Optimal effector functions in human natural killer cells rely upon autocrine bone morphogenetic protein signaling.

Natural killer (NK) cells are critical for innate tumor immunity due to their specialized ability to recognize and kill neoplastically transformed cells. However, NK cells require a specific set of cytokine-mediated signals to achieve optimal effector function. Th1-associated cytokines promote effector functions that are inhibited by the prototypic Th2 cytokine IL4 and the TGFß superfamily members TGFß1 and activin-A. Interestingly, the largest subgroup of the TGFß superfamily are the bone morphogenetic proteins (BMP), but the effects of BMP signaling on NK cell effector functions have not been evaluated. Here, we demonstrate that blood-circulating NK cells express type I and II BMP receptors, BMP-2 and BMP-6 ligands, and phosphorylated isoforms of Smad-1/-5/-8, which mediate BMP family member signaling. In opposition to the inhibitory effects of TGFß1 or activin-A, autocrine BMP signaling was supportive to NK cell function. Mechanistic investigations in cytokine and TLR-L-activated NK cells revealed that BMP signaling optimized IFNγ and global cytokine and chemokine production, phenotypic activation and proliferation, and autologous dendritic cell activation and target cytotoxicity. Collectively, our findings identify a novel auto-activatory pathway that is essential for optimal NK cell effector function, one that might be therapeutically manipulated to help eradicate tumors. Cancer Res; 74(18); 5019-31. ©2014 AACR.

A novel HLA-B18 restricted CD8+ T cell epitope is efficiently cross-presented by dendritic cells from soluble tumor antigen.

NY-ESO-1 has been a major target of many immunotherapy trials because it is expressed by various cancers and is highly immunogenic. In this study, we have identified a novel HLA-B*1801-restricted CD8(+) T cell epitope, NY-ESO-1(88-96) (LEFYLAMPF) and compared its direct- and cross-presentation to that of the reported NY-ESO-1(157-165) epitope restricted to HLA-A*0201. Although both epitopes were readily cross-presented by DCs exposed to various forms of full-length NY-ESO-1 antigen, remarkably NY-ESO-1(88-96) is much more efficiently cross-presented from the soluble form, than NY-ESO-1(157-165). On the other hand, NY-ESO-1(157-165) is efficiently presented by NY-ESO-1-expressing tumor cells and its presentation was not enhanced by IFN-γ treatment, which induced immunoproteasome as demonstrated by Western blots and functionally a decreased presentation of Melan A(26-35); whereas NY-ESO-1(88-96) was very inefficiently presented by the same tumor cell lines, except for one that expressed high level of immunoproteasome. It was only presented when the tumor cells were first IFN-γ treated, followed by infection with recombinant vaccinia virus encoding NY-ESO-1, which dramatically increased NY-ESO-1 expression. These data indicate that the presentation of NY-ESO-1(88-96) is immunoproteasome dependent. Furthermore, a survey was conducted on multiple samples collected from HLA-B18(+) melanoma patients. Surprisingly, all the detectable responses to NY-ESO-1(88-96) from patients, including those who received NY-ESO-1 ISCOMATRIX™ vaccine were induced spontaneously. Taken together, these results imply that some epitopes can be inefficiently presented by tumor cells although the corresponding CD8(+) T cell responses are efficiently primed in vivo by DCs cross-presenting these epitopes. The potential implications for cancer vaccine strategies are further discussed.

Processing and cross-presentation of individual HLA-A, -B, or -C epitopes from NY-ESO-1 or an HLA-A epitope for Melan-A differ according to the mode of antigen delivery.

