366 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1957 



carcinoma virus of the leopard frog studied by Lucke would appear 

 to be such a virus. Then there is the possibility that many may 

 be carrying viruses of etiological importance for cancer which for 

 one reason or another have not yet been discovered. The possibility 

 of mutation of latent viruses into a new strain of etiological impor- 

 tance must also be kept in mind. Pertinent to both of these possi- 

 bilities is the discovery during the past few years of dozens upon 

 dozens of hitherto unknown viruses in human beings. These con- 

 sist of the ECHO viruses isolated from the human intestinal tract, 

 the adenoviruses isolated from the upper respiratory tract and eyes 

 of man, and a group of viruses isolated from human sera. New 

 viruses of man are discovered almost every week. Thus we now have 

 many more human viruses than we know what to do with and there is 

 no reason to shy away from giving consideration to viruses as causa- 

 tive agents in human cancer for lack of the viruses. 



During the past few years there has been an almost unbelievably 

 rapid development of techniques by means of which it is now possible 

 to grow almost all kinds of human and animal cells in the test tube 

 and, as a consequence, vast new opportunities for experimentation 

 on human cells without danger to man have opened to us. These cells 

 are also providing a means for the isolation of new viruses, since many 

 kinds of cells are very susceptible to many viruses. The human 

 amnion cell, which my colleagues Elsa Zitcer, J0rgen Fogh, and 

 Thelma Dunnebacke first obtained from the full-term amnion in cell 

 culture, is proving of great use in this connection as well as in studies 

 on the transition from a normal to a potentially malignant cell. For 

 example, we are finding interesting changes in chromosome number 

 and in ability to grow in cortisone or X-ray treated animals as these 

 human amnion cells are passed in culture. It is also of interest that 

 one of the adenoviruses has been found to destroy human cancer cells 

 both in the human being and in the test tube. Thus a virus may cause 

 a cancer and a virus may destroy a cancer. Unfortunately in the case 

 of Huebner's studies on carcinoma of the human cervix not all of the 

 cancer cells were destroyed and the cancer eventually progressed. 

 However, Huebner, as well as others, is attempting to train a series 

 of viruses to grow on cancer cells, so this approach may not be too 

 hopeless. In the same way it is possible to train cells to respond to 

 viruses and this may provide even better test systems for human 

 viruses as yet undiscovered. Even if eventually one should find no 

 cancer virus among the large number of human viruses, the fact that 

 man carries so many viruses within his cells and that these are con- 

 tinually passing from person to person means that we should be ever 

 alert to the possibility of transduction by these viruses. Of course, 

 there is no confirmed case of transduction in higher organisms as yet. 



