Search PubMed⌕ Search

Biomedical subjects

David A Price

Publications and source records attributed to David A Price.

At least 73 records · Page 4Linked to original sources
PubMed2003

The CD8 T cell coreceptor exhibits disproportionate biological activity at extremely low binding affinities.

T lymphocytes recognize peptides presented in the context of major histocompatibility complex (MHC) molecules on the surface of antigen presenting cells. Recognition specificity is determined by the alphabeta T cell receptor (TCR). The T lymphocyte surface glycoproteins CD8 and CD4 enhance T cell antigen recognition by binding to MHC class I and class II molecules, respectively. Biophysical measurements have determined that equilibrium binding of the TCR with natural agonist peptide-MHC (pMHC) complexes occurs with KD values of 1-50 microm. The pMHCI/CD8 and pMHCII/CD4 interactions are significantly weaker than this (KD >100 microm), and the relative roles of TCR/pMHC and pMHC/coreceptor affinity in T cell activation remain controversial. Here, we engineer mutations in the MHCI heavy chain and beta2-microglobulin that further reduce or abolish the pMHCI/CD8 interaction to probe the significance of pMHC/coreceptor affinity in T cell activation. We demonstrate that the pMHCI/CD8 coreceptor interaction retains the vast majority of its biological activity at affinities that are reduced by over 15-fold (KD > 2 mm). In contrast to previous reports, we observe that the weak interaction between HLA A68 and CD8, which falls within this spectrum of reduced affinities, retains substantial functional activity. These findings are discussed in the context of current concepts of coreceptor dependence and the mechanism by which TCR coreceptors facilitate T cell activation.

Antigen Presentation↗
PubMed2003

CD8+ T cell-mediated suppression of intracellular Mycobacterium tuberculosis growth in activated human macrophages.

Animal models of tuberculosis point to a protective role for MHC class I-restricted CD8(+) T cells, yet it is unclear how these cells protect or whether such findings extend to humans. Here we report that macrophages infected with Mycobacterium tuberculosis, rapidly process and present an early secreted antigenic target (ESAT-6)-specific HLA class I-restricted CD8(+) T cell epitope. When cocultured with CD8(+) T cells restricted through classical HLA class I molecules the growth of bacilli within macrophages is significantly impaired after 7 days. This slow antimycobacterial activity did not correlate with macrophage lysis but required cell contact. We also found that inhibitors of apoptosis either had no effect or augmented the CD8-mediated suppressive activity, suggesting that an activation signal might be involved. Indeed we show that CD8(+) T cells were able to activate macrophages through receptors that include CD95 (Fas). Consistent with these findings the CD8-mediated suppression of mycobacterial growth was partially reversed by Fas blockade. These data identify a previously unrecognized CD8(+) T cell-mediated mechanism used to control an intracellular infection of macrophages.

Cell Communication↗
PubMed2003

The influence of macrophage inflammatory protein-1alpha on protective immunity mediated by antiviral cytotoxic T cells.

Macrophage inflammatory protein 1alpha (MIP-1alpha), a member of the CC-chemokine subfamily, is known to induce chemotaxis of a variety of cell types in vivo. Although the role of MIP-1alpha in inflammatory responses generated following primary infection of mice with many different pathogens has been characterized, the influence of this chemokine on the generation of antigen-specific T-cell responses in vivo is less well understood. This is important, as virus-specific CD8+ T lymphocytes (CTL) play a crucial role in defence against viral infections, both acutely and in the long term. In this study, we compared the ability of wild-type and MIP-1alpha-deficient (MIP-1alpha-/-) mice to mount CTL responses specific for the immunodominant epitope derived from influenza nucleoprotein (NP366-374). Influenza-specific CTL responses were compared with respect to frequency, cytotoxic activity and ability to clear subsequent infections with recombinant vaccinia viruses expressing the influenza NP. The results indicate that antiviral CTL generated in MIP-1alpha-/- mice are slightly impaired in their ability to protect against a subsequent infection. However, impaired in vivo CTL-mediated antiviral protection was found to be associated with reduced cytotoxicity rather than with a failure of the CTL to migrate to peripheral sites of infection.

