Abstract P3-05-01: Immune and transcriptional signatures of dendritic dell (DC) vaccination combined with chemotherapy in locally advanced, triple-negative breast cancer (TNBC) patients

BACKGROUND: Women with TNBC who do not achieve a pathologic complete response (pCR) with preoperative (preop) chemotherapy have a high risk of recurrence and death from BC. Immunotherapy is an attractive strategy as human BCs can be immunogenic, and enhancing the immune effector function may augment the cytotoxic effects of standard therapies.

CLINICAL TRIAL: Following IRB-approved informed consent, 10 pts with locally advanced TNBC received preop dose-dense doxorubicin/cyclophosphamide (AC) followed by paclitaxel and carboplatin (TCb) chemotherapy, combined with antigen-loaded (TNBC antigens: Cyclin B1, WT1, and control viral antigens: CEF) autologous monocyte-derived DC vaccinations administered intratumorally and subcutaneously. DCs were generated with GM-CSF and type I interferon, loaded with antigen in the form of long peptides and activated with innate ligands (LPS and Clo75) and CD40 ligand. Vaccines were given at 4 time points prior to definitive surgery, and 3 times post-surgery, pre- and post-radiation therapy (RT). Safety was the primary study endpoint, and pCR rate in breast and axilla was a secondary endpoint. Correlative studies included assessment of immune response via ELISpot and transcriptional profiling of blood samples collected over time.

RESULTS: All pts received the 4 vaccines during preop chemotherapy, and 7/10 received all 7 vaccines. At the time of definitive surgery, 4 pts achieved a pCR, 3 pts had macroscopic residual disease in the breast and axillary lymph nodes, and 3 pts had residual cancer burden scores of 1. As of June 1, 2017, all pts have been in follow-up for at least 1 year s/p completion of all vaccines, and 7/10 patients have no evidence of disease.

To assess immune signatures with IFN-γ-ELISpot, PBMCs from baseline (BL) and several time points during vaccine treatment were cultured with control peptides or with peptide libraries covering vaccine antigens. Using a linear mixed model to account for repeated and missing observations we found statistically significant (α = 0.05) increases in Cyclin B1, WT1, and CEF ELISpots in at least 1 time point post-DC vaccination and in follow-up. Compared to BL, Cyclin B1 and WT1 increased at 3 day pre-RT in 8/10 and 7/10 pts, respectively. To assess transcriptional signatures, a linear mixed model was utilized to determine statistically significant differences in fold-change over time compared to the BL and healthy controls. Modular analysis of differentially expressed transcripts at BL revealed downregulation of transcripts related to the monocyte lineage in 7/10 pts. Longitudinal analysis revealed profound transcriptional changes during AC with downregulation of lymphocyte modules and upregulation of innate and inflammation modules. While the latter ones have normalized during TCb and follow-up, T cell module remained substantially downregulated throughout treatment and follow-up.

CONCLUSIONS: Combination of preop chemotherapy and intratumoral and subcutaneous autologous DC vaccination is safe in locally advanced TNBC pts and is linked with profound changes in immune transcription signatures and with expansion of antigen-specific immune responses that can be detected in IFN-γ ELISpot.

Citation Format: Palucka AK, Roberts LK, Zurawski SM, Tarnowski J, Turner J, Wang X, Blankenship D, Smith JL, Levin MK, Finholt JP, Burkeholder SB, Timis R, Muniz LS, Dao T, Grant M, Banchereau J, Zurawski G, Pascual V, O'Shaughnessy JA. Immune and transcriptional signatures of dendritic dell (DC) vaccination combined with chemotherapy in locally advanced, triple-negative breast cancer (TNBC) patients [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-05-01.

