Colony-stimulating factors in inflammation and autoimmunity.

Although they were originally defined as haematopoietic-cell growth factors, colony-stimulating factors (CSFs) have been shown to have additional functions by acting directly on mature myeloid cells. Recent data from animal models indicate that the depletion of CSFs has therapeutic benefit in many inflammatory and/or autoimmune conditions and as a result, early-phase clinical trials targeting granulocyte/macrophage colony-stimulating factor and macrophage colony-stimulating factor have now commenced. The distinct biological features of CSFs offer opportunities for specific targeting, but with some associated risks. Here, I describe these biological features, discuss the probable specific outcomes of targeting CSFs in vivo and highlight outstanding questions that need to be addressed.

Mice lacking three myeloid colony-stimulating factors (G-CSF, GM-CSF, and M-CSF) still produce macrophages and granulocytes and mount an inflammatory response in a sterile model of peritonitis.

To assess the combined role of G-CSF, GM-CSF, and M-CSF in myeloid cell production, mice deficient in all three myeloid CSFs were generated (G-/-GM-/-M-/- mice). G-/-GM-/-M-/- mice share characteristics found in mice lacking individual cytokines: they are toothless and osteopetrotic and furthermore acquire alveolar proteinosis that is more severe than that found in either GM-/- or G-/-GM-/- mice. G-/-GM-/-M-/- mice have a significantly reduced lifespan, which is prolonged by antibiotic administration, suggesting compromised ability to control bacterial infection. G-/-GM-/-M-/- mice have circulating neutrophils and monocytes, albeit at significantly reduced numbers compared with wild-type mice, but surprisingly, have more circulating monocytes than M-/- mice and more circulating neutrophils than G-/-GM-/- mice. Due to severe osteopetrosis, G-/-GM-/-M-/- mice show diminished numbers of myeloid cells, myeloid progenitors, and B lymphocytes in the bone marrow, but have significantly enhanced compensatory splenic hemopoiesis. Although G-/-GM-/-M-/- mice have a profound deficiency of myeloid cells in the resting peritoneal cavity, the animals mount a moderate cellular response in a model of sterile peritonitis. These data establish that in the absence of G-CSF, GM-CSF, and M-CSF, additional growth factor(s) can stimulate myelopoiesis and acute inflammatory responses.

CSF-deficient mice--what have they taught us?

Haemopoietic growth factor-deficient mice have been particularly instructive for defining the usual physiological role of these factors. Mice now exist lacking the granulopoietic factors G-CSF, GM-CSF, M-CSF (CSF-1), SCF, several other factors influencing haemopoiesis (including erythropoietin, interleukins 5 and 6), combinations of these factors (GM- & M-CSF; G- & GM-CSF; G- & GM- & M-CSF) and several CSF receptor components. Most of these mice were generated by targeted gene disruption, others are spontaneously arising mutants. The phenotypes of these mice indicate that the granulopoietic factors have both unique and redundant roles in vivo. Some factors are uniquely important in baseline myelopoiesis. Experimental infection of CSF-deficient mice indicates unique roles for some factors in emergency 'overdrive' haemopoiesis. Recovery from myeloablation evaluates the role of CSFs in emergency 'restoring normality' haemopoiesis. Redundancy also exists in the capacity of CSFs to support complete granulocyte development in vivo. Some factors are not involved in all the in vivo roles suggested by the range of their actions demonstrable in vitro. Some CSFs have indispensable roles in non-haemopoietic tissues. Some factors have in vivo roles not anticipated from previous studies. Mice deficient in several factors have identified compensating roles for factors by revealing exacerbated and additional phenotypic features, and may unmask additional in vivo roles.

Granulocyte-macrophage colony-stimulating factor corrects macrophage deficiencies, but not osteopetrosis, in the colony-stimulating factor-1-deficient op/op mouse.

The op mutation in the mouse is in the coding region of the colony-stimulating factor-1 (CSF-1) gene, prevents formation of biologically active factor, and, thus, results in generalized macrophage deficiency and, in osteopetrosis, secondary to deficiency of osteoclasts. Although a few macrophages and osteoclasts are present in these mutants, it was not clear whether the inability of endogenous granulocyte-macrophage CSF (GM-CSF) to compensate for the absence of CSF-1 was due to the limitations of biological activity of this molecule or to its inability to reach respective target populations. In this study, we examined whether sc GM-CSF in large doses (20-40 micrograms/mouse.day) for 3 weeks would correct some or all of the deficiencies observed in mutant mice. All organ macrophage populations tested (liver, spleen, thymus, marrow, pleural, and peritoneal cavity) were significantly increased, reaching levels exceeding those observed in normal mice. Restoration of peritoneal and pleural macrophage populations by sc GM-CSF is of particular interest, because it was not previously observed in op/op mice treated with sc CSF-1. In contrast, there was no indication of increased bone resorption, no appearance of osteoclasts, and no tooth eruption in response to GM-CSF treatment. These data suggest that GM-CSF is able to compensate for the absence of CSF-1 during macrophage formation, but is unable to play a similar role in osteoclast differentiation.

Defective T-lymphocyte colony formation in patients with lupus nephritis.

To determine whether patients with systemic lupus erythematosus (SLE) and active nephritis have more profound defects in cell-mediated immunity (CMI), we studied T-colony-forming cells (TCFC) in 12 patients with lupus nephritis (LN) and 14 patients with chronic mesangial proliferative glomerulonephritis (CGN) without renal insufficiency. We also examined the activity of T-colony-stimulating factor (TCSF) in media conditioned by phytohaemagglutinin (PHA) stimulated peripheral blood lymphocytes (PHA-LCM). The levels of TCFC and TCSF were decreased in patients with LN compared with those in normal controls and lower in LN patients with the nephrotic syndrome (NS) than in those without NS. In contrast, these CMI parameters in CGN patients with or without NS did not differ from normal subjects. TCSF activity for TCFC in both normal individuals and LN patients was removed from PHA-LCM with interleukin 2 (IL 2) receptor bearing cultured T cells. These in vitro findings suggest that IL 2 is the essential factor contained in PHA-LCM. Our observations may lend further insight into the understanding of the immunoregulatory defect in LN.

Relative and absolute deficiency of bone marrow endogenous colony stimulating activity in acute myeloid leukemia: relation to response to chemotherapy.

The purpose of this study was to determine possible mechanisms for the recently observed association between insensitivity of acute myeloid leukemia (AML) clonogenic cells to colony stimulating activity (CSA) and poor response to induction chemotherapy. The bone marrow endogenous CSA was determined using semi-solid agar cultures by measuring the response of the AML patients' own clonogenic cells to endogenous CSA. The results show that whereas 31% (5/16) of patients at presentation have deficient bone marrow endogenous CSA production, over 50% (11/21) have relative deficiency of endogenous CSA, due to insensitivity of the patients' clonogenic cells to CSA. Although there is an association between relative deficiency of endogenous CSA and a poor response to therapy, the relationship is not close enough to explain the previously observed highly significant correlation between insensitivity to CSA and poor response to therapy. The CSA-insensitive phenotype and poor response to therapy, one via the tendency to relative endogenous CSA deficiency in the CSA-insensitive group and another via some additional feature of these poor response AML phenotypes which is independent of the presence or absence of endogenous CSA deficiency.