Mixed cultures of allogeneic dendritic cells are phenotypically and functionally stable - a potential for primary cell-based "off the shelf" product generation.

Vaccination against tumors using antigen-pulsed dendritic cell (DC) vaccines has greatly evolved over the last decade, with hundreds of active human clinical trials well on the way. The use of an autologous source for DC-based vaccine therapeutics remains the obvious choice in the majority of clinical studies; however, novel evidence suggests that an allogeneic source of DCs can yield success if administered in the right context. One of the challenges facing successful DC vaccination protocols is the generation of large enough numbers of DCs intended for vaccination and standardization of these procedures. In addition, variations in the quality of DC vaccines due to donor-to-donor variation represent an important therapeutic factor. To this day it has not been shown whether DCs from different donors can readily co-exist within the same co-culture for the extended periods required for vaccine manufacture. We demonstrate that generation of allogeneic DC co-cultures, generated from multiple unrelated donors, allows the preservation of their phenotypical and functional properties in vitro for up to 72 hours. Therefore, in the case of an allogeneic vaccination approach, one could ensure large numbers of DCs generated from a primary cell source intended for multiple vaccinations. By generating large amounts of ex vivo manufactured DCs from multiple donors, this would represent the possibility to ensure sufficient amounts of equipotent "off the shelf" product that could e.g. be used for an entire cohort of patients within a study.

Recent discoveries in dendritic cell tolerance-inducing pharmacological molecules.

Dendritic cells (DCs) represent one of the most important biological tools for cellular immunotherapy purposes. There are an increasing number of phase I and II studies, where regulatory or tolerogenic DCs (TolDCs) are utilized as negative vaccines, with the aim of inducing tolerogenic outcomes in patients with various autoimmune or chronic-inflammatory diseases, as well as in transplant settings. The induction of tolerogenic properties in DCs can be achieved by altering their activation state toward expression of immunosuppressive elements and/or by achieving resistance to maturation, which leads to insufficient co-stimulatory signal delivery and inability to efficiently present antigens. In the past, one of the most efficient ways to induce DC tolerance has been the application of selected pharmacological agents which actively induce a tolerogenic transcription program or inhibit major pro-inflammatory transcription factors such as Nf-κB. Important examples include immunosuppressants such as different corticosteroids, vitamin D3, rapamycin and others. The quality of TolDCs induced by different approaches is becoming a vital issue and recent evidence suggests substantial heterogeneity between variously-generated TolDCs as evidenced by their transcriptomic profile and function. The possibility of various "flavors" of TolDCs encourages future research in discovery of Tol-DC inducing agents to enrich various ways of DC manipulation. This would enable a broader range of tools to manipulate DC toward specific characteristics desirable in different disease settings. In recent years, several novel small molecules have been identified with the capacity to promote DC tolerogenic characteristics. In this review, we will present and discuss these novel findings and also highlight novel understandings of tolerogenic mechanisms by which DC tolerogenicity is induced by already established agents.

Synergistic Effects of Interferon-γ and Vitamin D3 Signaling in Induction of ILT-3highPDL-1high Tolerogenic Dendritic Cells.

In the past, interferon (IFN)-γ and vitamin D3 (vit D3) have both been associated with induction of tolerogenic characteristics in human dendritic cells (DCs). Although there are only a few reports on interdependency of their actions, the interplay between IFN-γ and vit D3 has been clearly demonstrated in certain aspects of immune reactivity. Since both agents have been associated with regulation of immune responses, we set out to examine their functional and mechanistic interactions in context of principal regulators of immunity, the DCs. Combined treatment with vit D3 and IFN-γ caused an extensive expression of immunoglobulin-like transcript (ILT)-3 and programmed death ligand (PDL)-1 on γ/D3DCs, significantly greater than that caused by vit D3 alone. Such γ/D3DCs retained all general DC characteristics. After CD40 ligand-induced activation, they produced increased amounts of IL-10 with almost absent production of IL-12p70. On the other hand, the co-stimulatory potential of γ/D3DCs was weak, with cells possessing the capacity to inhibit CD4+ T cell, CD8+ T cell, as well as memory T cell responses. Naive CD4+ T cells stimulated with γ/D3DCs produced increased amounts of IL-10 with concomitantly low IFN-γ production, upon T cell receptor activation. Additionally, γ/D3DCs completely inhibited granzyme B expression by CD8+ T cells. The percentage of FoxP3-positive cells in co-cultures with naive CD4+ T cells was significantly higher where γ/D3DCs were used as stimulators compared to DCs treated with vit D3 alone and it could be partially reversed by PDL-1 blockade. Interestingly, γ/D3DCs were inefficient at suppressing mDC-induced CD4+ T cell proliferation, but were twice as effective as D3DCs at suppressing mDC-induced CD8+ T cell proliferation. Blockade of indoleamine-2,3-dioxygenase did not reduce the tolerogenic phenotype induced by IFN-γ and vit D3 treatment. Examination of signaling pathways activation revealed a tendency toward increased ERK and Akt phosphorylation in γ/D3DCs. Inhibition of MEK/ERK and PI3K/mTOR pathways significantly reduced the expression of ILT-3 and PDL-1 on γ/D3DCs. In summary, we present the first evidence for existing synergy between IFN-γ and vit D3 in shaping a unique tolerogenic DC activation state.