- Email: [email protected]
The growth of human tumours in immune deprived mice
Europ. J. Cancer Vol. 10, pp. 473-476. Pergamon Press 1974. Printed in Great Britain
The Growth of Human Tumours in Immune Deprived Mice L. M. COBB* and B. C. V. MITCHLEY Department of Functional Pathology, Chester Beatty Research Institute, Institute of Cancer Research: Royal Cancer Hospital, Fulham Road, London SW3 6JB, England
Abstract--The growth of human tumours was studied in immune deprived mice. Immune deprivation was obtained by a combination of thymectomy, whole body irradiation and bone marrow replacement. Five hundred and twenty mice were implanted with 18 different types of tumour from 83 pat#nts. Tumour from 22 of these 83 patients grew in the immune deprived mice. The tumours that grew to a volume that threatened the survival of the mice were carcinomas of the colon, rectum, ovary, kidney and bronchus, and a glioma.
suppressed, without the need for giving continuous immunosuppressive treatment [2, 3, 4]. Two techniques have emerged and it is not yet clear which is most suitable for h u m a n tumour growth. One technique is to use mice with congenital thymic aplasia. These animals are also hairless and are referred to as " n u d e " mice. The thymic aplasia is the product of a recessive gene and therefore a carefully controlled breeding programme is required. The " n u d e " mice have so far been used particularly for the in vivo culture of carcinoma of the large bowel [2]. The second technique, which can be applied to most rodents, requires thymectomy followed by the destruction of lymphocytes by irradiation antithymocyte serum and cytotoxic drugs. T u m o u r implanted into immune deprived animals does not always grow. It is becoming apparent that certain types of tumour are more likely to "take" than others. It is the purpose of this paper to illustrate the types of tumour which are likely to grow in one form of immune deprived animal; that is the mouse prepared by thymectomy, whole body irradiation and bone marrow replacement. Having indicated the turnouts that appear to grow most successfully in this preparation the reasons for failure of other classes of tumour are considered
INTRODUCTION
THE GROWTH and metastasis of h u m a n tumours in experimental animals can now be studied by a n u m b e r of different methods. The recent and more successful methods require suppression of the immunological graft rejection processes. Previous techniques depended upon the fact that in certain areas of the body, such as the cheek pouch in the hamster, or the anterior chamber of the eye in rabbits, a graft was offered partial protection from the immunological rejection processes. In the case of the hamster cheek pouch grafts it was possible to enhance this partial protection by the destruction of lymphocytes using cortisone and antimitotic drugs [1]. A drawback to this latter technique was the necessity to treat with immunosuppressive drugs throughout the experiment. Such drugs could interfere with the growth of the tumour. Recently, it has been shown that h u m a n tumour can become established, and in some cases metastasise spontaneously, in animals in which the graft rejection process has been Accepted 12 March 1974. *Present address: Huntingdon Research Centre, Huntingdon PEI8 6ES, England. 473
474
L. M. Cobb and B. C. V. Mitchley
The possible clinical use of the growth of specimens of patient's tumour in immune deprived animals is discussed.
MATERIALS AND METHODS
Tumour specimens T u m o u r specimens reached the laboratory between 10 min and 4 hr after removal from the patient. T u m o u r areas that appeared to be viable were dissected out. One mm thick slices were cut for transplantation. Adjacent viable tumour was fixed in Bouin's solution and prepared by conventional methods for histological examination. The 1 mm thick slices of the tumour were pared to an area of approximately 9 m m 2 before being transplanted subcutaneously into the right flank of from 4 to 10 mice, depending on the size of the specimen from the patient. The mice were anaesthetized with ether. A total of 520 implantations were made from tumour removed from 83 patients.
Experimental animals Male and female CBA/Iac mice were used. The breeding stock were obtained from the Laboratory Animals Centre, Carshalton, Surrey, England. The mice were given sterile food and water ad libitum. Whenever it was thought possible that the growth of the transplant could be effected by sex hormones, the sex of the mouse was chosen to match the sex of the patient.
