequency, nor the capacity of tumor cells to activate NK cells. Instead, ILC1 infiltration into the tumor was found to be a critical determinant of NK1.1⁺ cell-dependent tumor growth. Finally, bulk tumor RNAseq analysis identified a gene expression signature associated with tumor sensitivity to NK1.1⁺ cells. ILC1 therefore appear to play an active role in inhibiting the antitumoral immune response, prompting to evaluate the differential tumor infiltration of ILC1 and NK cells in patients to optimize the harnessing of immunity in cancer therapies.

Tumor Microenvironment-Derived R-spondins Enhance Antitumor Immunity to Suppress Tumor Growth and Sensitize for Immune Checkpoint Blockade Therapy

Natural killer (NK) cells and T cells are key effectors of antitumor immune responses and major targets of checkpoint inhibitors. In multiple cancer types, we find that the expression of Wnt signaling potentiator R-spondin genes (e.g., RSPO3) is associated with favorable prognosis and positively correlates with gene signatures of both NK cells and T cells. Although endothelial cells and cancer-associated fibroblasts comprise the R-spondin 3-producing cells, NK cells and T cells correspondingly express the R-spondin 3 receptor LGR6 within the tumor microenvironment (TME). Exogenous expression or intratumor injection of R-spondin 3 in tumors enhanced the infiltration and function of cytotoxic effector cells, which led to tumor regression. NK cells and CD8+ T cells independently and cooperatively contributed to R-spondin 3-induced control of distinct tumor types. The effect of R-spondin 3 was mediated in part through upregulation of MYC and ribosomal biogenesis. Importantly, R-spondin 3 expression enhanced tumor sensitivity to anti-PD-1 therapy, thereby highlighting new therapeutic avenues.

SIGNIFICANCE

Our study identifies novel targets in enhancing antitumor immunity and sensitizing immune checkpoint inhibition, which provides a rationale for developing new immunotherapies against cancers. It also offers mechanistic insights on Wnt signaling-mediated modulation of anticancer immunity in the TME and implications for a putative R-spondin-LGR6 axis in regulating NK-cell biology. This article is highlighted in the In This Issue feature, p. 2945.

851 Harnessing innate immunity in cancer therapies: the example of natural killer cell engagers

Background

Most immunomodulatory approaches have focused on enhancing T-cell responses, with immune checkpoint inhibitors, chimeric antigen receptor T cells or bispecific antibodies. Although these therapies have led to exceptional successes, only a minority of cancer patients benefit from these treatments, highlighting the need to identify new cells and molecules that could be exploited in the next generation of immunotherapy. Given the crucial role of innate immune responses in immunity, harnessing these responses opens up new possibilities for tumor control. Antibody engineering provides us with great opportunities to induce synthetic immunity and to optimize the biological functions of innate immune cells, in particular by boosting the capacity of Natural Killer (NK) cells to kill tumor cells directly and to stimulate T-cell responses indirectly.

Methods

In order to leverage the advantages of harnessing NK cell effector functions, we used our Antibody-based NK cell Engager Therapeutics (ANKET) molecular platform1 and designed a new generation of molecules that can engage activating receptors NKp46 and CD16, the IL-2Rβ chain and a tumor antigen in a single tetra-specific molecule (ANKET4). The variant of interleukin-2 (IL-2v) integrated in the ANKET4 molecule is unable to bind the α-subunit of its receptor to limit regulatory T cell activation and IL-2Rα-mediated toxicity.

Results

In vitro, ANKET4 provides proliferation and activation signals targeted to NK cells and induces primary human NK cell cytolytic activity and the secretion of cytokines and chemokines only after binding to the tumor target. In mouse models of both invasive and solid tumors, ANKET4 induced NK cell proliferation and accumulation at the tumor bed, and had a higher anti-tumor efficacy than approved therapeutic antibodies targeting the same tumor antigen. Mechanistically, transcriptomic analysis and in-vivo studies revealed that the geometry of the ANKET4 molecule including NKp46, CD16 and IL-2 receptor binding moieties on the same molecule was essential for its strong activity which results from a synthetic cooperativity between immunoreceptor tyrosine-based activation motif (ITAM) and cytokine signaling pathways. In non-human primates, CD20-directed ANKET4 resulted in sustained CD20+ B-cell depletion with minimal systemic cytokine release and no clinical sign of toxicity.

