Rajendra Kumar-Singh
Ophthalmology
Adjunct Assistant Professor

Contribution to Society

Vision is one of the most valued of our senses. Many inherited diseases of the retina cause an untreatable loss of vision. The focus of our laboratory is to develop therapies for hereditary disorders of the retina. One type of retinal degeneration caused frequently by mutations in photoreceptor genes is known as Retinitis Pigmentosa (RP). RP affects approximately 1 in every 3,000 newborns worldwide, making it one of the most common causes of genetic blindness. Knowledge gained during the development of therapies for RP will also allow us to treat some more common diseases of the retina such as Macular Degeneration, which affects approximately 1 in every 3 individuals over the age of 70. Our research has implications for the treatment of RP and MD patients. Since photoreceptors are specialized neurons, we anticipate that vector development studies in our lab will also benefit the development of therapies for diseases of the Central Nervous System.

Research Summary

Some forms of RP in humans, dogs and mice have been associated with mutations in the gene encoding the β subunit of cyclic GMP phosphodiesterase (β-PDE), an essential component of visual transduction. The genetic defect in one mouse model of RP known as rd has been characterized in detail at the molecular level. We are developing methods of delivering normal versions of the b-PDE gene to the rd retina with the objective of preventing retinal degeneration. One very powerful method to deliver genes to the retina is to use the natural ability of viruses (also known as vectors) to enter human cells and deposit their genetic material. We have developed a class of vectors that have almost no viral genetic material, known as encapsidated adenovirus minichromosomes (EAM), now also termed "gutted" or "helper-dependent" vectors. We have demonstrated the use of these EAMs in rescuing photoreceptor degeneration in the rd mouse. Although successful, the therapy is transient and our focus is now shifted in attempting long term rescue of the rd retina.

Our current studies are aimed at developing vectors that will transduce photoreceptors more efficiently than currently available vectors. We are improving photoreceptor transduction by adenovirus pseudotyping and improving therapeutic effect by the use of protein transduction domains derived from viral proteins such as HSV VP22 and HIV TAT. When combined, these improved methods will allow for a powerful way to deliver genes to diseased photoreceptors.

Recent Publications

Kumar-Singh, R., and Chamberlain, J.S., Encapsidated Adenovirus Minichromosomes allow efficient delivery and expression of a 14Kb dystrophin cDNA to muscle cells. Human Molecular Genetics 5:913-921, 1996.

Hauser, M.A., Amalfitano A., Kumar-Singh R., Hauschka S.D., Chamberlain J.S. Improved adenoviral vectors for gene therapy of Duchenne muscular dystrophy. Neuromuscular Disorders 7(5):277-283, 1997.

Kumar-Singh, R., and Farber, D.B. Encapsidated adenovirus minichromosome- mediated delivery of genes to the retina: application to the rescue of photoreceptor degeneration. Human Molecular Genetics 7(12):1893-1900, 1998.

Kumar-Singh, R., Tran, K., Yamashita, C. and Farber, D.B. Construction and use of encapsidated adenovirus minichromosomes (gutted vectors) for gene delivery to photoreceptors. Methods in Enzymology 316; 724-743, 2000.

Lab Website