Technique of immune deprivation The technique used was based on work published by Miller in 1963 [5]. The mice were thymectomized at 4 weeks of age, 4 weeks later they were given 900 t a d whole body irradiation. Irradiation was given at 60 rad per rain using a 220 kV X-ray machine, hvl 0.4 m m Cu, focal distance 100 cm. Without a bone marrow graft this dose of irradiation would have been lethal. Within 6 hr of irradiation each mouse received 5 x 106 syngeneic femoral bone marrow cells intravenously. The tumour was implanted between 2 and 4 weeks after the irradiation and bone marrow replacement.
Observation of tumour implanted immune deprived mice The mice were observed 3-5 times weekly for 9 months, at the end of which time they were killed. Animals were killed before this time if they were ailing or if the turnout had reached a size of 9 m m 3. An extensive necropsy examination was carried out on all mice. A particular search was made for evidence of metastatic involvement of lymph nodes draining the site of implantation and of spread to
distant tissues. Tissues with signs of pathological changes were fixed in Bouin's solution. Sections were cut, and stained with haematoxylin and eosin.
Recording tumour growth The subcutaneously implanted tumours were measured once weekly. Particular note was taken of the turnouts at 2 sizes, 75 m m 3 and 9 cm 3. The 75 m m 3 stage was selected because experience showed that this was the smallest turnout volume at which it was possible to be confident that growing tumour was present, rather than a foreign body reaction. The second stage, 9 cm 3, was chosen because this volume approached the volume that wouId cause debility in the animal.
RESULTS
Subcutaneous tumour implants gaining a volume of 75 mm 3 Twenty-two tumours were established (gained a volume of 75 mm 3) of the 83 tumours implanted (Tables 1 and 2). Unfortunately, with a tumour at the volume of 75 turn 3, it was not possible to obtain a confirmatory biopsy and still allow normal growth of the tumour. However, in 8 mice a tumour of 75 m m 3 was present when the mice were killed at 9 months. In all these animals there was viable tumour. O f the 87 individual implants that gained 75 mm 3 26 subsequently regressed completely before 9 months.
Subcutaneous tumour implants growing to a volume of 9 cm 3 Only 10 of the 22 tumours that grew to a size of 75 m m ~ continued to grow to a volume of 9 cm 3 within the 9 month period (Table 1). These 10 consisted of 3 cases of carcinoma of colon, 3 cases of carcinoma of rectum, 1 case of carcinoma of ovary, 1 case of glioma, 1 case of hypernephroma and 1 case of carcinoma of bronchus. The histological appearance of the tumour removed from the animals was strikingly similar to areas of the respective patients tumours (Figs. 1-6).
Post-mortem findings In none of the mice examined macroscopically 9 months after implantation, or before 9 months if the tumour had reached 9 cm 3, was there any evidence of metastatic spread of the tumour. Twenty-nine of the 520 implanted mice died before the completion of the experiment from causes apparently unrelated to the
Fig. Fig.
2.
Carcinoma
4.
Teratoma
growing
3.
6.
Carcinoma
of
of bronchus
on removal from
the patient
growing subcutaneously in mice 6 months tumour is illustrated by Fig. 1. x 150.
Teratoma
subcutaneously Fig.
Fig.
Carcinoma
of the bronchus
Fig. Fig.
1.
5.
colon growing
of
testes
on removal
from
Carcinoma
after’
the patient
in mice 9 months after implantation Fig. 3. x 150. of colon on removal from
P246
from
patient
x 150.
imi)lantation P242.
subcutaneously in mice 5 months after implantation illustrated by Fig. 5. x 150.
the patient
rchose
x 150.
the patient P202.
