This study is supported by the National Natural Science Foundation of China (82101145) and the Beijing Natural Science Foundation (Z200014).

This study was approved by the Institutional Ethics Committee of Beijing Tongren Hospital, Capital Medical University. HESCs cell line H9 was from the WiCell Research Institute. Pre-warm the cell culture medium at room temperature (RT) for 30 min before the experiment.
1. Generation of human microglia
<ol>
	<li>Culture the hESCs in stem cell medium until the cell density reaches 80%-90%. Seed at least 1 x 106 cells in each well.</li>
	<li>Aspirate the stem cell me...

Microglia-Integrated Retinal Organoids: A Model for Studying Retinal Diseases

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(170), e62298 (2021).</li><li>Eiraku, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-organizing+optic-cup+morphogenesis+in+three-dimensional+culture.">Self-organizing optic-cup morphogenesis in three-dimensional culture.</a> Nature. 472 (7341), 51-56 (2011).</li><li>Ginhoux, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fate+mapping+analysis+reveals+that+adult+microglia+derive+from+primitive+macrophages.">Fate mapping analysis reveals that adult microglia derive from primitive macrophages.</a> Science. 330 (6005), 841-845 (2010).</li><li>Kierdorf, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microglia+emerge+from+erythromyeloid+precursors+via+pu.1-+and+irf8-dependent+pathways.">Microglia emerge from erythromyeloid precursors via pu.1- and irf8-dependent pathways.</a> Nat Neurosci. 16 (3), 273-280 (2013).</li><li>Schulz, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+lineage+of+myeloid+cells+independent+of+myb+and+hematopoietic+stem+cells.">A lineage of myeloid cells independent of myb and hematopoietic stem cells.</a> Science. 336 (6077), 86-90 (2012).</li><li>O'koren, E. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microglial+function+is+distinct+in+different+anatomical+locations+during+retinal+homeostasis+and+degeneration.">Microglial function is distinct in different anatomical locations during retinal homeostasis and degeneration.</a> Immunity. 50 (3), 723-737.e7 (2019).</li><li>Margeta, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apolipoprotein+E4+impairs+the+response+of+neurodegenerative+retinal+microglia+and+prevents+neuronal+loss+in+glaucoma.">Apolipoprotein E4 impairs the response of neurodegenerative retinal microglia and prevents neuronal loss in glaucoma.</a> Immunity. 55 (9), 1627-1644.e7 (2022).</li><li>Xu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+innate+responses+in+microglia+derived+from+retinoblastoma+patient-specific+IPSCs.">Enhanced innate responses in microglia derived from retinoblastoma patient-specific IPSCs.</a> Glia. 72 (5), 872-884 (2024).</li><li>Gosselin, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+environment-dependent+transcriptional+network+specifies+human+microglia+identity.">An environment-dependent transcriptional network specifies human microglia identity.</a> Science. 356 (6344), eaal3222 (2017).</li><li>Galatro, T. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcriptomic+analysis+of+purified+human+cortical+microglia+reveals+age-associated+changes.">Transcriptomic analysis of purified human cortical microglia reveals age-associated changes.</a> Nat Neurosci. 20 (8), 1162-1171 (2017).</li><li>Nakano, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-formation+of+optic+cups+and+storable+stratified+neural+retina+from+human+ESCs.">Self-formation of optic cups and storable stratified neural retina from human ESCs.</a> Cell Stem Cell. 10 (6), 771-785 (2012).</li><li>Kim, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=transcriptome+profiling,+and+functional+validation+of+cone-rich+human+retinal+organoids.">transcriptome profiling, and functional validation of cone-rich human retinal organoids.</a> Proc Natl Acad Sci U S A. 116 (22), 10824-10833 (2019).</li><li>Gao, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+microglia+derived+from+human+pluripotent+stem+cells+empower+retinal+organ.">Functional microglia derived from human pluripotent stem cells empower retinal organ.</a> Sci China Life Sci. 65 (6), 1057-1071 (2022).</li><li>Zhang, X., Jin, Z. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstruct+human+retinoblastoma+in+vitro.">Reconstruct human retinoblastoma in vitro.</a> J Vis Exp. (188), e62629 (2022).</li><li>Park, D. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IPS-cell-derived+microglia+promote+brain+organoid+maturation+via+cholesterol+transfer.">IPS-cell-derived microglia promote brain organoid maturation via cholesterol transfer.</a> Nature. 623 (7986), 397-405 (2023).</li><li>Usui-Ouchi, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrating+human+ipsc-derived+macrophage+progenitors+into+retinal+organoids+to+generate+a+mature+retinal+microglial+niche.">Integrating human ipsc-derived macrophage progenitors into retinal organoids to generate a mature retinal microglial niche.</a> Glia. 71 (10), 2372-2382 (2023).</li><li>Chichagova, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Incorporating+microglia-like+cells+in+human+induced+pluripotent+stem+cell-derived+retinal+organoids.">Incorporating microglia-like cells in human induced pluripotent stem cell-derived retinal organoids.</a> J Cell Mol Med. 27 (3), 435-445 (2023).</li></ol>

Due to the restricted availability of the human retina, our current comprehension of retinal inflammatory responses almost comes from animal models. To overcome this limitation, retinal organoids were differentiated. The development of retinal organoid models has been an active area of research, aiming to recapitulate the complexity of the human retina for disease modeling and therapeutic development. Several studies have reported successfully generating retinal organoids from human pluripotent stem cells<sup class="xref...

