Expression of the CD80 and CD86 molecules enhances cytotoxicity by human natural killer cells

Sleeping Beauty kit sets provide rapid and accessible generation of artificial antigen-presenting cells for natural killer cell expansion

Artificial antigen-presenting cells (aAPCs) offer a cost effective and convenient tool for the expansion of chimeric antigen receptor (CAR)-bearing T cells and NK cells. aAPCs are particularly useful because of their ability to efficiently expand low-frequency antigen-reactive lymphocytes in bulk cultures. Commonly derived from the leukemic cell line K562, these aAPCs lack most major histocompatibility complex expression and are therefore useful for NK cell expansion without triggering allogeneic T-cell proliferation. To combat difficulties in accessing existing aAPC lines, while circumventing the iterative lentiviral gene transfers with antibody-mediated sorting required for the isolation of stable aAPC clones, we developed a single-step technique using Sleeping Beauty (SB)-based vectors with antibiotic selection options. Our SB vectors contain options of two to three genes encoding costimulatory molecules, membrane-bound cytokines as well as the presence of antibiotic-resistance genes that allow for stable transposition-based transfection of feeder cells. Transfection of K562 with SB vectors described in this study allows for the surface expression of CD86, 4-1BBL, membrane-bound (mb) interleukin (IL)-15 and mbIL-21 after simultaneous transposition and antibiotic selection using only two antibiotics. aAPCs successfully expanded NK cells to high purity (80-95%). Expanded NK cells could be further engineered by lentiviral CAR transduction. The multivector kit set is publicly available and will allow convenient and reproducible in-house production of effective aAPCs for the in vitro expansion of primary cells.

Transfer learning between preclinical models and human tumors identifies a conserved NK cell activation signature in anti-CTLA-4 responsive tumors

BACKGROUND

Tumor response to therapy is affected by both the cell types and the cell states present in the tumor microenvironment. This is true for many cancer treatments, including immune checkpoint inhibitors (ICIs). While it is well-established that ICIs promote T cell activation, their broader impact on other intratumoral immune cells is unclear; this information is needed to identify new mechanisms of action and improve ICI efficacy. Many preclinical studies have begun using single-cell analysis to delineate therapeutic responses in individual immune cell types within tumors. One major limitation to this approach is that therapeutic mechanisms identified in preclinical models have failed to fully translate to human disease, restraining efforts to improve ICI efficacy in translational research.

METHOD

We previously developed a computational transfer learning approach called projectR to identify shared biology between independent high-throughput single-cell RNA-sequencing (scRNA-seq) datasets. In the present study, we test this algorithm's ability to identify conserved and clinically relevant transcriptional changes in complex tumor scRNA-seq data and expand its application to the comparison of scRNA-seq datasets with additional data types such as bulk RNA-seq and mass cytometry.

RESULTS

We found a conserved signature of NK cell activation in anti-CTLA-4 responsive mouse and human tumors. In human metastatic melanoma, we found that the NK cell activation signature associates with longer overall survival and is predictive of anti-CTLA-4 (ipilimumab) response. Additional molecular approaches to confirm the computational findings demonstrated that human NK cells express CTLA-4 and bind anti-CTLA-4 antibodies independent of the antibody binding receptor (FcR) and that similar to T cells, CTLA-4 expression by NK cells is modified by cytokine-mediated and target cell-mediated NK cell activation.

CONCLUSIONS

These data demonstrate a novel application of our transfer learning approach, which was able to identify cell state transitions conserved in preclinical models and human tumors. This approach can be adapted to explore many questions in cancer therapeutics, enhance translational research, and enable better understanding and treatment of disease.

CD80 expression is upregulated by TP53 activation in human cancer epithelial cells

CD80 is recognized as one of the most potent costimulatory molecules by which immune cells limit cancer progression; however, the current understanding of the regulation of its expression on human tumor cells is limited. The TP53 tumor suppressor plays a critical role in cancer and its significant role in the control of immune responses is emerging. Here, we evaluated the role of TP53 as a regulator of CD80 expression in human cancer cells. A set of well-known TP53-reactivating compounds were used on TP53-wild-type, TP53-deficient, TP53-mutated and TP53-knockdown cancer cell lines to determine if TP53 can regulate CD80. CD80 expression was analyzed in samples from patients with TP53-active vs TP53-inactive Colon Adenocarcinomas (COAD) from TCGA panCancer Atlas. We report that the pharmacological activation of TP53 can stimulate the expression of CD80 in human tumor cells of epithelial origin. We also provide evidence that CD80 expression exhibits a strong correlation with TP53 activation in a subgroup of colon tumors with better overall survival. These results confirm the link between TP53 and immune surveillance in human cancer and provide the possibility that conventional TP53-activation approaches for tumoricidal effects may be repurposed for immunotherapy strategies.

