Case Study: Assessment of CPCB-RPE1 Retinal Patch in a Postmortem Patient Two Years Post-Implantation

Article: Stem cell-derived retinal patch is shown to survive two years post-implantation
Source: University of California, Santa Barbara
Published: March 15, 2022

CPCB-RPE1 retinal patch in implanted eye 1 year post-op (upper right)

One area of research in the treatment of degenerative diseases of the retina, such as age-related macular degeneration (AMD), is through stem cells. These stem cells are delivered through subretinal injection or through the implantation of a patch of cells beneath the retina. Researchers at UCSB report a follow-up for the California Project to Cure Blindness – Retinal Pigment Epithelium 1 (CPCB-RPE1) patch, which has been in development since 2013 and consists of a monolayer of human stem cell-derived RPE cells cultured on an ultrathin membrane of biologically inert parylene. Early results of Phase 1 clinical trials were encouraging. Of the 15 patients in the initial cohort, four showed visual improvement and five experienced stabilization of their vision. More recently, one of the patients, named "Subject 125," passed away from pneumonia, allowing the researchers the opportunity to study her donated eyes postmortem and check the progress of their patch. Staining and immunoreactivity testing confirmed that the cells were donor RPE cells and that they were well-oriented in a polarized position (like in a natural retina). Furthermore, retinal histology revealed phagocytic activity, demonstrating that the RPE stem cells were functional in their role of recycling photoreceptor outer segment discs. Importantly, after two years, the presence of the patch did not trigger signs of rejection, such as inflammation, neovascularization, or scarring, even without immunosuppressants (which were stopped two months after implantation). The research team are working on Phase 2 of the clinical trials to test the patch's effectiveness, as well as developing advances to extend the patch's shelf life through cryopreservation and composite implants that combine multiple retinal cell types to treat various stages of retinal disease.

Retinal histopathology shows active RPE implant cells by presence of RPE65 (green) (B). Donor RPE cells express Na+/K+-ATPase (red) in a largely apical distribution consistent with mature and functional RPE (C). Donor RPE of the implant suggests presence of phagosomes containing photoreceptor outer segments; yellow immunofluorescence represents red-stained phagosomes (rhodopsin) in green-stained cytoplasm (RPE65) (G).

My rating of this study: ⭐⭐

Kashani AH, Lebkowski JS, Hinton DR, et al. "Survival of an HLA-mismatched, bioengineered RPE implant in dry age-related macular degeneration." Stem Cell Reports. 17(3):P448-458. 8 March 2022.
https://doi.org/10.1016/j.stemcr.2022.01.001

Spatio-Temporal FD-FF-OCT for Imaging of the Choroid

Article: OCT studies without noise. A new method for better detection of eye diseases. 
Source: Polish Academy of Sciences (Poland)
Published: March 14, 2022

En face imaging of the choroid using FD-FF-OCT with multimode fiber

The advent of optical coherence tomography (OCT), a noninvasive, quick, and accessible imaging modality, was a major advancement in easy detection and monitoring of ocular pathology, such as those that affect the retina, optic nerve, and cornea. Similar to technology such as ultrasound, but which uses light instead of sound, in this case, near-infrared light, OCT produces high-resolution 3-dimensional images, called tomograms, or 2-dimensional images in cross-section or en face. Engineers continue to make strides in improving this technology from the initial time domain OCTs to the more recent frequency domain OCTs (e.g., swept source and spectral domain OCTs), also called Fourier domain OCTs due to the mathematical theorem that the detector uses to correlate time with different light wavelengths. Researchers in Poland are exploring the use of multimode optical fibers to reduce background noise (speckle or cross-talk) in Fourier domain OCT. Unlike classical OCTs, which use partially coherent light (coherence in time but not space), the newly developed spatio-temporal optical coherence tomography (STOC-T) is the first OCT model that combines the properties of coherence interferometry in both time and space. The reduction in image speckle is especially suitable for imaging the choroid, which provides the blood supply to most of the eyeball and is the most posterior tissue that OCT technology assesses. The challenge of imaging at increased depth (with exceptional contrast) is explored by the researchers using multimode optical fibers. A press release explains, "Until now, such devices have been used repeatedly to transmit data, but no one considered the fact that each of the spatial patterns come out of the several hundred meters of such optical fiber at different times. This time-dependence results in several hundred OCT images being captured during a single measurement; when added together the composite pattern reduces unwanted effects such as speckle noise in totally passive way." Using FD-FF-OCT with the multimode optical fibers (300m length), the researchers were able to produce "noiseless" images of the choroid to the choroidal-scleral junction and high-contrast en face images of the choroid. Limitations to the technology at this point are restricted axial range and substantial data processing.

