Dendritic cells as adjuvants for class I major histocompatibility complex-restricted antitumor immunity

Human tumour and dendritic cell hybrids generated by electrofusion: potential for cancer vaccines

Hybrid cells created by fusion of antigen presenting and tumour cells have been shown to induce potent protective and curative anti-tumour immunity in rodent cancer models. The application of hybrid cell vaccines for human tumour therapy and the timely intervention in disease control are limited by the requirement to derive sufficient autologous cells to preserve homologous tumour antigen presentation. In this study, the efficiency of various methods of electrofusion in generating hybrid human cells have been investigated with a variety of human haemopoietic, breast and prostate cell lines. Cell fusion using an electrical pulse is enhanced by a variety of stimuli to align cells electrically or bring cells into contact. Centrifugation of cells after an exponential pulse from a Gene Pulser electroporation apparatus provided the highest yield of mixed cell hybrids by FACS analysis. An extensive fusogenic condition generated in human cells after an electrical pulse contradicts the presumption that prior cell contact is necessary for cell fusion. Alignment of cells in a concurrent direct current charge and osmotic expansion of cells in polyethylene glycol also generated high levels of cell fusion. Waxing of one electrode of the electroporation cuvette served to polarize the fusion chamber and increase cell fusion 5-fold. Optimisation of a direct current charge in combination with a fusogenic pulse in which fusion of a range of human cells approached or exceeded 30% of the total pulsed cells. The yield of hybrid prostate and breast cancer cells with dendritic cells was similar to the homologous cell fusion efficiencies indicating that dendritic cells were highly amenable to fusion with human tumour cells under similar electrical parameters. Elimination of unfused cells by density gradient and culture is possible to further increase the quantity of hybrid cells. The generation and purification of quantities of hybrid cells sufficient for human vaccination raises the possibility of rapid, autologous tumour antigen presenting vaccines for trial with common human tumours.

Dendritic cells purified from myeloma are primed with tumor-specific antigen (idiotype) and activate CD4+ T cells

Multiple myelomas produce tumor-specific antigen (TSA) in the form of idiotype (Id) on monoclonal Ig. CD4(+) T cells can recognize Id-peptide on MHC class II molecules and protect against challenges with MOPC315 cells, which are, as common for myelomas, class II-negative. The present study explains these previous results by demonstrating that Id can be transferred from myeloma cells to antigen-presenting cells (APC), which present processed Id-peptide on their class II molecules to Id-specific T cell receptor-transgenic (TCR-TG) CD4(+) T cells. Id-primed tumor APC were heterogeneous, the majority being dendritic cells with class II(+), CD11b(+) CD11c(+) CD40(+) CD80(+) CD86(+) markers. The APC were localized beneath CD31(+) endothelial cells of tumor microvessels, and their frequency declined with tumor progression. The APC could stimulate Id-specific naive TCR-TG, short-term polarized TCR-TG, and cloned CD4(+) T cells to proliferate and produce cytokines in vitro. Furthermore, small MOPC315 tumors established in Id-specific TCR-TG mice contained clusters of activated (CD69(+)CD25(+)) and proliferating (BrdUrd(+)) Id-specific transgenic CD4(+) blasts. The activated Id-specific T cells were located adjacent to Id-primed dendritic cells in the tumor. Thus, a TSA can be transferred in vivo from myeloma, and possibly other types of cancer cells to APC for MHC class II presentation to CD4(+) T cells.

Stimulatory and inhibitory differentiation of human myeloid dendritic cells

Dendritic cells (DCs) play a critical obligate role in presenting antigens to T cells for activation. In the process, upon antigen capture, DCs undergo maturation and become more stimulatory. Human myeloid DCs can be generated from various sources, including blood, bone marrow, and CD34(+) stem cells. As such, plastic-adherent monocytes from circulation have served as a ready source for generating myeloid DCs in culture in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) for translational research in active specific immunotherapy, especially in cancer, with the belief that they are essentially stimulatory or "immunogenic." Here we show that in vitro cultures of plastic-adherent circulating monocytes in GM-CSF and IL-4 followed by further maturation in interferon-gamma plus bacterial superantigens (DC maturing agents) can give rise to two diametrically opposite types of DCs-one stimulatory and another inhibitory. The stimulatory DCs express higher amounts of costimulatory molecules, synthesize IL-12, and efficiently stimulate naive allogeneic T cells in mixed lymphocyte reaction (MLR). The inhibitory DCs, in contrast, express lower concentrations of the critical costimulatory molecules, synthesize large amounts of IL-10, and are nonstimulatory in allogeneic primary MLR. Moreover, while the stimulatory DCs further amplify proliferation of T cells in lectin-driven proliferation assays, the inhibitory DCs totally block T cell proliferation in similar assays, in vitro. Most interestingly, neutralization of the endogenously derived IL-10 with anti-IL-10 antibody in DC cultures repolarizes the inhibitory DCs toward stimulatory phenotype. Accordingly, these observations have important implications in translational research involving myeloid DCs.

Autocrine activation-induced cell death of T cells by human peripheral blood monocyte-derived CD4+ dendritic cells

Mature T cells activated by antigen (Ag)-presenting cells are subject to various downmodulatory processes designed to maintain T cell homeostasis. Here we describe experiments in which mature T cells were subjected to apoptosis following stimulation with CD4(+) dendritic cells (DCs) during Ag presentation. The proliferative response of allogeneic T cells was increased by DCs at stimulator to responder (S/R) ratios ranging from 10(-3) to 1, whereas this response was decreased at S/R ratios ranging from 2 to 10. Allogeneic T cells stimulated with DCs at an S/R ratio of 5 underwent apoptosis, whereas this event was not observed in allogeneic T cells stimulated with DCs at an S/R ratio of 0.5. Stimulation of T cells with DCs at an S/R ratio of 5 induced a higher level of expression of CD95 ligand (CD95L) than stimulation of T cells cultured with DCs at an S/R ratio of 0.5, whereas similar levels of expression of CD28 and CD154 were observed in both cells. The abortive proliferation of mature T cells stimulated with DCs was prevented by blocking the CD95-CD95L system. Our results suggest that the CD4(+) DCs play counterregulatory roles in dictating T cell responses during Ag presentation.

Flt3 ligand (FL) and its influence on immune reactivity

Flt3 (fms-like tyrosine kinase 3) ligand (FL) is a potent hematopoietic cytokine that affects the growth and differentiation of progenitor and stem cells both in vivo and in vitro. Its capacity to augment strikingly the numbers of dendritic cells (rare antigen-presenting cells that induce and regulate immune responses) in mice and humans has stimulated considerable interest in its value as an investigational tool and therapeutic agent. In this review, we survey the hematopoietic properties and immunobiology of FL, and examine its therapeutic potential.

Percutaneous peptide immunization via corneum barrier-disrupted murine skin for experimental tumor immunoprophylaxis

H-2K(b)-restricted tumor epitope peptides, including tyrosinase-related protein 2 residues 181-188 (TRP-2) and connexin 37 residues 52-59 (MUT1), were applied to permeability barrier-disrupted C57BL/6 (B6) mouse skin from which the stratum corneum of the epidermis had been removed by tape-stripping. This procedure primed tumor-specific cytotoxic T lymphocytes (CTLs) in the lymph nodes and spleen, protected mice against subsequent challenge with corresponding tumor cells, and suppressed the growth of established tumors. Preventive and therapeutic effectiveness was correlated with the frequency of tumor-specific CTL precursors. MHC class II Ia(b+) cells separated from tape-stripped skin, compared with those from intact skin, exhibited a strong antigen-presenting capacity for CTL, suggesting that CTL expansion after peptide application is primarily mediated by epidermal Langerhans cells. Thus, percutaneous peptide immunization via barrier-disrupted skin provides a simple and noninvasive means of inducing potent anti-tumor immunity which may be exploited for cancer immunotherapy.

