Coupled As and Mn Redox Transformations in an Fe(0) Electrocoagulation System: Competition for Reactive Oxidants and Sorption Sites

Iron electrocoagulation (EC) can be used for the decentralized treatment of arsenic(As)-contaminated groundwater. Iron EC involves the electrolytic dissolution of an Fe(0) electrode to Fe(II). This process produces reactive oxidants, which oxidize As(III) and Fe(II) to As(V) and a range of Fe(III) (oxyhydr)oxide phases. Here, we investigated the impact of manganese (Mn) on As removal, since the two often co-occur in groundwater. In the absence of Mn(II), we observed rapid As(III) oxidation and the formation of As(V)-Fe(III) polymers. Arsenic removal was achieved upon aggregation of the As(V)-Fe(III) polymers. In the presence of Mn, the mechanism of As removal varied with pH. At pH 4.5, As(III) was oxidized rapidly by OH^• and the aggregation of the resulting As(V)-Fe(III) polymers was enhanced by the presence of Mn. At pH 8.5, As(III) and Mn(II) competed for Fe(IV), which led As(III) to persist in solution. The As(V) that did form was incorporated into a mixture of As(V)-Fe(III) polymers and a ferrihydrite-like phase that incorporated 8% Mn(III); some As(III) was also sorbed by these phases. At intermediate pH values, As(III) and Mn(II) also competed for the oxidants, but Mn(III) behaved as a reactive intermediate that reacted with Fe(II) or As(III). This result can explain the presence of As(V) in the solid phase. This detailed understanding of the As removal mechanisms in the presence of Mn can be used to tune the operating conditions of Fe EC for As removal under typical groundwater conditions.

Lymphatic endothelial cells prime naïve CD8+ T cells into memory cells under steady-state conditions

Lymphatic endothelial cells (LECs) chemoattract naïve T cells and promote their survival in the lymph nodes, and can cross-present antigens to naïve CD8+ T cells to drive their proliferation despite lacking key costimulatory molecules. However, the functional consequence of LEC priming of CD8+ T cells is unknown. Here, we show that while many proliferating LEC-educated T cells enter early apoptosis, the remainders comprise a long-lived memory subset, with transcriptional, metabolic, and phenotypic features of central memory and stem cell-like memory T cells. In vivo, these memory cells preferentially home to lymph nodes and display rapid proliferation and effector differentiation following memory recall, and can protect mice against a subsequent bacterial infection. These findings introduce a new immunomodulatory role for LECs in directly generating a memory-like subset of quiescent yet antigen-experienced CD8+ T cells that are long-lived and can rapidly differentiate into effector cells upon inflammatory antigenic challenge.

Adjuvant-free immunization with infective filarial larvae as lymphatic homing antigen carriers

Controlled infection with intestinal nematodes has therapeutic potential for preventing the symptoms of allergic and autoimmune diseases. Here, we engineered larvae of the filarial nematode Litomosoides sigmodontis as a vaccine strategy to induce adaptive immunity against a foreign, crosslinked protein, chicken egg ovalbumin (OVA), in the absence of an external adjuvant. The acylation of filarial proteins with fluorescent probes or biotin was not immediately detrimental to larval movement and survival, which died 3 to 5 days later. At least some of the labeled and skin-inoculated filariae migrated through lymphatic vessels to draining lymph nodes. The immunization potential of OVA-biotin-filariae was compared to that of an OVA-bound nanoparticulate carrier co-delivered with a CpG adjuvant in a typical vaccination scheme. Production of IFNγ and TNFα by restimulated CD4+ cells but not CD8+ confirmed the specific ability of filariae to stimulate CD4+ T cells. This alternative method of immunization exploits the intrinsic adjuvancy of the attenuated nematode carrier and has the potential to shift the vaccination immune response towards cellular immunity.

