Developing a novel thymus organoid as a cell therapy to correct autoimmunities

Abstract

Background & Aim Complete athymia results in severe immune deficiency, as the thymus is the organ responsible for equipping the body with functional and diverse T cells. Thymus epithelial cells (TECs) are critically important in the selection and education of effective T cells that do not aberrantly attack self-antigen. Thymus transplants are an investigational therapy at Duke for young patients born with athymia, most often seen in complete DiGeorge Anomaly (cDGA). MHC-unmatched donor thymus tissue is collected from infants that undergo elective cardiac surgery for treatment of congenital heart disease, cultured for 12-21 days, then implanted into the quadriceps muscle of a cDGA patient. These transplants save lives in an otherwise untreatable disease. However, the newly made immune system is not perfect, demonstrated by blunted T cell numbers and a high incidence of autoimmunities such as autoimmune hemolytic anemia in these patients. Our lab replicated clinical thymus transplants in an athymic nude mouse system with the goal of first understanding the mechanisms of immune reconstitution in order to improve T cell output and limit post-transplant immune dysregulation. Methods, Results & Conclusion Nude mice transplanted with cultured, neonatal, MHC-mismatched donor thymus achieve CD3+ T cell reconstitution at 4.86% (± 0.59 SEM) of recipient CD45+ ten weeks post-transplant compared to 38.6% (± 2.75 SEM) in wildtype mice and show a phenotypic skew to memory T cells over naive T cells. We also have data showing that recipient antigen presenting cells (APCs) enter donor thymus tissue and are responsible for the education of recipient T cells. Due to the lack of tissue-specific antigen expression in APCs that is normal in thymus epithelial cells, we hypothesized that this abnormal education may be responsible for the T cell abnormalities. We set out to create a transplantable thymus organoid system to replace donor tissue and mimic “normal” T cell thymic education to increase T cell numbers, T cell receptor diversity, and limit autoimmunity. Our data demonstrate T cell reconstitution in athymic mice as early as 2 weeks after transplantation with a microporous annealed particle (MAP) scaffold system seeded with stromal cells. This proposed system of thymus organoids may be therapeutically beneficial for many other disorders that are linked with thymic dysfunction or loss of immune tolerance, such as in aging or multiple sclerosis.