Black Raspberries and Protocatechuic Acid Mitigate DNFB-Induced Contact Hypersensitivity by Down-Regulating Dendritic Cell Activation and Inhibiting Mediators of Effector Responses

Contact hypersensitivity (CHS) is the most common occupational dermatological disease. Dendritic cells (DCs) mediate the sensitization stage of CHS, while T-cells facilitate the effector mechanisms that drive CHS. Black raspberry (Rubus occidentalis, BRB) and BRB phytochemicals possess immunomodulatory properties, but their dietary effects on CHS are unknown. We examined the effects of diets containing BRB and protocatechuic acid (PCA, a constituent of BRB and an anthocyanin metabolite produced largely by gut microbes), on CHS, using a model induced by 2,4-dinitrofluorobenze (DNFB). Mice were fed control diet or diets supplemented with BRB or PCA. In vitro bone-marrow derived DCs and RAW264.7 macrophages were treated with BRB extract and PCA. Mice fed BRB or PCA supplemented diets displayed decreased DNFB-induced ear swelling, marked by decreased splenic DC accumulation. BRB extract diminished DC maturation associated with reduced Cd80 expression and Interleukin (IL)-12 secretion, and PCA reduced IL-12. Dietary supplementation with BRB and PCA induced differential decreases in IL-12-driven CHS mediators, including Interferon (IFN)-γ and IL-17 production by T-cells. BRB extracts and PCA directly attenuated CHS-promoting macrophage activity mediated by nitric oxide and IL-12. Our results demonstrate that BRB and PCA mitigate CHS pathology, providing a rationale for CHS alleviation via dietary supplementation with BRB or BRB derived anthocyanins.

NK Cell-Based Immune Checkpoint Inhibition

Immunotherapy, with an increasing number of therapeutic dimensions, is becoming an important mode of treatment for cancer patients. The inhibition of immune checkpoints, which are the source of immune escape for various cancers, is one such immunotherapeutic dimension. It has mainly been aimed at T cells in the past, but NK cells are a newly emerging target. Simultaneously, the number of checkpoints identified has been increasing in recent times. In addition to the classical NK cell receptors KIRs, LIRs, and NKG2A, several other immune checkpoints have also been shown to cause dysfunction of NK cells in various cancers and chronic infections. These checkpoints include the revolutionized CTLA-4, PD-1, and recently identified B7-H3, as well as LAG-3, TIGIT & CD96, TIM-3, and the most recently acknowledged checkpoint-members of the Siglecs family (Siglec-7/9), CD200 and CD47. An interesting dimension of immune checkpoints is their candidacy for dual-checkpoint inhibition, resulting in therapeutic synergism. Furthermore, the combination of immune checkpoint inhibition with other NK cell cytotoxicity restoration strategies could also strengthen its efficacy as an antitumor therapy. Here, we have undertaken a comprehensive review of the literature to date regarding NK cell-based immune checkpoints.

Comparison of the molecular and cellular phenotypes of common mouse syngeneic models with human tumors

BACKGROUND

The clinical success of immune checkpoint inhibitors demonstrates that reactivation of the human immune system delivers durable responses for some patients and represents an exciting approach for cancer treatment. An important class of preclinical in vivo models for immuno-oncology is immunocompetent mice bearing mouse syngeneic tumors. To facilitate translation of preclinical studies into human, we characterized the genomic, transcriptomic, and protein expression of a panel of ten commonly used mouse tumor cell lines grown in vitro culture as well as in vivo tumors.

RESULTS

Our studies identified a number of genetic and cellular phenotypic differences that distinguish commonly used mouse syngeneic models in our study from human cancers. Only a fraction of the somatic single nucleotide variants (SNVs) in these common mouse cell lines directly match SNVs in human actionable cancer genes. Some models derived from epithelial tumors have a more mesenchymal phenotype with relatively low T-lymphocyte infiltration compared to the corresponding human cancers. CT26, a colon tumor model, had the highest immunogenicity and was the model most responsive to CTLA4 inhibitor treatment, by contrast to the relatively low immunogenicity and response rate to checkpoint inhibitor therapies in human colon cancers.

CONCLUSIONS

The relative immunogenicity of these ten syngeneic tumors does not resemble typical human tumors derived from the same tissue of origin. By characterizing the mouse syngeneic models and comparing with their human tumor counterparts, this study contributes to a framework that may help investigators select the model most relevant to study a particular immune-oncology mechanism, and may rationalize some of the challenges associated with translating preclinical findings to clinical studies.

Expression of ligands for activating natural killer cell receptors on cell lines commonly used to assess natural killer cell function

BACKGROUND

Natural killer cell responses to virally-infected or transformed cells depend on the integration of signals received through inhibitory and activating natural killer cell receptors. Human Leukocyte Antigen null cells are used in vitro to stimulate natural killer cell activation through missing-self mechanisms. On the other hand, CEM.NKr.CCR5 cells are used to stimulate natural killer cells in an antibody dependent manner since they are resistant to direct killing by natural killer cells. Both K562 and 721.221 cell lines lack surface major histocompatibility compatibility complex class Ia ligands for inhibitory natural killer cell receptors. Previous work comparing natural killer cell stimulation by K562 and 721.221 found that they stimulated different frequencies of natural killer cell functional subsets. We hypothesized that natural killer cell function following K562, 721.221 or CEM.NKr.CCR5 stimulation reflected differences in the expression of ligands for activating natural killer cell receptors.

