The generation of tolerogenic dendritic cells in SLE and study of their mechanisms of action and therapeutic application in a lupus mouse model

Abstract

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that is characterized by auto-reactive T and B lymphocytes and abundant auto-antibodies against nuclear components that form immune-complexes and lead to inflammation, organ dysfunction and failure. The current treatment for SLE includes corticosteroid and immunosuppressant agents which are associated with side effects. Immunotherapy such as tolerogenic dendritic cells (DCs) and regulatory T cells have potential therapeutic implications in autoimmune diseases. DCs are professional antigen presenting cells with important role in promoting immune response and maintaining peripheral tolerance. Alternatively activated DC (aaDC) derived from treating monocyte-derived DCs with vitamin D3 and dexamethasone has demonstrated tolerogenicity and suppressed activation and proliferation of allogeneic T cells in in vitro human studies. As circulating DCs in SLE patients were reported to be hyperactive with increased expression of co-stimulatory molecules and hyper-responsiveness to immunostimulatory stimuli. Therefore, this study aims to examine if aaDCs derived from SLE patients possess tolerogenic properties, to delineate the underlying mechanisms and to examine for therapeutic effect by adoptive transfer of tolerogenic DCs in lupus mouse model.

We found that lupus aaDCs derived in vitro displayed semi-mature phenotype with lower expression of co-stimulatory molecules compared with mature DCs. The tolerogenic phenotype remained stable despite challenge by CD40L, CpG-DNA and SLE serum. Lupus aaDCs showed comparable tolerogenic properties as aaDCs from healthy subjects with suppressive effect on allogeneic T cell activation and proliferation. In addition, lupus and normal aaDCs were shown to polarize normal and lupus naïve T cells into IL-10+ suppressive T cells that showed antigen-nonspecific suppressive effect on allogeneic third-party T cells. On the other hand, lupus and normal aaDCs skewed memory T cells to less inflammatory phenotype with reduced expression of IFN-ɤ and IL-17. Although aaDCs displayed a cytokine profile of IL-12loIL-10hi, addition of neutralizing anti-IL-10 and exogenous IL-12 did not reverse the suppressive effect of aaDCs on allogeneic T cells, suggesting their tolerogenicity was not related to cytokine imbalance between IL-12 and IL-10. Furthermore, aaDCs were found to express reduced level of RelB, a transcription factor regulating DC differentiation and maturation.

As RelB can be a potential target to induce stable tolerogenic DCs, we constructed RelB shRNA to silence RelB in bone marrow derived DCs (BMDCs) from MRL/MPJ mice. The RelB shRNA transduced BMDCs showed lower level of RelB compared with scramble control shRNA, and displayed tolerogenic phenotype with decreased co-stimulatory molecules, but had no effect on the expression of chemokine receptors. When co-cultured with allogenic CD4+ T cells, RelB shRNA modified BMDCs showed suppressive function on T cell activation and proliferation and increased the production of IL-10 by T cells. However, in vivo study based on 5 mice per treatment group did not show significant effect of RelB shRNA modified BMDCs on disease progress of lupus mice compared to control mice.

In conclusion, lupus aaDCs demonstrated tolerogenic properties with induction of IL-10 producing T cells with regulatory functions. RelB shRNA modified BMDCs showed tolerogenic properties in vitro but their in vivo effect on alleviation of murine lupus disease needs further study.