The human retina is a highly complex system composed of multiple layers with different types of cells that ensure that light stimuli are absorbed, processed and transmitted. To date, all attempts across the globe to grow a functional retina have remained unsuccessful. 

Cameron Cowan, Magdalena Renner and their team in Basel have been consistently working towards this target for several years and they have managed to culture a “retinal organoid”, a replica of the human retina. This is composed of multiple layers and reacts to light in the same fashion as the “original”.  

The researchers used skin or blood samples from patients to generate the retinal organoids. They initially transformed the cells from these samples into a stem cell-like condition and then cultured the retinal organoids from these stem cells. After 38 weeks, these exhibited many of the same types of cells as the retina in an adult human. However, in order to actually be able to compare the new cultures with the “original”, the researchers were once again stepping into the unknown. They developed a technique that, for the first time, allowed human retinas from deceased people to be preserved in a functional and light-sensitive condition over a lengthy period. Furthermore, they generated a comprehensive atlas that can be used to compare the gene patterns in the cells of the organoids with those in human retinas. 

Using the new mini organs, the researchers also demonstrated that genes associated with specific retinal diseases are expressed in the same cell types as in adult retina validating retinal organoids as a new tool to study retinal degeneration. There is the hope that individually tailored treatments can be developed in the future as retinal organoids are created from skin biopsies or blood from individual patients. This could provide a decisive advantage in research into retinal diseases, some of which result in blindness.

Cell Types of the Human Retina and Its Organoids at Single-Cell Resolution. Cameron S Cowan*, Magdalena Renner*, Martina De Gennaro, Brigitte Gross-Scherf, David Goldblum, Yanyan Hou, Martin Munz, Tiago M Rodrigues, Jacek Krol, Tamas Szikra, Rachel Cuttat, Annick Waldt, Panagiotis Papasaikas, Roland Diggelmann, Claudia P Patino-Alvarez, Patricia Galliker, Stefan E Spirig, Dinko Pavlinic, Nadine Gerber-Hollbach, Sven Schuierer, Aldin Srdanovic, Marton Balogh, Riccardo Panero, Akos Kusnyerik, Arnold Szabo, Michael B Stadler, Selim Orgül, Simone Picelli, Pascal W Hasler, Andreas Hierlemann, Hendrik P N Scholl, Guglielmo Roma, Florian Nigsch, Botond Roska. 
Cell. 2020 Sep 17; 182(6):1623-1640.e34. doi: 10.1016/j.cell.2020.08.013. 
*These authors contributed equally to this work.