[Show abstract][Hide abstract] ABSTRACT: Recent advances in cancer biology have revealed that many malignancies possess a hierarchal system, and leukemic stem cells (LSC) or leukemia-initiating cells (LIC) appear to be obligatory for disease progression. Acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia characterized by the formation of a PML-RARα fusion protein, leads to the accumulation of abnormal promyelocytes. In order to understand the precise mechanisms involved in human APL leukemogenesis, we established a humanized in vivo APL model involving retroviral transduction of PML-RARA into CD34+ hematopoietic cells from human cord blood and transplantation of these cells into immunodeficient mice. The leukemia well recapitulated human APL, consisting of leukemic cells with abundant azurophilic abnormal granules in the cytoplasm, which expressed CD13, CD33 and CD117, but not HLA-DR and CD34, were clustered in the same category as human APL samples in the gene expression analysis, and demonstrated sensitivity to ATRA. As seen in human APL, the induced APL cells showed a low transplantation efficiency in the secondary recipients, which was also exhibited in the transplantations that were carried out using the sorted CD34- fraction. In order to analyze the mechanisms underlying APL initiation and development, fractionated human cord blood was transduced with PML-RARA. Common myeloid progenitors (CMP) from CD34+/CD38+ cells developed APL. These findings demonstrate that CMP are a target fraction for PML-RARA in APL, whereas the resultant CD34- APL cells may share the ability to maintain the tumor.
PLoS ONE 11/2014; 9(11):e111082. DOI:10.1371/journal.pone.0111082 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We analyzed the function of a SEPT9-ABL1 fusion identified in a case of T-prolymphocytic leukemia with tyrosine kinase inhibitor (TKI) resistance. Five isoforms with different N-termini, including SEPT9a-ABL1, SEPT9b-ABL1, SEPT9d-ABL1, SEPT9e-ABL1 and SEPT9f-ABL1, were detected in the leukemic cells. All isoforms except SEPT9d-ABL1 are localized in the cytoplasm, undergo autophosphorylation and phosphorylate the downstream targets, STAT-5 and Crkl, and provided IL-3-independence and in vivo invasiveness to 32D cells. Additionally, these SEPT9-ABL1 isoforms were resistant to TKIs in vitro and in vivo, in comparison to BCR-ABL1. These findings demonstrated that SEPT9-ABL1 had oncogenic activity and conferred resistance to TKIs.
Leukemia Research 08/2014; 38(12). DOI:10.1016/j.leukres.2014.08.015 · 2.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: T-cell prolymphocytic leukemia (T-PLL), a rare type of peripheral T-cell leukemia, is characterized by marked splenomegaly with rapidly progressive lymphocytosis and a poor prognosis. Nine kinds of ABL1 chimeric genes have been identified in various kinds of hematological malignancies, such as chronic myeloid leukemia and B- or T- lymphoblastic leukemia. However, there have been no reports describing T-PLL cases with ABL1 rearrangements. We herein report a case of T-PLL with a novel SEPT9-ABL1 fusion gene which induced strong resistance to tyrosine kinase inhibitors such as imatinib and dasatinib.
Leukemia Research Reports 06/2014; 3(2). DOI:10.1016/j.lrr.2014.06.004
[Show abstract][Hide abstract] ABSTRACT: We examined the antileukemic effects of high concentrations of L-ascorbic acid (high AA) on human leukemic cells. In vitro, high AA markedly induced apoptosis in various leukemic cell lines by generating hydrogen peroxide (H2O2) but not in normal hematopoietic stem/progenitor cells. High AA significantly repressed leukemic cell proliferation as well as neoangiogenesis in immunodeficient mice. We then noted that in leukemic cells, HIF-1α transcription was strongly suppressed by high AA and correlated with the transcription of VEGF. Our data indicate that exposure to high AA markedly increased the intracellular AA content of leukemic cells and inhibited the nuclear translocation of NF-κB, which mediates expression of HIF-1α. We next generated K562 cells that overexpressed HIF-1α (K562-HIF1α cells) and assessed the mechanistic relationship between inhibition of HIF-1α transcription and the antileukemic effect of high AA. The ability of high AA to induce apoptosis was significantly lower in K562-HIF1α cells than in K562 cells in vitro. We found that expression of HIF-1α-regulated antiapoptotic proteins of the Bcl-2 family, such as Mcl-1, Bcl-xL, and Bcl-2, was significantly suppressed by high AA in K562 cells, but was sustained at higher levels in K562-HIF1α cells, regardless of high AA exposure. Moreover, repression of cell proliferation and neoangiogenesis by high AA was completely abrogated in mice receiving transplants of K562-HIF1α cells. These results indicate that, along with H2O2 generation, downregulation of HIF-1α transcription plays a crucial role in growth inhibition of human leukemic cells by high AA.
