Ba­boon sur­vives for six months af­ter re­ceiv­ing pig heart trans­plant

The Guardian Australia - - Science - Nicola Davis

The trans­plan­ta­tion of pig or­gans into hu­mans is a step closer to be­com­ing a re­al­ity af­ter re­searchers showed the or­gans can func­tion long-term in ba­boons.

The trans­plant­ing of or­gans from one species to an­other, known as xeno­trans­plan­ta­tion, has been the sub­ject of re­search for many years. Pro­po­nents say it could help get around a short­age of hu­man or­gans.

How­ever, there are numer­ous hur­dles to over­come, from viruses that could in­fect re­cip­i­ents – some­thing re­searchers have re­cently been us­ing gene-edit­ing tools to tackle – to pre­vent­ing re­jec­tion of the or­gans, as well as eth­i­cal con­sid­er­a­tions.

Re­searchers say they have made a ma­jor move for­ward by sig­nif­i­cantly in­creas­ing the sur­vival time of ba­boons whose hearts have been re­placed with those of pigs.

It is not the first time pig or­gans, in­clud­ing hearts, have been trans­planted into mon­keys. Pre­vi­ous work has showed that a pig heart can func­tion for more than two and a half years when trans­planted into the ab­domen of a ba­boon – although the ba­boon kept its own heart to pump blood around its body.

But when it comes to ac­tu­ally keep­ing ba­boons alive, pig hearts had only done the job for a max­i­mum of 57 days – and that was only achieved in one an­i­mal.

Now, writ­ing in the jour­nal Na­ture, re­searchers from Ger­many, Swe­den and Switzer­land re­port they have bro­ken through this bar­rier, with one ba­boon sur­viv­ing with a pig heart for more than six months.

Af­ter ini­tially dis­ap­point­ing re­sults, the team re­fined the trans­plant pro­ce­dure, switch­ing from pre­serv­ing donor hearts in cold stor­age to keep­ing them at 8C (46.4F) with flu­ids con­tain­ing oxy­gen, hor­mones, red blood cells and nu­tri­ents cir­cu­lat­ing through them. They also found it was nec­es­sary to give the mon­keys drugs to pre­vent the piglet heart from grow­ing too large and med­i­ca­tion to lower their blood pres­sure to match that of pigs.

“Hearts of pigs grow rapidly – even if they are out of the body of a pig – and we could stop that growth,” said the sur­geon Bruno Re­ichart, a co-au­thor of the study from Lud­wig Max­i­m­il­ian Univer­sity of Mu­nich, not­ing that if the heart is too big it can­not func­tion prop­erly.

The re­sults from five ba­boons show that while one had to be put down soon af­ter trans­plant, two lived healthily for three months with no sign of prob­lems – at which point the team put them down – while the re­main­ing two ba­boons were fol­lowed for 195 and 182 days re­spec­tively be­fore they were put down.

Re­ichart said that if fi­nan­cial back­ing were se­cured to al­low the team to carry out fur­ther re­search, in­clud­ing us­ing “cleaner” donor an­i­mals, clin­i­cal tri­als could be­gin in hu­mans in about three years. So far, the team’s work has been sup­ported by the Ger­man gov­ern­ment.

Writ­ing in an ac­com­pa­ny­ing ar­ti­cle, Christoph Knos­alla from the Ger­man Heart Cen­tre in Berlin said the In­ter­na­tional So­ci­ety for Heart and Lung Trans­plan­ta­tion pre­vi­ously sug­gested clin­i­cal tri­als of pig or­gan trans­plants could be on the cards once at least 10 pri­mates, and 60% of re­cip­i­ents, were shown to have sur­vived for three months or longer.

Bruce Whitelaw, a pro­fes­sor of an­i­mal biotech­nol­ogy at the Royal (Dick) school of ve­teri­nary stud­ies at the Univer­sity of Ed­in­burgh, said that while sci­en­tists had also been work­ing to grow hu­man or­gans in­side pigs and sheep, that tech­nol­ogy was still in its early stages and trans­plant­ing pig or­gans was a more im­me­di­ate pos­si­bil­ity. He said the main bar­ri­ers to clin­i­cal tri­als now ap­peared to be prac­ti­cal rather than tech­ni­cal.

“In a world where we don’t have enough or­gans to trans­plant and peo­ple are dy­ing be­cause of that, then any­thing that can in­crease the num­ber of or­gans is to be wel­comed,” he said.

Pho­to­graph: Halden Krog/AP

In pre­vi­ous stud­ies, the long­est a ba­boon had sur­vived af­ter re­ceiv­ing a pig heart was 57 days.

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