Distinct mechanisms of tumor resistance to NK killing: of mice and men

Basic immunologic study as a foundation for engineered therapeutic development

Bioengineering and drug delivery technologies play an important role in bridging the gap between basic scientific discovery and clinical application of therapeutics. To identify the optimal treatment, the most critical stage is to diagnose the problem. Often these two may occur simultaneously or in parallel, but in this review, we focus on bottom-up approaches in understanding basic immunologic phenomena to develop targeted therapeutics. This can be observed in several fields; here, we will focus on one of the original immunotherapy targets-cancer-and one of the more recent targets-regenerative medicine. By understanding how our immune system responds in processes such as malignancies, wound healing, and medical device implantation, we can isolate therapeutic targets for pharmacologic and bioengineered interventions.

Challenges and opportunities in the islet transplantation microenvironment: a comprehensive summary of inflammatory cytokine, immune cells, and vascular endothelial cells

It is now understood that islet transplantation serves as a β-cell replacement therapy for type 1 diabetes. Many factors impact the survival of transplanted islets, especially those related to the microenvironment. This review explored microenvironmental components, including vascular endothelial cells, inflammatory cytokines, and immune cells, and their profound effects on post-islet transplantation survival rates. Furthermore, it revealed therapeutic strategies aimed at targeting these elements. Current evidence suggests that vascular endothelial cells are pivotal in facilitating vascularization and nutrient supply and establishing a new microcirculation network for transplanted islets. Consequently, preserving the functionality of vascular endothelial cells emerges as a crucial strategy to enhance the survival of islet transplantation. Release of cytokines will lead to activation of immune cells and production and release of further cytokines. While immune cells hold undeniable significance in regulating immune responses, their activation can result in rejection reactions. Thus, establishing immunological tolerance within the recipient's body is essential for sustaining graft functionality. Indeed, future research endeavors should be directed toward developing precise strategies for modulating the microenvironment to achieve higher survival rates and more sustained transplantation outcomes. While acknowledging certain limitations inherent to this review, it provides valuable insights that can guide further exploration in the field of islet transplantation. In conclusion, the microenvironment plays a paramount role in islet transplantation. Importantly, we discuss novel perspectives that could lead to broader clinical applications and improved patient outcomes in islet transplantation.

Expression of CISH, an Inhibitor of NK Cell Function, Increases in Association with Ovarian Cancer Development and Progression

Epithelial ovarian cancer (OVCA), a fatal malignancy of women, disseminates locally. Although NK cells mount immune responses against OVCA, tumors inhibit NK cells, and the mechanism is not well understood. Cytokines stimulate NK cells; however, chronic stimulation exhausts them and induces expression of cytokine-inducible SH2-containing protein (CISH). Tumors produce anti-inflammatory cytokine interleukin (IL)-10 which may induce NK cell exhaustion. The goal of this study was to examine if CISH expression in NK cells increases during OVCA development and to determine the mechanism(s) of OVCA-induced CISH expression in NK cells. Normal ovaries (n = 7) were used for CISH, IL-10 and GRP78 expression. In tumor ovaries, CISH was examined in early and late stages (n = 14 each, all subtypes) while IL-10 and GRP78 expression were examined in early and late stage HGSC (n = 5 each). Compared to normal, the population of CISH-expressing NK cells increased and the intensity of IL-10 and GRP78 expression was significantly higher in OVCA (p < 0.05). CISH expression was positively correlated with IL-10 expression (r = 0.52, r = 0.65, p < 0.05 at early and late stages, respectively) while IL-10 expression was positively correlated with GRP78 expression (r = 0.43, r = 0.52, p < 0.05, respectively). These results suggest that OVCA development and progression are associated with increased CISH expression by NK cells which is correlated with tumor-induced persistent cellular stress.

