Vaccines for Autoimmune Diseases: Inducing Tolerance without Inflammation

Fighting against autoimmune diseases is a very challenging task. A novel approach consists of using antigen-specific tolerization that selectively blunt autoimmunity without compromising normal immune function. Physiological induction and maintenance of tolerance is based on the presentation of self-antigens by antigen-presenting cells (APCs) with low level expression of costimulatory molecules. In a recent paper published in Science [1], Christina Krienke, et al. tried to develop a therapeutic approach that would emulate natural mechanisms of immune tolerance for the treatment of some autoimmune diseases, as they had broad experience introducing liposomal formulation for systemic delivery of messenger RNA (mRNA)-encoded vaccine antigens into APCs[2]. mRNA vaccination induces strong type 1 T helper (Th1) cell responses driven by the IFN-α released from APCs, which is a typical inflammatory signal. Replacement of uridine (U) by incorporation of 1-methylpseudouridine (m1Ψ) and subsequent removal of mRNA contaminants is known to reduce the inflammatory properties of mRNA vaccines [3]. Authors suggested that the use of m1Ψ mRNA for in vitro delivery of autoimmune disease target antigens in a noninflammatory context would enable systemic tolerogenic antigen presentation in lymphoid tissues.

(A and B) Activation of splenic immune cells 24 hours after, and (C) IFN-α serum levels 6 hours after intravenous injection of lipid nanoparticles containing mRNAs and saline control. Whereas U mRNA elicits a high inflammatory response, the m1Ψ mRNA does not. Krienke C, et al. A noninflammatory mRNA vaccine for treatment of experimental autoimmune encephalomyelitis. Science. 2021 Jan 8;371(6525):145-153. doi: 10.1126/science.aay3638

To test their hypothesis, authors first engineered lipid nanoparticles consisting of nonimmunogenic (m1Ψ) or immunogenic (U) mRNA complexes that lack inherent adjuvant activity. mRNA coding for the reporter gene firefly luciferase (LUC) or saline (control) was administered to mice, and the expression of the LUC protein was assessed. Administration of U mRNA led to strong activation of APCs and T lymphocytes and secretion of high levels of IFN α, whereas the m1Ψ mRNA did not induce secretion of IFN-α or any other inflammatory cytokine. Furthermore, LUC expression was profoundly higher and prolonged in m1Ψ mRNA treated animals, suggesting that m1Ψ mRNA is suitable for noninflammatory delivery of proteins into APCs.

Then they wanted to study the effects of m1Ψ mRNA in an autoimmune disease, and chose experimental autoimmune encephalomyelitis (EAE) as a clinical mouse model of multiple sclerosis (MS), in which they previously demonstrated tolerance induction by selectively expressing the epitope of myelin oligodendrocyte glycoprotein MOG35-55 [4]. Mice were immunized with MOG35-55 m1Ψ mRNA or U mRNA and the expansion of T cells was assessed. Both MOG35-55-encoding mRNAs induced proliferation of CD4+ T cells, being m1Ψ mRNA superior, although the functional properties of the induced cells differed profoundly. MOG35-55 m1Ψ mRNA treatment was capable of expanding or inducing de novo T regulatory (Treg) cells that inhibited the in vitro proliferation of antigen-specific naïve CD4+ T cells in a dose-dependent manner. By contrast, T cells of MOG35-55 U mRNA or control-treated mice showed little to no suppressive activity. Whereas MOG35-55 U mRNA-expanded T cells exhibited a functional Th1 effector profile with secretion of inflammatory cytokines, CD4+ T cells from MOG35-55 m1Ψ mRNA-treated mice did not secreted them, even when exposed to very high antigen concentrations.

Left: CD4 staining in the spinal cord of EAE mice treated with m1Ψ mRNA or saline (control). Infiltrates are gone after MOG35-55 m1Ψ mRNA treatment. Right: Luxor fast blue staining reveals areas of demyelination in the spinal cord of mice from the left panel. Krienke C, et al. A noninflammatory mRNA vaccine for treatment of EAE. Science. 2021 Jan 8;371(6525):145-153. doi: 10.1126/science.aay3638.

They also found that MOG35-55 m1Ψ mRNA-induced antigen-specific CD4+ Treg cells do not suppress functional immune responses against nonmyelin antigens. Treatment with MOG35-55 m1Ψ mRNA was capable of blocking all clinical signs of EAE in mice, whereas control animals showed the typical course of disease with rapid monophasic progression. In mice started on MOG35-55 m1Ψ mRNA treatment when a paralysis of the tail or beginning of the hindlimbs were noted, further disease progression could be prevented, and motor functions were restored. Authors found that m1Ψ mRNA treatment rather than deleting autoreactive T cells, tips the immunological balance in favor of suppression of disease by promoting and expanding MOG35 55 Treg cells.