RESULTS

K562 expressed a higher intensity of ligands for Natural Killer G2D and the Natural Cytotoxicity Receptors, which are implicated in triggering natural killer cell cytotoxicity. 721.221 cells expressed a greater number of ligands for activating natural killer cell receptors. 721.221 expressed cluster of differentiation 48, 80 and 86 with a higher mean fluorescence intensity than did K562. The only ligands for activating receptor that were detected on CEM.NKr.CCR5 cells at a high intensity were cluster of differentiation 48, and intercellular adhesion molecule-2.

CONCLUSIONS

The ligands expressed by K562 engage natural killer cell receptors that induce cytolysis. This is consistent with the elevated contribution that the cluster of differentiation 107a function makes to total K562 induced natural killer cell functionality compared to 721.221 cells. The ligands expressed on 721.221 cells can engage a larger number of activating natural killer cell receptors, which may explain their ability to activate a larger frequency of these cells to become functional and secrete cytokines. The few ligands for activating natural killer cell receptors expressed by CEM.NKr.CCR5 may reduce their ability to activate natural killer cells in an antibody independent manner explaining their relative resistance to direct natural killer cell cytotoxicity.

Pomalidomide increases immune surface marker expression and immune recognition of oncovirus-infected cells

Most chronic viruses evade T-cell and natural killer (NK) immunity through downregulation of immune surface markers. Previously we showed that Pomalidomide (Pom) increases surface expression of major histocompatibility complex class I (MHC-I) in Kaposi sarcoma-associated herpesvirus-infected latent and lytic cells and restores ICAM-1 and B7-2 in latent cells. We explored the ability of Pom to increase immune surface marker expression in cells infected by other chronic viruses, including human T-cell leukemia virus type-1 (HTLV-1), Epstein-Barr virus (EBV), human papilloma virus (HPV), Merkel cell polyoma virus (MCV), and human immunodeficiency virus type-1 (HIV-1). Pom increased MHC-1, ICAM-1, and B7-2/CD86 in immortalized T-cell lines productively infected with HTLV-1 and also significantly increased their susceptibility to NK cell-mediated cytotoxicity. Pom enhancement of MHC-I and ICAM-1 in primary cells infected with HTLV-1 was abrogated by knockout of HTLV-1 orf-1. Pom increased expression of ICAM-1, B7-2 and MHC class I polypeptide related sequence A (MICA) surface expression in the EBV-infected Daudi cells and increased their T-cell activation and susceptibility to NK cells. Moreover, Pom increased expression of certain of these surface markers on Akata, Raji, and EBV lymphoblastic cell lines. The increased expression of immune surface markers in these virus-infected lines was generally associated with a decrease in IRF4 expression. By contrast, Pom treatment of HPV, MCV and HIV-1 infected cells did not increase these immune surface markers. Pom and related drugs may be clinically beneficial for the treatment of HTLV-1 and EBV-induced tumors by rendering infected cells more susceptible to both innate and adaptive host immune responses.

Prognostic values of the mRNA expression of natural killer receptor ligands and their association with clinicopathological features in breast cancer patients

BACKGROUND

Natural killer (NK) cells are lymphocytes of the innate immune system that have potent cytotoxic activity against tumor cells. NK cell recognition and activity towards cancer cells are regulated by an integrated interplay between numerous inhibitory and activating receptors acting in concert to eliminate tumor cells expressing cognate ligands. Despite strong evidence supporting the role of NK cells in breast cancer (BC) control, BC still develops and progresses to form large tumors and metastases. A major mechanism of BC escape from NK immunity is the alteration of the expression of NK receptor ligands. The aim of this study was to determine whether NK receptor ligands' mRNA expression might influence prognosis in BC patients and whether these effects differ by molecular subtypes and clinicopathological features.

METHODS

We used the KM plotter platform to analyze the correlation between mRNA expression of 32 NK receptor ligands and relapse-free survival (RFS) and overall survival (OS) in 3951 and 1402 BC patients, respectively. The association with tumor subtypes and clinicopathological features was determined. BC samples were split into high and low expression groups according to the best cutoff value and the two patient cohorts were compared by Kaplan-Meier survival plots. The hazard ratios with 95% confidence intervals and log rank P values were calculated and FDR-adjusted for multiple testing correction. The data was considered to be statistically significant when FDR-adjusted P value < 0.05.

RESULTS

High mRNA expression of around 80% of ligands for NK activating and inhibitory receptors associated with better RFS, which correlated with longer OS for only about half of the NK-activating ligands but for most NK-inhibitory ligands. Also, five NK-activating ligands correlated with worse prognosis. These prognostic values were differentially associated with the BC clinical criteria. In addition, the favorable prognostic influence of NK-activating ligands' upregulation, as a whole, was mainly significantly associated with HER2-positive and basal-like subtypes, lymph node positive phenotype, and high-grade tumors.

CONCLUSIONS

NK receptor ligands appear to play an important role in defining BC patient prognosis. Identification of a group of patients with worse prognosis expressing high levels of NK-activating ligands and low levels of NK-inhibitory ligands makes them ideal potential candidates for NK-based immunotherapy to eliminate residual tumor cells, prevent relapse and improve patient survival.

