Clinical and immunological control of experimental autoimmune encephalomyelitis by tolerogenic dendritic cells loaded with MOG-encoding mRNA

Background: Although effective in reducing relapse rate and delaying progression, current therapies for multiple sclerosis (MS) do not completely halt disease progression. T cell autoimmunity to myelin antigens is considered one of the main mechanisms driving MS. It is characterized by autoreactivity to disease-initiating myelin antigen epitope(s), followed by a cascade of epitope spreading, which are both strongly patient-dependent. Targeting a variety of MS-associated antigens by myelin antigen-presenting tolerogenic dendritic cells (tolDC) is a promising treatment strategy to re-establish tolerance in MS. Electroporation with mRNA encoding myelin proteins is an innovative technique to load tolDC with the full spectrum of naturally processed myelin-derived epitopes.

Methods: In this study, we generated murine tolDC presenting myelin oligodendrocyte glycoprotein (MOG) using mRNA electroporation and we assessed the efficacy of MOG mRNA-electroporated tolDC to dampen pathogenic T cell responses in experimental autoimmune encephalomyelitis (EAE). For this, MOG_35-55-immunized C57BL/6 mice were injected intravenously at days 13, 17, and 21 post-disease induction with 1α,25-dihydroxyvitamin D₃-treated tolDC electroporated with MOG-encoding mRNA. Mice were scored daily for signs of paralysis. At day 25, myelin reactivity was evaluated following restimulation of splenocytes with myelin-derived epitopes. Ex vivo magnetic resonance imaging (MRI) was performed to assess spinal cord inflammatory lesion load.

Results: Treatment of MOG_35-55-immunized C57BL/6 mice with MOG mRNA-electroporated or MOG_35-55-pulsed tolDC led to a stabilization of the EAE clinical score from the first administration onwards, whereas it worsened in mice treated with non-antigen-loaded tolDC or with vehicle only. In addition, MOG_35-55-specific pro-inflammatory pathogenic T cell responses and myelin antigen epitope spreading were inhibited in the peripheral immune system of tolDC-treated mice. Finally, magnetic resonance imaging analysis of hyperintense spots along the spinal cord was in line with the clinical score.

Conclusions: Electroporation with mRNA is an efficient and versatile tool to generate myelin-presenting tolDC that are capable to stabilize the clinical score in EAE. These results pave the way for further research into mRNA-electroporated tolDC treatment as a patient-tailored therapy for MS.