Types of organoids. (A) Tissue fragments and explants are generated from native tissue with little disruption to cell and ECM organization and no intermediate period in 2D culture. This limits total sample size and manipulability but is unmatched in mimicking the original tissue. (B) Reconstituted organoids are assembled in vitro from cultured or sorted cells. This permits cell expansion and modular assembly of components. However, some subpopulations or phenotypes, such as senescent and hormone-responsive cells, may be lost during culture. (C) Stem cell–derived organoids are differentiated from multipotent adult tissue stem cells or PSCs under the appropriate differentiation and maintenance conditions. PSCs specifically can generate rare tissue and cell types, but have limited maturity and lose the hallmarks of aging.