Immunization with heat shock protein 105-pulsed dendritic cells leads to tumor rejection in mice

Recently, we reported that heat shock protein 105 (HSP105) DNA vaccination induced anti-tumor immunity. In this study, we set up a preclinical study to investigate the usefulness of dendritic cells (DCs) pulsed with mouse HSP105 as a whole protein for cancer immunotherapy in vivo. The recombinant HSP105 did not induce DC maturation, and the mice vaccinated with HSP105-pulsed BM-DCs were markedly prevented from the growth of subcutaneous tumors, accompanied with a massive infiltration of both CD4+ T cells and CD8+ T cells into the tumors. In depletion experiments, we proved that both CD4+ T cells and CD8+ T cells play a crucial role in anti-tumor immunity. Both CD4+ T cells and CD8+ T cells specific to HSP105 were induced by stimulation with HSP105-pulsed DCs. As a result, vaccination of mice with BM-DCs pulsed with HSP105 itself could elicit a stronger tumor rejection in comparison to DNA vaccination.     

Induction of cellular immune responses against carcinoembryonic antigen in patients with metastatic tumors after vaccination with altered peptide ligand-loaded dendritic cells

Purpose: Dendritic cells (DCs) are characterized by their extraordinary capacity to induce T-cell responses, providing the opportunity of DC-based cancer vaccination protocols. In the present study, we conducted a phase I/II clinical trial to determine the capability of DCs differentiated from immunomagnetically isolated CD14+ monocytes and pulsed with a carcinoembyonic antigen-derived altered peptide (CEAalt) to induce specific CD8+ T cells in cancer patients. Experimental design: Nine patients with CEA-positive colorectal cancer (n=7) or lung cancer (n=2) were enrolled in this study. Autologous CD14+ monocytes were isolated by large-scale immunomagnetic separation and differentiated to mature DCs in sufficient numbers and at high purity. After incubation with the CEAalt peptide and keyhole limpet hemocyanin, DCs were administered to patients intravenously at dose levels of 1×10⁷ and 5×10⁷ cells. Patients received four immunizations every second week. Results: ELISPOT analysis revealed a vaccine-induced increase in the number of CEAalt peptide-specific Interferon (IFN)-gamma producing CD8+ T cells in five of nine patients and of CD8+ T lymphocytes recognizing the native CEA peptide in three of nine patients. In addition, CD8+ T lymphocytes derived from one patient exhibiting an immunological response after vaccination efficiently lysed peptide-loaded T2 cells and tumor cells. Immunization was well tolerated by all patients without severe signs of toxicity. Conclusion: Vaccination with CEAalt-pulsed DCs derived from immunomagnetically isolated CD14+ monocytes efficiently expand peptide-specific CD8+ T lymphocytes in vivo and may be a promising alternative for cancer immunotherapy.     

The timing of GM-CSF expression plasmid administration influences the Th1/Th2 response induced by an HIV-1-specific DNA vaccine

The mechanism of immune activation induced by a plasmid-encoding GM-CSF (pGM-CSF), administered in combination with a DNA vaccine encoding the envelope of HIV, was studied. Injecting pGM-CSF i.m. into mice 3 days before DNA vaccination primarily induced a Th2 response. Simultaneous administration of the DNA vaccine plus pGM-CSF activated both a Th1 and a Th2 response. When the plasmid was injected 3 days after DNA vaccination, enhancement of Th1 immunity predominated. These results suggest that the timing of cytokine expression determines the phenotype of the resultant Th response. After 3 days of pGM-CSF injection, the increased percentages of CD11c+, CD8+ cells were observed in the regional lymph nodes. In addition, many infiltrated cells, including S-100 protein-positive cells, were found in the pGM-CSF-injected tissue. The importance of these S-100+ cells or both CD8+ and CD11c+ cells, especially that of dendritic cells (DCs), was also studied. DCs derived from bone marrow and cultured in RPMI 1640 medium containing IL-4 and GM-CSF were incubated with DNA vaccine and then transferred into naive mice. Mice receiving DCs showed strong HIV-1-specific Th2 immune responses. Our results suggest that DCs play important roles in the activation or modification of the Th2-type immune response induced by DNA vaccination.     

