IL-21R-Targeted Nano-immunosuppressant Prevents Acute Rejection in Allogeneic Transplantation by Blocking Maturation of T Follicular Helper Cells

During organ transplantation, immune rejection is a primary cause of graft failure. In the underlying pathophysiology of rejection, T follicular helper (Tfh) cells and interleukin-21 (IL-21) play pivotal roles. Tfh cells exacerbate the humoral immune response by promoting B cell differentiation and antibody production, which leads to damage of the transplanted tissue. IL-21, a key pro-inflammatory cytokine, binds to its receptor (IL-21R) to enhance both the growth and function of Tfh cells, while also further driving B cell activation and differentiation into plasma cells. Building on this knowledge, we have developed a tacrolimus-based nano-inhibitor designed to target Tfh cells. This nano-inhibitor is constructed using a mPEG-PLGA-PLL (PEAL) scaffold, with IL-21R monoclonal antibodies conjugated to its surface, and tacrolimus encapsulated within the structure. In vitro experiments demonstrated that this nano-inhibitor effectively targets Tfh cells, inhibiting the differentiation of naive CD4+ T cells into Tfh cells. In co-culture systems of T and B cells, it significantly suppresses the activation of both cell types, leading to a reduction in IgG antibody production. In vivo, the nano-inhibitor selectively targets secondary lymphoid organs, reduces systemic inflammation, minimizes lymphocyte infiltration into the graft, and induces immune tolerance toward the transplanted tissue. In addition, no significant toxicity was observed in vitro or in vivo. As a therapeutic agent that simultaneously modulates both T and B cell responses, we believe it holds significant promise for broader applications in transplantation immunotherapy. STATEMENT OF SIGNIFICANCE: This study presents a groundbreaking nano-immunosuppressant designed to target both T and B cells, addressing the critical challenge of acute rejection in allogeneic transplantation. By combining tacrolimus nanoparticles with IL-21 receptor antibodies, this immunosuppressant effectively suppresses Tfh cell proliferation and B cell activation, significantly reducing IgG generation. The formulation enhances tacrolimus's bioavailability, minimizes off-target toxicity, and overcomes its narrow therapeutic window. In vitro and in vivo studies show reduced lymphocyte infiltration, lower inflammatory markers, and decreased nephrotoxicity compared to conventional tacrolimus.