Safety and Efficacy of Gene Transfer for Leber’s Congenital

Amaurosis

Ryan SmithOctober 20, 2008

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Rare inherited eye disease (1 in 80,000) Symptoms first occur in early infancy

◦ Irregular behavior, nystagmus Progresses through time resulting in total

blindness by 3rd or 4th decade of life No treatment (until now?...)

Described by Theodore Leber in 19th Century Amaurosis – Vision loss without any lesions Congenital – Not acquired, present at birth

Leber’s Congenital Amaurosis (LCA)

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LCA2

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Concept

CellVirus

DNA of Interest

Nucleus

Insert DNA into genome

Functional Protein

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Common human virus (80%) Not known to cause a disease

◦ Very mild immune response

Advantages◦ Integrates into the same place in

the genome nearly every time◦ Elicits no clear cytotoxic response◦ Actually shown to fight cancer

Adeno-Associated Virus (AAV)

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Disadvantages◦ Cannot hold a lot of DNA in the head◦ Efficiently packing it can require removing the

viral DNA This may cause it to not integrate in the proper

location

Adeno-associated Virus

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Identified three subjects (1 male, 2 female) age 19 to 26 with LCA2 and profound vision loss.

Put a cDNA of RPE65 gene with a chicken beta actin promoter into an AAV vector.

Injected AAV2.hRPE65v2 into subretinal tissue under general anesthesia.◦ Only in one eye (the worse based on objective

and subjective measurement) – Right in all three◦ Other used as a control

Method

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Patients’ vision and health evaluated before and after surgery

Subjective Vision tests:◦ Pupillary light reflex◦ Nystagmus testing

Objective Vision tests:◦ Visual Acuity tests◦ Goldmann visual-field examination◦ Ability to navigate an obstacle course

Method

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Injection caused localized retina detachment

Reattached 14 hours after surgery All patients showed unremarkable retinas

after surgery◦ Patient 2

developed outer lamellar cyst in fovea Also developed a macular hole

Surgery and Immediate Response

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Macular Hole

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Vector DNA only found in tear of patient 1 on day 1 after surgery

Vector was not observed to spread through the body

No humoral or cell-mediated immune response in any of the patients

Neutralizing antibody titers to AAV2 capsid observed in Patient 2, but went away over time

Post Surgery – Response to Vector

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Pupillary Light Response

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All patients showed an increased light sensitivity

The injected eye was approximately three times as sensitive to light than at baseline

The injected eye drove the light response in both eyes

In each situation the less functional eye became better than the previously better functioning eye

Pupillary Light Response

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Before and After Surgery

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Before and After Surgery cont.

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Patient 1◦ HM -> 20/1050 (P<0.001)

Patient 2◦ HM -> 20/710 (P<0.001)

Patient 3◦ 20/640 -> 20/290 (P=0.002)

Visual Field size increased Nystagmus was reduced Ability to navigate obstacle course improved

(for patient 2)

Results

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All patients showed improvement for 6 weeks, then improvement slowed (did not go away)

Reduction in nystagmus may account for improvement in uninjected eye

No apparent local or systemic effects of AAV

Discussion

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No inflammation or acute retinal toxicity Could be contraction of a preexisting

membrane stimulated by the surgery◦ Could be caused by the surgery

No reported vision loss by the patient◦ Definitely would cause vision loss to normally

functioning retina

Macular hole in patient 2

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These three patients will continue to be monitored

This was first of three experiment groups involving 9 people◦ First group got a small dose◦ Second group gets a medium dose◦ Third group gets a large dose

Possible improved response if patients are treated in childhood

Future Work

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Fin.