Blockade of allergic airway inflammation following systemic treatment with a B7-dendritic cell (PD-L2) cross-linking human antibody

We present a novel immunotherapeutic strategy using a human B7-DC cross-linking Ab that prevents lung inflammation, airway obstruction, and hyperreactivity to allergen in a mouse model of allergic inflammatory airway disease. Dendritic cells (DC) have the ability to skew the immune response toward a Th1 or Th2 polarity. The sHIgM12 Ab functions in vitro by cross-linking the costimulatory family molecule B7-DC (PD-L2) on DC up-regulating IL-12 production, homing to lymph nodes, and T cell-activating potential of these APCs. Using chicken OVA as a model Ag, the administration of sHIgM12 Ab to BALB/c mice blocked lung inflammation, airway pathology, and responsiveness to methacholine, even after animals were presensitized and a Th2-polarized immune response was established. This therapeutic strategy was ineffective in STAT4-deficient animals, indicating that IL-12 production is critical in this system. Moreover, the polarity of the immune response upon in vitro restimulation with Ag is changed in wild-type mice, with a resulting decrease in Th2 cytokines IL-4 and IL-5 and an increase in the immunoregulatory cytokine IL-10. These studies demonstrate that the immune response of hypersensitized responders can be modulated using B7-DC cross-linking Abs, preventing allergic airway disease upon re-exposure to allergen.     

B7-DC/PD-L2 cross-linking induces NF-kappaB-dependent protection of dendritic cells from cell death

Cross-linking cell surface molecules with IgM Abs is a specific approach for activating cells in vitro or in vivo. Dendritic cells (DC) activated with a human B7-DC (PD-L2)-specific IgM Ab can induce strong antitumor responses and block inflammatory airway disease in experimental models, yet the Ab-mediated molecular events promoting these responses remain unclear. Analysis of human or mouse DC treated with the B7-DC cross-linking Ab revealed PI3K-dependent phosphorylation of AKT accompanied by mobilization of NF-kappaB. Ab-activated DC up-regulated expression of cytokine and chemokine genes in an NF-kappaB-dependent manner. Importantly, PI3K-->AKT-->NF-kappaB activation was found to be indispensable for B7-DC cross-linking Ab-mediated protection of DC from cell death caused by cytokine withdrawal. Although other DC activators similarly protect DC from cell death, a synergy between cross-linking B7-DC and ligating RANK was observed. The parallel signaling events induced in human and mouse DC demonstrate that activation of cells using IgM Ab results in a response governed by a common mechanism and support the hypothesis that B7-DC cross-linking using this Ab may provide beneficial therapeutic immune modulation in human patients similar to those seen in animal models.     

Induction of a Th1 response from Th2-polarized T cells by activated dendritic cells: dependence on TCR:peptide-MHC interaction, ICAM-1, IL-12, and IFN-gamma

Dendritic cells (DC) are important regulators of T cell immunity. The degree of stimulation, the pattern of costimulatory molecules expressed, and the cytokines secreted by DC dictate the nature of the effector and memory cells generated, particularly with respect to their Th1 or Th2 phenotypes. In this study, we demonstrate that the addition of activated DC to spleen cultures containing established Th2-polarized CD4(+) T cells was sufficient to suppress Th2 and induce Th1 cytokines in a recall response, a phenomenon referred to as phenotype reversal. The ability of activated DC to induce phenotype reversal displayed exquisite Ag specificity. The DC activator B7-DC cross-linking Ab (XAb) was >10,000-fold more efficient at inducing phenotype reversal than the TLR agonists CpG-oligodeoxynucleotide and Gardiquimod. Characterization of the mechanisms governing phenotype reversal revealed the requirement for cognate interaction between the TCR:peptide-MHC complex, the expression of the costimulation/adhesion molecule ICAM-1, and secretion of IL-12 and IFN-gamma by the activated DC. The requirement for the costimulation/adhesion molecule SLAM (signaling lymphocytic activation molecule) was found to be quantitative. Thus, activation of DC, particularly by crosslinking B7-DC, can modulate well-established Th2 T cell responses in an Ag-specific manner. Because the regulation of mouse and human DC by B7-DC XAb overlaps in several significant ways, immune modulation with B7-DC XAb is a potential strategy for treating Th2-mediated diseases.     

