This is the first clinical gene therapy for Charcot-Marie-Tooth type 1A (CMT1A). The neurotrophin-3 (NT-3) encoding NTF3 gene will be delivered using self-complementary adeno- associated virus (scAAV) type 1 under control of a muscle-specific tMCK promoter. In the pre- clinical studies we administered AAV1.tMCK.NTF3 to the gastrocnemius muscle of the trembler J mouse, a naturally occurring animal model for CMT1A. The muscle served as a secretory site for NT-3 and detection of circulating serum NT-3 levels. Following NT-3 delivery we documented improvements in nerve regeneration, myelination, myelinated fiber density, sciatic nerve compound muscle action potential amplitude and functional performance on rotarod testing and hindlimb grip strength. The planned clinical trial will be an open-label, dose- ascending study in which scAAV1.tMCK.NTF3 will be administered one-time by multiple intramuscular injections to gastrocnemius and tibialis anterior muscles in both legs in CMT1A subjects with PMP22 gene duplications. Nine adult CMT1A patients, 15 to 35 years of age will be enrolled into one of two cohorts in this trial. The first three subjects, Cohort 1, will be enrolled at a low-minimally effective dose (2.0 X 1012 vg/kg) distributed bilaterally between both limbs. An additional six subjects will be enrolled with a 3-fold dose escalation (6.0 X 1012 vg/kg) in Cohort 2. Post-gene transfer monitoring will include follow up visits on days 7, 14, 30, 60, 90, 120, and 3 months 6, 9, 12, 15, 18 and 24 following gene transfer. Safety is a primary endpoint for this clinical gene transfer trial. The criteria used are defined by the FDA according to ?Common Terminology Criteria for Adverse Events (CTCAE)?. A Grade 3 event is considered an SAE referring to events that prohibit normal activities requiring medical attention). Events requiring medical treatment that are unanticipated and possibly, probably or definitely related qualify as Dose Limiting Toxicity and the FDA requires notification in 15 days. Enrollment will continue upon approval of DSMB and FDA. The secondary endpoint is efficacy defined as halting of the decline in abilities measured by the CMT Pediatric Scale (CMTPedS) at 2 years post gene transfer. This 11 item scale was developed by the Inherited Neuropathies Consortium (INC). Items in the CMTPedS include the Functional Dexterity Test, Nine-hole peg test, hand grip, foot plantarflexion, and foot dorsiflexion strength using handheld myometry, pinprick and vibration sensation, balance assessment, gait assessment, long jump, and six-minute walk test. The CMTPedS is a well-tolerated assessment that takes 25 minutes or less to administer. Although the CMTPedS has only been validated for use up to 20 years of age, clinical application to our adult population (ages 15-35) is highly applicable for our clinical trial (communication with INC) because the disease worsens in the older patients. Thus for CMT1A (the mildest variant of CMT neuropathy), older patients will exhibit significantly more weakness that in the younger population and following gene delivery of scAAV.tMCK.NTF3, we anticipate a more robust difference between baseline and treatment. If there is a full safety profile for the low dose we will move to the high dose level after discussion with FDA and DSMB. In our prior gene therapy trials, the FDA has encouraged use of maximum tolerated dose to fully appreciate efficacy at a dose safe for clinical application. In summary, safety is the primary outcome measure for this clinical trial. If there is no decline in CMTPedS we will have reached the secondary endpoint defining efficacy but as stated above, if this is achieved with safety, we will move to the higher dose with regulatory approval.
The proposed research is relevant to public health because CMT1A is the commonest inherited neuromuscular disorder affecting at least 1 in 2,500. This is a slowly progressive disease without known treatment. Patients usually present with lower limb motor symptoms (difficulty walking/foot deformity) beginning in the first two decades accompanied by lower leg muscle atrophy, weakness and sensory loss and frequent foot deformity. This proposed study investigates the safety of NTF gene delivery by adeno-associated virus leading to production of human Neurotrophic Factor-3 (NT3) that promotes nerve regrowth (regeneration) in CMT1A patients. Thus, this proposed research is relevant to the NINDS mission that pertains to supporting research into the causes and treatments of musculoskeletal diseases because it will identify a potential therapy that could prevent nerve damage and restore strength to CMT1A patients.
