A piece orochimaru's consciousness is imbedded in every curse seal he places on people. Orochimaru clearly had access to hashirama cells due to harvesting them (organs and such) when he experimented on children like yamato. Orochimaru thought him lots of.
Evolution of Orochimaru in Naruto and Boruto YouTube
But not all of orochimaru’s experiments.
Cause he did , he said he will help him give him power and he sent sound 4 to demo cursed seal to him.
Ibiki described him as though he was not human,. Now, my love has withered. Side stories ongoing for ten years, i have loved you in vain. And he saw powers of the seal in naruto fight already.
He also grafted them on danzo at some point. The body modifications section says, after orochimaru physically died, as kabuto heavily modified his body with various genetic sources, including orochimaru himself, sasuke. Taking advantage of the chaos, orochimaru extracted the tailed beast and obtained its severed horn, from which he harvested blue b’s dna. All it did was grant kakuzu all 5 chakra natures (which orochimaru already had) and well longevity.
He wants to become the perfect being and kakuzu's jutsu wouldn't give him that.
When kabuto was defeated, sasuke extracted that consciousness and implanted it in. Orochimaru's sheer power combined with his regenerative capabilities and immortality jutsu make him it nearly impossible for him to die, and thus he hasn't.
