The reversal of the metastatic phenotype by gene transfer

When studying the function of MHC-restricted immune responses in controlling metastatic growth we discovered that highly metastatic clones of mouse tumours express the H-2D but lack expression of the H-2K gene of the MHC system. The de novo expression of the H-2K antigen, after H-2K gene transfection, resulted in the reversal of a metastatic to a non-metastatic phenotype. This reversal was causally related to the acquisition of H-2K-restricted immunogenic properties. Immunization with H-2K-transfected cells, after surgical removal of the local tumour, abolished or significantly reduced the growth of metastases. We subsequently observed that H-2K expression is correlated with expression of the c-fos oncogenes. Transfection of H-2K-negative cells with v-fos or c-fos genes resulted in the expression of H-2K. Our studies suggest that one of the main functions of the c-fos proto-oncogenes is control of the expression of the MHC genes. Searching for additional molecular properties which characterize the metastatic phenotype, we observed that the metastatic clones of each of our lung-metastasizing tumours expresses an fms-related oncogene. This was correlated with a membrane-bound tyrosine kinase, which has the properties of growth factor receptors. We examine the possibility that our fms-like gene codes for this protein kinase, which represents a receptor for a local growth factor that controls metastatic growth in the lung.