Immunotherapy is becoming an increasingly attractive therapeutic alternative for conventional cancer therapy. In recent years Foxp3+ regulatory T-cells (TR) were identified as the major obstacle to effective cancer immunotherapy. The abundance of these cells in peripheral blood is increased in patients with multiple types of cancer and their prevalence among tumor-infiltrating lymphocytes correlated with poor clinical prognosis. In contrast, removal or inactivation of TR cells led to enhanced antitumor immune response and better efficacy of cancer vaccines. We report that Bone Morphogenic Protein Receptor 1α (BMPR1α, Alk-3), is expressed by activated effector CD4+ and TR cells and modulates functions of both cell types. Bone Morphogenic Proteins (BMPs) belong to the transforming growth factor (TGF)-β family of cytokines that also include TGFβ and activins. BMPs play crucial roles in- embryonic development, tissue differentiation and homeostasis and development of cancer. It was demonstrated that BMPs and activins synergize with TGFβ to regulate thymic T-cell development, maintain TR cells and control peripheral tolerance. Inactivation of BMPR1α in T-cells results in impaired thymic and peripheral generation of TR cells. BMPR1α -deficient activated T-cells produced higher level of interferon (IFN)-γ than BMPR1α-sufficient T-cells. Moreover, transplanted B16 melanoma tumors grew smaller in mice lacking expression of BMPR1α in T-cells and tumors had few infiltrating TR cells and a higher proportion of CD8+ T-cells than wild-type mice.

The cytokines of the transforming growth factor-β (TGF-β) family promote the growth and differentiation of multiple tissues, but the role of only the founding member, TGF-β, in regulating the immune responses has been extensively studied. TGF-β is critical to prevent the spontaneous activation of self-reactive T cells and sustain immune homeostasis. In contrast, in the presence of proinflammatory cytokines, TGF-β promotes the differentiation of effector T helper 17 (T17) cells. Abrogating TGF-β receptor signaling prevents the development of interleukin-17 (IL-17)-secreting cells and protects mice from T17 cell-mediated autoimmunity. We found that the receptor of another member of TGF-β family, bone morphogenetic protein receptor 1α (BMPR1α), regulates T helper cell activation. We found that the differentiation of T17 cells from naive CD4 T cells was inhibited in the presence of BMPs. Abrogation of BMPR1α signaling during CD4 T cell activation induced a developmental program that led to the generation of inflammatory effector cells expressing large amounts of IL-17, IFN-γ, and TNF family cytokines and transcription factors defining the T17 cell lineage. We found that TGF-β and BMPs cooperated to establish effector cell functions and the cytokine profile of activated CD4 T cells. Together, our data provide insight into the immunoregulatory function of BMPs.