Lack Of Immune Response Research Articles

Cytotoxicity analysis of hydrogels based on chitosan incorporated with variable amounts of silver nanoparticles

Event Abstract Back to Event Cytotoxicity analysis of hydrogels based on chitosan incorporated with variable amounts of silver nanoparticles Katarzyna Bialik-Wąs1, Bozena Tyliszczak1, Dorota Walczyk1, Dagmara Malina2 and Agnieszka Sobczak-Kupiec2 1 Department of Chemistry and Technology of Polymers, Cracow University of Technology, Poland 2 Institute of Inorganic Chemistry and Technology, Cracow University of Technology, Poland Recently, greater attention is devoted towards development of modern polymeric biomaterials of particular applications, mainly hydrogels defined also as superabsorbent polymers (SAP). Hydrogels based on chitosan and natural polymers constitute significant source of biocompatible, biodegradable matrices widely applied in biomedicine. The main assets of biomaterials constitute: biocompatibility, lack of allergic, toxic, mutagenic reactions, lack of immune response and inflammations[1]-[4]. In this study chitosan based hydrogels were formed by exposure to UV light, applying PEGDA 700 as crosslinking agent and 2-hydroxy-2-methylpropiophenone as photoinitiator. Initial mixture exposed to UV-light was comprised of 3% of chitosan, 2% of gelatin and accordingly: 1ml (1), 3ml (2) and 5ml (3) of silver nanoparticles (250ppm). Another samples 4 and 5 contained the same reagents as sample 2 and 3 but were enriched in 5ml of 0.3% aqueous solution of albumin. The main objective of performed analyses was based on evaluation of cytotoxicity performed on the cells of human dermis in vitro (BJ, ATCCÒ CRL-2522TM) according to MTT and XTT methods. The attained results are listed in tables 1 and 2. Table 1. Determination of cytotoxicity of hydrogel's extracts on human dermis cells applying MTT method. Table 2. Determination of cytotoxicity of hydrogel's extracts on human dermis cells applying XTT method. Received hydrogel matrices were subjected to analyses of swelling ability and incubation studies in distilled water and simulated body fluids. The morphology and dispersion of silver nanoparticles in three dimensional structure of hydrogels was determined by means of SEM equipped with EDS analysis. Moreover, the structures of received hydrogels were evaluated applying FT-IR spectroscopy. The positive values of the cytotoxicity analysis indicate formation of innovative hydrogel matrices with enhanced antibacterial activity. “The authors would like to thank the The National Centre for Research and Development (Grant no: LIDER//033/697/L-5/13/NCBR/2014) for providing financial support to this project”.

Galectin-1 reduced the effect of LPS on the IL-6 production in decidual cells by inhibiting LPS on the stimulation of IκBζ

Pregnancy is a complex process where several physiological pathways interact. The down-regulated inflammatory response and the abundance of anti-inflammatory molecules during gestation may explain the acceptance of the fetus and the lack of immune response against it, even though it is a foreign tissue for the mother. NF-κB is a key regulator of the transcription of inflammatory genes, such as IL-8, IL-1β, TNF-α, or IL-6. Increased NF-κB activity that leads to the production of proinflammatory cytokines may induce obstetric disorders, such as preterm birth or abortion. Low activity of this transcription factor is associated with the beneficial anti-inflammatory environment during fetus development until delivery. Galectin-1 (Gal-1) is a lectin-type glycan-binding protein that is able to down-regulate inflammation. It has been shown that Gal-1 is abundantly expressed at the feto-maternal interface in humans, where it promotes maternal immune tolerance to the fetal semi-allograft. Gal-1 tolerance-promoting mechanisms have been established for adaptive immune cells, such as T cells and dendritic cells. However, the role of this lectin has not been established in non-immune cells at the feto-maternal interface. Here, we determined that Gal-1 is able to block the stimulating effect of LPS on IL-6 in human decidua cells. Our results show that Gal-1 acts by inhibiting the stimulation of the LPS-induced IκBζ expression, an NF-κB regulator involved in IL-6 gene transcription.

OC-014: Molecular screening for cancer treatment optimization in head and neck cancer (MOSCATO 01)

OC-014: Molecular screening for cancer treatment optimization in head and neck cancer (MOSCATO 01)

Efficient gene delivery and multimodal imaging by lanthanide-based upconversion nanoparticles.