My rating of this study: ⭐⭐⭐⭐

Auksorius E, Borycki D, Wegrzyn P, et al. "Multimode fiber as a tool to reduce cross talk in Fourier-domain full-field optical coherence tomography." Optics Letters.  47(4):838-841. 2022.   https://doi.org/10.1364/OL.449498

Associations Between Retinal Layers and the Brain

Article: The Retina as a Possible Biomarker for Reduced Brain Matter
Source: University of Bonn (Germany)
Published: March 16, 2022
Article: The Retina as a Possible Biomarker for Reduced Brain Matter
Source: German Center for Neurodegenerative Diseases (Germany)
Published: March 15, 2022

SD-OCT of the retina

The retina is an extension of the brain and as such shares many neurological characteristics of brain matter. Researchers in Germany further explored the similarities between the two tissues as a means of using retinal imaging to assess potential biomarkers of brain atrophy. Called the Rhineland Study, this study involved almost 2,872 subjects who participated in retinal scans via spectral domain optical coherence tomography (SD-OCT) and brain scans via magnetic resonance imaging (MRI). Compared to techniques used in earlier studies, SD-OCT is a newer retinal imaging technology and allowed for more detailed imaging of all the retinal layers. The researchers then used computer software to compare the thickness and volume of the various retinal layers with the thickness and volume of brain structures. They found a close positive association between the volume (and microstructural integrity, as assessed by fractional anisotropy) of the inner retinal layers and the so-called white matter of the brain. By contrast, the outer retinal layers were associated with the brain's gray matter. These associations were particularly pronounced in the occipital lobe, where visual processing takes place, and, interestingly, also with volume of the hippocampus where memory is formed and is an area often affected in dementia. Because retinal scans are noninvasive, quick, and relatively accessible, they could be an easy method to detect and monitor brain atrophy and the progression of neurological degenerative diseases. The researchers next plan to expand their studies to larger patient groups and over longer periods to verify the results in clinical settings.

My rating of this study: ⭐⭐

Mauschitz MM, Lohner V, Koch A, et al. "Retinal layer assessments as potential biomarkers for brain atrophy in the Rhineland Study." Scientific Reports.  12:2757. 17 February 2022. https://doi.org/10.1038/s41598-022-06821-4 

Hybrid Müller Glia and Adult Stem Cells "Awaken" Potential for Mammalian Retinal Regeneration

Article: Cell fusion ‘awakens’ regenerative potential of human retina
Source: Centre for Genomic Regulation (Spain)
Published: March 15, 2022

Immunostaining of human retinal organoids microinjected with hybrids.
Cell fusion is enhanced by activation of the Wnt/beta-catenin pathway (top).  