Animals↗
PubMed2003

Discordant outcomes following failure of antiretroviral therapy are associated with substantial differences in human immunodeficiency virus-specific cellular immunity.

Many individuals chronically infected with human immunodeficiency virus type 1 (HIV-1) experience a recrudescence of plasma virus during continuous combination antiretroviral therapy (ART) due either to the emergence of drug-resistant viruses or to poor compliance. In most cases, virologic failure on ART is associated with a coincident decline in CD4(+) T lymphocyte levels. However, a proportion of discordant individuals retain a stable or even increasing CD4(+) T lymphocyte count despite virological failure. In order to address the nature of these different outcomes, we evaluated virologic and immunologic variables in a prospective, single-blinded, nonrandomized cohort of 53 subjects with chronic HIV-1 infection who had been treated with continuous ART and monitored intensively over a period of 19 months. In all individuals with detectable viremia on ART, multiple drug resistance mutations with similar impacts on viral growth kinetics were detected in the pol gene of circulating plasma virus. Further, C2V3 env gene analysis demonstrated sequences indicative of CCR5 coreceptor usage in the majority of those with detectable plasma viremia. In contrast to this homogeneous virologic pattern, comprehensive screening with a range of antigens derived from HIV-1 revealed substantial immunologic differences. Discordant subjects with stable CD4(+) T lymphocyte counts in the presence of recrudescent virus demonstrated potent virus-specific CD4(+) and CD8(+) T lymphocyte responses. In contrast, subjects with virologic failure associated with declining CD4(+) T lymphocyte counts had substantially weaker HIV-specific CD4(+) T lymphocyte responses and exhibited a trend towards weaker HIV-specific CD8(+) T lymphocyte responses. Importantly the CD4(+) response was sustained over periods as long as 11 months, confirming the stability of the phenomenon. These correlative data lead to the testable hypothesis that the consequences of viral recrudescence during continuous ART are modulated by the HIV-specific cellular immune response.

Adult↗
PubMed2003

The KIGS experience with the addition of gonadotropin-releasing hormone agonists to growth hormone (GH) treatment of children with idiopathic GH deficiency.

Although recombinant techniques have enabled the production of limitless amounts of human growth hormone (GH), and clinical methods for diagnosis and treatment have been greatly enhanced, the mean final heights of children with idiopathic GH deficiency (IGHD) treated with GH remain in the range of -1.3 standard deviation scores (SDS) below normal height. One of the methods used to increase height outcomes is to delay the onset and progression of puberty to allow for a longer 'pre-pubertal' growth phase. We reviewed the KIGS (Pharmacia International Growth Database) data of patients with IGHD who had been treated with gonadotropin-releasing hormone agonists (GnRHa) in order to see if a greater gain in height could be achieved by altering the tempo of pubertal maturation. Near-final height data were analysed in 39 adolescents (out of a total of 249) who had received GH + GnRHa therapy and were compared with similar data from 1,893 patients with IGHD treated with GH alone. The total change in height SDS in boys who received GH alone was +1.6, in contrast to +1.1 in GH + GnRHa-treated boys; the total change in height SDS in girls who received GH alone was +1.4 in contrast to +1.1 in girls treated with GH + GnRHa. The near final height SDS in girls treated with GH + GnRHa was 1.0 below the mid-parental target height (MPH), whereas there was only a -0.5 SDS difference in girls treated with GH. Approximation to the MPH did not differ in boys between the two treatment groups. These data suggest that the attainment of a substantial height SDS by manipulating the tempo of puberty is limited, but that optimizing growth during the pre-pubertal phase is a more important factor.

Adolescent↗
PubMed2003

Prediction of response to growth hormone treatment in short children born small for gestational age: analysis of data from KIGS (Pharmacia International Growth Database).