Nanoparticles have been explored as nonviral gene carriers for years because of the simplicity of surface modification and lack of immune response. Lanthanide-based upconversion nanoparticles (UCNPs) are becoming attractive candidates for biomedical applications in virtue of their unique optical properties and multimodality imaging ability. Here, we report a UCNPs-based structure with polyethylenimine coating for both efficient gene transfection and trimodality imaging. Cytotoxicity tests demonstrated that the nanoparticles exhibited significantly decreased cytotoxicity compared to polyethylenimine polymer. Further, in vitro studies revealed that the gene carriers are able to transfer the enhanced green fluorescence protein (EGFP) plasmid DNA into Hela cells in higher transfection efficiency than PEI. Gene silencing was also examined by delivering bcl-2 siRNA into Hela cells, resulting in significant downregulation of target bcl-2 mRNA. More importantly, we demonstrated the feasibility of upconversion gene carriers to serve as effective contrast agents for MRI/CT/UCL trimodality imaging both in vitro and in vivo. The facile fabrication process, great biocompatibility, enhanced gene transfection efficiency, and great bioimaging ability can make it promising for application in gene therapy.

Strategies to overcome trastuzumab resistance in HER2-overexpressing breast cancers: focus on new data from clinical trials.

Breast cancers over-express the human epidermal growth factor receptor 2 (HER2) in about 15% of patients. This transmembrane tyrosine kinase receptor activates downstream signaling pathways and leads to proliferation of cancer cells. Trastuzumab, an anti-HER2 monoclonal antibody, improves outcome in women with early and metastatic breast cancer. Resistance to trastuzumab involves the phosphoinositide 3-kinase/mammalian target of rapamycin (PI3K/mTOR) pathway, truncation of the Her2 receptor or lack of immune response. The last decade has seen major advances in strategies to overcome resistance to trastuzumab. This includes the development of antibody-drug conjugates, dual HER2 inhibition strategies, inhibition of PI3K/mTOR pathway and development of modulators of immune checkpoints.

A new anti-tumor strategy based on in vivo tumstatin overexpression after plasmid electrotransfer in muscle

The NC1 domains from the different α(IV) collagen chains were found to exert anti-tumorigenic and/or anti-angiogenic activities. A limitation to the therapeutic use of these matrikines is the large amount of purified recombinant proteins, in the milligram range in mice that should be administered daily throughout the experimental procedures. In the current study, we developed a new therapeutic approach based on tumstatin (NC1α3(IV)) overexpression in vivo in a mouse melanoma model. Gene electrotransfer of naked plasmid DNA (pDNA) is particularly attractive because of its simplicity, its lack of immune responsiveness and its safety. The pDNA electrotransfer in muscle mediates a substantial gene expression that lasts several months. A pVAX1© vector containing the tumstatin cDNA was injected into the legs of C57BL/6 mice and submitted to electrotranfer. Sera were collected at different times and tumstatin was quantified by ELISA. Tumstatin secretion reached a plateau at day 21 with an expression level of 12μg/mL. For testing the effects of tumstatin expression on tumor growth in vivo, B16F1 melanoma cells were subcutaneously injected in mice 7days after empty pVAX1© (Mock) or pVAX1©–tumstatin electrotransfer. Tumstatin expression triggered a large decrease in tumor growth and an increase in mouse survival. This new therapeutic approach seems promising to inhibit tumor progression in vivo.

A Pilot Study of Anti-CTLA4 Antibody Ipilimumab in Patients with Synovial Sarcoma

Background. Patients with recurrent synovial sarcomas have few options for systemic therapy. Since they express large amounts of endogenous CT (cancer testis) antigens such as NY-ESO-1, we investigated the clinical activity of single agent anti-CTLA4 antibody ipilimumab in patients with advanced or metastatic synovial sarcoma. Methods. A Simon two-stage phase II design was used to determine if there was sufficient activity to pursue further. The primary endpoint was tumor response rate by RECIST 1.0. Patients were treated with ipilimumab 3 mg/kg intravenously every 3 weeks for three cycles and then restaged. Retreatment was possible for patients receiving an extra three-week break from therapy. Sera and peripheral blood mononuclear cells were collected before and during therapy to assess NY-ESO-1-specific immunity. Results. Six patients were enrolled and received 1–3 cycles of ipilimumab. All patients showed clinical or radiological evidence of disease progression after no more than three cycles of therapy, for a RECIST response rate of 0%. The study was stopped for slow accrual, lack of activity, and lack of immune response. There was no evidence of clinically significant either serologic or delayed type hypersensitivity responses to NY-ESO-1 before or after therapy. Conclusion. Despite high expression of CT antigens by synovial sarcomas of patients treated in this study, there was neither clinical benefit nor evidence of anti-CT antigen serological responses. Assessment of the ability of synovial sarcoma cell lines to present cancer-germ cell antigens may be useful in determining the reason for the observed lack of immunological or clinical activity.

