Early expression of mature αß TCR in CD4-CD8- T cell progenitors enables MHC to drive development of T-ALL bearing NOTCH mutations.

During normal T cell development in mouse and human, a low-frequency population of immature CD4-CD8- double-negative (DN) thymocytes expresses early, mature αß T cell antigen receptor (TCR). We report that these early αß TCR+ DN (EADN) cells are DN3b-DN4 stage and require CD3δ but not major histocompatibility complex (MHC) for their generation/detection. When MHC - is present, however, EADN cells can respond to it, displaying a degree of coreceptor-independent MHC reactivity not typical of mature, conventional αß T cells. We found these data to be connected with observations that EADN cells were susceptible to T cell acute lymphoblastic leukemia (T-ALL) transformation in both humans and mice. Using the OT-1 TCR transgenic system to model EADN-stage αß TCR expression, we found that EADN leukemogenesis required MHC to induce development of T-ALL bearing NOTCH1 mutations. This leukemia-driving MHC requirement could be lost, however, upon passaging the tumors in vivo, even when matching MHC was continuously present in recipient animals and on the tumor cells themselves. These data demonstrate that MHC:TCR signaling can be required to initiate a cancer phenotype from an understudied developmental state that appears to be represented in the mouse and human disease spectrum.

Breaking tolerance with engineered class I antigen-presenting molecules.

Successful efforts to activate T cells capable of recognizing weak cancer-associated self-antigens have employed altered peptide antigens to activate T cell responses capable of cross-reacting on native tumor-associated self. A limitation of this approach is the requirement for detailed knowledge about the altered self-peptide ligands used in these vaccines. In the current study we considered allorecognition as an approach for activating CTL capable of recognizing weak or self-antigens in the context of self-MHC. Nonself antigen-presenting molecules typically contain polymorphisms that influence interactions with the bound peptide and TCR interface. Recognition of these nonself structures results in peptide-dependent alloimmunity. Alloreactive T cells target their inducing alloantigens as well as third-party alloantigens but generally fail to target self-antigens. Certain residues located on the alpha-1/2 domains of class I antigen-presenting molecules primarily interface with TCR. These residues are more conserved within and across species than are residues that determine peptide antigen binding properties. Class I variants designed with amino acid substitutions at key positions within the conserved helical structures are shown to provide strong activating signals to alloreactive CD8 T cells while avoiding changes in naturally bound peptide ligands. Importantly, CTL activated in this manner can break self-tolerance by reacting to self-peptides presented by native MHC. The ability to activate self-tolerant T cells capable of cross-reacting on self-peptide-MHC in vivo represents an approach for inducing autoimmunity, with possible application in cancer vaccines.

Chronic respiratory disease disparity between American Indian/Alaska Native and white populations, 2011-2018.

BACKGROUND: American Indian/Alaska Native (AI/AN) populations have been disproportionately affected by chronic respiratory diseases for reasons incompletely understood. Past research into disease disparity using population-based surveys mostly focused on state-specific factors. The present study investigates the independent contributions of AI/AN racial status and other socioeconomic/demographic variables to chronic respiratory disease disparity in an 11-state region with historically high AI/AN representation. Using data from the Behavioral Risk Factor Surveillance System (BRFSS) spanning years 2011-2018, this work provides an updated assessment of disease disparity and potential determinants of respiratory health in AI/AN populations. METHODS: This cross-sectional study used data from the BRFSS survey, 2011-2018. The study population included AI/AN and non-Hispanic white individuals resident in 11 states with increased proportion of AI/AN individuals. The yearly number of respondents averaged 75,029 (62878-87,350) which included approximately 5% AI/AN respondents (4.5-6.3%). We compared the yearly adjusted prevalence for chronic respiratory disease, where disease status was defined by self-reported history of having asthma and/or chronic obstructive pulmonary disease (COPD). Multivariable logistic regression was performed to determine if being AI/AN was independently associated with chronic respiratory disease. Covariates included demographic (age, sex), socioeconomic (marital status, education level, annual household income), and behavioral (smoking, weight morbidity) variables. RESULTS: The AI/AN population consistently displayed higher adjusted prevalence of chronic respiratory disease compared to the non-Hispanic white population. However, the AI/AN race/ethnicity characteristic was not independently associated with chronic respiratory disease (OR, 0.93; 95% CI, 0.79-1.10 in 2017). In contrast, indicators of low socioeconomic status such as annual household income of <$10,000 (OR, 2.02; 95% CI, 1.64-2.49 in 2017) and having less than high school education (OR, 1.37; 95% CI, 1.16-1.63 in 2017) were positively associated with disease. These trends persisted for all years analyzed. CONCLUSIONS: This study highlighted that AI/AN socioeconomic burdens are key determinants of chronic respiratory disease, in addition to well-established risk factors such as smoking and weight morbidity. Disease disparity experienced by the AI/AN population is therefore likely a symptom of disproportionate socioeconomic challenges they face. Further promotion of public health and social service efforts may be able to improve AI/AN health and decrease this disease disparity.