from
whose
tumour is ilLustrak*d
by
x 150. from
the patient
whose
(to face
tumour
is
p. 474)
475
The Growth of Human Tumours in Immune Deprived Mice Table 1. Twenty-two tumours growing successfully: Fraction of tumour implantsfrom eachpatient growing to 75 mm 3 and 9 cm3; and the time, post implantation, at which these volumes were reached
Identity P P P P P P P P P
91 202 234 300 224 137 293 39 210
P 88 P 105 P P P P P P P P P P P
246 303 338 95 337 208 122 55 146 242 181
Tumour volume Time taken Turnout volume Time taken of 75 m m 3 (months) of 9 em 3 (months)
Tumour Ca. colon Ca. colon Ca. colon Ca. colon Ca. rectum Ca. rectum Ca. rectum Hypernephroma Ca. ovary (pseudomucinous) Ca. ovary (pseudomucinous) Ca. ovary (granulosacell) Ca. bronchus Ca. bronchus Glioma Ca. larynx Ca cervix Melanoma Melanoma Neuroblastoma Teratoma Teratoma Fibrosarcoma
6/10 6/6 4/6 (1/6)* 1/5 (1/5) 4/6 6/8 (2/8) 6/6 2/5
I-5 2-3 2-4½ 6 1-2½ 1-1½ 1-1½ 2-2½
5/10 6/6 3/6 0/5 4/6 3/8 4/6 1/5
3-7 3½-9 6-8 -4-5 3-6½ 4-5 8
5/8 (2/8)
3-3½
2/8
7-9
2/6
4-6
0/6
--
10/10 (6/10) 5/5 (2/5) 4/6 (3/6) 2/5 2/6 3/7 (2/7) 5/5 (2/5) 1/5 3/5 (1/5) 2/5 6/6 (4/6) 2/7
5-9 2-4½ 3-9 2-3 3-5 7-9 3-9 2 5-6½ 2-4 2-9 1-5
0/6 3/5 0/6 2/5 0/6 0/7 0/5 0/5 0/5 0/5 0/6 0/7
-6-8½ -5-6 ---------
*The fraction in brackets indicates implants regressing spontaneously before termination of the experiment at 9 months.
Table 2. Implantation of human tumour in immune deprived mice. Number of patients from whom tumour implants reached a volume of 75 mm 3 and 9 cm3 Tumour Growth Ca. colon Ca. rectum Hypernephroma Ca. ovary Ca. bronchus Glioma Ca. larynx Ca. cervix Melanoma Neuroblastoma Teratoma Fibrosarcoma No growth Ca. pancreas Ca. breast Ca. bladder Ca. stomach Lymphsarcoma Hodgkin's disease
75 m m a 9 cm a 4/5* 3/5 1/3 3/6 2/4 1/3 I/5 1/4 1/ 1 2/4 1/4
3/5* 3/5 1/3 1/6 1/4 1/3 0/5 0/4 0/7 0/1 0/4 0/2
0/I 0/I0 0/3 0/3 0/8 0/7
0/1 0/10 0/10 0/3 0/4 0/5
2/7
*This fraction is the number of patients from whom successful tumour growth was obtained divided by the total number of patients bearing that particular tumour.
implanted tumour, and most probably related to the animals having received irradiation at a high dose level.
DISCUSSION Carcinoma of the large bowel will grow with relative ease subcutaneously in immune deprived mice [6]. The implanted tumour frequently grows progressively until it threatens to overwhelm the host. On other occasions the tumour grows for some months and then regresses. In this series of tumours from 83 patients the only other types of tumour that grew as successfully were carcinomas of the ovary, kidney and bronchus, and a glioma. However, this was by no means an exhaustive survey either in numbers and types of tumours or period of post-implantation observation. There is as yet no clear indication why some tumours grow well in immune deprived mice and others not at all. At one time it was thought that the mucin secreted by the ovarian and large bowel tumour ceils contributed to their successful growth in the foreign host. Although this m a y be so, in the later stages of this study non mucin secreting tumours of the large bowel
476
L. M. Cobb and B. C. V. Mitchley
were observed to proliferate as successfully as those secreting large amounts of mucin. In work to be published elsewhere we have observed with some tumours an extensive polymorph and macrophage infiltration and destruction of the implant within 48 hr of implantation. The reaction was frequently so severe that very few viable tumour cells could be identified. Other tumour implants were found to have provoked no cellular reaction by the host at 48 hr and to be obviously viable. The changes in volume of an established tumour are the outward manifestation of the delicate balance of cell proliferation and cell death. This balance is tipped towards cell proliferation in the "natural" host of a tumour except in the event of spontaneous regression. It is perhaps not surprising to find that when a tumour is transplanted to a foreign host the delicate balance can become tipped towards cell death. The regressions observed some months after tumours appeared to be establish-
ed may have been due to a slowly developing immunological rejection [7], or the eventual restraint of tumour growth by the tissue control factors of the host. U p until the last few years most of our experience with transplanted tumours has been with the rapidly proliferating anaplastic animal tumours. These tumours provide the experimentalist with quick results, but in some cases their relevance to the slowly growing malignant tumours of man must be questioned. If more work is to be done using the early passages of human tumour in immune deprived rodents, we shall have to be prepared to wait months rather than days for results because the implanted human tumour generally grows at much the same rate as is observed in the patient. It will be some years before we are able to relate the behaviour and response to therapy of a patient's tumour growing in a mouse to the likely behaviour of that piece o f t u m o u r had it remained in the patient.