Spaceflight alters expression of microRNA during T cell activation (109.16)

Abstract Returning astronauts have experienced altered immune function and increased vulnerability to infection during spaceflights dating back to Apollo and Skylab suggesting that immune-suppression is a major barrier to safe, long-term human space habitation and travel. We present definitive evidence that early signal transduction events are inhibited by the microgravity (ug) environment of spaceflight. Human leukocytes were stimulated with T cell mitogens onboard the International Space Station using a 1g centrifuge as the Earth’s 1g control. Microarray analysis demonstrated significant (p< .05) differential expression of 54 genes in ug vs 1g conditions. Fifty percent of the genes most significantly inhibited in ug as compared to 1g showed marked over-representation of NFKB binding sites in their promoter regions. Qrtpcr confirmed that upregulation of key genes in the NFKB pathway were inhibited in ug. Inhibition of the NFKB pathway leads to activation dysfunction during spaceflight. Lack of immune response in microgravity occurs at the cellular level. In our recent spaceflight studies of early T cell activation, we have discovered that the expression of miRNAs in both man and mouse require gravity for appropriate regulation. MiRNAs expressed during activation in normal gravity (g), were down regulated in spaceflight. These data suggest that gravity may regulate T-cell activation by two separate mechanisms; promoter regions and microRNA.

Short Communication: Lack of Immune Response in Rapid Progressor Morphine-Dependent and SIV/SHIV-Infected Rhesus Macaques Is Correlated with Downregulation of TH1 Cytokines

Our previous studies have shown two distinct disease patterns (rapid and normal onset of clinical symptoms) in morphine-dependent SHIV/SIV-inoculated rhesus macaques. We have also shown that control as well as 50% of morphine-dependent macaques (normal progressor) developed humoral and cellular immune responses whereas the other half of the morphine-dependent macaques (rapid progressor) did not develop antiviral immune responses after infection with SIV/SHIV. In the present study, we analyzed the association between cytokine production, immune response, and disease progression. To study the immunological effects of morphine at cytokine levels in the context of a lentiviral infection, we inoculated rhesus macaques with a mixture of SHIV(KU-18), SHIV(89.6)P, and SIV/17E-Fr. These animals were followed for a period of 56 weeks for cytokine level production in plasma. Drug-dependent rapid disease progressors exhibited an increase in IL-18 and IL-1Ra and a decrease in IL-12 levels in the plasma. Morphine-dependent normal progressors and control macaques exhibited an increase in both IL-18 and IL-12, whereas IL-Ra levels remained constant throughout the observation period. These results suggest that rapid disease progression in relation to morphine dependency may be the result of an altered cytokine profile.

Viral hemorrhagic septicemia and infectious pancreatic necrosis viruses replicate differently in rainbow trout gonad and induce different chemokine transcription profiles

Viral hemorrhagic septicemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV) are two rainbow trout ( Oncorhynchus mykiss) pathogens. While IPNV is known to be vertically transmitted to the next generation through the oocyte, VHSV is known to replicate in the ovary and be transmitted horizontally through the ovarian fluid. In this work, we wanted to study whether these differences had an effect on the immune response triggered in the ovary, with a focus on the chemokine response. We have studied the kinetics of viral gene expression and the sites of replication, confirming that great differences exist between the replication of the two viruses in the gonad. Next, we studied the levels of expression of several CXC and CC chemokines in the ovary and found that while VHSV strongly triggered chemokine transcription, IPNV had almost no effect. This lack of immune response might be an advantage that permits its vertical transmission.

Clinical Heterogeneity of CLL: Role for Immune Dysregulation Mediated by the Lymph Node Microenvironment.

