Antitumor resistance formation in animals in early neonatal period

Immunization of new-born mice during the first three days after birth enhances immunity in adult life, and it remains high throughout the entire life course. The antitumor resistance is raised so high in order to produce cancerogenesis blockade caused by 20-methylcholanthrene injection to adult animals even one year after vaccination. The dynamics of growth of new-borns shows that immediately after birth the animal growth proceeds very quickly, following an exponential law. The same occurs in rats and even in human beings. Vaccination of animals during fast growth phase ensures an antitumor effect, while vaccination after fast growth phase leads to antitumor immunity breakdown. It was assumed fetal lymphocytes do not attain full sexual maturity and their cytotoxic properties start developing only after birth. This hypothesis is in full agreement with our results. Vaccination of new-borns during fast growth phase leads to a significant increase of immature lymphocytes of those clones which are sensitive to an injected antigen. Upon vaccination termination, these lymphocytes attain complete maturation and remain in tissues, thereby ensuring a prolonged and high immunity. Our earlier experiments clearly demonstrated the increase in lymphocytes number in animals which had been exposed to early postnatal immunization. The kinetic analysis showed that full tumor destruction would be only possible if the rate of tumor cells destruction by cytotoxic lymphocytes is greater than the rate of tumor cells reproduction, as the tumor is incapable to make up for loss of its own cells. Immunization during fast growth phase does allow maximum increase in the number of cytotoxic lymphocytes and, thereby, enhance an entire cell immunity - unattainable after full lymphocyte maturation.