"Not sure why Uncle Sam should be thanked for taking the £500,000."
Because that country provided the circumstances under which the R&D necessary to provide such a facility could be provided. Such research cannot take place in the UK because of its obsession with its "Jewel in the Crown", the NHS. Private development and provision is looked upon as almost a criminal offence and those taking advantage of it are looked upon as pariahs who seek to destroy "free" healthcare. Uncle Sam deserves some thanks because without the regime encouraged by its government Zac would almost certainly not have been cured. This country could not or would not provide the treatment but a facility in the USA would - and strange as it may seem, they won't do it for nothing.