Antigen-Specific Immunotherapeutic Vaccine for Experimental Autoimmune Myasthenia Gravis

Abstract

Myasthenia gravis (MG) and experimental autoimmune myasthenia gravis (EAMG) are caused by antibody-mediated autoimmune responses to muscle nicotinic acetylcholine receptors (AChRs) that impair neuromuscular transmission thereby causing muscle weakness. Previously, we discovered that i. p. injection of a therapeutic vaccine consisting of bacterially-expressed cytoplasmic domains of human AChR subunits reduced development of chronic EAMG in rats. Here we show that immunization with the therapeutic vaccine in adjuvant does not induce EAMG, thus is safe. Potency and efficacy of the therapeutic vaccine were greatly increased by administering repeated low doses subcutaneously in incomplete Freund’s adjuvant. Onset of chronic EAMG could be prevented. Established chronic EAMG could be rapidly reversed, modeling therapy of chronic MG. Therapy reduced pathological antibodies assayed by immune precipitation of a main immunogenic region chimera. Successfully treated rats exhibited long-term resistance to re-induction of EAMG, modeling a lasting cure of MG. A long-term effect of therapy was to change isotype of the pathogenic antibody response from IgG2b that fixes complement to IgG1 that does not. Prevention and reversal of chronic EAMG was not caused by the isotype switch, but the isotype switch may contribute to resistance to reinduction of EAMG. Immunization with AChR cytoplasmic domains in adjuvant is promising as a safe, antigen-specific, potent, effective, rapidly acting, and long lasting approach to therapy of MG.

AChR-specific immunosuppressive therapy of myasthenia gravis

“…Before innervation and after denervation g is replaced by e. The areas in red highlight the MIR which is located at the extracellular tip of a1 subunits and is the target of half or more of the autoantibodies to muscle AChRs in human MG and rat EAMG [45]. Figure taken from Luo and Lindstrom [94]. more of autoantibodies in human MG or EAMG [44][45][46].…”

“…Theoretically, therapy with the cytoplasmic domains should be safe. Safety is demonstrated by the facts that: (1) rats repeatedly immunized with the cytoplasmic domains in TiterMax adjuvant do not develop EAMG, although they produced antibodies which can bind to solubilized native AChRs; and (2) serum antibodies from these rats do not bind the MIR, passively transfer EAMG, or cause antigenic modulation of AChR [94].…”

“…In order to test the efficiency and potency of therapy with the AChR cytoplasmic domains, we have employed two contiguous cytoplasmic domain constructs that encompass the large cytoplasmic domains of human muscle AChR b1, a1, and g subunits and those of human muscle AChR e, a1, and d subunits respectively (Table 1) [79,94]. Together, these two constructs reflect the order of subunits around the ion channel (Fig.…”

“…Thus, adjuvants may enhance the potency and efficacy of therapy with the cytoplasmic domains. We found that specific immunosuppression of EAMG with a therapeutic vaccine consisting of human AChR cytoplasmic domains is more potent when it is administered s.c. in adjuvant immediately after the acute phase [94]. As a therapeutic adjuvant, the modest adjuvant incomplete Freund's adjuvant (IFA) is more effective than the more potent adjuvant TiterMax that is used with Torpedo AChR to induce EAMG.…”

Current Treatment, Emerging Translational Therapies, and New Therapeutic Targets for Autoimmune Myasthenia Gravis

“…DNA vaccinations have also been proposed, but, as with peptide vaccines, a primary concern is the potential for exacerbation of the anti-AChR immune response. Recently, immunization with AChR cytoplasmic domains in adjuvant has been proposed as a promising antigen-specific therapeutic approach to MG [148]. As the cytoplasmic AChR epitopes are not expressed extracellularly and would not be accessible to the immune system, this approach may circumvent concerns regarding disease exacerbation.…”