Complex sentence: However, the controlled conditions present in the "in vitro" system differ significantly from those "in vivo" and may give misleading results therefore in vitro studies are usually followed by "in vivo" studies.
Split into simpler sentences: However, the controlled conditions present in the "in vitro" system differ significantly from those "in vivo", and may give misleading results. Therefore in vitro studies are usually followed by "in vivo" studies.