PLoS ONE 04/2013; 8(4):e62717. DOI:10.1371/journal.pone.0062717 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Stem cells of highly regenerative organs including blood are susceptible to endogenous DNA damage caused by both intrinsic and extrinsic stress. Response mechanisms to such stress equipped in hematopoietic stem cells (HSCs) are crucial in sustaining hematopoietic homeostasis but remain largely unknown. In this study, we demonstrate that serial transplantation of human HSCs into immunodeficient mice triggers replication stress that induces incremental elevation of intracellular reactive oxygen species (ROS) levels and the accumulation of persistent DNA damage within the human HSCs. This accumulation of DNA damage is also detected in HSCs of clinical HSC transplant patients and elderly individuals. A forced increase of intracellular levels of ROS by treatment with a glutathione synthetase inhibitor aggravates the extent of DNA damage, resulting in the functional impairment of HSCs in vivo. The oxidative DNA damage activates the expression of cell-cycle inhibitors in a HSC specific manner, leading to the premature senescence among HSCs, and ultimately to the loss of stem cell function. Importantly, treatment with an antioxidant can antagonize the oxidative DNA damage and eventual HSC dysfunction. The study reveals that ROS play a causative role for DNA damage and the regulation of ROS have a major influence on human HSC aging.
[Show abstract][Hide abstract] ABSTRACT: Cultured epidermal autografts and cultured skin substitute are vulnerable to infection. Human beta defensin (HBD)-3 is an antimicrobial peptide that exhibits a wide-spectrum antimicrobial activity against gram-positive/negative bacteria and fungi. This study determined whether normal human keratinocytes (NHKs) and human dermal fibroblasts (HDFs) transfected with the HBD-3 gene secrete HBD-3 peptide with an antimicrobial activity. An adenovirus vector with an HBD-3 cDNA inserted downstream of the CMV promoter (ADhBD3) was created. The HBD-3 gene was introduced into NHKs and HDFs via ADhBD3 infection. HBD-3 gene expression in each type of transfected cells was evaluated by RT-PCR. The presence of HBD-3 peptide in the culture supernatants of each type of transfected cells was evaluated by Western blotting. The antimicrobial activities of the culture supernatants of each type of transfected cells against several bacterial strains were also measured. Both NHKs and HDFs infected with ADhBD3 expressed the HBD-3 gene and secreted HBD-3 peptide into culture supernatants. These supernatants exhibited a strong bacteriocidal activity against a Staphylococcus aureus reference strain and methicillin-resistant S. aureus (MRSA). NHKs and HDFs transfected with the HBD-3 gene secrete HBD-3 peptide with an antimicrobial activity against S. aureus and MRSA.
Burns: journal of the International Society for Burn Injuries 09/2010; 37(1):109-16. DOI:10.1016/j.burns.2010.08.004 · 1.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hematopoiesis is a dynamic and strictly regulated process orchestrated by self-renewing hematopoietic stem cells (HSCs) and the supporting microenvironment. However, the exact mechanisms by which individual human HSCs sustain hematopoietic homeostasis remain to be clarified. To understand how the long-term repopulating cell (LTRC) activity of individual human HSCs and the hematopoietic hierarchy are maintained in the bone marrow (BM) microenvironment, we traced the repopulating dynamics of individual human HSC clones using viral integration site analysis. Our study presents several lines of evidence regarding the in vivo dynamics of human hematopoiesis. First, human LTRCs existed in a rare population of CD34(+)CD38(-) cells that localized to the stem cell niches and maintained their stem cell activities while being in a quiescent state. Second, clonally distinct LTRCs controlled hematopoietic homeostasis and created a stem cell pool hierarchy by asymmetric self-renewal division that produced lineage-restricted short-term repopulating cells and long-lasting LTRCs. Third, we demonstrated that quiescent LTRC clones expanded remarkably to reconstitute the hematopoiesis of the secondary recipient. Finally, we further demonstrated that human mesenchymal stem cells differentiated into key components of the niche and maintained LTRC activity by closely interacting with quiescent human LTRCs, resulting in more LTRCs. Taken together, this study provides a novel insight into repopulation dynamics, turnover, hierarchical structure, and the cell cycle status of human HSCs in the recipient BM microenvironment.