Indirect Recruitment of a CD40 Signaling Pathway in Dendritic Cells by B7-DC Cross-Linking Antibody Modulates T Cell Functions

The human IgM B7-DC XAb protects mice from tumors in both therapeutic and prophylactic settings. Its mechanism of action is mediated by its binding to B7-DC/PD-L2 molecules on the surface of dendritic cells (DCs) to induce a multimolecular cap and subsequent activation of signaling cascades that determine a unique combination of DC phenotypes. One such phenotype, the B7-DC XAb-induced antigen accumulation in mTLR-matured DCs, has been linked to signaling through TREM-2, but the signals required for other DC phenotypes critical for the therapeutic effects in animal models remain unclear. Here, FRET and co-immunoprecipitation studies show that CD40 is recruited to the multi-molecular complex by B7-DC XAb. Signals emanating from CD40 are important, as CD40^−/− DCs treated with B7-DC XAb (DC^XAb) activated DAP12, but failed to activate NFκB, and were not protected from cell death upon cytokine withdrawal or treatment with Vitamin D₃. CD40^−/− DC^XAb also failed to secrete IL-6 and were unable to support the conversion of T regulatory cells into IL-17+ effector T cells in vitro. Importantly, the expression of CD40 was required for the overall ability of B7-DC XAb to induce anti-tumor CTL, to provide protection from a number of tumor types, and for DC^XAb to be effective anti-tumor vaccines in vivo. These results indicate that B7-DC XAb modulation of DC phenotypes is through its ability to indirectly recruit common signaling molecules and elements of their endogenous signaling pathways through targeted binding to a cell-specific surface determinant.     

NK cells enhance dendritic cell response against parasite antigens via NKG2D pathway

Recent studies have shown that NK-dendritic cell (DC) interaction plays an important role in the induction of immune response against tumors and certain viruses. Although the effect of this interaction is bidirectional, the mechanism or molecules involved in this cross-talk have not been identified. In this study, we report that coculture with NK cells causes several fold increase in IL-12 production by Toxoplasma gondii lysate Ag-pulsed DC. This interaction also leads to stronger priming of Ag-specific CD8+ T cell response by these cells. In vitro blockade of NKG2D, a molecule present on human and murine NK cells, neutralizes the NK cell-induced up-regulation of DC response. Moreover, treatment of infected animals with Ab to NKG2D receptor compromises the development of Ag-specific CD8+ T cell immunity and reduces their ability to clear parasites. These studies emphasize the critical role played by NKG2D in the NK-DC interaction, which apparently is important for the generation of robust CD8+ T cell immunity against intracellular pathogens. To the best of our knowledge, this is the first work that describes in vivo importance of NKG2D during natural infection.     