Abstract 1243Poster Board I-265Chronic lymphocytic leukemia (CLL) is the most common adult leukemia and is clinically very heterogeneous. Following diagnosis, some patients do not require treatment for several years whereas others have a more aggressive disease thus requiring immediate treatment. Understanding the molecular basis of clinical heterogeneity in CLL will enhance our ability to treat this presently incurable disease effectively. CLL cells in the patient body proliferate/survive for a long time resulting in their accumulation in bone marrow (BM), lymph nodes (LN), and blood (PB). However, CLL cells do not survive for a long time once they are removed from the body, suggesting that an in vivo microenvironment provides essential proliferation/survival signals to CLL cells. Therefore, to elucidate the precise role of microenvironments on the CLL cell proliferation/survival and migration, in this study, we have analyzed CLL cells from PB (n=20), BM (n=18), and LN (n=15) from patients for their gene expression profiles using microarray. Differentially expressed genes and their associated cellular pathways were identified using significant analysis of microarray (SAM) and gene set enrichment analyses (GSEA). Among the six pathways/gene expression signatures identified (BCR-, BAFF/April-, NFκB-, PI3K/Akt, cytokine-, and tolerogenic) the most significant pathways in CLL biology are the BCR-, NFκB-, PI3K/Akt pathways and tolerogenic signature associated genes with immune dysregulation particularly with CLL cells from LN. We have already reported the differential expression of CLL cell proliferation and survival related genes belonging to BCR and NFαB pathways (Mittal et al, 2008 Blood-ASH Annual Meeting Abstract 546, page 112). In this report we have focused on differentially expressed genes associated with the tolerogenic signature and PI3K/Akt pathway. Among the eighty-three differentially expressed genes in the tolerogenic signature, based on their known role in immune regulation and/or level of significant expression comparing CLL cells from PB or BM, a few selected genes were further studied to understand their possible role in clinical heterogeneity of CLL. These genes are: CAV1, CD47, CCNB2, IL2Rαa, FOXP3, ZWINT, TGFβR1, IL22, IL10Rαa, INDO, APC, and STAT1. There was a significant increase in the expression of CD47, IL-10Rαa, CAV1, APC, CCNB2, and STAT1 in the LN cells from CLL patients; whereas the expression of IL-22R was decreased in the LN cells. These genes have been shown to be associated with immunosuppression indicating a lack of immune response against CLL in the lymph node. In addition, MAPK pathway associated genes are known to increase the survival/proliferation of tumor cells, including CLL cells. Specifically, genes associated with PI3K/Akt pathway, a part of MAPK pathways are also overexpressed in CLL cells from LN that includes AKT, 4E-BP1, PSMC4 and PDK1 genes indicating the importance of PI3K/Akt pathway in proliferation/survival of CLL cells in LN microenvironment. Based on these results, we hypothesize that differentially expressed genes belonging to the tolerogenic signature in LN of CLL patients down regulate the immune response against CLL, thus leading to enhanced disease progression whereas, overexpressed proliferation/survival-related genes belong to PI3K/Akt pathway promote proliferation/survival of CLL cells. (This work was supported by the CLL Foundation, Houston, TX and National Institutes of Health, Bethesda, MD, INBRE Grant # P20 RR016469). DisclosuresNo relevant conflicts of interest to declare.