Lymph node metastases: the importance of the microenvironment

BACKGROUND

Although, to the authors' knowledge, no prospective randomized clinical trial has demonstrated improvement in survival following the radical dissection of lymph nodes in the treatment of cancer patients, lymphadenectomy is still routinely performed for curative purposes. For many years, regional lymph nodes (RLNs) in tumor-bearing hosts have been considered anatomic barriers to the systematic dissemination of tumor cells. More recently, the belief has been held that lymph nodes play a completely passive role, by virtue of the observations that many lymphatic and lymphaticovenous shunts bypass RLNs and allow both lymphatic and hematogenous dissemination of malignant cells at an early stage in the vast majority of cancers. Furthermore, surgical removal of RLNs apparently has no effect, deleterious or beneficial, on the well-being of the host.

METHODS

A comprehensive and critical review of the scientific literature was conducted to evaluate, from a biologic point of view, the role played by RLNs during the interactions between the tumor and the host's immune system.

RESULTS

Recent advances in our understanding of the molecular events of antigen recognition by T cells and T-cell activation have provided strong experimental evidence to demonstrate that these secondary lymphoid organs constitute the primary sites where the specific recognition of tumor antigens and the proper activation of the immune system take place. Indeed, the notion that naive T cells are induced or silenced by tumor cells in the periphery may today be questioned, because effective induction can only occur in these secondary lymphoid organs where cell-to-cell interactions are properly guided and cells can meet in an appropriate cytokine-enriched microenvironment.

CONCLUSIONS

Promising results obtained in the human setting with the use of dendritic cells as novel immunotherapeutic tools have recently renewed interest in active immunotherapy for the treatment of solid tumors. However, for accomplishing this goal, the maintenance of the integrity of the immune system remains a crucial issue. Studies showing that radical tumor-draining RLN dissections exert a markedly negative influence on the efficacy of postoperative immunotherapy protocols in mice as well as in humans seem to support adoption of a more conservative approach regarding uninvolved RLNs in the treatment of cancer patients.

Transduction and utility of the granulocyte-macrophage colony-stimulating factor gene into monocytes and dendritic cells by adeno-associated virus

The genetic manipulation of antigen-presenting dendritic cells (DC) offers promise for stimulating the immune response, in particular for anticancer and antiviral protocols. As adeno-associated virus (AAV) has shown promise as a gene delivery vector for transducing a variety of hematopoietic cell types, we have investigated AAV's ability to genetically alter DC. In this analysis, we modified the standard granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) treatment of adherent monocytes to generate DC. In our protocol, adherent monocytes were first infected with an AAV/GM-CSF/Neo vector, and the addition of IL-4 was delayed for 2 days to allow for a brief period of monocyte proliferation. AAV-mediated transduction of the GM-CSF and Neo genes into monocytes/DC precursors was demonstrated by G418 selection, GM-CSF secretion, GM-CSF RNA expression (reverse transcriptase-polymerase chain reaction amplification [RT-PCR]), and cell proliferation. Cells resulting from infection with AAV/GM-CSF/Neo virus, and subsequent IL-4 and tumor necrosis factor-alpha (TNF-alpha) treatment, displayed multiple classic markers consistent with mature DC. Finally, chromosomal integration of the AAV vector was also demonstrated in sorted CD83+ DC. These data strongly suggest that AAV vectors will be useful for the genetic manipulation of DC and suggest that the transduction of the GM-CSF gene was able to fully replace the need for exogenous GM-CSF in the production of mature DC.

Treatment with tumor necrosis factor-alpha and granulocyte-macrophage colony-stimulating factor increases epidermal Langerhans' cell numbers in cancer patients

Dendritic cells (DCs) initiate primary and stimulate secondary T-cell responses. We conducted a phase I trial of tumor necrosis factor (TNF-alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in patients with cancer to increase DCs in peripheral blood or skin based on in vitro data that showed that CD34(+) hematopoietic precursors require these cytokines to mature into functional antigen-presenting DCs. Eleven patients were treated for 7 days with GM-CSF, 125 microg/m(2) twice daily as subcutaneous injections, and TNF-alpha as a continuous infusion at dose levels of 25, 50, or 100 microg/m(2)/day. The maximum tolerated dose of TNF-alpha was 50 microg/m(2)/day with this dose of GM-CSF; dose-limiting toxicities occurred in both patients treated with 100 microg/m(2)/day. One became thrombocytopenic and the other had transient confusion. Epidermal Langerhans' cells were quantitated by S100 staining of skin biopsies and DC precursors in peripheral blood by colony-forming unit dendritic (CFU-dendritic) assays. S100-positive cells in the epidermis doubled after treatment (2.55 S100(+) cells/high-power field before treatment to 6.05 after treatment, p = 0.029). CFU-dendritic in peripheral blood increased after treatment in 3 colorectal cancer patients but not in 3 patients with melanoma. CD11c(+) or CD123(+), HLA-DR(bright), lineage-negative dendritic cell precursors were not increased in peripheral blood mononuclear cells. This trial demonstrates that treatment with TNF-alpha and GM-CSF can increase the number of DCs in the skin and the number of dendritic cell precursors in the blood of some patients with cancer. This approach may increase the efficacy of vaccination to tumor antigens in cancer patients.

Induction of Tumor Immunity by Removing CD25+CD4+ T Cells: A Common Basis Between Tumor Immunity and Autoimmunity

This study shows that removal of a T cell subpopulation can evoke effective tumor immunity in otherwise nonresponding animals. Elimination of CD25-expressing T cells, which constitute 5–10% of peripheral CD4+ T cells in normal naive mice, elicited potent immune responses to syngeneic tumors in vivo and eradicated them. The responses were mediated by tumor-specific CD8+ CTLs and tumor-nonspecific CD4−8− cytotoxic cells akin to NK cells. Furthermore, in vitro culture of CD25+4+ T cell-depleted splenic cell suspensions prepared from tumor-unsensitized normal mice led to spontaneous generation of similar CD4−8− cytotoxic cells capable of killing a broad spectrum of tumors; reconstitution of CD25+4+ T cells inhibited the generation. In this culture, self-reactive CD25−4+ T cells responding to self peptides/class II MHC complexes on APCs spontaneously proliferated upon removal of CD25+4+ T cells, secreting large amounts of IL-2. The IL-2 thus produced appeared to be responsible for the generation of CD4−8− NK cells as lymphokine-activated killer cells, because direct addition of an equivalent amount of IL-2 to the culture of CD4−8− cells generated similar lymphokine-activated killer/NK cells, whereas coculture of normal CD4−8− cells with CD25−4+ T cells from IL-2-deficient mice did not. Thus, removal of immunoregulatory CD25+4+ T cells can abrogate immunological unresponsiveness to syngeneic tumors in vivo and in vitro, leading to spontaneous development of tumor-specific effector cells as well as tumor-nonspecific ones. This novel way of evoking tumor immunity would help to devise effective immunotherapy for cancer in humans.