Conclusions

Tetra-specific ANKET4 thus constitutes a technological platform combining the induction of NK cell proliferation and effector functions with a manageable safety profile, supporting its clinical development for next-generation cancer immunotherapies.

Reference

Gauthier L, Morel A, Anceriz N, Rossi B, Blanchard-Alvarez A, Grondin G, et al. Multifunctional natural killer cell engagers targeting NKp46 trigger protective tumor immunity. Cell 2019;177(7):1701–13 e16.

Ethics Approval

Primary immune cells were purified from buffy coats from healthy donors obtained from Etablissement Francais du Sang (EFS, Marseille) with written consent from each volunteer.All mouse experiments were performed in accordance with the rules of the Innate Pharma ethics committee and were approved by the Ministère de l’Enseignement Supérieur, de la Recherche et de l’Innovation – France (APAFIS# 19272 ).All non human-primate procedures were conducted according to European guidelines for animal care and use for scientific purposes (Directive 63-2010, ”Journal Officiel des Communautés Européennes”, L276, September 22, 2010) and according to CEA institutional guidelines. The study was approved by the local ethical committee under the number A18_080 and by the French Administration (APAFIS#20525-2019050616506478 v1)

852 Trifunctional NKp46/CD16a-NK cell engager targeting CD123 overcomes acute myeloid leukemia resistance to ADCC

Background

There is a clear need for targeted therapies to treat acute myeloid leukemia (AML), the most common acute leukemia in adults. CD123 (IL-3 receptor alpha chain) is an attractive target for AML treatment.1 However, cytotoxic antibody targeting CD123 proved insufficiently effective in a combination setting in phase II/III clinical trials.2 T-cell engagers targeting CD123 displayed some clinical efficacy but were often associated with cytokine release syndrome and neurotoxicity.3 Interest in the use of NK cells for therapeutic interventions has increased in recent years, as a potential safer alternative to T cells. Several NK-cell activating receptors, such as CD16a, NKG2D, and the natural cytotoxicity receptors NKp30 and NKp46, can be targeted to induce antitumor immunity. We previously reported the development of trifunctional NK-cell engagers (NKCEs) targeting a tumor antigen on cancer cells and co-engaging NKp46 and CD16a on NK cells.4

Methods

We report here the design, characterization and preclinical development of a novel trifunctional NK cell engager (NKCE) targeting CD123 on AML cells and engaging the activating receptors NKp46 and CD16a on NK cells. The CD123 NKCE therapeutic molecule was engineered with humanized antibodies targeting NKp464 and CD123.5 We compared CD123-NKCE and a cytotoxic ADCC-enhanced antibody (Ab) targeting CD123, in terms of antitumor activity in vitro, ex vivo and in vivo. Pharmacokinetic, pharmacodynamic and safety profile of CD123-NKCE were evaluated in non-human primate (NHP) studies.

Results

The expression of the high affinity Fc gamma receptor CD64 on patient-derived AML cells inhibited the ADCC of the Ab targeting CD123 in vitro and ex vivo, but not the antitumor activity of CD123-NKCE. CD123-NKCE had potent antitumor activity against primary AML blasts and AML cell lines, promoted strong NK-cell activation and induced cytokine secretion only in the presence of AML target cells. Its antitumor activity in mouse model was greater than that of the comparator antibody. Moreover, CD123-NKCE had strong and prolonged pharmacodynamic effects in NHP when used at very low doses, was well-tolerated up to high 3 mg/kg dose and triggered only minor cytokine release.

Conclusions

The data for activity, safety, pharmacokinetics, and pharmacodynamics provided here demonstrate the superiority of CD123-NKCE over comparator cytotoxic antibody, in terms of antitumor activity in vitro, ex vivo, in vivo, and its favorable safety profile, as compared to T-cell therapies. These results constitute proof-of-principle for the efficacy of CD123-NKCE for controlling AML tumors in vivo, and provide consistent support for their clinical development.