Exploiting the role of endogenous lymphoid-resident dendritic cells in the priming of NKT cells and CD8+ T cells to dendritic cell-based vaccines

Transfer of antigen between antigen-presenting cells (APCs) is potentially a physiologically relevant mechanism to spread antigen to cells with specialized stimulatory functions. Here we show that specific CD8+ T cell responses induced in response to intravenous administration of antigen-loaded bone marrow-derived dendritic cells (BM-DCs), were ablated in mice selectively depleted of endogenous lymphoid-resident langerin+ CD8α+ dendritic cells (DCs), suggesting that the antigen is transferred from the injected cells to resident APCs. In contrast, antigen-specific CD4+ T cells were primed predominantly by the injected BM-DCs, with only very weak contribution of resident APCs. Crucially, resident langerin+ CD8α+ DCs only contributed to the priming of CD8+ T cells in the presence of maturation stimuli such as intravenous injection of TLR ligands, or by loading the BM-DCs with the glycolipid α-galactosylceramide (α-GalCer) to recruit the adjuvant activity of activated invariant natural killer-like T (iNKT) cells. In fact, injection of α-GalCer-loaded CD1d-/- BM-DCs resulted in potent iNKT cell activation, suggesting that this glycolipid antigen can also be transferred to resident CD1d+ APCs. While iNKT cell activation per se was independent of langerin+ CD8α+ DCs, some iNKT cell-mediated activities were reduced, notably release of IL-12p70 and transactivation of NK cells. We conclude that both protein and glycolipid antigens can be exchanged between distinct DC species. These data suggest that the efficacy of DC-based vaccination strategies may be improved by the incorporation of a systemic maturation signal aimed to engage resident APCs in CD8+ T cell priming, and α-GalCer may be particularly well suited to this purpose.     

Capacities of migrating CD1b+ lymph dendritic cells to present Salmonella antigens to naive T cells

Dendritic cells (DCs) are well known as professional antigen-presenting cells (APC) able to initiate specific T-cell responses to pathogens in lymph nodes (LN) draining the site of infection. However, the respective contribution of migratory and LN-resident DCs in this process remains unclear. As DC subsets represent important targets for vaccination strategies, more precise knowledge of DC subsets able to present vaccine antigens to T cells efficiently is required. To investigate the capacities of DCs migrating in the lymph (L-DCs) to initiate a specific T-cell response, we used physiologically generated DCs collected from a pseudoafferent lymphatic cannulation model in sheep. The CD1b+ L-DCs were assessed for presenting antigens from the vaccine attenuated strain of Salmonella enterica serovar Abortusovis. CD1b+ L-DCs were able to phagocytose, process and to present efficiently Salmonella antigens to effector/memory T cells in vitro. They were shown to be efficient APC for the priming of allogeneic naive T cells associated with inducing both IFN-γ and IL-4 responses. They were also efficient in presenting Salmonella antigens to autologous naive T cells associated with inducing both IFN-γ and IL-10 responses. The capacities of L-DCs to process and present Salmonella antigens to T cells were investigated in vivo after conjunctival inoculation of Salmonella. The CD1b+ L-DCs collected after inoculation were able to induce the proliferative response of CD4+ T cells suggesting the in vivo capture of Salmonella antigens by the CD1b+ L-DCs, and their potential to present them directly to CD4+ T cells. In this study, CD1b+ L-DCs present potential characteristics of APC to initiate by themselves T cell priming in the LN. They could be used as target cells for driving immune activation in vaccinal strategies.     

Naive helper T cells from BCG-vaccinated volunteers produce IFN-gamma and IL-5 to mycobacterial antigen-pulsed dendritic cells

Mycobacterium bovis bacillus Calmette-Guérin (BCG) is a live vaccine that has been used in routine vaccination against tuberculosis for nearly 80 years. However, its efficacy is controversial. The failure of BCG vaccination may be at least partially explained by the induction of poor or inappropriate host responses. Dendritic cells (DCs) are likely to play a key role in the induction of immune response to mycobacteria by polarizing the reactivity of T lymphocytes toward a Th1 profile, contributing to the generation of protective cellular immunity against mycobacteria. In this study we aimed to investigate the production of Th1 and Th2 cytokines by naive CD4+ T cells to mycobacterial antigen-pulsed DCs in the group of young, healthy BCG vaccinated volunteers. The response of naive helper T cells was compared with the response of total blood lymphocytes. Our present results clearly showed that circulating naive CD45RA+CD4+ lymphocytes from BCG-vaccinated subjects can become effector helper cells producing IFN-gamma and IL-5 under the stimulation by autologous dendritic cells presenting mycobacterial protein antigen-PPD or infected with live M. bovis BCG bacilli.     