Human dendritic cells mediate cellular apoptosis via tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)

TRAIL (TNF-related apoptosis-inducing ligand) is a member of the TNF family that induces apoptosis in a variety of cancer cells. In this study, we demonstrate that human CD11c(+) blood dendritic cells (DCs) express TRAIL after stimulation with either interferon (IFN)-gamma or -alpha and acquire the ability to kill TRAIL-sensitive tumor cell targets but not TRAIL-resistant tumor cells or normal cell types. The DC-mediated apoptosis was TRAIL specific, as soluble TRAIL receptor blocked target cell death. Moreover, IFN-stimulated interleukin (IL)-3 receptor (R)alpha(+) blood precursor (pre-)DCs displayed minimal cytotoxicity toward the same target cells, demonstrating a clear functional difference between the CD11c(+) DC and IL-3Ralpha(+) pre-DC subsets. These results indicate that TRAIL may serve as an innate effector molecule on CD11c(+) DCs for the elimination of spontaneously arising tumor cells and suggest a means by which TRAIL-expressing DCs may regulate or eliminate T cells responding to antigen presented by the DCs.

Human Dendritic Cells Very Efficiently Present a Heterologous Antigen Expressed on the Surface of Recombinant Gram-Positive Bacteria to CD4+ T Lymphocytes

Recombinant Streptococcus gordonii expressing on the surface the C-fragment of tetanus toxin was tested as an Ag delivery system for human monocyte-derived dendritic cells (DCs). DCs incubated with recombinant S. gordonii were much more efficient than DCs pulsed with soluble C-fragment of tetanus toxin at stimulating specific CD4+ T cells as determined by cell proliferation and IFN-γ release. Compared with DCs treated with soluble Ag, DCs fed with recombinant bacteria required 102- to 103-fold less Ag and were at least 102 times more effective on a per-cell basis for activating specific T cells. S. gordonii was internalized in DCs by conventional phagocytosis, and cytochalasin D inhibited presentation of bacteria-associated Ag, but not of soluble Ag, suggesting that phagocytosis was required for proper delivery of recombinant Ag. Bacteria were also very potent inducers of DC maturation, although they enhanced the capacity of DCs to activate specific CD4+ T cells at concentrations that did not stimulate DC maturation. In particular, S. gordonii dose-dependently up-regulated expression of membrane molecules (MHC I and II, CD80, CD86, CD54, CD40, CD83) and reduced both phagocytic and endocytic activities. Furthermore, bacteria promoted in a dose-dependent manner DC release of cytokines (IL-6, TNF-α, IL-1β, IL-12, TGF-β, and IL-10) and of the chemokines IL-8, RANTES, IFN-γ-inducible protein-10, and monokine induced by IFN-γ. Thus, recombinant Gram-positive bacteria appear a powerful tool for vaccine design due to their extremely high capacity to deliver Ags into DCs, as well as induce DC maturation and secretion of T cell chemoattractans.

Dendritic cells need T cell help to prime cytotoxic T cell responses to strong antigens

Peptide-pulsed mouse dendritic cells (DC) primed peptide-specific CD8+ cytotoxic T cell responses very effectively if they expressed minor histocompatibility antigens, which could stimulate a CD4+ T helper cell response. These DC could also prime most syngeneic mice, although there was no deliberate immunization for help (the DC were prepared in syngeneic mouse serum, to avoid any response to fetal calf serum antigens). In contrast, DC were unable to prime MHC class II-deficient mice for cytotoxic responses to the classical helper-dependent antigens Qa1a and HY. More strikingly, Balb.B DC failed to prime B6 MHC class II-deficient mice for cytotoxic responses to Balb minor antigens, even though these two strains differ at more than 40 minor histocompatibility loci. When peptide-pulsed DC were prepared without enzymes (used to release DC from lymphoid tissues), they failed to prime the majority of normal syngeneic mice, even though they expressed high levels of B7 and ICAM-1 co-stimulatory molecules, suggesting that help was provided by responses to antigens in the enzyme cocktail. The enzyme treatment itself did not provide signals that could substitute for help, since DC prepared with enzymes could not prime MHC class II-deficient mice. The observation that highly immunogenic minor-incompatible DC failed to prime MHC class II-deficient mice suggests that in the absence of inflammatory signals, even strong antigens cannot stimulate CD8+ T cell responses without help.

Therapy of established tumour with a hybrid cellular vaccine generated by using granulocyte-macrophage colony-stimulating factor genetically modified dendritic cells

Dendritic cells (DCs) are the most powerful of all antigen-presenting cells and play a critical role in the induction of primary immune responses. DC-based vaccination represents a potentially powerful strategy for cancer immunotherapy. In this study, a new approach for a DC-based melanoma vaccine was described. Splenic DCs from C57BL/6 mice were fused with B16 melanoma cells, and the resultant B16/DC hybrid cells expressed major histocompatibility complex (MHC) molecules - B7 as well as the B16 tumour marker M562 - which were enriched by Ia-mediated positive selection with a MiniMACS column. The fusion rates were 12.7-26.8%. To generate hybrid tumour vaccines with potentially greater potent therapeutic efficacy, we genetically engineered DCs with granulocyte-macrophage colony-stimulating factor (GM-CSF) prior to cell fusion. Recombinant adenovirus vector was used to mediate gene transfer into DCs with high efficiency and DCs expressed GM-CSF at 96-138 ng/105 cells/ml 24 hr after GM-CSF gene transfer. GM-CSF gene-modified DCs (DC.GM) exhibited higher expression of B7 and co-stimulatory capacity in mixed lymphocyte reaction (MLR). Fusion of DC.GM with B16 cells generated B16/DC.GM hybrid cells secreting GM-CSF at 59-63 ng/105 cells/ml. Immunization of C57BL/6 mice with the B16/DC hybrid vaccine elicited a specific cytotoxic T-lymphocyte (CTL) response and protected the immunized mice from B16 tumour challenge, reduced pulmonary metastases and extended the survival of B16 tumour-bearing mice. The B16/DC.GM hybrid vaccine was able to induce a CTL response and protective immunity more potently and tended to be therapeutically more efficacious than the B16/DC vaccine. In vivo depletion of T-cell subsets demonstrated that both CD8+ and CD4+ T cells were essential for the therapeutic effects of B16/DC and B16/DC.GM hybrid vaccines. Additionally, other non-specific effector cells may also contribute to tumour rejection induced by the B16/DC.GM hybrid vaccine. These data indicate that a DC-based hybrid tumour vaccine may be an attractive strategy for cancer immunotherapy, and that GM-CSF gene-modified DCs may lead to the generation of hybrid vaccines with potentially increased therapeutic efficacy.

Cytolytic T-cell responses to human dendritic cells and macrophages infected with Mycobacterium bovis BCG and recombinant BCG secreting listeriolysin

Cytolytic T-cell responses from 63 normal blood donors were monitored in a Mycobacterium bovis BCG infection system in vitro. We wanted to know whether cultured dendritic cells were capable of potentiating the cytolytic T-cell responses to M. bovis BCG. Infected cultured dendritic cells were up to ten times more effective antigen-presenting cells than macrophages in proliferative assays, while cytolytic T-cell induction did not differ significantly between dendritic cells and macrophages. Separated CD4+ and CD8+ T-cell subsets contributed equally to lysis of infected targets. Experiments comparing wild-type M. bovis BCG strain with two new recombinant M. bovis BCG strains secreting listeriolysin revealed statistically significant higher maximal lysis values for recombinant M. bovis BCG. We conclude from our in vitro infection system with mycobacteria that dendritic cells are superior to macrophages in proliferative assays but equal to macrophages in their ability to induce cytolytic T-cell responses. Moreover, our data suggest that recombinant M. bovis BCG vaccine strains secreting listeriolysin improve cytolytic T-cell responses.

