Homologs of the Saccharomyces cerevisiae Sir2 protein, sirtuins, promote longevity in many organisms. Studies of the sirtuin SIRT3 have so far been limited to cell culture systems. Here, we investigate the localization and function of SIRT3 in vivo. We show that endogenous mouse SIRT3 is a soluble mitochondrial protein. To address the function and relevance of SIRT3 in the regulation of energy metabolism, we generated and phenotypically characterized SIRT3 knockout mice. SIRT3-deficient animals exhibit striking mitochondrial protein hyperacetylation, suggesting that SIRT3 is a major mitochondrial deacetylase. In contrast, no mitochondrial hyperacetylation was detectable in mice lacking the two other mitochondrial sirtuins, SIRT4 and SIRT5. Surprisingly, despite this biochemical phenotype, SIRT3-deficient mice are metabolically unremarkable under basal conditions and show normal adaptive thermogenesis, a process previously suggested to involve SIRT3. Overall, our results extend the recent finding of lysine acetylation of mitochondrial proteins and demonstrate that SIRT3 has evolved to control reversible lysine acetylation in this organelle.Conserved from bacteria to humans, the sirtuin family of NAD ϩ -dependent protein deacetylase/mono-ADP-ribosyltransferase enzymes controls a variety of cellular processes such as aging, metabolism, and gene silencing (18,24). It has been proposed that sirtuins mediate the longevity-promoting effects of calorie restriction (CR) in yeast, worms, flies, and mice (4,17,22,24). Seven mammalian sirtuins (SIRT1 to -7) are known (11,12,18,24). At least three sirtuins (SIRT3, SIRT4, and SIRT5) localize to mitochondria, suggesting the existence of sirtuin substrates in that organelle (19,26,28,(31)(32)(33). Several lines of evidence link SIRT3 to metabolism: SIRT3 is down-regulated in muscle from diabetic animals (37) and upregulated in white and brown adipose tissue in response to CR (33). Overexpression of SIRT3 in cells affects expression of genes involved in mitochondrial function (33). SIRT3 regulates the acetylation level and activity of acetyl-coenzyme A synthetase 2, a protein that may play a role in energy production in mammals under starvation conditions (20,31). SIRT4 is an ADP-ribosyltransferase that has been implicated in regulating amino acid-stimulated insulin secretion in mice via modification of glutamate dehydrogenase (GDH) (19). No functions have been reported for SIRT5.

Caregivers of Alzheimer’s disease patients endure chronic stress associated with a decline of immune function. To assess the psychological and immunological changes of caregivers, we compared depressive symptoms, PBMC composition, in vitro activation-induced proliferation and cytokine production, and telomere length and telomerase activity of 82 individuals (41 caregivers and 41 age- and gender-matched controls). We found depressive symptoms were significantly higher in caregivers than in controls (p < 0.001). Correspondingly, caregivers had significantly lower T cell proliferation but higher production of immune-regulatory cytokines (TNF-α and IL-10) than controls in response to stimulation in vitro. We examined the impact of these changes on cellular replicative lifespan and found that caregivers had significantly shorter telomere lengths in PBMC than controls (6.2 and 6.4 kb, respectively, p < 0.05) with similar shortening in isolated T cells and monocytes and that this telomere attrition in caregivers was not due to an increase of shorter telomere possessing T cell subsets in PBMC. Finally, we showed that basal telomerase activity in PBMC and T cells was significantly higher in caregivers than in controls (p < 0.0001), pointing to an unsuccessful attempt of cells to compensate the excessive loss of telomeres in caregivers. These findings demonstrate that chronic stress is associated with altered T cell function and accelerated immune cell aging as suggested by excessive telomere loss.

