Parasite Eve by Hideaki Sena

When Dr. Nagashima loses his wife in a mysterious car crash, he is overwhelmed with grief but also an eerie sense of purpose; he becomes obsessed wiht reincarnating his dead wife. Her donated kidney is transplanted into a young girl wiht a debilitating disorder, bu the doctor also feels compelled to keep a small sample of her liver in his laboratory. When these cells start mutating rapidly, a consciousness bent on determining its own fate awakens, bent on becoming the new dominant species on earth.

Parasite Eve was the basis of the hugely popular videogame of the same name in the U.S. and has been cinematized in Japan.