A model was developed that allows physicians to individualize GH treatment in children born short for gestational age (SGA) who fail to show spontaneous catch-up growth. Data from children (n = 613) in a large pharmacoepidemiological survey, the KIGS (Pharmacia International Growth Database), or who had participated in clinical trials were used to develop the model. Another group of similar children (n = 68) from KIGS was used for validation. In the first year of GH treatment, the growth response correlated positively with GH dose, weight at the start of GH treatment, and midparental height SD score and negatively with age at treatment start. Using this model, 52% of the variability of the growth response could be explained, with a mean error SD of 1.3 cm. GH dose was the most important response predictor (35% of variability), followed by age at treatment start. The second year growth response was best predicted by a three-parameter model (height velocity in yr 1 of treatment, age at start of treatment, and GH dose), which accounted for 34% of the variability, with an error SD of 1.1 cm. The first year response to GH treatment was the most important predictor of the second year response, accounting for 29% of the variability. No statistically significant differences between the predicted and observed growth responses were found when the models were applied to the validation groups. In conclusion, using simple variables, we have developed a model that can be used in clinical practice to adjust the GH dose to achieve the desired growth response in patients born SGA. Furthermore, this model can be used to provide patients with a realistic expectation of treatment and may help to identify compliance problems or other underlying causes of treatment failure.

Body Height↗
PubMed2003

The mathematical model for total pubertal growth in idiopathic growth hormone (GH) deficiency suggests a moderate role of GH dose.

The role of GH treatment during total pubertal growth (TPG) is still unclear. We developed a prediction model for TPG (centimeters) through a multiple regression analysis of various prepubertal parameters in 303 adolescents with idiopathic GH deficiency from the KIGS database. Prepubertal catch-up growth and near-adult height were achieved, and GH dose was kept constant at approximately 30 micro g/kg.d. The model was validated on a cohort of 36 patients from one center. Four TPG predictors explained 70% of the variability with an error SD of 4.2 cm: gender (TPG in males was >11.3 cm vs. that in females), age at onset of puberty (negative), height SD score minus midparental height SD score at puberty onset (negative), and mean GH dose during puberty (positive). Our analysis suggests that TPG in idiopathic GH deficiency is only moderately dependent on GH dose. The use of a higher GH dosage at the onset of puberty should thus depend on the individual's height development. The TPG model aids in the planning of individually optimized and cost-effective GH treatment.

Adolescent↗
PubMed2003

A new missense mutation in the growth hormone-releasing hormone receptor gene in familial isolated GH deficiency.

OBJECTIVE: Mutations in the GH-releasing hormone (GHRH) receptor (GHRHR) gene (GHRHR) cause autosomal recessive familial isolated GH deficiency (IGHD). We searched for GHRHR mutations in two siblings with IGHD type IB and a history of parental consanguinity. DESIGN: We analyzed peripheral genomic DNA of an index patient. After identifying a novel mutation in the GHRHR, we performed functional studies in order to confirm that the mutation causes receptor malfunction. METHODS: The entire GHRHR was analyzed in the index case by denaturing gradient gel electrophoresis. Abnormally migrating bands were isolated and sequenced. The mutated area was then sequenced in all family members whose DNA was available. The newly found mutation was inserted into a GHRHR cDNA. Wild-type and mutant cDNAs were expressed into CHO cells and the cyclic AMP (cAMP) response to GHRH was measured. In order to determine whether the mutant receptor was properly expressed on the cell membrane surface, CHO cells were transfected with wild-type or mutant GHRHR cDNA containing a FLAG epitope tag in the extracellular N-terminus. RESULTS: Both patients were homozygous for a new missense mutation in codon 176, corresponding to the second transmembrane domain of the receptor protein that replaces alanine with valine (A176V). The mother and three unaffected siblings were heterozygous for the mutation; DNA from the father was not available. Cells expressing the A176V receptor had a significantly reduced cAMP response to GHRH, despite appropriate expression on the cell surface. CONCLUSIONS: We describe two siblings with IGHD due to a new mutation in the GHRHR that disrupts GHRH signaling and leads to GHRH resistance.

Child↗
PubMed2002

Residual HIV-specific CD4 and CD8 T cell frequencies after prolonged antiretroviral therapy reflect pretreatment plasma virus load.