The TLR-7 agonist, imiquimod, enhances dendritic cell survival and promotes tumor antigen-specific T cell priming: relation to central nervous system antitumor immunity

Immunotherapy represents an appealing option to specifically target CNS tumors using the immune system. In this report, we tested whether adjunctive treatment with the TLR-7 agonist imiquimod could augment antitumor immune responsiveness in CNS tumor-bearing mice treated with human gp100 + tyrosine-related protein-2 melanoma-associated Ag peptide-pulsed dendritic cell (DC) vaccination. Treatment of mice with 5% imiquimod resulted in synergistic reduction in CNS tumor growth compared with melanoma-associated Ag-pulsed DC vaccination alone. Continuous imiquimod administration in CNS tumor-bearing mice, however, was associated with the appearance of robust innate immune cell infiltration and hemorrhage into the brain and the tumor. To understand the immunological mechanisms by which imiquimod augmented antitumor immunity, we tested whether imiquimod treatment enhanced DC function or the priming of tumor-specific CD8+ T cells in vivo. With bioluminescent, in vivo imaging, we determined that imiquimod dramatically enhanced both the persistence and trafficking of DCs into the draining lymph nodes after vaccination. We additionally demonstrated that imiquimod administration significantly increased the accumulation of tumor-specific CD8+ T cells in the spleen and draining lymph nodes after DC vaccination. The results suggest that imiquimod positively influences DC trafficking and the priming of tumor-specific CD8+ T cells. However, inflammatory responses induced in the brain by TLR signaling must also take into account the local microenvironment in the context of antitumor immunity to induce clinical benefit. Nevertheless, immunotherapeutic targeting of malignant CNS tumors may be enhanced by the administration of the innate immune response modifier imiquimod.     

Preferential induction of CD4+ T cell responses through in vivo targeting of antigen to dendritic cell-associated C-type lectin-1

Targeting of Ags and therapeutics to dendritic cells (DCs) has immense potential for immunotherapy and vaccination. Because DCs are heterogeneous, optimal targeting strategies will require knowledge about functional specialization among DC subpopulations and identification of molecules for targeting appropriate DCs. We characterized the expression of a fungal recognition receptor, DC-associated C-type lectin-1 (Dectin-1), on mouse DC subpopulations and investigated the ability of an anti-Dectin-1 Ab to deliver Ag for the stimulation of immune responses. Dectin-1 was shown to be expressed on CD8alpha-CD4-CD11b+ DCs found in spleen and lymph nodes and dermal DCs present in skin and s.c. lymph nodes. Injection of Ag-anti-Dectin-1 conjugates induced CD4+ and CD8+ T cell and Ab responses at low doses where free Ag failed to elicit a response. Notably, qualitatively different immune responses were generated by targeting Ag to Dectin-1 vs CD205, a molecule expressed on CD8alpha+CD4-CD11b- DCs, dermal DCs, and Langerhans cells. Unlike anti-Dectin-1, anti-CD205 conjugates failed to elicit an Ab response. Moreover, when conjugates were injected i.v., anti-Dectin-1 stimulated a much stronger CD4+ T cell response and a much weaker CD8+ T cell response than anti-CD205. The results reveal Dectin-1 as a potential targeting molecule for immunization and have implications for the specialization of DC subpopulations.     