As the limited source of the human retina, the differentiation of human stem cells into three-dimensional (3D) retinal organoids represents a promising in vitro model for simulating the retina1. It contains different cell types in the retina, including photoreceptors, retinal ganglion cells, bipolar cells, M&#252;ller cells, horizontal cells, and astrocytes2. This model enables the emulation and study of both retinal development mechanisms and the pathogenesis of retinal diseases. However, due to the directional differentiation method, retinal organoids were derived from the neuroectoderm3, lacking many other cell types originating from different germ layers, such as microglia from the yolk sac and perivascular cells from the mesoderm4,5,6.
At present, many retinal diseases, such as retinitis pigmentosa7, glaucoma8, and retinoblastoma9, have been proven to be closely related to microglia within the retina. However, due to the lack of proper research models, specific mechanisms illustrating the relationship between microglia and these diseases still remain unclear. While mice have served as a favorable model for studying retinal diseases, recent studies have highlighted significant differences between mouse and human microglia in terms of lifespan, proliferation rate, and the absence of human homologous genes10,11. These findings suggested that conclusions drawn from mouse models may not be entirely reliable, emphasizing the importance of constructing human retinal organoids containing microglia.
Over the past few decades, various methods for the 3D differentiation of retinal organoids have been developed12,13. To facilitate the co-culture operation of microglia within retinal organoids, we have selected a differentiation method involving a transition from adherent to suspension culture. This approach successfully enables microglia to be incorporated into the retinal organoids, maintaining them for at least 60 days14.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acctuase</td>
			<td>Stemcell Technologies</td>
			<td>07920</td>
			<td></td>
		</tr>
		<tr>
			<td>Advanced DMEM/F12</td>
			<td>Thermo</td>
			<td>12634-010</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-CRX(M02)</td>
			<td>abnova</td>
			<td>H00001406-M02</td>
			<td>Antibody; dilution as per the manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>Anti-IBA1</td>
			<td>Abcam</td>
			<td>ab5076</td>
			<td>Antibody; dilution as per the manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>B27</td>
			<td>Life Technologies</td>
			<td>17105-041</td>
			<td></td>
		</tr>
		<tr>
			<td>Dispase (1U/mL)</td>
			<td>Stemcell Technologies</td>
			<td>07923</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM basic</td>
			<td>Gibco</td>
			<td>10566-016</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM/F12</td>
			<td>Gibco</td>
			<td>10565-042</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>Gibco</td>
			<td>C141905005BT</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Thermo</td>
			<td>15575020</td>
			<td></td>
		</tr>
		<tr>
			<td>F12</td>
			<td>Gibco</td>
			<td>11765-054</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Biological Industry</td>
			<td>04-002-1A</td>
			<td></td>
		</tr>
		<tr>
			<td>Gelatin</td>
			<td>Sigma</td>
			<td>G7041-100G</td>
			<td>Solid</td>
		</tr>
		<tr>
			<td>Glutamax</td>
			<td>Gibco</td>
			<td>35050-061</td>
			<td></td>
		</tr>
		<tr>
			<td>H9 cell line</td>
			<td>WiCell Research Institute</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>IL-3</td>
			<td>RD Systems&#160;</td>
			<td>203-IL-050</td>
			<td></td>
		</tr>
		<tr>
			<td>IL-34</td>
			<td>PeproTech</td>
			<td>200-34-50UG</td>
			<td></td>
		</tr>
		<tr>
			<td>KSR</td>
			<td>Gibco</td>
			<td>10828028</td>
			<td></td>
		</tr>
		<tr>
			<td>Matrix</td>
			<td>Corning</td>
			<td>356231</td>
			<td></td>
		</tr>
		<tr>
			<td>M-CSF</td>
			<td>RD Systems&#160;</td>
			<td>216-MC-500&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>MEM Non-essential Amino Acid Solution</td>
			<td>Sigma</td>
			<td>M7145</td>
			<td></td>
		</tr>
		<tr>
			<td>N2</td>
			<td>Life Technologies</td>
			<td>17502-048</td>
			<td></td>
		</tr>
		<tr>
			<td>Neurobasal</td>
			<td>Gibco</td>
			<td>21103-049</td>
			<td></td>
		</tr>
		<tr>
			<td>Pen/strep</td>
			<td>Gibco</td>
			<td>15140-122</td>
			<td></td>
		</tr>
		<tr>
			<td>Stem cell medium&#160;</td>
			<td>Stemcell Technologies</td>
			<td>5990</td>
			<td></td>
		</tr>
		<tr>
			<td>Taurine</td>
			<td>Sigma</td>
			<td>T-8691-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>X-ViVO</td>
			<td>LONZA</td>
			<td>04-418Q</td>
			<td></td>
		</tr>
		<tr>
			<td>Y27632</td>
			<td>Selleck</td>
			<td>S1049</td>
			<td></td>
		</tr>
		<tr>
			<td>&#946;-mercaptoethanol</td>
			<td>Life Technologies</td>
			<td>21985-023</td>
			<td></td>
		</tr>
	</tbody>
</table>

