Short-term Flt3L treatment effectively mobilizes functional macaque dendritic cells

Nonhuman Primate Models of Immunosenescence

Due to a dramatic increase in life expectancy, the number of individuals aged 65 and older is rapidly rising. This presents considerable challenges to our health care system since advanced age is associated with a higher susceptibility to infectious diseases due to immune senescence. However, the mechanisms underlying age-associated dysregulated immunity are still incompletely understood. Advancement in our comprehension of mechanisms of immune senescence and development of interventions to improve health span requires animal models that closely recapitulate the physiological changes that occur with aging in humans. Nonhuman primates (NHPs) are invaluable preclinical models to study the underlying causal mechanism of pathogenesis due to their outbred nature, high degree of genetic and physiological similarity to humans, and their susceptibility to human pathogens. In this chapter, we review NHP models available for biogerontology research, advantages and challenges they present, and advances they facilitated. Furthermore, we emphasize the utility of NHPs in characterizing immune senescence, evaluating interventions to reverse aging of the immune system, and development of vaccine strategies that are better suited for this vulnerable population.

Treatment with Fms-like tyrosine kinase 3 ligand reverses lung dendritic cell immunoparalysis and ameliorates zymosan-induced secondary lung injury in mice

Depletion and dysfunction of dendritic cells in the lung can induce local immunoparalysis, which often leads to multiple organ dysfunction syndrome (MODS)-associated mortality. A therapeutic strategy that reverses this immunoparalysis is required. In the present study, we examined the effects of in vivo Fms-like tyrosine kinase 3 ligand (Flt3L) treatment on zymosan (zym)-induced secondary lung injury and dendritic cell (DC) immunoparalysis. BALBc mice were divided randomly into four groups (20/group): (1) sham [intraperitoneal (i.p.) saline] + vehicle [subcutaneous (s.c.) 0·01% mouse serum albumin]; (2) sham + Flt3L (s.c.); (3) zym (i.p.) + vehicle; and (4) zym + Flt3L. Injections were for 9 consecutive days; 12 days later we examined: survival rate (monitored for 12 days); lung tissue histopathology (haematoxylin and eosin staining); plasma indices of lung function (pH, PaO(2) , PaCO(2) , HCO(3) (-) ); DC subsets in lung tissue; and lung DCs production of interleukin (IL)-12p70 and IL-10. Zym administration resulted in increased mortality associated with significant lung histopathological changes and abnormal blood gas indices; however, these pathological changes were ameliorated by Flt3L treatment. Zym injections also resulted in significant reductions in DC subsets recovered from lungs [CD11c(+) major histocompatibility complex (MHC)-II/I-A(d+) , CD11c(+) CD11b(+) and CD11c(+) B220(+) ]. Importantly, in-vivo Flt3L treatment reversed these trends for DC immunoparalysis by increasing the percentages of recovered DC subsets concomitant with increased DC production of IL-12 p70 and decreased IL-10 production. These results suggest that Flt3L may have therapeutic potential for reversing DC immunoparalysis and ameliorating lung injury secondary to MODS.

Simian immunodeficiency virus interactions with macaque dendritic cells

This chapter summarizes advances in the following areas: (1) dendritic cell (DC)-mediated simian immunodeficiency virus (SIV) transmission, (2) role of DCs in innate and adaptive immunity against SIV, and (3) approaches to harness DC function to induce anti-SIV responses. The nonhuman primate (NHP) model of human immunodeficiency virus (HIV) infection in rhesus macaques and other Asian NHP species is highly relevant to advance the understanding of virus-host interactions critical for transmission and disease pathogenesis. HIV infection is associated with changes in frequency, phenotype, and function of the two principal subsets of DCs, myeloid DCs and plasmacytoid DCs. DC biology during pathogenic SIV infection is strikingly similar to that observed in HIV-infected patients. The NHP models provide an opportunity to dissect the requirements for DC-driven SIV infection and to understand how SIV distorts the DC system to its advantage. Furthermore, the SIV model of mucosal transmission enables the study of the earliest events of infection at the portal of entry that cannot be studied in humans, and, importantly, the involvement of DCs. Nonpathogenic infection in African NHP hosts allows investigations into the role of DCs in disease control. Understanding how DCs are altered during SIV infection is critical to the design of therapeutic and preventative strategies against HIV.