Dynamic Analysis of Human Natural Killer Cell Response at Single-Cell Resolution in B-Cell Non-Hodgkin Lymphoma

Natural killer (NK) cells are phenotypically and functionally diverse lymphocytes that recognize and kill cancer cells. The susceptibility of target cancer cells to NK cell-mediated cytotoxicity depends on the strength and balance of regulatory (activating/inhibitory) ligands expressed on target cell surface. We performed gene expression arrays to determine patterns of NK cell ligands associated with B-cell non-Hodgkin lymphoma (b-NHL). Microarray analyses revealed significant upregulation of a multitude of NK-activating and costimulatory ligands across varied b-NHL cell lines and primary lymphoma cells, including ULBP1, CD72, CD48, and SLAMF6. To correlate genetic signatures with functional anti-lymphoma activity, we developed a dynamic and quantitative cytotoxicity assay in an integrated microfluidic droplet generation and docking array. Individual NK cells and target lymphoma cells were co-encapsulated in picoliter-volume droplets to facilitate monitoring of transient cellular interactions and NK cell effector outcomes at single-cell level. We identified significant variability in NK-lymphoma cell contact duration, frequency, and subsequent cytolysis. Death of lymphoma cells undergoing single contact with NK cells occurred faster than cells that made multiple short contacts. NK cells also killed target cells in droplets via contact-independent mechanisms that partially relied on calcium-dependent processes and perforin secretion, but not on cytokines (interferon-γ or tumor necrosis factor-α). We extended this technique to characterize functional heterogeneity in cytolysis of primary cells from b-NHL patients. Tumor cells from two diffuse large B-cell lymphoma patients showed similar contact durations with NK cells; primary Burkitt lymphoma cells made longer contacts and were lysed at later times. We also tested the cytotoxic efficacy of NK-92, a continuously growing NK cell line being investigated as an antitumor therapy, using our droplet-based bioassay. NK-92 cells were found to be more efficient in killing b-NHL cells compared with primary NK cells, requiring shorter contacts for faster killing activity. Taken together, our combined genetic and microfluidic analysis demonstrate b-NHL cell sensitivity to NK cell-based cytotoxicity, which was associated with significant heterogeneity in the dynamic interaction at single-cell level.

Analysis of the regulatory function of natural killer cells from patients with systemic lupus erythematosus

Natural killer (NK) cells participate in the regulation of the immune response. However, the immunomodulatory function of NK cells in systemic lupus erythematosus (SLE) is not well understood. The aim of this study was to evaluate the regulatory function of NK cells in SLE patients and to identify the NK cells involved in the pathogenesis of this complex disease. We analysed the expression of NK receptors and co-stimulatory molecules in peripheral NK cells (CD3^- CD56⁺ ) from SLE patients, as well as the numbers of human leucocyte antigen D-related (HLA-DR)/CD11c⁺ NK cells. In addition, NK cell regulatory function was assessed by the detection of NK cell-mediated dendritic cell (DC) lysis. We found that SLE patients showed increased numbers of immunoglobulin-like transcript 2 (ILT2)⁺ , CD86⁺ and CD134⁺ NK cells. Furthermore, NK cells from SLE patients induced higher levels of DC lysis. We were able to identify a new subset of NK cells co-expressing CD11c and HLA-DR. These atypical NK cells were increased in SLE patients when compared with controls. We have identified an expanded new subset of NK cells in SLE patients. This is the first study, to our knowledge, which demonstrates that NK cells in SLE patients have an altered phenotype with a high expression of receptors characteristic of dendritic cells. Our results suggest that the impairment in the regulatory function of NK cells, together with the increased number of DC-like NK cells, could play an important role in the development of SLE and highlight the importance of NK cells as a future therapeutic target.

Expression Profiles of Ligands for Activating Natural Killer Cell Receptors on HIV Infected and Uninfected CD4⁺ T Cells

Natural Killer (NK) cell responses to HIV-infected CD4 T cells (iCD4) depend on the integration of signals received through inhibitory (iNKR) and activating NK receptors (aNKR). iCD4 activate NK cells to inhibit HIV replication. HIV infection-dependent changes in the human leukocyte antigen (HLA) ligands for iNKR on iCD4 are well documented. By contrast, less is known regarding the HIV infection related changes in ligands for aNKR on iCD4. We examined the aNKR ligand profiles HIV p24⁺ HIV iCD4s that maintained cell surface CD4 (iCD4⁺), did not maintain CD4 (iCD4⁻) and uninfected CD4 (unCD4) T cells for expression of unique long (UL)-16 binding proteins-1 (ULBP-1), ULBP-2/5/6, ULBP-3, major histocompatibility complex (MHC) class 1-related (MIC)-A, MIC-B, CD48, CD80, CD86, CD112, CD155, Intercellular adhesion molecule (ICAM)-1, ICAM-2, HLA-E, HLA-F, HLA-A2, HLA-C, and the ligands to NKp30, NKp44, NKp46, and killer immunoglobulin-like receptor 3DS1 (KIR3DS1) by flow cytometry on CD4 T cells from 17 HIV-1 seronegative donors activated and infected with HIV. iCD4⁺ cells had higher expression of aNKR ligands than did unCD4. However, the expression of aNKR ligands on iCD4 where CD4 was downregulated (iCD4⁻) was similar to (ULBP-1, ULBP-2/5/6, ULBP-3, MIC-A, CD48, CD80, CD86 and CD155) or significantly lower than (MIC-B, CD112 and ICAM-2) what was observed on unCD4. Thus, HIV infection can be associated with increased expression of aNKR ligands or either baseline or lower than baseline levels of aNKR ligands, concomitantly with the HIV-mediated downregulation of cell surface CD4 on infected cells.