Antigens reversibly conjugated to a polymeric glyco-adjuvant induce protective humoral and cellular immunity

Fully effective vaccines for complex infections must elicit a diverse repertoire of antibodies (humoral immunity) and CD8⁺ T-cell responses (cellular immunity). Here, we present a synthetic glyco-adjuvant named p(Man-TLR7), which, when conjugated to antigens, elicits robust humoral and cellular immunity. p(Man-TLR7) is a random copolymer composed of monomers that either target dendritic cells (DCs) via mannose-binding receptors or activate DCs via Toll-like receptor 7 (TLR7). Protein antigens are conjugated to p(Man-TLR7) via a self-immolative linkage that releases chemically unmodified antigen after endocytosis, thus amplifying antigen presentation to T cells. Studies with ovalbumin (OVA)-p(Man-TLR7) conjugates demonstrate that OVA-p(Man-TLR7) generates greater humoral and cellular immunity than OVA conjugated to polymers lacking either mannose targeting or TLR7 ligand. We show significant enhancement of Plasmodium falciparum-derived circumsporozoite protein (CSP)-specific T-cell responses, expansion in the breadth of the αCSP IgG response and increased inhibition of sporozoite invasion into hepatocytes with CSP-p(Man-TLR7) when compared with CSP formulated with MPLA/QS-21-loaded liposomes-the adjuvant used in the most clinically advanced malaria vaccine. We conclude that our antigen-p(Man-TLR7) platform offers a strategy to enhance the immunogenicity of protein subunit vaccines.

Oxidation-sensitive polymersomes as vaccine nanocarriers enhance humoral responses against Lassa virus envelope glycoprotein

Lassa virus (LASV) causes severe hemorrhagic fever with high mortality, yet no vaccine currently exists. Antibodies targeting viral attachment proteins are crucial for protection against many viral infections. However, the envelope glycoprotein (GP)-1 of LASV elicits weak antibody responses due to extensive glycan shielding. Here, we explored a novel vaccine strategy to enhance humoral immunity against LASV GP1. Using structural information, we designed a recombinant GP1 immunogen, and then encapsulated it into oxidation-sensitive polymersomes (PS) as nanocarriers that promote intracellular MHCII loading. Mice immunized with adjuvanted PS (LASV GP1) showed superior humoral responses than free LASV GP1, including antibodies with higher binding affinity to virion GP1, increased levels of polyfunctional anti-viral CD4 T cells, and IgG-secreting B cells. PS (LASV GP1) elicited a more diverse epitope repertoire of anti-viral IgG. Together, these data demonstrate the potential of our nanocarrier vaccine platform for generating virus-specific antibodies against weakly immunogenic viral antigens.

Vaccine nanocarriers: Coupling intracellular pathways and cellular biodistribution to control CD4 vs CD8 T cell responses

Nanoparticle delivery systems are known to enhance the immune response to soluble antigens (Ags) and are thus a promising tool for the development of new vaccines. Our laboratory has engineered two different nanoparticulate systems in which Ag is either encapsulated within the core of polymersomes (PSs) or decorated onto the surface of nanoparticles (NPs). Previous studies showed that PSs are better at enhancing CD4 T cells and antibody titers, while NPs preferentially augment cytotoxic CD8 T cells. Herein, we demonstrate that the differential activation of T cell immunity reflects differences in the modes of intracellular trafficking and distinct biodistribution of the Ag in lymphoid organs, which are both driven by the properties of each nanocarrier. Furthermore, we found that Ags within PSs promoted better CD4 T cell activation and induced a higher frequency of CD4 T follicular helper (Tfh) cells. These differences correlated with changes in the frequency of germinal center B cells and plasma cell formation, which reflects the previously observed antibody titers. Our results show that PSs are a promising vector for the delivery of Ags for B cell vaccine development. This study demonstrates that nanocarrier design has a large impact on the quality of the induced adaptive immune response.

