Steven Μ. Albelda

Cell-cell and cell-substratum interactions are mediated through several different families of receptors. In addition to targeting cell adhesion to specific extracellular matrix proteins and ligands on adjacent cells, these receptors influence many diverse processes including cellular growth, differentiation, junction formation, and polarity. Several families of adhesion receptors have been identified. These include: 1) the integrins, heterodimeric molecules that function both as cell-substratum and cell-cell adhesion receptors; 2) the adhesion molecules of the immunoglobulin superfamily, which are involved in cell-cell adhesion and especially important during embryo-genesis, wound healing, and the inflammatory response; 3) the cadherins, developmentally regulated, calcium-dependent homophilic cell-cell adhesion proteins; 4) the LEC-CAMs, cell adhesion molecules with lectin-like domains that mediate white blood cell/endothelial cell adhesion; and 5) homing receptors that target lymphocytes to specific lymphoid tissue. In this review we summarize recent data describing the structure and function of some of these cell adhesion molecules (with special emphasis on the integrin family) and discuss the possible role of these molecules in development, inflammation, wound healing, coagulation, and tumor metastasis.

PURPOSE: Myeloid suppressor (Gr-1(+)/CD11b(+)) cells accumulate in the spleens of tumor-bearing mice where they contribute to immunosuppression by inhibiting the function of CD8(+) T cells and by promoting tumor angiogenesis. Elimination of these myeloid suppressor cells may thus significantly improve antitumor responses and enhance effects of cancer immunotherapy, although to date few practical options exist. EXPERIMENTAL DESIGN: The effect of the chemotherapy drug gemcitabine on the number of (Gr-1(+)/CD11b(+)) cells in the spleens of animals bearing large tumors derived from five cancer lines grown in both C57Bl/6 and BALB/c mice was analyzed. Suppressive activity of splenocytes from gemcitabine-treated and control animals was measured in natural killer (NK) cell lysis and Winn assays. The impact of myeloid suppressor cell activity was determined in an immunogene therapy model using an adenovirus expressing IFN-beta. RESULTS: This study shows that the chemotherapeutic drug gemcitabine, given at a dose similar to the equivalent dose used in patients, was able to dramatically and specifically reduce the number of myeloid suppressor cells found in the spleens of animals bearing large tumors with no significant reductions in CD4(+) T cells, CD8(+) T cells, NK cells, macrophages, or B cells. The loss of myeloid suppressor cells was accompanied by an increase in the antitumor activity of CD8(+) T cells and activated NK cells. Combining gemcitabine with cytokine immunogene therapy using IFN-beta markedly enhanced antitumor efficacy. CONCLUSIONS: These results suggest that gemcitabine may be a practical strategy for the reduction of myeloid suppressor cells and should be evaluated in conjunction with a variety of immunotherapy approaches.

BRAF encodes a RAS-regulated kinase that mediates cell growth and malignant transformation kinase pathway activation. Recently, we have identified activating BRAF mutations in 66% of melanomas and a smaller percentage of many other human cancers. To determine whether BRAF mutations account for the MAP kinase pathway activation common in non-small cell lung carcinomas (NSCLCs) and to extend the initial findings in melanoma, we screened DNA from 179 NSCLCs and 35 melanomas for BRAF mutations (exons 11 and 15). We identified BRAF mutations in 5 NSCLCs (3%; one V599 and four non-V599) and 22 melanomas (63%; 21 V599 and 1 non-V599). Three BRAF mutations identified in this study are novel, altering residues important in AKT-mediated BRAF phosphorylation and suggesting that disruption of AKT-induced BRAF inhibition can play a role in malignant transformation. To our knowledge, this is the first report of mutations documenting this interaction in human cancers. Although >90% of BRAF mutations in melanoma involve codon 599 (57 of 60), 8 of 9 BRAF mutations reported to date in NSCLC are non-V599 (89%; P < 10(-7)), strongly suggesting that BRAF mutations in NSCLC are qualitatively different from those in melanoma; thus, there may be therapeutic differences between lung cancer and melanoma in response to RAF inhibitors. Although uncommon, BRAF mutations in human lung cancers may identify a subset of tumors sensitive to targeted therapy.

Neutrophil-endothelial cell interactions are mediated by interacting sets of cell adhesion molecules (CAMs) and chemoattractant/activator molecules to form an "adhesion cascade." The initial phase of inflammation, a transient slowing of neutrophils in postcapillary venules, is mediated by selectins. Subsequently, firm adhesion of neutrophils to the vessel wall occurs via interaction of the CD11/CD18 (beta 2) integrins to endothelial ligands such as intercellular adhesion molecule-1 (ICAM-1). This binding requires activation of CD11/CD18 by exposure of the neutrophil to a variety of activating/chemoattractant molecules, such as platelet-activating factor or interleukin-8. Finally, transmigration into tissues occurs, a process that requires both a chemotactic stimulus and engagement of platelet-endothelial cell adhesion molecule-1 (PECAM-1). Several approaches have been used to probe the role of CAMs in vivo. These include the use of blocking antibodies, chimeric selectin-immunoglobulin proteins, sialyl Lewisx oligosaccharides and peptides, along with the study of humans and animals with genetically determined adhesion deficiencies. These studies demonstrate that CAM blockade can effectively inhibit inflammation; however, there appear to be clear differences in the adhesion requirements for particular types of inflammation. By understanding the CAM/chemoattractant profiles involved in specific disease states, it may be possible to precisely and effectively target therapy to a wide variety of inflammatory diseases.