Transcriptional Regulation of the Human IL5RA Gene through Alternative Promoter Usage during Eosinophil Development.

Regulation of the IL-5 receptor alpha (IL5RA) gene is complicated, with two known promoters (P1 and P2) driving transcription, and two known isoforms (transmembrane and soluble) dichotomously affecting the signaling potential of the protein products. Here, we sought to determine the patterns of P1 and P2 promoter usage and transcription factor occupancy during primary human eosinophil development from CD34+ hematopoietic stem cell progenitors. We found that during eosinophilopoiesis, both promoters were active but subject to distinct temporal regulation, coincident with combinatorial interactions of transcription factors, including GATA-1, PU.1, and C/EBP family members. P1 displayed a relatively constant level of activity throughout eosinophil development, while P2 activity peaked early and waned thereafter. The soluble IL-5Rα mRNA peaked early and showed the greatest magnitude fold-induction, while the signaling-competent transmembrane isoform peaked moderately. Two human eosinophilic cell lines whose relative use of P1 and P2 were similar to eosinophils differentiated in culture were used to functionally test putative transcription factor binding sites. Transcription factor occupancy was then validated in primary cultures by ChIP. We conclude that IL-5-dependent generation of eosinophils from CD34+ precursors involves complex and dynamic activity including both promoters, several interacting transcription factors, and both signaling and antagonistic protein products.

iNKT cells ameliorate human autoimmunity: Lessons from alopecia areata.

Alopecia areata (AA) is understood to be a CD8+/NKG2D+ T cell-dependent autoimmune disease. Here, we demonstrate that human AA pathogenesis of is also affected by iNKT10 cells, an unconventional T cell subtype whose number is significantly increased in AA compared to healthy human skin. AA lesions can be rapidly induced in healthy human scalp skin xenotransplants on Beige-SCID mice by intradermal injections of autologous healthy-donor PBMCs pre-activated with IL-2. We show that in this in vivo model, the development of AA lesions is prevented by recognized the iNKT cell activator, α-galactosylceramide (α-GalCer), which stimulates iNKT cells to expand and produce IL-10. Moreover, in pre-established humanized mouse AA lesions, hair regrowth is promoted by α-GalCer treatment through a process requiring both effector-memory iNKT cells, which can interact directly with CD8+/NKG2D+ T cells, and IL-10. This provides the first in vivo evidence in a humanized model of autoimmune disease that iNKT10 cells are key disease-protective lymphocytes. Since these regulatory NKT cells can both prevent the development of AA lesions and promote hair re-growth in established AA lesions, targeting iNKT10 cells may have preventive and therapeutic potential also in other autoimmune disorders related to AA.

IL-12 Signals through the TCR To Support CD8 Innate Immune Responses.

CD8 T cells must integrate antigenic and inflammatory signals to differentiate into efficient effector and memory T cells able to protect us from infections. The mechanisms by which TCR signaling and proinflammatory cytokine receptor signaling cooperate in these processes are poorly defined. In this study, we show that IL-12 and other proinflammatory cytokines transduce signals through the TCR signalosome in a manner that requires Fyn activity and self-peptide-MHC (self-pMHC) interactions. This mechanism is crucial for CD8 innate T cell functions. Loss of Fyn activity or blockade of self-pMHC interactions severely impaired CD8 T cell IFN-γ and NKG2D expression, proliferation, and cytotoxicity upon cytokine-mediated bystander activation. Most importantly, in the absence of self-pMHC interactions, CD8 memory T cells fail to undergo bystander activation upon an unrelated infection. Thus, CD8 T cell bystander activation, although independent of cognate Ag, still requires self-pMHC and TCR signaling.

