According to first reaction by Denis Logunov (don't have a link on this) the open letter doesn't worth to answer. Unless The lancet asks to react.
imho: It actually shouldn't be a surprise that if the government is corrupted, the other governmental institutions most likely do not function well either. This research center is a governmental institution. And might be interested and involved in some political games as well.
[1]: https://www.thelancet.com/journals/lancet/article/PIIS0140-6...
[2]: https://cattiviscienziati.com/2020/09/07/note-of-concern/
upd: formatting