Processing of antibodies bound to B-cell lymphomas and lymphoblastoid cell lines

Previous experiments demonstrated that some human B-cell lymphoma cell lines were unusual in that antibodies bound to the cell surface dissociated at high levels. This did not occur with non-B-cell hematologic tumors or with carcinomas. In this study, additional B-cell lymphoma and lymphoblastoid (Epstein-Barr virus-transformed) cell lines were tested.

The antibodies selected for most experiments, MA103 and anti-CD45, react with relatively high avidity to the cell surface. Antibodies to CD19, CD20, and CD22 also were tested on certain cell lines. The antibodies were labeled with 125I. After binding to the surface of viable cells, unbound antibody was washed away, and the fate of the bound antibody was investigated for 2-3 days.

Of the eight B-cell lymphomas tested, three had high levels of dissociation, two had low levels of dissociation, and three had intermediate levels of dissociation. The six lymphoblastoid cell lines had only slightly elevated levels of dissociation, relative to non-B cell lines. Sublines of Raji and Ramos cells were identified that varied greatly in the level of antibody dissociation. The level of dissociation from lymphomas was correlated with the tendency of the cell lines to cluster, with single cells displaying less dissociation than clustered cells. However, some exceptions to this correlation were noted. Cell lines such as Ramos, which showed little dissociation of anti-CD20, displayed relatively rapid catabolism of this antibody.

The level of antibody dissociation as well as the rate of antibody catabolism will affect the results of radioimmunotherapy strongly because these factors affect the time interval for which the cells are in contact with the radioisotope. Different B-cell lines display markedly different levels of dissociation. There is some evidence suggesting that antibody dissociation is high with fresh human tumor cells, but further investigation of this point is required.