Maternal IL-6 can cause T-cell-mediated juvenile alopecia by non-scarring follicular dystrophy in mice.

Aiming to decipher immunological mechanisms of the autoimmune disorder alopecia areata (AA), we hypothesized that interleukin-6 (IL-6) might be associated with juvenile-onset AA, for which there is currently no experimental model. Upon intramuscular transgenesis to overexpress IL-6 in pregnant female C57BL/6 (B6) mice, we found that the offspring displayed an initial normal and complete juvenile hair growth cycle, but developed alopecia around postnatal day 18. This alopecia was patchy and reversible (non-scarring) and was associated with upregulation of Ulbp1 expression, the only mouse homolog of the human AA-associated ULBP3 gene. Alopecia was also associated with inflammatory infiltration of hair follicles by lymphocytes, including alpha-beta T cells, which contributed to surface hair loss. Despite these apparently shared traits with AA, lesions were dominated by follicular dystrophy that was atypical of human AA disease, sharing some traits consistent with B6 alopecia and dermatitis. Additionally, juvenile-onset alopecia was followed by complete, spontaneous recovery of surface hair, without recurrence of hair loss. Prolonging exposure to IL-6 prolonged the time to recovery, but once recovered, repeating high-dose IL-6 exposure de novo did not re-induce alopecia. These data suggest that although substantial molecular and cellular pathways may be shared, functionally similar alopecia disorders can occur via distinct pathological mechanisms.

Combinatorial Immunoprofiling in Latent Tuberculosis Infection. Toward Better Risk Stratification.

RATIONALE: Most immunocompetent patients diagnosed with latent tuberculosis infection (LTBI) will not progress to tuberculosis (TB) reactivation. However, current diagnostic tools cannot reliably distinguish nonprogressing from progressing patients a priori, and thus LTBI therapy must be prescribed with suboptimal patient specificity. We hypothesized that LTBI diagnostics could be improved by generating immunomarker profiles capable of categorizing distinct patient subsets by a combinatorial immunoassay approach. OBJECTIVES: A combinatorial immunoassay analysis was applied to identify potential immunomarker combinations that distinguish among unexposed subjects, untreated patients with LTBI, and treated patients with LTBI and to differentiate risk of reactivation. METHODS: IFN-γ release assay (IGRA) was combined with a flow cytometric assay that detects induction of CD25(+)CD134(+) coexpression on TB antigen-stimulated T cells from peripheral blood. The combinatorial immunoassay analysis was based on receiver operating characteristic curves, technical cut-offs, 95% bivariate normal density ellipse prediction, and statistical analysis. Risk of reactivation was estimated with a prediction formula. MEASUREMENTS AND MAIN RESULTS: Sixty-five out of 150 subjects were included. The combinatorial immunoassay approach identified at least four different T-cell subsets. The representation of these immune phenotypes was more heterogeneous in untreated patients with LTBI than in treated patients with LTBI or unexposed groups. Patients with IGRA(+) CD4(+)CD25(+)CD134(+) T-cell phenotypes had the highest estimated reactivation risk (4.11 ± 2.11%). CONCLUSIONS: These findings suggest that immune phenotypes defined by combinatorial assays may potentially have a role in identifying those at risk of developing TB; this potential role is supported by risk of reactivation modeling. Prospective studies will be needed to test this novel approach.

Signalling protein complexes isolated from primary human skin-resident T cells can be analysed by Multiplex IP-FCM.

Studying signal transduction in skin-resident T cells (sr-T cells) can be limited by the small size of clinical biopsies. Here, we isolated sr-T cells from clinical samples and analysed signalling protein complexes by multiplex immunoprecipitation detected by flow cytometry (mIP-FCM). In samples from two independent donors, antigenic stimulation induced signalling proteins to join shared complexes that were observed in seven pairwise combinations among five proteins. This demonstrates that sr-T cells isolated from small clinical samples provide sufficient material for mIP-FCM-based analysis of signalling-induced protein complexes. We propose that this strategy may be useful for gaining improved mechanistic insight of sr-T cell signal transduction associated with dermatological disease.

Adjuvant Delivery Method and Nanoparticle Charge Influence Peptide Amphiphile Micelle Vaccine Bioactivity.