Delivery of liposome-encapsulated HIV type 1 proteins to human dendritic cells for stimulation of HIV type 1-specific memory cytotoxic T lymphocyte responses

An important aspect of vaccine development involves delivery of antigens to antigen-presenting cells for the induction of potent antigen-specific T lymphocyte responses. We investigated the effect of a cationic liposome, lipofectin, on delivery of whole proteins to human dendritic cells (DCs) derived from blood mononuclear cells by culture in interleukin 4 and granulocyte-monocyte colony-stimulating factor for stimulation of human immunodeficiency virus type 1 (HIV-1)-specific memory cytotoxic T lymphocyte (CTL) responses. Delivery of HIV-1 Gag, Pol, and Env proteins to DCs by lipofectin stimulated greater anti-HIV-1 memory CTL responses in cells from HIV-1-infected subjects than those induced by DCs loaded with protein alone. The CTLs were CD8+ and HLA class I restricted. Antigen presentation was enhanced by chloroquine, but blocked by brefeldin A and peptide aldehyde inhibitors of proteasomes, indicating that the classic MHC class I cytosolic pathway was used for processing and presentation of HIV-1 protein by the DCs. Stimulation of anti-HIV-1 CTLs by this safe, inexpensive, and broadly applicable approach may be used in DC-based therapies for HIV-1 infection.

Prospects of immunotherapy for the treatment of prostate carcinoma--a review

The treatment of prostate carcinoma is dependent on the stage of the disease. Patients who present with clinically localized cancer or locally advanced tumors can be potentially cured by radical prostatectomy, radiation, and hormonal therapy. However, disease progression can occur in 30-50% of patients diagnosed with clinically localized cancer. The bone is the predominant site of metastases. Metastatic prostate cancer is first treated by androgen blockade but within a few months becomes hormone refractory. Hormone refractory metastatic prostate cancer is not responsive to conventional treatments, and patients have an expected survival of less than a year. It is essential to develop new approaches for the treatment of hormone refractory metastatic disease. Immunotherapy, based on enhancement of the host immune response against the tumor, has been used as an alternative therapy for the treatment of metastatic cancers refractory to conventional therapy in particular for melanoma and renal cell carcinoma. In this review, we will summarize various immunotherapeutic approaches developed over the last 18 years, and we will address the potential of immunotherapy for the treatment of metastatic prostate carcinoma by reviewing preclinical studies and initial clinical trials performed in this field.

Induction of human papillomavirus-specific CD4(+) and CD8(+) lymphocytes by E7-pulsed autologous dendritic cells in patients with human papillomavirus type 16- and 18-positive cervical cancer

Human papillomavirus (HPV) type 16 (HPV 16) and HPV type 18 (HPV 18) are implicated in the induction and progression of the majority of cervical cancers. Since the E6 and E7 oncoproteins of these viruses are expressed in these lesions, such proteins might be potential tumor-specific targets for immunotherapy. In this report, we demonstrate that recombinant, full-length E7-pulsed autologous dendritic cells (DC) can elicit a specific CD8(+) cytotoxic T-lymphocyte (CTL) response against autologous tumor target cells in three patients with HPV 16- or HPV 18-positive cervical cancer. E7-specific CTL populations expressed strong cytolytic activity against autologous tumor cells, did not lyse autologous concanavalin A-treated lymphoblasts or autologous Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL), and showed low levels of cytotoxicity against natural killer cell-sensitive K562 cells. Cytotoxicity against autologous tumor cells could be significantly blocked by anti-HLA class I (W6/32) and anti-CD11a/LFA-1 antibodies. Phenotypically, all CTL populations were CD3(+)/CD8(+), with variable levels of CD56 expression. CTL induced by E7-pulsed DC were also highly cytotoxic against an allogeneic HLA-A2(+) HPV 16-positive matched cell line (CaSki). In addition, we show that specific lymphoproliferative responses by autologous CD4(+) T cells can also be induced by E7-pulsed autologus DC. E7-specific CD4(+) T cells proliferated in response to E7-pulsed LCL but not unpulsed LCL, and this response could be blocked by anti-HLA class II antibody. Finally, with two-color flow cytometric analysis of intracellular cytokine expression at the single-cell level, a marked Th1-like bias (as determined by the frequency of gamma interferon- and interleukin 4-expressing cells) was observable for both CD8(+) and CD4(+) E7-specific lymphocyte populations. Taken together, these data demonstrate that full-length E7-pulsed DC can induce both E7-specific CD4(+) T-cell proliferative responses and strong CD8(+) CTL responses capable of lysing autologous naturally HPV-infected cancer cells in patients with cervical cancer. These results may have important implications for the treatment of cervical cancer patients with active or adoptive immunotherapy.

Treatment of intracranial gliomas with bone marrow-derived dendritic cells pulsed with tumor antigens

OBJECT

An approach toward the treatment of intracranial gliomas was developed in a rat experimental model. The authors investigated the ability of "professional" antigen-presenting cells (dendritic cells) to enhance host antitumor immune responses when injected as a vaccine into tumor-bearing animals.

METHODS

Dendritic cells, the most potent antigen-presenting cells in the body, were isolated from rat bone marrow precursors stimulated in vitro with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4. Cultured cell populations were confirmed to be functional antigen-presenting cells on the basis of expressed major histocompatibility molecules, as analyzed by fluorescence-activated cell sorter cytofluorography. These dendritic cells were then pulsed (cocultured) ex vivo with acid-eluted tumor antigens from 9L glioma cells. Thirty-eight adult female Fischer 344 rats harboring 7-day-old intracranial 9L tumors were treated with three weekly subcutaneous injections of either control media (10 animals), unpulsed dendritic cells (six animals), dendritic cells pulsed with peptides extracted from normal rat astrocytes (10 animals), or 9L tumor antigen-pulsed dendritic cells (12 animals). The animals were followed for survival. At necropsy, the rat brains were removed and examined histologically, and spleens were harvested for cell-mediated cytotoxicity assays. The results indicate that tumor peptide-pulsed dendritic cell therapy led to prolonged survival in rats with established intracranial 9L tumors implanted 7 days prior to the initiation of vaccine therapy in vivo. Immunohistochemical analyses were used to document a significantly increased perilesional and intratumoral infiltration of CD8+ and CD4+ T cells in the groups treated with tumor antigen-pulsed dendritic cells compared with the control groups. In addition, the results of in vitro cytotoxicity assays suggest that vaccination with these peptide-pulsed dendritic cells can induce specific cytotoxic T lymphocytes against 9L tumor cells.

CONCLUSIONS

Based on these results, dendritic antigen-presenting cells pulsed with acid-eluted peptides derived from autologous tumors represent a promising approach to the immunotherapy of established intracranial gliomas. which may serve as a basis for designing clinical trials in patients with brain tumors.

