The Exchange is a collection of casual podcast discussions featuring key opinion leaders in our community. If you would like to participate or would like to recommend a podcast guest please email us at bd@biomere.com.
In this two-part webinar, Dr. Shoichet discusses two methods of cell regeneration in the central nervous system. The first method involves cell transplantation in the retina, and the second focuses on stimulating endogenous stem cells to replace neurons after a stroke.
For the retinal approach, photoreceptor (PR) and retinal pigment epithelium (RPE) cells suspended in a hyaluronan–methylcellulose hydrogel are injected subretinally into two mouse models of blindness. Delivering both PR and RPE cells in the hydrogel improves vision, prevents cell clumping, and reduces inflammation. This strategy could potentially be applied to treat age-related macular degeneration or retinitis pigmentosa.
In the second approach, Dr. Shoichet describes a less invasive method to stimulate endogenous stem cells to differentiate into neurons following stroke damage. An osmotic minipump delivers therapeutics such as cyclosporine A and erythropoietin in the hydrogel to repair damaged cells and promote tissue regeneration. Delivering known stem cell differentiators in the hydrogel has been shown to enhance tissue regeneration and restore function in mouse and rat stroke models.
In this two-part webinar, Dr. Shoichet discusses two methods of cell regeneration in the central nervous system. The first method involves cell transplantation in the retina, and the second focuses on stimulating endogenous stem cells to replace neurons after a stroke.
For the retinal approach, photoreceptor (PR) and retinal pigment epithelium (RPE) cells suspended in a hyaluronan–methylcellulose hydrogel are injected subretinally into two mouse models of blindness. Delivering both PR and RPE cells in the hydrogel improves vision, prevents cell clumping, and reduces inflammation. This strategy could potentially be applied to treat age-related macular degeneration or retinitis pigmentosa.
In the second approach, Dr. Shoichet describes a less invasive method to stimulate endogenous stem cells to differentiate into neurons following stroke damage. An osmotic minipump delivers therapeutics such as cyclosporine A and erythropoietin in the hydrogel to repair damaged cells and promote tissue regeneration. Delivering known stem cell differentiators in the hydrogel has been shown to enhance tissue regeneration and restore function in mouse and rat stroke models.
In this webinar, Dr. Do presents novel data on electrical signal propagation through cone cells in the fovea of primates. Unlike other neuron types, foveal cones show minimal signal loss, and several biophysical parameters contributing to this high-fidelity signal propagation are identified. The experimental results contrast with computational models based solely on tissue anatomy, emphasizing the importance of incorporating both anatomical and physiological factors to fully understand tissue function.
In this webinar, Dr. Do describes the structure and function of intrinsically photosensitive retinal ganglion cells (ipRGCs) in mouse and primate eyes, focusing on how these cells are tuned to specific light intensities. His work demonstrates a significant depolarization block that occurs as light intensity increases, highlighting the precise firing of ipRGCs needed for rapid decoding of irradiance.
In this basic science presentation, Dr. Do discusses the key role of intrinsically photosensitive retinal ganglion cells (ipRGCs) in processing light signals and explains the tri-stable states of the melanopsin pigment, which are essential for circadian clock function and nonimage vision. Image vision enables object recognition, while nonimage vision senses overall light intensity to regulate circadian rhythms, sleep, pupil response, and hormonal activity. Rods and cones express visual pigments that trigger downstream signaling in response to light, producing an electrical signal that is transmitted to retinal ganglion cells through the optic nerve.
ipRGCs process light signals either through rods and cones or independently of them, transmitting signals that influence pupil dilation, circadian rhythm, melatonin production, photophobia, and pain responses. Ablation of ipRGCs removes most light-responsive functions. Humans and primates have the highest visual acuity and contrast resolution due to the fovea, which is unique to these species. Located in the center of the macula, the fovea has a high density of cones that degenerate in age-related macular degeneration (AMD). This degeneration suggests that replacing foveal cones could be a potential approach for cell therapies targeting AMD.
In the second presentation on nonclinical ophthalmology studies, Dr. Milton focuses primarily on in vivo gene therapies. Gene therapies for ocular diseases typically use AAVs delivered intravitreally or subretinally. Cell therapies can be encapsulated in a device for intravitreal implantation, but this approach has had limited success.
Key CMC considerations include dose concentration, low endotoxin levels, minimal empty capsids, minimal particulate matter, and ensuring the transgene is compatible with the viral vector delivery system. The FDA has published guidance for inherited retinal diseases that can also be applied to other ocular diseases. The overall non-clinical plan should be lean, follow the 3Rs guidelines, and avoid excessive caution.
Dr. Milton also presents a case study evaluating an AAV8 vector carrying the RLBP1 transgene, which highlights the key considerations for nonclinical studies.