TRANSLATIONAL IMPACT

The pathogenic Gram-positive bacterium Listeria monocytogenes causes severe acute infection in immunocompromised people including the very young and the very old. L. monocytogenes is the third most common cause of bacterial meningitis in neonates and causes abortion and stillbirth. Outbreaks of listeriosis continue to occur sporadically, recently claiming 20 lives in Canada. Whereas acute listeriosis is well-modeled in animals, chronic infection is more difficult to study and is consequently poorly understood. Bone marrow has been shown to harbor L. monocytogenes, suggesting that bone might be an important chronic reservoir from which the pathogen can infect the central nervous system. However, this infection is difficult to study because it involves only a few bacteria and the extent of infection cannot be assessed until after the animal is sacrificed.Here, the authors use live animal imaging to examine bone marrow infection by L. monocytogenes. As in previous imaging studies of this pathogen in the gallbladder, they found that bone marrow is another site of chronic infection. In vivo bioluminescence demonstrated that bone marrow infection by this bacterium is focal, and that the foci appear after both oral and intravenous infection. Furthermore, although L. monocytogenes is hypothesized to be an obligate intracellular pathogen, highly attenuated mutants that are defective in intracellular replication can colonize the bone marrow, focally, for many weeks. Persistence of L. monocytogenes in this compartment supports the idea that the bone marrow is a niche for this, and perhaps other, pathogens.Listeriosis can be very difficult to treat, sometimes requiring intravenous antibiotics for weeks. Studies of persistent bacterial infection should consider the bone marrow as a possible site of residual infection during, and after, treatment. In addition, this study demonstrates that the growth mechanism of attenuated L. monocytogenes is unclear; this is significant because attenuated strains are now in clinical trials to induce immune responses and eradicate established tumors without causing disease. The presence of L. monocytogenes in bone marrow might facilitate the induction of such immunity or, conversely, such persistence may indicate a lack of immune response and the induction of tolerance. Thus, in order to maximize efficacy and to ensure the safety of this treatment, future experiments should address immune stimulation in the bone marrow because this substantially sized niche might be beneficial, or detrimental, to anti-cancer therapy and other efforts.

P24. Lack of Immune Response to Transgene-Encoded Protein After in Utero Injection of Adeno-Associated Viral Vectors

P24. Lack of Immune Response to Transgene-Encoded Protein After in Utero Injection of Adeno-Associated Viral Vectors

Lack of immune responses against multiple sclerosis–associated retrovirus/human endogenous retrovirus W in patients with multiple sclerosis

The multiple sclerosis-associated retrovirus (MSRV), originally identified in cell cultures from patients with multiple sclerosis (MS), is closely related to the human endogenous retrovirus family type W (HERV-W). Different lines of evidence appear compatible with a potential role of MSRV/HERV-W in the pathogenesis of MS. The authors therefore analyzed humoral and cellular immune responses against MSRV/HERV-W antigens in patients with MS, patients with other inflammatory and noninflammatory neurological diseases, and healthy controls, using indirect immunofluorescence and enzyme-linked immunospot assays. Antibodies against the HERV-W envelope (Env) protein, Syncytin-1, were found in one of 50 patients with MS and none of 59 controls, whereas antibodies against MSRV matrix and capsid (Gag) or Env proteins were not detectable in any of the patients or controls. Similarly, in a screening of human leukocyte antigen (HLA)-B7+ patients with MS (n = 23) and controls (n = 29) for cytotoxic T-lymphocyte responses against 36 predicted HLA-B7-restricted MSRV/HERV-W Gag-, protease-, and reverse transcriptase-derived peptides, no such responses could be detected in any of the subjects studied. These data suggest that there are no appreciable humoral or cellular immune responses against MSRV/HERV-W in patients with MS. While this may be due to immunological tolerance of physiologically expressed HERV-W proteins, strategies other than measurement of immune responses will be required to further elucidate the relationship between MSRV/HERV-W and MS.

Neonatal and Infantile Immune Responses to Encapsulated Bacteria and Conjugate Vaccines

Encapsulated bacteria are responsible for the majority of mortality among neonates and infants. The major components on the surface of these bacteria are polysaccharides which are important virulence factors. Immunity against these components protects against disease. However, most of the polysaccharides are thymus-independent (TI)-2 antigens which induce an inadequate immune response in neonates and infants. The mechanisms that are thought to play a role in the unresponsiveness of this age group to TI-2 stimuli will be discussed. The lack of immune response may be overcome by conjugating the polysaccharides to a carrier protein. This transforms bacterial polysaccharides from a TI-2 antigen into a thymus-dependent (TD) antigen, thereby inducing an immune response and immunological memory in neonates and infants. Such conjugated vaccines have been shown to be effective against the most common causes of invasive disease caused by encapsulated bacteria in neonates and children. These and several other approaches in current vaccine development will be discussed.