References

Ehninger A, Kramer M, Rollig C, et al. Distribution and levels of cell surface expression of CD33 and CD123 in acute myeloid leukemia. Blood Cancer J 2014;4:e218.

Montesinos P, Gail J Roboz GJ, et al. Safety and efficacy of talacotuzumab plus decitabine or decitabine alone in patients with acute myeloid leukemia not eligible for chemotherapy: results from a multicenter, randomized, phase 2/3 study. Leukemia 2021;35(1):62–74.

Uy GL, Aldoss I, Foster MC, et al. Flotetuzumab as salvage immunotherapy for refractory acute myeloid leukemia. Blood 2021;137(6):751–762.

Gauthier L, Morel A, Anceriz N, et al. Multifunctional natural killer cell engagers targeting NKp46 trigger protective tumor immunity. Cell 2019;177(7):1701–13.

Jin L, Lee EM, Ramshaw HS, et al. Monoclonal antibody-mediated targeting of CD123, IL-3 receptor alpha chain, eliminates human acute myeloid leukemic stem cells. Cell Stem Cell 2009;5:31–42.

Targeting MICA/B with cytotoxic therapeutic antibodies leads to tumor control

Background: MICA and MICB are tightly regulated stress-induced proteins that trigger the immune system by binding to the activating receptor NKG2D on cytotoxic lymphocytes. MICA and MICB are highly polymorphic molecules with prevalent expression on several types of solid tumors and limited expression in normal/healthy tissues, making them attractive targets for therapeutic intervention. Methods: We have generated a series of anti-MICA and MICB cross-reactive antibodies with the unique feature of binding to the most prevalent isoforms of both these molecules. Results: The anti-MICA and MICB antibody MICAB1, a human IgG1 Fc-engineered monoclonal antibody (mAb), displayed potent antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) of MICA/B-expressing tumor cells in vitro. However, it showed insufficient efficiency against solid tumors in vivo, which prompted the development of antibody-drug conjugates (ADC). Indeed, optimal tumor control was achieved with MICAB1-ADC format in several solid tumor models, including patient-derived xenografts (PDX) and carcinogen-induced tumors in immunocompetent MICAgen transgenic mice. Conclusions: These data indicate that MICA and MICB are promising targets for cytotoxic immunotherapy.

Targeting MICA/B with cytotoxic therapeutic antibodies leads to tumor control

Background: MICA and MICB are tightly regulated stress-induced proteins that trigger the immune system by binding to the activating receptor NKG2D on cytotoxic lymphocytes. MICA and MICB are highly polymorphic molecules with prevalent expression on several types of solid tumors and limited expression in normal/healthy tissues, making them attractive targets for therapeutic intervention. Methods: We have generated a series of anti-MICA and MICB cross-reactive antibodies with the unique feature of binding to the most prevalent isoforms of both these molecules. Results: The anti-MICA and MICB antibody MICAB1, a human IgG1 Fc-engineered monoclonal antibody (mAb), displayed potent antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) of MICA/B-expressing tumor cells in vitro. However, it showed insufficient efficiency against solid tumors in vivo, which prompted the development of antibody-drug conjugates (ADC). Indeed, optimal tumor control was achieved with MICAB1-ADC format in several solid tumor models, including patient-derived xenografts (PDX) and carcinogen-induced tumors in immunocompetent MICAgen transgenic mice. Conclusions: These data indicate that MICA and MICB are promising targets for cytotoxic immunotherapy.

NKG2A expression identifies a subset of human Vδ2 T cells exerting the highest antitumor effector functions

Human Vδ2 cells are innate-like γδ T effectors performing potent immune surveillance against tumors. The constitutive expression of NKG2A identifies a subset of Vδ2 T cells licensed with an intrinsic hyper-responsiveness against cancer. Indeed, the transcriptomic profiles of NKG2A⁺ and NKG2A^- cells characterize two distinct "intralineages" of Vδ2 T lymphocytes that appear early during development, keep their phenotypes, and show self-renewal capabilities in adult life. The hyper-responsiveness of NKG2A⁺ Vδ2 T cells is counterbalanced by the inhibitory signaling delivered by human leukocyte antigen E (HLA-E) expressed on malignant cells as a tumor-escape mechanism. However, either masking or knocking out NKG2A restores the capacity of Vδ2 T cells to exert the highest effector functions even against HLA-E⁺ tumors. This is highly relevant in the clinic, as the different degrees of engagement of the NKG2A-HLA-E checkpoint in hepatocellular carcinoma, glioblastoma, and non-small cell lung cancer directly impact patients' overall survival. These findings open avenues for developing combined cellular and immunologic anticancer therapies.

