Epidermolysis
Bullosa is a set of genetically inherited conditions affecting 1 in at least 17,000 of the
population. A fault in a gene causes the skin to be extremely fragile. The layers of the
skin do not adhere properly and painful widespread blisters occur very easily. Currently
there is no effective treatment. However it is widely anticipated that gene therapy will
eventually provide a cure for patients for patients suffering from EB.
This project continues the groundbreaking work on gene therapy for dystrophic EB by Dr
Hovnanian and his colleagues which has received regular funding from DebRA. The purpose of
the project is to investigate the use of human artificial chromosomes (HACs) to restore
the expression of type VII collagen in epidermal cells from patients affected by recessive
dystrophic EB.
The disease is caused by defects in the type VII collagen gene (COL7A1) which encodes
anchoring fibrils – structures which play an important role in securing the epidermis
to the underlying dermis. A majority of patients with RDEB have mutations in COL7A1
leading to the absence of the production of functional type VII collagen, resulting in the
absence of anchoring fibril formation.
It is thought that an efficient way of treating patients would be by grafting selected
areas using epidermal cells from the patient which have been modified to express normal
type VII collagen. Whilst whole body grafting is not feasible, localised treatments could
have the effect of preventing fusion of fingers and the development of skin cancer.
However, a major difficulty in the case of RDEB concerns restoring stable expression of
COL7A1 in patient cells whilst maintaining their potential to form epithelia suitable for
grafting. Integration systems (vectors) which have been used successfully in junctional EB
cannot be used because of the large size of the COL7A1 gene.
"Dr Larin and her group have spent the past six years developing human artificial
chromosomes (HACs) for the delivery and study of entire genes into cells." These
minichrimosomes are engineered to mimic normal chromosomes, i.e. to replicate, divide and
segregate cells, which should allow for their maintenance during cell division and promote
stable expression. The team will introduce a copy of the human type VII collagen gene
(which they have previously shown to be functional) into the HAC vectors. These vectors
carrying COL7A1 will be transferred into RDEB keratinocytes and cells will be tested for
the presence of minichromosomes. Positive cells will be expanded and tested for the
production of normal type VII collagen protein over a period of months.