BACKGROUND: Virus-specific cellular immune responses mediated by CD4 and CD8 T lymphocytes are thought to be central to the effective control of HIV-1 replication in vivo. However, quantitative correlations between HIV-specific T lymphocyte frequencies and plasma virus load (pVL) have proved difficult to establish in infected human individuals. This most likely reflects the complex interactions between the virus and these immune effector cells in the absence of treatment. OBJECTIVE: To assess frequencies of HIV-specific T lymphocytes after prolonged suppression of viral replication, i.e., under conditions where the effects of virus on the immune response are standardized and minimized, thereby fixing an important variable in a dynamic multivariate system. METHODS: HIV-specific CD4 and CD8 T lymphocyte frequencies were measured in 122 individuals after prolonged periods of successful combination antiretroviral therapy (ART) administered during chronic HIV-1 infection. RESULTS: The residual frequency of both CD4 and CD8 T lymphocytes specific for HIV-1 was inversely related to the pretreatment pVL. This relationship appeared to be non-linear, indicating the presence of a threshold pretreatment pVL level above which HIV-specific CD4 and CD8 T lymphocyte responses could not be maintained when antigenic drive was suppressed. Substantial populations of functional HIV-specific CD4 and CD8 T lymphocytes were generally detectable after prolonged ART only in those individuals with a pretreatment plasma HIV-1 RNA < 100,000 copies/ml. CONCLUSION: These findings identify a quantitative immune associate of host-virus interactions in established HIV-1 infection.

Adult↗
PubMed2002

Stimulation of HIV-specific cellular immunity by structured treatment interruption fails to enhance viral control in chronic HIV infection.

Potent antiretroviral therapy (ART) suppresses HIV-1 viral replication and results in decreased morbidity and mortality. However, prolonged treatment is associated with drug-induced toxicity, emergence of drug-resistant viral strains, and financial constraints. Structured therapeutic interruptions (STIs) have been proposed as a strategy that could boost HIV-specific immunity, through controlled exposure to autologous virus over limited time periods, and subsequently control viral replication in the absence of ART. Here, we analyzed the impact of repeated STIs on virological and immunological parameters in a large prospective STI study. We show that: (i) the plateau virus load (VL) reached after STIs correlated with pretreatment VL, the amount of viral recrudescence during the treatment interruptions, and the off-treatment viral rebound rate; (ii) the magnitude and the breadth of the HIV-specific CD8(+) T lymphocyte response, despite marked interpatient variability, increased overall with STI. However, the quantity and quality of the post-STI response was comparable to the response observed before any therapy; (iii) individuals with strong and broad HIV-specific CD8(+) T lymphocyte responses at baseline retained these characteristics during and after STI; (iv) the increase in HIV-specific CD8(+) T lymphocyte frequencies induced by STI was not correlated with decreased viral set point after STI; and (v) HIV-specific CD4(+) T lymphocyte responses increased with STI, but were subsequently maintained only in patients with low pretreatment and plateau VLs. Overall, these data indicate that STI-induced quantitative boosting of HIV-specific cellular immunity was not associated with substantial change in viral replication and that STI was largely restoring pretherapy CD8(+) T cell responses in patients with established infection.

Anti-HIV Agents↗
PubMed2002

Complete mapping of a novel HLA A*6801-restricted HIV-1 Tat epitope directly with a rapid modified enzyme-linked immunospot assay.

We identified a novel HLA A*6801-restricted HIV-1 Tat-derived cytotoxic T lymphocyte (CTL) epitope using an adapted enzyme-linked immunospot assay that allows the rapid ex vivo identification of CTL epitopes together with their associated HLA Class I restriction elements. The optimal 11 amino acid residue Tat epitope efficiently stabilized the refolding of monomeric peptide-HLA A6801 complexes in vitro and fluorochrome-labelled, tetrameric peptide-HLA A6801 complexes stained CD8 T cells specific for this epitope directly ex vivo.

Enzyme-Linked Immunosorbent Assay↗
PubMed2002

Serum leptin and IGF-I during growth hormone treatment in chronic renal failure.