Müller glia are support cells in the retina where they perform a variety of functions, from channeling light to mitigating cellular stress. The Müller glia of lower vertebrates, such as salamanders and fish, have the capacity to regenerate neural tissue—that is, engage in mitosis—in response to retinal damage; however, this capacity is lost in mammalian retinas and visual impairment due to retinal damage is permanent. Researchers in Spain wanted to explore the regenerative potential of these glial cells combined with stem cells as a therapeutic opportunity in humans, noting that cell fusion events, although rare, also occur in human tissues of the liver, brain, and gastrointestinal tract. In the study, the team of scientists conducted in vitro fusion of Müller glia and cells derived from adult human mesenchymal and hematopoietic stem and progenitor cells (adipose and bone marrow stem cells). The resulting hybrid cells were then injected into a retinal organoid model, where they were observed to successfully engraft into the tissue and differentiate into cells that closely resemble retinal ganglion cells. The authors write, importantly, "cell fusion efficiency is enhanced by inflammatory signals [from the retina] and that the activation of the Wnt/beta-catenin pathway increases differentiation of the hybrids into neuronal-like cells." The findings show that Müller glia retain regenerative activity, and that hybrids between Müller glia and adult stem cells might be a promising stem cell-mediated therapy for human retina regeneration that could be used to treat visual impairment. The researchers next plan to investigate why the hybrid cells, with four complete sets of chromosomes, do not result in chromosomal instability or cancer development; they hypothesize that cells of the retina have a mechanism that acts as a genetic reservoir (similar to those found in the human liver) to regulate chromosome segregation. 

My rating of this study: ⭐⭐

Bonilla-Pons SA, Nakagawa S, Bahima EG, et al. "Müller glia fused with adult stem cells undergo neural differentiation in human retinal models." eBioMedicine.  77:103914. 1 March 2022. https://doi.org/10.1016/j.ebiom.2022.103914 

Regenerative Treatment of Diabetic Retinal Microvascular Pathology Using Stem Cells

Article: Study shows human induced pluripotent stem cells improve visual acuity, vascular health
Source: Indiana University School of Medicine
Published: March 10, 2022

Vascular density assessment in retinas of diabetic mice injected with
either saline or KNA cells. All parameters indicate a restoration
of retinal vascularity with KNA cell treatment compared to saline
control injection. Notably, blood vessel growth was robust
without giving rise to teratomas.

According to the Center for Disease Control and Prevention, more than 37 million people in the U.S. have diabetes, with complications affecting the microvasculature of organs such as the kidneys and eyes and of peripheral nerves. A team of researchers conducted a multi-site study investigating the use of human induced pluripotent stem cells (hiPSCs) as a regenerative approach in the treatment of microvascular diseases, such as in diabetic retinopathy. In this pre-clinical study, investigators genetically reprogrammed diabetic and non-diabetic peripheral blood cells into hiPSCs and matured the cells into a specific mesoderm subset, KNA+ mesoderm, that had high clonal proliferative potential and specification into cells similar to endothelial colony forming cells (ECFC). These stem cells were delivered by intravitreal injection to mice with type 2 diabetic retinal dysfunction. Results showed that the ECFCs formed functional blood vessels in vivo, effectively increasing vascular density and perfusion to retinal tissue. Electroretinography and optokinetic nystagmus vision testing showed significant improvement in neural retinal response and visual acuity, respectively. They hypothesized that the hiPSC-derived vascular reparative cells may serve as a source of endothelial precursors. The authors report, "Transcriptomic analysis showed that differentiation of hiPSCs derived from diabetics into KNA+ cells was sufficient to change baseline differences in gene expression caused by the diabetic status and reprogram diabetic cells to a pattern similar to KNA+ cells derived from nondiabetic hiPSCs." That is, these findings show a pre-clinical proof-of-concept that KNA+ cells can be used to restore perfusion and correct vascular dysfunction.

My rating of this study: ⭐⭐⭐

Gil C, Chakraborty D, Vieira CP, et al. "Specific mesoderm subset derived from human pluripotent stem cells ameliorates microvascular pathology in type 2 diabetic mice." Science Advances.  8(9). 4 March 2022. https://www.science.org/doi/10.1126/sciadv.abm5559

Intracrine Activity in Meibomian Gland Dysfunction and Treatment with NAD Precursor, in Mice

Article: Mutant mice shed no tears
Source: Kyoto University (Japan)
Published: March 10, 2022