Single-cell transcriptomic landscape reveals tumor specific innate lymphoid cells associated with colorectal cancer progression

Innate lymphoid cells (ILCs) are tissue-resident lymphocytes differing from conventional T lymphocytes in having no antigen-specific receptors. ILCs include natural killer (NK) cells, helper-like ILC1s, ILC2s, and ILC3s, and lymphoid tissue-inducer (LTi) cells. Tumor ILCs are frequently found in various cancers, but their roles in cancer immunity and immunotherapy remain largely unclear. We report here the single-cell characterization of blood and gut helper-like ILC subsets in healthy conditions and in colorectal cancer (CRC). The healthy gut contains ILC1s, ILC3s, and ILC3/NKs, but no ILC2s. Additional tumor-specific ILC1-like and ILC2 subsets were identified in CRC patients. Signaling lymphocytic activation molecule family member 1 (SLAMF1) was found to be selectively expressed on tumor-specific ILCs, and higher levels of SLAMF1⁺ ILCs were observed in the blood of CRC patients. The SLAMF1-high group of CRC patients had a significantly higher survival rate than the SLAMF1-low group, suggesting that SLAMF1 is an anti-tumor biomarker in CRC.

Healthy gut contains ILC1s, ILC3s, and ILC3/NKs, but no ILC2s

Blood and tumor ILCs from CRC patients have unique transcriptomic features

Tumor tissue from CRC patients contains a tumor specific ILC1-like subset and ILC2s

SLAMF1 is identified as an anti-tumor biomarker in CRC

Blockade of the co-inhibitory molecule PD-1 unleashes ILC2-dependent antitumor immunity in melanoma

Group 2 innate lymphoid cells (ILC2s) are essential to maintain tissue homeostasis. In cancer, ILC2s can harbor both pro-tumorigenic and anti-tumorigenic functions, but we know little about their underlying mechanisms or whether they could be clinically relevant or targeted to improve patient outcomes. Here, we found that high ILC2 infiltration in human melanoma was associated with a good clinical prognosis. ILC2s are critical producers of the cytokine granulocyte-macrophage colony-stimulating factor, which coordinates the recruitment and activation of eosinophils to enhance antitumor responses. Tumor-infiltrating ILC2s expressed programmed cell death protein-1, which limited their intratumoral accumulation, proliferation and antitumor effector functions. This inhibition could be overcome in vivo by combining interleukin-33-driven ILC2 activation with programmed cell death protein-1 blockade to significantly increase antitumor responses. Together, our results identified ILC2s as a critical immune cell type involved in melanoma immunity and revealed a potential synergistic approach to harness ILC2 function for antitumor immunotherapies.

Natural killer cell engagers in cancer immunotherapy: Next generation of immuno-oncology treatments

Immuno-oncology is revolutionizing the treatment of cancers, by inducing the recognition and elimination of tumor cells by the immune system. Recent advances have focused on generating or unleashing tumor antigen-specific T-cell responses, leading to alternative treatment paradigms for many cancers. Despite these successes, the clinical benefit has been limited to a subset of patients and certain tumor types, highlighting the need for alternative strategies. One innovative approach is to broaden and amplify antitumoral immune responses by targeting innate immunity. Particularly, the aim has been to develop new antibody formats capable of stimulating the antitumor activity of innate immune cells, boosting not only their direct role in tumor elimination, but also their function in eliciting multicellular immune responses ultimately resulting in long-lasting tumor control by adaptive immunity. This review covers the development of a new class of synthetic molecules, natural killer cell engagers (NKCEs), which are built from fragments of monoclonal antibodies (mAbs) and are designed to harness the immune functions of NK cells in cancer. As currently shown in preclinical studies and clinical trials, NKCEs are promising candidates for the next generation of tumor immunotherapies.