[Show abstract][Hide abstract] ABSTRACT: Hematopoietic stem cells (HSCs) consist of heterogenous subpopulations, one of which is CD34(-) HSCs. Recent development of successful engraftment by intra-bone marrow transplantation revealed severe combined immunodeficiency (scid) mouse-repopulating cell (SRC) activity in human CD34(-) cord blood (CB) cells. On the other hand, CD34(-) cells from bone marrow (BM) cells remain relatively undefined. Here, we investigated pre-SRC populations in human BM CD34(-) cells and the effect of the niche-related factor, angiopoietin-1, on them.
Two populations in BM CD34(-) cells (namely M cells and S cells) were purified by flow cytometry. Then, they were cocultured with six growth factors on the hematopoietic-supportive mouse BM stromal cell line, HESS-5 or AHESS-5 that were engineered to produce human angiopoietin-1, because we detected Tie2 expression on M cells and S cells. Cultured cells were assessed for their in vitro and in vivo hematopietic activities.
After 7 days in coculture, AHESS-5 was stronger more effective than HESS-5 in converting M and S cells to CD34(+) cells (M cells: 67.4% vs 17.5%, n =6, p < 0.001) (S cells: 42.3% vs 2.3%, n = 6, p < 0.001). Furthermore, both M and S cells were able to engraft in immunodeficient mice after they were cocultured on AHESS-5.
Results suggest that angiopoietin-1 supports SRC activities in human CD34(-) BM cells, as murine studies demonstrated. Furthermore, identification of previously undetected subpopulations of BM CD34(-) HSCs unveils heterogenous components in the stem cell pool.
[Show abstract][Hide abstract] ABSTRACT: To characterize human hematopoietic stem cells (HSCs), xenotransplantation techniques such as the severe combined immunodeficiency (SCID) mouse repopulating cell (SRC) assay have proven the most reliable methods thus far. While SRC quantification by limiting dilution analysis (LDA) is the gold standard for measuring in vitro expansion of human HSCs, LDA is a statistical method and does not directly establish that a single HSC has self-renewed in vitro. This would require a direct clonal method and has not been done. By using lentiviral gene marking and direct intra-bone marrow injection of cultured CD34+ CB cells, we demonstrate here the first direct evidence for self-renewal of individual SRC clones in vitro. Of 74 clones analyzed, 20 clones (27%) divided and repopulated in more than 2 mice after serum-free and stroma-dependent culture. Some of the clones were secondary transplantable. This indicates symmetric self-renewal divisions in vitro. On the other hand, 54 clones (73%) present in only 1 mouse may result from asymmetric divisions in vitro. Our data demonstrate that current ex vivo expansion conditions result in reliable stem cell expansion and the clonal tracking we have employed is the only reliable method that can be used in the development of clinically appropriate expansion methods.
[Show abstract][Hide abstract] ABSTRACT: Recent studies have shown that bone marrow (BM) contains cells capable of differentiating into myocytes in vivo. However, addition of demethylation drugs has been necessary to induce myocyte differentiation from BM cells in vitro, and precise mechanisms of BM cells' conversion to myocytes and the origin of those cells have not been established. We investigated the expression of myogenic markers during differentiation and maturation of myocytes from BM-derived multipotent adult progenitor cells (MAPC) under physiological culture condition.
Frozen BM samples from 21 healthy donors were used as a source of MAPC. To induce myocyte differentiation MAPC was cultured in the presence of 5% FCS, VEGF, bFGF, and IGF-1, and the expressions of myocyte markers were examined at various time points. We also investigated engraftment and differentiation of MAPC-derived myocytes in vivo.
