To define the role of indoleamine 2,3-dioxygenase (IDO) in driving pathogenic B cell responses that lead to arthritis and to determine if inhibitors of the IDO pathway can be used in conjunction with therapeutic B cell depletion to prevent the reemergence of autoantibodies and arthritis following reconstitution of the B cell repertoire.
Immunoglobulin-transgenic mice were treated with the IDO inhibitor 1-methyltryptophan (1-MT) and monitored for the extent of autoreactive B cell activation. Arthritic K/BxN mice were treated with B cell depletion alone or in combination with 1-MT. Mice were monitored for the presence of autoantibody-secreting cells, inflammatory cytokines, and joint inflammation.
Treatment with 1-MT did not affect the initial activation or survival of autoreactive B cells, but it did inhibit their ability to differentiate into autoantibody-secreting cells. Treatment with anti-CD20 depleted the B cell repertoire and attenuated arthritis symptoms; however, the arthritis symptoms rapidly returned as B cells repopulated the repertoire. Administration of 1-MT prior to B cell repopulation prevented the production of autoantibodies and inflammatory cytokines and flare of arthritis symptoms.
IDO activity is essential for the differentiation of autoreactive B cells into antibody-secreting cells, but it is not necessary for their initial stages of activation. Addition of 1-MT to therapeutic B cell depletion prevents the differentiation of autoantibody-secreting cells and the recurrence of autoimmune arthritis following reconstitution of the B cell repertoire. These data suggest that IDO inhibitors could be used in conjunction with B cell depletion as an effective cotherapeutic strategy in the treatment of rheumatoid arthritis.