Dendritic cells and immunity against cancer

T cells can reject established tumours when adoptively transferred into patients, thereby demonstrating the power of the immune system for cancer therapy. However, it has proven difficult to maintain adoptively transferred T cells in the long term. Vaccines have the potential to induce tumour-specific effector and memory T cells. However, clinical efficacy of current vaccines is limited, possibly because tumours skew the immune system by means of myeloid-derived suppressor cells, inflammatory type 2 T cells and regulatory T cells (Tregs), all of which prevent the generation of effector cells. To improve the clinical efficacy of cancer vaccines in patients with metastatic disease, we need to design novel and improved strategies that can boost adaptive immunity to cancer, help overcome Tregs and allow the breakdown of the immunosuppressive tumour microenvironment. This can be achieved by exploiting the fast increasing knowledge about the dendritic cell (DC) system, including the existence of distinct DC subsets that respond differentially to distinct activation signals, (functional plasticity), both contributing to the generation of unique adaptive immune responses. We foresee that these novel cancer vaccines will be used as monotherapy in patients with resected disease and in combination with drugs targeting regulatory/suppressor pathways in patients with metastatic disease.

Assessing oncologic benefit in clinical trials of immunotherapy agents

BACKGROUND

USA Food and Drug Administration approval for cancer therapy requires demonstration of patient benefit as a marker of clinical efficacy. Prolonged survival is the gold standard for demonstration of efficacy, but other end points such as antitumor response, progression-free survival, quality of life, or surrogate end points may be used.

DESIGN

This study was developed based on discussion during a roundtable meeting of experts in the field of immunotherapy.

RESULTS

In most clinical trials involving cytotoxic agents, response end points use RECIST based on the premise that 'effective' therapy causes tumor destruction, target lesion shrinkage, and prevention of new lesions. However, RECIST may not be appropriate in trials of immunotherapy. Like other targeted agents, immunotherapies may mediate cytostatic rather than direct cytotoxic effects, and these may be difficult to quantify with RECIST. Furthermore, significant time may elapse before clinical effects are quantifiable because of complex response pathways. Effective immunotherapy may even mediate transient lesion growth secondary to immune cell infiltration.

CONCLUSIONS

RECIST may not be an optimal indicator of clinical benefit in immunotherapy trials. This article discusses alternative clinical trial designs and end points that may be more relevant for immunotherapy trials and may offer more effective prediction of survival in pivotal phase III studies.

Comprehensive analysis of melanoma antigen specific T cell repertoire: EPIMAX (EPItope MAXimum)

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Background: We have demonstrated in phase I clinical trial treating 20 patients with metastatic melanoma that dendritic cells (DCs) loaded with killed allogeneic tumor cells can elicit immune and clinical responses. Loading DC vaccines with killed allogeneic tumor cells allows: i) presentation of antigens via both MHC class I and class II, ii) strong help, iii) applicability to any cancer, and iv) loading tumor antigen independent of HLA haplotype of the patient. However, this renders the immunomonitoring step complex as the antigens and their restriction elements are unknown. To address this issue, we developed EPIMAX. Methods: EPIMAX measures simultaneously cell proliferation and secretion of multiple cytokines that distinguish Type 1, Type 2 cytokines and IL-10 secretion using Luminex. Briefly, 5x105 CFSE-labeled PBMCs are plated with peptide pools of overlapping peptide libraries from appropriate antigens. After 48hrs, supernatants are transferred for cytokine determination. After an additional 6 days of culture, cell proliferation is analyzed by flow cytometry after staining for surface markers CD4 and CD8. Results: We demonstrated that EPIMAX permits us to assess: i) Specificity and breadth of induced immune responses, ii) Type of induced immunity (Type I, Type II, IL-10), and iii) Function of specific T cells as measured by cytokine secretion and proliferation. To date 8 patients with stage IV melanoma were analyzed at baseline and after vaccination with DCs loaded with killed allogeneic melanoma cells. We assessed epitopes derived from MART-1, NY-ESO1, TRP-1 and gp100. Analysis of CD8+T cells: We have identified 15 melanoma antigen CD8+T cell epitopes in 8 patients. These include: three Tc0 epitopes (IL2), and twelve Tc1 epitopes triggering IP-10 secretion. Analysis of CD4+T cells: We have identified 15 melanoma antigen CD4+T cell epitopes in 5 patients. These include: nine Th0 epitopes (IL2), four Th1 epitopes (IFNγ) and two Th2 epitopes (IL13). Finally, we analyzed secretion of IL-10 and found thus far IL-10 secreting CD4+T cells in seven patients. Further studies demonstrated that these T cells have regulatory function. Conclusions: EPIMAX permits comprehensive assessment of melanoma antigen specific T cell repertoire.