Blockade of B7-H1 suppresses the development of chronic intestinal inflammation

A newly identified costimulatory molecule, programmed death-1 (PD-1), provides a negative signal that is essential for immune homeostasis. However, it has been suggested that its ligands, B7-H1 (PD-L1) and B7-dendritic cells (B7-DC; PD-L2), could also costimulate T cell proliferation and cytokine secretion. Here we demonstrate the involvement of PD-1/B7-H1 and B7-DC interaction in the development of colitis. We first examined the expression profiles of PD-1 and its ligands in both human inflammatory bowel disease and a murine chronic colitis model induced by adoptive transfer of CD4(+)CD45RB(high) T cells to SCID mice. Second, we assessed the therapeutic potential of neutralizing anti-B7-H1 and/or B7-DC mAbs using this colitis model. We found significantly increased expression of PD-1 on T cells and of B7-H1 on T, B, and macrophage/DCs in inflamed colon from both inflammatory bowel disease patients and colitic mice. Unexpectedly, the administration of anti-B7-H1, but not anti-B7-DC, mAb after transfer of CD4(+)CD45RB(high) T cells suppressed wasting disease with colitis, abrogated leukocyte infiltration, and reduced the production of IFN-gamma, IL-2, and TNF-alpha, but not IL-4 or IL-10, by lamina propria CD4(+) T cells. These data suggest that the interaction of PD-1/B7-H1, but not PD-1/B7-DC, might be involved in intestinal mucosal inflammation and also show a possible role of interaction between B7-H1 and an as yet unidentified receptor for B7-H1 in inducing T cell activation.     

B7-H1-induced apoptosis as a mechanism of immune privilege of corneal allografts

The programmed death-1 (PD-1) costimulatory pathway has been demonstrated to play a role in the regulation of immune responses and peripheral tolerance. We investigated the role of this pathway in establishing an immune privilege status of corneal allografts in mice. B7-H1, but not B7-DC or PD-1, was expressed constitutively in the eye, i.e., cornea, iris-ciliary body, and retina. After corneal allografting, PD-1(+)CD4(+) T cells infiltrated and adhered with B7-H1(+) corneal endothelium. Blockade of PD-1 or B7-H1, but not B7-DC, led to accelerated corneal allograft rejection. In B7-H1-expressing corneal allografts, apoptosis of the infiltrating PD-1(+)CD4(+) or CD8(+) T cells was observed, after which there was allograft acceptance. In contrast, B7-H1 blockade suppressed apoptosis of infiltrating PD-1(+) T cells, which led to allograft rejection. In vitro, destruction of corneal endothelial cells by alloreactive T cells was enhanced when the cornea was pretreated with anti-B7-H1 Ab. This is the first demonstration that the constitutive expression of B7-H1 plays a critical role in corneal allograft survival. B7-H1 expressed on corneal endothelial cells maintains long-term acceptance of the corneal allografts by inducing apoptosis of effector T cells within the cornea.     

The ability of two Listeria monocytogenes vaccines targeting human papillomavirus-16 E7 to induce an antitumor response correlates with myeloid dendritic cell function

Previous work from our laboratory has shown that Lm-LLO-E7 induces complete regression of approximately 75% of established TC-1 tumors, whereas Lm-E7 only slows the growth of such tumors. In this study, we examine the effects of Lm-LLO-E7 vs Lm-E7 on APCs. We hypothesize that the difference in antitumor efficacy of the two vaccines is due to the ability of each of these vectors to render immature dendritic cells (DCs) effective APCs in terms of MHC class II or costimulatory molecule expression. We also examine the ability of these vectors to stimulate cytokine production by DCs. Both vectors induced IL-12 and TNF-alpha, but only Lm-LLO-E7 induced IL-2 production by DCs. Lm-LLO-E7 also induced significantly higher levels of MHC class II molecules, CD40, and B7 costimulatory molecules (CD86, B7-H1, and B7-DC) on DCs than Lm-E7. Interestingly, a shift of CD11c(+) cells from CD86(low) to CD86(high) is observed post-Lm-LLO-E7 infection. A similar shift is also observed for B7-H1 and B7-DC molecules. Moreover, Lm-LLO-E7, but not Lm-E7-pulsed DCs, stimulate naive T cell proliferation. These results indicate that Lm-LLO-E7 is more effective than Lm-E7 at inducing DC maturation. This effect is independent of the E7 Ag, because Lm-LLO-NP, and a mixture of Lm-LLO-NP and Lm-E7 induce the same changes in DC phenotype as Lm-LLO-E7. Taken together, the changes in DC expression correlate well with the differences in antitumor efficacy between these two vaccines.     

