Laboratory models of minimal residual cancer; development and preliminary immunotherapy studies

It is the author's contention that if we wish to investigate immunotherapy for cancer in laboratory models, the model must reproduce or at least mimic the biological conditions which are encountered in clinical oncologic practice. The usual experimental animal tumor systems do not satisfy this requirement. They are usually studied as primary transplants of rapidly progressive tumors which kill in a few weeks, and experimental treatments are usually started within a day of two after implantation, before the tumor is detectable by ordinary methods of examination. In clinical oncology the existence of cancer is seldom suspected until it reaches a clinically detectable mass, and it is then treated by various established methods which, if not curative, at least reduce tumor mass temporarily before the tumor recurs locally or at distant sites. A cancer patient, therefore, has a rather prolonged exposure to his tumor and an opportunity to develop immune and other biological responses to it. Present animal models are therefore inadequate for immunotherapy research. This paper examines the prerequisites for more accetable experimental tumor models for immunotherapeutic research, describes a step-by-step investigation leading to the development of what to seems to be more appropriate models, and describes preliminary immunotherapy studies in one of the models, in which parabiosis is used as a means of transfering antitumor resistance to the "patients" from specificially immunized donors.