No significant financial relationships to disclose.

Long-term survival in patients with metastatic melanoma vaccinated with melanoma-antigen loaded dendritic cells

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Background: Previous clinical trials have demonstrated safety and tolerability of cancer antigen-loaded dendritic cells (DCs) in the treatment of metastatic melanoma. Further, DCs administered to patients with metastatic melanoma are immunogenic and induce durable clinical responses even in patients who failed previous cytotoxic therapy. This report is an analysis of long term clinical outcomes of DC vaccinated patients from our institution. Methods: Between March 1999 and February 2005 seventy patients with metastatic melanoma were treated with DC vaccines in four sequential phase I-IIa clinical trials. Most patients had M1b or M1c metastatic disease. DCs were generated either from CD34+ hematopoietic progenitors or from monocytes. Forty nine HLA-A*0201+ patients received vaccines pulsed with melanoma antigen derived peptides (MART-1, MAGE-3, TYR and gp100). Twenty one patients received DCs loaded with killed allogeneic melanoma cells. KLH was used as helper antigen and, in HLA-A*0201+ patients, Flu-Matrix peptide was used as control antigen. Patients received up to eight DC vaccinations over a maximum of 7 months. Results: DC vaccinations were safe and tolerable. Fifteen out of 70 (21%) patients are alive as of November 2006. The median survival in this group of surviving patients is 46 months (range 22–92 months). Three patients had no evidence of disease upon completion of DC vaccinations by clinical and positron emission tomography scanning. Four patients had experienced objective clinical responses by RECIST criteria (2 CRs and 2 PRs) based on clinical examination and computerized tomography or magnetic resonance imaging. These included two patients that had failed previous cytotoxic and cytokine therapy. Eight patients are alive with disease. Five of 15 long term survivors had no additional therapy other than DC vaccinations including a patient with CR of liver lesions who remains free of disease 80 months post DC vaccination. Conclusions: DC vaccines bring clinical benefit and elicit durable responses in a fraction of patients with metastatic melanoma. These vaccines may provide a survival advantage. Future studies are underway to improve DC vaccine efficacy for treatment of metastatic melanoma.

No significant financial relationships to disclose.

Vaccination of stage IV melanoma patients with dendritic cells generated ex vivo with type I interferon and loaded with heat-treated killed allogeneic melanoma cells—Preliminary report from the phase II clinical trial

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Background: We have previously demonstrated in phase I clinical trial treating 20 patients with metastatic melanoma that dendritic cells (DCs) loaded with killed allogeneic tumor cells can elicit immune and clinical responses. In that study DCs were generated from monocytes with GM-CSF and IL-4 and activated with a combination of TNF and soluble CD40 ligand. Two patients who had failed previous therapy including DTIC, achieved durable objective clinical responses, one CR and one PR lasting ≥ 20 months. We describe here the development of a high-throughput method for generating DC vaccines with improved immunogenicity and preliminary data from their evaluation in a Phase II trial in metastatic melanoma. Methods: We have initiated a phase II clinical trial (IRB #005–065; BB-IND #12339) enrolling patients with stage IV melanoma who failed first line therapy with DTIC and/or temozolomide with or without IL-2. Patients will receive seven injections of an autologous DC vaccine generated from monocytes by culturing with GM-CSF and Type I interferon and loaded with heat-treated and killed allogeneic Colo829 melanoma cells. Vaccine is generated in a closed system and stored frozen. Patients are vaccinated over 18 weeks. The trial is based on an initial toxicity evaluation in the first 10 patients on top of a 2-stage response rule - 1/19 to continue and 5/30 to accept. The trial is expected to accrue a total of 32 subjects. The primary end-points of this trial are the rate of objective clinical response and the safety/feasibility of the vaccination preparation. Results: To date seven patients were enrolled and begun vaccinations. Vaccine has been successfully generated for all enrolled patients. Thus far, a total of 20 vaccinations have been administered. Vaccinations were safe and tolerable.