Serum leptin decreases during growth hormone (hGH) treatment and pre-treatment values have been suggested as a predictor of the response to hGH in GH deficiency (GHD) but not in non-GHD syndromes. To investigate whether this holds true in children with chronic renal failure (CRF), we evaluated changes in serum leptin, insulin-like growth factor-I (IGF-I) and height before(b) and during the 1st year (3 months, 6 months, 9 months, 12 months) of hGH treatment (1 IU/kg per week) in 11 children (median age(b) 10.1 years, mean height(b) -2.9 SDS) with CRF. Serum leptin and IGF-I were compared with values from healthy children. Each patient also served as his/her own control, with values during treatment compared with those before treatment. Growth improved in all patients during treatment (mean change(12 m) +7.2 cm, change in height SDS(12 m) +0.5, P=0.001). Weight decreased (median decrease(12 m) 0.3 SDS, P=0.02) but body mass index (BMI) and serum leptin did not change during treatment. Serum IGF-I levels were low before (mean -1.1 SDS) but increased during hGH treatment, the increment being greatest at 10 days (mean increment +1.9 SDS, P<0.0001). Serum leptin(b) did not correlate with change in serum IGF-I(10d), height(12 m) or weight(12 m). Serum IGF-I SDS(b) correlated with height SDS at 12 months ( r=0.80, P=0.006) of hGH treatment. Serum leptin(b) correlated with BMI ( r(s)=0.75, P=0.01). Levels adjusted for BMI did not differ from values in healthy children and did not change during treatment. Despite an IGF-I and growth response during hGH treatment, serum leptin did not change and pre-treatment values did not predict the growth response in these children with CRF.

Adipose Tissue↗
PubMed2002

HIV preferentially infects HIV-specific CD4+ T cells.

HIV infection is associated with the progressive loss of CD4(+) T cells through their destruction or decreased production. A central, yet unresolved issue of HIV disease is the mechanism for this loss, and in particular whether HIV-specific CD4(+) T cells are preferentially affected. Here we show that HIV-specific memory CD4(+) T cells in infected individuals contain more HIV viral DNA than other memory CD4(+) T cells, at all stages of HIV disease. Additionally, following viral rebound during interruption of antiretroviral therapy, the frequency of HIV viral DNA in the HIV-specific pool of memory CD4(+) T cells increases to a greater extent than in memory CD4(+) T cells of other specificities. These findings show that HIV-specific CD4(+) T cells are preferentially infected by HIV in vivo. This provides a potential mechanism to explain the loss of HIV-specific CD4(+) T-cell responses, and consequently the loss of immunological control of HIV replication. Furthermore, the phenomenon of HIV specifically infecting the very cells that respond to it adds a cautionary note to the practice of structured therapy interruption.

Anti-HIV Agents↗
PubMed2002

Novel CD8+ T cell antagonists based on beta 2-microglobulin.

The CD8 coreceptor of cytotoxic T lymphocytes binds to a conserved region of major histocompatibility complex class I molecules during recognition of peptide-major histocompatibility complex (MHC) class I antigens on the surface of target cells. This event is central to the activation of cytotoxic T lymphocyte (CTL) effector functions. The contribution of the MHC complex class I light chain, beta(2)-microglobulin, to CD8alphaalpha binding is relatively small and is mediated mainly through the lysine residue at position 58. Despite this, using molecular modeling, we predict that its mutation should have a dramatic effect on CD8alphaalpha binding. The predictions are confirmed using surface plasmon resonance binding studies and human CTL activation assays. Surprisingly, the charge-reversing mutation, Lys(58) --> Glu, enhances beta(2)m-MHC class I heavy chain interactions. This mutation also significantly reduces CD8alphaalpha binding and is a potent antagonist of CTL activation. These results suggest a novel approach to CTL-specific therapeutic immunosuppression.

Amino Acid Sequence↗
PubMed2002

T lymphocyte responses against human parvovirus B19: small virus, big response.

Parvovirus B19 elicits both humoral and cellular immune responses. Recently some advances have been made in determining the frequencies, peptide targets and function of virus-specific CD8+ T lymphocyte responses. A single HLA B35-restricted epitope derived from the NS1 protein has been studied so far, but others clearly exist. Surprisingly large, persistent responses have been detected in healthy seropositive individuals, using interferon-gamma ELISpot assays and HLA class I peptide tetramers. Similar techniques are available for exploration of the CD4+ T cell epitopes, although less detail is currently available. Mapping of cellular immune responses against the entire B19 genome (the parvovirus "immunome") is now possible and if similarly large populations are found consistently, this could yield important insight into normal immunological control and abnormalities in B19-related disease.

