In early experiments on cell-mediated cytotoxicity against tumor target cells, both in cancer patients and animal models, investigators consistently observed what was termed a "natural" reactivity; that is, a certain population of cells seemed to be able to lyse tumor cells without having been previously sensitized to them.
Nos primeiros experimentos sobre citotoxicidade mediada por células contra células tumorais, tanto en pacientes cancerosos coma en modelos animais, os investigadores observaron claramente o que se denominou reactividade "natural", é dicir, certas poboacións de células parecían poder lisar células tumorais sen que fosen previamente sensibilizadas a elas.