Effects of administration of progenipoietin 1, Flt-3 ligand, granulocyte colony-stimulating factor, and pegylated granulocyte-macrophage colony-stimulating factor on dendritic cell subsets in mice

Murine Flt3 ligand expands distinct dendritic cells with both tolerogenic and immunogenic properties

Human Flt3 ligand can expand dendritic cells (DC) and enhance immunogenicity in mice. However, little is known about the effects of murine Flt3 ligand (mFlt3L) on mouse DC development and function. We constructed a vector to transiently overexpress mFlt3L in mice. After a single treatment, up to 44% of splenocytes became CD11c(+) and the total number of DC increased 100-fold. DC expansion effects lasted for >35 days. mFlt3L DC were both phenotypically and functionally distinct. They had increased expression of MHC and costimulatory molecules and expressed elevated levels of B220 and DEC205 but had minimal CD4 staining. mFlt3L DC also had a markedly altered cytokine profile, including lowered secretion of IL-6, IL-10, IFN-gamma, and TNF-alpha, but had a slightly increased capacity to stimulate T cells in vitro. However, in a variety of in vivo models, DC expanded by mFlt3L induced tolerogenic effects on T cells. Adoptive transfer of Ag-pulsed mFlt3L splenic DC to naive mice actually caused faster rates of tumor growth and induced minimal CTL compared with control DC. mFlt3L also failed to protect against tumors in which human Flt3 ligand was protective, but depletion of CD4(+) T cells restored tumor protection. Our findings 1) demonstrate that mFlt3L has distinct effects on DC development, 2) suggest an important role for mFlt3L in generating DC that have tolerogenic effects on T cells, and 3) may have application in immunotherapy in generating massive numbers of DC for an extended duration.

GM-CSF expands dendritic cells and their progenitors in mouse liver

Dendritic cells (DCs) are rare but ubiquitous antigen-presenting cells situated in lymphoid and nonlymphoid organs throughout the body. The study of DCs located in the liver has been restricted by their relative scarcity and the difficulty of their isolation. Because granulocyte-macrophage colony-stimulating factor (GM-CSF) is a critical growth factor for DCs in vitro, we postulated that it would expand hepatic DCs in vivo. We found that adenoviral-mediated GM-CSF overexpression in normal mice increased the number of liver DCs 400-fold to more than 100 million cells. GM-CSF-recruited DCs were CD11c(+)DEC205(-) and had high expression of major histocompatibility complex (MHC) class II, CD54, and CD80 but low CD40 and CD86 staining. Further maturation occurred after overnight culture. In addition to CD11c(+)DEC205(-) DCs, a population of CD11c(-)DEC205(low/-) cells resembling DC progenitors described previously in normal mice was expanded as serum GM-CSF levels increased. GM-CSF-recruited CD11c(+)DEC205(-) DCs and CD11c(-)DEC205(low/-) cells had different functional capabilities. CD11c(+)DEC205(-) DCs captured far more protein antigen in vivo, produced higher amounts of interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha, and induced greater allogeneic and antigen-specific T-cell stimulation. A proportion of CD11c(-)DEC205(low/-) cells differentiated into CD11c(+) cells and gained T-cell stimulatory ability when cultured in the presence of GM-CSF. In conclusion, our findings show that GM-CSF can profoundly influence recruitment and development of DCs in murine liver.

Long-term maintenance of gp120-specific immune responses by genetic vaccination with the HIV-1 envelope genes linked to the gene encoding Flt-3 ligand

