In human breast carcinomas, overexpression of the macrophage colony–stimulating factor (CSF-1) and its receptor (CSF-1R) correlates with poor prognosis. To establish if there is a causal relationship between CSF-1 and breast cancer progression, we crossed a transgenic mouse susceptible to mammary cancer with mice containing a recessive null mutation in the CSF-1 gene (Csf1op) and followed tumor progression in wild-type and null mutant mice. The absence of CSF-1 affects neither the incidence nor the growth of the primary tumors but delayed their development to invasive, metastatic carcinomas. Transgenic expression of CSF-1 in the mammary epithelium of both Csf1op/Csf1op and wild-type tumor-prone mice led to an acceleration to the late stages of carcinoma and to a significant increase in pulmonary metastasis. This was associated with an enhanced infiltration of macrophages into the primary tumor. These studies demonstrate that the growth of mammary tumors and the development to malignancy are separate processes and that CSF-1 selectively promotes the latter process. CSF-1 may promote metastatic potential by regulating the infiltration and function of tumor-associated macrophages as, at the tumor site, CSF-1R expression was restricted to macrophages. Our data suggest that agents directed at CSF-1/CSF-1R activity could have important therapeutic effects.

The effects of colony-stimulating factor 1 (CSF-1), the primary regulator of mononuclear phagocyte production, are thought to be mediated by the CSF-1 receptor (CSF-1R), encoded by the c-fms proto-oncogene. To investigate the in vivo specificity of CSF-1 for the CSF-1R, the mouse IntroductionColony-stimulating factor 1 (CSF-1) regulates the survival, proliferation, and differentiation of mononuclear phagocytic cells and is the primary regulator of mononuclear phagocyte production in vivo. 1,2 However, CSF-1 also regulates cells of the female reproductive tract and plays an important role in fertility. 3,4 The effects of CSF-1 are mediated by a high-affinity receptor tyrosine kinase (CSF-1R) [5][6][7][8] encoded by the c-fms proto-oncogene. 9 The CSF-1R is expressed on primitive multipotent hematopoietic cells, 10,11 mononuclear phagocyte progenitor cells, 12 monoblasts, promonocytes, monocytes, 5,6 tissue macrophages, 6,13-15 osteoclasts, 16 B cells, 17,18 smooth muscle cells, 19 and neurons. 20,21 CSF-1R messenger RNA (mRNA) is expressed in Langerhans cells, 22 in the female reproductive tract, in oocytes and embryonic cells of the inner cell mass and trophectoderm, 23 in decidual cells, [24][25][26] and in cells of the trophoblast. 24,25 The expression of the CSF-1R on primitive hematopoietic cells that are unable to proliferate in vitro in response to CSF-1 alone 10,11 but are able to proliferate and differentiate if stimulated with combinations of CSF-1 and other hematopoietic growth factors 10,11,27 suggests that CSF-1R is involved in the regulation of more primitive hematopoietic cells than those that form macrophage colonies in vitro in response to CSF-1 alone.Mice homozygous for the mutation osteopetrotic 28 possess an inactivating mutation in the coding region of the CSF-1 gene and are devoid of detectable CSF-1. 29,30 These Csf1 op /Csf1 op mice are osteopetrotic because of an early and marked deficiency of osteoclasts 28 that spontaneously recovers with age, 31,32 probably because of the action of vascular endothelial growth factor. 33 However, the phenotype of these mice is pleiotropic. 3 They are toothless; have low body weight, low growth rate, and skeletal abnormalities; and are deficient in tissue macrophages. 2,28,30,34,35 They have defects in both male and female fertility, neural development, the dermis, and synovial membranes. 3 The pleiotropic phenotype of the Csf1 op /Csf1 op mouse may be due to a reduction in trophic and/or scavenger functions of the tissue macrophages regulated by CSF-1, secondary to the reduction of their concentration in tissues, 2 because outside the female reproductive tract the CSF-1R is primarily expressed in mononuclear phagocytes. 1,3 However, it is possible that some of these effects may also be due to loss of function of other cells such as neuronal cells and muscle precursors, which have also been reported to express the CSF-1R. 20,36 To address the questions of whether CSF-1 activates other receptors besides the CSF-1R and, conversely, whether the CSF-1R me...

Tuberculosis remains a leading cause of death worldwide, despite the availability of effective chemotherapy and a vaccine. Bacillus Calmette-Gué rin (BCG), the tuberculosis vaccine, is an attenuated mutant of Mycobacterium bovis that was isolated after serial subcultures, yet the functional basis for this attenuation has never been elucidated. A single region (RD1), which is absent in all BCG substrains, was deleted from virulent M. bovis and Mycobacterium tuberculosis strains, and the resulting ⌬RD1 mutants were significantly attenuated for virulence in both immunocompromised and immunocompetent mice. The M. tuberculosis ⌬RD1 mutants were also shown to protect mice against aerosol challenge, in a similar manner to BCG. Interestingly, the ⌬RD1 mutants failed to cause cytolysis of pneumocytes, a phenotype that had been previously used to distinguish virulent M. tuberculosis from BCG. A specific transposon mutation, which disrupts the Rv3874 Rv3875 (cfp-10 esat-6) operon of RD1, also caused loss of the cytolytic phenotype in both pneumocytes and macrophages. This mutation resulted in the attenuation of virulence in mice, as the result of reduced tissue invasiveness. Moreover, specific deletion of each transcriptional unit of RD1 revealed that three independent transcriptional units are required for virulence, two of which are involved in the secretion of ESAT-6 (6-kDa early secretory antigenic target). We conclude that the primary attenuating mechanism of bacillus Calmette-Gué rin is the loss of cytolytic activity mediated by secreted ESAT-6, which results in reduced tissue invasiveness. B acillus Calmette-Guérin (BCG) was first isolated fromMycobacterium bovis after serial subculturing in ox bile medium (1, 2), when Drs. Calmette and Guérin set out to test the hypothesis that a bovine tubercle bacillus could transmit pulmonary tuberculosis after oral administration (1, 3, 4). However, unexpectedly after the 39th passage, the strain was unable to kill experimental animals (1, 2), and showed no reversion to virulence even after the authors had performed over 200 passages (3), which is consistent with the attenuating mutation being a deletion mutation. In proceeding studies, BCG was determined to be able to protect animals receiving a lethal challenge of virulent tubercle bacilli (5), and in 1921 was first used as an anti-tuberculous vaccine (6). Presently, an estimated 3 billion doses have been used to vaccinate the human population against tuberculosis, yet the mechanism that causes the attenuation of BCG remains unknown.Mahairas et al. (6) first compared the genomic sequences of BCG and M. bovis, by using subtractive hybridization, and found that there were three regions of difference (designated RD1, RD2, and RD3) present in the genome of M. bovis, but missing in BCG. Behr et al. (7), and others (8), later identified 16 large deletions, including RD1-RD3, which were present in the Mycobacterium tuberculosis genome but absent in BCG. Eleven of these 16 deletions were unique to M. bovis whereas the remaining 5 del...