assembling retinal organoids with microglia

Due to the limited accessibility of the human retina, retinal organoids (ROs) are the best model for studying human retinal disease, which could reveal the mechanism of retinal development and the occurrence of retinal disease. Microglia (MG) are unique resident macrophages in the retina and central nervous system (CNS), serving crucial immunity functions. However, retinal organoids lack microglia since their differentiation origin is the yolk sac. The specific pathogenesis of microglia in these retinal diseases remains unclear; therefore, the establishment of a microglia-incorporated retinal organoid model turns out to be necessary. Here, we successfully constructed a co-cultured model of retinal organoids with microglia derived from human stem cells. In this article, we differentiated microglia and then co-cultured to retinal organoids in the early stage. As the incorporation of immune cells, this model provides an optimized platform for retinal disease modeling and drug screening to facilitate in-depth research on the pathogenesis and treatment of retinal and CNS-related diseases.

Generation of Human Microglia to Combine Them with Retinal Organoids for Improved Disease Modeling

Assembling Retinal Organoids with Microglia

To begin, obtain the human embryonic stem cells in the stem cell medium with a cell density of 80 to 90%After removing the spent medium, rinse the cells in each well with one milliliter of 1X DPBS. Incubate the stem cell colonies in each well with one milliliter of 0.5 millimolar EDTA for approximately five minutes at 37 degrees Celsius. Check the colony morphology to confirm that the edges are slightly curled up with loose gaps.Aspirate the EDTA, and if necessary, incubate cells at 37 degrees Celsius for another one to two minutes, but not exceeding eight minutes. Gently rinse the cells in each well with six milliliters of medium A containing six microliters of 10 millimolar ROCK inhibitor Y-27632 solution. Gently tap the bottom of the dish to help rinse the cells.After 24 hours, observe the cells under the microscope to confirm the embryo body formation. Using a 10 milliliter pipette, collect the embryo bodies into a 15 milliliter centrifugal tube and wait for the embryo bodies to settle to the bottom for five minutes. Then carefully aspirate the supernatant and resuspend the embryo bodies in six milliliters of fresh medium A.Transfer them into a new low adhesion well of a six-well plate and culture in a 37 degrees Celsius incubator.On day four, coat a 10 centimeter dish with three milliliters of 0.1%fish gelatin solution and incubate for at least one hour in a 5%carbon dioxide, 37 degrees Celsius incubator. Then remove the gelatin solution and rinse the dish once with five to six milliliters of 1X DPBS. Carefully collect the embryo bodies into a 15 milliliter centrifugal tube and wait for the embryo bodies to settle to the bottom In five minutes.Gently resuspend the embryo bodies with 15 milliliters of medium B and transfer them to the coated 10 centimeter dish. Culture in a 37 degrees Celsius, 5%carbon dioxide incubator for one week after 49 days. Centrifuge the cells at 200 x g for five minutes at room temperature.Carefully aspirate the supernatant and resuspend the cells with two milliliters of fresh medium C.Transfer into a new low adhesion well of a six-well plate. Incubate the plate in a 5%carbon dioxide, 37 degrees Celsius incubator. On day 56, replace the spent medium with two milliliters of medium C per well.Examine the plate under a microscope to identify the branched microglia adhere to the bottom of the low adhesion well. To harvest microglia for co-culturing, gently replace the medium C in each well with one milliliter Accutase and incubate at 37 degrees Celsius for three minutes. Using a five milliliter pipette, collect the microglia cells into a 15 milliliter tube and centrifuge the cells at 200 x g for five minutes at room temperature.After discarding the supernatant, suspend the microglia with one milliliter of medium E.

The procedure for generating retinal organoids is described in our previous study15. Here, we show the representative results of microglia and co-culture microglia and retinal organoids.
Here, we demonstrate each stage of microglia differentiation (Figure 1A). Day 0 represents the stage of stem cell culture. Then, the stem cells were digested and cultured for EB formation. In the initial 4 days of the process, cells will form EBs (<strong c...

Microglia are unique resident immune cells in the retina, playing crucial roles in various retinal degenerative diseases. Generating a co-culture model of retinal organoids with microglia can facilitate a better understanding of the pathogenesis and development progress of retinal diseases.

Due to the limited accessibility of the human retina, retinal organoids (ROs) are the best model for studying human retinal disease, which could reveal ...

assembling-retinal-organoids-with-microglia