Dose‐dependent recognition of irradiated isogeneic mouse lymphoma cells: Study by terminal dilution assay

Abstract

Quantitative dose-response survival curves for mouse leukemic tumor cells in vivo became possible by means of the end-point dilution assay of Hewitt and Wilson (1959), whose results were later confirmed and extended by Berry and Andrews (1961). The loss of reproductive integrity with ionizing radiations thus determined provided quantitative evidence that mammalian tumor cell radiation response in vivo was similar to that of cells irradiated and assayed in vitro by colony-forming ability (Puck and Marcus, 1956). Additional evidence supporting the in vivo survival curves determined by the TD50 method, was provided by the fact that the regrowth of surviving leukemic cells irradiated in vitro could be predicted by cell survival based on the TD50 method and upon the length of life (survival time) of isologous animals receiving transplants of irradiated leukemic cells (Maruyama et al., 1967). In addition, the radiation dose required to render known numbers of leukemic cell nonviable (" sterilizing " dose or SD50 assay) correlated with the TD50 survival curve, provided the recipients were immunologically suppressed by prior whole-body irradiation before they were challenged with the irradiated tumor cells (Maruyama, 1967). In the latter studies it was found that intact animals which were not immunologically suppressed developed a smaller proportion of tumor takes than the pre-irradiated animals.In these experiments, a systematic study of the effect of recipient whole-body X-irradiation before challenge by tumor cells a t the end point of terminal dilution (TD50) assay was investigated. The purpose was to determine the effect and the contribution of weak host-resistance to the overall TD50 survival curve, and the relative effect upon the assay of cells sub-lethally injured by small and large doses of X-irradiation. These results are the subject of this report. MATERIAL AND METHODS AnimalsInbred C57BL/Ka mice about 8-12 weeks of age were used. In each experiment, all recipients were matched for age, sex and size. All animals are descendants of a brother-sister, single-line

Inactivation of an x‐irradiated tumor by independent processes in in vivo

“…However, the choice was arbitrary and represented the simplest form which adequately described the data. Such a curve was found for an experimental lymphoma (Maruyama, 1968), hence the approach is considered relevant to the analysis of the present data. The immune-radioinactivation curve (Process 2) was determined from the differences in cell survival found as a function of radiation dose in non-suppressed and immune-suppressed recipients.…”

“…Evidence that recognition is possible has now been presented for the LSA tumor (Maruyama and Johnson, 1969). It is much more effective with the irradiated tumor (Maruyama, 1968;Maruyama and Johnson, 1969). Likewise the simple addition of large numbers of killed cells to uninjured tumor does not enhance recognition.…”

“…Therefore, the immunecompetent host may contribute by modifying the irradiated cell response in vivo, owing to the immunological resistance of the host against the tumor. Certain tumor cell X-ray survival curves show a systematic deviation from exponential linearity when studied in non-suppressed animals using syngeneic animals and tumors (Maruyama, 1967(Maruyama, , 1968. In this communication we attempt to analyze this phenomenon and to propose that the dose-response curve arises from where S = fraction surviving; D = radiation dose; K = a parameter defining slope; n = extrapolation number, or zero dose intercept with ordinate axis (Alper et al, 1960); e = base of natural logarithms.…”

“…It does not require a detectable pretreatmentinduced resistance (Maruyama, 1968), although, if resistance can be actively produced (Scott, 1961) it may contribute to the survival curve.…”

“…Once a " recognition " threshold is exceeded, further tumor cell inactivation appears to follow kinetics approximated by an exponential process (Maruyama, 1968). …”