REFERENCES
1. 2.
3. 4. 5. 6. 7.
H . W . TOOLAN,Growth of human tumours in cortisone-treated laboratory animals: the possibility of obtaining permanently transplantable human tumours. Cancer Res. 13, 389 (1953). C . O . POVLSEN and J. RVGAARD, Heterotransplantation of human adenocarcinomas of the colon and rectum to the mouse mutant nude. A study of nine consecutive transplantations. Aeta path. microbiol, scan& Sect. A, 79~ 159 (1971). L.M. COBB,Metastic spread of human tumour inplanted into thymectomized, antithymocyte serum treated hamsters. Brit. J. Cancer26, 183 (1972). L . M . COBB, E. A. M. BOESENand A. M. NEVILLE, Clear cell carcinoma of the human ovary transplanted to the peritoneal cavity of the hamster. Transplantation 16, 76 (1973). J . F . A . P . MILLER, Role of the thymus in recovery of the immune mechanism in the irradiated adult mouse. Proc. Soc. exp. Biol. 112, 785 (1963). L . M . COBB, The behaviour of carcinoma of the large bowel in man following transplantation into immune-deprived mice. Brit. J. Cancer 28, 400 (1973). P . C . L . BEVERLEYand E. SimPSON, Humoral responses to tumour xenografts in ALS-treated mice. Int. J. Cancer 6, 415 (1970).
The Growth of Human Tumours in Immune Deprived Mice L. M. COBB* and B. C. V. MITCHLEY Department of Functional Pathology, Chester Beatty Research Institute, Institute of Cancer Research: Royal Cancer Hospital, Fulham Road, London SW3 6JB, England
Abstract--The growth of human tumours was studied in immune deprived mice. Immune deprivation was obtained by a combination of thymectomy, whole body irradiation and bone marrow replacement. Five hundred and twenty mice were implanted with 18 different types of tumour from 83 pat#nts. Tumour from 22 of these 83 patients grew in the immune deprived mice. The tumours that grew to a volume that threatened the survival of the mice were carcinomas of the colon, rectum, ovary, kidney and bronchus, and a glioma.
suppressed, without the need for giving continuous immunosuppressive treatment [2, 3, 4]. Two techniques have emerged and it is not yet clear which is most suitable for h u m a n tumour growth. One technique is to use mice with congenital thymic aplasia. These animals are also hairless and are referred to as " n u d e " mice. The thymic aplasia is the product of a recessive gene and therefore a carefully controlled breeding programme is required. The " n u d e " mice have so far been used particularly for the in vivo culture of carcinoma of the large bowel [2]. The second technique, which can be applied to most rodents, requires thymectomy followed by the destruction of lymphocytes by irradiation antithymocyte serum and cytotoxic drugs. T u m o u r implanted into immune deprived animals does not always grow. It is becoming apparent that certain types of tumour are more likely to "take" than others. It is the purpose of this paper to illustrate the types of tumour which are likely to grow in one form of immune deprived animal; that is the mouse prepared by thymectomy, whole body irradiation and bone marrow replacement. Having indicated the turnouts that appear to grow most successfully in this preparation the reasons for failure of other classes of tumour are considered
INTRODUCTION
THE GROWTH and metastasis of h u m a n tumours in experimental animals can now be studied by a n u m b e r of different methods. The recent and more successful methods require suppression of the immunological graft rejection processes. Previous techniques depended upon the fact that in certain areas of the body, such as the cheek pouch in the hamster, or the anterior chamber of the eye in rabbits, a graft was offered partial protection from the immunological rejection processes. In the case of the hamster cheek pouch grafts it was possible to enhance this partial protection by the destruction of lymphocytes using cortisone and antimitotic drugs [1]. A drawback to this latter technique was the necessity to treat with immunosuppressive drugs throughout the experiment. Such drugs could interfere with the growth of the tumour. Recently, it has been shown that h u m a n tumour can become established, and in some cases metastasise spontaneously, in animals in which the graft rejection process has been Accepted 12 March 1974. *Present address: Huntingdon Research Centre, Huntingdon PEI8 6ES, England. 473
474
L. M. Cobb and B. C. V. Mitchley
The possible clinical use of the growth of specimens of patient's tumour in immune deprived animals is discussed.
