Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation in the joints, leading to pain, stiffness and cartilage damage. Immune regulatory failure or imbalance in anti- and pro-inflammatory responses could lead towards autoimmune diseases. However, the initial trigger that causes this faulty immune regulation is often unknown which is also the case in RA. Therefore, it is not possible yet to treat the initiation of disease in an antigen specific way, which means that current medication is directed towards relief of symptoms. To cure disease, restoring immune tolerance is required. For this reason, therapies that restore the immune balance are being explored. In this thesis we investigated two possible approaches: tolerogenic dendritic cells and nanoparticles containing TNF siRNA.
Tolerogenic dendritic cells
Dendritic cells (DCs) are important players in the immune system for their ability to activate and dampen the immune system. DCs can be modulated in the laboratory into tolerogenic dendritic cells (tolDCs), these tolDCs could restore immune tolerance. In this thesis, we have shown that tolDCs, induced by dexamethasone and 1,25-dihydroxyvitamin D3, do not induce new regulatory T cells but dampen the activation and proliferation of CD4+ T cells. This results in overall more Tregs and an immune-regulatory state. Since the autoantigen in RA is unknown, we sought possible alternative autoantigens. We investigated HSPs as possible surrogate autoantigens. Since roughly eighty percent of both healthy donors and inflammatory arthritis patients showed a CD4+ T cell response towards HSPs, we reasoned that HSPs could be used to modulate CD4+ T cell responses in humans. Furthermore, tolDCs pulsed with HSP or control peptides induced a Tr1 phenotype in the CD4+ T cells.
TNF is a pro-inflammatory cytokine that plays an important role in the pathogenesis of RA. RNA interference therapy could be a solution to inhibit excessive TNF production and dampen inflammation in RA. However, to get TNF siRNA across the cell membrane a drug delivery system such as nanoparticles are needed. Especially in autoimmunity, the delivery system itself should not induce any additional (pro-inflammatory) immune responses. Two nanoparticle types were designed to deliver TNF siRNA without extra immune activation. After showing that TNF siRNA is able to inhibit TNF production in a macrophage cell line, we tested the nanoparticles in an in vivo experimental arthritis model. Both the nanoparticle types containing TNF siRNA restrained arthritic symptoms after local administration, indicating that TNF was silenced in vivo.
Since the route of administration of these tolerogenic therapies can influence the outcome, we compared two non-traditional routes (intradermal and intranasal) of vaccination. We noticed differences in immune cell activation and cytokine production, which illustrates that the micromilieu and immune response differ greatly between the several administration routes.
The results described in this thesis may bring us a step closer towards developing immune tolerance-inducing therapies for Rheumatoid arthritis and possibly also other auto immune diseases.