Activation of human peripheral IgM+ B cells is transiently inhibited by BCR-independent aggregation of Fc gammaRIIB

Immune complexes can trigger a SHIP-1-independent proapoptotic signal in mouse class-switched IgG(+) B cells and plasma cells by binding to Fc gammaRIIB, in the absence of concomitant coaggregation with BCR, hence regulating plasma cell survival and participating in the selection of B cells producing high affinity Abs during secondary Ab responses. By contrast, we demonstrate in the present study that the unique aggregation of Fc gammaRIIB on human peripheral IgM(+) B cells does not induce apoptosis but transiently inhibits B cell proliferation and calcium influx triggered by BCR cross-linking. Using human peripheral B cells and IIA1.6 lymphoma B cells expressing wild-type human Fc gammaRIIB (IIA1.6-Fc gammaRIIB), we also show that the unique aggregation of human Fc gammaRIIB induces ITIM phosphorylation. This aggregation provokes the recruitment of phosphorylated SHIP-1 by Fc gammaRIIB and inhibits the constitutive phosphorylation of Akt in human IIA1.6-Fc gammaRIIB cells. This inhibitory signaling pathway is abrogated in IIA1.6 cells expressing ITIM-mutated Fc gammaRIIB (Fc gammaRIIB(Y292G)), suggesting that ITIM phosphorylation is necessary for Fc gammaRIIB-induced B cell blockade. Overall, we demonstrate that the unique aggregation of Fc gammaRIIB on human peripheral IgM(+) B cells is sufficient to transiently down-regulate their activation without inducing apoptosis. Our results suggest that Fc gammaRIIB could negatively regulate IgM(+) B cells before class-switch occurrence and that its unique engagement by immune complexes represents a reversible checkpoint for peripheral IgM(+) B cells.     

Anergic responses characterize a large fraction of human autoreactive naive B cells expressing low levels of surface IgM

B cell anergy represents an important mechanism of peripheral immunological tolerance for mature autoreactive B cells that escape central tolerance enforced by receptor editing and clonal deletion. Although well documented in mice, the extent of its participation in human B cell tolerance remains to be fully established. In this study, we characterize the functional behavior of strictly defined human naive B cells separated on the basis of their surface IgM (sIgM) expression levels. We demonstrate that cells with lower sIgM levels (IgM(lo)) are impaired in their ability to flux calcium in response to either anti-IgM or anti-IgD cross-linking and contain a significantly increased frequency of autoreactive cells compared with naive B cells with higher levels of sIgM. Phenotypically, in healthy subjects, IgM(lo) cells are characterized by the absence of activation markers, reduction of costimulatory molecules (CD19 and CD21), and increased levels of inhibitory CD22. Functionally, IgM(lo) cells display significantly weaker proliferation, impaired differentiation, and poor Ab production. In aggregate, the data indicate that hyporesponsiveness to BCR cross-linking associated with sIgM downregulation is present in a much larger fraction of all human naive B cells than previously reported and is likely to reflect a state of anergy induced by chronic autoantigen stimulation. Finally, our results indicate that in systemic lupus erythematosus patients, naive IgM(lo) cells display increased levels of CD95 and decreased levels of CD22, a phenotype consistent with enhanced activation of autoreactive naive B cells in this autoimmune disease.     

Colocalization of expansion of the splenic marginal zone population with abnormal B cell activation and autoantibody production in B6 mice with an introgressed New Zealand Black chromosome 13 interval

