Increase in plasmacytoid and myeloid dendritic cells by progenipoietin-1, a chimeric Flt-3 and G-CSF receptor agonist, in SIV-Infected rhesus macaques

Distinct phenotype, longitudinal changes of numbers and cell-associated virus in blood dendritic cells in SIV-infected CD8-lymphocyte depleted macaques

Loss of circulating CD123+ plasmacytoid dendritic cells (pDCs) during HIV infection is well established. However, changes of myeloid DCs (mDCs) are ambiguous since they are studied as a homogeneous CD11c+ population despite phenotypic and functional heterogeneity. Heterogeneity of CD11c+ mDCs in primates is poorly described in HIV and SIV infection. Using multiparametric flow cytometry, we monitored longitudinally cell number and cell-associated virus of CD123+ pDCs and non-overlapping subsets of CD1c+ and CD16+ mDCs in SIV-infected CD8-depleted rhesus macaques. The numbers of all three DC subsets were significantly decreased by 8 days post-infection. Whereas CD123+ pDCs were persistently depleted, numbers of CD1c+ and CD16+ mDCs rebounded. Numbers of CD1c+ mDCs significantly increased by 3 weeks post-infection while numbers of CD16+ mDCs remained closer to pre-infection levels. We found similar changes in the numbers of all three DC subsets in CD8 depleted animals as we found in animals that were SIV infected animals that were not CD8 lymphocyte depleted. CD16+ mDCs and CD123+ pDCs but not CD1c+ mDCs were significantly decreased terminally with AIDS. All DC subsets harbored SIV RNA as early as 8 days and then throughout infection. However, SIV DNA was only detected in CD123+ pDCs and only at 40 days post-infection consistent with SIV RNA, at least in mDCs, being surface-bound. Altogether our data demonstrate that SIV infection differently affects CD1c+ and CD16+ mDCs where CD16+ but not CD1c+ mDCs are depleted and might be differentially regulated in terminal AIDS. Finally, our data underline the importance of studying CD1c+ and CD16+ mDCs as discrete populations, and not as total CD11c+ mDCs.

Whole blood stimulation with Toll-like receptor (TLR)-7/8 and TLR-9 agonists induces interleukin-12p40 expression in plasmacytoid dendritic cells in rhesus macaques but not in humans

Macaques provide important animal models in biomedical research into infectious and chronic inflammatory disease. Therefore, a proper understanding of the similarities and differences in immune function between macaques and humans is needed for adequate interpretation of the data and translation to the human situation. Dendritic cells are important as key regulators of innate and adaptive immune responses. Using a new whole blood assay we investigated functional characteristics of blood plasmacytoid dendritic cells (pDC), myeloid dendritic cells (mDC) and monocytes in rhesus macaques by studying induction of activation markers and cytokine expression upon Toll-like receptor (TLR) stimulation. In a head-to-head comparison we observed that rhesus macaque venous blood contained relatively lower numbers of pDC than human venous blood, while mDC and monocytes were present at similar percentages. In contrast to humans, pDC in rhesus macaques expressed the interleukin (IL)-12p40 subunit in response to TLR-7/8 as well as TLR-9 stimulation. Expression of IL-12p40 was confirmed by using different monoclonal antibodies and by reverse transcription-polymerase chain reaction (RT-PCR). Both in humans and rhesus macaques, TLR-4 stimulation induced IL-12p40 expression in mDC and monocytes, but not in pDC. The data show that, in contrast to humans, pDC in macaques are able to express IL-12p40, which could have consequences for evaluation of human vaccine candidates and viral infection.

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.

Dendritic cells and regulation of alloimmune responses: relevance to outcome and therapy of organ transplantation

Dendritic cells are uniquely well-equipped for antigen capture, processing and presentation. They are highly-efficient antigen-presenting cells that induce and regulate T-cell reactivity. Due to their inherent tolerogenicity, immature dendritic cells offer considerable potential as candidate cellular vaccines for negative regulation of immune reactivity/promotion of tolerance. Both classic myeloid and, more recently, characterized plasmacytoid dendritic cells, exhibit tolerogenic properties. Manipulation of dendritic cells differentiation/ maturation in the laboratory using cytokines, pharmacologic agents or genetic engineering approaches can render stably immature dendritic cells that promote organ transplant tolerance in rodents. There are also indications from human studies of the ability of dendritic cells to promote T-cell tolerance and induce T-regulatory cells, with potential for therapeutic application in organ transplantation. In addition, recent clinical observations suggest that modulation of dendritic cell function (e.g., by immunosuppressive drugs) affects the outcome of transplantation. The challenge confronting applied dendritic cell biology is the identification of optimal strategies and therapeutic regimens to allow the potential of these powerful immune regulatory cells to be realized in the clinic.