Immune complex-loaded dendritic cells are superior to soluble immune complexes as antitumor vaccine

Dendritic cells (DCs) play an important role in the induction of T cell responses. Fc gammaRs, expressed on DCs, facilitate the uptake of complexed Ag, resulting in efficient MHC class I and MHC class II Ag presentation and DC maturation. In the present study, we show that prophylactic immunization with DCs loaded with Ag-IgG immune complexes (ICs) leads to efficient induction of tumor protection in mice. Therapeutic vaccinations strongly delay tumor growth or even prevent tumors from growing out. By depleting CD4+ and CD8+ cell populations before tumor challenge, we identify CD8+ cells as the main effector cells involved in tumor eradication. Importantly, we show that DCs that are preloaded in vitro with ICs are at least 1000-fold more potent than ICs injected directly into mice or DCs loaded with the same amount of noncomplexed protein. The contribution of individual Fc gammaRs to Ag presentation, T cell response induction, and induction of tumor protection was assessed. We show that Fc gammaRI and Fc gammaRIII are capable of enhancing MHC class I-restricted Ag presentation to CD8+ T cells in vitro and that these activating Fc gammaRs on DCs are required for efficient priming of Ag-specific CD8+ cells in vivo and induction of tumor protection. These findings show that targeting ICs via the activating Fc gammaRs to DCs in vitro is superior to direct IC vaccination to induce protective tumor immunity in vivo.     

Cellular interactions involved in Th cell memory

The cellular interactions involved in maintaining CD4+ T cell memory have hitherto not been identified. In this report, we have investigated the roles played by B cells and dendritic cells (DCs) in this process. We show that long-lasting Th cell memory depends on the presence of B cells, but that direct Ag presentation by B cells is not required. Instead, Ag presentation by DCs is critical for the survival of memory Th cells. DCs presenting specific Ag can be detected in animals long after immunization. These findings support a model in which B cells provide an environment in which Ags may be trapped and retained. This Ag is periodically presented to memory CD4+ T cells by DCs, providing an essential survival signal.     

A novel CD4-CD8alpha+CD205+CD11b- murine spleen dendritic cell line: establishment, characterization and functional analysis in a model of vaccination to toxoplasmosis

Dendritic cells (DCs) play an essential role in the induction of immune responses to pathogen infections. Native DCs are difficult to obtain in large numbers and consequently the vast majority of DCs employed in all experiments are derived from bone marrow progenitors. In an attempt to solve this problem, we have established a novel CD8alpha(+) DC line (H-2(k)) from spleen, which we have named SRDC line, and which is easy to culture in vitro. These cells display similar morphology, phenotype and activity to CD4(-)CD8alpha(+)CD205(+)CD11b(-) DCs purified ex vivo. Toxoplasma gondii antigen was shown to be taken up by these cells and to increase class I and class II major histocompatibility complex (MHC), CD40, CD80 and CD86 surface expression. We report that vaccination with T. gondii antigen-pulsed SRDCs, which synthesize large amounts of interleukin-12, induced protective immune responses against this intracellular pathogen in syngeneic CBA/J mice. This protection was associated with strong cellular and humoral immune responses at systemic and intestinal levels. Spleen and mesenteric lymph node cell proliferations were correlated with a Th1/Th2-type response and a specific SRDC homing to spleen and intestine was observed. The SRDC or CD4(-)CD8alpha(+)CD205(+)CD11b(-) DC line can be expected to be a very useful tool for immunobiology studies of DC.     

Dendritic cell vaccination induces tumor epitope-specific Th1 immune response in medullary thyroid carcinoma.

The existence of inherited aggressive forms of medullary thyroid carcinoma (MTC) and their resistance to classical therapies make it a prime candidate for adoptive immunotherapy. Highly potent antigen-presenting cells, namely dendritic cells (DCs), may serve as an interesting tool for anticancer vaccination. Here we report on the IN VITRO findings of a vaccination trial in five MTC patients, who were treated with a new DC generation protocol consisting of granulocyte-macrophage colony-stimulating factor and interferon-alpha (IFN-DCs). These cells were pulsed with tumor-specific calcitonin and administered twice. In two patients who responded to therapy we found a large increase (in mean 2.9+/-1.9%) of antigen-specific IFN-gamma-secreting CD4+ cells as well as an increase of granzyme B positive CD8+ cells (mean 2.2+/-0.2%) in the peripheral blood. In parallel, a decrease of CD4+/CD25+/FoxP3+ regulatory T cells was seen. Importantly, IN VITRO stimulation of PBMC with 10 different 15mer calcitonin peptides resulted in the identification of two HLA class II epitope regions within the central part of full-length calcitonin. These data were in accordance with the results drawn from the computer-based algorithm epitope prediction software SYFPEITHI. Measurement of different pro- and anti-angiogenic factors did not allow for a distinct outcome of prediction of the treated patients. In summary, we have demonstrated that immunization with IFN-DCs leads to a tumor epitope-specific immune response in MTC patients and may, therefore, represent a promising tool for future vaccination trials.     