Expression of surface antigens during the differentiation of human dendritic cells vs macrophages from blood monocytes in vitro

High expression of MHC antigens and adhesion/costimulation molecules is considered as one of the major characteristics qualifying macrophages (M) and dendritic cells (DC) as professional antigen presenting cells. Since accessory activity of M is known to be weaker than that of DC but both M or DC can differentiate from blood monocytes (MO) depending on culture conditions (i.e. GM-CSF vs GM-CSF/IL-4), we investigated the kinetics of expression of MHC antigens and several adhesion/costimulation molecules during the differentiation of DC or M from blood MO. Blood MO cultured with GM-CSF consistently induced M that showed adherence to plastic and CD14 expression. In contrast, MO cultured with GM-CSF/IL-4 rapidly became nonadherent, acquired DC morphology and lost CD14 expression. M but not DC proliferated as demonstrated by [H3]thymidine incorporation. MHC Class I was highly expressed in both M and DC. In contrast, MHC Class II molecules were significantly higher on DC compared to M. CD80 was upregulated on both DC and M but only on a subset of cells. CD80 expression peaked at day 3 on M and declined thereafter, while on DC expression increased significantly until day 10. CD86 was upregulated on the majority of DC and M. However, while M maintained stable expression of CD86 after day 3, DC progressively upregulated CD86 throughout the culture period. CD1a expression was initially low in both cell types and peaked at day 3 in M declining thereafter, while expression remained stable on DC until day 10. ICAM-1 expression was significantly upregulated on M when compared to DC at day 3. However, on M, ICAM-1 expression became undetectable by day 5 while on DC it increased through day 10. Similarly, CD40 was transiently expressed on M until day 5, while on DC it continuously increased until day 10. Finally, in contrast to other antigens, LFA-3 was always more strongly expressed on M than DC at all culture periods. Taken together, these data suggest that M showed a rapid but transient upregulation in the expression of adhesion/costimulation molecules, suggesting that maximal accessory ability is reached by M at an earlier time point than DC. Significant differences in surface antigen expression DC vs M were recognizable for MHC class II, CD86, CD80, CD1a, CD40 and ICAM-1. Specifically, major differences occurred for MHC class II, CD86, CD40 and ICAM-1. Therefore, the higher accessory ability of DC compared to M in naive T cell priming may be related to qualitative and quantitative differences in expression of these immunologically important surface molecules.

Enhanced therapeutic efficacy of tumor RNA-pulsed dendritic cells after genetic modification with lymphotactin

Pulsing dendritic cells (DCs) with tumor cell-derived mRNA is regarded as an attractive alternative in the development of DC-based tumor vaccines. Our aim is to improve the therapeutic efficacy of DC-based tumor RNA vaccines by augmenting the preferential chemotaxis of DCs to T cells. Mouse bone marrow-derived DCs were genetically modified with lymphotactin (Lptn) by adenovirus vector, which conferred on DCs preferential chemotaxis to CD4+ and CD8+ T cells (Cao et al., 1998). Lptn gene-modified DCs (Lptn-DCs) were pulsed with tumor mRNA and used for vaccination in the tumor models of 3LL lung carcinoma and B16 melanoma. In both tumor models, immunization with 4 X 10(4) tumor RNA-pulsed Lptn-DCs induced more potent CTL activity, compared with their counterparts, specifically against tumor cells and Mut1 or tyrosinase-related protein 2 (TRP-2) peptide-pulsed RMA-S cells, and rendered the immunized mice resistant to tumor challenge much more effectively. CD8+ T cells were necessary and sufficient to generate the protection of Lptn-DC-based RNA tumor vaccines, and CD4+ T cells were required for the induction of tumor rejection. In the preestablished 3LL and B16 tumor models, vaccination with DC-based or LacZ-DC-based tumor RNA vaccines (2 X 10(5) cells) could reduce pulmonary metastasis and extend survival of tumor-bearing mice, but was less effective than the Lptn-DC counterpart (with 60-80% mice surviving). When the immunizing dose was decreased to 4 X 10(4) cells, Lptn-DC-based tumor vaccines rather than their counterparts were still significantly effective. Our studies provide a potential strategy to improve the efficacy of DC-based vaccines, and a new approach to immunological intervention by chemokines.

Human PBMC-derived dendritic cells transduced with an adenovirus vectorinduce cytotoxic T-lymphocyte responses against a vector-encoded antigen in vitro

Dendritic cells (DC) are among the most potent antigen-presenting cells known and play an important role in the initiation of antigen-specific T-lymphocyte responses. Several recent studies have demonstrated that DC expressing vector-encoded tumor-associated antigens can induce protective and therapeutic immunity in murine cancer models. In the current study we set out to examine in vitro the utility of adenovirus vectors in the transduction of human DC for the induction of antigen-specific T-lymphocyte responses against a defined vector-encoded antigen. DC were derived from the adherent fraction of PBMC by culture in defined medium containing GM-CSF and IL-4. A replication-defective E1/E3-deleted type 5 adenovirus vector encoding bacterial beta-galactosidase (beta-gal) under the transcriptional control of a CMV promoter was used to transduce DC at multiplicities of infection (MOI) up to 1000. While high MOI were required to achieve efficient transduction there was no significant effect on DC morphology, immunophenotype or potency in allogeneic lymphocyte proliferation assays. Furthermore, transduced DC-induced antigen-specific CTL activity against adenoviral proteins and more significantly, the vector-encoded antigen beta-gal. These data clearly demonstrate the potential of adenovirus vectors in anticancer DC vaccine strategies and provide an important link between existing animal data and human clinical application.

Dendritic cells: expansion and differentiation with hematopoietic growth factors

Dendritic cells are critical initiators of immune responses mediated by T and B lymphocytes. Dendritic cells process antigens captured in the periphery, then emigrate to lymphoid organs. There they complete their maturation by upregulating important accessory molecules and secreting cytokines, all of which support potent stimulation of antigen-specific lymphocytes. These lymphocytes return to the periphery to complete the immune response. Investigators have discovered culture systems that use exogenous hematopoietic cytokines to support the growth, differentiation, and maturation of dendritic cells in larger numbers and greater purity than was ever before possible. This has rendered dendritic cells accessible to detailed experimental evaluations and clinical applications. Dendritic cells provide a powerful means of controlling both normal and pathologic immunity.

Emergence of Regulatory CD4+ T Cell Response to Repetitive Stimulation with Antigen-Presenting Cells In Vitro: Implications in Designing Antigen-Presenting Cell-Based Tumor Vaccines

Because APCs play a crucial role in the generation of T cell-mediated immune responses, numerous clinical trials with APC-based vaccines have been initiated in different types of human cancers. Encouraging results have emerged from some of these initial studies. Thus far, APC-based vaccinations usually include multiple rounds of immunization. With this approach, although we and others have detected induction of Ag-specific CTL responses in vaccinated patients after stimulation with the same APC-based immunogen, in vitro we also find that repetitive in vitro stimulation with Ag-loaded APC can, at times, lead to the emergence of noncytolytic CD4+ T cells exhibiting the characteristic phenotype of Th2 cells. These noncytolytic CD4+ T cells synthesize large quantities of type 2 cytokines such as IL-4 and IL-10 on stimulation with the autologous APC or tumor cells in an MHC class II-restricted manner. Further, these CD4+ T cells and a cell-free supernatant factor block the activation of fresh T lymphocytes. The supernatant factor also exhibits a marked inhibitory effect on the expression of the costimulatory molecules, CD80 and CD86, by APC. The inhibitory effect of the supernatant factor can be abrogated by neutralizing IL-10 in the supernatant. These observations therefore have implications in the APC-based tumor vaccine protocol design.

