Serological Observations on Spontaneous Regression of Implants of Jensen's Rat Sarcoma

Abstract

Previous researches have shown that the inoculation of an animal with minced heterologous tumour induces the formation of cytotoxins which have a marked affinity for cancer cells in general (1; 2). More recently it has been shown that similar cytotoxins can be produced by repeatedly inoculating immune animals with homologous tumour emulsions (3), and this reaction has been fully confirmed by cinematograph films (4). It seemed of interest, therefore, to enquire whether the spontaneous regression of implanted tumours is related to the production of cytotoxins of the same type as those previously described. The present investigation has consisted in regular estimations of the cytotoxins in the sera of rats into which Jensen's rat sarcoma had been implanted. It has been found that a definite co-relation exists between the concentration of cytotoxins found and the ultimate fate of the implants. Experimental Methods Of the 70 rats studied, in 37 the tumour grew progressively, in 20 it regressed after growing for varying periods, and 13 of the implants did not grow at all. The rats were inoculated in batches varying in number from 6 to 12. In general the sera were examined first on the fifth or sixth day after implantation, and thereafter daily or every second day until the fate of the implant was certain. The superficial areas of the tumours were measured at corresponding times. The cytotoxin content of the sera was estimated by applying them to one-day-old tissue cultures of Jensen rat sarcoma. The method of preparation and feeding of these cultures followed exactly that previously described (2; 3). The “titre” of cytotoxins in the sera was estimated by counting the percentage of emigrated cells killed, half to one hour after the application of the test serum. It should be emphasised that when only a small proportion of the cultured cells are killed, they must be estimated by direct observation of the culture within a short time, since the dead cells disappear very rapidly as the result of phagocytosis by the large preponderance of surviving cells. Normal rat serum has never, in many hundreds of tests, been found to have any toxic effect on Jensen rat sarcoma cultures.