Polyclonal B cell activation is a prominent feature of the lupus-prone New Zealand Black (NZB) mouse strain. We have previously demonstrated linkage between a region on NZB chromosome 13 and increased costimulatory molecule expression on B cells. In this study we have produced C57BL/6 congenic mice with an introgressed homozygous NZB interval extending from approximately 24 to 73 cM on chromosome 13 (denoted B6.NZBc13). We show that B6.NZBc13 female mice not only have enhanced B cell activation but also share many other B cell phenotypic characteristics with NZB mice, including expansion of marginal zone and CD5+ B cell populations, increased numbers of IgM ELISPOTs, and increased serum levels of total IgM and IgM autoantibodies. In addition these mice have increased T cell activation, increased numbers of germinal centers, mild glomerulonephritis, and produce high-titer IgM and IgG anti-chromatin Abs. Male B6.NZBc13 mice have a less pronounced cellular phenotype, lacking expansion of the marginal zone B cell population and IgG anti-chromatin Ab production, indicating the presence of gender dimorphism for this locus. Thus, we have identified a genetic locus that recapitulates with fidelity the B cell phenotypic abnormalities in NZB mice, and we demonstrate that this locus is sufficient to induce an autoimmune phenotype. The data provide further support to the contention that immune abnormalities leading to altered B cell activation and selection contribute to the development of autoimmunity in NZB mice.     

Molecular characterization of human 4Ig-B7-H3, a member of the B7 family with four Ig-like domains

In an effort to characterize molecules with immunoregulatory potential, we raised mAbs to human dendritic cells. We selected an Ab that recognizes a molecule that is induced on monocytes differentiated in vitro toward dendritic cells. Retroviral expression cloning identified this molecule as B7-H3, a member of the B7 family described recently. In contrast to an earlier report, in which B7-H3 was described as a molecule consisting of two Ig-like domains, our cDNA encoded a type I membrane protein with four Ig-like domains, and the molecule identified by us was therefore named 4Ig-B7-H3. mRNA analysis as well as Western blotting experiments performed by us did not reveal evidence for a small B7-H3. B7-H3 is not expressed on peripheral blood lymphocytes, monocytes, or granulocytes. Upon in vitro stimulation, the expression of B7-H3 is induced on T cells, B cells, and NK cells. A number of different approaches were used to investigate the function of human B7-H3. In contrast to an earlier report, our data do not support a costimulatory role of B7-H3 in anti-CD3-mediated activation of the TCR-complex resulting in T cell proliferation and IFN-gamma production.     

Murine B7-H3 is a negative regulator of T cells

T cell activation is regulated by the innate immune system through positive and negative costimulatory molecules. B7-H3 is a novel B7-like molecule with a putative receptor on activated T cells. Human B7-H3 was first described as a positive costimulator, most potently inducing IFN-gamma production and cellular immunity. In this study we examined the expression and function of mouse B7-H3. B7-H3 is mostly expressed on professional APCs; its expression on dendritic cells appears to be up-regulated by LPS. In contrast to human B7-H3, we found that mouse B7-H3 protein inhibited T cell activation and effector cytokine production. An antagonistic mAb to B7-H3 enhanced T cell proliferation in vitro and led to exacerbated experimental autoimmune encephalomyelitis in vivo. Therefore, mouse B7-H3 serves as a negative regulator of T cell activation and function.     

The limitation of IL-10-exposed dendritic cells in the treatment of experimental autoimmune myasthenia gravis and myasthenia gravis

Dendritic cells (DC) are highly specialized antigen presenting cells that play critical roles as instigators and regulators of immune responses including B cell function, antibody synthesis and isotype switch. In this study, we compared immunotherapeutic effect of IL-10-treated DC (IL-10-DC) via both intraperitoneal (i.p.) and subcutaneous (s.c.) delivery in rats with incipient experimental autoimmune myasthenia gravis (EAMG). Spleen DC were isolated from onset of EAMG on day 39 post-immunization, exposed in vitro to IL-10, and then injected into incipient EAMG at dose of 1 x 10(6) cells/rat on day 5 after immunization. Intraperitoneal administration of IL-10-DC suppressed clinical scores, anti-acetylcholine receptors (AChR) antibody secreting cells, antigen-specific IL-10/IFN-gamma production and T cell proliferation compared to control EAMG rats. Importantly, IL-10-DC, if given by s.c. route, failed to ameliorate clinical sign of EAMG. Simultaneously, T cell proliferation, anti-AChR antibody secreting cells and IL-10/IFN-gamma production had no alteration, as compared to control EAMG rats. Both in vitro and in vivo experiments showed that treatment of IL-10 inhibited the migration of DC toward MIP-3beta and lymph node, indicating that in vitro manipulation of DC with IL-10 alters the migration of DC that influences the therapeutic effect in the treatment of autoimmune diseases. In MG patients, neither the improvement of clinical symptom nor the alteration of immunological parameter was observed through s.c. delivery of IL-10-DC, suggesting the limitation of IL-10-DC in the treatment of MG patients.     