Combination blockade of KLRG1 and PD-1 promotes immune control of local and disseminated cancers

Checkpoint blockade therapy is effective against many cancers; however, new targets need to be identified to treat patients who do not respond to current treatment or demonstrate immune escape. Here, we showed that blocking the inhibitory receptor Killer cell lectin-like receptor G1 (KLRG1) enhances anti-tumor immunity mediated by NK cells and CD8⁺ T cells. We found that loss of KLRG1 signaling alone significantly decreased melanoma and breast cancer tumor growth in the lungs of mice. In addition, we demonstrated that KLRG1 blockade can synergize with PD-1 checkpoint therapy to increase the therapeutic efficacy compared to either treatment alone. This effect was even observed with tumors that do not respond to PD-1 checkpoint therapy. Double blockade therapy led to significantly decreased tumor size, increased frequency and activation of CD8⁺ T cells, and increased NK cell frequency and maturation in the tumor microenvironment. These findings demonstrate that KLRG1 is a novel checkpoint inhibitor target that affects NK and T cell anti-tumor immunity, both alone and in conjunction with established immunotherapies.

ILC3s control splenic cDC homeostasis via lymphotoxin signaling

The spleen contains a myriad of conventional dendritic cell (cDC) subsets that protect against systemic pathogen dissemination by bridging antigen detection to the induction of adaptive immunity. How cDC subsets differentiate in the splenic environment is poorly understood. Here, we report that LTα1β2-expressing Rorgt+ ILC3s, together with B cells, control the splenic cDC niche size and the terminal differentiation of Sirpα+CD4+Esam+ cDC2s, independently of the microbiota and of bone marrow pre-cDC output. Whereas the size of the splenic cDC niche depended on lymphotoxin signaling only during a restricted time frame, the homeostasis of Sirpα+CD4+Esam+ cDC2s required continuous lymphotoxin input. This latter property made Sirpα+CD4+Esam+ cDC2s uniquely susceptible to pharmacological interventions with LTβR agonists and antagonists and to ILC reconstitution strategies. Together, our findings demonstrate that LTα1β2-expressing Rorgt+ ILC3s drive splenic cDC differentiation and highlight the critical role of ILC3s as perpetual regulators of lymphoid tissue homeostasis.

Campylobacter infection promotes IFNγ-dependent intestinal pathology via ILC3 to ILC1 conversion

Innate lymphoid cells (ILCs) are a heterogeneous family of immune regulators that protect against mucosal pathogens but can also promote intestinal pathology. Although the plasticity between ILCs populations has been described, the role of mucosal pathogens in inducing ILC conversion leading to intestinal pathology remains unclear. Here we demonstrate that IFNγ-producing ILCs are responsible for promoting intestinal pathology in a mouse model of enterocolitis caused by Campylobacter jejuni, a common human enteric pathogen. Phenotypic analysis revealed a distinct population of IFNγ-producing NK1.1^-T-bet⁺ILCs that accumulated in the intestine of C. jejuni-infected mice. Adoptive transfer experiments demonstrated their capacity to promote intestinal pathology. Inactivation of T-bet in NKp46⁺ ILCs ameliorated disease. Transcriptome analysis and cell-fate mapping experiments revealed that IFNγ-producing NK1.1^-ILCs correspond to ILC1 profile and develop from RORγt⁺ progenitors. Collectively, we identified a distinct population of NK1.1^-ex-ILC3s that promotes intestinal pathology through IFNγ production in response to C. jejuni infection.

