Cell based therapy for eye disease

Question 1

Corneal disease - incidence and secondary to?

Answer 1

2nd leading cause of vision loss

10 million across the world - in developing world mostly due to infection. In developed world due to acid and burns.

Question 2

What is the cornea?

Answer 2

Transparent, convex tissue which forms the outer shell of an eyeball. Cover 1/6 of the iris.
Transparent so allows light into the eye –> has refractile power to focus light onto the retina.

Question 3

Function of the cornea?

Answer 3

Protective barrier. Impermeable to dust, microbes and chemicals.

Question 4

Corneal innervation - relevance? Importance?

Answer 4

Most highly innervated structure in the body
Sensory nerves are abundant
Important for blink reflex, wound healing and tear production

Question 5

What would be the ideal properties of an engineered cornea and why?

Answer 5

• TRANSPARENT AND REFRACTIVE –> Biomarerial used needs to have a good tensile strength and be avascular to prevent angiogenesis but allow innervation and allow adequate mass transport

Question 6

WHICH LAYER OF THE CORNEA WOULD BE MOST AMENABLE TO TISSUE ENGINEERING?

Answer 6

Epithelial layer –> replaces every 5-7 days – could potentially harvest stem cells involved in this process?

Question 7

Corneal transplantation - what does it involve and why important?

Answer 7

Removal of cornea from donor eye and replacement at site of damage in recipient.
Sourcing of cornea difficult but logistics make it available to 7% of effected people worldwide

Question 8

KERATOPROSTHESIS - when is it needed ? What does it involve?

Answer 8

For patients with repeated failed corneal grafts
Optical polymethylmethacrylate – this is anchored in place with a titanium locking ring
Lifelong antibiotics required –> controls inflammation, infection and incidence of glaucoma

Question 9

Examples of 3 diseases impacting 3 different layers of the cornea?

Answer 9

• Epithelium –> limbel stem cell deficiency
• Stroma –> Dystrophy
• Endothelium –> Bullous keratopathy

Question 10

How does the corneal epithelium regenerate?

Answer 10

Limbal epithelial stem cells allow this.
They are located at the corneal border between the sclera and cornea. These cells reside in NICHES –> cells undergo asymmetric division and divide rapidly in the basal cell layer. One daughter cell stays in the niche and one moves out, leaves the niche and differentiates to give rise to cells in the basal layer.
Depletion of limbal stem cells –> regeneration stops and differentiated cells die off.

Question 11

Names of cell types that arise from epithelial regeneration?

Answer 11

WING CELL LAYER –> post mitotic cell

SQUAMOUS LAYER –> terminally differentiates cells

Question 12

Limbal stem cell deficiency –> types?

Answer 12

Congenital –> Anridia
External –> acid/alkali/thermal burns, pseudopemphigoid
Internal –> stevens-johnson syndrome, occular pemphigoid

Question 13

How can you treat limbal cell deficiency?

Answer 13

Limbal stem cell transplant

Question 14

Examples of other sources of cells for corneal epithelium - why are they needed? Example?

Answer 14

In cases where autologous sourcing of limbal stem cells is not possible
- mucosal stem cells –> Doesn’t scar mucosal tissue and no damage to the healthy eye. Does however increase the risk of neovascularisation of the cornea

Question 15

What can result from dysregulation of collagen in the stroma? How?

Answer 15

Loss of transparency
Injury to stroma –> keratocytes will differentiate to fibroblastic phenotype and are stimulated to produce myofibroblasts by TGFB. These myofibroblasts undergo corneal remodelling and ECM proteins are laid down in an irregular shape. Scarring occurs.

Question 16

Biomaterials approach to cornea replacement

Answer 16

• Acellular at time of implantation
• Promote cell repopulation by the host’s cells and innervation
  A range of materials used, including decellularised cornea, collagen and self-assembling peptides

Question 17

Cell based approach to cornea replacement - use of limbal stromal cells?

Answer 17

Remodel stromal scarring in model animals

Suppress fibrotic scar formation (Presence of anti inflammatory properties to prevent the recruitment of neutrophils in wound healing)

Question 18

Advs and Disavds to biomaterials approach to cornea replacement?

Answer 18

Recombinant human collagen cell-free implants
Endogenous cell recruitment
Regenerated neo-corneas stably integrated
No need for immune suppression
Nerve and stromal cell repopulation
- Visual acuity could be improved (better materials used)

Question 19

Challenges in recreating the corneal epithelium

Answer 19

Continuous replacement of the epithelial cells
Maintaining integrity as a barrier
Optical transparency

Question 20

Challenges in recreating the stroma

Answer 20

Optical transparency

High tensile strength of tissue

Question 21

Challenges for recreating the endothelium?

Answer 21

Human corneal endothelium does not regenerate!
Endothelial cells have a finite life span leading to a decrease in density with age!
At birth: 3500-4000 cells/mm2 -> only 2300 cells/mm2 by age 85
Minimum amount necessary for function is ~500 cells/mm2
Also limited proliferative ability in culture

Question 22

Problem with recreating corneas sensory innervation – what is problem with transplant patients?

Answer 22

Sensory innervation of the cornea is essential.
Transplant patients have limited innervation
FUTURE DIRECTION –> how can innervation be recapitulated? Potential use of growth factors?