Characterization of human ovarian carcinoma‐associated antigens defined by novel monoclonal antibodies with tumor‐restricted specificity

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Abstract
Three new monoclonal antibodies (MAbs) (MOv16, MOv18 and MOv19) were raised against human ovarian carcinoma. To obtain more specific reagents than those produced so far, we adopted the following experimental approach which consisted of: (1) the selection of a poorly differentiated ovarian carcinoma which was unreactive with all the MAb previously selected in our laboratory; and (2) the application of a particular immunization protocol. The reactivity of the selected MAbs was studied by solid‐phase RIA on live and fixed cells from tumor cell lines and by immunofluorescence on frozen sections from surgical specimens. The MAb MOv16 reacted with 60% of ovarian carcinomas as well as with a high percentage of other carcinomas and with some normal tissues. In contrast, MOv18 and MOv19 appeared to have restricted specificities for ovarian carcinomas and cystadenomas. Reactivity on other carcinomas was only observed in a few cases and no reactivity was found on non‐epithelial tumors or normal tissues. Immunoprecipitation experiments indicated that MOv16 recognizes a 48‐50‐kDA protein, whereas MOv18 and MOv19 both identify a 38‐40 kDA glycoprotein band. Cross‐competition experiments, together with a double‐determinant immunoradiometric assay which uses MOv18 as catcher and MOv19 as tracer, suggested that they recognize different epitopes carried by the same molecule. The affinity constants of MOv18 and MOv19 were estimated to be in the range of 108 ‐ 109 M‐1. Taken together, the properties of these antibodies, their restricted ovarian tumor specificities and relative high affinity constants, suggest that they could represent promising tools for in vivo applications.