Innate lymphoid cell recovery and occurrence of GvHD after hematopoietic stem cell transplantation

Lymphocytes are essential for microbial immunity, tumor surveillance, and tissue homeostasis. However, the in vivo development and function of helper-like innate lymphoid cells (ILCs) in humans remain much less well understood than those of T, B, and NK cells. We monitored hematopoietic stem cell transplantation (HSCT) to determine the kinetics of ILC development in both children and adults. It was found that, unlike NK cells, helper-like ILCs recovered slowly, mirroring the pattern observed for T cells, with normalization achieved at 1 year. The type of graft and the proportion of CD34⁺ cells in the graft did not significantly affect ILC reconstitution. As HSCT is often complicated by acute or chronic graft-versus-host disease (GVHD), the potential role of ILC subsets in maintaining tissue integrity in these conditions was also analyzed. It was found that GVHD was associated with lower levels of activated and gut-homing NKp44⁺ ILCP, consistent with a non-redundant role of this ILC subset in preventing this life-threatening disorder in lymphopenic conditions.

Complement cascade in severe forms of COVID-19: Recent advances in therapy

The complement system is an essential component of the innate immune system. The three complement pathways (classical, lectin, alternative) are directly or indirectly activated by the SARS‐CoV‐2 (severe acute respiratory syndrome coronavirus 2). In the most severe forms of COVID‐19, overactivation of the complement system may contribute to the cytokine storm, endothelial inflammation (endotheliitis) and thrombosis. No antiviral drug has yet been shown to be effective in COVID‐19. Therefore, immunotherapies represent a promising therapeutic in the immunopathological phase (following the viral phase) of the disease. Complement blockade, mostly C5a‐C5aR axis blockade, may prevent acute respiratory distress syndrome (ARDS) from worsening or progression to death. Clinical trials are underway.

Liver type 1 innate lymphoid cells develop locally via an interferon-γ-dependent loop

The pathways that lead to the development of tissue-resident lymphocytes, including liver type 1 innate lymphoid cells (ILC1s), remain unclear. We show here that the adult mouse liver contains Lin-Sca-1+Mac-1+ hematopoietic stem cells derived from the fetal liver. This population includes Lin-CD122+CD49a+ progenitors that can generate liver ILC1s but not conventional natural killer cells. Interferon-γ (IFN-γ) production by the liver ILC1s themselves promotes the development of these cells in situ, through effects on their IFN-γR+ liver progenitors. Thus, an IFN-γ-dependent loop drives liver ILC1 development in situ, highlighting the contribution of extramedullary hematopoiesis to regional immune composition within the liver.

Maternal diesel particle exposure promotes offspring asthma through NK cell-derived granzyme B

Mothers living near high-traffic roads before or during pregnancy are more likely to have children with asthma. Mechanisms are unknown. Using a mouse model, here we showed that maternal exposure to diesel exhaust particles (DEP) predisposed offspring to allergic airway disease (AAD, murine counterpart of human asthma) through programming of their NK cells; predisposition to AAD did not develop in DEP pups that lacked NK cells and was induced in normal pups receiving NK cells from WT DEP pups. DEP NK cells expressed GATA3 and cosecreted IL-13 and the killer protease granzyme B in response to allergen challenge. Extracellular granzyme B did not kill, but instead stimulated protease-activated receptor 2 (PAR2) to cooperate with IL-13 in the induction of IL-25 in airway epithelial cells. Through loss-of-function and reconstitution experiments in pups, we showed that NK cells and granzyme B were required for IL-25 induction and activation of the type 2 immune response and that IL-25 mediated NK cell effects on type 2 response and AAD. Finally, experiments using human cord blood and airway epithelial cells suggested that DEP might induce an identical pathway in humans. Collectively, we describe an NK cell-dependent endotype of AAD that emerged in early life as a result of maternal exposure to DEP.

NK cell-derived GM-CSF potentiates inflammatory arthritis and is negatively regulated by CIS

Despite increasing recognition of the importance of GM-CSF in autoimmune disease, it remains unclear how GM-CSF is regulated at sites of tissue inflammation. Using GM-CSF fate reporter mice, we show that synovial NK cells produce GM-CSF in autoantibody-mediated inflammatory arthritis. Synovial NK cells promote a neutrophilic inflammatory cell infiltrate, and persistent arthritis, via GM-CSF production, as deletion of NK cells, or specific ablation of GM-CSF production in NK cells, abrogated disease. Synovial NK cell production of GM-CSF is IL-18–dependent. Furthermore, we show that cytokine-inducible SH2-containing protein (CIS) is crucial in limiting GM-CSF signaling not only during inflammatory arthritis but also in experimental allergic encephalomyelitis (EAE), a murine model of multiple sclerosis. Thus, a cellular cascade of synovial macrophages, NK cells, and neutrophils mediates persistent joint inflammation via production of IL-18 and GM-CSF. Endogenous CIS provides a key brake on signaling through the GM-CSF receptor. These findings shed new light on GM-CSF biology in sterile tissue inflammation and identify several potential therapeutic targets.