Investigating the susceptibility of treatment-resistant oesophageal tumours to natural killer cell-mediated responses

The majority of oesophageal adenocarcinoma (OAC) patients do not respond to multimodal treatment regimens and face dismal survival rates. Natural killer (NK) cells are crucial anti-tumour immune cells, and this study investigated the susceptibility of treatment-resistant OAC cells to these potent tumour killers. Natural killer receptor (NKR) ligand expression by OE33CisP (cisplatin-sensitive) and OE33CisR (cisplatin-resistant) cells was investigated. The immunomodulatory effects of OE33CisP and OE33CisR cells on NK cell phenotype and function were assessed. Finally, the impact of chemotherapy regimens on NKR ligand shedding was examined. Our data revealed significantly less surface expression of activating ligands B7-H6, MICA/B, ULBP-3 and activating/inhibitory ligands PVRL-1 and PVRL-4 by OE33CisR cells, compared to OE33CisP cells. Co-culture with OE33CisR cells reduced the frequencies of NKp30⁺ and NKp46⁺ NK cells and increased frequencies of TIGIT⁺, FasL⁺ and TRAIL⁺ NK cells. Frequencies of IFN-γ-producing NK cells increased while frequencies of TIM-3⁺ NK cells decreased after culture with OE33CisP and OE33CisR cells. Frequencies of circulating NKp30⁺ NK cells were significantly lower in OAC patients with the poorest treatment response and in patients who received FLOT chemotherapy, while B7-H6 shedding by OAC tumour cells was induced by FLOT. Overall, OE33CisR cells express less activating NKR ligands than OE33CisP cells and have differential effects on NKR expression by NK cells. However, neither cell line significantly dampened NK cell cytokine production, death receptor expression or degranulation. In addition, our data indicate that FLOT chemotherapy may promote B7-H6 shedding and immune evasion with detrimental consequences in OAC patients.

Extracellular vesicle-mediated communication between hepatocytes and natural killer cells promotes hepatocellular tumorigenesis

Hepatocellular carcinoma (HCC) is frequently characterized by metabolic and immune remodeling in the tumor microenvironment. We previously discovered that liver-specific deletion of fructose-1, 6-bisphosphatase 1 (FBP1), a gluconeogenic enzyme ubiquitously suppressed in HCC tissues, promotes liver tumorigenesis and induces metabolic and immune perturbations closely resembling human HCC. However, the underlying mechanisms remain incompletely understood. Here, we reported that FBP1-deficient livers exhibit diminished amounts of natural killer (NK) cells and accelerated tumorigenesis. Using the diethylnitrosamine-induced HCC mouse model, we analyzed potential changes in the immune cell populations purified from control and FBP1-depleted livers and found that NK cells were strongly suppressed. Mechanistically, FBP1 attenuation in hepatocytes derepresses an zeste homolog 2 (EZH2)-dependent transcriptional program to inhibit PKLR expression. This leads to reduced levels of PKLR cargo proteins sorted into hepatocyte-derived extracellular vesicles (EVs), dampened activity of EV-targeted NK cells, and accelerated liver tumorigenesis. Our study demonstrated that hepatic FBP1 depletion promotes HCC-associated immune remodeling, partly through the transfer of hepatocyte-secreted, PKLR-attenuated EVs to NK cells.

NK Cells in Myeloproliferative Neoplasms (MPN)

Simple Summary

NK cells are important innate immune effectors that contribute substantially to tumor control, however the role of NK cells in haematological cancers is not as well understood. The aim of this review is to highlight the importance of the role of NK cells in the management of Ph+ Myeloproliferative Neoplasms, and emphasize the need and possible benefits of a more in-depth investigation into their role in classical MPNs and show potential strategies to harness the anti-tumoral capacities of NK cells.

