For whatever reason XOMA stock under big pressure, could be tax selling, short playing, GS loan solution not as good as some people expected, no partnership news yet or maybe some bad things we don't know. So it's wise not to be too greedy especially on margin since short term anything can happen.
On the otherhand, science is science, if XOMA052 is real, data so far suggests very likely, then sooner or later this investment will reward big. With other potential good news like milestone payment, new contracts and ofcourse partnership news promised by CEO by end of the year, there is no reason to sell now. imo