Frozen BM-derived MAPC, cultured under the physiological myogenic condition, demonstrated spatial expression patterns of several myocyte markers similar to that of authentic myocyte differentiation. When injected into murine muscles, MAPC treated with the myogenic condition engrafted and differentiated into myocyte marker-positive cells and myotubes in vivo.
For the first time, we were able to induce myocyte formation from BM cells under the physiological condition in vitro and demonstrated that treating cells with this condition prior to intramuscular injection increased efficiency of engraftment and differentiation in vivo.
[Show abstract][Hide abstract] ABSTRACT: Putative myogenic and endothelial (myo-endothelial) cell progenitors were identified in the interstitial spaces of murine skeletal muscle by immunohistochemistry and immunoelectron microscopy using CD34 antigen. Enzymatically isolated cells were characterized by fluorescence-activated cell sorting on the basis of cell surface antigen expression, and were sorted as a CD34+ and CD45- fraction. Cells in this fraction were approximately 94% positive for Sca-1, and mostly negative (<3% positive) for CD14, 31, 49, 144, c-kit, and FLK-1. The CD34+/45- cells formed colonies in clonal cell cultures and colony-forming units displayed the potential to differentiate into adipocytes, endothelial, and myogenic cells. The CD34+/45- cells fully differentiated into vascular endothelial cells and skeletal muscle fibers in vivo after transplantation. Immediately after sorting, CD34+/45- cells expressed only c-met mRNA, and did not express any other myogenic cell-related markers such as MyoD, myf-5, myf-6, myogenin, M-cadherin, Pax-3, and Pax-7. However, after 3 d of culture, these cells expressed mRNA for all myogenic markers. CD34+/45- cells were distinct from satellite cells, as they expressed Bcrp1/ABCG2 gene mRNA (Zhou et al., 2001). These findings suggest that myo-endothelial progenitors reside in the interstitial spaces of mammalian skeletal muscles, and that they can potentially contribute to postnatal skeletal muscle growth.
The Journal of Cell Biology 05/2002; 157(4):571-7. DOI:10.1083/jcb.200112106 · 9.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To support immune reconstitution after cord blood transplantation, immunotherapy using gene-modified dendritic cells (DCs), the most potent antigen-presenting cells, can be a powerful strategy for preventing infection and recurrence. To investigate the applicability of lentiviral vector-transduced DCs compared to retroviral vectors, we transduced umbilical cord blood (CB) CD34(+) cells, then expanded and differentiated them into DCs.
We transduced CB CD34(+) cells by vesicular stomatitis virus G-protein pseudotyped self-inactivating lentiviral vector or retroviral vectors carrying the enhanced green fluorescent protein gene. The cells were expanded in the stroma-dependent culture system and transferred to the culture condition for developing DCs. The efficiency of transduction and expression of the transgene in severe combined immunodeficiency (SCID) mice-repopulating cells (SRCs) and DCs were compared between lentiviral vector and retroviral vectors. Induced DCs were cocultured with allogeneic or autologous T cells to test the ability to present antigens.
CB CD34(+) cells transduced by lentiviral vector and expanded ex vivo sustained stable transgene expression and multipotentiality by assessing SRCs assay and clonogenic assay of bone marrow cells from the transplanted mice. DCs derived from these cells expressed green fluorescent protein and surface markers CD1a, CD80, and HLA-DR and showed potent allo-stimulatory activity as well as nontransduced DCs did. On the other hand, we did not detect transgene expression in SRCs and DCs transduced by retroviral vectors.
Gene-modified DCs derived from ex vivo expanded CB CD34(+) cells transduced by lentiviral vector will be useful in future immunotherapy protocols.
