Organ specific neoantigens reactive in the leukocyte adherence inhibition assay: affinity purification of human colon carcinoma antigen and its cross-reactive protein using monoclonal antibodies.

A monoclonal antibody (mAb) was prepared against a semipurified preparation of an organ specific neoantigen (OSN) reactive in the leukocyte adherence inhibition (LAI) assay. The mAb (LC20.1) induces a positive LAI response when incubated with leukocytes of normal individuals in the presence of OSN derived from either human colon or lung carcinoma cell lines. Absorption of crude OSN preparations from these cell lines on immobilized LC20.1 mAb eliminates all the LAI reactive material suggesting that the mAb recognizes a common determinant on OSN from both colon and lung carcinomas. The LC20 mAb was used to affinity purify the colon cancer OSN as well as a cross-reactive normal protein from the urine of colon cancer patients and healthy donors, respectively. The colon cancer OSN and normal cross-reactive protein display an apparent molecular weight of 29,000, have a similar linear tryptic peptide map, and are indistinguishable by isoelectric focusing analysis. Regardless of the molecular similarity, only the colon cancer OSN preparation could induce a positive LAI when incubated with leukocytes of colon cancer patients. Seven additional anti-colon cancer OSN mAbs were prepared against purified material. These mAbs can be divided into three groups, each of which recognizes a distinct antigenic determinant that is shared by the colon cancer neoantigen and its cross-reactive normal protein.