Non-human primate dendritic cells

Non-human primates (NHP) are essential translational models for biomedical research. Dendritic cells (DC) are a group of antigen presenting cells (APC) that play pivotal roles in the immunobiology of health and disease and are attractive cells for adoptive immunotherapy to stimulate and suppress immunity. DC have been studied extensively in humans and mice but until recently, have not been well characterized in NHP. This review considers the available data about DC across a range of NHP species and summarizes the understanding of in vitro-propagated DC and in vivo-isolated DC, which is now established. It is clear that although NHP DC exist within the paradigm of human DC, there are important functional and phenotypic differences when compared with human DC subsets. These differences need to be taken into account when designing preclinical, translational studies of DC therapy using NHP models.

Dissecting the role of dendritic cells in simian immunodeficiency virus infection and AIDS

Human immunodeficiency virus (HIV) infection is associated with the loss of the two principal types of dendritic cell (DC), myeloid DC (mDC) and plasmacytoid DC (pDC), but the mechanism of this loss and its relationship to AIDS pathogenesis remain ill-defined. The nonhuman primate is a powerful model to dissect this response for several reasons. Both DC subsets have been well characterized in nonhuman primates and shown to have strikingly similar phenotypic and functional characteristics to their counterparts in the human. Moreover, decline of mDC and pDC occurs in rhesus macaques with end-stage simian immunodeficiency virus (SIV) infection, the model of HIV infection in humans. In this brief review, we discuss what is known about DC subsets in pathogenic and nonpathogenic nonhuman primate models of HIV infection and highlight the advances and controversies that currently exist in the field.

Cytokine adjuvants for vaccine therapy of neoplastic and infectious disease

Vaccination, the revolutionary prophylactic immunotherapy developed in the eighteenth century, has become the most successful and cost-effective of medical remedies available to modern society. Due to the remarkable accomplishments of the past century, the number of diseases and pathogens for which a traditional vaccine approach might reasonably be employed has dwindled to unprecedented levels. While this happy scenario bodes well for the future of public health, modern immunologists and vaccinologists face significant challenges if we are to address the scourge of recalcitrant pathogens like HIV and HCV and well as the significant obstacles to immunotherapy imposed by neoplastic self. Here, the authors review the clinical and preclinical literature to highlight the manner by which the host immune system can be successfully manipulated by cytokine adjuvants, thereby significantly enhancing the efficacy of a wide variety of vaccination platforms.

Decreased numbers of peripheral blood dendritic cells in patients with coronary artery disease are associated with diminished plasma Flt3 ligand levels and impaired plasmacytoid dendritic cell function

We investigated whether activation of circulating DCs (dendritic cells) or levels of Flt3L (FMS-like tyrosine kinase 3 ligand) and GM-CSF (granulocyte/macrophage colony-stimulating factor), haematopoietic growth factors important for DC differentiation, could account for reduced blood DC numbers in CAD (coronary artery disease) patients. Concentrations of Flt3L and GM-CSF were measured in plasma from CAD patients (n = 15) and controls (n = 12). Frequency and phenotype of mDCs (myeloid dendritic cells) and pDCs (plasmacytoid dendritic cells) were analysed by multicolour flow cytometry in fresh blood, and after overnight incubation with TLR (Toll-like receptor)-4 or -7 ligands LPS (lipopolysaccharide) or IQ (imiquimod). DC function was measured by IL (interleukin)-12 and IFN (interferon)-α secretion. Circulating numbers of CD11c+ mDCs and CD123+ pDCs and frequencies of CD86+ and CCR-7+ (CC chemokine receptor type 7) mDCs, but not pDCs, were declined in CAD. In addition, plasma Flt3L, but not GM-CSF, was lower in patients and positively correlated with blood DC counts. In response to LPS, mDCs up-regulated CD83 and CD86, but CCR-7 expression and IL-12 secretion remained unchanged, similarly in patients and controls. Conversely, pDCs from patients had lower CD83 and CCR-7 expression after overnight incubation and had a weaker IQ-induced up-regulation of CD83 and IFN-α secretion. In conclusion, our results suggest that reduced blood DC counts in CAD are, at least partly, due to impaired DC differentiation from bone marrow progenitors. Decreased levels of mDCs are presumably also explained by activation and subsequent migration to atherosclerotic plaques or lymph nodes. Although mDCs are functioning normally, pDCs from patients appeared to be both numerically and functionally impaired.