The ability of dendritic cells (DCs) to cross-present protein tumor antigens to cytotoxic T lymphocytes (CTLs) underpins the success of therapeutic cancer vaccines. We studied cross-presentation of the cancer/testis antigen, NY-ESO-1, and the melanoma differentiation antigen, Melan-A by human DC subsets. Monocyte-derived DCs (MoDCs) efficiently cross-presented human leukocyte associated (HLA)-A2-restricted epitopes from either a formulated NY-ESO-1/ISCOMATRIX vaccine or when either antigen was mixed with ISCOMATRIX adjuvant. HLA-A2 epitope generation required endosomal acidification and was proteasome-independent for NY-ESO-1 and proteasome-dependent for Melan-A. Both MoDCs and CD1c(+) blood DCs cross-presented NY-ESO-1-specific HLA-A2(157-165)-, HLA-B7(60-72)-, and HLA-Cw3(92-100)-restricted epitopes when formulated as an NY-ESO-1/ISCOMATRIX vaccine, but this was limited when NY-ESO-1 and ISCOMATRIX adjuvant were added separately to the DC cultures. Finally, cross-presentation of NY-ESO-1(157-165)/HLA-A2, NY-ESO-1(60-72)/HLA-B7, and NY-ESO-1(92-100)/HLA-Cw3 epitopes was proteasome-dependent when formulated as immune complexes (ICs) but only proteasome-dependent for NY-ESO-1(60-72)/HLA-B7-restricted cross-presentation facilitated by ISCOMATRIX adjuvant. We demonstrate, for the first time, proteasome-dependent and independent cross-presentation of HLA-A-, B-, and C-restricted epitopes within the same full-length tumor antigen by human DCs. Our findings identify important differences in the capacities of human DC subsets to cross-present clinically relevant, full-length tumor antigens and how vaccine formulation impacts CTL responses in vivo.

Presentation of tumour antigens by dendritic cells and challenges faced.

The use of dendritic cells (DCs) for the generation of anti-tumour immunity has been the focus of a vast array of scientific and clinical studies. The ability of DCs to present protein tumour antigens (T-Ags) to CD4(+) and CD8(+) T cells is pivotal to the success of therapeutic cancer vaccines. DC's specialised capacity to cross-present exogenous Ags onto major histocompatibility (MHC) class I molecules for the generation of T-Ag-specific cytotoxic T lymphocytes (CTLs) has made these cells the focal point of vaccine-based immunotherapy of cancer. However, although DC-based strategies can induce T cell responses in cancer patients, recent reviews of clinical studies demonstrate that DC-based approaches have essentially failed to meet their clinical end points. These findings highlight the need to re-evaluate the DC-based vaccine strategies and incorporate recent advancements in DC biology and tumour immunology. The current review considers the issues related to how best to target the Ag-processing pathway of DCs, the role of adjuvants, the appropriate conditioning of the DCs and strategies to overcome tumour-mediated immune escape.

Development of prophylactic and therapeutic vaccines using the ISCOMATRIX adjuvant.

Adjuvants are components that when added to subunit antigen (Ag) vaccines boost their immunogenicity and thus immune efficacy. However, there are few adjuvants that are approved for clinical use resulting in a critical need for the development of safe and effective adjuvants for use in both prophylactic and therapeutic vaccines. The paucity of appropriate adjuvants is more chronic for the development of therapeutic vaccines for cancer and chronic infectious disease, which need to induce cytotoxic T-cell responses via cross-presentation of the vaccine Ag by dendritic cells. The ISCOMATRIX adjuvant represents a unique adjuvant system that facilitates Ag delivery and presentation as well as immunomodulation to provide enhanced and accelerated immune responses. The immune responses generated are of broad specificity to the vaccine Ag, and include robust antibody responses of multiple subclasses as well as both CD4(+) and CD8(+) T-cell responses. Here we discuss our understanding of the mechanisms of action by which ISCOMATRIX adjuvant may facilitate these integrated immune responses and touch on insights gained through its clinical experience.

Activin-A attenuates several human natural killer cell functions.

Dendritic-cell (DC) and natural killer (NK)-cell interactions are critical in sculpting the adaptive immune response. However, the mechanisms by which DCs down-regulate NK-cell functions are not well understood. NK-cell function is inhibited by transforming growth factor beta (TGF-beta), but DCs do not appear to produce TGF-beta. We have previously shown that activated human DCs produce large amounts of activin-A, a TGF-beta superfamily member, which autoregulates DC function. The present report shows that NK-cells express type I and II activin receptors and that activin-A triggers NK-cell Smad 2/3 signaling. Furthermore, activin-A directly regulates NK cell functions by (1) down-regulating the T-box transcription factor T-bet and interferon gamma (IFN-gamma) but not perforin or granzyme mRNA; (2) suppressing NK-cell IFN-gamma production as potently as TGF-beta; and (3) suppressing NK-cell CD25 expression and proliferation and sculpting NK-cell cytokine and chemokine profiles. Interestingly, unlike TGF-beta, activin-A weakly down-regulates the NK-cell natural cytotoxicity receptors (NCRs) NKp30 and NKG2D but does not attenuate their cytotoxic function. These findings provide the first evidence for a novel immune regulatory role of activin-A during DC-mediated NK-cell regulation, highlighting the potential of antagonizing activin-A signaling in vivo to enhance NK cell-mediated immune functions and adaptive immunity.