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Durable clinical responses in patients with metastatic melanoma vaccinated with dendritic cells loaded with killed allogeneic melanoma cells

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Background: We demonstrated that DCs loaded with killed allogeneic tumors can cross-prime tumor-specific naïve CD8+T cells in vitro. Clinically this approach would overcome HLA restriction inherent to peptide vaccines and allow diversification of immune responses including priming of many clones of CD8+ and CD4+ T cells. Methods: Twenty (20) patients with metastatic melanoma were vaccinated with autologous monocyte-derived DCs loaded with killed allogeneic Colo829 melanoma cell line. A total of 8 vaccines were administered at monthly intervals. DCs were generated from monocytes by culturing with GM-CSF and IL-4 and activated by additional culture with TNFα and CD40 ligand. KLH was used as a control antigen. The first patient was accrued December, 2002 and the last November, 2003. Results: DC vaccinations induced durable objective clinical responses in two patients who had progressive metastatic disease after previous cytotoxic chemotherapy. One patient experienced a CR and one patient a PR both remissions have lasted ≥ 20 months. Fourteen patients were alive at 12 months and 9 patients are alive at the end of 2005. The estimated median overall survival is 22 months with a range of 2–31 months. DC vaccination led to elicitation of CD8+T cell immunity specific to MART-1 tissue differentiation antigen, suggesting that cross-priming/presentation of melanoma antigens by the DC vaccines had occurred in vivo. Vaccinations were safe and tolerable. There were no significant adverse events. Conclusions: The present results justify the design of larger follow-up studies to assess the immunological and clinical response to DC vaccines in patients with metastatic melanoma and other malignant diseases.

No significant financial relationships to disclose.

Induction of dendritic cell differentiation by IFN-alpha in systemic lupus erythematosus

Dendritic cells (DCs) are important in regulating both immunity and tolerance. Hence, we hypothesized that systemic lupus erythematosus (SLE), an autoimmune disease characterized by autoreactive B and T cells, may be caused by alterations in the functions of DCs. Consistent with this, monocytes from SLE patients' blood were found to function as antigen-presenting cells, in vitro. Furthermore, serum from SLE patients induced normal monocytes to differentiate into DCs. These DCs could capture antigens from dying cells and present them to CD4-positive T cells. The capacity of SLE patients' serum to induce DC differentiation correlated with disease activity and depended on the actions of interferon-alpha (IFN-alpha). Thus, unabated induction of DCs by IFN-alpha may drive the autoimmune response in SLE.

Lipopolysaccharides from distinct pathogens induce different classes of immune responses in vivo

