Immortalized cell lines derived from mice lacking both type I and type II IFN receptors unify some functions of immature and mature dendritic cells

Prolonged exposure to simulated microgravity diminishes dendritic cell immunogenicity

Immune dysfunction due to microgravity remains a hurdle in the next step of human space exploration. Dendritic cells (DC) represent a critical component of immunity, given their role in the detection of invaders and the subsequent task of activating T cells to respond and eliminate the threat. Upon encounter with microbes, DC undergo a process of maturation, whereby the cells upregulate the expression of surface proteins and secrete cytokines, both required for the optimal activation of CD4⁺ and CD8⁺ T cells. In this study, DC were cultured from 2–14 days in a rotary cell culture system, which generates a simulated microgravity (SMG) environment, and then the cells were assessed for maturation status and the capacity to activate T cells. Short-term culture (<72 h) of DC in SMG resulted in an increased expression of surface proteins associated with maturation and interleukin-6 production. Subsequently, the SMG exposed DC were superior to Static control DC at activating both CD4⁺ and CD8⁺ T cells as measured by interleukin-2 and interferon-γ production, respectively. However, long-term culture (4–14 d) of DC in SMG reduced the expression of maturation markers and the capacity to activate T cells as compared to Static DC controls.

Transfection of a mouse dendritic cell line by plasmid DNA-loaded PLGA microparticles in vitro

Targeting of DC for DNA vaccination may be achieved by DNA-loaded poly(lactide-co-glycolide) (PLGA) biodegradable microparticles, since DC efficiently capture these microparticles in vitro and in vivo. DNA was encapsulated in PLGA microparticles by spray-drying. Various additives were tested and process parameters adjusted in order to prevent degradation of the DNA during encapsulation. The highest degree of supercoiled DNA was maintained by adding a strong buffering agent, such as PBS or NaHCO(3), whereas the cryoprotective lactose did not show a significant protective effect. DNA-containing PLGA microparticles were administered to a mouse DC line. Transfection efficacy was compared with commonly employed cationic transfectants and was visually assessed by green fluorescent protein expression. Transfection rate was very low in DC for all microparticle formulations and was comparable with commonly used cationic transfectants. It is concluded that the transfection of DC using PLGA microparticles is feasible, but efforts need to be undertaken to improve transfection efficiency in vitro, which may in addition lead to improved immune responses in vivo.

Flt3 ligand-treated neonatal mice have increased innate immunity against intracellular pathogens and efficiently control virus infections

Flt-3 ligand (FL), a hematopoetic growth factor, increases the number of dendritic cells (DCs), B cells, and natural killer cells in adult mice but the effect in neonates was unknown. We show that FL treatment of newborn mice induced a >100-fold increase in the innate resistance against infection with herpes simplex virus type 1 and Listeria monocytogenes. This resistance required interferon (IFN)-alpha/beta for viral and interleukin (IL)-12 for bacterial infections. Long-term survival after viral but not bacterial infection was increased approximately 100-fold by FL treatment. After treatment, CD11c(+)/major histocompatibility complex type II(+) and CD11c(+)/B220(+) DC lineage cells were the only cell populations increased in the spleen, liver, peritoneum, and skin. DC induction was independent of IFNs, IL-2, -4, -7, -9, -15, and mature T and B cells. The data suggest that FL increases the number of DCs in neonates and possibly in other immune-compromised individuals, which in turn improves IFN-alpha/beta- and IL-12-associated immune responses.

Antitumor activities of human dendritic cells derived from peripheral and cord blood

AIM: To observe the biological specialization of human peripheral blood dendritic cells (DC) and cord blood derived DC and its effects on effector cells killing human hepatocarcinoma cell line BEL-7402 in vitro.

METHODS: The DC biological characteristics were detected with immunohistochemical and MTT assay. Two antitumor experimental groups are: peripheral blood DC and cord blood DC groups. Peripheral blood DC groups used LAK cells as the effector cells and BEL-7402 as target cells, while cord blood DC groups used CTL induced by tumor antigen twice pulsed DC as effector cells and BEL-7402 as target cells, additional peripheral blood DC and cord blood DC are added to observe its stimulating activities to effector cells. The effector¡äs cytotoxicity to tumor cells were detected with neutral red colorimetric assay at two effector/ target ratios of 5:1 and 10:1.

RESULTS: Peripheral blood DC and cord blood DC highly expressed HLA-ABC, HLA-DR, HLA-DQ, CD54 and S-100 protein. The stimulating activities to lymphocyte proliferation were compared between experimental groups (DC added) and control group (no DC added), in six experiment subgroups,the DC/lymphocyte ratio was sequentially 0.25:100, 0.5:100, 1:100, 2:100, 4:100 and 8:100, A values(^-x±s) were 0.75396 ± 0.009, 0.84916 ± 0.010, 0.90894 ± 0.012, 0.98371 ± 0.007, 1.01299 ± 0.006 and 1.20384 ± 0.006 in peripheral blood DC groups and 0.77650 ± 0.005, 0.83008 ± 0.007, 0. 92725 ± 0.007, 1.05990 ± 0.010, 1.15583 ± 0.011, 1. 22983 ± 0.011 in cord blood DC groups. A value was 0.59517 ± 0.005 in control group. The stimulating activities were higher in experimental groups than in control group (P < 0.01), which were increased when the DC concentration was enlarged (P < 0.01). Two differently derived DCs had the same phenotypes and similar stimulating activities (P > 0.05). In peripheral blood DC groups, the cytotoxicity (^-x±s) of the LD groups (experimental groups) and L groups (control group) was 58.16% ± 2.03% (5:1), 46c18% ± 2.25% (10:1) and 38c13% ± 1.29% (5:1) and 65.40% ± 1.56% (10:1) respectively; in cord blood DC groups, TD groups (experimental groups) and T groups (control groups) were 69.71% ± 2.33% (5:1), 77.64% ± 1.94% (10:1) and 56.89% ± 1.82% (5:1) and 60.99% ± 1.42% (10:1) respectively. The cytotoxicity activities were enhanced with increased effector/target ratio (P < 0.01). At the same effector/target ratio, the cytotoxicity of experimental groups were bigger than that of control groups (P < 0.01). The cytotoxicity activities of cord blood DC groups were higher than that of peripheral blood DC groups (P < 0.01).

