What response letter are you referring to? Here is imtesty's transcript on that topic. I don't see any reference to a letter.

It could be construed that "upon written confirmation from the FDA" is a letter.

Introducing myself after the fact, I've been watching RVX since 2007 and been an owner since 2013.  Got in cheap during one of their regular tankings, made the mistake at not selling at $4.  Still have fingers crossed but after BOM's failed topline, at my age I doubt I'll get full benefit from future developments.