The adaptive immune system has evolved distinct responses against different pathogens, but the mechanism(s) by which a particular response is initiated is poorly understood. In this study, we investigated the type of Ag-specific CD4(+) Th and CD8(+) T cell responses elicited in vivo, in response to soluble OVA, coinjected with LPS from two different pathogens. We used Escherichia coli LPS, which signals through Toll-like receptor 4 (TLR4) and LPS from the oral pathogen Porphyromonas gingivalis, which does not appear to require TLR4 for signaling. Coinjections of E. coli LPS + OVA or P. gingivalis LPS + OVA induced similar clonal expansions of OVA-specific CD4(+) and CD8(+) T cells, but strikingly different cytokine profiles. E. coli LPS induced a Th1-like response with abundant IFN-gamma, but little or no IL-4, IL-13, and IL-5. In contrast, P. gingivalis LPS induced Th and T cell responses characterized by significant levels of IL-13, IL-5, and IL-10, but lower levels of IFN-gamma. Consistent with these results, E. coli LPS induced IL-12(p70) in the CD8alpha(+) dendritic cell (DC) subset, while P. gingivalis LPS did not. Both LPS, however, activated the two DC subsets to up-regulate costimulatory molecules and produce IL-6 and TNF-alpha. Interestingly, these LPS appeared to have differences in their ability to signal through TLR4; proliferation of splenocytes and cytokine secretion by splenocytes or DCs from TLR4-deficient C3H/HeJ mice were greatly impaired in response to E. coli LPS, but not P. gingivalis LPS. Therefore, LPS from different bacteria activate DC subsets to produce different cytokines, and induce distinct types of adaptive immunity in vivo.

Interleukin 15 skews monocyte differentiation into dendritic cells with features of Langerhans cells

Langerhans cells (LCs) represent a subset of immature dendritic cells (DCs) specifically localized in the epidermis and other mucosal epithelia. As surrounding keratinocytes can produce interleukin (IL)-15, a cytokine that utilizes IL-2Rgamma chain, we analyzed whether IL-15 could skew monocyte differentiation into LCs. Monocytes cultured for 6 d with granulocyte/macrophage colony-stimulating factor (GM-CSF) and IL-15 differentiate into CD1a(+)HLA-DR(+)CD14(-)DCs (IL15-DCs). Agents such as lipopolysaccharide (LPS), tumor necrosis factor (TNF)alpha, and CD40L induce maturation of IL15-DCs to CD83(+), DC-LAMP(+) cells. IL15-DCs are potent antigen-presenting cells able to induce the primary (mixed lymphocyte reaction [MLR]) and secondary (recall responses to flu-matrix peptide) immune responses. As opposed to cultures made with GM-CSF/IL-4 (IL4-DCs), a proportion of IL15-DCs expresses LC markers: E-Cadherin, Langerin, and CC chemokine receptor (CCR)6. Accordingly, IL15-DCs, but not IL4-DCs, migrate in response to macrophage inflammatory protein (MIP)-3alpha/CCL20. However, IL15-DCs cannot be qualified as "genuine" Langerhans cells because, despite the presence of the 43-kD Langerin, they do not express bona fide Birbeck granules. Thus, our results demonstrate a novel pathway in monocyte differentiation into dendritic cells.

Immune and clinical responses in patients with metastatic melanoma to CD34(+) progenitor-derived dendritic cell vaccine

Immunization to multiple defined tumor antigens for specific immune therapy of human cancer has thus far proven difficult. Eighteen HLA A*0201(+) patients with metastatic melanoma received injections s.c. of CD34(+)progenitor-derived autologous dendritic cells (DCs), which included Langerhans cells. DCs were pulsed with peptides derived from four melanoma antigens [(MelAgs) MelanA/MART-1, tyrosinase, MAGE-3, and gp100], as well as influenza matrix peptide (Flu-MP) and keyhole limpet hemocyanin (KLH) as control antigens. Overall immunological effects were assessed by comparing response profiles using marginal likelihood scores. DC injections were well tolerated except for progressive vitiligo in two patients. DCs induced an immune response to control antigens (KLH, Flu-MP) in 16 of 18 patients. An enhanced immune response to one or more MelAgs was seen in these same 16 patients, including 10 patients who responded to >2 MelAgs. The two patients failing to respond to both control and tumor antigens experienced rapid tumor progression. Of 17 patients with evaluable disease, 6 of 7 patients with immunity to two or less MelAgs had progressive disease 10 weeks after study entry, in contrast to tumor progression in only 1 of 10 patients with immunity to >2 MelAgs. Regression of >1 tumor metastases were observed in seven of these patients. The overall immunity to MelAgs after DC vaccination is associated with clinical outcome (P = 0.015).