Toll-like receptor 8 agonist nanoparticles mimic immunomodulating effects of the live BCG vaccine and enhance neonatal innate and adaptive immune responses

Background

Newborns display distinct immune responses, leaving them vulnerable to infections and impairing immunization. Targeting newborn dendritic cells (DCs), which integrate vaccine signals into adaptive immune responses, might enable development of age-specific vaccine formulations to overcome suboptimal immunization.

Objective

Small-molecule imidazoquinoline Toll-like receptor (TLR) 8 agonists robustly activate newborn DCs but can result in reactogenicity when delivered in soluble form. We used rational engineering and age- and species-specific modeling to construct and characterize polymer nanocarriers encapsulating a TLR8 agonist, allowing direct intracellular release after selective uptake by DCs.

Methods

Chemically similar but morphologically distinct nanocarriers comprised of amphiphilic block copolymers were engineered for targeted uptake by murine DCs in vivo, and a range of TLR8 agonist–encapsulating polymersome formulations were then synthesized. Novel 96-well in vitro assays using neonatal human monocyte-derived DCs and humanized TLR8 mouse bone marrow–derived DCs enabled benchmarking of the TLR8 agonist–encapsulating polymersome formulations against conventional adjuvants and licensed vaccines, including live attenuated BCG vaccine. Immunogenicity of the TLR8 agonist adjuvanted antigen 85B (Ag85B)/peptide 25–loaded BCG-mimicking nanoparticle formulation was evaluated in vivo by using humanized TLR8 neonatal mice.

Results

Although alum-adjuvanted vaccines induced modest costimulatory molecule expression, limited T_H-polarizing cytokine production, and significant cell death, BCG induced a robust adult-like maturation profile of neonatal DCs. Remarkably, TLR8 agonist polymersomes induced not only newborn DC maturation profiles similar to those induced by BCG but also stronger IL-12p70 production. On subcutaneous injection to neonatal mice, the TLR8 agonist–adjuvanted Ag85B peptide 25 formulation was comparable with BCG in inducing Ag85B-specific CD4⁺ T-cell numbers.

Conclusion

TLR8 agonist–encapsulating polymersomes hold substantial potential for early-life immunization against intracellular pathogens. Overall, our study represents a novel approach for rational design of early-life vaccines.

Primary Human and Rat β-Cells Release the Intracellular Autoantigens GAD65, IA-2, and Proinsulin in Exosomes Together With Cytokine-Induced Enhancers of Immunity

The target autoantigens in several organ-specific autoimmune diseases, including type 1 diabetes (T1D), are intracellular membrane proteins, whose initial encounter with the immune system is poorly understood. Here we propose a new model for how these proteins can initiate autoimmunity. We found that rat and human pancreatic islets release the intracellular β-cell autoantigens in human T1D, GAD65, IA-2, and proinsulin in exosomes, which are taken up by and activate dendritic cells. Accordingly, the anchoring of GAD65 to exosome-mimetic liposomes strongly boosted antigen presentation and T-cell activation in the context of the human T1D susceptibility haplotype HLA-DR4. Cytokine-induced endoplasmic reticulum stress enhanced exosome secretion by β-cells; induced exosomal release of the immunostimulatory chaperones calreticulin, Gp96, and ORP150; and increased exosomal stimulation of antigen-presenting cells. We propose that stress-induced exosomal release of intracellular autoantigens and immunostimulatory chaperones may play a role in the initiation of autoimmune responses in T1D.

Polypropylene Sulfide Nanoparticle p24 Vaccine Promotes Dendritic Cell-Mediated Specific Immune Responses against HIV-1

Delivery of vaccine formulations into the dermis using antigen-coated microneedle patches is a promising and safe approach because of efficient antigen delivery and safety. We evaluated an intradermal vaccine using HIV-1 p24 Gag peptide-conjugated polypropylene sulfide nanoparticles to induce immunity against HIV-1. This peptide-conjugated polypropylene sulfide nanoparticle formulation did not accelerate the maturation of blood- or skin-derived subsets of dendritic cells, either generated in vitro or purified ex vivo, despite efficient uptake in the absence of adjuvant. Moreover, dendritic cell-mediated capture of particulate antigen in this form induced potent HIV-1-specific CD4(+) T-cell responses, as well as B-cell-mediated antibody production. Nanoparticle-based intradermal antigen delivery may therefore provide a new option in the global effort to develop an effective vaccine against HIV-1.