Vaccines are an indispensable public health measure that have enabled the eradication, near elimination, and prevention of a variety of pathogens. As research continues and our understanding of immunization strategies develops, subunit vaccines have emerged as exciting alternatives to existing whole vaccine approaches. Unfortunately, subunit vaccines often possess weak antigenicity, requiring delivery devices and adjuvant supplementation to improve their utility. Peptide amphiphile micelles have recently been shown to function as both delivery devices and self-adjuvanting systems that can be readily associated with molecular adjuvants to further improve vaccine-mediated host immunity. While promising, many "design rules" associated with the plethora of underlying adjustable parameters in the generation of a peptide amphiphile micelle vaccine have yet to be uncovered. This work explores the impact micellar adjuvant complexation method and incorporated antigen type have on their ability to activate dendritic cells and induce antigen specific responses. Interestingly, electrostatic complexation of CpG to micelles resulted in improved in vitro dendritic cell activation over hydrophobic association and antigen|adjuvant co-localization influenced cell-mediated, but not antibody-mediated immune responses. These exciting results complement those previously published to build the framework of a micelle vaccine toolbox that can be leveraged for future disease-specific formulations.

IgG Fab fragments forming bivalent complexes by a conformational mechanism that is reversible by osmolytes.

Generated by proteolytic cleavage of immunoglobulin, Fab fragments possess great promise as blocking reagents, able to bind receptors or other targets without inducing cross-linking. However, aggregation of Fab preparations is a common occurrence, which generates intrinsic stimulatory capacity and thwarts signal blockade strategies. Using a panel of biochemical approaches, including size exclusion chromatography, SDS-PAGE, mass spectrometry, and cell stimulation followed by flow cytometry, we have measured the oligomerization and acquisition of stimulatory capacity that occurs in four monoclonal IgG Fabs specific for TCR/CD3. Unexpectedly, we observed that all Fabs spontaneously formed complexes that were precisely bivalent, and these bivalent complexes possessed most of the stimulatory activity of each Fab preparation. Fabs composing bivalent complexes were more susceptible to proteolysis than monovalent Fabs, indicating a difference in conformation between the Fabs involved in these two different states of valency. Because osmolytes represent a class of compounds that stabilize protein folding and conformation, we sought to determine the extent to which the amino acid osmolyte l-proline might impact bivalent Fab complexation. We found that l-proline (i) inhibited the adoption of the conformation associated with bivalent complexation, (ii) preserved Fab monovalency, (iii) reversed the conformation of preformed bivalent Fabs to that of monovalent Fabs, and (iv) separated a significant percentage of preformed bivalent complexes into monovalent species. Thus, Fab fragments can adopt a conformation that is compatible with folding or packing of a bivalent complex in a process that can be inhibited by osmolytes.

Toward T cell protein-protein interaction activity relevant to alopecia areata.

Development of better therapies for the T cell-mediated autoimmune disease alopecia areata (AA) could be expedited by an improved understanding of the immunologic signals underlying its pathogenesis. To approach this, our group is mounting a new technological and analytical platform, multiplex immunoprecipitation detected by flow cytometry (MIF). MIF is designed to allow analysis of collections of protein-protein interactions that participate in T cell signaling webs. Early experiments suggest that MIF can detect the increased protein-protein interaction network activity that occurs under conditions of T cell antigenic stimulation. Future experiments will focus on application of MIF to T cells isolated from AA or control patient samples, to identify critical T cell signaling complexes associated with the disorder.

Slow angled-descent forepaw grasping (SLAG): an innate behavioral task for identification of individual experimental mice possessing functional vision.

BACKGROUND: There is significant interest in the generation of improved assays to clearly identify experimental mice possessing functional vision, a property that could qualify mice for inclusion in behavioral and neuroscience studies. Widely employed current methods rely on mouse responses to visual cues in assays of reflexes, depth perception, or cognitive memory. However, commonly assessed mouse reflexes can sometimes be ambiguous in their expression, while depth perception assays are sometimes confounded by variation in anxiety responses and exploratory conduct. Furthermore, in situations where experimental groups vary in their cognitive memory capacity, memory assays may not be ideal for assessing differences in vision. RESULTS: We have optimized a non-invasive behavioral assay that relies on an untrained, innate response to identify individual experimental mice possessing functional vision: slow angled-descent forepaw grasping (SLAG). First, we verified that SLAG performance depends on vision and not olfaction. Next, all members of an age-ranged cohort of 158 C57BL/6 mice (57 wild-type, 101 knockout, age range 44-241 days) were assessed for functional vision using the SLAG test without training or conditioning. Subjecting the population to a second innate behavioral test, Dark Chamber preference, corroborated that the functional vision assessment of SLAG was valid. CONCLUSIONS: We propose that the SLAG assay is immediately useful to quickly and clearly identify experimental mice possessing functional vision. SLAG is based on a behavioral readout with a significant innate component with no requirement for training. This will facilitate the selection of mice of known sighted status in vision-dependent experiments that focus on other types of behavior, neuroscience, and/or cognitive memory.