Inhibition of mechanistic target of rapamycin promotes dendritic cell activation and enhances therapeutic autologous vaccination in mice

Dendritic cells (DCs) are potent inducers of T cell immunity, and autologous DC vaccination holds promise for the treatment of cancers and chronic infectious diseases. In practice, however, therapeutic vaccines of this type have had mixed success. In this article, we show that brief exposure to inhibitors of mechanistic target of rapamycin (mTOR) in DCs during the period that they are responding to TLR agonists makes them particularly potent activators of naive CD8(+) T cells and able to enhance control of B16 melanoma in a therapeutic autologous vaccination model in the mouse. The improved performance of DCs in which mTOR has been inhibited is correlated with an extended life span after activation and prolonged, increased expression of costimulatory molecules. Therapeutic autologous vaccination with DCs treated with TLR agonists plus the mTOR inhibitor rapamycin results in improved generation of Ag-specific CD8(+) T cells in vivo and improved antitumor immunity compared with that observed with DCs treated with TLR agonists alone. These findings define mTOR as a molecular target for augmenting DC survival and activation, and document a novel pharmacologic approach for enhancing the efficacy of therapeutic autologous DC vaccination.     

Liposomal delivery of CTL epitopes to dendritic cells

The induction of strong and long lasting T-cell response, CD4+ or CD8+, is a major requirement in the development of efficient vaccines. An important aspect involves delivery of antigens to dendritic cells (DCs) as antigen presenting cells (APCs) for the induction of potent antigen-specific CD8+ T lymphocyte (CTLs) responses. Protein or peptide-based vaccines become an attractive alternative to the use of live cell vaccines to stimulate CTL responses for the treatment of viral diseases or malignancies. However, vaccination with proteins or synthetic peptides representing discrete CTL epitopes have failed in most instances due to the inability for exogenous antigens to be properly presented to T cells via major histocompatibility complex (MHC) class I molecules. Modern vaccines, based on either synthetic or natural molecules, will be designed in order to target appropriately professional APCs and to co-deliver signals able to facilitate activation of DCs. In this review, we describe the recent findings in the development of lipid-based formulations containing a combination of these attributes able to deliver tumor- or viral-associated antigens to the cytosol of DCs. We present in vitro and pre-clinical studies reporting specific immunity to viral, parasitic infection and tumor growth.     

Impaired circulating myeloid DCs from myeloma patients

BACKGROUND: In clinical trials, cancer patients have received immunotherapy based on DCs generated from leukapheresed blood. It would therefore be an advantage to be able to measure blood levels and estimate the phenotype of DC before leukapheresis, to estimate the yield required for preparation of vaccines, or ex vivo stimulation of T cells for adoptive immunotherapy. METHODS: Recently, circulating lineage negative (Lin-) myeloid DC cells and their precursors have been identified by flow cytometry. We apply this strategy to the screening of blood samples from patients with multiple myeloma, in an attempt to characterize and quantitate the subset. By a direct flow cytometry approach, the blood levels of circulating lineage (CD3, CD19, CD14) negative, CD33++, HLA-DR+ cells were estimated before and following ex vivo cell differentiation, and phenotyped by MAbs with specificity against HLA-DR, HLA-ABC, CD1a, CD11c, CD33, CD40, CD49d, CD49e, CD54, CD80, CD83, and CD86. RESULTS: This study demonstrated that multiple myeloma patients have a 50% reduced blood level of Lin-, CD33++, HLA-DR+ myeloid DC, but a DC-precursor level within normal range. Furthermore, GM-CSF and IL-4 ex vivo stimulated DCs demonstrated an impaired up-regulation of the co-stimulatory molecule CD80 and the adhesion molecule CD54. DISCUSSION: These results may have clinical implications as a predictor for yield and functionality of the harvested DCs to be used in vaccination of myeloma patients.     

