Assessment of Human Natural Killer Cell Events Driven by FcγRIIIa Engagement in the Presence of Therapeutic Antibodies.

One mechanism of action for clinical efficacy by therapeutic antibodies is the promotion of immune-related functions, such as cytokine secretion and cytotoxicity, driven by FcγRIIIa (CD16) expressed on natural killer (NK) cells. These observations have led to research focusing on methods to increase Fc receptor-mediated events, which include removal of a fucose moiety found on the Fc portion of the antibody. Further studies have elucidated the mechanistic changes in signaling, cellular processes, and cytotoxic characteristics that increase ADCC activity with afucosylated antibodies. Additionally, other studies have shown the potential benefits of these antibodies in combination with small molecule inhibitors. These experiments demonstrated the molecular and cellular mechanisms underlying the benefits of using afucosylated antibodies in combination settings. Many of these observations were based on an artificial in vitro activation assay in which the FcγRIIIa on human NK cells was activated by therapeutic antibodies. This assay provided the flexibility to study downstream effector NK cell functions, such as cytokine production and degranulation. In addition, this assay has been used to interrogate signaling pathways and identify molecules that can be modulated or used as biomarkers. Finally, other therapeutic molecules (i.e., small molecule inhibitors) have been added to the system to provide insights into the combination of these therapeutics with therapeutic antibodies, which is essential in the current clinical space. This manuscript aims to provide a technical foundation for performing this artificial human NK cell activation assay. The protocol demonstrates key steps for cell activation as well as potential downstream applications that range from functional readouts to more mechanistic observations.

A Novel Liposome Formulation Carrying Both an Insulin Peptide and a Ligand for Invariant Natural Killer T Cells Induces Accumulation of Regulatory T Cells to Islets in Nonobese Diabetic Mice.

Type 1 diabetes (T1D) is an autoimmune disease caused by the destruction of pancreatic ß cells by autoantigen-reactive diabetogenic cells. Antigen-specific therapies using islet autoantigens for restoring immune tolerance have emerged as promising approaches for the treatment of T1D but have been unsuccessful in humans. Herein, we report that RGI-3100-iB, a novel liposomal formulation carrying both α-galactosylceramide (α-GalCer), which is a representative ligand for invariant natural killer T (iNKT) cells, and insulin B chain 9-23 peptide, which is an epitope for CD4+ T cells, could induce the accumulation of regulatory T cells (Tregs) in islets in a peptide-dependent manner, followed by the remarkable prevention of diabetes onset in nonobese diabetic (NOD) mice. While multiple administrations of a monotherapy using either α-GalCer or insulin B peptide in a liposomal formulation was confirmed to delay/prevent T1D in NOD mice, RGI-3100-iB synergistically enhanced the prevention effect of each monotherapy and alleviated insulitis in NOD mice. Immunopathological analysis showed that Foxp3+ Tregs accumulated in the islets in RGI-3100-iB-treated mice. Cotransfer of diabetogenic T cells and splenocytes of NOD mice treated with RGI-3100-iB, but not liposomal α-GalCer encapsulating an unrelated peptide, to NOD-SCID mice resulted in the prevention of diabetes and elevation of Foxp3 mRNA expression in the islets. These data indicate that the migration of insulin B-peptide-specific Tregs to islet of NOD mice that are involved in the suppression of pathogenic T cells related to diabetes onset and progression could be enhanced by the administration of liposomes containing α-GalCer and insulin B peptide.

Invariant natural killer T cells ameliorate murine chronic GVHD by expanding donor regulatory T cells.

