Table 2.
Description of main studies performing organoid transplantation.
| Organ | Ref. | Methods to evaluate engraftment, maturation, organoid behavior, and physiologic responses | Site of transplantation (orthotopic or ectopic) | Limitations |
|---|---|---|---|---|
| Intestine | [46] | Bile acid uptake; HS; IHC; GFP+ mouse-derived organoids | Orthotopic—omentum | Variation between different rodents or species; improvement of engraftment and intestine debridement needed |
| Intestine | [47] | MV; TRITC-dextran analysis; EGFP+ cells; IM; body weight | Orthotopic—colon | Optimization needed |
| Intestine | [38] | MV; HS; IM; qPCR; TEM; LGR5 reporter; permeability; peptide uptake | Ectopic—kidney capsule | — |
| Intestine | [48] | qPCR; HS; TEM; IM; RNAseq | Ectopic—kidney capsule | It is unclear if gene expression variation between distinct development stages has truly functional significance |
| Intestine | [49] | MV; FM of mCherry expressing organoids; HS; IM; wound closure quantification; in situ hybridization | Ectopic—kidney capsule | — |
| Intestine | [50] | iPSC lines expressing reporters for ex vivo FI; HS; live-cell imaging | Ectopic—kidney capsule/orthotopic—intestinal lumen | — |
| Intestine | [51] | Survival rate; percent of engraftment and size of organoids; IHC; HS | Orthotopic—mesentery | Impossibility to directly compare two models of transplantation; level of organoid functionalization and maturation was not evaluated |
| Pancreas | [52] | MV; IF for human origin marker; trilineage differentiation potential; HS; IF for acinar and ductal markers | Orthotopic | |
| Pancreas | [53] | Insulin IHC; human C-peptide serum measurement in PO, ES-PP, and ECM; vessel area of harvested grafts and vessel numbers | Ectopic—intraperitoneal cavity | — |
| Pancreas | [54] | Blood glucose measurements; IM; qPCR; IHC; human C-peptide serum measurements | Ectopic—under the kidney capsule | Significant islet loss in the early posttransplant period |
| Liver | [37] | MV; dextran infusion at day 3; connections' visualization among HUVECs and host vessels; quantification of human vessels; functional vessel length between human iPSC-LB x HUVEC human MSC transplants | Ectopic | — |
| Liver | [44] | ELISA; qPCR; IM; IHC | Ectopic—intraperitoneal cavity | Cell encapsulation did not completely eliminate the immune responses induced by foreign cells; fibrosis was reported. Further work is needed to develop iPS-H for clinical uses |
| Liver | [55] | MV; ELISA; IHC; IF analysis; cytochrome P450 3A4 and urea assay | Ectopic—renal subcapsule space | Further efforts are necessary to evaluate the use of SDC-LOs in clinical treatment |
| Retina | [56] | IHC; IM assays; retinal sections; expression of phototransduction and synaptic markers; ERG measurements | Orthotopic—subretinal space | Photoreceptor replacement procedures need to be optimized; risk of initiating tumor growth; proper differentiation and sorting methods aimed at specific target cell types are needed, as well as long-term studies to assess safety, and development of strategies to promote synapse formation and potential functional repair |
| Retina | [57] | IM assays; FC; GFP measurement | Orthotopic—superior and inferior hemispheres of the eye (subretinal space) | Further investigation of potential functionality of the transplanted cells |
| Retina | [58] | OKT response testing and SC electrophysiological recording; IHC for donor and retinal markers; spectral-domain OCT imaging and quantification | Orthotopic—subretinal space | Improve retina transplant lamination |
| Kidney | [59] | IHC; IF; IM assays; molecules' expression to assess maturation; VEGF injection; CM | Orthotopic—beneath the renal capsule | Ethical concern regarding the use of exogenous spinal cord cell layer; draining collection system is needed, as well as further maturation techniques to obtain a more robust collecting system and excretory function |
