Intravenous immunoglobulin attenuates airway inflammation through induction of forkhead box protein 3-positive regulatory T cells.

BACKGROUND: Intravenous immunoglobulin (IVIG) is a frequently used disease-modifying therapy for a large spectrum of autoimmune and inflammatory conditions, yet its mechanisms of action are incompletely understood. Using a robust murine model of antigen-driven allergic airways disease, we have demonstrated that IVIG markedly improves ovalbumin (OVA)-induced airway hyperresponsiveness characterized by 4- to 6-fold enhancement in regulatory T (Treg) cells in pulmonary and associated lymphoid tissues. OBJECTIVE: We sought to determine whether IVIG induces antigen-specific Treg cells and to address cellular interactions that lead to induction of Treg cells by IVIG. METHODS: C57Bl/6 mice were sensitized and challenged by means of intranasal OVA exposure. IVIG or albumin control was administered 24 hours before challenge. Treg cells were tracked by using green fluorescent protein (GFP)-forkhead box protein 3 (Foxp3) knock-in reporter mice (Foxp3(GFP)), and Treg cell and dendritic cell (DC) phenotypes and activities were elucidated by using coculture and flow cytometry. RESULTS: IVIG therapy of OVA-sensitized and OVA-challenged mice induced antigen-specific forkhead box protein 3 (Foxp3)-positive Treg cells from non-Treg cell precursors. The induced Treg cells home specifically to the lungs and draining lymph nodes and have greatly potentiated suppressive activity compared with that seen in Treg cells purified from control mice. Induction of Treg cells is mediated by tolerogenic DCs generated after IVIG exposure. Compared with albumin-treated, OVA-exposed mice, IVIG-primed DCs express altered Notch ligands, including increased Delta-4 and reduced Jagged-1 levels, reflecting decreased T(H)2 polarization. Furthermore, IVIG-primed DCs can stimulate Treg cell differentiation from uncommitted Foxp3(-)CD4(+) T cells ex vivo, and adoptive transfer of IVIG-primed DCs abrogates airway hyperresponsiveness and induces Treg cells. CONCLUSION: The anti-inflammatory effects of IVIG therapy can be mediated by the immunomodulation of DCs, creating a bridge that induces antigen-specific, highly suppressive Treg cells.

Specific synthetic lethal killing of RAD54B-deficient human colorectal cancer cells by FEN1 silencing.

Mutations that cause chromosome instability (CIN) in cancer cells produce "sublethal" deficiencies in an essential process (chromosome segregation) and, therefore, may represent a major untapped resource that could be exploited for therapeutic benefit in the treatment of cancer. If second-site unlinked genes can be identified, that when knocked down, cause a synthetic lethal (SL) phenotype in combination with a somatic mutation in a CIN gene, novel candidate therapeutic targets will be identified. To test this idea, we took a cross species SL candidate gene approach by recapitulating a SL interaction observed between rad54 and rad27 mutations in yeast, via knockdown of the highly sequence- and functionally-related proteins RAD54B and FEN1 in a cancer cell line. We show that knockdown of RAD54B, a gene known to be somatically mutated in cancer, causes CIN in mammalian cells. Using high-content microscopy techniques, we demonstrate that RAD54B-deficient human colorectal cancer cells are sensitive to SL killing by reduced FEN1 expression, while isogenic RAD54B proficient cells are not. This conserved SL interaction suggests that extrapolating SL interactions observed in model organisms for homologous genes mutated in human cancers will aid in the identification of novel therapeutic targets for specific killing of cancerous cells exhibiting CIN.

Chromatid cohesion defects may underlie chromosome instability in human colorectal cancers.

Although the majority of colorectal cancers exhibit chromosome instability (CIN), only a few genes that might cause this phenotype have been identified and no general mechanism underlying their function has emerged. To systematically identify somatic mutations in potential CIN genes in colorectal cancers, we determined the sequence of 102 human homologues of 96 yeast CIN genes known to function in various aspects of chromosome transmission fidelity. We identified 11 somatic mutations distributed among five genes in a panel that included 132 colorectal cancers. Remarkably, all but one of these 11 mutations were in the homologs of yeast genes that regulate sister chromatid cohesion. We then demonstrated that down-regulation of such homologs resulted in chromosomal instability and chromatid cohesion defects in human cells. Finally, we showed that down-regulation or genetic disruption of the two major candidate CIN genes identified in previous studies (MRE11A and CDC4) also resulted in abnormal sister chromatid cohesion in human cells. These results suggest that defective sister chromatid cohesion as a result of somatic mutations may represent a major cause of chromosome instability in human cancers.