Abstract

Myeloproliferative neoplasms (MPNs) comprise a heterogenous group of hematologic neoplasms which are divided into Philadelphia positive (Ph+), and Philadelphia negative (Ph−) or classical MPNs. A variety of immunological factors including inflammatory, as well as immunomodulatory processes, closely interact with the disease phenotypes in MPNs. NK cells are important innate immune effectors and substantially contribute to tumor control. Changes to the absolute and proportionate numbers of NK cell, as well as phenotypical and functional alterations are seen in MPNs. In addition to the disease itself, a variety of therapeutic options in MPNs may modify NK cell characteristics. Reports of suppressive effects of MPN treatment strategies on NK cell activity have led to intensive investigations into the respective compounds, to elucidate the possible negative effects of MPN therapy on control of the leukemic clones. We hereby review the available literature on NK cells in Ph+ and Ph− MPNs and summarize today’s knowledge on disease-related alterations in this cell compartment with particular focus on known therapy-associated changes. Furthermore, we critically evaluate conflicting data with possible implications for future projects. We also aim to highlight the relevance of full NK cell functionality for disease control in MPNs and the importance of considering specific changes related to therapy in order to avoid suppressive effects on immune surveillance.

Mass Production of Highly Active NK Cells for Cancer Immunotherapy in a GMP Conform Perfusion Bioreactor

NK cells have emerged as promising candidates for cancer immunotherapy, especially due to their ability to fight circulating tumor cells thereby preventing metastases formation. Hence several studies have been performed to generate and expand highly cytotoxic NK cells ex vivo, e.g., by using specific cytokines to upregulate both their proliferation and surface expression of distinct activating receptors. Apart from an enhanced activity, application of NK cells as immunotherapeutic agent further requires sufficient cell numbers and a high purity. All these parameters depend on a variety of different factors including the starting material, additives like cytokines as well as the culture system. Here we analyzed PBMC-derived NK cells of five anonymized healthy donors expanded under specific conditions in an innovative perfusion bioreactor system with respect to their phenotype, IFNγ production, and cytotoxicity in vitro. Important features of the meander type bioreactors used here are a directed laminar flow of medium and control of relevant process parameters. Cells are cultivated under "steady state" conditions in perfusion mode. Our data demonstrate that expansion of CD3⁺ T cell depleted PBMCs in our standardized system generates massive amounts of highly pure (>85%) and potent anti-cancer active NK cells. These cells express a variety of important receptors driving NK cell recruitment, adhesion as well as activation. More specifically, they express the chemokine receptors CXCR3, CXCR4, and CCR7, the adhesion molecules L-selectin, LFA-1, and VLA-4, the activating receptors NKp30, NKp44, NKp46, NKG2D, DNAM1, and CD16 as well as the death ligands TRAIL and Fas-L. Moreover, the generated NK cells show a strong IFNγ expression upon cultivation with K562 tumor cells and demonstrate a high cytotoxicity toward leukemic as well as solid tumor cell lines in vitro. Altogether, these characteristics promise a high clinical potency of thus produced NK cells awaiting further evaluation.

Immunological aspects of allogeneic pancreatic islet transplantation: a comparison between mouse and human

Pancreatic islet allotransplantation is a treatment for patients with severe forms of type 1 diabetes. As long-term graft function and survival are not yet optimal, additional studies are warranted in order to continue improving transplant outcomes. The mechanisms of islet graft loss and tolerance induction are often studied in murine diabetes models. Despite numerous islet transplantation studies successfully performed over recent years, translation from experimental mouse models to human clinical application remains elusive. This review aims at critically discussing the strengths and limitations of current mouse models of diabetes and experimental islet transplantation. In particular, we will analyze the causes leading to diabetes and compare the immunological mechanisms responsible for rejection between mouse and human. A better understanding of the experimental mouse models should facilitate translation to human clinical application.

