At a very cursory level, it means a $60M company is being absorbed into a $260M company, so the net impact of a positive event is roughly proportionally reduced.
Imagine a $60M company announcing $60M in profits.
Imagine a $320M company ($60M+$260M) announcing $60M in profits.
This is why I usually sell small companies when they are bought by larger ones. In this case, however, the 'large' company is relatively small and the potential profits could be larger than the $60M (based on opinion and historical biotech trends, not an analysis of Asterias).
Does that help?