‘Survival gene’ Bcl-xl potentiates DNA-raised antitumor immunity

Genetic vaccines to potentiate the effective CD103+ dendritic cell-mediated cross-priming of antitumor immunity

The development of effective cancer vaccines remains an urgent, but as yet unmet, clinical need. This deficiency is in part due to an incomplete understanding of how to best invoke dendritic cells (DC) that are crucial for the induction of tumor-specific CD8(+) T cells capable of mediating durable protective immunity. In this regard, elevated expression of the transcription factor X box-binding protein 1 (XBP1) in DC appears to play a decisive role in promoting the ability of DC to cross-present Ags to CD8(+) T cells in the therapeutic setting. Delivery of DNA vaccines encoding XBP1 and tumor Ag to skin DC resulted in increased IFN-α production by plasmacytoid DC (pDC) from skin/tumor draining lymph nodes and the cross-priming of Ag-specific CD8(+) T cell responses associated with therapeutic benefit. Antitumor protection was dependent on cross-presenting Batf3(+) DC, pDC, and CD8(+) T cells. CD103(+) DC from the skin/tumor draining lymph nodes of the immunized mice appeared responsible for activation of Ag-specific naive CD8(+) T cells, but were dependent on pDC for optimal effectiveness. Similarly, human XBP1 improved the capacity of human blood- and skin-derived DC to activate human T cells. These data support an important intrinsic role for XBP1 in DC for effective cross-priming and orchestration of Batf3(+) DC-pDC interactions, thereby enabling effective vaccine induction of protective antitumor immunity.

Genome-wide analysis of alternative splicing during dendritic cell response to a bacterial challenge

The immune system relies on the plasticity of its components to produce appropriate responses to frequent environmental challenges. Dendritic cells (DCs) are critical initiators of innate immunity and orchestrate the later and more specific adaptive immunity. The generation of diversity in transcriptional programs is central for effective immune responses. Alternative splicing is widely considered a key generator of transcriptional and proteomic complexity, but its role has been rarely addressed systematically in immune cells. Here we used splicing-sensitive arrays to assess genome-wide gene- and exon-level expression profiles in human DCs in response to a bacterial challenge. We find widespread alternative splicing events and splicing factor transcriptional signatures induced by an E. coli challenge to human DCs. Alternative splicing acts in concert with transcriptional modulation, but these two mechanisms of gene regulation affect primarily distinct functional gene groups. Alternative splicing is likely to have an important role in DC immunobiology because it affects genes known to be involved in DC development, endocytosis, antigen presentation and cell cycle arrest.

Enhanced function of cytotoxic T lymphocytes induced by dendritic cells modified with truncated PSMA and 4-1BBL

Interactions between costimulatory molecules and their receptors are vital for Ag-presenting dendritic cells (DCs) to initiate T cells activation, expansion and their antitumor immune responses. Augmentation of costimulatory signal due to the interaction of DCs and T cells may amplify, sustain and drive diversity of cytotoxic T lymphocytes (CTLs) and consequently enhance the antitumor response. 4-1BBL/4-1BB is such a pair of costimulatory ligand and receptor, playing an important role in the co-stimulation of CTLs. Previously, we demonstrated that DCs transduced with recombinant adenovirus encoding truncated PSMA (tPSMA) and m4-1BBL could induce prostate cancer regression in mouse models. In the present study, we further explored the adjuvant role of 4-1BBL in modulating CTLs activation induced by tPSMA gene-pulsed DCs. The apoptosis and cytotoxicity against tPSMA expressing RM-1 cells of CTLs were determined. Results showed that tPSMA gene-pulsed DCs effectively induced T lymphocyte activation and cytotoxicity, which was enhanced by upregulated expression of 4-1BBL, displaying better cell viability, lower CTLs apoptosis, higher expression anti-apoptotic protein of Bcl-xL and phosphorylation of P38, enhanced NF-κB activation, as well as more IFN-γ production. These results demonstrated that 4-1BBL may play a significant role in the co-stimulation pathway for Ag-presenting DCs-mediated CTLs activity, which might be a beneficial adjuvant factor for DCs-based cancer immunotherapy.