T-cell epitope strength in WAP-T mouse mammary carcinomas is an important determinant in PD1/PD-L1 immune checkpoint blockade therapy

Using the SV40 transgenic WAP-T/WAP-T_NP mouse models for mammary carcinomas, we compared the response to immune checkpoint blockade therapy in tumor mice expressing either SV40 T-antigen containing the LCMV NP-epitope (T-Ag_NP in WAP-T_NP mice), or the unmodified T-antigen (T-Ag in WAP-T mice). Specifically, we asked, whether the presence of the highly immunogenic NP-epitope in T-Ag_NP influences this response in comparison to the weakly immunogenic T-cell epitopes of T-Ag in WAP-T tumor mice. Treatment of WAP-T_NP tumor mice with either anti-PD1 or anti-PD-L1 antibodies led to tumor regression, with anti-PD-L1 treatment being more effective. However, tumors had fully re-appeared after 21 days, indicating that CTL exhaustion had been rapidly re-established. Surprisingly, the same treatment applied to WAP-T tumor mice resulted in a significantly prolonged period of tumor regression. We provide evidence that in contrast to the weak antigenic stimuli exerted by T-cell epitopes of T-Ag, the strong antigenic stimulus of the NP-epitope in T-Ag_NP has a dual effect: (i) a rapid generation of active NP-specific CTLs, accompanied (ii) by accelerated CTL exhaustion. Our data support the hypothesis that the immunogenicity of tumor antigen T-cell epitopes strongly influences the success of immune checkpoint blockade therapy.

Soluble NKG2D ligands in the ovarian cancer microenvironment are associated with an adverse clinical outcome and decreased memory effector T cells independent of NKG2D downregulation

The immune receptor NKG2D is predominantly expressed on NK cells and T cell subsets and confers anti-tumor activity. According to the current paradigm, immune surveillance is counteracted by soluble ligands shed into the microenvironment, which down-regulate NKG2D receptor expression. Here, we analyzed the clinical significance of the soluble NKG2D ligands sMICA and sULBP2 in the malignancy-associated ascites of ovarian cancer. We show that high levels of sMICA and sULBP2 in ascites were associated with a poor prognosis. Ascites inhibited the activation of normal NK cells, which, in contrast to the prevailing notion, was not associated with decreased NKG2D expression. Of note, an inverse correlation of soluble NKG2D ligands with effector memory T cells and a direct correlation with pro-tumorigenic CD163⁺CD206⁺ macrophages was observed. Thus, the role of soluble NKG2D ligands within the ovarian cancer microenvironment is more complex than anticipated and does not exclusively function via NKG2D downregulation.

Silencing NKG2D ligand-targeting miRNAs enhances natural killer cell-mediated cytotoxicity in breast cancer

NKG2D is one of the major activating receptors of natural killer (NK) cells and binds to several ligands (NKG2DLs). NKG2DLs are expressed on malignant cells and sensitize them to early elimination by cytotoxic lymphocytes. We investigated the clinical importance of NKG2DLs and the mechanism of NKG2DL regulation in breast cancer (BC). Among the NKG2DLs MICA/B and ULBP1/2/3, the expression levels of MICA/B in BC tissues were inversely associated with the Tumor Node Metastasis stage. We first found that the high expression of MICB, but not MICA, was an independent prognostic factor for overall survival in patients with BC. Investigation into the mechanism revealed that a group of microRNAs (miRNAs) belonging to the miR-17-92 cluster, especially miR-20a, decreased the expression of ULBP2 and MICA/B. These miRNAs downregulated the expression of MICA/B by targeting the MICA/B 3'-untranslated region and downregulated ULBP2 by inhibiting the MAPK/ERK signaling pathway. Functional analysis showed that the silencing of NKG2DL-targeting miRNAs in BC cells increased NK cell-mediated cytotoxicity in vitro and inhibited immune escape in vivo. In addition, histone deacetylase inhibitors (HDACis) increased NKG2DL expression in BC cells by inhibiting members of the miR-17-92 cluster. Thus, targeting miRNAs with antisense inhibitors or HDACis may represent a novel approach for increasing the immunogenicity of BC.

