Factors Influencing the Quantitative Estimation of the In Vivo Survival of Cells From Solid Tumors2

Abstract

Three solid mouse tumors have been maintained by serial isologous passage in C3H/Km and C57BL/Ka mice. Endpoint dilution assays were performed to provide data for TDSO calculations. Immunological compatibility was tested by inoculation of recipients twice with at least 10⁵ radiation-killed (10,000 rads) tumor cells 2 weeks apart and determination of the TDSO for living cells of the same tumor lines 2 weeks after the second immunizing treatment. The C3H/Km sarcoma, KHT, was not antigenic, while the C57BL/Ka sarcoma, KHG, showed definite evidence of antigenicity. The addition of at least 2 × 10⁵ radiation-killed cells to living inocula had littie pronounced effect on transplantability; titrations performed with such cells added, however, appeared to yield more uniform take and TD50 data. KHT grew equally well in several subcutaneous sites and intramuscularly. Systematic determination of the TDSO of KHT between the eighth and 72d isologous passage demonstrated that the TDSO continuously underwent minor Ouctuations, owing presumably to methodological and statistical factors; however, a major change consisting of a decrease to approximately 10% of the earlier level occurred between the 21 sf and 23d passage, presumably because of intrinsic biological changes in the tumor cells. Careful analysis established that a tumor such as KHT which is nonantigenic by the test employed here can be inoculated into at least 4 sites simultaneously in the same animal to provide data for TDSO computation reliably and efficiently, but an antigenic tumor such as KHG shows evidence of site interaction in multiply-inoculated mice. The construction of radiation dose-survival curves from TD50 data is greatly facilitated and the precision of such curves enhanced if the TD50's of irradiated tumor cells are expressed as fractions of the TD50's of simultaneously obtained control preparations.