Modes of Antigen Presentation by Lymph Node Stromal Cells and Their Immunological Implications

Antigen presentation is no longer the exclusive domain of cells of hematopoietic origin. Recent works have demonstrated that lymph node stromal cell (LNSC) populations, such as fibroblastic reticular cells, lymphatic and blood endothelial cells, not only provide a scaffold for lymphocyte interactions but also exhibit active immunomodulatory roles that are critical to mounting and resolving effective immune responses. Importantly, LNSCs possess the ability to present antigens and establish antigen-specific interactions with T cells. One example is the expression of peripheral tissue antigens, which are presented on major histocompatibility complex (MHC)-I molecules with tolerogenic consequences on T cells. Additionally, exogenous antigens, including self and tumor antigens, can be processed and presented on MHC-I complexes, which result in dysfunctional activation of antigen-specific CD8⁺ T cells. While MHC-I is widely expressed on cells of both hematopoietic and non-hematopoietic origins, antigen presentation via MHC-II is more precisely regulated. Nevertheless, LNSCs are capable of endogenously expressing, or alternatively, acquiring MHC-II molecules. Transfer of antigen between LNSC and dendritic cells in both directions has been recently suggested to promote tolerogenic roles of LNSCs on the CD4⁺ T cell compartment. Thus, antigen presentation by LNSCs is thought to be a mechanism that promotes the maintenance of peripheral tolerance as well as generates a pool of diverse antigen-experienced T cells for protective immunity. This review aims to integrate the current and emerging literature to highlight the importance of LNSCs in immune responses, and emphasize their role in antigen trafficking, retention, and presentation.

Steady-state antigen scavenging, cross-presentation, and CD8+ T cell priming: a new role for lymphatic endothelial cells

Until recently, the known roles of lymphatic endothelial cells (LECs) in immune modulation were limited to directing immune cell trafficking and passively transporting peripheral Ags to lymph nodes. Recent studies demonstrated that LECs can directly suppress dendritic cell maturation and present peripheral tissue and tumor Ags for autoreactive T cell deletion. We asked whether LECs play a constitutive role in T cell deletion under homeostatic conditions. In this study, we demonstrate that murine LECs under noninflamed conditions actively scavenge and cross-present foreign exogenous Ags to cognate CD8(+) T cells. This cross-presentation was sensitive to inhibitors of lysosomal acidification and endoplasmic reticulum-golgi transport and was TAP1 dependent. Furthermore, LECs upregulated MHC class I and the PD-1 ligand PD-L1, but not the costimulatory molecules CD40, CD80, or CD86, upon Ag-specific interactions with CD8(+) T cells. Finally, Ag-specific CD8(+) T cells that were activated by LECs underwent proliferation, with early-generation apoptosis and dysfunctionally activated phenotypes that could not be reversed by exogenous IL-2. These findings help to establish LECs as APCs that are capable of scavenging and cross-presenting exogenous Ags, in turn causing dysfunctional activation of CD8(+) T cells under homeostatic conditions. Thus, we suggest that steady-state lymphatic drainage may contribute to peripheral tolerance by delivering self-Ags to lymph node-resident leukocytes, as well as by providing constant exposure of draining peripheral Ags to LECs, which maintain tolerogenic cross-presentation of such Ags.