34 Lack of immune response associated with expression of the yeast Ndi1 enzyme in rodents

34 Lack of immune response associated with expression of the yeast Ndi1 enzyme in rodents

Lack of immune response to transgene-encoded protein after in-utero gene therapy

Lack of immune response to transgene-encoded protein after in-utero gene therapy

Developing Antiangiogenic Peptide Drugs for Angiogenesis-Related Diseases

Angiogenesis is regulated by stimulators and inhibitors and involve multiple biological processes including endothelial cell proliferation, migration, cell-cell and cell-matrix adhesion, assembly into tube structures as well as apoptosis. Designing and developing peptides for therapeutic application to inhibit angiogenesis is an important area in antiangiogenic drug development. Small peptides have advantages over proteins for therapeutic application, due to their stability, solubility, increased bio-availability and lack of immune response in the host cell. Endogenous protein angiogenesis stimulators and inhibitors hold vital information for designing antiangiogenic peptides for drug development. These proteins function through their interaction with extracellular matrix molecules, cell surface receptors, proteases, as well as growth factors and cytokines. Conserved domains such as thrombospondin type 1 repeats (TSRs), kringle domains as well as critical amino acid residues present in these domains are involved in their functions. By exploiting these properties, several small peptides have been designed, synthetically made and being tested for therapeutic efficacy. Peptides derived from type 1 repeat of thrombospondin, alpha 4 and beta 1 chains of laminin, arginine rich N terminus of endostatin, leucine rich repeat 5 of decorin, pigment epithelium derived factor and N terminal of parathyroid hormone are examples of small antiangiogenic peptides derived from endogenous proteins. Such bioactive peptides are further modified physico-chemically to increase their potency and stability. In addition, phage-display library screening and combinatorial approach are also in use to identify novel antiangiogenic peptides targeting tumour and various proteins. This review will provide a comprehensive summary of the current status of the antiangiogenic peptides and their relevance for drug designing and development. Several critical issues that need to be resolved in translating this concept into clinical practice are also discussed.

An All-Human Culture Model Supporting Human B Lymphopoesis

Pregnancy is a complex process where several physiological pathways interact. The down-regulated inflammatory response and the abundance of anti-inflammatory molecules during gestation may explain the acceptance of the fetus and the lack of immune response against it, even though it is a foreign tissue for the mother. NF-κB is a key regulator of the transcription of inflammatory genes, such as IL-8, IL-1β, TNF-α, or IL-6. Increased NF-κB activity that leads to the production of proinflammatory cytokines may induce obstetric disorders, such as preterm birth or abortion. Low activity of this transcription factor is associated with the beneficial anti-inflammatory environment during fetus development until delivery. Galectin-1 (Gal-1) is a lectin-type glycan-binding protein that is able to down-regulate inflammation. It has been shown that Gal-1 is abundantly expressed at the feto-maternal interface in humans, where it promotes maternal immune tolerance to the fetal semi-allograft. Gal-1 tolerance-promoting mechanisms have been established for adaptive immune cells, such as T cells and dendritic cells. However, the role of this lectin has not been established in non-immune cells at the feto-maternal interface. Here, we determined that Gal-1 is able to block the stimulating effect of LPS on IL-6 in human decidua cells. Our results show that Gal-1 acts by inhibiting the stimulation of the LPS-induced IκBζ expression, an NF-κB regulator involved in IL-6 gene transcription.

High Accumulation of T Regulatory Cells Prevents the Activation of Immune Responses in Aged Animals

In our previous in vivo study we demonstrated that young BALB/c mice effectively rejected the BM-185 tumor cells expressing enhanced GFP (EGFP) as a surrogate tumor Ag. In contrast, old BALB/c mice succumbed to the BM-185-EGFP tumors, indicating that there is a deficiency in old animals preventing the rejection of immunogenic tumors. There is cumulative evidence indicating that regulatory T (T(reg)) cells control the activation of primary and memory T cell responses. However, very little is known about whether there is a relation between T(regs) and the lack of immune responses in the aged. We evaluated young and aged animals, and our results demonstrated that there are significantly more CD4+CD25+FoxP3+ and CD8+CD25+FoxP3+ T(regs) in the spleen and lymph nodes of old animals when compared with the young. Depletion of CD25+ cells with anti-CD25 mAb induces the rejection of BM-185-EGFP cells, restores antitumor T cell cytotoxic activity, and results in the generation of a protective memory response against the BM-185 wild-type tumors in old mice. Furthermore, vaccination with CpG-oligodeoxynucleotide decreases the number of T(reg) cells in old animals to the same levels as young mice, restoring the primary and memory antitumor immune responses against BM-185-EGFP tumors. Taken together, these results indicate that there is a direct correlation between the expansion of T(reg) cells and immune deficiency in the old, and that depletion of these cells might be critical for restoring immune responses in aged animals.