[Show abstract][Hide abstract] ABSTRACT: NK cells and dendritic cells (DCs) are both important in the innate host defense. However, the role of DCs in NK cell-mediated cytotoxicity is unclear. In this study, we designed two culture systems in which human cord blood CD34(+) cells from the same donor were induced to generate NK cells and DCs, respectively. Coculture of the NK cells with DCs resulted in significant enhancement of NK cell cytotoxicity and IFN-gamma production. However, NK cell cytotoxicity and IFN-gamma production were not increased when NK cells and DCs were grown together separated by a transwell membrane. Functional studies demonstrated that 1) concanamycin A, a selective inhibitor of perforin/granzyme B-based cytolysis, blocked DC-stimulated NK cytotoxicity against K562 cells; and 2) neutralizing mAb against Fas ligand (FasL) significantly reduced DC-stimulated NK cytotoxicity against Fas-positive Jurkat cells. In addition, a marked increase of FasL mRNA and FasL protein expression was observed in DC-stimulated NK cells. The addition of neutralizing mAb against IL-18 and IL-12 significantly suppressed DC-stimulated NK cell cytotoxicity. Neutralizing IFN-gamma Ab almost completely inhibited NK cell cytotoxicity against Jurkat cells. These observations suggest that DCs enhance NK cell cytotoxicity by up-regulating both perforin/granzyme B- and FasL/Fas-based pathways. Direct interaction between DCs and NK cells is necessary for DC-mediated enhancement of NK cell cytotoxicity. Furthermore, DC-derived IL-18 and IL-12 were involved in the up-regulation of NK cell cytotoxicity, and endogenous IFN-gamma production plays an important role in Fas-mediated cytotoxicity.
The Journal of Immunology 03/2001; 166(3):1590-600. DOI:10.4049/jimmunol.166.3.1590 · 5.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Clinical application of cytotoxic T lymphocytes (CTL) induced in vitro is extensively used for the treatment of viral infection and malignant diseases. We produced anti H-2d CTL in vitro from C57BL/6 (B6) splenocytes presensitized with (B6 x DBA/2) F1 (BDF1) splenocytes to establish a model system of CTL therapy. The specificity and cytotoxic activity were high enough (E/T ratio 1:1 = 38.8%) to induce graft versus host reaction. Though the total number of B6 splenocytes decreased by 0.27 during the 4 days of culture, the number of CD8+ lymphocytes increased 1.3-fold. When more than 5 x 10(6) cells of H-2d-reactive CTL were transplanted into BDF1 mice, mice died within 2 days postinduction. This lethal effect was not seen in the mice induced with ConA-stimulated T cells. Histological examination of the lungs and liver revealed massive infiltration of neutrophils in alveoli and the necrosis of hepatocytes. Therefore, this protocol was shown to be effective to produce alloantigen-specific CTLs and applicable to in vitro manipulation such as retrovirus-mediated gene transfer.
[Show abstract][Hide abstract] ABSTRACT: Human CD34(-) hematopoietic stem cells (HSCs) have been identified as potential precursors of CD34(+) HSCs by using xenogeneic transplantation systems. However, the properties of CD34(+) cells generated from CD34(-) cells have not been precisely analyzed due to the lack of an in vitro system in which CD34(+) cells are continuously produced from CD34(-) cells. We conducted this study to determine whether CD34(+) cells generated in vitro from CD34(-) cells have long-term multilineage reconstitution abilities. Lin(-)CD34(-) population isolated from human cord blood was cultured in the presence of murine bone marrow stroma cell line, HESS-5, and human cytokines, thrombopoietin, Flk2/Flt3 ligand, stem cell factor, granulocyte colony-stimulating factor, interleukin 3 (IL-3), and IL-6. They were analyzed weekly for their surface markers expressions, colony-forming cells, long-term culture initiating cells (LTC-IC), and SCID repopulating cells (SRC) abilities up to 30 days of culture. In this culture system, more than 10(7) CD34(+) cells can be continuously generated from 10(4) CD34(-) cells over 30 days. These CD34(+) cells produce colony-forming units, LTC-IC, and SRC with multi-lineage differentiation, all of which are characteristic features of hematopoietic stem/progenitor cells. These findings suggest that CD34(-) HSCs have extensive potential for the generation of CD34(+) HSCs in vitro. This system provides a novel and potentially useful procedure to generate CD34(+) cells for clinical transplantation and gene therapy.
[Show abstract][Hide abstract] ABSTRACT: Adherence is an essential and prerequisite step for the colonization of mucosal surfaces by enterotoxigenic Escherichia coli (ETEC). We studied the effect of bovine lactoferrin (BLF) on the adherence of ETEC to human epithelial cells in vitro, and to intestinal mucosa of ICR germfree mice in vivo. In the in vitro study, BLF was found to inhibit the adherence of ETEC. This adhesion-inhibiting activity of BLF was found to lessen with decreasing BLF concentration, but the data obtained suggest a positive inhibitory effect of BLF against the adhesion of ETEC cells. In the in vivo study, the counts of adherent bacteria in various sections of the intestinal tract (duodenum, jejunoileum, and large intestine) were lower in the BLF group than in the control group, suggesting the possible action of BLF as an intestinal tract adherence-blocking agent with regards to ETEC.
