Splenocytes from mice immunized with Xiphophorus melanoma cells were fused with the P3X63-Ag8.653 mouse myeloma cell line. Three MoAb were developed which recognized membrane bound antigens on the primary fish melanoma and on cell cultures derived from chemically induced melanoma. The MoAb displayed positive reactions with a melanin free albino melanoma, thus excluding melanin as the target structure. The antigens defined by these MoAb were not detected in the nontransformed tissue of tumor bearing and tumor free animals, normal fish melanocytes and fish rhabdomyosarcoma, thus providing evidence for the existence of MAA in Xiphophorus. The antigens were also present to varying degrees on the surface of second passage and permanent fish embryofibroblast cultures, implying that the defined MAA probably represent carcino-embryonic antigens. Cultured Xiphophorus cells displayed significant heterogeneity of antigen expression most probably due to the in vitro culture conditions. The three MoAb did not recognize membrane bound antigens on the 11 human tissues and 19 xenogeneic cell lines (including melanoma) tested, except for one remarkable although weak reaction with the human melanoma cell line SK-Mel 93. Additionally, the three MoAb revealed a few weak crossreactivities with intracellular structures of these xenogeneic tumors and cell lines. These results indicate a distribution of the MAA predominantly restricted to Xiphophorus, but leave the possibility of the existence of common polypeptide sequences in human and Xiphophorus melanoma. Six out of 20 antibodies raised against human melanoma reacted with Xiphophorus primary melanoma or permanent cell lines, thus confirming the concept of interspecies MAA.

Clauss G, Lohmeyer J and Anders F.
Genetisches Institut
Zentrum für Innere Medizin
Universität Giessen, FRG