Activity and safety of CTLA-4 blockade combined with vaccines in cynomolgus macaques

The immune modulatory molecule CTLA-4 (CD152), through interactions with the B7 costimulatory molecules, has been shown to be a negative regulator of T cell activation in various murine model systems. Abs that block CTLA-4 function can enhance immune responses that mediate potent antitumor activity. However, CTLA-4 blockade can also exacerbate autoimmune disease. The safety and activity of anti-CTLA-4 Abs in primates has not been addressed. To that end, we generated human Abs against CTLA-4 using transgenic mice expressing human Ig genes. A high affinity Ab (10D1) that blocked the binding of CTLA-4 to the B7-1 and B7-2 ligands and had cross-reactivity with macaque CTLA-4 was chosen for further development. Administration of 10D1 to cynomolgus macaques significantly enhanced Ab responses to hepatitis surface Ag and a human melanoma cell vaccine. Anti-self Ab responses as measured by immunoassays using lysate from melanocyte-rich tissues were elicited in those animals receiving the melanoma cell vaccine and anti-CTLA-4 Ab. Remarkably, chronic administration of 10D1 did not result in measurable polyclonal T cell activation, significant alteration of the lymphocyte subsets, or induce clinically observable autoimmunity. Repeated dosing of the 10D1 did not elicit monkey anti-human Ab responses in the monkeys. These observations support the development of CTLA-4 blockade for human immunotherapy.     

Mixed xenogeneic chimerism induces donor-specific humoral and cellular immune tolerance for cardiac xenografts

Xenotransplantation has been suggested as a potential solution to the critical shortage of donor organs. However, success has been limited by the vigorous rejection response elicited against solid organs transplanted across species barriers. Mixed xenogeneic bone marrow chimeras resulting from the transplantation of a mixture of host and donor marrow (B10 mouse + F344 rat --> B10 mouse) results in donor-specific cross-species transplantation tolerance for subsequent nonvascularized skin and islet grafts. Furthermore, compared with fully xenogeneic chimeras (rat --> mouse), mixed xenogeneic chimeras exhibit superior immunocompetence for infectious agents in vivo and in vitro, suggesting that the immune system is intact. The ability to establish long-term humoral and cellular tolerance for primarily vascularized xenografts in vivo, in the setting of both recipient and donor Ig and effector cell production, has not previously been characterized. Mixed xenogeneic chimeras exhibit donor-specific humoral tolerance as evident by the absence of anti-donor Ab and Ab-dependent donor-specific cytotoxicity in vitro and intravascular IgM deposition within donor-strain (F344) cardiac xenografts in vivo. F344 cardiac xenografts are accepted (median > or =180 days) without clinical or histologic evidence of rejection, suggesting cellular tolerance. In contrast, MHC-disparate third-party mouse (B10.BR) and rat (ACI or WF) grafts are rejected (median of 23 and 41 days, respectively) in association with extensive mononuclear cell infiltration and vascular deposits of mouse IgM. These results demonstrate that mixed xenogeneic chimerism establishes donor-specific humoral and cellular tolerance and permits the successful transplantation of even primarily vascularized xenografts in the setting of intact Ab production.     