ISCOMATRIX adjuvant induces efficient cross-presentation of tumor antigen by dendritic cells via rapid cytosolic antigen delivery and processing via tripeptidyl peptidase II.

Cancer vaccines aim to induce antitumor CTL responses, which require cross-presentation of tumor Ag to CTLs by dendritic cells (DCs). Adjuvants that facilitate cross-presentation of vaccine Ag are therefore key for inducing antitumor immunity. We previously reported that human DCs could not efficiently cross-present the full-length cancer/testis Ag NY-ESO-1 to CTL unless formulated as either an immune complex (NY-ESO-1/IC) or with ISCOMATRIX adjuvant. We now demonstrate that NY-ESO-1/ICs induce cross-presentation of HLA-A2- and HLA-Cw3-restricted epitopes via a proteasome-dependent pathway. In contrast, cross-presentation of NY-ESO-1/ISCOMATRIX vaccine was proteasome independent and required the cytosolic protease tripeptidyl peptidase II. Trafficking studies revealed that uptake of ICs and ISCOMATRIX vaccine by DCs occurred via endocytosis with delivery to lysosomes. Interestingly, ICs were retained in lysosomes, whereas ISCOMATRIX adjuvant induced rapid Ag translocation into the cytosol. Ag translocation was dependent on endosomal acidification and IL-4-driven differentiation of monocytes into DCs. This study demonstrates that Ag formulation determines Ag processing and supports a role for tripeptidyl peptidase II in cross-presentation of CTL epitopes restricted to diverse HLA alleles.

A long, naturally presented immunodominant epitope from NY-ESO-1 tumor antigen: implications for cancer vaccine design.

The tumor antigen NY-ESO-1 is a promising cancer vaccine target. We describe here a novel HLA-B7-restricted NY-ESO-1 epitope, encompassing amino acids 60-72 (APRGPHGGAASGL), which is naturally presented by melanoma cells. The tumor epitope bound to HLA-B7 by bulging outward from the peptide-binding cleft. This bulged epitope was not an impediment to T-cell recognition, however, because four of six HLA-B7(+) melanoma patients vaccinated with NY-ESO-1 ISCOMATRIX vaccine generated a potent T-cell response to this determinant. Moreover, the response to this epitope was immunodominant in three of these patients and, unlike the T-cell responses to bulged HLA class I viral epitopes, the responding T cells possessed a remarkably broad TCR repertoire. Interestingly, HLA-B7(+) melanoma patients who did not receive the NY-ESO-1 ISCOMATRIX vaccine rarely generated a spontaneous T-cell response to this cryptic epitope, suggesting a lack of priming of such T cells in the natural anti-NY-ESO-1 response, which may be corrected by vaccination. Together, our results reveal several surprising aspects of antitumor immunity and have implications for cancer vaccine design.

Simultaneous presentation and cross-presentation of immune-stimulating complex-associated cognate antigen by antigen-specific B cells.

We demonstrate that uptake of oligomeric cognate antigen (OVA-hen egg lysozyme, OVA-HEL) alone or incorporated in immune-stimulating complexes (ISCOMS) facilitates presentation and simultaneous cross-presentation of OVA by HEL-specific B cells in vitro. HEL-specific B cells stimulated CD8(+) T cell responses in vitro to the same extent as bone marrow-derived dendritic cells. Cross-presentation by specific B cells required endosomal acidification, proteasomal processing and classical MHC class I/peptide transport. Specific B cells also acquired both antigens rapidly in vivo and presented them to CD4(+) T cells. However, only HEL-specific B cells from OVA-HEL ISCOMS-immunised mice could cross-present OVA to naive OVA-specific CD8(+) T cells. Antigen-specific B cells were also activated selectively by OVA-HEL ISCOMS in vitro and importantly, the presence of HEL-specific B cells promoted the persistence of clonal expansion of OVA-specific CD8(+) T cells after in vivo immunisation with OVA-HEL ISCOMS. These results demonstrate preferential MHC class I and class II processing of cognate antigen incorporated in ISCOMS by specific B cells in vitro and in vivo, highlighting the ability of ISCOMS to target B cells and offering novel insights into the role of B cells in cross-presentation to CD8(+) T cells.

Activin-A: a novel dendritic cell-derived cytokine that potently attenuates CD40 ligand-specific cytokine and chemokine production.