Nonhuman primate models of human immunology

Nonhuman primates have been used for biomedical research for several decades. The high level of genetic homology to humans coupled with their outbred nature has made nonhuman primates invaluable preclinical models. In this review, we summarize recent advances in our understanding of the nonhuman primate immune system, with special emphasis on studies carried out in rhesus macaque (Macaca mulatta). We highlight the utility of nonhuman primates in the characterization of immune senescence and the evaluation of new interventions to slow down the aging of the immune system.

Mobilization of CD34+ progenitor cells in association with decreased proliferation in the bone marrow of macaques after administration of the Fms-like tyrosine kinase 3 ligand

Fms-like tyrosine kinase 3 ligand (FLT3-L) is critical for the differentiation and self-renewal of CD34+ progenitor cells in primates and has been used therapeutically to mobilize progenitor and dendritic cells in vivo. However, little is known regarding the expansion of progenitor cells outside of peripheral blood, particularly in bone marrow (BM), where progenitor cells primarily reside. Evaluation of FLT3-L-mediated cell mobilization during lentivirus infections, where the numbers of CD34+ progenitor cells are reduced, is limited. We enumerated frequencies and absolute numbers of CD34+ progenitor cells in blood and BM of naive and SIV- or SHIV-infected macaques during and after the administration of FLT3-L. Flow cytometric analyses revealed that, while CD34+ cells increased in the circulation, no expansion was observed in BM. Furthermore, in the BM intracellular Ki67, a marker of cell proliferation, was downregulated in CD34+ progenitor cells but was upregulated significantly in the bulk cell population. Although the exact mechanism(s) remains unclear, these data suggest that CD34+ cell mobilization in blood was the result of cellular emigration from BM and not the proliferation of CD34+ cells already in the periphery. It is possible that the decreased progenitor cell proliferation observed in BM is evidence of a negative regulatory mechanism preventing hyperproliferation and development of neoplastic cells.

[Roles of dendritic cell in disease progression of AIDS primate models]

Non-human primate models are widely used in research of AIDS mechanism, transmission, vaccine and drugs. Dendritic cells (DC), as antigen presenting cells linking the innate immunity and acquired immunity, play a pivotal role in AIDS progression. Studies on the change of DC subsets number, phenotype and function in AIDS non-human primate models are important for revealing some mechanism of AIDS progression. This article reviews the progress in DC subsets of non-human primate AIDS models, which will provide an avenue for further study in AIDS.

Cyclophosphamide induces dynamic alterations in the host microenvironments resulting in a Flt3 ligand-dependent expansion of dendritic cells

Preconditioning a recipient host with lymphodepletion can markedly augment adoptive T cell therapy. However, the precise mechanisms involved are poorly understood. In a recent study, we observed a significant increase in the circulating levels of dendritic cells (DCs; CD11c(+)CD11b(+)) during the recovery from cyclophosphamide (CTX)-induced lymphodepletion. Herein, we demonstrate that the CTX-induced DC expansion was not altered by adjuvant chemotherapy or tumor burden but was augmented by coadministration of granulocyte-colony stimulating factor. Although the increase in the number of DCs was preceded by a systemic expansion of a population expressing the phenotype of myeloid-derived suppressor cells (Gr-1(+)CD11b(+)), depletion of these Gr-1(+) cells had no effect on the noted expansion. Moreover, when Gr-1(high)CD11b(high) cells were sorted from CTX-treated mice and adoptively transferred into control or CTX-treated recipients, they did not differentiate into DCs. Post-CTX expansion of DCs was associated with proliferation of DCs in bone marrow (BM) during the lymphopenic phase and in the blood and spleen during the recovery phase. Furthermore, adoptive transfer of BM cells from CTX-treated mice produced equal numbers of DCs in the blood of either CTX-treated or untreated recipients. CTX induced a dynamic surge in the expression of growth factors and chemokines in BM, where CCR2 and Flt3 signaling pathways were critical for DC expansion. In sum, our data suggest that CTX induces proliferation of DCs in BM prior to their expansion in the periphery. Targeting DCs at these phases would significantly improve their contribution to the clinical application of lymphodepletion to adoptive immunotherapy.