Aging-associated B7-DC+ B cells enhance anti-tumor immunity via Th1 and Th17 induction

Because most patients with cancer are aged and because immunological functions are altered during aging, it is important to account for aging-associated immunological alterations in the design of new cancer immunotherapies. We thus compared immune populations in young and aged mice and found that B7-DC(+) (PD-L2/CD273) B cells, a minor population in young mice, were significantly increased in aged mice. Induction of both Th1 and Th17 cells was significantly augmented by B7-DC(+) B cells from aged mice, and this effect was blocked with anti-B7-DC antibodies in vitro and in vivo. Moreover, retardation of tumor growth in aged mice was largely B7-DC dependent. Tumor growth in young mice was significantly inhibited by immunization with B7-DC(+) B cells from aged mice owing to increased induction of tumor antigen-specific cytotoxic T lymphocytes. These data indicate that B7-DC(+) B cells could play an important role in aging-associated cancer immunopathology as well as in other aging-associated diseases and further suggest that B7-DC(+) B cells have potential for future cancer immunotherapy.     

Immune evasion by neocartilage-derived chondrocytes: Implications for biologic repair of joint articular cartilage

Degeneration of joint articular cartilage is a leading cause of disability worldwide, and is due in large part to the fact that adult articular cartilage is unable to undergo effective intrinsic repair. To overcome this barrier, we have developed a tissue engineering strategy which harnesses the superior anabolic activity of juvenile chondrocytes to produce a scaffold-independent, living neocartilage graft. Preclinical studies demonstrate that bioengineered neocartilage survives allogeneic and xenogeneic transplantation, suggesting the utility of universal donor-derived neocartilage for joint repair. However, the mechanism underlying neocartilage transplant tolerance remains poorly understood. We show here that neocartilage-derived chondrocytes are unable to stimulate allogeneic T cells in vitro, and they do not constitutively express cell surface molecules required for induction of T cell immune responses, including major histocompatibility complex (MHC) Class II antigens and costimulatory molecules B7-1 and B7-2. Additionally, chondrocytes suppress, in a contact-dependent manner, the proliferation of activated T cells, with suppression associated with chondrocyte expression of multiple negative regulators of immune responses, including B7 family members (B7-H1, B7-DC, B7-H2, B7-H3, and B7-H4), chondromodulin-I and indoleamine 2,3-dioxygenase. Thus, the survival of transplanted bioengineered neocartilage may depend on both passive and active mechanisms of immune evasion.     

Vitamin D3 affects differentiation, maturation, and function of human monocyte-derived dendritic cells

We studied the effects of 1alpha,25-dihydroxyvitamin D3 (1alpha, 25-(OH)2D3) on differentiation, maturation, and functions of dendritic cells (DC) differentiated from human monocytes in vitro in the presence of GM-CSF and IL-4 for 7 days. Recovery and morphology were not affected by 1alpha,25-(OH)2D3 up to 100 nM. DC differentiated in the presence of 10 nM 1alpha,25-(OH)2D3 (D3-DC) showed a marked decrease in the expression of CD1a, while CD14 remained elevated. Mannose receptor and CD32 were significantly increased, and this correlated with an enhancement of endocytic activity. Costimulatory molecules such as CD40 and CD86 were slightly decreased or nonsignificantly affected (CD80 and MHC II). However, after induction of DC maturation with LPS or incubation with CD40 ligand-transfected cells, D3-DC showed marginal increases in MHC I, MHC II, CD80, CD86, CD40, and CD83. The accessory cell function of D3-DC in classical MLR was also inhibited. Moreover, allogeneic T cells stimulated with D3-DC were poor responders in a second MLR to untreated DC from the same or an unrelated donor, thus indicating the onset of a nonspecific hyporesponsivity. In conclusion, our data suggest that 1alpha,25-(OH)2D3 may modulate the immune system, acting at the very first step of the immune response through the inhibition of DC differentiation and maturation into potent APC.