Abstract 298: Tumor-associated lymphatic vessels: Hijacking mechanisms of peripheral tolerance

Lymphatic vessels drain fluid, antigens, and immune cells from the periphery to the lymph nodes (LNs). In addition to transporting activated dendritic cells to mount adaptive immune responses in the LN, lymphatic drainage is brings soluble antigens from the periphery to LN-resident immature dendritic cells and B cells. It is also the most common site for cancer metastasis. Despite its importance, the role of tumor-associated lymphatic vessels and their drainage to the LN in regulating host immune responses to the tumor is poorly understood. We show that tumor expression of VEGF-C, the most potent lymphatic growth factor, promotes pro-tumor immune tolerance by several mechanisms. For one, it enhances drainage to the draining LN, where tumor antigens along with suppressive cytokines bathe the LN and could affect B and T cell education there. Second, tumor VEGF-C upregulates CCL21 in the tumor stroma and surrounding lymphatic vessels, which itself promotes T cell infiltration and suppression. Third, VEGF-C drives peritumoral and LN lymphangiogenesis, which can modulate the myeloid cell repertoire towards more suppressive phenotypes. These changes resulted in increased infiltrations of regulatory T cells and myeloid-derived suppressor cells, and increased levels of regulatory cytokines. Interestingly, VEGF-C-expressing tumors were impervious to prior immunization against tumor antigen, unlike control-transfected tumors, which were hindered by the vaccine-induced immune response. Together, these findings suggest that lymphatic drainage serves to maintain peripheral tolerance and that tumors may hijack such mechanisms to escape host immunity.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 298. doi:1538-7445.AM2012-298

VEGF-C promotes immune tolerance in B16 melanomas and cross-presentation of tumor antigen by lymph node lymphatics

Tumor expression of the lymphangiogenic factor VEGF-C is correlated with metastasis and poor prognosis, and although VEGF-C enhances transport to the draining lymph node (dLN) and antigen exposure to the adaptive immune system, its role in tumor immunity remains unexplored. Here, we demonstrate that VEGF-C promotes immune tolerance in murine melanoma. In B16 F10 melanomas expressing a foreign antigen (OVA), VEGF-C protected tumors against preexisting antitumor immunity and promoted local deletion of OVA-specific CD8(+) T cells. Naive OVA-specific CD8(+) T cells, transferred into tumor-bearing mice, were dysfunctionally activated and apoptotic. Lymphatic endothelial cells (LECs) in dLNs cross-presented OVA, and naive LECs scavenge and cross-present OVA in vitro. Cross-presenting LECs drove the proliferation and apoptosis of OVA-specific CD8(+) T cells ex vivo. Our findings introduce a tumor-promoting role for lymphatics in the tumor and dLN and suggest that lymphatic endothelium in the local microenvironment may be a target for immunomodulation.

Abstract LB-151: Tumor VEGF-C promotes immune suppression and tolerance

The expression of the vascular endothelial growth factor, VEGF-C, is correlated with tumor invasion and hypothesized to induce metastasis through enhanced lymphangiogenesis and the creation of an “escape route”. However, new evidence suggests that VEGF-C can induce invasion in the absence of obvious tumor lymphangiogenesis, and furthermore, that lymphatic transport may play a role in modulating immunity. Still however, the role of the lymphatics as players in anti-tumor immunity and tumor invasion remains unexplored. Here we present a new model for VEGF-C induced tumor-invasion in which VEGF-C and lymphatic endothelial cells play a direct role in the suppression of anti-tumor immunity. Using a B16 F10 mouse melanoma that overexpresses VEGF-C, we demonstrated that VEGF-C induces the expression of the lymphoid homing cytokine, CCL21, within the stroma of the tumor and drives lymphocyte trafficking, fluid drainage and metastasis to the sentinel draining lymph node. Within the tumor stroma VEGF-C recruited a more regulatory immune cell infiltrate including increased regulatory T cells (CD25+FoxP3+) and M2 macrophages (CD11b+CD80-CD206+) and decreased antigen specific cytotoxic T cells (CD8+Trp2+). To test the ability of this mediated VEGF-C response to overcome host immunity we engineered a B16 F10 line to express ovalbumin (OVA) as a model tumor antigen. When we preimmunized the mice against OVA we observed that VEGF-C provided protection against vaccine (OVA/LPS) induced anti-tumor immunity. Growth of OVA bearing tumors was inhibited with vaccination and correlated with an increase in CD8+ antigen specific cytotoxic T cells. However, neither the growth nor the infiltration of cytotoxic T cells was affected by vaccination when the tumors also overexpressing VEGF-C. Additionally, to determine the fate of antigen specific CD8+ we adoptively transferred OT-I T cells by tail vein injection and observed their homing to the draining lymph nodes and tumor. In these microenvironments, when exposed to VEGF-C, adoptively transferred cells lost function over time as shown by the detection of Annexin V and decreased IFNγ expression. These results suggest that the expression of VEGF-C by a primary tumor not only promotes metastasis through the expansion of the lymphatic network but also through an immunological switch within the tumor and draining lymph node. We therefore present one of the first studies to identify an active, rather than passive, role for the lymphangiogenic growth factor, VEGF-C, and local lymphatic endothelial cells in the regulation of tumor immunity.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-151. doi:10.1158/1538-7445.AM2011-LB-151