Systemic dendritic cell mobilization associated with administration of FLT3 ligand to SIV- and SHIV-infected macaques

Reports indicate that myeloid and plasmacytoid dendritic cells (mDCs and pDCs), which are key effector cells in host innate immune responses, can be infected with HIV-1 and are reduced in number and function during the chronic phase of HIV disease. Furthermore, it was recently demonstrated that a sustained loss of mDCs and pDCs occurs in SIV-infected macaques. Since loss of functional DC populations might impair innate immune responses to opportunistic microorganisms and neoplastic cells, we explored whether inoculation of naive and SIV- or SHIV-infected pigtailed macaques with the hematopoietic cytokine FLT3-ligand (FLT3-L) would expand the number of mDCs and pDCs in vivo. After the macaques received supraphysiologic doses of FLT3-L, mDCs, pDCs, and monocytes increased up to 45-fold in blood, lymph nodes, and bone marrow (BM), with DC expansion in the BM preceding mobilization in blood and lymphoid tissues. FLT3-L also increased serum levels of IL-12, at least transiently, and elicited higher surface expression of HLA-DR and the activation markers CD25 and CD69 on NK and T cells. During and after treatment of infected animals, APCs increased in number and were activated; however, CD4(+) T cell numbers, virion RNA, and anti-SIV/SHIV antibody titers remained relatively stable, suggesting that FLT3-L might be a safe modality to expand DC populations and provide therapeutic benefit during chronic lentivirus infections.

Surface phenotype and rapid quantification of blood dendritic cell subsets in the rhesus macaque

BACKGROUND

The study of dendritic cell (DC) biology in the rhesus macaque is becoming increasingly important but is limited by incomplete characterization and the lack of a rapid assay to quantify cells.

METHODS

We characterized the surface phenotype of myeloid (mDC) and plasmacytoid DC (pDC) subsets in healthy rhesus macaque blood and developed a flow cytometry-based assay for absolute DC determinations.

RESULTS

Rhesus CD11c(+) mDC were CD16(+) CD11b(+) CD56(lo) CD8(-) CD1c(-) whereas CD123(+) pDC lacked expression of these markers. Precise DC determinations were performed using a rapid two-step assay combining the analysis of whole blood and peripheral blood leukocytes (PBL).

CONCLUSIONS

Antibodies to CD11b, CD56 and CD16 must be omitted from the lineage antibody cocktail to prevent inadvertent gating-out of DC when analyzing rhesus blood. The combined whole-blood/PBL quantification assay will be invaluable for the rapid and repeated monitoring of blood DC counts in this species.

Expression and function of Toll-like receptors on dendritic cells and other antigen presenting cells from non-human primates

Antigen presenting cells (APCs), especially dendritic cells (DCs), play a crucial role in immune responses against infections by sensing microbial invasion through Toll-like receptors (TLRs). In this regard, TLR ligands are attractive candidates for use in humans and animal models as vaccine adjuvants. So far, no studies have been performed on TLR expression in non-human primates such as rhesus macaques. Therefore, we studied the TLR expression patterns in different subsets of APC in rhesus macaques and compared them to similar APC subsets in human. Also, expression was compared with corresponding DC subsets from different organs from mice. Here we show by semi-quantitative RT-PCR, that blood DC subsets of rhesus macaque expressed the same sets of TLRs as those of human but substantially differed from mouse DC subsets. Macaque myeloid DCs (MDCs) expressed TLR3, 4, 7 and 8 whereas macaque plasmacytoid DCs (PDCs) expressed only TLR7 and 9. Additionally, TLR expression patterns in macaque monocyte-derived dendritic cells (mo-DCs) (i.e., TLR3, 4, 8 and 9), monocytes (i.e., TLR4, 7, and 8) and B cells (i.e., TLR4, 7, 8, and 9) were also similar to their human counterparts. However, the responsiveness of macaque APCs to certain TLR ligands partially differed from that of human in terms of phenotype differentiation and cytokine production. Strikingly, in contrast to human mo-DCs, no IL-12p70 production was observed when macaque mo-DCs were stimulated with TLR ligands. In addition, CD40 and CD86 phenotypic responses to TLR8 ligand (poly U) in mo-DCs of macaque were higher than that of human. Despite these functional differences, our results provide important information for a rational design of animal models in evaluating TLR ligands as adjuvant in vivo.

