Figure 1.

Generation of organoids highlighting the starting cell source, method of generation, features, and challenges

(A) Tissue stem cell-derived organoids are generated from a patient biopsy, can be repeatedly passaged, and are relatively fast to expand. While multicellular, the self-renewing epithelium includes tissue-specific stem cells, and these ensure that organoids can be propagated upon dissociation and replating. Additional tissue complexity can be engineered via the inclusion of other cell types and engineering of more complex environments/scaffolds. The relevance of this will depend upon the biological question. The image shows a murine intestinal epithelial organoid stained for beta-catenin (red) and Lyzosyme (green).

(B) Pluripotent stem cell-derived organoids require the derivation of a pluripotent stem cell line. This diagram illustrates an induced pluripotent stem cell pathway commencing with a patient biopsy and requiring reprogramming. An alternative is derivation of a new line from the inner cell mass of the blastocyst. All tissue types can be generated from a PSC clone. The resulting organoids are highly multicellular and reflect the target tissue morphology. Organoid formation requires a multi-step differentiation protocol during which there is the risk of off-target cell type formation or the retention of residual undifferentiated stem cells/progenitors. The resulting tissue contains immature cell types and often cannot be passaged. Protocols are being developed to mature component cell types. The image shows a kidney organoid generated from a human iPSC control cell line stained for NEPHRIN (white), LTL (blue), E-CADHERIN (green), and GATA3 (red).