MATERIALS AND METHODS
Tumour specimens T u m o u r specimens reached the laboratory between 10 min and 4 hr after removal from the patient. T u m o u r areas that appeared to be viable were dissected out. One mm thick slices were cut for transplantation. Adjacent viable tumour was fixed in Bouin's solution and prepared by conventional methods for histological examination. The 1 mm thick slices of the tumour were pared to an area of approximately 9 m m 2 before being transplanted subcutaneously into the right flank of from 4 to 10 mice, depending on the size of the specimen from the patient. The mice were anaesthetized with ether. A total of 520 implantations were made from tumour removed from 83 patients.
Experimental animals Male and female CBA/Iac mice were used. The breeding stock were obtained from the Laboratory Animals Centre, Carshalton, Surrey, England. The mice were given sterile food and water ad libitum. Whenever it was thought possible that the growth of the transplant could be effected by sex hormones, the sex of the mouse was chosen to match the sex of the patient.
Technique of immune deprivation The technique used was based on work published by Miller in 1963 [5]. The mice were thymectomized at 4 weeks of age, 4 weeks later they were given 900 t a d whole body irradiation. Irradiation was given at 60 rad per rain using a 220 kV X-ray machine, hvl 0.4 m m Cu, focal distance 100 cm. Without a bone marrow graft this dose of irradiation would have been lethal. Within 6 hr of irradiation each mouse received 5 x 106 syngeneic femoral bone marrow cells intravenously. The tumour was implanted between 2 and 4 weeks after the irradiation and bone marrow replacement.
Observation of tumour implanted immune deprived mice The mice were observed 3-5 times weekly for 9 months, at the end of which time they were killed. Animals were killed before this time if they were ailing or if the turnout had reached a size of 9 m m 3. An extensive necropsy examination was carried out on all mice. A particular search was made for evidence of metastatic involvement of lymph nodes draining the site of implantation and of spread to
distant tissues. Tissues with signs of pathological changes were fixed in Bouin's solution. Sections were cut, and stained with haematoxylin and eosin.
Recording tumour growth The subcutaneously implanted tumours were measured once weekly. Particular note was taken of the turnouts at 2 sizes, 75 m m 3 and 9 cm 3. The 75 m m 3 stage was selected because experience showed that this was the smallest turnout volume at which it was possible to be confident that growing tumour was present, rather than a foreign body reaction. The second stage, 9 cm 3, was chosen because this volume approached the volume that wouId cause debility in the animal.
RESULTS
Subcutaneous tumour implants gaining a volume of 75 mm 3 Twenty-two tumours were established (gained a volume of 75 mm 3) of the 83 tumours implanted (Tables 1 and 2). Unfortunately, with a tumour at the volume of 75 turn 3, it was not possible to obtain a confirmatory biopsy and still allow normal growth of the tumour. However, in 8 mice a tumour of 75 m m 3 was present when the mice were killed at 9 months. In all these animals there was viable tumour. O f the 87 individual implants that gained 75 mm 3 26 subsequently regressed completely before 9 months.