Increased frequency of pre-germinal center B cells and plasma cell precursors in the blood of children with systemic lupus erythematosus

We have analyzed the blood B cell subpopulations of children with systemic lupus erythematosus (SLE) and healthy controls. We found that the normal recirculating mature B cell pool is composed of four subsets: conventional naive and memory B cells, a novel B cell subset with pregerminal center phenotype (IgD(+)CD38(+)centerin(+)), and a plasma cell precursor subset (CD20(-)CD19(+/low)CD27(+/++) CD38(++)). In SLE patients, naive and memory B cells (CD20(+)CD38(-)) are approximately 90% reduced, whereas oligoclonal plasma cell precursors are 3-fold expanded, independently of disease activity and modality of therapy. Pregerminal center cells in SLE are decreased to a lesser extent than conventional B cells, and therefore represent the predominant blood B cell subset in a number of patients. Thus, SLE is associated with major blood B cell subset alterations.

Sensing pathogens and tuning immune responses

The immune system is capable of making qualitatively distinct responses against different microbial infections, and recent advances are starting to reveal how it manages this complex task. An integral component of the immune system is a network of cells known as dendritic cells (DCs), which sense different microbial stimuli and convey this information to lymphocytes. A better understanding of DC biology has allowed a model to be constructed in which the type of immune response to an infection is viewed as a function of several determinants, including the subpopulation of DCs, the nature of the microbe, microbe recognition receptors, and the cytokine microenvironment.

Dendritic cells: On the move from bench to bedside

As dendritic cells increasingly become the adjuvant of choice in new approaches to cancer immunotherapy, a degree of protocol standardization is required to aid future large-scale clinical trials.

Modulating the immune response with dendritic cells and their growth factors

Different subsets of dendritic cells (DCs) appear to play a role in determining the specific cytokines secreted by T helper (Th) cells. A model is proposed that links together factors such as the pathogen, microenvironment, DCs and T cells in a mechanism that results in a flexible determination of T-cell polarization.

IL-6 switches the differentiation of monocytes from dendritic cells to macrophages

Monocytes can give rise to either antigen presenting dendritic cells (DCs) or scavenging macrophages. This differentiation is initiated when monocytes cross the endothelium. But the regulation of DC and macrophage differentiation in tissues remains elusive. When stimulated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4), monocytes yield DCs. However, we show here that the addition of fibroblasts switches differentiation to macrophages. On contact with monocytes, fibroblasts release IL-6, which up-regulates the expression of functional M-CSF receptors on monocytes. This allows the monocytes to consume their autocrine M-CSF. Thus, the interplay between IL-6 and M-CSF switches monocyte differentiation to macrophages rather than DCs, and IL-6 is an essential factor in the molecular control of antigen presenting cell development.

Identification of centerin: a novel human germinal center B cell-restricted serpin

For naive B cells to mature in response to antigen triggering and become either plasma cells or memory B cells, a complex array of events takes place within germinal centers (GC) of secondary lymphoid organs. With the long-term objective of defining and characterizing molecules that control the generation of GC, we have subtracted RNA messages derived from highly purified B cells at the follicular mantle stage of differentiation from GC B cells. Using this approach, we have identified a novel molecule, centerin, belonging to the family of serine-protease inhibitors or serpins. Transcription of centerin is highly restricted to GC B cells and their malignant counterparts, Burkitt's lymphoma lines. The putative centerin protein shares the highest sequence identity with thyroxine-binding globulin and possesses arginine/serine at its P1/P1' active site, suggesting that it interacts with a trypsin-like protease(s). In addition, several other sequence features of centerin also indicate that it serves as a bonafide protease inhibitor. Finally, we demonstrate differentially up-regulated transcription of this novel gene by resting, naive B cells stimulated in vitro via CD40 signaling, while Staphylococcus aureus Cowan strain-mediated B cell activation fails to generate this reponse. Because CD40 signaling is required for naive B cells to enter the GC reaction and for GC B cells to survive, it is likely that centerin plays a role in the development and/or sustaining of GC.

