Acute/relapsing experimental autoimmune encephalomyelitis: Induction of long lasting, antigen-specific tolerance by syngeneic bone marrow transplantation

Experimental autoimmune encephalomyelitis (EAE) is an inducible autoimmune disease widely used as a model of the acute/relapsing stage of multiple scl erosis. We have Previously shown that treatment of EAE-mice with high doses of cyclophosphamide (CY) (350 mg kg), followed by syngeneic bone marrow tr ansplantation (SBMT), completely abrogates the clinical paralytic signs and even prevents the appearance of new relapses in the chronic-relapsing mode l of the disease. In the present study we examined whether this treatment p rotocol induces long term tolerance and whether this tolerance is antigen-s pecific. EAE was induced by immunization with spinel cord homogenate (MSCH) in complete Freund's adjuvant (CFA). The treatment with CY and SBMT was Pe rformed on day 6 post immunization. Treated and untreated mice were rechall enged with MSCH, or a non-relevant antigen (OVA) in CFA at various stages a fter the first paralytic attack. In contrast to previous date showing that animals recovering from acute EAE are usually refractory to re-induction of the disease, repeated injections of MSCH at different sites from the initi al immunization, followed by i.v. injection of inactivated Bordetella bacte ria, 2, 4 and 6 months after the initial EAE-induction, caused a severe and usually lethal relapse in all the untreated, control animals. Mice treated with CY and SBMT were resistant to all rechallenges with the some encephal itogenic inoculum. Following the second rechallenge, peripheral lymph node cells were examined in vitro for their proliferative responses to myelin an tigens or to OVA. Lymphocytes obtained from CY+SBMT treated mice did not pr oliferate in vitro in response to myelin basic protein (MBP), but prolifera ted against OVA, when immunized with this antigen, after SBMT Adoptive tran sfer of lymphocytes from tolerant mice to naive recipients did not transfer resistance to EAE-induction. Our results indicate that high doses of CY, f ollowed by SBMT, induce long term antigen-specific tolerance presumably by a mechanism of clonal deletion or anergy.