The most common cause of dry eyes is age-associated dysfunction of the meibomian glands, which are glands in the eyelids and produce the lipid layer of the tear film that prevents tear evaporation. This age-related dysfunction is thought to be due to a decline of the sex steroid hormones testosterone and estrogen, produced by the enzyme 3-hydroxyl-steroid dehydrogenase (3-HSD). Though the sex steroid hormones are classically associated with the endocrine organs, and travel throughout the body through the bloodstream, a new study by researchers in Japan using a genetically modified mouse model indicate that the meibomian glands depend on a more recently discovered intracrine system in which the hormone acts in the tissue where it is synthesized. Lead author of the study states, "Indeed, disturbed intracrine 3-HSD enzyme activity in mutant mice was found to result in atrophy of the gland, which further led to the disorder." The enzyme 3-HSD is of particular interest for its circadian activity, which regulates behaviors such as sleep, menstrual cycles, and hormone secretion. In the meibomian glands, 3-HSD is regulated by cofactor nicotinamide adenine dinucleotide (NAD), a coenzyme found in every cell and also sold as an over-the-counter supplement. When nicotinamide mononucleotide (NMN), a NAD precursor, is administered topically to mice before sleep, when 3-HSD activity peaks, it elevated the amount of NAD needed to reboot 3-HSD activity. Periodic administration of NMN in mice 4 times nightly over 90 days reduced atrophy of the meibomian glands, thereby alleviating dryness of the eyes. The researchers emphasize NMN's benefits in not only being a local therapy, but also a non-steroidal agent, which avoids the adverse or unanticipated effects of hormones.

Mouse eyes treated with vehicle (left eye) and NAD precursor nicotinamide riboside or nicotinamide mononucleotide (right eye); arrows indicate areas of epithelial defect in eyes not treated with active agent 

My rating of this study: ⭐⭐

Sasaki L, Hamada Y, Yarimizu D, et al. "Intracrine activity involving NAD-dependent circadian steroidogenic activity governs age-associated meibomian gland dysfunction." Nature Aging.  2:105-114. 10 February 2022. https://doi.org/10.1038/s43587-021-00167-8 

White Sclera Enhances Eye Gaze Communication

Article: The language of the eyes
Source: University of Konstanz (Germany)
Published: March 8, 2022

A uniform white sclera in humans
enhances visibility of eye gaze direction

The sclera, the tough protective layer that provides structure to the shape of the eyeball, is white in humans. But this is not uniformly the case in animals, even among primates such as chimpanzees, humans' closest relatives. Researchers studying the significance of the sclera's color discovered that the white of the eye contributes decisively to the visibility of eye gaze direction through its basic color properties. In the experiments, humans and chimpanzees—the cross-species comparison enabling novel differentiation among competing hypotheses, the researchers note—were presented with images on a computer screen, varied in brightness and size of stimulus against varied background shading and distancing ("visually challenging conditions"), and tasked with distinguishing gaze direction for both groups. They found that both humans and chimpanzees distinguished eye-gaze directions of humans better than those of chimpanzees, especially in the visually challenging conditions. Furthermore, when the contrast polarity of the eyes of chimpanzees was reversed compared to what is normal, that is, showing a white sclera and a darker iris, both humans and chimpanzees were able to distinguish gaze direction of the chimpanzees better, indicating that uniform whiteness of the sclera facilitates the visibility of eye gaze direction even across species. Sometimes taken for granted in daily life, the ability to understand the language of the eyes is something we rely on in social activities and when interacting with one another face to face, where eye-gaze signaling is used for communication such as joint attention. First author of the study comments, "We owe this to the formation of the whites of the eye. Humans might have evolved this distinguishing eye feature for conspecific communication...In doing so, humans have probably evolved a unique communicative style critical for their hallmark social activities." 

Human and chimpanzee stimulus eyes in direct and averted (20°) gaze
in normal and reversed contrast polarities, varied in brightness and size

My rating of this study: ⭐

Kano F, Kawaguchi Y and Hanling Y. "Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees." eLife.  8 March 2022. https://doi.org/10.7554/eLife.74086