Immunological control of human leukemia: discussion.

Human leukemias are many diseases. Even if discussion is restricted to human acute leukemias, the topic ordinari ly discussed in the context of animal model systems, these still are many diseases. They are subclassif ied by characteristics of cytological type. In some animal model systems one can modify the host by such maneuvers as aging or by sptenectomy or thymectomy and thereby alter the cytological type of leukemia that appears. Thus different acute leukemias in man may be interrelated. The different morphologies or different antigens do not necessarily imply different et iological agents. The classic disease called acute leukemia of chi ldhood peaks at about 3 to 4 years of age. The frequency of acute leukemia drops to a constant plateau of low incidence until about age 40, after which it cont inuously increases until the end of life. The cytological type is predominant ly acute lymphocyt ic in chi ldhood and changes to acute myelocytic and myelomonocyt ic in adult life (8). Acute leukemia is a group of diseases with rapid growth kinetics. With what we know about the kinetics of leukemic cell mult ipl icat ion, the t ime from presumptive onset to symptoms or to death is very short. The l ikel ihood of making a diagnosis of acute leukemia by using immunodiagnost ic techniques before recognizable clinical features appear is, in my view, remote. One need only look at current practice in pediatrics and how often pediatricians use antibiot ics for diseases known to have bacterial or igin wi thout making bacterial cultures. Although acute leukemia is the commonest cancer of chi ldhood, it still consti tutes only 4 to 8 cases among 100,000 children per year, superimposed upon thousands and thousands of viral and bacterial diseases for which diagnostic tests are not now taken. It is improbable that immunological tests for diagnosis would make any signif icant impact on leukemia discovery and treatment, even if a test were available. The same phenomenon is true in adults. There is, in my view, no accepted known virus responsible for human leukemia. The observation of virus recovery from acute myelocytic leukemia is a few months old but is not yet accepted as demonstrat ion of a causal agent, albeit an associated one (6). This detracts, for the present, from the concept of a vaccine prepared from a leukemic virus. Acute lymphocytic leukemia occurs primari ly in the 1st decade of life. This should be the easiest of all leukemias to prevent. Furthermore, one could gain an end point while the investigator was still alive. Despite its early occurrence,