DNA vaccines target dendritic cells (DC) to induce Ag-specific immune responses in animals. Potent HIV-specific immunity could be achieved by efficient priming of the immune system by DNA vaccines. We investigated a novel DNA vaccine approach based on the role of growth factors in DC expansion and differentiation. To this end, we constructed chimeric genes encoding the HIV envelope glycoproteins physically linked to the extracellular domain of Fms-like tyrosine kinase receptor-3 ligand (FLex; a DC growth factor; both mouse (m)FLex and human (h)FLex). These chimeric gene constructs synthesized biologically active, oligomeric FLex:gp120 fusion proteins and induced DC expansion (CD11c(+)CD11b(+)) when injected i.v. into mice. This DC expansion is comparable to that achieved by FLex DNA encoding native FLex protein. When delivered intramuscularly as DNA vaccines, hFLex:gp120 induced high frequencies of gp120-specific CD8(+) T cells in the presence or absence of FLex DNA-induced DC expansion, but gp120 and mFLex:gp120 elicited only low to moderate levels of Ag-specific CD8(+) T cells. In contrast, mFLex:gp120 induced high levels of anti-gp120 Abs under identical conditions of DNA vaccination. However, the Ab levels in mice immunized with DNA vaccines encoding hFLex:gp120 and gp120 proteins were low without DC expansion, but reached high levels comparable to that elicited by mFLex:gp120 only after the second boost in the presence of DC expansion. Importantly, the gp120-specific CD8(+) T cells persisted at high frequency for 114 days (16 wk) after a booster injection. These experiments provide insight into the importance of modulating DC function in vivo for effective genetic vaccination in animals.

Dendritic cell precursor populations of mouse blood: identification of the murine homologues of human blood plasmacytoid pre-DC2 and CD11c+ DC1 precursors

Immature and predendritic cells (pre-DCs) of human blood are the most readily accessible human DC sources available for study ex vivo. Murine homologues of human blood DCs have not been described. We report the isolation and characterization of 2 populations of precursor DCs in mouse blood. Mouse blood cells with the surface phenotype CD11c(lo)CD11b(-)CD45RA(hi) closely resemble human plasmacytoid cells (or pre-DC2) by morphology and function. On stimulation with oligonucleotides containing CpG motifs (CpG), these cells make large amounts of type 1 interferons and rapidly develop into DCs that bear CD8, though they may be distinct from the CD8(+) DCs in the unstimulated mouse. A second population of cells with the surface phenotype CD11c(+)CD11b(+)CD45RA(-) closely resembles the immediate precursors of pre-DC1, rapidly transforming into CD8(-) DCs after tumor necrosis factor-alpha (TNF-alpha) stimulation. These findings indicate the close relationship between human and mouse DCs, provided cells are obtained directly from equivalent source materials.

ICSBP is essential for the development of mouse type I interferon-producing cells and for the generation and activation of CD8alpha(+) dendritic cells

Interferon (IFN) consensus sequence-binding protein (ICSBP) is a transcription factor playing a critical role in the regulation of lineage commitment, especially in myeloid cell differentiation. In this study, we have characterized the phenotype and activation pattern of subsets of dendritic cells (DCs) in ICSBP(-/-) mice. Remarkably, the recently identified mouse IFN-producing cells (mIPCs) were absent in all lymphoid organs from ICSBP(-/-) mice, as revealed by lack of CD11c(low)B220(+)Ly6C(+)CD11b(-) cells. In parallel, CD11c(+) cells isolated from ICSBP(-/-) spleens were unable to produce type I IFNs in response to viral stimulation. ICSBP(-/-) mice also displayed a marked reduction of the DC subset expressing the CD8alpha marker (CD8alpha(+) DCs) in spleen, lymph nodes, and thymus. Moreover, ICSBP(-/-) CD8alpha(+) DCs exhibited a markedly impaired phenotype when compared with WT DCs. They expressed very low levels of costimulatory molecules (intercellular adhesion molecule [ICAM]-1, CD40, CD80, CD86) and of the T cell area-homing chemokine receptor CCR7, whereas they showed higher levels of CCR2 and CCR6, as revealed by reverse transcription PCR. In addition, these cells were unable to undergo full phenotypic activation upon in vitro culture in presence of maturation stimuli such as lipopolysaccharide or poly (I:C), which paralleled with lack of Toll-like receptor (TLR)3 mRNA expression. Finally, cytokine expression pattern was also altered in ICSBP(-/-) DCs, as they did not express interleukin (IL)-12p40 or IL-15, but they displayed detectable IL-4 mRNA levels. On the whole, these results indicate that ICSBP is a crucial factor in the regulation of two possibly linked processes: (a) the development and activity of mIPCs, whose lack in ICSBP(-/-) mice may explain their high susceptibility to virus infections; (b) the generation and activation of CD8alpha(+) DCs, whose impairment in ICSBP(-/-) mice can be responsible for the defective generation of a Th1 type of immune response.