Dendritic cells capture killed tumor cells and present their antigens to elicit tumor-specific immune responses

Due to their capacity to induce primary immune responses, dendritic cells (DC) are attractive vectors for immunotherapy of cancer. Yet the targeting of tumor Ags to DC remains a challenge. Here we show that immature human monocyte-derived DC capture various killed tumor cells, including Jurkat T cell lymphoma, malignant melanoma, and prostate carcinoma. DC loaded with killed tumor cells induce MHC class I- and class II-restricted proliferation of autologous CD8+ and CD4+ T cells, demonstrating cross-presentation of tumor cell-derived Ags. Furthermore, tumor-loaded DC elicit expansion of CTL with cytotoxic activity against the tumor cells used for immunization. CTL elicited by DC loaded with the PC3 prostate carcinoma cell bodies kill another prostate carcinoma cell line, DU145, suggesting recognition of shared Ags. Finally, CTL elicited by DC loaded with killed LNCap prostate carcinoma cells, which express prostate specific Ag (PSA), are able to kill PSA peptide-pulsed T2 cells. This demonstrates that induced CTL activity is not only due to alloantigens, and that alloantigens do not prevent the activation of T cells specific for tumor-associated Ags. This approach opens the possibility of using allogeneic tumor cells as a source of tumor Ag for antitumor therapies.

Dendritic cell based tumor vaccines

Dendritic cells (DC) constitute a unique system of cells that induce, sustain and regulate immune responses. Distributed as sentinels throughout the body, DC are poised to capture antigen (Ag), migrate to draining lymphoid organs, and, after a process of maturation, select Ag-specific lymphocytes to which they present the processed Ag, thereby inducing immune responses. DC present Ag to CD4(+) T cells which in turn regulate multiple effectors, including CD8(+) cytotoxic T cells, B cells, NK cells, macrophages and eosinophils, all of which contribute to the protective immune responses. Several key features of the DC system may be highlighted: (1) the existence of different DC subsets that share biological functions, yet display unique ones such as polarization of T cell responses towards Type 1 or Type 2 or regulation of B cell responses; (2) the functional specialization of DC according to their differentiation/maturation stages; and (3) the plasticity of DC which is determined by the microenvironment (e.g. cytokines) and may manifest as (i) the final differentiation into either DC (enhanced antigen presentation) or macrophage (enhanced antigen degradation); (ii) the induction of immunity or tolerance; and (iii) the polarization of T cell responses. Because of these unique properties, DC represent both vectors and targets for immunological intervention in numerous diseases and are optimal candidates for vaccination protocols both in cancer and infectious diseases.

Immunobiology of dendritic cells

Dendritic cells (DCs) are antigen-presenting cells with a unique ability to induce primary immune responses. DCs capture and transfer information from the outside world to the cells of the adaptive immune system. DCs are not only critical for the induction of primary immune responses, but may also be important for the induction of immunological tolerance, as well as for the regulation of the type of T cell-mediated immune response. Although our understanding of DC biology is still in its infancy, we are now beginning to use DC-based immunotherapy protocols to elicit immunity against cancer and infectious diseases.

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.

Naked antigen-presenting molecules on dendritic cells

Antigen-presenting cells work to present peptides derived from exogenous and endogenous antigens to circulating T cells, sparking off an immune response. Dendritic cells are unique amongst antigen-presenting cells, not least for their newly described ability to circumvent the need to internalize exogenous antigens before presenting them.