Activin-A is a transforming growth factor-beta (TGF-beta) superfamily member that plays a pivotal role in many developmental and reproductive processes. It is also involved in neuroprotection, apoptosis of tumor and some immune cells, wound healing, and cancer. Its role as an immune-regulating protein has not previously been described. Here we demonstrate for the first time that activin-A has potent autocrine effects on the capacity of human dendritic cells (DCs) to stimulate immune responses. Human monocyte-derived DCs (MoDCs) and the CD1c(+) and CD123(+) peripheral blood DC populations express both activin-A and the type I and II activin receptors. Furthermore, MoDCs and CD1c(+) myeloid DCs rapidly secrete high levels of activin-A after exposure to bacteria, specific toll-like receptor (TLR) ligands, or CD40 ligand (CD40L). Blocking autocrine activin-A signaling in DCs using its antagonist, follistatin, enhanced DC cytokine (IL-6, IL-10, IL-12p70, and tumor necrosis factor-alpha [TNF-alpha]) and chemokine (IL-8, IP-10, RANTES, and MCP-1) production during CD40L stimulation, but not TLR-4 ligation. Moreover, antagonizing DC-derived activin-A resulted in significantly enhanced expansion of viral antigen-specific effector CD8(+) T cells. These findings establish an immune-regulatory role for activin-A in DCs, highlighting the potential of antagonizing activin-A signaling in vivo to enhance vaccine immunogenicity.

The combined CTA1-DD/ISCOM adjuvant vector promotes priming of mucosal and systemic immunity to incorporated antigens by specific targeting of B cells.

The cholera toxin A1 (CTA1)-DD/QuilA-containing, immune-stimulating complex (ISCOM) vector is a rationally designed mucosal adjuvant that greatly potentiates humoral and cellular immune responses. It was developed to incorporate the distinctive properties of either adjuvant alone in a combination that exerted additive enhancing effects on mucosal immune responses. In this study we demonstrate that CTA1-DD and an unrelated Ag can be incorporated together into the ISCOM, resulting in greatly augmented immunogenicity of the Ag. To demonstrate its relevance for protection against infectious diseases, we tested the vector incorporating PR8 Ag from the influenza virus. After intranasal immunization we found that the immunogenicity of the PR8 proteins were significantly augmented by a mechanism that was enzyme dependent, because the presence of the enzymatically inactive CTA1R7K-DD mutant largely failed to enhance the response over that seen with ISCOMs alone. The combined vector was a highly effective enhancer of a broad range of immune responses, including specific serum Abs and balanced Th1 and Th2 CD4(+) T cell priming as well as a strong mucosal IgA response. Unlike unmodified ISCOMs, Ag incorporated into the combined vector could be presented by B cells in vitro and in vivo as well as by dendritic cells; it also accumulated in B cell follicles of draining lymph nodes when given s.c. and stimulated much enhanced germinal center reactions. Strikingly, the enhanced adjuvant activity of the combined vector was absent in B cell-deficient mice, supporting the idea that B cells are important for the adjuvant effects of the combined CTA1-DD/ISCOM vector.

The role of dendritic cells in regulating mucosal immunity and tolerance.

The intestinal immune system discriminates between invasive pathogens and antigens that are harmless, such as food proteins and commensal bacteria. The latter groups of antigens normally induce tolerance and a breakdown in this homeostatic process can lead to diseases such as coeliac disease or Crohn's disease. The nature ofthe intestinal immune response depends on how antigen is presented to CD4+ T cells by dendritic cells (DCs). Both oral tolerance and priming are influenced by the numbers and activation status of DCs in the gut and its draining lymphoid tissues, and our current work indicates that dietary proteins are taken up preferentially by DCs in the lamina propria of the small intestine. These then migrate to interact with antigen-specific CD4+ T cells in the mesenteric lymph node. In vivo and in vitro studies using purified lamina propria DCs suggest these may play a unique role in the regulation of intestinal immune responses. We propose that local DCs are the gatekeepers of the mucosal immune system, inducing tolerance under physiological conditions, but being sufficiently responsive to inflammatory stimuli to allow T cell priming and protective immunity when necessary. In addition, we will discuss evidence that adjuvant vectors such as ISCOMS may be effective mucosal vaccines due to an ability to activate intestinal DCs.

The role of antigen-presenting cells and interleukin-12 in the priming of antigen-specific CD4+ T cells by immune stimulating complexes.