Dendritic cell secretion of IL-15 is induced by recombinant huCD40LT and augments the stimulation of antigen-specific cytolytic T cells

Dendritic cells (DC) are professional antigen-presenting cells which stimulate strong proliferative and cytolytic T cell responses. Stimulation of CD40 on dendritic cells by its ligands and anti-CD40 antibodies induces maturation and enhances DC stimulatory ability. In order to understand the mechanism by which ligand:CD40 interactions augment DC function, we assessed the role of T cell stimulatory cytokines IL-12 and IL-15 in the function of DC stimulated with soluble trimeric CD40L, a recombinant fusion protein incorporating three covalently linked extracellular CD40L domains (huCD40LT). Peripheral blood derived DC treated with huCD40LT and/or IFN-gamma were used to stimulate T cell responses in vitro to specific antigens. DC treated with huCD40LT or IFN-gamma/huCD40LT stimulated enhanced T cell proliferation to CASTA, a soluble protein from C. albicans, induced T cells with augmented antigen-specific lysis, and increased the yield of antigen-specific IFN-gamma-producing T cells. IL-15 production by DC was enhanced in cultures treated with huCD40LT and correlated with expansion of antigen-specific cytolytic T cells. Addition of a neutralizing anti-IL-15 monoclonal antibody inhibited the expansion of viral and tumor antigen-specific T cells stimulated by IFN-gamma and huCD40LT-treated DC. In contrast, this enhanced stimulatory ability of DC did not appear to depend on synthesis of IL-12 since huCD40LT treatment stimulated the generation of antigen-specific cytokine producing and cytolytic T cells without increased IL-12 production. Addition of anti-IL-12 monoclonal antibody did not inhibit expansion of these cells. These data suggest that production of IL-15 but not IL-12 is an important factor in the enhanced immunostimulatory ability of huCD40LT-treated DC.

Calcium responses elicited in human T cells and dendritic cells by cell-cell interaction and soluble ligands

The interactions between a human CD4+ T cell clone and monocyte-derived human dendritic cells (DC) were analyzed with an imaging system. The first question addressed was the relationship between the formation of a contact zone and the triggering of a Ca2+ response in the T cells, in the presence or absence of antigen. Interaction of T cells with DC pulsed with the antigen led to the formation of a stable contact zone, followed by the appearance in the T cells of large and sustained Ca2+ oscillations. In the absence of antigen, contact zones formed normally and, surprisingly, Ca2+ responses were also observed, characterized by rare and small transients. Antigen-independent Ca2+ responses were not MHC restricted. The possible influence of Ca2+ responses in the DC on the efficiency of antigen presentation was then Investigated. In DC, Ca2+ responses can be elicited by a variety of stimuli: cell adhesion, platelet-activating factor, UTP and chemotactic molecules (formyl-Met-Leu-Pro, RANTES, MIP-1beta and SDF-1alpha). Importantly, Ca2+ responses were also induced in approximately 30% of DC as a result of their interaction with T cells. However, the efficiency of antigen presentation (as judged by the percentage of T cells presenting a Ca2+ response) was independent of the Ca2+ level in DC. Thus, imaging the interactions between human T cells and DC led us to observe two novel phenomena: DC-induced but antigen-independent Ca2+ responses in T cells and T cell-induced Ca2+ responses in DC.

Prospects for the therapeutic use of anticancer vaccines

Although a century has passed since initial attempts were made to stimulate the immune system to destroy tumour, the immunotherapy of cancer is still in the early stages. Historically, a variety of specific and nonspecific immunostimulatory strategies have been administered with only modest clinical success. However, recent advances in tumour immunology, most notably the identification of genes encoding for cancer regression antigens, have paved the way for the development of a variety of novel and specific vaccine approaches. These include vaccines based on tumour cells, carbohydrates, peptides and heat-shock proteins, DNA-based vaccination, and the use of recombinant bacteria and viruses to deliver antigens or the DNA coding for them. While several of these approaches have yielded exciting clinical results, a number of immunological and host obstacles to the successful application of cancer vaccines remain. Further research is needed on the optimum choice of antigen, delivery vector, adjuvant and administration regimen.

Generation of large numbers of fully mature and stable dendritic cells from leukapheresis products for clinical application

Dendritic Cell (DC)-based vaccination approaches in man require a reproducible DC generation method that can be performed in conformity with GMP (Good Manufacturing Practice) guidelines and that circumvents the need for multiple blood drawings to generate DC. To this end we modified our previously described method to generate mature DC from CD14 + monocytes by a two step method (priming in GM-SF + IL-4 followed by maturation in monocyte conditioned medium) for use with leukapheresis products as a starting population. Several adaptations were necessary. We established, for example, a modified adherence step to reliably enrich CD14 + DC precursors from apheresis mononuclear cells. The addition of GM-CSF + IL-4 at the onset of culture proved disadvantageous and was, therefore, delayed for 24 h. DC development from apheresis cells occurred faster than from fresh blood or buffy coat, and was complete after 7 days. Monocyte conditioned medium when added on day 6 resulted in fully mature and stable DC (veiled, highly migratory and T cell sensitizing cells with a characteristic phenotype such as 85% CD83 + , p55/fascin + , CD115/M-CSF-R - , CD86 + ) already after 24 h. The mature DC progeny were shown to remain stable and viable if cultured for another 1-2 days in the absence of cytokines, and to be resistant to inhibitory effects of IL-10. Freezing conditions were established to generate DC from frozen aliquots of PBMC or to freeze mature DC themselves for later use. The approach yields large numbers of standardized DC (5-10 x 10(8) mature CD83 + DC/leukapheresis) that are suitable for performing sound DC-based vaccination trials that can be compared with each other.

High level of retrovirus-mediated gene transfer into dendritic cells derived from cord blood and mobilized peripheral blood CD34+ cells

Dendritic cells (DCs), the most potent antigen-presenting cells, can be generated from CD34+ hematopoietic stem cells and used for generating therapeutic immune responses. To develop immunotherapy protocols based on genetically modified DCs, we have investigated the conditions for high-level transduction of a large amount of CD34+-derived DCs. Thus, we have used an efficient and clinically applicable protocol for the retroviral transduction of cord blood (CB) or mobilized peripheral blood (MPB) CD34+ cells based on infection with gibbon ape leukemia virus (GALV)-pseudotyped retroviral vectors carrying the nls-LacZ reporter gene. Infected cells have been subsequently cultured under conditions allowing their dendritic differentiation. The results show that using a growth factor combination including granulocyte-macrophage colony-stimulating factor plus tumor necrosis factor alpha plus interleukin 4 plus stem cell factor plus Flt3 ligand, more than 70% of DCs derived from CB or MPB CD34+ cells can be transduced. Semiquantitative PCR indicates that at least two proviral copies per cell were detected. Transduced DCs retain normal immunophenotype and potent T cell stimulatory capacity. Finally, by using a semisolid methylcellulose assay for dendritic progenitors (CFU-DCs), we show that more than 90% of CFU-DCs can be transduced. Such a highly efficient retrovirus-mediated gene transfer into CD34+-derived DCs makes it possible to envision the use of this methodology in clinical trials.

Generation of Tumor Immunity by Bone Marrow-Derived Dendritic Cells Correlates with Dendritic Cell Maturation Stage

Bone marrow-derived dendritic cells (BmDC) are potent APC and can promote antitumor immunity in mice when pulsed with tumor Ag. This study aimed to define the culture conditions and maturation stages of BmDC that enable them to optimally function as APC in vivo. BmDC cultured under various conditions (granulocyte-macrophage CSF (GM-CSF) or GM-CSF plus IL-4 alone or in combination with Flt3 ligand, TNF-α, LPS, or CD40 ligand (CD40L)) were analyzed morphologically, phenotypically, and functionally and were tested for their ability to promote prophylactic and/or therapeutic antitumor immunity. Each of the culture conditions generated typical BmDC. Whereas cells cultured in GM-CSF alone were functionally immature, cells incubated with CD40L or LPS were mature BmDC, as evident by morphology, capacity to internalize Ag, migration into regional lymph nodes, IL-12 secretion, and alloantigen or peptide Ag presentation in vitro. The remaining cultures exhibited intermediate dendritic cell maturation. The in vivo Ag-presenting capacity of BmDC was compared with respect to induction of both protective tumor immunity and immunotherapy of established tumors, using the poorly immunogenic squamous cell carcinoma, KLN205. In correspondence to their maturation stage, BmDC cultured in the presence of CD40L exhibited the most potent immunostimulatory effects. In general, although not entirely, the capacity of BmDC to induce an antitumor immune response in vivo correlated to their degree of maturation. The present data support the clinical use of mature, rather than immature, tumor Ag-pulsed dendritic cells as cancer vaccines and identifies CD40L as a potent stimulus to enhance their in vivo Ag-presenting capacity.