Antigens, Viral↗
PubMed2002

Functional discrepancies in HIV-specific CD8+ T-lymphocyte populations are related to plasma virus load.

The potent ability of current antiretroviral drug regimens to control human immunodeficiency Virus-1 (HIV-1) replication, in conjunction with the clinical practice of structured therapeutic interruptions, provides a system in which virus levels are manipulated during a persistent infection in humans. Here, we exploit this system to examine the impact of variable plasma virus load (pVL) on the functionality of HIV-specific CD8+ T-lymphocyte populations. Using both ELISpot methodology and intracellular cytokine staining for interferon (IFN)-gamma to assess functional status, together with fluorochrome-labeled peptide-major histocompatibility complex (pMHC) class I tetramer analysis to detect the physical presence of CD8+ T lymphocytes expressing cognate T-cell receptors (TCRs), we observed that the proportion of HIV-specific CD8+ T lymphocytes capable of mounting an effector response to antigen challenge directly ex vivo is related to the kinetics of virus exposure. Specifically, (a) after prolonged suppression of pVL with antiretroviral therapy (ART), physical and functional measures of HIV-specific CD8+ T-lymphocyte frequencies approximated; and (b) the percentage of functionally responsive cells in the HIV-specific CD8+ T lymphocyte populations declined substantially when therapy was discontinued and pVL recrudesced in the same patients. These results corroborate and extend observations in animal models that describe nonresponsive CD8+ T lymphocytes in the presence of high levels of antigen load and have implications for the interpretation of quantitative data generated by methods that rely on functional readouts.

Anti-HIV Agents↗
PubMed2002

Suppression of puberty with long-acting goserelin (Zoladex-LA): effect on gonadotrophin response to GnRH in the first treatment cycle.

BACKGROUND AND OBJECTIVES: Depot GnRH analogues are widely used in the treatment of precocious puberty, or suppression of relatively early puberty where growth or psychosocial well-being may be compromised. One example is Zoladex (Z goserelin 3.6 mg), which can be given every 4 weeks. This injection frequency may not always achieve adequate suppression of pubertal signs. A long-acting form, Zoladex-LA 10.8 mg, has now been introduced with a potential duration of action of 12 weeks. In order to assess the efficacy of Zoladex-LA in gonadotrophin suppression we have measured LH and FSH responses to GnRH at diagnosis and 8 and 12 weeks after injection in a group of children treated with Zoladex-LA for central precocious or early puberty. METHODS: Forty-nine children (40 girls) with clinical evidence of central precocious puberty (CPP) or early puberty (EP) were started on Zoladex-LA, either de novo (n = 29) or on changing from Zoladex. Ages at diagnosis ranged from 1.7 to 10.6 years (median 7.8 years). Twenty-three had a structural cause with abnormality on magnetic resonance/computerized tomography (MR/CT) head scan, nine had a syndrome or nonspecific brain injury, and in 17 the cause was idiopathic. RESULTS: At diagnosis, in the de novo group, median peak LH was 13.6 IU/l and median peak FSH was 12.0 IU/l. By 12 weeks gonadotrophins were suppressed to 0.9 and 0.8 IU/l, respectively. In the previously treated group, median peak LH at diagnosis was 12.8 IU/l and median peak FSH was 15.0 IU/l with suppression to 0.8 and 1.1 IU/l, respectively, at 12 weeks. In the latter group peak FSH was higher than peak LH at both 8 and 12 weeks (P < 0.05) and there was a significant rise in peak LH (P < 0.05) and FSH (P = 0.01) between 8 and 12 weeks. There was no correlation between age at diagnosis and peak LH or FSH at 8 or 12 weeks. Nevertheless, individual patients in both groups showed evidence of incomplete gonadotrophin suppression at 12 weeks. CONCLUSION: Zoladex-LA induces a significant reduction in gonadotrophins over 12 weeks. However, there are individuals, particularly those previously on Zoladex, in whom gonadotrophin suppression is waning by 12 weeks. As found with Zoladex, some children with precocious puberty treated with Zoladex-LA may require increased injection frequency, although correlation with clinical evidence of suppression needs to be studied further.

Antineoplastic Agents, Hormonal↗