PREDICTION OF THE ROLE OF GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR IN ANIMALS AND MAN FROM IN-VITRO RESULTS

The possibility of predicting the clinical effects of cytokines from i n vitro data is discussed, using GM-CSF as an example. GM-CSF incubate d with bone marrow cells has been shown to induce proliferation and co lony formation, predominantly of the colony-forming unit granulocyte a nd granulocyte-macrophage types. Daily treatment of normal monkeys wit h GM-CSF resulted in transient neutropenia followed by neutrophilia. A fter withdrawal of GM-CSF the neutrophil levels returned to baseline. Predictably, GM-CSF administration results in accelerated neutrophil r ecovery in patients with chemotherapy-induced neutropenia. GM-CSF has also been shown to induce microbial killing by neutrophils and monocyt es in vitro. This activity translated into a dose-related protection o f GM-CSF-pretreated mice infected with lethal doses of micro-organisms . Interleukin-3 (IL-3) increases the cellularity of the bane marrow an d GM-CSF can induce mobilization of bone marrow cells into the periphe ral blood. Therefore, it was predicted and subsequently proved that a combination of these cytokines is synergistic, increasing the yields o f peripheral blood progenitor cells which could be collected and then retransplanted into patients undergoing myeloablative chemotherapy. Mo nkeys injected with recombinant human IL-3 and GM-CSF had increased an tibody titres to human IL-3 compared with monkeys given IL-3 alone, su ggesting a potential use of GM-CSF which was not predicted from its in vitro results, that of vaccine adjuvancy. Thus, for any new mediator a broad range of tests of its activity in vitro may enable prediction of its activity in vivo, but it is also important to document any unex pected effects in in vivo studies which may give indications of new us es.