Influences of Tumor Cell Number at Primary Transplantation and Surgical Removal of Tumor on the Development of the Host Immune Reaction

In order to know about some aspect of immunological surveillance mechanism which has been postulated to be operating in normal host, in-vivo MeA tumor challenge experiments were carried out with varing dose of tumor cells at different host conditions. Results. of tumor incidenc in C,H/HeN mice transplanted with varing number of tumor cells, C,H/HeN mice rechallanged with certain number of autochthnous tumor cells after the surgical removal of tumor and C,H/HeN mice rechallangcd with certain number of autochthnouse tumor cells which had rejected the primary cell transplantation, and of latent period in tumor formation are summarized as follows; 1. Tumor incidence obtained from foot-pad inoculation of 10', 5 X 10', 5 x 10', 5 X 10' and 10' tumor cell dose per mouse wase 23.8%. 57.1%. 89.7%, 100% and 97.6%, respectively and 50% tumor cell dese (which is defined as tumor cell number necessary for the establishment of tumor in 50% of mice tested) calculated by Probit analysis was 3.9 x 10' cells per mouse. 2. Mice surviving the intial foot-pad inoculation of small numbers of tumor cell doses were divided into two groups by the existence of immune memory which had been assessed by rechallenging with more than TDso at 5 weeks after the date of primaryinoculation. The memory was induced in the mice which had' rejected the 5 x 104 tumor cell inoculum per mouse., but not induced in the other mice group which had' rejected 5 X 10" or 10' tumor cell inoculum per mouse.. 3. CaH/HeN mice were resistant to the rechaUenging autochthonous MCA tumor after the surgical resection of the primary tumor mass. 4. No statistical differences in the resistance to the MCA tumor were observed between young (6-8 weeks old) and old (2~12 months) CaH/HeN mice groups. 5. Latent period from the day of inital tumor graft to that of development of palpable tumor mass was prolonged in mice. of which the tumor was removed sur gicaUy