Characterization of plasmacytoid dendritic cells in bone marrow of pig-tailed macaques

Plasmacytoid dendritic cells (pDCs), one of two types of bone marrow (BM)-derived blood DCs, play an important role in linking innate and adaptive immune responses. However, little is known about the nature of pDCs that reside in the BM. Because the simian immunodeficiency virus-macaque model closely mimics human immunodeficiency virus disease in humans, with both infections inducing a decrease in pDCs, we characterized and compared pDCs in the BM with those in peripheral blood (PB) of healthy pig-tailed macaques. The results revealed that pDCs from both compartments had the same CD123++ HLA-DR+ Lin- phenotype and were similar in size. Although BM-derived pDCs (BM-pDCs) were 3-fold greater in frequency and 10-fold greater in number, they had lower cell surface expression of both HLA-DR and the costimulatory molecule CD86 than did PB-pDCs. Both BM- and PB-pDCs responded ex vivo to synthetic CpG oligodeoxynucleotides and inactivated influenza virus by upregulating HLA-DR and CD86 and secreting cytokines; however, stimulated BM-pDCs secreted less alpha interferon and tumor necrosis factor alpha per cell than did PB-pDCs. These results suggest that while BM-pDCs appear to be phenotypically less mature than PB-pDCs, they do respond to pathogens. Thus, during acute infections, these cells could initiate immune responses either in the BM or after rapidly migrating from the BM into the periphery. A better characterization of pDCs in blood and tissues will be beneficial for future studies of macaques that focus on either pathogenesis or vaccine development.

Adjuvanting a DNA vaccine with a TLR9 ligand plus Flt3 ligand results in enhanced cellular immunity against the simian immunodeficiency virus

DNA vaccines offer promising strategies for immunization against infections. However, their clinical use requires improvements in immunogenicity. We explored the efficacy of Toll-like receptor (TLR) ligands (TLR-Ls) on augmenting the immunogenicity of a DNA prime–modified vaccinia virus Ankara (MVA) boost vaccine against SIV. Rhesus macaques were injected with Fms-like tyrosine kinase 3 (Flt3)–ligand (FL) to expand dendritic cells (DCs) and were primed with a DNA vaccine encoding immunodeficiency virus antigens mixed with ligands for TLR9 or TLR7/8. Subsequently, the animals were boosted with DNA and twice with recombinant MVA expressing the same antigens. TLR9-L (CpG DNA) mediated activation of DCs in vivo and enhanced the magnitude of antigen-specific CD8⁺ interferon (IFN) γ⁺ T cells and polyfunctional CD8⁺ T cells producing IFN-γ, tumor necrosis factor α, and interleukin 2. Although this trial was designed primarily as an immunogenicity study, we challenged the animals with pathogenic SIVmac₂₅₁ and observed a reduction in peak viremia and cumulative viral loads in the TLR9-L plus FL-adjuvanted group relative to the unvaccinated group; however, the study design precluded comparisons between the adjuvanted groups and the group vaccinated with DNA/MVA alone. Viral loads were inversely correlated with the magnitude and quality of the immune response. Thus, the immunogenicity of DNA vaccines can be augmented with TLR9-L plus FL.

Infusion of Stably Immature Monocyte-Derived Dendritic Cells Plus CTLA4Ig Modulates Alloimmune Reactivity in Rhesus Macaques

BACKGROUND

Immature dendritic cells (DC) can promote long-term transplant survival in rodents. We assessed the impact of stably immature, donor-derived DC on alloimmune reactivity in rhesus macaques.

METHODS

CD14 monocytes isolated from leukapheresis products of Macacca mulatta were cultured in granulocyte-macrophage colony stimulating factor plus interleukin (IL)-4+/-vitamin (vit) D3, and IL-10. Major histocompatibility complex class II and cosignaling molecule expression was determined on CD11c cells by flow cytometry. T-cell allostimulatory capacity of the DC, including DC exposed to proinflammatory cytokines, was determined in mixed leukocyte reaction. To test their influence in vivo, purified DC were infused intravenously into allogeneic recipients, either alone or followed by CTLA4Ig, 24 hr later. Proliferative responses of recipient CFSE-labeled T cells to donor or third party DC, cytokine production by stimulated T cells, and circulating alloantibody levels were determined by flow cytometry, up to 100 days postinfusion.

RESULTS

VitD3/IL-10-conditioned, monocyte-derived DC were resistant to maturation and failed to induce allogeneic T cell proliferation in vitro. After their infusion, an increase in anti-donor and anti-third party T-cell reactivity was observed, that subsequently subsided to fall significantly below pretreatment levels (by day 56) only in animals also given CTLA4Ig. No increase in circulating immunoglobulin (Ig) M or IgG anti-donor alloantibody titers compared with pretreatment values was detected. With DC+CTLA4Ig infusion, alloreactive IL-10-producing T cells were prevalent in the circulation after day 28.

