842 



SCIENCE 



[N. S. Vol. XLII. No. 1093 



THE EFFECT OF X-RAY ON THE RESISTANCE TO 

 CANCER IN MICEi 



It has been shown in previous communica- 

 tions that the resistance to heteroplastic tissue 

 grafts apparently depends on the activity of 

 the lymphocyte. The facts on which this con- 

 elusion is based are briefly as follows: The 

 chick embryo, which normally lacks the abil- 

 ity to destroy a heteroplastic tissue graft, if 

 supplied with a bit of adult lymphoid tissue, 

 becomes as resistant as the adult in this re- 

 spect. Furthermore, an adult animal deprived 

 of the major portion of its lymphoid system 

 by repeated small doses of X-ray, no longer 

 has the power to destroy a graft of foreign 

 tissue, and this tissue will grow actively. The 

 chief characteristic of a failing heteroplastic 

 graft in the unsuitable host is a marked local 

 accumulation of lymphocytes. The histolog- 

 ical picture is identical in a failing cancer 

 graft in an immune animal of the same spe- 

 cies. Synchronous with the establishment of 

 the cancer immunity and during the period in 

 which the lymphocytes are accumulating 

 around the cancer graft, there is a lymphocytic 

 crisis in the circulating blood. This is found 

 in the actively immunized animals as well as 

 in those possessing a natural immunity, but is 

 totally lacking in animals susceptible to the 

 cancer graft. If the lymphoid crisis be pre- 

 vented in immune animals by a previous de- 

 struction of the lymphoid elements with X- 

 ray the potentially immune animal is changed 

 to a susceptible one. 



We have noted that while repeated expos- 

 ures to X-ray will destroy the lymphoid ele- 

 ments of an animal, one small dose will stimu- 

 late these same cells. With this artificial 

 method of producing a lymphocytosis we have 

 attempted to study the relation of this condi- 

 tion to the resistance of mice to their own 

 spontaneous tumors. For evident reasons it 

 was necessary to rule out the complicated 

 question of the direct effect of X-ray on the 



1 From the Laboratories of The Eoekef eller In- 

 stitute for Medical Eesearoh. Abstract of paper 

 presented at the New York meeting of the Na- 

 tional Academy of Sciences. 



cancer. In order to do this we have removed 

 the cancer at operation, and with the cancer 

 out the animal has been subjected to a stimu- 

 lating dose of X-ray. Immediately after this 

 a graft of the original tumor was replaced in 

 the groin of the animal. As a control the 

 same procedure was carried out, but with X- 

 ray treatment omitted. As a further check to 

 the results cancers were removed from a num- 

 ber of animals and in this set the cancers were 

 exposed directly to the same amount of X-ray 

 that the animals in the first group had received. 

 After this a graft of the tumor was returned 

 to the original host. 



The results of these three experiments are 

 to be judged by two criteria. First, whether 

 or not there is a return of the disease, either 

 at the site of removal of the cancer, or at the 

 point of inoculation of the returned graft; 

 and second, the time at which the returned 

 graft starts in active growth, if at all. The 

 figures on these points are given in the fol- 

 lowing table. 



Series I . . . 

 Series II . . 

 Series III. . 



Immune 

 Per 

 Cent. 



50.0 

 3.4 

 0.0 



Local 

 Recurrence 

 of Tumor 

 Per Cent. 



21.2 

 48.3 

 40.0 



Average Time lor 



Appearance of 



Graft. 



5 wks. and 4 days. 

 1 wk. and 5 days. 

 1 wk. and 3 days. 



Series I. was composed of 52 animals 

 treated by X-ray while the cancer was outside 

 of the body, with later a return of a graft of 

 the tumor. Series II. was made up of 29 con- 

 trol animals in which the cancer was removed 

 and a graft returned without treatment to 

 either animal or tumor. Series III. was made 

 up of ten animals from which the cancer was 

 removed and the cancer subjected directly to 

 the same amount of X-ray that the animals re- 

 ceived in the first series, and later a graft of 

 this X-rayed cancer returned to its original 

 host. 



It will be seen from these figures that an X- 

 ray dose which produced a lymphocytosis when 

 administered direct to the animal was suffi- 

 cient to render 50 per cent, of the mice so 

 treated immune to a returned graft of their 