| Kidney | [60] | IF; nanoelectron microscopy; in vivo imaging; IM; SEM analysis; repeated intravital multiphoton imaging; TEM | Orthotopic—under renal capsule | Development of a glomerular filtration unit is needed |
| Kidney | [61] | In vivo injection of dextran–FITC into the CAM; IF analysis; IHC; TEM analysis | Ectopic—CAM of chick embryos | Development of methods to improve organoid differentiation (in vivo or in vitro), such as biomimetic approaches, is needed |
| Kidney | [62] | Whole-mount and section staining; FC | Orthotopic—under renal capsules | Formal proof using dye injection into the host circulation and examination of physiological functions in reconstituted kidneys are needed; differences between transplanted organoids and branching patterns of intrarenal arterioles from in vivo kidneys |
| Brain | [63] | GFP+ detection; neuroepithelial ventricular zone analysis; level of gliogenesis; IM; axonal outgrowth and synaptic connectivity analysis; cranial glass window; two-photon calcium imaging; electrophysiological with cross-correlation; optogenetic control | Orthotopic—retrosplenial cortex | Improvements in vascular system, neuronal circuits, and immune system are needed, as well as understanding the complex physiological context of the brain |
| Brain | [64] | Fluorescent protein; ICC; GPF expression; cerebral organoid and the graft area measurements; blood vessels and microvasculature quantification; IHC; IM; neuronal differentiation | Orthotopic—frontoparietal cortex | Technical difficulties or increased cell death before engraftment; controlling stem cell proliferation after engraftment and developing a more complex cerebral organoid are needed; ethical concerns |
| Brain | [65] | IF; IHC; behavior tests (dysfunction, mNSS); image quantification; measurement of neural connectivity and brain functionality | Orthotopic—middle cerebral artery | — |
| Brain | [66] | HS; IM; FI; cell morphology; photostimulation of grafted cells | Orthotopic—medial prefrontal cortex | — |
| Heart | [67] | Beating; voltage-sensitive dye imaging; vasculogenesis; neovascularization; IM; organization of sarcomeric structures; RT-qPCR | Ectopic—internal abdominal muscle with a basket | Maturations details (pre- and posttransplant) |
| Lung | [68] | IM | Ectopic—kidney capsule, omentum, or fat pad | Additional cues for tissue maturation are needed, as well as variability across transplants |
| Lung | [69] | IF; HS; dot blot | Ectopic—kidney capsule | Terminal maturation; branching seems random; nature of mesenchyme is unclear; in vitro culture biases to restricted cell types |
| Lung | [70] | IM; size evaluation; proliferation | Ectopic—kidney capsule | Ectopic transplantation is limited and does not resemble true regenerative potential |
| Lung | [71] | IM; pulse oximetry; qPCR | Orthotopic | Better elucidation regarding transcriptional changes and signals in AT2 transplanted organoids; better optimization of organoid transplant |
| Lung | [72] | IHC; H&E; imaging | Ectopic—epididymal blood vessels and fat pad | PEG did not support maturation over the 8 weeks; increase in immune cell recruitment in PEG scaffolds due to hydrogel swelling |
Abbreviations: CM: confocal microscopy; ERG measurements: electroretinogram; FC: flow cytometry; FI: fluorescence imaging; FITC: fluorescein isothiocyanate; FM: fluorescence microscopy; (E)GFP: (enhanced) green fluorescent protein; H&E: hematoxylin and eosin staining; HS: histology; ICC: immunocytochemistry; IF: immunofluorescence; IHC: immunohistochemistry; IM: immunostaining; LGR5: leucine-rich repeat-containing G-protein coupled receptor 5; MV: macroscopic view; OKT: optokinetic response; qPCR: quantitative polymerase chain reaction; RNAseq: RNA sequencing; SEM: scanning electron microscopy; TEM: transmission electron microscopy; TRITC: tetramethylrhodamine isothiocyanate.