CONCLUSIONS

Maturation-resistant rhesus DC infusion is well-tolerated. DC+CTLA4Ig infusion modulates allogeneic T-cell responses and results in hyporesponsiveness to donor and third party alloantigens.

Parallel Loss of Myeloid and Plasmacytoid Dendritic Cells from Blood and Lymphoid Tissue in Simian AIDS

The loss of myeloid (mDC) and plasmacytoid dendritic cells (pDC) from the blood of HIV-infected individuals is associated with progressive disease. It has been proposed that DC loss is due to increased recruitment to lymph nodes, although this has not been directly tested. Similarly as in HIV-infected humans, we found that lineage-negative (Lin(-)) HLA-DR(+)CD11c(+)CD123(-) mDC and Lin(-)HLA-DR(+)CD11c(-)CD123(+) pDC were lost from the blood of SIV-infected rhesus macaques with AIDS. In the peripheral lymph nodes of SIV-naive monkeys the majority of mDC were mature cells derived from skin that expressed high levels of HLA-DR, CD83, costimulatory molecules, and the Langerhans cell marker CD1a, whereas pDC expressed low levels of HLA-DR and CD40 and lacked costimulatory molecules, similar to pDC in blood. Surprisingly, both DC subsets were depleted from peripheral and mesenteric lymph nodes and spleens in monkeys with AIDS, although the activation status of the remaining DC subsets was similar to that of DC in health. In peripheral and mesenteric lymph nodes from animals with AIDS there was an accumulation of Lin(-)HLA-DR(moderate)CD11c(-)CD123(-) cells that resembled monocytoid cells but failed to acquire a DC phenotype upon culture, suggesting they were not DC precursors. mDC and pDC from the lymphoid tissues of monkeys with AIDS were prone to spontaneous death in culture, indicating that apoptosis may be a mechanism for their loss in disease. These findings demonstrate that DC are lost from rather than recruited to lymphoid tissue in advanced SIV infection, suggesting that systemic DC depletion plays a direct role in the pathophysiology of AIDS.

Local and systemic effects of intranodally injected CpG-C immunostimulatory-oligodeoxyribonucleotides in macaques

Immunostimulatory CpG-C oligodeoxyribonucleotides (ISS-ODNs) represent a promising strategy to enhance vaccine efficacy. We have shown that the CpG-C ISS-ODN C274 stimulates macaque blood dendritic cells (DCs) and B cells and augments SIV-specific IFN-gamma responses in vitro. To further explore the potential of C274 for future vaccine studies, we assessed the in vivo effects of locally administered C274 (in naive and healthy infected macaques). Costimulatory molecules were marginally increased on DCs and B cells within cells isolated from C274-injected lymph nodes (LNs). However, cells from C274-injected LNs exhibited heightened responsiveness to in vitro culture. This was particularly apparent at the level of CD80 (less so CD86) expression by CD123(+) plasmacytoid DCs and was further boosted in the presence of additional C274 in vitro. Notably, cells from C274-injected LNs secreted significantly elevated levels of several cytokines and chemokines upon in vitro culture. This was more pronounced when cells were exposed to additional stimuli in vitro, producing IFN-alpha, IL-3, IL-6, IL-12, TNF-alpha, CCL2, CCL3, CCL5, and CXCL8. Following C274 administration in the absence of additional SIV Ag, endogenous IFN-gamma secretion was elevated in LN cells of infected animals, but SIV-specific responses were unchanged. Endogenous and SIV-specific responses decreased in blood, before the SIV-specific responses rebounded by 2 wk after C274 treatment. Elevated IFN-alpha, CCL2, and CCL5 were also detected in the plasma after C274 injection. Thus, locally administered C274 has local and systemic activities, supporting the potential for CpG-C ISS-ODNs to boost immune function to enhance anti-HIV vaccine immunogenicity.