In the first part of the session on nonclinical ophthalmology studies, Dr. Sasseville focuses on key considerations for low molecular weight therapies. Age-related macular degeneration (AMD) has three discrete stages: early (often asymptomatic), intermediate, and late. About 10% of late-stage AMD cases develop into either wet (neovascularized) or dry AMD. Wet AMD is multi-factorial, and treatments vary depending on the underlying causes, while there are currently no approved therapies for dry AMD. Dry eye disease is also multi-factorial, with multiple available treatments. Another group of vision loss–causing conditions is inherited retinal diseases, with more than 250 implicated genes.
There are multiple routes of administration for ocular therapies. Intravitreal administration is the most common overall, while intracameral delivery is preferred for low molecular weight therapies. Other routes for these therapies include topical, subconjunctival, and suprachoroidal administration. Subretinal delivery is typically used for gene therapies.
Preclinical safety studies for ocular therapies generally involve four key elements: identifying a relevant animal model species, selecting routes of administration, determining study duration, and setting dosing frequency. Endpoints in ocular studies focus on structural and functional assessments, including examination of eye structures, measurement of retinal thickness and intraocular pressure, and imaging-based endpoints.
Ocular toxicity from systemic delivery is uncommon but can be a significant hurdle if it occurs, as side effects may include cataracts, edema, degeneration, and neuritis. Localized ocular toxicity is more common and requires careful analysis to identify and understand the causative factors.
In this webinar, Jeff discusses Chameleon’s EVADER™ gene therapy platform, which is designed to evade the immune system, overcome the neutralizing immune response, expand the treatable patient population, and enable multiple dosing. The platform encapsulates AAVs in a lipid bilayer with specific immune cell inhibitors and has demonstrated increased infectivity, delivery, and transgene expression in preclinical models. The EVADER™ platform is currently being used to develop gene therapies for multiple diseases in collaboration with biotech and pharmaceutical companies.
In this webinar, Dr. Muñoz-Alía explains how the measles virus can be engineered to target tumors as an oncolytic virus (OV). One of the main challenges in using the measles virus as an OV is the presence of neutralizing antibodies resulting from childhood measles vaccination.
To effectively direct the measles virus to specific tumors, viral envelope proteins from the canine distemper virus are inserted to replace the measles virus membrane fusion proteins. This gene therapy approach demonstrates efficient transduction of tumor cells while avoiding the neutralizing antibody response in myeloma and ovarian cancer animal models.
In this webinar, Dr. Gao presents a comprehensive overview of the key principles, history, current challenges, and future directions of human gene therapy, with a focus on AAV gene therapy for rare diseases. The session also highlights AAV capsid engineering to modulate target tissue tropism and biodistribution, with examples of using AAV for gene replacement, gene addition, gene silencing, and in vivo gene editing in preclinical studies.
Additionally, Dr. Gao reviews strategies to overcome immunological barriers to enhance the efficacy of AAV-mediated gene therapy.
In this webinar, Dr. Maguire discusses technological innovations in adeno-associated virus (AAV) vectors designed to address challenges in delivering AAV vectors to target organs and avoiding immune detection. He focuses on two approaches for improving AAV gene delivery to the central nervous system (CNS).
The first approach involves screening AAV capsid libraries in both in vitro and in vivo models to identify and validate clones with enhanced CNS delivery. The second approach uses extracellular vesicles or microvesicles to improve the efficiency of AAV delivery to multiple organs, including the brain, eye, liver, and inner ear.
In this presentation, Dr. Gao provides an overview of current trends in gene therapy, beginning with definitions of in vivo gene therapies and ex vivo modification of patient cells. Gene therapy includes four major approaches: gene replacement, gene therapy, gene addition, and gene activation.
An example of successful gene replacement is Canavan’s disease, where a gene therapy approach was developed to systemically deliver AAV9 across the blood-brain barrier (BBB) to deliver a transgene encoding the missing enzyme needed to break down N-acetyl aspartate in neuronal cell mitochondria. A clinical trial involving a single two-year-old child with Canavan’s disease demonstrated high efficacy, a good safety profile, and most importantly, the child is alive today with a good quality of life.
Nonhuman primates (NHPs) offer more translational value than rodents for gene therapy when using multiple AAV serotypes, including AAV3, AAV8, and AAV9. NHPs are primarily used for safety studies; however, because disease state NHP models are lacking, efficacy studies are not typically conducted.
RNA-based therapies can be broadly classified as RNA editing, RNA silencing, and readthrough therapy to reverse premature translational termination. AAV-based therapies can address premature translation termination by delivering suppressor tRNAs. Suppressor tRNA differs from normal tRNA by one nucleotide, and a library of suppressor tRNAs can be developed for different amino acids. It is important to note that efficacy is typically determined by delivery efficiency rather than tRNA binding.