Tumor-Infiltrating Natural Killer Cells

Because of their potent antitumor activity and their proinflammatory role, natural killer (NK) cells are at the forefront of efforts to develop immuno-oncologic treatments. NK cells participate in immune responses to tumors by killing target cells and producing cytokines. However, in the immunosuppressive tumor microenvironment, NK cells become dysfunctional through exposure to inhibitory molecules produced by cancer cells, leading to tumor escape. We provide an overview of what is known about NK tumor infiltration and surveillance and about the mechanisms by which NK cells become dysfunctional. SIGNIFICANCE: The functions of tumor-infiltrating NK cells may be impaired. This review aims to describe the various mechanisms by which tumors alter NK-cell functions.

Association of COVID-19 inflammation with activation of the C5a-C5aR1 axis

Coronavirus disease 2019 (COVID-19) is a disease caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has resulted in a pandemic1. The C5a complement factor and its receptor C5aR1 (also known as CD88) have a key role in the initiation and maintenance of several inflammatory responses by recruiting and activating neutrophils and monocytes1. Here we provide a longitudinal analysis of immune responses, including phenotypic analyses of immune cells and assessments of the soluble factors that are present in the blood and bronchoalveolar lavage fluid of patients at various stages of COVID-19 severity, including those who were paucisymptomatic or had pneumonia or acute respiratory distress syndrome. The levels of soluble C5a were increased in proportion to the severity of COVID-19 and high expression levels of C5aR1 receptors were found in blood and pulmonary myeloid cells, which supports a role for the C5a-C5aR1 axis in the pathophysiology of acute respiratory distress syndrome. Anti-C5aR1 therapeutic monoclonal antibodies prevented the C5a-mediated recruitment and activation of human myeloid cells, and inhibited acute lung injury in human C5aR1 knock-in mice. These results suggest that blockade of the C5a-C5aR1 axis could be used to limit the infiltration of myeloid cells in damaged organs and prevent the excessive lung inflammation and endothelialitis that are associated with acute respiratory distress syndrome in patients with COVID-19.

The Innate Part of the Adaptive Immune System

The innate immune response provides a first line of defense against common microorganisms and, for more complex and/or recurring situations where pathogens must be eliminated, an adaptive immune response has emerged and evolved to provide better protection against subsequent infections. However, such dichotomy has to be reevaluated because innate B cells (e.g., B1 and marginal zone B cells) and the newly described innate lymphoid cells (iLC) have been found to exhibit innate-like properties, such as antigen internalization, regulatory B cell functions, and helper T cell activities. In addition, the production and function of natural antibodies (nAbs) by innate B cells and their capacity to activate the classical complement pathway constitute additional important mechanisms at the junction of innate and adaptive immunity as well as the recent integration of platelets into the innate immune spectrum. There is no doubt that these mechanisms present an advantage in immunity and homeostasis particularly during the first years of life, but arguments are arising to consider that these precursors may have detrimental effects in a variety of autoimmune/inflammatory diseases, allergies and cancers, as well as in response to immunotherapy. Accordingly, and as presented in this special issue of Clinical Reviews in Allergy and Immunology, a better comprehension of the key molecular and cellular actors implicated at the crossroads of the innate and adaptive immune response represents a new challenge in our understanding of the immunological and immunopathological responses.

