Why Is Gene Therapy-Focused REGENXBIO Stock Trading Higher Today?

Earlier on Wednesday, REGENXBIO Inc RGNX reported additional interim safety and efficacy in the Phase 1/2 AFFINITY DUCHENNE trial of RGX-202 in patients with Duchenne muscular dystrophy ages 4 to11 years old.

As of February 6, 2024, RGX-202 has been well tolerated with no drug-related serious adverse events in five patients aged 4.4 to 12.1 at dose level 1 (1×1014 genome copies (GC)/kg body weight) and dose level 2 (2×1014 GC/kg body weight). 

In new data from the third patient, aged 6.6 years, who received RGX-202 at dose level 1, RGX-202 microdystrophin expression was measured to be 83.4% compared to control at three months. 

A reduction from baseline in serum creatinine kinase (CK) levels of 93% was observed at ten weeks.

All three patients, at dose level 1, who completed three-month trial assessments indicated encouraging increases in expression of RGX-202 microdystrophin and reduction from baseline in serum CK levels, supporting evidence of clinical improvement.

Elevated CK levels are associated with muscle injury and are uniformly elevated in Duchenne patients. The mean (SD) RGX-202 microdystrophin expression levels (change from baseline) at three months following RGX-202 administration were 44.4%.

REGENXIO expects to make a pivotal dose determination in mid-2024, share initial strength and functional assessment data for both dose levels, and initiate a pivotal trial in the second half of 2024.

The company plans to use RGX-202 microdystrophin expression as a surrogate endpoint to support the FDA marketing application filing using the accelerated approval pathway.

Later on Wednesday, REGENXBIO announced topline results from the Phase 1/2/3 CAMPSIITE trial of RGX-121 in patients up to 5 years old diagnosed with Mucopolysaccharidosis Type II (MPS II), also known as Hunter syndrome.

The trial met its primary endpoint with statistical significance.

In the pivotal phase, MPS II patients treated with RGX-121 achieved decreased cerebrospinal fluid levels of D2S6, a key biomarker of brain disease activity, below maximum attenuated disease levels at 16 weeks.

Patients receiving RGX-121 demonstrated an 86% median reduction in D2S6, approaching normal levels.

New long-term follow-up of patients treated with RGX-121 in the dose-finding phase also showed a high rate of patients for whom trial investigators chose to discontinue standard-of-care intravenous enzyme replacement therapy (ERT) or were allowed to remain ERT-naïve. At the pivotal dose level, 80% of patients were ERT-free at the last time point.

As of January 3, 2024, RGX-121 continues to be well tolerated in 25 patients dosed across all phases of the CAMPSIITE trial.

REGENXBIO expects to file an FDA marketing application in the second half of 2024. 

Price Action: RGNX shares are up 11.80% at $14.89 on the last check Wednesday.

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