Molecular checkpoints controlling natural killer cell activation and their modulation for cancer immunotherapy

Natural killer (NK) cells have gained considerable attention as promising therapeutic tools for cancer therapy due to their innate selectivity against cancer cells over normal healthy cells. With an array of receptors evolved to sense cellular alterations, NK cells provide early protection against cancer cells by producing cytokines and chemokines and exerting direct cytolytic activity. These effector functions are governed by signals transmitted through multiple receptor–ligand interactions but are not achieved by engaging a single activating receptor on resting NK cells. Rather, they require the co-engagement of different activating receptors that use distinct signaling modules, due to a cell-intrinsic inhibition mechanism. The redundancy of synergizing receptors and the inhibition of NK cell function by a single class of inhibitory receptor suggest the presence of common checkpoints to control NK cell activation through different receptors. These molecular checkpoints would be therapeutically targeted to harness the power of NK cells against diverse cancer cells that express heterogeneous ligands for NK cell receptors. Recent advances in understanding the activation of NK cells have revealed promising candidates in this category. Targeting such molecular checkpoints will facilitate NK cell activation by lowering activation thresholds, thereby providing therapeutic strategies that optimize NK cell reactivity against cancer.

PAX5 interacts with RIP2 to promote NF-κB activation and drug-resistance of B-lymphoproliferative disorders

Paired box protein 5 (PAX5) plays a lineage determination role in B-cell development. However, high expression of PAX5 has been also found in various malignant diseases including B-lymphoproliferative disorders (B-LPDs), but its functions and mechanisms in these diseases are still unclear. Here, we show that PAX5 induces drug-resistance through association and activation of receptor-interacting serine/threonine-protein kinase2 (RIP2) and subsequent activation of NF-κB signaling and anti-apoptosis genes expression in B-lymphoproliferative cells. Furthermore, PAX5 is able to interact with RIP1-3, modulating both RIP1- mediated TNFR and RIP2-mediated NOD1 and NOD2 pathways. Our findings describe a novel function of PAX5 in regulating RIP1 and RIP2 activation, which is at least involved in chemo drug-resistance in B-LPDs.

CTLA-4 is expressed by activated mouse NK cells and inhibits NK Cell IFN-γ production in response to mature dendritic cells

NK cells express an array of activating and inhibitory receptors that determine NK cell responses upon triggering by cognate ligands. Although activating NK cell receptors recognize mainly ligands expressed by stressed, virus-infected, or transformed cells, most inhibitory receptors engage MHC class I, preventing NK cell activation in response to healthy cells. In this study, we provide insight into the regulation and function of additional receptors involved in mouse NK cell responses: CTLA-4 and CD28. CTLA-4 and CD28 engage the same ligands, B7-1 and B7-2, which are primarily expressed by APCs, such as dendritic cells. Our data demonstrate that activation of mouse NK cells with IL-2 induces the expression of CTLA-4 and upregulates CD28. CTLA-4 expression in IL-2-expanded NK cells was further up- or downregulated by IL-12 or TGF-β, respectively. Using gene-deficient NK cells, we show that CD28 induces, and CTLA-4 inhibits, IFN-γ release by NK cells upon engagement by the recombinant ligand, B7-1, or upon coculture with mature dendritic cells. Notably, we show that mouse NK cells infiltrating solid tumors express CD28 and CTLA-4 and respond to stimulation with recombinant B7-1, suggesting that the NK cell responses mediated by the CD28/CTLA-4:B7-1/B7-2 system could be of importance during malignant disease. Accordingly, our study might have implications for immunotherapy of cancer based on blocking anti-CTLA-4 mAbs.

Anti-tumor immunity in a model of acute myeloid leukemia

Whole-cell vaccines allow the induction of anti-tumor immune responses without the need to define tumor antigens. We wished to directly compare, for the first time, the capacity of B7-1, B7-2 and 4-1BB ligand (4-1BBL) costimulatory molecules to convert murine and human acute myeloid leukemia (AML) cells into whole vaccines. 32Dc-kit is a murine myeloid cell line, which develops an AML-like disease over a protracted period, emulating human AML disease development. 32Dc-kit cells were modified to express elevated levels of B7-1, B7-2 or 4-1BBL, and each led to tumor rejection, although only mice injected with 32Dc-kit/B7-2 cells were able to reject subsequent parental tumor cell challenge. T-cell deficient nude mice were able to reject the 32Dc-kit variants, but they could not reject parental cell challenge; however, we found no evidence of cytotoxic T lymphocyte or natural killer (NK) activity ex vivo suggesting that tumor cell killing was mediated by an immune response that could not be recapitulated using purified NK or T cells as lone effectors. In human allogeneic mixed lymphocyte reactions (MLRs), we found no single costimulatory molecule was more effective, suggesting that the induction of a universal anti-tumor response will require a combination of costimulatory molecules.

