TGFB1 and myelofibrosis: Given the fibrosis observed following treatment with TGFβ, and the current lack of adequate in vitro and in vivo systems for modeling cancer-induced bone marrow fibrosis, we first seeded the organoids with cells from healthy donors and patients with myelofibrosis, and tested the impact of engraftment on the remodeling of the bone marrow organoid “niche.”