CONCLUSION: Peripheral blood DC and cord blood DC are mature DC in morphology and function, both can enhance the effector cell killing activities to hepatocarcinoma cells. DC pulsed with tumor antigen can induce higher specific CTL activity than unpulsed DC.

Effect of a cancer vaccine prepared by fusions of hepatocarcinoma cells with dendritic cells

AIM: To prepare a cancer vaccine (H₂₂-DC) expressing high levels of costimulatory molecules based on fusions of hepatocarcinoma cells (H₂₂) with dendritic cells (DC) of mice and to analyze the biological characteristics and induction of specific CTL activity of H₂₂-DC.

METHODS: DCs were isolated from murine spleen by metrizamide density gradient centrifugation, purified based on its characteristics of semi-adhesion to culture plates and FcR^-, and were cultured in the medium containing GM-CSF and IL-4. A large number of DC were harvested. DCs were then fused with H₂₂ cells by PEG and the fusion cells were marked with CD11c MicroBeads. The H₂₂-DC was sorted with Mimi MACS sorter. The techniques of cell culture, immunocytochemistry and light microscopy were also used to test the characteristics of growth and morphology of H₂₂-DC in vitro. As the immunogen, H₂₂-DC was inoculated subcutaneously into the right armpit of BALB/C mice, and their tumorigenicity in vivo was observed. MTT was used to test the CTL activity of murine spleen in vitro.

RESULTS: DC cells isolated and generated were CD11c+ cells with irregular shape, and highly expressed CD80, CD86 and CD54 molecules. H₂₂ cells were CD11c^- cells with spherical shape and bigger volume, and did not express CD80, CD86 and CD54 molecules. H₂₂-DC was CD11c⁺ cells with bigger volume, being spherical, flat or irregular in shape, and highly expressed CD80, CD86 and CD54 molecules, too. H₂₂-DC was able to divide and proliferate in vitro, but its activity of proliferation was significantly decreased as compared with H₂₂ cells and its growth curve was flatter than H₂₂ cells. After subcutaneous inoculation over 60 d, H₂₂-DC showed no tumorigenecity in mice, which was significantly different from control groups (P < 0.01). The spleen CTL activity against H₂₂ cells in mice implanted with fresh H₂₂-DC was significantly higher than control groups (P < 0.01).

CONCLUSION: H₂₂-DC could significantly stimulate the specific CTL activity of murine spleen, which suggests that the fusion cells have already obtained the function of antigen presenting of parental DC and could present H₂₂ specific antigen which has not been identified yet, and H₂₂-DC could induce antitumor immune response; although simply mixed H₂₂ cells with DC could stimulate the specific CTL activity which could inhibit the growth of tumor in some degree, it could not prevent the generation of tumor. It shows that the DC vaccine is likely to become a helpful approach in immunotherapy of hepatocarcinoma.

Revision of the functional analysis and structural features of immortalized dendritic cell lines derived from mice lacking both type I and type II interferon receptors

Cell lines with dendritic morphology were obtained from several organs of mice lacking both type I and II interferon receptors after a retroviral immortalization procedure. Their surface antigen phenotype was analyzed by flow cytometry with monoclonal antibodies and their functional capabilities to induce antigen dependent specific immune response was also determined. Two representative cell lines called AG101 (skin-derived) and AG116 (brain-derived) were cloned and analyzed in more detail. Cytometric analysis showed that they constitutively expressed the cell surface markers CD45, CD1 1b, MHC class II, F4/80, N418, B7-2 and ICAM1. Despite both cell lines expressing Thy-1 only, the AG116 show CD4 but both were negative for CD8 and B220. The functional analysis showed that the cell lines were capable and very efficient at actively taking up, processing and presenting soluble antigens like Ovalbumin (OVA). The processed protein was presented by both cell lines to the OVA-peptide-specific T cell hybridoma BO97.105, which responded specifically with the production of IL-2. In addition AG101 and AG116 cells were able to induce in naive allogeneic T cells, a mixed lymphocyte reaction, determined by T cell proliferation and T cell dependent L-2 production. Moreover, the capability to prime naive syngeneic T cells was also demonstrated by loading AG101 and AG116 cells with soluble antigens, then co-culturing with naive T cells which yielded both T cell proliferation and IL-2 production. The cell lines priming capability was shown to be quite similar, as freshly isolated and cultured cutaneous dendritic cells from 129Sv/Lv mice (wtDCs) to prime naive T cells. In addition to a basal production of IL-6, the cell lines were found to increase their synthesis of IL-6 and IL-12 p40 after interaction with T cells in a similar way as mature wtDCs. Also it was determined that DC cell lines devoid of functional IFN system allow the replication of infectious agents like BDV and even are able to induce in vivo a specific humoral response against proteins of the BDV. Therefore, the cell lines AG101 and AG116 show structural and functional features of DCs. They are able to take up, process and present antigens as well as prime naive T cell in a similar manner as nontransformed DC. Therefore, these cell lines will be useful for studying the interactions between DC and the effectors cells of the immune response at the clonal level and in the absence of functional interferon receptors.