Minimal requirement for induction of natural cytotoxicity and intersection of activation signals by inhibitory receptors

Natural killer (NK) cells provide innate control of infected and neoplastic cells. Multiple receptors have been implicated in natural cytotoxicity, but their individual contribution remains unclear. Here, we studied the activation of primary, resting human NK cells by Drosophila cells expressing ligands for receptors NKG2D, DNAM-1, 2B4, CD2, and LFA-1. Each receptor was capable of inducing inside-out signals for LFA-1, promoting adhesion, but none induced degranulation. Rather, release of cytolytic granules required synergistic activation through coengagement of receptors, shown here for NKG2D and 2B4. Although engagement of NKG2D and 2B4 was not sufficient for strong target cell lysis, collective engagement of LFA-1, NKG2D, and 2B4 defined a minimal requirement for natural cytotoxicity. Remarkably, inside-out signaling induced by each one of these receptors, including LFA-1, was inhibited by receptor CD94/NKG2A binding to HLA-E. Strong inside-out signals induced by the combination of NKG2D and 2B4 or by CD16 could overcome CD94/NKG2A inhibition. In contrast, degranulation induced by these receptors was still subject to inhibition by CD94/NKG2A. These results reveal multiple layers in the activation pathway for natural cytotoxicity and that steps as distinct as inside-out signaling to LFA-1 and signals for granule release are sensitive to inhibition by CD94/NKG2A.

CD28/B7-mediated co-stimulation is critical for early control of murine cytomegalovirus infection

Control of acute murine cytomegalovirus (MCMV) infection is dependent upon both innate and adaptive immune responses, relying primarily upon natural killer (NK) and T-cell responses for control. Although CD28/B7 plays a clear role in T-cell responses in many antigen systems including some viral infections, the importance of co-stimulation during MCMV infection is unconfirmed. In addition, recent data suggest that CD28/B7 co-stimulation might also be important to Ly49H+ NK-cell expansion. We therefore hypothesized that CD28/B7 co-stimulation is critical to viral control after MCMV infection, and further that CD28/B7 co-stimulation plays a role in MCMV-specific T- and NK-cell responses. To test these hypotheses, we utilized C57BL/6 mice lacking the co-stimulatory molecules B7-1 and B7-2 or CD28. After primary infection with MCMV, viral titers are significantly elevated in mice lacking CD28 or B7 compared with wild-type mice. Impaired viral control is associated with significant defects in peripheral T-cell responses to MCMV, which appear to be dependent upon CD28/B7 co-stimulation. Abnormal hepatic T-cell responses in CD28(-/-) mice are preceded by impaired MCMV-specific Ly49H+ NK-cell responses. Cytokine evaluations confirm that CD28/B7 co-stimulation is not required for non-specific antiviral responses. We conclude that CD28-mediated co-stimulation is critical for early viral control during acute MCMV infection.

CD28-stimulated ERK2 phosphorylation is required for polarization of the microtubule organizing center and granules in YTS NK cells

Activation of natural killer (NK) cell cytotoxicity requires adhesion and formation of a conjugate with a susceptible target cell, followed by actin polymerization, and polarization of the microtubule organizing center (MTOC) and cytolytic granules to the NK cell immune synapse. Here, by using the YTS NK cell line as a model, CD28 is shown to be an activating receptor. It signals cytotoxicity in a process dependent on phosphoinositide-3 kinase activation, leading to sustained extracellular signal-regulated kinase 2 (ERK2) phosphorylation. ERK and phospho-ERK localize to microtubule filaments. Neither conjugation with targets nor actin polymerization is affected by blocking ERK2 activation. However, both polarization of the MTOC and cytolytic granules to the synaptic region and NK cell cytotoxicity are strongly reduced by blocking ERK2 activation. A role for the CD28/CD80 interaction in cytotoxicity of human peripheral NK cells also was established. By contrast, lymphocyte function-associated antigen 1 (LFA-1) ligation transduces only a transient ERK2 activation and fails to induce killing in YTS cells. Thus, in YTS cells, a CD28 signal is used to polarize the MTOC and cytolytic granules to the NK cell immune synapse by stimulating sustained ERK2 activation.

Preterm delivery induced by LPS in syngeneically impregnated BALB/c and NOD/SCID mice