Accelerated CD8+ T-cell memory and prime-boost response after dendritic-cell vaccination

Efficient boosting of memory T-cell numbers to protective levels generally requires a relatively long interval between immunizations. Decreasing this interval could be crucial in biodefense and cancer immunotherapy, in which rapid protective responses are essential. Here, we show that vaccination with peptide-coated dendritic cells (DCs) generated CD8+ T cells with the phenotype and function of memory cells within 4-6 d. These early memory CD8+ T cells underwent vigorous secondary expansion in response to a variety of booster immunizations, leading to elevated numbers of effector and memory T cells and enhanced protective immunity. Coinjection of CpG oligodeoxynucleotides, potent inducers of inflammation that did not alter the duration of DC antigen display, prevented the rapid generation of memory T cells in wild-type mice but not in mice lacking the interferon (IFN)-gamma receptor. These data show that DC vaccination stimulates a pathway of accelerated generation of memory T cells, and suggest that events of inflammation, including the action of IFN-gamma on the responding T cells, control the rate of development of memory CD8+ T cells.     

Requirement of mature dendritic cells for efficient activation of influenza A-specific memory CD8+ T cells

It is critical to identify the developmental stage of dendritic cells (DCs) that is most efficient at inducing CD8+ T cell responses. Immature DCs can be generated from monocytes with GM-CSF and IL-4, while maturation is accomplished by the addition of stimuli such as monocyte-conditioned medium, CD40 ligand, and LPS. We evaluated the ability of human monocytes and immature and mature DCs to induce CD8+ effector responses to influenza virus Ags from resting memory cells. We studied replicating virus, nonreplicating virus, and the HLA-A*0201-restricted influenza matrix protein peptide. Sensitive and quantitative assays were used to measure influenza A-specific immune responses, including MHC class I tetramer binding assays, enzyme-linked immunospot assays for IFN-gamma production, and generation of cytotoxic T cells. Mature DCs were demonstrated to be superior to immature DC in eliciting IFN-gamma production from CD8+ effector cells. Furthermore, only mature DCs, not immature DCs, could expand and differentiate CTL precursors into cytotoxic effector cells over 7 days. An exception to this was immature DCs infected with live influenza virus, because of the virus's known maturation effect. Finally, mature DCs pulsed with matrix peptide induced CTLs from highly purified CD8+ T cells without requiring CD4+ T cell help. These differences between DC stages were independent of Ag concentrations or the number of immature DCs. In contrast to DCs, monocytes were markedly inferior or completely ineffective stimulators of T cell immunity. Our data with several qualitatively different assays of the memory CD8+ T cell response suggest that mature cells should be considered as immunotherapeutic adjuvants for Ag delivery.     

Flt3-ligand and granulocyte colony-stimulating factor mobilize distinct human dendritic cell subsets in vivo

Dendritic cells (DCs) have a unique ability to stimulate naive T cells. Recent evidence suggests that distinct DC subsets direct different classes of immune responses in vitro and in vivo. In humans, the monocyte-derived CD11c+ DCs induce T cells to produce Th1 cytokines in vitro, whereas the CD11c- plasmacytoid T cell-derived DCs elicit the production of Th2 cytokines. In this paper we report that administration of either Flt3-ligand (FL) or G-CSF to healthy human volunteers dramatically increases distinct DC subsets, or DC precursors, in the blood. FL increases both the CD11c+ DC subset (48-fold) and the CD11c- IL-3R+ DC precursors (13-fold). In contrast, G-CSF only increases the CD11c- precursors (>7-fold). Freshly sorted CD11c+ but not CD11c- cells stimulate CD4+ T cells in an allogeneic MLR, whereas only the CD11c- cells can be induced to secrete high levels of IFN-alpha, in response to influenza virus. CD11c+ and CD11c- cells can mature in vitro with GM-CSF + TNF-alpha or with IL-3 + CD40 ligand, respectively. These two subsets up-regulate MHC class II costimulatory molecules as well as the DC maturation marker DC-lysosome-associated membrane protein, and they stimulate naive, allogeneic CD4+ T cells efficiently. These two DC subsets elicit distinct cytokine profiles in CD4+ T cells, with the CD11c- subset inducing higher levels of the Th2 cytokine IL-10. The differential mobilization of distinct DC subsets or DC precursors by in vivo administration of FL and G-CSF offers a novel strategy to manipulate immune responses in humans.