Why are dendritic cells central to cancer immunotherapy?

Dendritic cell (DC)-based immunotherapy is rapidly emerging as a viable alternative to radiation or chemotherapy in the treatment of cancer. The resurgence of interest in cancer immunotherapy reflects the promising results that have been obtained in both animal models and early clinical trials with the DC-based approach. Here I suggest that this optimism is justified because the efficient capture and presentation of antigens by DCs is central to the induction of an immune response. I argue that the mechanism by which DCs capture antigen suggests that the immune system might actually be 'blind' to tumours, thereby challenging the theory of immune surveillance.

Generation of dendritic cells from fresh and frozen cord blood CD34+ cells

Dendritic cells (DCs) are professional antigen-presenting cells that are required for the initiation of the immune response. DCs have been shown to be generated from CD34(+) pluripotent hematopoietic progenitor cells in the bone marrow and cord blood (CB), but relatively little is known about the effect of cryopreservation on functional maturation of DCs from hematopoietic stem cells. In this work we report the generation of DCs from cryopreserved CB CD34(+) cells. CB CD34(+) cells were cryopreserved at -80 degreesC for 2 days. Cryopreserved CB CD34(+) cells as well as freshly isolated CB CD34(+) cells cultured with granulocyte-macrophage colony-stimulating factor (GM-CSF)/stem cell factor (SCF)/tumor necrosis factor-alpha (TNF-alpha) for 14 days gave rise to CD1a+/CD4(+)/CD11c+/CD14(-)/CD40(+)/CD80(+ )/CD83(+)/CD86(+)/HLA-DR+ cells with dendritic morphology. DCs derived from cryopreserved CB CD34(+) cells showed a similar endocytic capacity for fluorescein isothiocyanate-labeled dextran and lucifer yellow when compared with DCs derived from freshly isolated CB CD34(+) cells. Flow cytometric analysis revealed that two CC chemokine receptors (CCRs), CCR-1 and CCR-3, were expressed on the cell surface of DCs derived from both cryopreserved and freshly isolated CB CD34(+) cells, and these DCs exhibited similar chemotactic migratory capacities in response to regulated on activation normal T-cell expressed and secreted. DCs derived from cryopreserved as well as freshly isolated CB CD34(+) cells were more efficient than peripheral blood mononuclear cells in the primary allogeneic T-cell response. These results indicate that frozen CB CD34(+) cells cultured with GM-CSF/TNF-alpha/SCF gave rise to dendritic cells which were morphologically, phenotypically and functionally similar to DCs derived from fresh CB CD34(+) cells.

A novel dendritic cell population in human blood: one-step immunomagnetic isolation by a specific mAb (M-DC8) and in vitro priming of cytotoxic T lymphocytes

Originating from a common progenitor cell, dendritic cells (DC) appear to develop along early branched pathways into various yet ill-defined subpopulations residing at various sites throughout the body where they capture and present antigen in the most professional fashion. Here we give evidence for a unique subpopulation of human DC circulating in blood that account for 0.5-1% of blood leukocytes only, their most specific characteristic being the expression of a cell surface protein recognized by a novel monoclonal antibody (M-DC8) which enables their isolation by a one-step immunomagnetic procedure. The isolated cells (> 97% pure) present morphologically as typical dendritic cells. They express the Fc(gamma)RIII (CD16), so far not found on DC, and avidly phagocytose latex beads as well as opsonized erythrocytes. These cells not only present antigens efficiently to naive T cells but also induce purified CD8+ T cells to become alloantigen-specific cytotoxic cells. Furthermore, when loaded with a tyrosinase-derived peptide they stimulate T cells from normal donors and melanoma patients to exhibit MHC-restricted specific cytotoxicity against melanoma cells.

Lymphotactin Gene-Modified Bone Marrow Dendritic Cells Act as More Potent Adjuvants for Peptide Delivery to Induce Specific Antitumor Immunity

Dendritic cells (DC) are regarded as attractive candidates for cancer immunotherapy. Our aim is to improve the therapeutic efficacy of DC-based tumor vaccine by augmenting DC preferential chemotaxis on T cells. Mouse bone marrow-derived DC were transduced with lymphotactin (Lptn) gene by adenovirus vector. The supernatants from Lptn gene-modified DC (Lptn-DC) were capable of attracting CD4+ and CD8+ T cells in a chemotaxis assay, whereas their mock control could not. Lptn expression of Lptn-DC was further confirmed by RT-PCR. Lptn-DC were pulsed with Mut1 peptide and used for vaccination. Immunization with the low dose (1 × 104) of Mut1 peptide-pulsed DC induced weak CTL activity, whereas the same amounts of Mut1 peptide-pulsed Lptn-DC markedly induced specific CTL against 3LL tumor cells. A single immunization with 1 × 104 Mut1 peptide-pulsed Lptn-DC could render mice resistant to a 5 × 105 3LL tumor cell challenge completely, but their counterpart could not. The protective immunity induced by Mut1 peptide-pulsed Lptn-DC depends on both CD4+ T cells and CD8+ T cells rather than NK cells in the induction phase and depends on CD8+ T cells rather than CD4+ T cells and NK cells in the effector phase. Moreover, the involvement of CD28/CTLA4 costimulation pathway and IFN-γ are also necessary. When 3LL tumor-bearing mice were treated with 1 × 104 Mut1 peptide-pulsed Lptn-DC, their pulmonary metastases were significantly reduced, whereas the same low dose of Mut1 peptide-pulsed DC had no obvious therapeutic effects. Our data suggest that Lptn-DC are more potent adjuvants for peptide delivery to induce protective and therapeutic antitumor immunity.

Dendritic Cell Immunization Breaks Cytotoxic T Lymphocyte Tolerance in Hepatitis B Virus Transgenic Mice

Hepatitis B virus (HBV) transgenic mice that are immunologically tolerant to HBV-encoded Ags represent a model of chronic HBV infection suitable for the development of therapeutic immunization strategies before testing in humans. Five lineages of HBV transgenic mice were immunized with plasmid DNA that encodes hepatitis B surface Ag (HBsAg) or with cytokine-activated bone marrow-derived dendritic cells (DCs) in an attempt to break tolerance to HBsAg at the B and T cell levels. DNA immunization stimulated an Ab response but not a cytotoxic T lymphocyte response to HBsAg in two of the five transgenic lineages studied. In contrast, infusion of activated transgenic or nontransgenic DCs stimulated a splenic CTL response in all three transgenic lineages immunized in this manner at precursor frequencies comparable to those in nontransgenic mice, indicating that DC function is normal, and HBsAg-specific CTLs are present but functionally silent in these transgenic animals. Importantly, none of the animals developed hepatitis or displayed suppressed viral gene expression or replication following either DNA immunization or DC administration even in the presence of anti-hepatitis B surface (HBs) Abs and HBs-specific CTLs. These results indicate that Ag presentation by cytokine-activated DCs can break tolerance and trigger an anti-viral CTL response in HBV transgenic mice, and they suggest that this strategy is more efficient than DNA immunization in this setting. Nonetheless, more efficient immunization strategies are needed to stimulate an immune response of sufficient quality and magnitude to achieve an immunotherapeutic antiviral effect.