Expression of coinhibitory receptors such as CTLA-4 and PD-1 on effector and Treg cells is a key mechanism of immune homeostasis. Treatment of EAE mice with MOG35-55 m1Ψ mRNA combined with anti-PD-1 or anti-CTLA-4 antibodies aggravated the disease in control groups, in accordance with the known unleashing effect of checkpoint blockade on autoreactive T cells [5]. Furthermore, both CTLA-4 and PD-1 blockade almost completely abolished the EAE protective effect of MOG35-55 m1Ψ mRNA, effect that may be driven by two independent mechanisms: a) the invigoration of preexistent T effector cells, or b) the inhibition of the de novo induction of antigen-specific Treg cells, which also depends on PD-1 signaling [6]. These results suggest that disease-mediating T cells are suppressed but not deleted in mice treated with antigen-encoding m1Ψ mRNA and that both PD-1 and CTLA-4 signaling critically contribute to the induction and maintenance of antigen-specific tolerance.

Disease severity in MOG35-55-induced EAE treated with m1ΨmRNA was significantly lower than the control mice.  Krienke C, et al. A noninflammatory mRNA vaccine for treatment of EAE. Science. 2021 Jan 8;371(6525):145-153. doi: 10.1126/science.aay3638.

In sum, this work demonstrated that delivery of autoantigens into APCs within lymphoid tissues exploits a highly effective natural mechanism for induction and maintenance of peripheral tolerance. Presentation of autoantigens in a noninflammatory context leads to an expansion of antigen-specific effector Treg cells that suppress antigen-specific autoreactive T effector cells and exert a bystander immunosuppression, thus enabling disease control even in a complex model of autoimmunity. Treg cell activity exerts tissue-specific immune regulation rather than pan-immune suppression [7], which is in line with previous studies indicating that T cell tolerance to tissue-restricted self-antigens is actively mediated by antigen-specific Treg cells rather than due to their deletion [8].

Repetitive administration of m1Ψ mRNA is not compromised by induction of autoantigen-specific antibody responses. Furthermore, production of mRNA vaccines is fast and cost-efficient, and virtually any autoantigen can be encoded by mRNA. Similar to that which has been successfully executed in the settings of personalized cancer vaccines [9], tailoring the treatment for disease-causing antigens of individual patients is conceivable. Researchers can also combine m1Ψ mRNA encoding either multiple autoantigens or autoantigens that confer bystander tolerance, enabling control of more complex autoimmune diseases.

mRNA vaccines constitute the future of a new era of vaccine developments, with a potential to be applied to a wide variety of infections or autoimmune diseases. This is definitely a huge leap forward in the way to find a cure for MS and other autoimmune diseases, and we will look forward to see further developments in this area.

References

1. Krienke, C., et al., A noninflammatory mRNA vaccine for treatment of experimental autoimmune encephalomyelitis. Science, 2021. 371(6525): p. 145-153.

2. Kranz, L.M., et al., Systemic RNA delivery to dendritic cells exploits antiviral defence for cancer immunotherapy. Nature, 2016. 534(7607): p. 396-401.

3. Kariko, K., et al., Generating the optimal mRNA for therapy: HPLC purification eliminates immune activation and improves translation of nucleoside-modified, protein-encoding mRNA. Nucleic Acids Res, 2011. 39(21): p. e142.

4. Yogev, N., et al., Dendritic cells ameliorate autoimmunity in the CNS by controlling the homeostasis of PD-1 receptor(+) regulatory T cells. Immunity, 2012. 37(2): p. 264-75.

5. Yshii, L.M., R. Hohlfeld, and R.S. Liblau, Inflammatory CNS disease caused by immune checkpoint inhibitors: status and perspectives. Nat Rev Neurol, 2017. 13(12): p. 755-763.

6. Wang, L., et al., Programmed death 1 ligand signaling regulates the generation of adaptive Foxp3+CD4+ regulatory T cells. Proc Natl Acad Sci U S A, 2008. 105(27): p. 9331-6.

7. Clemente-Casares, X., et al., Expanding antigen-specific regulatory networks to treat autoimmunity. Nature, 2016. 530(7591): p. 434-40.

8. Legoux, F.P., et al., CD4+ T Cell Tolerance to Tissue-Restricted Self Antigens Is Mediated by Antigen-Specific Regulatory T Cells Rather Than Deletion. Immunity, 2015. 43(5): p. 896-908.

9. Sahin, U. and O. Tureci, Personalized vaccines for cancer immunotherapy. Science, 2018. 359(6382): p. 1355-1360.

Related Articles

Perioperative Immunotherapy: Different Treatment Strategies to Multiply Therapy Effectiveness
Immunoengineering, New Technologies for Biotherapy Enhancement
Combination of antibodies with chemotherapeutic agents to attack the heart of the tumor