[Show abstract][Hide abstract] ABSTRACT: The administration of bovine lactoferrin (LF) with 1 mg/g body weight before the murine cytomegalovirus (MCMV) infection completely protected the BALB/c mice from death due to the infection. In these LF-treated mice, a significant increase in the activity was found in the NK cells but not in the cytolytic T lymphocytes which recognized an MCMV-derived peptide. Moreover, the elimination of the NK cell activity by an injection with anti-asialo GM1 antibody abrogated such augmented resistance, thus supporting the hypothesis that the LF-mediated antiviral effect in vivo is performed through the augmentation of NK cell activity. No such LF-mediated antiviral effect in vivo with the increased NK cell activity was found in athymic nude mice, whereas it was restored completely by the transfer of splenic T cells from LF-treated donors. These findings therefore suggest that T lymphocytes induce both the augmentation of NK cell activity and the resultant antiviral effect in the LF-treated hosts.
Archives of Virology 02/1996; 141(10):1875-89. DOI:10.1007/BF01718201 · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cytomegalovirus (CMV) establishes a latent infection in its host; however, the organ sites of viral latency and its mechanism still remain to be fully clarified. To elucidate this issue, a latent infection with murine (M) CMV was attempted to induce in mice and the organ sites of the latent viral genome were examined for more than one year by a polymerase chain reaction (PCR). As a result, latent MCMV DNA was detectable in both the lung and the spleen as late as 59 weeks after infection. The heart was also observed to be a target organ of latent MCMV DNA, though the amount of viral DNA was much less than that seen in the lung and spleen. In germfree (GF) mice, on the other hand, no such latent viral DNA was observed in the spleens, while it was seen, but to a significantly smaller degree, in the lungs and the hearts than in the same organs of specific pathogen-free (SPF) mice. The amount of infectious virions generated in the host appeared to be almost equal between the GF and SPF mice. The above findings therefore suggest that the spleen, lung and heart are target organs for MCMV latency and the indigenous bacterial flora, which are not colonizing in GF mice, play an important role in the establishment of such viral latency in SPF mice.
Archives of Virology 02/1995; 140(5):853-64. DOI:10.1007/BF01314962 · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effects of food restriction on immune function was investigated in germfree (GF) and specific pathogen-free (SPF) mice. They were maintained from five weeks of age under either full-fed or food-restricted conditions to 4.5 grams per day (equivalent to approximately 80% of full-fed intake) of a commercial diet. Longest survival rate was attained in food-restricted SPF mice followed by food-restricted GF, full-fed GF, and full-fed SPF animals. Food-restricted GF mice showed shorter survival rate than their SPF counterparts. This result suggests that food restriction may be just as effective as GF status for extending life span. Immune function declined significantly with age in full-fed groups of GF and SPF mice. In both food-restricted GF and SPF mice, mitogenic response to concanavalin A or lipopolysaccharide and antibody response to sheep red blood cells were lower early in life and became higher later in life as compared with full-fed mice. Hence, the maintenance of effective immunological function until old age may be the reason for food-restricted groups to live slightly longer than full-fed groups.
[Show abstract][Hide abstract] ABSTRACT: An investigation was undertaken to study the effects of germfree (GF) status and mild food restriction on life span in GF and specific pathogen-free (SPF) male ICR mice either full-fed (ad libitum) or on a restricted diet of 4.5 grams per day (equivalent to approximately 80% of full-fed intake) from five-week-old. The mean life span of the full-fed SPF and GF mice was 75.9 and 88.9 weeks respectively, while the mean life span of the food-restricted SPF and GF mice was 117.5 and 109.6 weeks, respectively. Mice in both GF and SPF food-restricted groups were characterized by lower body weight and increased survival. These findings suggest that the cessation of growth may be importantly and perhaps causally related to longevity. The GF mice survived longer than the SPF mice, but the combination of GF status with food restriction did not seem to extend life span more than food restriction alone.