Chronic graft-versus-host-disease (cGVHD) can cause multiorgan system disease, typically with autoimmune-like features, resulting in high mortality and morbidity caused by treatment limitations. Invariant natural killer T cells (iNKTs), a small population characterized by expression of a semi-invariant T-cell receptor, rapidly produce copious amounts of diverse cytokines on activation that exert potent immune regulatory function. Here, we show that iNKTs are significantly reduced in a cGVHD murine model that recapitulates several aspects of autoimmunity and organ fibrosis observed in patients with cGVHD. Low iNKT infused doses effectively prevented and, importantly, reversed established cGVHD, as did third-party iNKTs. iNKTs suppressed the autoimmune response by reducing the germinal center (GC) reaction, which was associated with an increase in total Tregs and follicular Tregs (Tfr) that control the GC reaction, along with pathogenic antibody production. Treg depletion during iNKT infusions completely abolished iNKT efficacy in treating cGVHD. iNKT cell interleukin 4 production and GC migration were critical to cGVHD reversal. In vivo stimulation of iNKT cells by α-galactosyl-ceramide was effective in both preventing and treating cGVHD. Together, this study demonstrates iNKT deficiency in cGVHD mice and highlights the key role of iNKTs in regulating cGVHD pathogenesis and as a potentially novel prophylactic and therapeutic option for patients with cGVHD.

Increased Foxp3+Helios+ Regulatory T Cells and Decreased Acute Graft-versus-Host Disease after Allogeneic Bone Marrow Transplantation in Patients Receiving Sirolimus and RGI-2001, an Activator of Invariant Natural Killer T Cells.

Regulatory T (Treg) cells play a central role in immune tolerance and prevention of aberrant immune responses. Several studies have suggested that the risk of graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT) can be ameliorated by increasing Tregs. We have developed an approach of in vivo expansion of Tregs with RGI-2001, a novel liposomal formulation of a synthetic derivative of alpha-galactosylceramide, a naturally occurring ligand that binds to CD1 and activates and expands invariant natural killer cells. In preclinical studies, a single intravenous infusion of RGI-2001 expanded Treg and could ameliorate GVHD in a mouse model of allogeneic HCT. To explore the role of RGI-2001 in clinical HCT, we initiated a phase 2A clinical trial (n = 29), testing 2 different doses of RGI-2001 administered as a single infusion on day 0 of allogeneic HCT. RGI-2001 was well tolerated and without infusion reactions or cytokine release syndrome. A subset of patients (8 of 29, 28%) responded to RGI-2001 by inducing a markedly increased number of cells with a Treg phenotype. The Treg had a high Ki-67 index and were almost exclusively Helios+ and Foxp3+, indicating that their accumulation was due to expansion of natural Treg. Notably, the incidence of grade 2 to 4 GVHD in the 8 patients who responded to RGI-2001 was 12.5%, compared with 52.4% in the 21 patients who did not respond. No grade 3 or 4 GVHD was observed in the responder group, compared with a 9.5% incidence among nonresponders. Immunosuppression with sirolimus was also associated with a low incidence of GVHD, suggesting that RGI-2001 may have synergized with sirolimus to promote Treg expansion.

Pharmacologic expansion of donor-derived, naturally occurring CD4(+)Foxp3(+) regulatory T cells reduces acute graft-versus-host disease lethality without abrogating the graft-versus-leukemia effect in murine models.

Adoptive transfer of regulatory T cells (Tregs) prevents graft-versus-host disease (GVHD) in mouse models, indicating a pivotal role for Tregs in controlling GVHD. The present study demonstrates the efficacy of Tregs pharmacologically induced in vivo in GVHD prevention. A single i.v. administration of a liposomal formulation of α-galactosylceramide (RGI-2001) at the time of allogeneic bone marrow transplantation with spleen cells significantly prolonged the survival of mice experiencing lethal acute GVHD. RGI-2001 expanded donor-derived CD4(+)Foxp3(+) Tregs in the spleen, lymph nodes, and bone marrow in a dose-dependent manner. On day 15 posttransplantation, the spleens of mice treated with RGI-2001 (1 µg/kg) contained 5-fold higher percentages or 10-fold higher numbers of CD4(+)Foxp3(+) Tregs compared with the spleens of untreated mice. Host-specific immunosuppression was introduced in treated mice, whereas the responsiveness to third-party alloantigens and leukemia cells was maintained. Using Foxp3:GFP reporter mice as donors, it was clearly shown that RGI-2001 expanded the pre-existing naturally occurring Tregs (nTregs) in donor spleen cells. Finally, RGI-2001 synergized with a subtherapeutic dose of rapamycin in nTreg expansion and further prolonged survival. Our results provide the first demonstration of the efficacy of nTregs pharmacologically expanded in vivo in preventing acute GVHD without abrogation of the beneficial graft-versus-leukemia effect.

