Well given how kuma left Revos for her, and also how he became obedient to WG.... He probably cured using something from WG.
I think Kuma used his fruit to repel the illness out of Bonney and took it on himself. Would explain why he turned himself into an android since he didn’t have long left anyways
Unless, this is no cure, so Kuma willingly gave up his body to the disease, however, Vegapunk got slick, and made him a new body, which he will put Kuma's memories in.
That is the running theory after all, that Kuma-Seraphim will inherit Kuma's consciousness, so it could fit, and would make a nice twist. Since they couldn't cure the disease, Vegapunk figured out a way to just transfer Kuma's consciousness to a new body.