It depends on the in vitro experiment and the context. Something like "kills cancer cell" is nearly meaningless (hence the famous XKCD comic). Here, this is a w

It depends on the in vitro experiment and the context. Something like "kills cancer cell" is nearly meaningless (hence the famous XKCD comic). Here, this is a well known mechanism of action (remember balto and the diphtheria antitoxin and the Iditarod? This is fancy antitoxin kind of). And the in vitro experiment is a test to show that it is a neutralizing antibody that binds to the virus and stops entry. The in vitro model is the exact same mechanism of entry the virus uses in the body. While there are still lots of unknowns and unknown unknowns, and of course sorrento will have to run through extensive (or perhaps less extensive under the circumstances) clinical testing before we know for sure it works, this is more promising than your usual popsci "strawberry shortcake kills cancer cells on vitro" experiment. We also have some human data from convalescent sera I believe, amd this is essentially just controlled, high quality convalescent sera that you dont need to extract from humans, so even more validation there, which is why so many people are excited about and pursuing and antibody approach (sorrento isn't the only one or the first to develop a neutralizing antibody to covid)