Subcutaneous tumour implants growing to a volume of 9 cm 3 Only 10 of the 22 tumours that grew to a size of 75 m m ~ continued to grow to a volume of 9 cm 3 within the 9 month period (Table 1). These 10 consisted of 3 cases of carcinoma of colon, 3 cases of carcinoma of rectum, 1 case of carcinoma of ovary, 1 case of glioma, 1 case of hypernephroma and 1 case of carcinoma of bronchus. The histological appearance of the tumour removed from the animals was strikingly similar to areas of the respective patients tumours (Figs. 1-6).
Post-mortem findings In none of the mice examined macroscopically 9 months after implantation, or before 9 months if the tumour had reached 9 cm 3, was there any evidence of metastatic spread of the tumour. Twenty-nine of the 520 implanted mice died before the completion of the experiment from causes apparently unrelated to the
Fig. Fig.
2.
Carcinoma
4.
Teratoma
growing
3.
6.
Carcinoma
of
of bronchus
on removal from
the patient
growing subcutaneously in mice 6 months tumour is illustrated by Fig. 1. x 150.
Teratoma
subcutaneously Fig.
Fig.
Carcinoma
of the bronchus
Fig. Fig.
1.
5.
colon growing
of
testes
on removal
from
Carcinoma
after’
the patient
in mice 9 months after implantation Fig. 3. x 150. of colon on removal from
P246
from
patient
x 150.
imi)lantation P242.
subcutaneously in mice 5 months after implantation illustrated by Fig. 5. x 150.
the patient
rchose
x 150.
the patient P202.
from
whose
tumour is ilLustrak*d
by
x 150. from
the patient
whose
(to face
tumour
is
p. 474)
475
The Growth of Human Tumours in Immune Deprived Mice Table 1. Twenty-two tumours growing successfully: Fraction of tumour implantsfrom eachpatient growing to 75 mm 3 and 9 cm3; and the time, post implantation, at which these volumes were reached
Identity P P P P P P P P P
91 202 234 300 224 137 293 39 210
P 88 P 105 P P P P P P P P P P P
246 303 338 95 337 208 122 55 146 242 181
Tumour volume Time taken Turnout volume Time taken of 75 m m 3 (months) of 9 em 3 (months)
Tumour Ca. colon Ca. colon Ca. colon Ca. colon Ca. rectum Ca. rectum Ca. rectum Hypernephroma Ca. ovary (pseudomucinous) Ca. ovary (pseudomucinous) Ca. ovary (granulosacell) Ca. bronchus Ca. bronchus Glioma Ca. larynx Ca cervix Melanoma Melanoma Neuroblastoma Teratoma Teratoma Fibrosarcoma
6/10 6/6 4/6 (1/6)* 1/5 (1/5) 4/6 6/8 (2/8) 6/6 2/5
I-5 2-3 2-4½ 6 1-2½ 1-1½ 1-1½ 2-2½
5/10 6/6 3/6 0/5 4/6 3/8 4/6 1/5
3-7 3½-9 6-8 -4-5 3-6½ 4-5 8
5/8 (2/8)
3-3½
2/8
7-9
2/6
4-6
0/6
--
10/10 (6/10) 5/5 (2/5) 4/6 (3/6) 2/5 2/6 3/7 (2/7) 5/5 (2/5) 1/5 3/5 (1/5) 2/5 6/6 (4/6) 2/7
5-9 2-4½ 3-9 2-3 3-5 7-9 3-9 2 5-6½ 2-4 2-9 1-5
0/6 3/5 0/6 2/5 0/6 0/7 0/5 0/5 0/5 0/5 0/6 0/7
-6-8½ -5-6 ---------
*The fraction in brackets indicates implants regressing spontaneously before termination of the experiment at 9 months.
Table 2. Implantation of human tumour in immune deprived mice. Number of patients from whom tumour implants reached a volume of 75 mm 3 and 9 cm3 Tumour Growth Ca. colon Ca. rectum Hypernephroma Ca. ovary Ca. bronchus Glioma Ca. larynx Ca. cervix Melanoma Neuroblastoma Teratoma Fibrosarcoma No growth Ca. pancreas Ca. breast Ca. bladder Ca. stomach Lymphsarcoma Hodgkin's disease
75 m m a 9 cm a 4/5* 3/5 1/3 3/6 2/4 1/3 I/5 1/4 1/ 1 2/4 1/4
3/5* 3/5 1/3 1/6 1/4 1/3 0/5 0/4 0/7 0/1 0/4 0/2
0/I 0/I0 0/3 0/3 0/8 0/7
0/1 0/10 0/10 0/3 0/4 0/5
2/7
*This fraction is the number of patients from whom successful tumour growth was obtained divided by the total number of patients bearing that particular tumour.
implanted tumour, and most probably related to the animals having received irradiation at a high dose level.