IntroductionTargeted mAb-based therapies provide effective and safe treatments for hematologic malignancies. Rituximab, which specifically targets the B-cell antigen CD20, has had the greatest success, revolutionizing the treatment of the 2 most common forms of nonHodgkin lymphoma: follicular and diffuse large B-cell lymphoma. In addition, mAb-based therapies targeting CD52 (alemtuzumab) and CD33 (gemtuzumab ozogamicin) have been approved for the treatment of chronic lymphocytic leukemia and acute myelogenous leukemia, respectively. Despite the progress of these strategies, they do have limitations. Only a fraction of patients respond to rituximab, and the majority of those who do respond will eventually relapse. Treatment with alemtuzumab and gemtuzumab are limited by safety concerns, and many additional hematologic malignancies do not respond to treatment with any of these targeted therapies. Various therapies based on alternate mAbs, including second-generation anti-CD20 mAbs and those targeting alternate cell-surface proteins such as CD19, CD22, CD30, CD37, CD40, and CD74, have been developed and are at different stages of clinical testing in the hopes of providing approaches to treating a broader spectrum of hematologic malignancies that are poorly served by existing therapies. 1,2 Whereas targeting of cell-surface antigens themselves can mediate antitumor activity through the induction of apoptosis, most mAb-based activity against hematologic malignancies is reliant on either Fc-mediated effector functions such as complementdependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity 3,4 or is engineered through the conjugation of an immunotoxin or radiolabeled isotope. 1 Considering the potential of naturally occurring CTLs to mediate cell lysis, various strategies have also been explored to recruit CTLs to mediate tumor cell killing. Tumor-specific CTLs exert extremely potent effects through recognition of the corresponding peptide/MHC complex recognized by their TCR, and are among the most potent cells that mediate antitumor effects. A major limitation in generating tumorspecific CTLs in vivo is that their induction requires the use of vaccine strategies, such as dendritic cell-based vaccines, 5 that are capable of breaking tolerance to cancer self-antigens. One alternative is ex vivo expansion and activation of rare, tumor-specific CTLs for reinfusion into cancer patients. 6 However, cancer cells can down-regulate MHC expression as an escape mechanism, thus preventing the ability of CTLs to recognize their antigenic peptide. The genetic manipulation of patients' T cells to express chimeric antigen receptors comprising a tumor-specific antigen and T cellactivating properties before their adoptive transfer provides a non-MHC-restricted approach to targeting cancer, as was shown recently in the treatment of lymphoma with T cells engineered to recognize CD19. 7 However, the patient-specific manipulation and risk associated with this procedure represent major limitations to its expanded use. Alt...

Purpose: The goal of this research was to harness a monoclonal antibody (mAb) discovery platform to identify cell-surface antigens highly expressed on cancer and develop, through Fc optimization, potent mAb therapies toward these tumor-specific antigens.Experimental Design: Fifty independent mAbs targeting the cell-surface immunoregulatory B7-H3 protein were obtained through independent intact cell-based immunizations using human tissue progenitor cells, cancer cell lines, or cell lines displaying cancer stem cell properties. Binding studies revealed this natively reactive B7-H3 mAb panel to bind a range of independent B7-H3 epitopes. Immunohistochemical analyses showed that a subset displayed strong reactivity to a broad range of human cancers while exhibiting limited binding to normal human tissues. A B7-H3 mAb displaying exquisite tumor/normal differential binding was selected for humanization and incorporation of an Fc domain modified to enhance effectormediated antitumor function via increased affinity for the activating receptor CD16A and decreased binding to the inhibitory receptor CD32B.Results: MGA271, the resulting engineered anti-B7-H3 mAb, mediates potent antibody-dependent cellular cytotoxicity against a broad range of tumor cell types. Furthermore, in human CD16A-bearing transgenic mice, MGA271 exhibited potent antitumor activity in B7-H3-expressing xenograft models of renal cell and bladder carcinoma. Toxicology studies carried out in cynomolgus monkeys revealed no significant test article-related safety findings.Conclusions: This data supports evaluation of MGA271 clinical utility in B7-H3-expressing cancer, while validating a combination of a nontarget biased approach of intact cell immunizations and immunohistochemistry to identify novel cancer antigens with Fc-based mAb engineering to enable potent antitumor activity.