Immunoprotective tumor antigens of experimental tumors are selectively extracted by 1-butanol. Human organ-specific cancer neoantigens (OSNs) are tumor substances in cancer extracts to which patients with cancer of the same organ respond in the in vitro assay of leukocyte adherence inhibition. Here we determined whether OSNs as measured by leukocyte adherence inhibition assay are also selectively solubilized by 2.5% (v/v) 1-butanol. Butanol extracts of live tissue-cultured human cancer cells as well as extracts of primary breast cancer contained OSNs as determined by leukocyte reactivity in leukocyte adherence inhibition. With two-phase butanol, OSN activity was recovered in the aqueous and not in the organic phase, indicating that OSN is not a lipoprotein. The butanol-soluble OSN, whether allogeneic or autologous, was recognized by the T4 subset of T-cells in association with Class II major histocompatibility complex antigens of monocytes. Autologous OSN was extracted from membrane preparations of autologous primary cancer. Butanol extracts contained the previously identified Mr 40,000 protein OSN. Butanol removed about 50% of the Mr 40,000 protein OSN from live cancer cell membranes. Probably because of residual OSN in the membrane fragments and the ability of OSN to reassociate with the membrane, the T8 subset of pure T-cells responded positively to autologous cancer extracts. Passage of the autologous extract through an anti-Class I major histocompatibility complex antigen affinity column but not through a control affinity column negated the activity of the extract with pure autologous T-cells. The results indicate that human OSNs share with immunoprotective tumor antigens of experimental tumors the unique physicochemical property of being selectively extracted by 2.5% butanol.

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This investigation was supported by USPHS Grant CA 31976 awarded by the National Cancer Institute, Department of Health and Human Services, and a grant from the National Cancer Institute of Canada and Medical Research Council of Canada.

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