CANCER - A BIOLOGICAL PROBLEM WITHOUT ANY NATURAL IMMUNOLOGICAL SOLUTION - A UNIFIED THEORY, WITH IMPLICATIONS FOR GRAFTS, PREGNANCY AND TUMOR IMMUNOPROPHYLAXIS

Stem tumour cells would be paraembryonal cells, major histocompatibili ty complex lacking and able of inducing adjoining cells to become tumo ur differentiated cells with major histocompatibility complex; thus, t hey would generate a histological tumour organization into paraembryon al cell clusters surrounded by tumour-differentiated cells. Such an or ganization, actually found in recent studies, might be one factor resp onsible for the limits of the immunotherapies carried out so far. But, there might be another, perhaps more important, factor. Analysis of o ntogenetic aspects of MHC-nonrestricted immunity would lead, indeed, t o the prediction that natural killer clones reactive for stem tumour c ells (paraembryonal cells) would be missing in the adult organism, sin ce they would be deleted in particular ontogenetic phases. This might explain why natural killer cells locate only in certain organs and nea rly not at all in tumour sites. By such an analysis, possible evolutiv e and functional correlations between natural killer cells and heat sh ock proteins, hemopoietic histocompatibility, major histocompatibility complex molecules are suggested. From here, explanations and implicat ions for grafts, pregnancy and tumour immunoprophylaxis arise.