Intramuscular immunization with plasmid coexpressing tumour antigen and Flt-3L results in potent tumour regression

Dendritic cells (DC) are professional antigen-presenting cells capable of initiating a potent primary immune response, making them an attractive target for cancer immunotherapy. Flt-3 ligand (Flt-3L) is a haematopoietic growth factor that efficiently induces DC expansion in vivo. To achieve a more efficient and effective method of priming tumour-specific, DC-mediated immune response, we generated a DNA vaccine comprising both human Flt-3L and the tumour antigen, MUC-1 (pNGVL-hFLex-MUC-1). We report that pNGVL-hFLex-MUC-1 is able to induce antigen-specific CTL immunity in vivo, resulting in a potent anti-tumour response, and that the Flt-3L component is essential to the efficacy of the DNA vaccine. Moreover, the route of immunization is critical in determining the type of immune response generated; intramuscular (i.m.) immunization with pNGVL-hFLex-MUC-1 conferred tumour protection in contrast to poor response with hydrodynamic-based intravenous delivery. Post-i.m. immunization, we observed a massive infiltration of mononuclear cells to the injection site, comprised predominantly of CD11c(+)/CD8alpha(-) DC. Therefore, we propose that Flt-3L acts as an adjuvant to recruit DC, thereby priming the anti-tumour response. However, systemic expansion of DC prior to immunization did not enhance the specific cellular response, suggesting that it is in situ recruitment or expansion of DC that is critical for pNGVL-hFLex-MUC-1 potency.

Dendritic cells and HIV infection: activating dendritic cells to boost immunity

Dendritic cells (DCs) are white blood cells that coordinate innate and adaptive immunity. They are distributed within epithelia and mucosal-associated lymphoid tissues, positioned to entrap incoming pathogens or vaccines. Human immunodeficiency virus (HIV) and the non-human primate equivalent (SIV) exploit DCs to amplify infection, underscoring the need to harness strategies that promote presentation of virus by DCs to stimulate potent anti-viral immunity instead of virus transmission. Two main subsets of DCs need to be considered: myeloid (MDC) and plasmacytoid (PDC) subsets. Using the SIV-macaque system to advance oral vaccine research, we examined macaque PDC and MDC biology, identifying ways to activate DCs and boost antiviral immunity. Immunostimulatory oligodeoxyribonucleotides (ISS-ODNs) stimulated PDC/MDC mixtures to up-regulate co-stimulatory molecule expression and to secrete both IFN-alpha and IL-12. Additionally, ISS-ODNs augmented SIV-specific IFN-gamma responses induced by virus-bearing DCs. ISS-ODN-driven DC activation is being pursued to improve oral/nasopharyngeal mucosal vaccines and therapies against HIV.

CpG-C immunostimulatory oligodeoxyribonucleotide activation of plasmacytoid dendritic cells in rhesus macaques to augment the activation of IFN-gamma-secreting simian immunodeficiency virus-specific T cells

There are two principle subsets of dendritic cells (DCs); CD11c(+)CD123(-) myeloid DCs (MDCs) and CD11c(-)CD123(+) plasmacytoid DCs (PDCs). DC activation via TNF-TNFRs (e.g., CD40L) and TLRs (e.g., immunostimulatory oligodeoxyribonucleotides (ISS-ODNs)) is crucial for maximal stimulation of innate and adaptive immunity. Macaque DC biology is being studied to improve HIV vaccines using the SIV macaque model. Using lineage (Lin) markers to exclude non-DCs, Lin(-)HLA-DR(+)CD11c(+)CD123(-) MDCs and Lin(-)HLA-DR(+)CD11c(-)CD123(+) PDCs were identified in the blood of uninfected macaques and healthy macaques infected with SIV or simian-human immunodeficiency virus. Overnight culture of DC-enriched Lin-depleted cells increased CD80 and CD86 expression. IL-12 production and CD80/CD86 expression by MDC/PDC mixtures was further enhanced by CD40L and ISS-ODN treatment. A CpG-B ISS-ODN increased CD80/CD86 expression by PDCs, but resulted in little IFN-alpha secretion unless IL-3 was added. In contrast, a CpG-C ISS-ODN and aldrithiol-2-inactivated (AT-2) SIV induced considerable PDC activation and IFN-alpha release without needing exogenous IL-3. The CpG-C ISS-ODN also stimulated IL-12 release (unlike AT-2 SIV) and augmented DC immunostimulatory activity, increasing SIV-specific T cell IFN-gamma production induced by AT-2 SIV-presenting MDC/PDC-enriched mixtures. These data highlight the functional capacities of MDCs and PDCs in naive as well as healthy, infected macaques, revealing a promising CpG-C ISS-ODN-driven DC activation strategy that boosts immune function to augment preventative and therapeutic vaccine efficacy.