DISCUSSION Carcinoma of the large bowel will grow with relative ease subcutaneously in immune deprived mice [6]. The implanted tumour frequently grows progressively until it threatens to overwhelm the host. On other occasions the tumour grows for some months and then regresses. In this series of tumours from 83 patients the only other types of tumour that grew as successfully were carcinomas of the ovary, kidney and bronchus, and a glioma. However, this was by no means an exhaustive survey either in numbers and types of tumours or period of post-implantation observation. There is as yet no clear indication why some tumours grow well in immune deprived mice and others not at all. At one time it was thought that the mucin secreted by the ovarian and large bowel tumour ceils contributed to their successful growth in the foreign host. Although this m a y be so, in the later stages of this study non mucin secreting tumours of the large bowel
476
L. M. Cobb and B. C. V. Mitchley
were observed to proliferate as successfully as those secreting large amounts of mucin. In work to be published elsewhere we have observed with some tumours an extensive polymorph and macrophage infiltration and destruction of the implant within 48 hr of implantation. The reaction was frequently so severe that very few viable tumour cells could be identified. Other tumour implants were found to have provoked no cellular reaction by the host at 48 hr and to be obviously viable. The changes in volume of an established tumour are the outward manifestation of the delicate balance of cell proliferation and cell death. This balance is tipped towards cell proliferation in the "natural" host of a tumour except in the event of spontaneous regression. It is perhaps not surprising to find that when a tumour is transplanted to a foreign host the delicate balance can become tipped towards cell death. The regressions observed some months after tumours appeared to be establish-
ed may have been due to a slowly developing immunological rejection [7], or the eventual restraint of tumour growth by the tissue control factors of the host. U p until the last few years most of our experience with transplanted tumours has been with the rapidly proliferating anaplastic animal tumours. These tumours provide the experimentalist with quick results, but in some cases their relevance to the slowly growing malignant tumours of man must be questioned. If more work is to be done using the early passages of human tumour in immune deprived rodents, we shall have to be prepared to wait months rather than days for results because the implanted human tumour generally grows at much the same rate as is observed in the patient. It will be some years before we are able to relate the behaviour and response to therapy of a patient's tumour growing in a mouse to the likely behaviour of that piece o f t u m o u r had it remained in the patient.
REFERENCES
1. 2.
3. 4. 5. 6. 7.
H . W . TOOLAN,Growth of human tumours in cortisone-treated laboratory animals: the possibility of obtaining permanently transplantable human tumours. Cancer Res. 13, 389 (1953). C . O . POVLSEN and J. RVGAARD, Heterotransplantation of human adenocarcinomas of the colon and rectum to the mouse mutant nude. A study of nine consecutive transplantations. Aeta path. microbiol, scan& Sect. A, 79~ 159 (1971). L.M. COBB,Metastic spread of human tumour inplanted into thymectomized, antithymocyte serum treated hamsters. Brit. J. Cancer26, 183 (1972). L . M . COBB, E. A. M. BOESENand A. M. NEVILLE, Clear cell carcinoma of the human ovary transplanted to the peritoneal cavity of the hamster. Transplantation 16, 76 (1973). J . F . A . P . MILLER, Role of the thymus in recovery of the immune mechanism in the irradiated adult mouse. Proc. Soc. exp. Biol. 112, 785 (1963). L . M . COBB, The behaviour of carcinoma of the large bowel in man following transplantation into immune-deprived mice. Brit. J. Cancer 28, 400 (1973). P . C . L . BEVERLEYand E. SimPSON, Humoral responses to tumour xenografts in ALS-treated mice. Int. J. Cancer 6, 415 (1970).