Whole virus influenza vaccine activates dendritic cells (DC) and stimulates cytokine production by peripheral blood mononuclear cells (PBMC) while subunit vaccines support T cell proliferation

Three types of trivalent influenza vaccines were analysed for their in vitro stimulatory properties on immune cells from young healthy volunteers. A whole inactivated virus (WV) vaccine, a conventional subunit (c-SU) preparation and a new virosomal subunit (v-SU) vaccine were used. Blood-derived DC up-regulated MHC class II, CD54, CD80 and CD86 after exposure to WV vaccine, indicating their functional maturation, but were only moderately affected by subunit (SU) vaccines. In addition, IL-12 and tumour necrosis factor-alpha (TNF-alpha) secretion by DC were markedly enhanced by WV, but not by SU vaccines. The production of IL-2 and interferon-gamma (IFN-gamma) by PBMC was also strongly stimulated by WV, but much less by SU vaccines, among which the v-SU vaccine was a better stimulator of IL-2 secretion. In contrast to WV vaccine both SU vaccines were powerful stimulators of PBMC proliferation. Our results suggest that the presence of influenza core components leads to the activation of DC and triggers the production of cytokines by PBMC. SU vaccines are in contrast excellent stimulators of T cell growth. A combination of WV and SU vaccines in immunization regimes might allow optimal T cell priming as well as the efficient generation and maintenance of memory cells.

Fully mobilizing host defense: building better vaccines

Developments in methods for identifying antigens from infectious agents and cancers has provided exciting new opportunities in prevention and treatment through vaccination. In many of these situations, however, traditional immunization techniques do not stimulate protective immunity because they fail to fully mobilize the appropriate immune responses. This limitation, together with new insights into the underlying mechanism of immune responses, has spurred development of several new approaches for vaccine delivery. We discuss some of the current efforts being developed to provide effective vaccine delivery systems.

Dendritic cells induce autoimmune diabetes and maintain disease via de novo formation of local lymphoid tissue

Activation of autoreactive T cells can lead to autoimmune diseases such as insulin-dependent diabetes mellitus (IDDM). The initiation and maintenance of IDDM by dendritic cells (DC), the most potent professional antigen-presenting cells, were investigated in transgenic mice expressing the lymphocytic choriomeningitis virus glycoprotein (LCMV-GP) under the control of the rat insulin promoter (RIP-GP mice). We show that after adoptive transfer of DC constitutively expressing the immunodominant cytotoxic T lymphocyte (CTL) epitope of the LCMV-GP, RIP-GP mice developed autoimmune diabetes. Kinetic and functional studies of DC-activated CTL revealed that development of IDDM was dependent on dose and timing of antigenic stimulation. Strikingly, repeated CTL activation by DC led to severe destructive mononuclear infiltration of the pancreatic islets but also to de novo formation of islet-associated organized lymphoid structures in the pancreatic parenchyma. In addition, repetitive DC immunization induced IDDM with lymphoid neogenesis also in perforin-deficient RIP-GP mice, illustrating that CD8(+) T cell-dependent inflammatory mechanisms independent of perforin could induce IDDM. Thus, DC presenting self-antigens not only are potent inducers of autoreactive T cells, but also help to maintain a peripheral immune response locally; therefore, the induction of autoimmunity against previously ignored autoantigens represents a potential hazard, particularly in DC-based antitumor therapies.

Antigen-dependent and -independent Ca2+ responses triggered in T cells by dendritic cells compared with B cells

Dendritic cells (DCs) are much more potent antigen (Ag)-presenting cells than resting B cells for the activation of naive T cells. The mechanisms underlying this difference have been analyzed under conditions where ex vivo DCs or B cells presented known numbers of specific Ag-major histocompatibility complex (MHC) complexes to naive CD4(+) T cells from T cell antigen receptor (TCR) transgenic mice. Several hundred Ag-MHC complexes presented by B cells were necessary to elicit the formation of a few T-B conjugates with small contact zones, and the resulting individual T cell Ca2+ responses were all-or-none. In contrast, Ag-specific T cell Ca2+ responses can be triggered by DCs bearing an average of 30 Ag-MHC complexes per cell. Formation of T-DC conjugates is Ag-independent, but in the presence of the Ag, the surface of the contact zone increases and so does the amplitude of the T cell Ca2+ responses. These results suggest that Ag is better recognized by T cells on DCs essentially because T-DC adhesion precedes Ag recognition, whereas T-B adhesion requires Ag recognition. Surprisingly, we also recorded small Ca2+ responses in T cells interacting with unpulsed DCs. Using DCs purified from MHC class II knockout mice, we provide evidence that this signal is mostly due to MHC-TCR interactions. Such an Ag-independent, MHC-triggered calcium response could be a survival signal that DCs but not B cells are able to deliver to naive T cells.

Generation of stable monocyte-derived dendritic cells in the presence of high concentrations of homologous or autologous serum: influence of extra-cellular pH

Recent studies have highlighted the high degree of differentiation of monocytes. Indeed, dendritic cells (DC) can be generated from monocytes, in the presence of appropriate cytokines. However, human serum is usually avoid in such cultures. Here, we report that human serum does not inhibit generation of mature DC from blood monocytes, but rather that extra-cellular pH may play an important role in the regulation of monocyte differentiation. Indeed, monocytes cultured at pH 7.4 in the presence of high concentrations of human serum developed efficiently into mature DC, as opposed with monocytes cultured at pH 7. These pH 7.4 cultured DC presented features characteristic of mature DC, at the phenotypical, functional and morphological levels. In addition, these DC were stable, with respect to their sustained expression of CD83 and CD86, upon withdrawal of cytokines. Finally, when autologous plasma was used instead of homologous serum, differentiation of monocytes into mature DC was efficient, as well. Thus, altogether, our data show the importance of extra-cellular pH on differentiation of monocyte-derived DC in the presence of human serum, which should be maintained at plasma levels.

Induction of antigen presentation by macrophages after phagocytosis of tumour apoptotic cells

Due to their resistance to classical chemotherapies, most human colorectal cancers have a high incidence and a poor prognosis. Immunotherapy using interleukin 2 (IL2) has provided disappointing results in the treatment of these cancers. Recently, however, we have demonstrated that a treatment combining a cell-differentiating agent, sodium butyrate (NaBut) with IL2 resulted in a remission of established peritoneal colorectal carcinomatosis in rats. Separately, neither NaBut nor IL2 treatment cured these tumour-bearing rats. NaBut is known to induce cell differentiation and subsequent apoptosis in epithelial cells, while IL2 stimulates the immune cells capable of participating in tumour rejection. We postulated that the significant therapeutic effect of NaBut/IL2 treatment could be attributed to a NaBut-induced increase in the immunogenicity of the cancer cells. We report here that NaBut induced an apoptotic process in rat colon tumour cells in vivo and in vitro. We observed, in an efficient cure, colocalization of apoptotic bodies and monocytes/macrophages at the periphery of the tumour. We propose that these apoptotic bodies are phagocytosed in vivo by the macrophages. We also showed in vitro that a subpopulation of macrophages involved in the phagocytic clearance of apoptotic cells expresses cell surface molecules associated with antigen presentation and stimulates the proliferation of naive splenocytes. Our data suggest that therapies that recruit massive induction of the apoptotic process in tumour cells could favour tumour antigen presentation via their specific phagocytosis by antigen-presenting cells (APCs). We propose that the development of specific therapies that stimulate both tumour cell apoptosis and the immune system could offer new opportunities in anti-cancer treatments of poorly immunogenic cancer cells.