General Conclusions

Abstract

The purpose of this book is to examine whether the immunodepression mediated by suppressor cells has any influence on the carcinogenetic process or on the promotion of tumor progression and metastatic spread. The experimental approaches used to resolve this question must cope, however, with limitations imposed by deriving data from humans rather than from experimental animals. First, unlike using experimental animals, it is not always possible to reduce the “noise” of irrelevant factors such as the activity of drug-induced suppressor cells (see chapter on Induction of Suppressor Cells by Immunostimulants, p. 5) or immunosuppression related to aging (449). Secondly, again unlike in experimental animals, the suppressor-cell function of the cancer patients is always measured by tests in vitro while it is clear that such tests do not always reflect the immunological status in vivo (4). Furthermore, the use of an in vitro test permits the introduction of artifacts, such as induction of suppressor cells by the serum supplementing the culture medium (195). Such tests, if not appropriately controlled, can easily lead to wrong conclusions attributing the suppressor-cell activity to the malignant state rather than to environmental factors.