Natural killers or ILC1s? That is the question

Group 1 innate lymphoid cells (ILCs) comprise the natural killer (NK) cells and ILC1s. Both cells co-exist in peripheral tissues and despite effort to characterize the molecular identity and developmental pathways of ILC1s, their relationship with NK cells remains elusive. ILC1s and NK cells share many common features and analysis of ILC1s in tissues revealed a great heterogeneity and distinct transcriptional requirement of each ILC1 subsets complexifying the organization of this group. Here, we discuss whether ILC1 and NK cells can be considered as distinct lineages based on their origin, location, phenotype or transcriptional regulation. Discrimination of NK cells and ILC1s represent an important challenge to unravel the individual functions of these cells during infection and tumor immunosurveillance.

Blocking Antibodies Targeting the CD39/CD73 Immunosuppressive Pathway Unleash Immune Responses in Combination Cancer Therapies

Immune checkpoint inhibitors have revolutionized cancer treatment. However, many cancers are resistant to ICIs, and the targeting of additional inhibitory signals is crucial for limiting tumor evasion. The production of adenosine via the sequential activity of CD39 and CD73 ectoenzymes participates to the generation of an immunosuppressive tumor microenvironment. In order to disrupt the adenosine pathway, we generated two antibodies, IPH5201 and IPH5301, targeting human membrane-associated and soluble forms of CD39 and CD73, respectively, and efficiently blocking the hydrolysis of immunogenic ATP into immunosuppressive adenosine. These antibodies promoted antitumor immunity by stimulating dendritic cells and macrophages and by restoring the activation of T cells isolated from cancer patients. In a human CD39 knockin mouse preclinical model, IPH5201 increased the anti-tumor activity of the ATP-inducing chemotherapeutic drug oxaliplatin. These results support the use of anti-CD39 and anti-CD73 monoclonal antibodies and their combination with immune checkpoint inhibitors and chemotherapies in cancer.

Role of the KLRG1 pathway during the immune response to cancer

Immunotherapy drugs targeting T cells have been successfully developed for a variety of different cancers. In contrast, comparably less work has been done on targeting natural killer (NK) cells for immunotherapy. NK cells are intriguing targets for a number of different reasons, including their cytotoxic abilities and relatively lower autoimmunity risks. Thus, treatments that target NK cells, either alone or in conjunction with T cells, should be explored for the development of new treatments. One of the most well-known immunotherapy targets, programmed death-1 (PD-1) has recently been implicated in modulating NK cell function in cancer and demonstrates that targeting NK cells is an important aspect of cancer treatment. In addition to PD-1, there are many checkpoint molecules that may be capable of impacting NK cell function. One such target is KLRG1, a well conserved C-type lectin inhibitory receptor expressed on NK cells, which contains an ITIM in its cytoplasmic domain. To determine the role of KLRG1, and expand on the role of PD-1, as potential NK cell checkpoints, we developed a series of mice deficient for KLRG1 and PD-1, and took advantage of the NK sensitive cancer model B16. Following administration of B16-E-cadherin, we found that KLRG1 deficient animals had significantly fewer tumors in the lung tissue, compared to wild type controls. In addition, B16-E-cadherin resulted in a higher number of tumors in wild-type mice, compared to the parental B16 cell line. Altogether, these data suggest that KLRG1 is a checkpoint target candidate.

Inflammation-induced lactate leads to the rapid loss of hepatic tissue resident NK cells

The liver harbors two main innate lymphoid cell (ILC) populations, conventional NK (cNK) cells and tissue-resident NK (trNK) cells also called ILC1s. While the antiviral functions of cNK cells have been well established, trNK cell functions are only beginning to be uncovered. Using the MCMV model of infection, we found that in contrast to liver cNK cells, the trNK cell population initially undergoes a contraction phase prior to a recovery phase to homeostatic levels. The rapid contraction phase is due to apoptosis, while the recovery phase occurs via proliferation in situ. Liver trNK cell apoptosis is not mediated by fratricide, liver lymphocytes, or inflammatory cytokines. Instead, we found that liver trNK cell apoptosis is the consequence of an increased sensitivity to lactic acid. Interestingly, MCMV infection lead to an increase of lactate in the liver, which was supported by changes in lactate dehydrogenase expression. Mechanistic analysis indicates that trNK cell sensitivity to lactate is linked to impaired mitochondrial functions. These findings underscore the unique properties of the liver resident NK cell compartment.