Strategies of lipopolysaccharide (LPS) stimulation with or without previous toll-like receptor 4 (TLR4) blocking were pursued to investigate the mechanism of LPS-induced preterm delivery in syngeneically impregnated BALB/c and non-obese diabetic (NOD)/LtSz-scid/scid (NOD/SCID [severe combined immunodeficiency] for short) mice. The LPS-stimulated mice were killed at the beginning of preterm labor and pooled placentas were collected in each mouse. Cell surface expression of TLR4, CD80, and intracellular TNF-alpha in placenta CD45(+) cell population was determined by flow cytometry. It displayed that preterm delivery could be induced by LPS in BALB/c, while the NOD/SCID seemed to be resistant to LPS induction. TLR4 expression was not changed in either BALB/c or NOD/SCID mice upon LPS-stimulation, but the CD45(+)CD80(+) cell percentage was elevated in both groups. The CD45(+)TNF-alpha(+) cell percentage was increased merely in BALB/c after the stimulation, while no such trend was observed in NOD/SCID mice. In BALB/c, the effect of LPS on CD80 and TNF-alpha expression could be abrogated by previous TLR4 blocking, subsequently prevent LPS-induced preterm delivery. In another design, NK cell blocking was performed at earlier stage of gestation by injections of anti-asialo GM1 antiserum (ASGM1). It appeared that LPS-induced preterm delivery could be partially prevented by this blocking in BALB/c mice. Such data, together with the diversity of sensitivity to LPS induction observed in BALB/c and NOD/SCID mice, imply that LPS interacts with TLR4, triggers the mobilization of CD45(+)CD80(+) cells, results in elevated production of inflammatory cytokines, and finally results in preterm delivery. In addition, NK cells may be involved in the signaling cascade, and the lack of functional NK cells in the NOD/SCID may be why these mice appeared to be less sensitive to LPS-induced premature labor.

Contemplating the murine test tube: lessons from natural killer cells andCryptococcus neoformans

Murine experimentation has provided many useful tools, including the ability to knockout or over-express genes and to perform experiments that are limited by ethical considerations. Over the past century, mice have imparted valuable insights into the biology of many systems, including human immunity. However, although there are many similarities between the immune response of humans and mice, there are also many differences; none is more prominent than when examining natural killer cell biology. These differences include tissue distribution, effector molecules, receptor repertoire, and cytokine responses, all of which have important implications when extrapolating the studies to the human immune responses to Cryptococcus neoformans.

B7-1-HSA (CD80-CD24), a recombinant hybrid costimulatory molecule retains ligand binding and costimulatory functions

Optimal activation of naïve T lymphocyte requires two signals; an antigen-specific signal initiated by engagement of TCR with the antigen-MHC complex and a costimulatory signal independent of the antigen receptor complex. Without the costimulatory signal, T cells become anergic. Various adhesion molecules, such as B7-1 (CD80) and heat stable antigen (HSA, CD24), expressed on antigen presenting cells have been demonstrated to provide costimulatory signals to T cells. It was reported that the combinations of different adhesion molecules could induce even stronger immune response. In this study, we made a hybrid costimulatory molecule, B7-1-HSA, and tested its T cell stimulatory function. Chinese hamster ovary (CHO) cells expressing this hybrid molecule bound both anti-CD80 and anti-CD24 monoclonal antibodies, and induced stronger T cell proliferation than CHO cells expressing B7-1 or HSA alone. These results suggest that the B7-1-HSA hybrid molecule can deliver two costimulatory signals simultaneously that can synergize in inducing T cell proliferation. The purified B7-1-HSA protein reacted with both anti-B7-1 and anti-HSA mAbs in Western blotting and specifically mediated adhesion of Jurkat cells. Furthermore, purified B7-1-HSA molecule spontaneously incorporated onto cell membrane through its glycolipid anchor suggesting that this hybrid costimulatory molecule can be used in protein transfer to develop effective cancer vaccines.

Phase I study of the intratumoral administration of recombinant canarypox viruses expressing B7.1 and interleukin 12 in patients with metastatic melanoma

The objective of this study was to evaluate the safety and activity of the intratumoral administration of the immune costimulatory molecule, B7.1, encoded by a vector derived from the canarypox virus, ALVAC (ALVAC-B7.1), alone and with the intratumoral injection of ALVAC encoding the immune-stimulatory cytokine, interleukin 12 (ALVAC-IL-12). Fourteen patients with metastatic melanoma who had s.c. nodules received intratumoral injections on days 1, 4, 8, and 11. Nine patients were given escalating doses of up to 25 x 10(8) plaque-forming units of ALVAC-B7.1. Five patients were given 25 x 10(8) plaque-forming units of ALVAC-B7.1 combined with ALVAC-IL-12 50% tissue culture infective dose of 2 x 10(6). Toxicity was mild to moderate and consisted of inflammatory reactions at the injection site and fever, chills, myalgia, and fatigue. Higher levels of B7.1 mRNA were observed in ALVAC-B7.1-injected tumors compared with saline-injected control tumors. Higher levels of intratumoral vascular endothelial growth factor and IL-10, cytokines with immune suppressive activities, were also observed in ALVAC-B7.1- and ALVAC-IL-12-injected tumors compared with saline-injected controls. Serum levels of vascular endothelial growth factor increased at day 18 and returned to baseline at day 43. All patients developed antibody to ALVAC. Intratumoral IL-12 and IFN-gamma mRNA decreased. Changes in serum IL-12 and IFN-gamma levels were not observed. Tumor regressions were not observed. The intratumoral injections of ALVAC-B7.1 and ALVAC-IL-12 were well tolerated at these dose levels and at this schedule and resulted in measurable biological response. This response included the production of factors that may suppress the antitumor immunologic activity of these vectors.

