Tumor-specific Antigens of Putatively Nonviral Tumors1

anisms of the animals in which the neoplasms originate. Al most all of the putatively nonviral tumors are individually specific and few, if any, cross-reactions occur among them. The antigenic titer varies greatly and is related to the latent period and the immunologie reactivity of the tumor host. This rela tionship is almost certainly due to immunoselection. The an tigens are found in early premalignant lesions and the immune mechanism suppresses many of these before they reach macro scopic size and before they undergo progression to malignancy. It is hypothesized that the tumor antigens represent an altera tion in a normal cell-surface regulatory site or sites. Whether they are encoded but repressed in the genome of the normal cell or are the result of mutation has not been determined.