The p50 subunit of NF-κB orchestrates dendritic cell lifespan and activation of adaptive immunity

Dendritic cells play a central role in keeping the balance between immunity and immune tolerance. A key factor in this equilibrium is the lifespan of DC, as its reduction restrains antigen availability leading to termination of immune responses. Here we show that lipopolysaccharide-driven DC maturation is paralleled by increased nuclear levels of p50 NF-κB, an event associated with DC apoptosis. Lack of p50 in murine DC promoted increased lifespan, enhanced level of maturation associated with increased expression of the proinflammatory cytokines IL-1, IL-18 and IFN-β, enhanced capacity of activating and expanding CD4⁺ and CD8⁺ T cells in vivo and decreased ability to induce differentiation of FoxP3⁺ regulatory T cells. In agreement, vaccination of melanoma-bearing mice with antigen-pulsed LPS-treated p50^−/− BM-DC boosted antitumor immunity and inhibition of tumor growth. We propose that nuclear accumulation of the p50 NF-κB subunit in DC, as occurring during lipopolysaccharide-driven maturation, is a homeostatic mechanism tuning the balance between uncontrolled activation of adaptive immunity and immune tolerance.

Intradermal naked plasmid DNA immunization: mechanisms of action

Plasmid DNA is a promising vaccine modality that is regularly examined in prime-boost immunization regimens. Recent advances in skin immunity increased our understanding of the sophisticated cutaneous immune network, which revived scientific interest in delivering vaccines to the skin. Intradermal administration of plasmid DNA via needle injection is a simple and inexpensive procedure that exposes the plasmid and its encoded antigen to the dermal immune surveillance system. This triggers unique mechanisms for eliciting local and systemic immunity that can confer protection against pathogens and tumors. Understanding the mechanisms of intradermal plasmid DNA immunization is essential for enhancing and modulating its immunogenicity. With regard to vaccination, this is of greater importance as this routine injection technique is highly desirable for worldwide immunization. This article will focus on the current understanding of the mechanisms involved in antigen expression and presentation during primary and secondary syringe and needle intradermal plasmid DNA immunization.

Genetic targeting of the active transcription factor XBP1s to dendritic cells potentiates vaccine-induced prophylactic and therapeutic antitumor immunity

In vivo dendritic cells (DC) targeting is an attractive approach with potential advantages in vaccine efficacy, cost, and availability. Identification of molecular adjuvants to in vivo "modulate " DC to coordinately render improved Th1 and CD8 T cell immunity, and attenuated deleterious Treg effects, is a critical challenge. Here, we report that in vivo genetic targeting of the active transcription factor XBP1s to DC (XBP1s/DC) potentiated vaccine-induced prophylactic and therapeutic antitumor immunity in multiple tumor models. This immunization strategy is based on a genetic vaccine encoding both cytomegalovirus (CMV)-driven vaccine Aghsp70 and DC-specific CD11c-driven XBP1s. The novel targeted vaccine induced durable Th1 and CD8 T cell responses to poorly immunogenic self/tumor antigen (Ag) and attenuated tumor-associated Treg suppressive function. Bone marrow (BM)-derived DC genetically modified to simultaneously overexpress XBP1s and express Aghsp70 upregulated CD40, CD70, CD86, interleukin (IL)-15, IL-15Rα, and CCR7 expression, and increased IL-6, IL-12, and tumor necrosis factor (TNF)-α production in vitro. XBP1s/DC elevated functional DEC205(+)CD8α(+)DC in the draining lymph nodes (DLN). The data suggest a novel role for XBP1s in modulating DC to potentiate tumor vaccine efficacy via overcoming two major obstacles to tumor vaccines (i.e., T cell hyporesponsiveness against poorly immunologic self/tumor Ag and tumor-associated Treg-mediated suppression) and improving DEC205(+)CD8α(+)DC.

Dynamics of dendritic cell maturation are identified through a novel filtering strategy applied to biological time-course microarray replicates

Background

Dendritic cells (DC) play a central role in primary immune responses and become potent stimulators of the adaptive immune response after undergoing the critical process of maturation. Understanding the dynamics of DC maturation would provide key insights into this important process. Time course microarray experiments can provide unique insights into DC maturation dynamics. Replicate experiments are necessary to address the issues of experimental and biological variability. Statistical methods and averaging are often used to identify significant signals. Here a novel strategy for filtering of replicate time course microarray data, which identifies consistent signals between the replicates, is presented and applied to a DC time course microarray experiment.

Results

The temporal dynamics of DC maturation were studied by stimulating DC with poly(I:C) and following gene expression at 5 time points from 1 to 24 hours. The novel filtering strategy uses standard statistical and fold change techniques, along with the consistency of replicate temporal profiles, to identify those differentially expressed genes that were consistent in two biological replicate experiments. To address the issue of cluster reproducibility a consensus clustering method, which identifies clusters of genes whose expression varies consistently between replicates, was also developed and applied. Analysis of the resulting clusters revealed many known and novel characteristics of DC maturation, such as the up-regulation of specific immune response pathways. Intriguingly, more genes were down-regulated than up-regulated. Results identify a more comprehensive program of down-regulation, including many genes involved in protein synthesis, metabolism, and housekeeping needed for maintenance of cellular integrity and metabolism.