Antagonistic nature of T helper 1/2 developmental programs in opposing peripheral induction of Foxp3+ regulatory T cells.

Recent studies have highlighted the importance of peripheral induction of Foxp3-expressing regulatory T cells (Tregs) in the dominant control of immunological tolerance. However, Foxp3(+) Treg differentiation from naïve CD4(+) T cells occurs only under selective conditions, whereas the classical T helper (Th) 1 and 2 effector development often dominate T cell immune responses to antigen stimulation in the periphery. The reason for such disparity remains poorly understood. Here we report that Th1/Th2-polarizing cytokines can potently inhibit Foxp3(+) Treg differentiation from naïve CD4(+) precursors induced by TGF-beta. Furthermore, antigen receptor-primed CD4(+) T cells are resistant to Treg induction because of autocrine production of IFNgamma and/or IL-4, whereas neutralizing IFNgamma and IL-4 not only can potentiate TGF-beta-mediated Foxp3 induction in vitro but can also enhance antigen-specific Foxp3(+) Treg differentiation in vivo. Mechanistically, inhibition of Foxp3(+) Treg development by Th1/Th2-polarizing cytokines involves the activation of Th1/Th2 lineage transcription factors T-bet and GATA-3 through the canonical Stat1-, Stat4-, and Stat6-dependent pathways. Using IFNgamma and IL-4 knockouts and retrovirus-mediated transduction of T-bet and GATA-3, we further demonstrate that enforced expression of the Th1/Th2 lineage-specific transcription factors is sufficient to block Foxp3 induction and Treg differentiation independent of the polarizing/effector cytokines. Thus, our study has unraveled a previously unrecognized mechanism of negative cross-regulation of Foxp3(+) Treg fate choice by Th1/Th2 lineage activities. In addition, these findings also provide an attainable explanation for the general paucity of antigen-triggered de novo generation of Foxp3(+) Tregs in the periphery.

MEKK3 is essential for lipopolysaccharide-induced interleukin-6 and granulocyte-macrophage colony-stimulating factor production in macrophages.

Mitogen-activated protein/ERK kinase kinase 3 (MEKK3) is a Ser/Thr protein kinase belonging to the MEKK/STE11 subgroup of the MAP3K family. Recently, we found that MEKK3 plays a critical role in interleukin-1 (IL-1) receptor and Toll-like receptor 4 signalling using established primary mouse embryonic fibroblast (MEF) cell lines. However, the function of MEKK3 in immune cells has not been studied because germ-line MEKK3 knockout mice are embryonically lethal between embryonic days 10 and 11. In this study, we used small interference RNA to the mouse Mekk3 gene to specifically knock down MEKK3 expression in the macrophage line Raw264.7. We found that the lipopolysaccharide-induced IL-6 and granulocyte-macrophage colony-stimulating factor (GM-CSF) production was dramatically decreased in MEKK3 knockdown cells whereas the tumour necrosis factor-alpha and IL-1beta production were not affected. We also observed that the ERK1/2, p38 and JNK MAPK induction in MEKK3 knockdown cells were moderately inhibited within the first 60 min of stimulation, while the ERK and p38 were more severely inhibited after 2-4 hr of stimulation. Degradation of IkappaBalpha was also partially blocked in MEKK3 knockdown cells. Notably, the impairment in IL-6 and GM-CSF production in the MEKK3 knockdown cells was restored by reintroducing a human Mekk3 cDNA that could not be targeted by mouse Mekk3-siRNAs. In conclusion, this study showed that MEKK3 is a crucial and specific regulator of the proinflammatory cytokines IL-6 and GM-CSF in macrophages and provided a novel method for investigating MEKK3 function in other immune cells.

The adaptor protein CARD9 is required for innate immune responses to intracellular pathogens.