Human and mouse plasmacytoid dendritic cells

By virtue of their enormous potential to produce type I interferons it is clear that plasmacytoid dendritic cells are major players in the host defense against viruses and various pathogens. Plasmacytoid dendritic cells were first identified in humans and very recently the mouse equivalents have been isolated. This review focuses, where possible, on a comparison between the cells in these two species. The mouse and human plasmacytoid DC are remarkably similar in surface phenotype and they display similar responses to pathogenic stimuli. The discovery of the mouse plasmacytoid dendritic cells has allowed for further biological properties of these cells to be investigated and it is now clear that they represent a long-lived family of cells that differentiate into novel dendritic cells upon microbiologic stimulation.

Mouse plasmacytoid cells: long-lived cells, heterogeneous in surface phenotype and function, that differentiate into CD8(+) dendritic cells only after microbial stimulus

The CD45RA(hi)CD11c(int) plasmacytoid predendritic cells (p-preDCs) of mouse lymphoid organs, when stimulated in culture with CpG or influenza virus, produce large amounts of type I interferons and transform without division into CD8(+)CD205(-) DCs. P-preDCs express CIRE, the murine equivalent of DC-specific intercellular adhesion molecule 3 grabbing nonintegrin (DC-SIGN). P-preDCs are divisible by CD4 expression into two subgroups differing in turnover rate and in response to Staphylococcus aureus. The kinetics of bromodeoxyuridine labeling and the results of transfer to normal recipient mice indicate that CD4(-) p-preDCs are the immediate precursors of CD4(+) p-preDCs. Similar experiments indicate that p-preDCs are normally long lived and are not the precursors of the short-lived steady-state conventional DCs. However, in line with the culture studies on transfer to influenza virus-stimulated mice the p-preDCs transform into CD8(+)CD205(-) DCs, distinct from conventional CD8(+)CD205(+) DCs. Hence as well as activating preexistant DCs, microbial infection induces a wave of production of a new DC subtype. The functional implications of this shift in the DC network remain to be determined.

Endogenous granulocyte-macrophage colony-stimulating factor overexpression in vivo results in the long-term recruitment of a distinct dendritic cell population with enhanced immunostimulatory function

GM-CSF is critical for dendritic cell (DC) survival and differentiation in vitro. To study its effect on DC development and function in vivo, we used a gene transfer vector to transiently overexpress GM-CSF in mice. We found that up to 24% of splenocytes became CD11c+ and the number of DC increased up to 260-fold to 3 x 10(8) cells. DC numbers remained substantially elevated even 75 days after treatment. The DC population was either CD8alpha+CD4- or CD8alpha-CD4- but not CD8alpha+CD4+ or CD8alpha-CD4+. This differs substantially from subsets recruited in normal or Flt3 ligand-treated mice or using GM-CSF protein injections. GM-CSF-recruited DC secreted extremely high levels of TNF-alpha compared with minimal amounts in DC from normal or Flt3 ligand-treated mice. Recruited DC also produced elevated levels of IL-6 but almost no IFN-gamma. GM-CSF DC had robust immune function compared with controls. They had an increased rate of Ag capture and caused greater allogeneic and Ag-specific T cell stimulation. Furthermore, GM-CSF-recruited DC increased NK cell lytic activity after coculture. The enhanced T cell and NK cell immunostimulation by GM-CSF DC was in part dependent on their secretion of TNF-alpha. Our findings show that GM-CSF can have an important role in DC development and recruitment in vivo and has potential application to immunotherapy in recruiting massive numbers of DC with enhanced ability to activate effector cells.