ABSTRACT
This chapter discusses a number of factors and reviews some of the methods that have been used to circumvent the supposed suppression of tumorigenicity. Tumorigenicity, operationally defined as the ability to grow and produce tumors in an in vivo environment, is a crucial feature of the malignant behavior of tumor cells. A large variety of human cancer cell lines and tumor tissue specimens could be propagated in nude mice, often as serially transplantable tumor lines. The role macrophages play in the prevention of human tumor growth in nude mice is based largely on indirect evidence. The probability of acceptance of human tumor transplants in the nude mouse varies considerably for different tumor types. Cyclophosphamide, an alkylating agent with antitumor activity, has been shown to modulate immune reactions in a very complex manner. The rationale of the treatment with anti-mouse interferon serum is based on the prevention of interferon-mediated augmentation of NK cell activity upon tumor implantation.