Physical and functional bivalency observed among TCR/CD3 complexes isolated from primary T cells.

Unlike BCR and secreted Ig, TCR expression is not thought to occur in a bivalent form. The conventional monovalent model of TCR/CD3 is supported by published studies of complexes solubilized in the detergent digitonin, in which bivalency was not observed. We revisited the issue of TCR valency by examining complexes isolated from primary αß T cells after solubilization in digitonin. Using immunoprecipitation followed by flow cytometry, we unexpectedly observed TCR/CD3 complexes that contained two TCRs per complex. Standard anti-TCR Abs, being bivalent themselves, tended to bind with double occupancy to bivalent TCRs; this property masked the presence of the second TCR per complex in certain Ab binding assays, which may partially explain why previous data did not reveal these bivalent complexes. We also found that the prevalence of bivalency among fully assembled, mature TCR/CD3 complexes was sufficient to impact the functional performance of immunoprecipitated TCRs in binding antigenic peptide/MHC-Ig fusion proteins. Both TCR positions per bivalent complex required an Ag-specific TCR to effect optimal binding to these soluble ligands. Therefore, we conclude that in primary T cells, TCR/CD3 complexes can be found that are physically and functionally bivalent. The expression of bivalent TCR/CD3 complexes has implications regarding potential mechanisms by which Ag may trigger signaling. It also suggests the possibility that the potential for bivalent expression could represent a general feature of Ag receptors.

Basal and antigen-induced exposure of the proline-rich sequence in CD3ε.

The CD3ε cytoplasmic tail contains a conserved proline-rich sequence (PRS) that influences TCR-CD3 expression and signaling. Although the PRS can bind the SH3.1 domain of the cytosolic adapter Nck, whether the PRS is constitutively available for Nck binding or instead represents a cryptic motif that is exposed via conformational change upon TCR-CD3 engagement (CD3Δc) is currently unresolved. Furthermore, the extent to which a cis-acting CD3ε basic amino acid-rich stretch (BRS), with its unique phosphoinositide-binding capability, might impact PRS accessibility is not clear. In this study, we found that freshly harvested primary thymocytes expressed low to moderate basal levels of Nck-accessible PRS ("open-CD3"), although most TCR-CD3 complexes were inaccessible to Nck ("closed-CD3"). Ag presentation in vivo induced open-CD3, accounting for half of the basal level found in thymocytes from MHC(+) mice. Additional stimulation with either anti-CD3 Abs or peptide-MHC ligands further elevated open-CD3 above basal levels, consistent with a model wherein antigenic engagement induces maximum PRS exposure. We also found that the open-CD3 conformation induced by APCs outlasted the time of ligand occupancy, marking receptors that had been engaged. Finally, CD3ε BRS-phosphoinositide interactions played no role in either adoption of the initial closed-CD3 conformation or induction of open-CD3 by Ab stimulation. Thus, a basal level of open-CD3 is succeeded by a higher, induced level upon TCR-CD3 engagement, involving CD3Δc and prolonged accessibility of the CD3ε PRS to Nck.

Multiplex IP-FCM (immunoprecipitation-flow cytometry): Principles and guidelines for assessing physiologic protein-protein interactions in multiprotein complexes.