Interaction Between Natural Killer and Dendritic Cells: the Role of CD40, CD80 and Major Histocompatibility Complex Class I Molecules in Cytotoxicity Induction and Interferon-gamma Production

This study focuses on the differential role of CD40 and CD80 costimulatory molecules and major histocompatibility complex class I (MHC-I) antigens in the regulation of the interplay between dendritic cells (DCs) and interleukin (IL)-2-activated human natural killer (NK) lymphocytes. Our data indicate that CD40 and CD80 molecules might play a preferential role in the induction of cytotoxic function but not in the interferon-gamma(IFN-gamma) production by human IL-2-activated NK effectors in the presence of autologous and allogeneic DCs. In addition, a critical role of CD94-dependent MHC-I recognition in the regulation of both IFN-gamma production and target cell lysis was shown in the functional interaction between NK and DCs.

Two-signal requirement for activation and effector function of natural killer cell response to allogeneic tumor cells

Optimal activation of T cells requires delivery of both antigenic and costimulatory signals. It is unclear, however, if the function of the natural killer (NK) cells is also modulated by these 2 signals. Here we report that efficient control of solid allogeneic tumors by NK cells depends on codelivery of both B7-1 and major histocompatibility complex (MHC) class I on the tumor cells. The codelivery is required for optimal expansion and effector function of NK cells in response to both melanoma and plasmocytoma that expressed allogeneic MHC class I. Our results demonstrate that the 2 signals required for T-cell function also can regulate NK immunity and reveal an important similarity between the innate NK response and the adaptive T-cell response.

Regulation of HLA-DR and co-stimulatory molecule expression on natural killer T cells by granulocyte-macrophage colony-stimulating factor

A subset of mononuclear cells present in most tissues coexpresses receptors of both natural killer (NK) and T cells. Although linked to antiviral immunity, the function of these putative NKT cells is uncertain. We present evidence that human CD56+ DR- NKT cells exhibit hybrid adaptive and innate immune functions. These cells spontaneously lysed tumour cell targets and upon engagement of T-cell antigen receptors secreted the cytokines interferon-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF). Conversely, GM-CSF treatment transformed the NKT cells into dendritic cells, inducing rapid expression of HLA-DR and the co-stimulatory molecules CD80 and CD86. The ability to stimulate tetanus toxoid-specific responses from naïve T cells was acquired within 3 days of activating CD56+ NKT cells with GM-CSF. These results suggest a potential role for NKT cells in the initiation and control of primary immunity during the acute phase of infection.

Human NK cell-mediated cytotoxicity triggered by CD86 and Gal alpha 1,3-Gal is inhibited in genetically modified porcine cells

Delayed xenograft rejection is a major hurdle that needs to be addressed to prolong graft survival in pig-to-primate xenotransplantation. NK cell activation has been implicated in delayed xenograft rejection. Both Ab-dependent and independent mechanisms are responsible for the high susceptibility of porcine cells to human NK cell-mediated cytotoxicity. Previous reports demonstrated a role of Galalpha1,3-Gal Ag in triggering the Ab-independent responses. We hypothesize that expression of CD80 and/or CD86 on porcine cells may also play a role in NK cell activation as human NK cells express a variant of CD28. Our initial analysis showed that porcine endothelial cells and fibroblasts express CD86, but not CD80. Genetic engineering of these cells to express hCD152-hCD59, a chimeric molecule designed to block CD86 in cis, was accompanied by a reduction in susceptibility to human NK cell-mediated cytotoxicity. The use of a specific anti-porcine CD86-blocking Ab and the NK92 and YTS cell lines further confirmed the involvement of CD86 in triggering NK cell-mediated lysis of porcine cells. Maximal protection was achieved when hCD152-hCD59 was expressed in H transferase-transgenic cells, which show reduced Galalpha1,3-Gal expression. In this work, we describe two mechanisms of human NK cell-mediated rejection of porcine cells and demonstrate that genetically modified cells resist Ab-independent NK cell-mediated cytotoxicity.

Inhibition of CD28-mediated natural cytotoxicity by KIR2DL2 does not require p56(lck) in the NK cell line YT-Indy

CD28 functions as a cytotoxicity activation receptor in the NK cell line YT-Indy. To analyze the requirement of p56(lck) kinase in the function of killer inhibitory receptors, we transfected the p56(lck) negative YT-Indy cell line with the cl43 gene encoding for KIR2DL2. Pervanadate treatment revealed KIR2DL2 phosphorylation in YT-Indy-cl43, as well as SHP1/SHP2 recruitment. YT-Indy-cl43 cells were inhibited in their ability to lyse target cells expressing HLA-Cw3, a ligand for KIR2DL2. This inhibition was blocked by anti-KIR2DL2 or anti-HLA class I mAb. CD28 crosslinking on YT-Indy-cl43 enhanced tyrosine phosphorylation of PLC-gamma1. The simultaneous ligation of KIR2DL2 with mAb resulted in a decrease in CD28-induced tyrosine phosphorylation of PLC-gamma1 confirming that dephosphorylation of this protein is involved in the KIR2DL2-induced inhibition of CD28-mediated cytotoxicity. As YT-Indy-cl43 did not express detectable levels of p56(lck), these results indicate that this kinase is not required for transmitting the negative signals generated by KIR2DL2 ligation.