Effect of inhibition of dynein function and microtubule-altering drugs on AAV2 transduction

Over the past decade, adeno-associated (AAV) virus has emerged as an important vector for gene therapy. As a result, understanding its basic biology, including intracellular trafficking, has become increasingly important. Here, we describe the effect of inhibiting dynein function or altering the state of microtubule polymerization on rAAV2 transduction. Overexpression of dynamitin, resulting in a functional inhibition of the minus-end-directed microtubule motor protein dynein, did not inhibit transduction. Equally, treatment of cells with nocodazole, or concentrations of vinblastine that result in the disruption of microtubules, had no significant effect on transduction. In contrast, high concentrations of Taxol and vinblastine, resulting in microtubule stabilization and the formation of tubulin paracrystals respectively, reduced rAAV2 transduction in a vector-dose-dependent manner. These results demonstrate that AAV2 can infect HeLa cells independently of dynein function or an intact microtubule network.

pH-Dependent lytic peptides discovered by phage display

Lipid membranes compartmentalize eukaryotic cells and separate the cell interior from the extracellular milieu. So far, studies of peptide and protein interactions with membranes have largely been limited to naturally occurring peptides or to sequences designed on the basis of structural information and biophysical parameters. To expand on these studies, utilizing a system with minimal assumptions, we used phage-display technology to identify 12 amino acid-long peptides that bind to liposomes at pH 5.0 but not at pH 7.5. Of the nineteen peptides discovered, three were able to cause leakage of liposome contents. Multivalent presentation of these membrane-active peptides by conjugation onto poly(l-Lysine) enhanced their lytic potential. The secondary structures were analyzed by circular dichroism in aqueous 2,2,2-trifluoroethanol and in buffered aqueous solutions, both in the presence and absence of liposomes. Two of the three lytic peptides show alpha helical profiles, whereas none of the nonlytic peptides formed stable secondary structures. The diverse characteristics of the peptides identified in this study demonstrate that phage-displayed peptide library screens on lipid membranes result in the discovery of nonclassical membrane-active peptides, whose study will provide novel insights into peptide-membrane interactions.

Plasmid DNA encapsulation and release from solvent diffusion nanospheres

The first step toward hydrophobic polymer-based nanospheres for gene delivery is to encapsulate and release plasmid DNA. However, encapsulating large hydrophilic molecules in very small nanospheres has been difficult, and only a few examples exist in the literature. For example, maximizing protein and peptide as well as small molecule encapsulation requires adjustments in pH or addition of excipients to charge neutralize, and make less hydrophilic, the compound to be encapsulated. Following this model, we have used a cationic lipid to load and release plasmid DNA from nanospheres made by the phase inversion/solvent diffusion method.