There is significant interest in the development of methods with the potential to increase access to 'the interactome' for both experimental and clinical applications. Immunoprecipitation detected by flow cytometry (IP-FCM) is a robust, biochemical method that can be used for measuring physiologic protein-protein interactions (PPI) in multiprotein complexes (MPC) with high sensitivity. Because it is based on antibody-mediated capture of protein complexes onto microspheres, IP-FCM is potentially compatible with a multiplex platform that could allow simultaneous assessment of many physiologic PPI. Here, we consider the principles of ambient analyte conditions (AAC) and inter-bead independence, and provide a template set of experiments showing how to convert singleplex IP-FCM to multiplex IP-FCM, including assays to confirm the validity of the experimental conditions for data acquisition. We conclude that singleplex IP-FCM can be successfully upgraded to multiplex format, and propose that the unique strengths of multiplex IP-FCM make it a method that is likely to facilitate the acquisition of new PPI data from primary cell sources.

Lower female survival from an opportunistic infection reveals progesterone-driven sex bias in trained immunity.

Immune responses differ between females and males, although such sex-based variance is incompletely understood. Observing that bacteremia of the opportunistic pathogen Burkholderia gladioli caused many more deaths of female than male mice bearing genetic deficiencies in adaptive immunity, we determined that this was associated with sex bias in the innate immune memory response called trained immunity. Female attenuation of trained immunity varies with estrous cycle stage and correlates with serum progesterone, a hormone that decreases glycolytic capacity and recall cytokine secretion induced by antigen non-specific stimuli. Progesterone receptor antagonism rescues female trained immune responses and survival from controlled B. gladioli infection to magnitudes similar to those of males. These data demonstrate progesterone-dependent sex bias in trained immunity where attenuation of female responses is associated with survival outcomes from opportunistic infection.

Mechanism of T cell tolerance induced by myeloid-derived suppressor cells.

Ag-specific T cell tolerance plays a critical role in tumor escape. Recent studies implicated myeloid-derived suppressor cells (MDSCs) in the induction of CD8(+) T cell tolerance in tumor-bearing hosts. However, the mechanism of this phenomenon remained unclear. We have found that incubation of Ag-specific CD8(+) T cells, with peptide-loaded MDSCs, did not induce signaling downstream of TCR. However, it prevented subsequent signaling from peptide-loaded dendritic cells. Using double TCR transgenic CD8(+) T cells, we have demonstrated that MDSC induced tolerance to only the peptide, which was presented by MDSCs. T cell response to the peptide specific to the other TCR was not affected. Incubation of MDSCs with Ag-specific CD8(+) T cells caused nitration of the molecules on the surface of CD8(+) T cells, localized to the site of physical interaction between MDSC and T cells, which involves preferentially only TCR specific for the peptide presented by MDSCs. Postincubation with MDSCs, only nitrotyrosine-positive CD8(+) T cells demonstrated profound nonresponsiveness to the specific peptide, whereas nitrotyrosine-negative CD8(+) T cells responded normally to that stimulation. MDSCs caused dissociation between TCR and CD3zeta molecules, disrupting TCR complexes on T cells. Thus, these data describe a novel mechanism of Ag-specific CD8(+) T cell tolerance in cancer.

B7-H1 expression on old CD8+ T cells negatively regulates the activation of immune responses in aged animals.

T cell responses are compromised in the elderly. The B7-CD28 family receptors are critical in the regulation of immune responses. We evaluated whether the B7-family and CD28-family receptors were differentially expressed in dendritic cells, macrophages, and CD4(+) and CD8(+) T cells from young and old mice, which could contribute to the immune dysfunction in the old. Although most of the receptors were equally expressed in all cells, >85% of the old naive CD8(+) T cells expressed B7-H1 compared with 25% in the young. Considering that B7-H1 negatively regulates immune responses, we hypothesized that expression of B7-H1 would downregulate the function of old CD8(+) T cells. Old CD8(+) T cells showed reduced ability to proliferate, but blockade of B7-H1 restored the proliferative capacity of old CD8(+) T cells to a level similar to young CD8(+) T cells. In vivo blockade of B7-H1 restored antitumor responses against the B7-H1(-) BM-185-enhanced GFP tumor, such that old animals responded with the same efficiency as young mice. Our data also indicate that old CD8(+) T cells express lower levels of TCR compared with young CD8(+) T cells. However, following antigenic stimulation in the presence of B7-H1 blockade, the levels of TCR expression were restored in old CD8(+) T cells, which correlated with stronger T cell activation. These studies demonstrated that expression of B7-H1 in old CD8(+) T cells impairs the proper activation of these cells and that blockade of B7-H1 could be critical to optimally stimulate a CD8 T cell response in the old.