The caspase-recruitment domain-containing adaptor protein CARD9 regulates the innate signaling responses to fungal infection. Here we show that CARD9 is required for innate immune responses against intracellular pathogens. We generated Card9(-/-) mice and found that CARD9-deficient macrophages had defects in activation of the kinases p38 and Jnk but not of transcription factor NF-kappaB after bacterial and viral infection. CARD9-deficient mice failed to clear infection and showed altered cytokine production after challenge with Listeria monocytogenes. In wild-type cells, we found CARD9 inducibly associated with both the intracellular 'biosensor' Nod2 and the serine-threonine kinase RICK. Our data demonstrate that CARD9 has a critical function in Nod2-mediated activation of p38 and Jnk in innate immune responses to intracellular pathogens.

OX40 ligand shuts down IL-10-producing regulatory T cells.

IL-10-producing CD4(+) type 1 regulatory T (Tr1) cells play a critical role in the maintenance of peripheral tolerance. Although immunosuppressive drugs, cytokines, costimulatory molecules, and immature dendritic cells are implicated in the induction of Tr1 cells, the signals that negatively regulate the generation and function of Tr1 cells have been elusive. We report that OX40 ligand (OX40L) completely inhibited the generation of IL-10-producing Tr1 cells from naïve and memory CD4(+) T cells induced by the immunosuppressive drugs dexamethasone and vitamin D3. This unique function of OX40L was not shared by two costimulatory TNF family members, GITR ligand and 4-1BB ligand. OX40L strongly inhibited the generation of IL-10-producing Tr1 cells induced by two physiologic stimuli, the inducible costimulatory ligand and immature dendritic cells. In addition, OX40L strongly inhibited IL-10 production and suppressive function of differentiated IL-10-producing Tr1 cells. These two novel functions of OX40L shed light on the mechanism by which OX40/OX40L regulates immunity and tolerance.

Specialization, kinetics, and repertoire of type 1 interferon responses by human plasmacytoid predendritic cells.

Recent studies suggest plasmacytoid predendritic cells (pDCs) and myeloid dendritic cells (mDCs) have the functional plasticity to produce similar amounts of type 1 interferons (IFNs) and interleukin-12 (IL-12), challenging the concept and existence of DC subsets with distinct function. In this study, we demonstrate that previous studies showed human pDCs produce large amounts of IL-12 because of contaminating mDCs. Using highly purified human DC subsets, we found that although pDCs make 300 times more IFN-alpha than mDCs and mDCs make 13 times more IL-12 p70 than pDCs in response to all the toll-like receptor ligands and CD40 ligands, pDCs rapidly make large amounts of IFN-alpha within the first 12 hours of activation and become refractory to further stimulation. pDCs preferentially expressed the transcriptional factors critical for type 1 IFN, but not for IL-12 transcription, and they dedicated 60% of new transcriptional activity to make 19 type 1 IFN subtypes. This study provides formal proof that the plasticity of DC subsets is limited and that different DC subsets evolve to perform distinct functions in linking innate and adaptive immunity.

TSLP-activated dendritic cells induce an inflammatory T helper type 2 cell response through OX40 ligand.

We recently showed that dendritic cells (DCs) activated by thymic stromal lymphopoietin (TSLP) prime naive CD4(+) T cells to differentiate into T helper type 2 (Th2) cells that produced high amounts of tumor necrosis factor-alpha (TNF-alpha), but no interleukin (IL)-10. Here we report that TSLP induced human DCs to express OX40 ligand (OX40L) but not IL-12. TSLP-induced OX40L on DCs was required for triggering naive CD4(+) T cells to produce IL-4, -5, and -13. We further revealed the following three novel functional properties of OX40L: (a) OX40L selectively promoted TNF-alpha, but inhibited IL-10 production in developing Th2 cells; (b) OX40L lost the ability to polarize Th2 cells in the presence of IL-12; and (c) OX40L exacerbated IL-12-induced Th1 cell inflammation by promoting TNF-alpha, while inhibiting IL-10. We conclude that OX40L on TSLP-activated DCs triggers Th2 cell polarization in the absence of IL-12, and propose that OX40L can switch IL-10-producing regulatory Th cell responses into TNF-alpha-producing inflammatory Th cell responses.

