Therapeutic Effects of Anti-Bone Morphogenetic Protein and Activin Membrane-Bound Inhibitor Treatment in Psoriasis and Arthritis

OBJECTIVE

The transforming growth factor β (TGFβ) inhibitor BAMBI (bone morphogenetic protein and activin membrane-bound inhibitor) has been shown to control differentiation of CD4+ T lymphocytes into either tolerogenic Treg cells or pathogenic Th17 cells, through the regulation of TGFβ and interleukin-2 (IL-2) signaling strength. The present study was undertaken to explore the potential beneficial effects of this strategy of pharmacologic inhibition using novel anti-BAMBI monoclonal antibodies (mAb) in different experimental murine models of chronic skin and joint inflammatory/autoimmune disease.

METHODS

Development of Saccharomyces cerevisiae mannan-induced psoriatic arthritis (MIP) (n = 18-30 mice per group), imiquimod-induced skin psoriasis (n = 20-30 mice per group), or type II collagen-induced arthritis (CIA) (n = 13-16 mice per group) was analyzed in a total of 2-5 different experiments with either wild-type (WT) or BAMBI-deficient B10.RIII mice that were left untreated or treated with mAb B101.37 (mouse IgG1 anti-BAMBI), a mouse IgG1 anti-TNP isotype control, anti-CD25, or anti-TGFβ mAb.

RESULTS

Treatment of normal mice with IgG1 anti-BAMBI mAb clone B101.37 led to expansion of Treg cells in vivo, and had both preventive and therapeutic effects in mice with MIP (each P < 0.05 versus controls). The conferred protection against disease progression was found to be mediated by Treg cells, which controlled the activation and expansion of pathogenic IL-17-producing cells, and was dependent on the level of TGFβ activity. Furthermore, treatment with B101.37 mAb blocked both the development of skin psoriasis induced by imiquimod and the development of CIA in mice (each P < 0.05 versus controls). Finally, pharmacologic inhibition of BAMBI with the IgM anti-BAMBI mAb B143.14 also potentiated the suppressive activity of Treg cells in vitro (P < 0.001 versus controls).

CONCLUSION

These results in murine models identify BAMBI as a promising new therapeutic target for chronic inflammatory diseases and other pathologic conditions modulated by Treg cells.

BAMBI is a negative regulator of humoral immune responses

BAMBI (Bone Morphogenetic Protein and Activin Membrane Bound Inhibitor) is a plasma membrane-associated negative regulator of TGFβ signaling. Using mice deficient in BAMBI and anti-BAMBI monoclonal antibodies, we have recently demonstrated the contribution of this TGFβ inhibitor to the regulation of CD4 T-cell differentiation into pathogenic TH17 cells and tolerogenic regulatory T cells. In the present study, we explored the possible involvement of BAMBI in the control of humoral immune responses. We demonstrated that BAMBI-KO mice developed increased antibody responses against T-independent antigens. In addition, these mutant mice also exhibited enhanced antibody responses against several T-dependent antigens administered by different routes and even in the absence of adjuvants. Using adoptive CD4 T-cell transfer experiments and double WT/BAMBI-KO bone marrow chimeric mice we showed that in the mutant mice, B cells exhibited intrinsic defects that improved their interaction with antigen-specific activated CD4 T cells and their subsequent activation and differentiation into germinal center B cells and antibody secreting cells. In fact, B cells from BAMBI-KO mice exhibited enhanced proliferative responses in vitro and expressed higher levels of surface molecules involved in CD4:B cell interactions. Finally, we demonstrated here that the enhanced T-dependent antibody responses observed in BAMBI-KO mice were reverted after long-term treatment with an anti-TGFβ monoclonal antibody. In conclusion, our present study described for the first time a negative role of BAMBI in the control of T-independent and Tdependent antibody responses through the regulation of TGFβ signaling.

BAMBI, a new molecular target in autoimmunity

We have previous demonstrated that BAMBI (BMP and Activin Membrane Bound Inhibitor) negatively regulates the functional differentiation of CD4 T cells into tolerogenic regulatory T-cells (Tregs) and positively the differentiation into pro-inflammatory TH17 cells. Accordingly, mice deficient in BAMBI are resistant against the development of collagen type II-induced arthritis (CIA). To analyze the therapeutic effects of BAMBI inhibition in normal mice in the development of autoimmunity, we developed new inhibitory mouse anti-mouse BAMBI mAbs. Treatment of B10RIII wild type (WT) mice with a high dose of a mouse IgG1 anti-mouse BAMBI mAb (clone B101.37; 2 mg/mice/week), but not with a low dose of B101.37 (0.3 mg/mice/week) or a high dose of an irrelevant IgG1 mAb (2 mg/mice/week), inhibited the development of CIA as efficiently as observed in B10RIII.BAMBI-KO mice.

We further explore the therapeutic potential of B101.37 in experimental models of psoriasis (Ps) and psoriasis arthritis (PsA). A single ip injection of mannan from Saccharomyces cerevisiae induces an acute inflammation resembling human Ps and PsA in B10RIII.WT but with a reduced severity in B10RIII.BAMBI-KO mice. Again, treatment of WT mice with B101.37, but not with an irrelevant IgG1 antibody, protects the animals against mannan-induced PsA and Ps by a Treg- and TGFβ-dependent mechanism. B101.37 also exhibits a therapeutic activity against mannan-induced PsA and Ps once the disease has been established. Similar results have been observed in a model of Ps induced after the topic administration of the TLR-7 agonist imiquimod. Altogether, our results demonstrate the beneficial effects of BAMBI inhibitors in the treatment of autoimmune skin and joint diseases.