Table 1.

Overview of representative human organoids.

Organ types	Available cell types	Characteristics/function	Limitations
Brain	Neural stem/progenitor cells, radial glia, neurons, astrocytes, and oligodendrocytes[71,135,136]	Modeling development of specific brain regions, cortical layering, early neurogenesis, synapse formation, and spontaneous electrical activity	Size limit due to oxygen and nutrient diffusion constraints; lack of microvascular differentiation; absence of microglial cells; can not replicate complex neural connections and projection; lack of higher-order neural network functions
Spinal cord	Motor neurons, interneurons, progenitor cells, astrocytes, and oligodendrocytes[137–139]	Modeling the early development of the neural tube, axon growth, neurotransmission of sensory inputs and motor outputs	Limited maturation of spinal structures; incomplete myelination; lack of peripheral tissue integration; absence of immune response
Retina	Photoreceptors, bipolar, horizontal, amacrine, ganglion cells, and Müller cells[140–142]	Modeling simulating light signal processing	Lack of vascularization; limited optic nerve formation and incomplete retinal structure; lack a specific cone cell-rich region similar to the human central fovea
Heart	Cardiomyocytes, cardiac fibroblasts, endothelial cells, epicardial cells, and endocardial cells[143–145]	Modeling functional characteristics such as contractility, cavity formation, action potential propagation, and forming vascular-like structures	Incomplete heart chamber formation; limited electrical activity; insufficient integration with vasculature and lack of true perfusion through blood vessels
Liver	Hepatocytes, cholangiocytes, Kupffer cells, hepatic stellate cells, and liver sinusoidal endothelial cells[146–148]	Modeling the production of albumin and the secretion of bile acids and accumulating glycogen and producing albumin and bile acids	Limited bile duct formation and immune interactions; lack of full functional vascular network; lack of full metabolic complexity
Kidney	Multiple lineages such as nephron progenitors, ureteric buds, stromal progenitors, and vascular endothelial cells[21,73,149]	Modeling key renal functions such as glomerular filtration and tubular reabsorption	Lack of full functional vascular network and filtration systems; lack of distal nephrons (distal renal tubules and loops of Henle); insufficient maturation of the collecting ducts; limited nephron complexity
Lung	Basal cells, club cells, alveolar type 2 epithelial cells[150–152]	Replicating the functional capabilities of basal cells in self-renewal and differentiation, club cells in mucin production for airway protection, and alveolar type 2 epithelial cells in differentiating into AEC1s for gas exchange	Lack of terminal cellular maturity, particularly mature alveolar lineages, and progressive branching formation; absence of vascularization and immune cells
Pancreas	Islet cells, ductal cells, and acinar cells, which can differentiate into various pancreatic cell types, including β-cells, under specific culture conditions[153–155]	Replicating insulin secretion and endocrine function	Lack of islet maturation; low differentiation efficiency and long-term instability; lack of a complete vascular system and interactions with other pancreatic cell types and non-pancreatic tissues
Intestine	Intestinal stem cells, epithelial cells, including absorptive enterocytes and secretory cells like goblet, Paneth, and enteroendocrine cells[156–158]	Modeling the natural polarity and functionality of the intestinal epithelium	Lack of the full complement of the in vivo intestinal environment, including a complete immune cell community, neural cells, and microbiota
Blood vessels	Endothelial cells, pericytes, and vascular smooth muscle cells[159–161]	Modeling angiogenesis, vascular maturation, and the interaction between endothelial cells and pericytes; blood vessels can be formed within 2–3 weeks	Limited vessel maturation and connection structures; lack of perfusable capillary networks; insufficient integration with other tissues or organoids for perfusion

AEC1s: alveolar epithelial type 1 cells.