Phosphatidylinositol-3-kinase activity during in vitro dendritic cell generation determines suppressive or stimulatory capacity

Tolerogenic Dendritic Cells and T-Regulatory Cells at the Clinical Trials Crossroad for the Treatment of Autoimmune Disease; Emphasis on Type 1 Diabetes Therapy

Tolerogenic dendritic cells and T-regulatory cells are two immune cell populations with the potential to prevent the onset of clinical stage type 1 diabetes, and manage the beginning of underlying autoimmunity, at the time-at-onset and onwards. Initial phase I trials demonstrated that the administration of a number of these cell populations, generated ex vivo from peripheral blood leukocytes, was safe. Outcomes of some of these trials also suggested some level of autoimmunity regulation, by the increase in the numbers of regulatory cells at different points in a network of immune regulation in vivo. As these cell populations come to the cusp of pivotal phase II efficacy trials, a number of questions still need to be addressed. At least one mechanism of action needs to be verified as operational, and through this mechanism biomarkers predictive of the underlying autoimmunity need to be identified. Efficacy in the regulation of the underlying autoimmunity also need to be monitored. At the same time, the absence of a common phenotype core among the different dendritic cell and T-regulatory cell populations, that have completed phase I and early phase II trials, necessitates a better understanding of what makes these cells tolerogenic, especially if a uniform phenotypic core cannot be identified. Finally, the inter-relationship of tolerogenic dendritic cells and T-regulatory cells for survival, induction, and maintenance of a tolerogenic state that manages the underlying diabetes autoimmunity, raises the possibility to co-administer, or even to serially-administer tolerogenic dendritic cells together with T-regulatory cells as a cellular co-therapy, enabling the best possible outcome. This is currently a knowledge gap that this review aims to address.

Co-Stimulation-Impaired Bone Marrow-Derived Dendritic Cells Prevent Dextran Sodium Sulfate-Induced Colitis in Mice

Dendritic cells (DC) are important in the onset and severity of inflammatory bowel disease (IBD). Tolerogenic DC induce T-cells to become therapeutic Foxp3+ regulatory T-cells (Tregs). We therefore asked if experimental IBD could be prevented by administration of bone marrow-derived DC generated under conventional GM-CSF/IL-4 conditions but in the presence of a mixture of antisense DNA oligonucleotides targeting the primary transcripts of CD40, CD80, and CD86. These cell products (which we call AS-ODN BM-DC) have demonstrated tolerogenic activity in preventing type 1 diabetes and preserving beta cell mass in new-onset type 1 diabetes in the NOD mouse strain, in earlier studies. In addition to measuring efficacy in prevention of experimental IBD, we also sought to identify possible mechanism(s) of action. Weight, behavior, stool frequency, and character were observed daily for 7–10 days in experimental colitis in mice exposed to dextran sodium sulfate (DSS) following injection of the AS-ODN BM-DC. After euthanasia, the colons were processed for histology while spleen and mesenteric lymph nodes (MLNs) were made into single cells to measure Foxp3+ Treg as well as IL-10+ regulatory B-cell (Breg) population frequency by flow cytometry. AS-ODN BM-DC prevented DSS-induced colitis development. Recipients of these cells exhibited significant increases in Foxp3+ Treg and IL-10+ Breg in MLN and spleen. Histological examination of colon sections of colitis-free mice remained largely architecturally physiologic and mostly free of leukocyte infiltration when compared with DSS-treated animals. Although DSS colitis is mainly an innate immunity-driven condition, our study adds to the growing body of evidence showing that Foxp3+ Treg and IL-10 Bregs can suppress a mainly innate-driven inflammation. The already-established safety of human DC generated from monocytic progenitors in the presence of the mixture of antisense DNA targeting the primary transcripts of CD40, CD80, and CD86 in humans offers the potential to adapt them for clinical IBD therapy.

Generation of antigen-specific Foxp3+ regulatory T-cells in vivo following administration of diabetes-reversing tolerogenic microspheres does not require provision of antigen in the formulation

We have developed novel antisense oligonucleotide-formulated microspheres that can reverse hyperglycemia in newly-onset diabetic mice. Dendritic cells taking up the microspheres adopt a restrained co-stimulation ability and migrate to the pancreatic lymph nodes when injected into an abdominal region that is drained by those lymph nodes. Furthermore, we demonstrate that the absolute numbers of antigen-specific Foxp3+ T regulatory cells are increased only in the lymph nodes draining the site of administration and that these T-cells proliferate independently of antigen supply in the microspheres. Taken together, our data add to the emerging model where antigen supply may not be a requirement in "vaccines" for autoimmune disease, but the site of administration - subserved by lymph nodes draining the target organ - is in fact critical to foster the generation of antigen-specific regulatory cells. The implications of these observations on "vaccine" design for autoimmunity are discussed and summarized.

In vivo delivery of nucleic acid-formulated microparticles as a potential tolerogenic vaccine for type 1 diabetes

Originally conceived as a method to silence transcription/translation of nascent RNA, nucleic acids aimed at downregulating gene expression have been shown to act at multiple levels. Some of the intriguing features of these gene-silencing nucleic acids include activation of molecular signals in immune cells which confer tolerogenic properties. We have discovered a method to induce stable tolerogenic ability to dendritic cells ex vivo using a mixture of phosphorothioate-modified antisense DNA targeting the primary transcripts of CD40, CD80 and CD86. Autologous human dendritic cells generated in the presence of these oligonucleotides prevent and reverse type 1 diabetes (T1D) in the non-obese diabetic (NOD) strain mouse model of the human disease, and have been shown to be safe in established diabetic human patients. Even though this ex vivo approach is clinically feasible, we have gone beyond a cell therapy approach to develop a "population-targeting" microsphere formulation of the three antisense oligonucleotides. Effectively, such a product could constitute an "off-the-shelf" vaccine. In this paper, we describe the progress made in developing this approach, as well as providing some insight into potential molecular mechanisms of action.

A role for tolerogenic dendritic cell-induced B-regulatory cells in type 1 diabetes mellitus

PURPOSE OF REVIEW

To review the important recent findings on the nature, characteristics and function of novel populations of immunosuppressive B-lymphocytes (Bregs) and their possible role as a regulatory cell population, potentially responsive to dendritic cells, in preventing and possibly controlling type 1 diabetes mellitus.

RECENT FINDINGS

Although almost all of the experimental work in immunosuppressive B-lymphocyte biology has focused on their role in arthritis and experimental inflammatory bowel disease, only recently has a role for Bregs in the regulation of type 1 diabetes been looked at more extensively. IL-10-producing Bregs are of significant interest, more so because of their potential modulation by tolerogenic dendritic cells. Additionally, novel populations have been discovered that could also be relevant in the regulation of diabetes autoimmunity. The unexpected discovery of a novel population of Bregs, whose frequency was upregulated in our phase I clinical trial of tolerogenic autologous dendritic cell administration in humans, opens a new frontier for basic and translational research into these novel cell populations.

SUMMARY

Bregs are a recently rediscovered population of suppressive lymphocytes whose activation, differentiation and function could be sensitive to tolerogenic dendritic cell networks. Modulation of these dendritic cell networks, or the Bregs directly, offers novel options to attenuate and reverse type 1 diabetes autoimmunity as a possible cure for the disease.