What happened

Shares of Apellis Pharmaceuticals (NASDAQ:APLS), a clinical-stage biopharmaceutical company, fell on Thursday after Regeneron (NASDAQ:REGN) released top-line data for pozelimab. Investors worried that Apellis' lead candidate APL-2 won't be able to compete and hammered the stock 13.6% lower on Thursday.

So what 

Today, Regeneron announced successful results for pozelimab, an experimental treatment for a rare blood disorder called paroxysmal nocturnal hemoglobinuria (PNH). After eight weeks of treatment with the injectible antibody, levels of lactate dehydrogenase (LDH) fell to normal levels for all six patients treated. 

The back of a frustrated man with his hands on his head, looking at a sinking stock chart.

Image source: Getty Images.

In September, Apellis began a phase 3 study with APL-2 and PNH patients following a successful six-patient phase 2 trial. In phase 2, Apellis' candidate also lowered LDH to normal levels, although not quite as low as scores that Regeneron posted for pozelimab.

Now what

Investors should know that APL-2 targets a different part of the immune system than pozelimab. It's still unclear which approach is better after single-arm studies with small groups from different populations, but we can say that commercial success is far from guaranteed.

If the PNH indication doesn't work out, though, APL-02 is also in a phase 3 trial with patients losing their sight to geographic atrophy secondary to age-related macular edema (GA). Around 1 million Americans are losing their sight to GA and there aren't any available treatments to prevent its progression.