Antigenic Heterogeneity of Human Colorectal Cancer Cell Lines Analyzed by a Panel of Monoclonal Antibodies. I. Heterogeneous Expression of la-Like and HLA-Like Antigenic Determinants

: The pattern of reactivity of 10 monoclonal antibodies (MCA) developed against human lymphoid leukemia cells and tested with human T-cells, B-cells, as well T-lymphoma and B-lymphoma cell lines suggested that six of them detect la-like determinants, three detect HLA-like determinants, and the remaining one detects a non-Ia B-cell antigen. With the use of three binding assays, the six MCA that appeared to detect Ia-like determinants reacted strongly with the human colorectal cancer cell (CCC) line LoVo, and none of the three MCA that reacted with HLA-like determinants reacted with this cell line. Immunoprecipitation and polyacrylamide gel electrophoresis analysis confirmed the apparent specificities of the MCA for Ia-like and HLA molecules, demonstrated the presence of Ia-like molecules in LoVo, and failed to detect HLA in these cells. The cellular enzyme-linked immunosorbent assay was used for the testing of our anti-Ia and anti-HLA MCA with 15 other CCC lines. Marked heterogeneity was found in the expression of different Ia-like and HLA determinants defined by different or overlapping subsets of MCA, which suggested that these determinants might be present on different molecules or that different conformations of the same molecules exist in various CCC lines. Analysis of the surface phenotype of subclones of LoVo cells revealed the presence of stable variant cell subpopulations, which lost reactivity with four out of six of the anti-Ia-like MCA but retained at least one Ia-like molecule recognized by two of our MCA. All of the subclones maintained the HLA-negative phenotype. The possible immunologic and diagnostic consequences of the presence or absence of Ia-like or HLA markers on nonlymphoid tumor cells are discussed.