Conclusions

The new filtering strategy emphasizes the importance of consistent and reproducible results when analyzing microarray data and utilizes consistency between replicate experiments as a criterion in both feature selection and clustering, without averaging or otherwise combining replicate data. Observation of a significant down-regulation program during DC maturation indicates that DC are preparing for cell death and provides a path to better understand the process. This new filtering strategy can be adapted for use in analyzing other large-scale time course data sets with replicates.

DNA vaccination with T-cell epitopes encoded within Ab molecules induces high-avidity anti-tumor CD8+ T cells

Stimulation of high-avidity CTL responses is essential for effective anti-tumor and anti-viral vaccines. In this study we have demonstrated that a DNA vaccine incorporating CTL epitopes within an Ab molecule results in high-avidity T-cell responses to both foreign and self epitopes. The avidity and frequency was superior to peptide, peptide-pulsed DC vaccines or a DNA vaccine incorporating the epitope within the native Ag. The DNA Ab vaccine was superior to an identical protein vaccine that can only cross-present, indicating a role for direct presentation by the DNA vaccine. However, the avidity of CTL responses was significantly reduced in Fc receptor gamma knockout mice or if the Fc region was removed suggesting that cross presentation of Ag via Fc receptor was also important in the induction of high-avidity CTL. These results suggest that generation of high-avidity CTL responses by the DNA vaccine is related to its ability to both directly present and cross-present the epitope. High-avidity responses were capable of efficient anti-tumor activity in vitro and in vivo. This study demonstrates a vaccine strategy to generate high-avidity CTL responses that can be used in anti-tumor and anti-viral vaccine settings.

Transcriptional IL-15-directed in vivo DC targeting DNA vaccine

Dendritic cells (DC) engineered in vitro by DNA encoding OVAhsp70 and IL-15 up-regulated their expressions of CD80, CD86, CCR7 and IL-15Ralpha and promoted their productions of IL-6, IL-12 and TNF-alpha. Transcriptional IL-15-directed in vivo DC targeting DNA vaccine encoding OVAhsp70 elicited long-lasting Th1 and CTL responses and anti-B16OVA activity. CD8T cell-mediated primary tumor protection was abrogated by DC or CD4T cell depletion during the induction phase of immune responses. However, CD4T cell depletion during immunization did not impair CD8T cell-dependent long-lasting tumor protection. Furthermore, in vivo DC-derived IL-15 exerted the enhancements of cellular and humoral immune responses and antitumor immunity elicited by OVAhsp70 DNA vaccine. Importantly, the potency of this novel DNA vaccine strategy was proven using a self/tumor Ag (TRP2) in a clinically relevant B16 melanoma model. These findings have implications for developing next generation DNA vaccines against cancers and infectious diseases in both healthy and CD4 deficient individuals.

The optimal interval for dendritic cell vaccination following adoptive T cell transfer is important for boosting potent anti-tumor immunity

The gradual induction of immune responses by dendritic cell (DC) vaccination or the rapid decrease of adoptively transferred T cells may be major limitations in complete treatment of established tumors by active or passive immunization. The numbers of carcinoembryonic antigen (CEA)-specific T cells increased on 7th day and decreased from 2 weeks after repeated vaccination with CEA-peptide-pulsed DCs. Adoptively transferred CEA-specific T cells were detectable on day 1 and reached their peak by day 4, and thereafter decreased. On the basis of these results, a combined immunotherapy of DC vaccination following adoptive T cell transfer was performed to overcome these limitations of each modality. The injection of DCs within 1 day after adoptive T cell transfer showed a synergistic effect. However, when the DC vaccine was administered on day 3 or 7, CEA-specific T cells gradually declined. This concomitant immunization significantly inhibited the tumor growth than the DC vaccine administered on day 3 or 7 in 10 days tumor model. Moreover, the concomitant immunization showed potent anti-tumor effects resulting in complete inhibition of tumor growth in 2 days tumor model. These results suggest that the optimal interval for the DC vaccination following adoptive T cell transfer is important for boosting antigen-specific T cell responses and this combined immunotherapy may provide a potent therapeutic strategy for cancer treatment.