Dynamics of the spleen and its significance in a murine H22 orthotopic hepatoma model

The dynamics of the spleen during tumor progression remains incompletely understood. In this study, we established a murine H22 orthotopic hepatoma model and dynamically detected alterations in the percentages of immunocytes in the spleen. We observed a prominent myeloid-derived suppressor cell (MDSC) accumulation during the early response which persisted through all the stages of tumor growth. In addition, the percentage of regulatory T cells (Tregs) increased by week 2. Although the percentage of CD3(+)CD49b(+) natural killer T (NKT) cells increased by day 3, and that of CD3(+)CD4(+) T cells slightly increased by week 1, they decreased to either normal or lower levels compared with those of normal mice. The percentages of total CD3(+), CD3(+)CD4(+), and CD3(+)CD8(+) T cells decreased by week 2, and that of NK cells decreased by week 3. The activation of non-Treg CD4(+) T cells was scarce. Moreover, splenic MDSCs of tumor-bearing mice suppressed the activation of splenocytes. Therefore, a negative immune response gradually prevailed over a positive immune response during tumor growth. In addition, splenectomy was performed at the time of tumor inoculation, and we found that splenectomy could prolong the survival time, reduce the tumor weights, decrease the ascites volumes, and ameliorate the immune status of the tumor-bearing mice. Splenectomy also decreased the percentage of MDSCs and increased the percentages of CD8(+) T cells, NK, and NKT cells in tumor tissues. Additionally, splenectomy decreased the percentage of MDSCs and increased that of CD8(+) T cells in peripheral blood. Overall, our findings suggest that immune-negative cells are dominant in the spleen during tumor progression. Splenectomy could be helpful to improve the immune responses of tumor-bearing hosts.

Human cancer cells with stem cell-like phenotype exhibit enhanced sensitivity to the cytotoxicity of IL-2 and IL-15 activated natural killer cells

Tumors harbor a population of cancer stem cells (CSCs) which can drive tumor progression and therapeutical resistance. Nature killer (NK) cells are best known for their ability to directly recognize and kill malignant cells. However, the susceptibility of cancer stem cells to NK cells is not fully understood. Here we demonstrated that human CD44+CD24- breast CSCs were shown enhanced sensitivity to IL-2 and IL-15 activated NK cells. CD44+CD24- CSCs expressed higher levels of NKG2D ligands ULBP1, ULBP2 and MICA. Blockade assay showed that the sensitivity of CSCs to NK cells-mediated lysis was mainly dependent on NKG2D. Furthermore, redox oxygen species (ROS)-low tumor cells were more sensitive to NK cells. The presence of antioxidant enzymes inhibitor L-S,R-buthionine sulfoximine or H2O2 retarded the cytotoxicity of NK cells to CD44+CD24- CSCs. In addition, NK cells could readily target CD133+ colonal CSCs. Our findings provide novel targets for NK cells-based immunotherapy and are of great importance for translational medicine.

Antibody targeting soluble NKG2D ligand sMIC refuels and invigorates the endogenous immune system to fight cancer

Human tumor-derived soluble NKG2D sMIC paralyzes the immune system through multiple pathways. Targeting soluble MIC with a nonblocking sMIC-neutralizing anti-MIC antibody effectuated and revamped endogenous innate and adoptive antitumor responses. Therapy induced regression of primary tumors and eliminated metastasis in preclinical models.

Role of HLA-B associated transcript 3 in immune diseases

HLA-B associated transcript 3 (BAT3/Scythe/BAG6) is a member of the BAG protein family which can regulate the cell cycle. Recently, BAT3 has also been identified to have immunoregulatory function through kinds of mechanisms. First, BAT3 can promote the maturation of dendritic cells (DCs), the activity of macrophages and the expression of major histocompatibility complex (MHC)-Ⅱ on antigen presenting cells (APCs) to regulate chronic inflammation. Second, BAT3 can suppress T cell immunoglobulin and mucin domain 3 (Tim-3)-mediated cell death and exhaustion of T helper cell type 1 (Th1) to exacerbate autoimmune diseases. Finally, BAT3 can regulate the cytotoxicity of natural killer cells (NKs) in a NKp30-dependent manner to play a part in tumor immune evasion and tumor rejection. Further details about BAT3 and its involvement in immunity and immunity-associated diseases will benefit the novel strategy for treatment of immune diseases.