Nucleic acids of mammalian origin can act as endogenous ligands for Toll-like receptors and may promote systemic lupus erythematosus.

Raised serum levels of interferon (IFN)-alpha have been observed in systemic lupus erythematosus (SLE) patients, and these levels are correlated with both disease activity and severity. The origin of this IFN-alpha is still unclear, but increasing evidence suggests the critical involvement of activated plasmacytoid predendritic cells (PDCs). In SLE patients, DNA and RNA viruses, as well as immune complexes (ICs), that consist of autoantibodies specific to self-DNA and RNA protein particles can stimulate production of IFN-alpha. We have developed three series of oligonucleotide (ODN)-based inhibitors of Toll-like receptor (TLR) signaling. These ODNs include inhibitors of TLR9, inhibitors of TLR7 but not TLR9, and sequences that inhibit both TLR7 and TLR9. Specificity of these inhibitors is confirmed by inhibition of IFN-alpha production by PDCs in response to DNA or RNA viruses. We show that mammalian DNA and RNA, in the form of ICs, are potent self-antigens for TLR9 and TLR7, respectively, and induce IFN-alpha production by PDCs. This work suggests that TLRs may have a critical role in the promotion of lupus through the induction of IFN-alpha by PDCs. These inhibitors of TLR signaling thus represent novel therapeutic agents with potential for the treatment of lupus.

Inhibitors of TLR-9 act on multiple cell subsets in mouse and man in vitro and prevent death in vivo from systemic inflammation.

In parallel with the discovery of the immunostimulatory activities of CpG-containing oligodeoxynucleotides, several groups have reported specific DNA sequences that could inhibit activation by CpG-containing oligodeoxynucleotides in mouse models. We show that these inhibitory sequences, termed IRS, inhibit TLR-9-mediated activation in human as well as mouse cells. This inhibitory activity includes proliferation and IL-6 production by B cells, and IFN-alpha and IL-12 production by plasmacytoid dendritic cells. Our studies of multiple cell types in both mice and humans show the optimal IRS to contain a GGGG motif within the sequence, and the activity to require a phosphorothioate backbone. Although the GGGG motif readily itself leads to formation of a tetrameric oligodeoxynucleotide structure, inhibitory activity resides exclusively in the single-stranded form. When coinjected with a CpG oligodeoxynucleotide in vivo, IRS were shown to inhibit inflammation through a reduction in serum cytokine responses. IRS do not need to be injected at the same site to inhibit, demonstrating that rapid, systemic inhibition of TLR-9 can be readily achieved. IRS can also inhibit a complex pathological response to ISS, as shown by protection from death after massive systemic inflammation induced by a CpG-containing oligodeoxynucleotides.

IL-10 regulates plasmacytoid dendritic cell response to CpG-containing immunostimulatory sequences.

Immunostimulatory sequences (ISS) are short oligonucleotides containing unmethylated cytosine-phosphate-guanine (CpG) dinucleotides that stimulate innate immune responses through Toll-like receptor-9 on B cells and plasmacytoid dendritic cell (PDC) precursors. The anti-inflammatory cytokine interleukin (IL)-10 is predicted to be a potent inhibitor of many of the activities described for ISS, and this may impact the use of ISS in disease states characterized by elevated IL-10. As the activities of ISS on PDCs are central to many clinical applications of ISS, we have studied the effects of IL-10 on PDC stimulation by 3 distinct classes of ISS. IL-10 inhibited cytokine production and survival of ISS-activated PDCs; however, IL-12 induction was much more sensitive to inhibition than interferon (IFN)-alpha induction. Within the PDC population are cells that respond to ISS by producing either IL-12 or IFN-alpha but not both cytokines. IL-12-producing PDCs require costimulation through CD40 and appear more mature than IFN-alpha-producing PDCs. The 3 distinct classes of ISS differed with respect to induction of PDC maturation and T-cell priming capacity. IL-10 regulated PDC activation but did not inhibit the subsequent T-cell-priming ability of PDCs already activated by ISS.