Immune stimulating complexes (ISCOMs) containing the saponin adjuvant Quil A are vaccine adjuvants that promote a wide range of immune responses in vivo, including delayed-type hypersensitivity (DTH) and the secretion of both T helper 1 (Th1) and Th2 cytokines. However, the antigen-presenting cell (APC) responsible for the induction of these responses has not been characterized. Here we have investigated the role of dendritic cells (DC), macrophages (Mphi) and B cells in the priming of antigen-specific CD4+ T cells in vitro by ISCOMs containing ovalbumin (OVA). OVA ISCOMs pulsed bone marrow (BM)-derived DC but not BM Mphi, nor naïve B cells prime resting antigen-specific CD4+ T cells, and this response is greatly enhanced if DC are activated with lipopolysaccharide (LPS). Of the APC found in the spleen, only DC had the capacity to prime resting antigen specific CD4+ T cells following exposure to OVA ISCOMs in vitro, while Mphi and B cells were ineffective. DC, but not B cells purified from the draining lymph nodes of mice immunized with OVA ISCOMs also primed resting antigen-specific CD4+ T cells in vitro, suggesting that DC are also critical in vivo. Using DC and T cells from interleukin (IL)-12 p40-/- mice, we also identified a crucial role for IL-12 in the priming of optimal CD4+ T cell responses by OVA ISCOMs. We suggest that DC are the principal APC responsible for the priming of CD4+ T cells by ISCOMs in vivo and that directed targeting of these vectors to DC may enhance their efficancy as vaccine adjuvants.

Dendritic cell maturation enhances CD8+ T-cell responses to exogenous antigen via a proteasome-independent mechanism of major histocompatibility complex class I loading.

Immune stimulating complexes (ISCOMS) containing the saponin adjuvant Quil A are vaccine adjuvants that induce a wide range of immune responses in vivo, including strong class I major histocompatibility complex (MHC)-restricted cytotoxic T-lymphocyte activity. However, the antigen-presenting cell responsible for the induction of these responses has not been characterized. Here we have investigated the role of dendritic cells (DC) in the priming of antigen-specific CD8+ T cells in vitro by ISCOMS containing ovalbumin. Resting bone marrow DC pulsed with ovalbumin ISCOMS efficiently prime resting CD8+ T cells through a mechanism that is transporter associated with antigen processing (TAP) dependent, but independent of CD40 ligation and CD4+ T-cell help. Lipopolysaccharide-induced maturation of DC markedly enhances their ability to prime CD8+ T cells through a mechanism which is also independent of CD4+ T-cell help, but is dependent on CD40 ligation. Furthermore, DC maturation revealed a TAP-independent mechanism of CD8+ T-cell priming. Our results also show that class I MHC-restricted presentation of ovalbumin in ISCOMS by DC is sensitive to chloroquine and brefeldin A but insensitive to lactacystin. We suggest that DC may be the principal antigen-presenting cells responsible for the priming of CD8+ T cells by ISCOMS in vivo and that targeting these vectors to activated DC may enhance their presentation via a novel pathway of class I antigen processing.

A role for dendritic cells in the priming of antigen-specific CD4+ and CD8+ T lymphocytes by immune-stimulating complexes in vivo.

Immune-stimulating complexes (ISCOMS) are adjuvant vectors which are unusual in being able to prime both CD4(+) and CD8(+) T cells by parenteral and mucosal routes. However, their mode of action is unclear and to define better the cellular interactions involved we have studied the ability of ISCOMS containing ovalbumin (OVA) to prime TCR transgenic CD4(+) or CD8(+) T cells in vivo. Immunization with OVA ISCOMS caused activation and clonal expansion of CD4(+) and CD8(+) T cells in the T cell areas of the draining lymph nodes, followed by the migration of both CD4(+) and CD8(+) T cells into the B cell follicle. The T cells were primed to proliferate and secrete IFN-gamma after re-stimulation in vitro with the appropriate OVA peptide and CD8(+) T cell priming occurred in the absence of CD4(+) T cells. Increasing the number of dendritic cells (DC) in vivo with flt3 ligand augmented the expansion and activation of the OVA-specific T cells, particularly CD8(+) T cells. These studies indicate DC play a central role in the priming of both CD4(+) and CD8(+) T cells in vivo, and suggest that an ability to target DC may allow ISCOMS to be powerful vaccine vectors for stimulating protective immunity.