[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.

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.

Plasmacytoid dendritic cell dynamics and alpha interferon production during Simian immunodeficiency virus infection with a nonpathogenic outcome

We addressed the role of plasmacytoid dendritic cells (PDC) in protection against AIDS in nonpathogenic simian immunodeficiency virus (SIVagm) infection in African green monkeys (AGMs). PDC were monitored in blood and lymph nodes (LNs) starting from day 1 postinfection. We observed significant declines in blood during acute infection. However, PDC then returned to normal levels, and chronically infected AGMs showed no decrease of PDC in blood. There was a significant increase of PDC in LNs during acute infection. Blood PDC displayed only weak alpha interferon (IFN-alpha) responses to TLR9 agonist stimulation before infection. However, during acute infection, both blood and LN PDC showed a transiently increased propensity for IFN-alpha production. Bioactive IFN-alpha was detected in plasma concomitant with the peak of viremia, though levels were only low to moderate in some animals. Plasma interleukin 6 (IL-6) and IL-12 were not increased. In conclusion, PDC were recruited to the LNs and displayed increased IFN-alpha production during acute infection. However, increases in IFN-alpha were transient. Together with the lack of inflammatory cytokine responses, these events might play an important role in the low level of T-cell activation which is associated with protection against AIDS in nonpathogenic SIVagm infection.

Effect of SIVmac infection on plasmacytoid and CD1c+ myeloid dendritic cells in cynomolgus macaques

Dendritic cells (DCs) are known to be essential for the induction and regulation of immune responses. Non-human primates are essential in biomedical research and contribute to our understanding of the involvement of DCs in human infectious diseases. However, no direct single-platform method for quantifying DC precursors has yet been optimized in macaques to give accurate absolute blood counts of these rare-event cell populations in the blood. We adapted a rapid whole-blood assay for the absolute quantification of DCs in cynomolgus macaques by four-colour flow cytometry, using a single-platform assay compatible with human blood. Cynomolgus macaque plasmacytoid DCs (pDCs) and CD1c(+) myeloid DCs (CD1c(+) mDCs) were quantified in the blood of 34 healthy macaques and the results obtained were compared with those for blood samples from 11 healthy humans. In addition, circulating absolute numbers of pDCs were quantified in cynomolgus macaques chronically infected with SIVmac. During infection, pDC counts decreased whereas circulating CD1c(+) mDC counts increased. Information regarding absolute pDC and mDC counts in non-human primates may improve our understanding of the role of these cells in SIV/HIV infection and in other infectious diseases.

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.

Growth factor-induced mobilization of dendritic cells in kidney and liver of rhesus macaques: implications for transplantation

Hematopoietic growth factors (HGF) mobilize potential tolerogenic cells in transplant donors. Fms-like tyrosine kinase 3 ligand (Flt3L) mobilizes stem cells and dendritic cells (DCs) in human and nonhuman primate blood. Blood and renal and liver biopsies were obtained from untreated and Flt3L-mobilized rhesus macaques. Flt3L increased the number of myeloid CD11c(hi) and plasmacytoid CD123(hi) precursors in blood and both myeloid CD11c(+) HLA-DR(+) fascin(+) (CD45RA(-)) DCs and putative plasmacytoid CD11c(lo) CD45RA(hi) DC precursors in liver and kidneys, without affecting organ function. DC in Flt3L-treated monkeys were concentrated in the glomeruli and interstitium of kidneys, and in the portal triads and parenchyma of liver. These DCs exhibited the phenotype of immature antigen-presenting cells (APCs; CD83(-) CD86(lo) CCR5(+) CCR7(-)). HGF-induced changes reversed significantly within 7 days of Flt3L withdrawal. Therapeutic protocols that mobilize donor hematopoietic cells should consider the influence of HGF on the APC constituency of prospective organ allografts.

Development of murine plasmacytoid dendritic cell subsets

Plasmacytoid predendritic cells (pDC) are a haematopoietic cell population with a characteristic plasma cell-like morphology found in many tissues of the mouse, including blood, thymus, bone marrow, liver, and the T-cell areas of lymphoid organs. Recent studies of pDC have revealed them to be crucial mediators linking the innate and adaptive arms of the immune system. In this review, rather than focus on pDC function, we focus on recent evidence regarding pDC development. We examine the requirements for pDC development from several perspectives, including organ localization, cytokine requirements, development from myeloid- and lymphoid-restricted bone marrow precursors, expression of lineage-restricted markers, transcription factor dependence, and markers that separate pDC into distinct subsets.