Tumourigenic phenotypes of human melanoma cell lines in nude mice determined by an active antitumour mechanism.

Ten human melanoma cell lines (HMCL) were tested for their ability to grow subcutaneously in nude mice. Using a standard inoculum, the HMCL could be characterized by their highly, fairly or poorly xenografting phenotype. These phenotypes were stable and the phenotype of one HMCL was recovered within cell clones derived from it. The role of nude mice natural defences in the expression of HMCL xenografting phenotypes was studied. Sublethal whole body irradiation and silica pretreatment of recipients enabled poorly tumourigenic HMCL to grow in most animals without affecting their splenic NK activity. Admixture of BCG or MDP encapsulated in liposomes with highly tumourigenic HMCL resulted in the abrogation of tumour growth in naive nude mice. The long lasting abrogating of NK activity in vivo by treatment with anti-asialo-GM1 anti-serum did not enhance the growth of a poorly tumourigenic HMCL. The HMCL were found to be resistant to in vitro murine NK activity. These results showed that the expression of the HMCL xenografting phenotypes could be controlled by the nude mice natural defences. NK cells did not seem to be largely involved whereas macrophages might be good candidates as anti-xenograft effectors.