Gp41 Peptide Research Articles

Identification of HIV gp41 membrane proximal epitope tetramer reactive populations of B220+ B cells and B220lo/neg basophils in gp41 peptide-immunized mice (45.3)

Abstract 2F5 is a rare, neutralizing human mAb specific for the HIV gp41 membrane proximal region (MPER). Recently, we showed that 2F5 is a cardiolipin-binding, polyreactive autoantibody. To determine if MPER antibodies (Ab) are controlled by tolerance mechanisms, BALB/c mice were immunized with HIV-1 gp140 envelope or gp41 peptides. Immunized mice were screened for serum MPER Ab and for 2F5 antigen-specific B cells using 2F5 epitope B cell tetramers. Immunization in Ribi adjuvant did not induce anti-MPER Ab, whereas similar immunizations in TLR9, an adjuvant designed to break tolerance, did. Interestingly, in mice immunized with gp41 peptide, but not gp140, we found two distinct populations of 2F5 tetramer+ cells in bone marrow, spleen, and blood: a polyclonally-induced B220hi B-cell population that bound 2F5 tetramers via their surface Ig and a B220lo/neg cell population induced by immunization. Histological and cell surface phenotypic analysis of the B220lo/neg 2F5 tetramer+ cells indicated these were primarily basophils that bound 2F5 tetramers via MPER Ab bound to FcR. At present, the immunoregulatory significance of these distinct anti-MPER reactive populations is unknown, but their further characterization and the types of Ab they produce/bind should help in delineating why induction of neutralizing anti-MPER Ab is not achieved, despite the generation of a robust non-neutralizing MPER B cell and Ab response.

A Phase I Study of Immunization Using Particle-Mediated Epidermal Delivery of Genes for gp100 and GM-CSF into Uninvolved Skin of Melanoma Patients

We examined in vivo particle-mediated epidermal delivery (PMED) of cDNAs for gp100 and granulocyte macrophage colony-stimulating factor (GM-CSF) into uninvolved skin of melanoma patients. The aims of this phase I study were to assess the safety and immunologic effects of PMED of these genes in melanoma patients. Two treatment groups of six patients each were evaluated. Group I received PMED with cDNA for gp100, and group II received PMED with cDNA for GM-CSF followed by PMED for gp100 at the same site. One vaccine site per treatment cycle was biopsied and divided for protein extraction and sectioning to assess transgene expression, gold-bead penetration, and dendritic cell infiltration. Exploratory immunologic monitoring of HLA-A2(+) patients included flow cytometric analyses of peripheral blood lymphocytes and evaluation of delayed-type hypersensitivity to gp100 peptide. Local toxicity in both groups was mild and resolved within 2 weeks. No systemic toxicity could be attributed to the vaccines. Monitoring for autoimmunity showed no induction of pathologic autoantibodies. GM-CSF transgene expression in vaccinated skin sites was detected. GM-CSF and gp100 PMED yielded a greater infiltration of dendritic cells into vaccine sites than did gp100 PMED only. Exploratory immunologic monitoring suggested modest activation of an antimelanoma response. PMED with cDNAs for gp100 alone or in combination with GM-CSF is well tolerated by patients with melanoma. Moreover, pathologic autoimmunity was not shown. This technique yields biologically active transgene expression in normal human skin. Although modest immune responses were observed, additional investigation is needed to determine how to best utilize PMED to induce antimelanoma immune responses.

Changes in HIV-specific antibody responses and neutralization titers in patients under ART

In this study, we tested for antibody reactivities against gp120 and gp41-derived peptides, recombinant gp160, gp41 and tat in HIV-positive sera under antiretroviral therapy (ART) and determined their neutralization capacity. As a baseline, sera from patients in stage A, B and C of the disease, long term non-progressors (LNPs) and HIV-negative individuals were included. Compared to LNPs or sera from patients in group A, the reactivity of sera in stage B or C against gp120-derived peptides was reduced parallel to disease progression. Reactivity of these samples was compared with sera of patients under ART. Parallel to the decrease of viral load, the reactivity against gp120 and gp41-derived epitopes, recombinant gp160 and gp41 or the native gp120/41 complex was significantly reduced. Antibody-mediated neutralization of HIV-1 was detectable prior to ART but revealed substantial decreases coupled with progression of therapy. Responses to recombinant tat dropped after three months of therapy, increased however at later time points to initial levels. These data indicate that in parallel to the decrease in viral load and antibodies against gp120, the neutralization capacity of sera under ART is reduced, and can not be compensated by an increase in tat-specific antibodies.

Gp120-mediated cytotoxicity of human brain microvascular endothelial cells is dependent on p38 mitogen-activated protein kinase activation

Breakdown of the blood-brain barrier has been shown to contribute to neurological disorders that are prevalent in human immunodeficiency virus type 1 (HIV-1)-infected individuals, but the mechanisms involved in HIV-1-associated blood-brain barrier dysfunction remain incompletely understood. Using human brain microvascular endothelial cells (HBMECs) that constitute the blood-brain barrier, the authors determined the cytotoxic effects of gp120 on HBMECs. The authors showed that gp120 induced cytotoxicity of HBMECs derived from children, which required cotreatment with interferon (IFN)-gamma. IFN-gamma treatment exhibited up-regulation of the chemokine receptors CCR3 and CCR5 in children's HBMECs. In contrast, HBMECs isolated from adults were not responsive to gp120-mediated cytotoxicity. Peptides of gp120 representing binding regions for CD4 and chemokine receptors as well as CD4 antibody inhibited gp120-mediated cytotoxicity of HBMECs. RANTES, as expected, inhibited M-tropic gp120-mediated HBMEC cytotoxicity, whereas stromal cell-derived factor (SDF)-1alpha failed to inhibit T-tropic gp120-mediated cytotoxicity. Of interest, gp120 peptides representing non-CD4/non-chemokine receptor binding regions inhibited gp120-mediated HBMEC cytotoxicity. In addition, the authors showed that gp120-mediated HBMEC cytotoxicity involved p38 mitogen-activated protein kinase pathway. Taken together, these findings showed that gp120, in the presence of IFN-gamma, can cause dysfunction of the blood-brain barrier endothelium via MAPK pathways involving several gp120-HBMEC interactions.

Peptide Vaccination of Patients With Metastatic Melanoma

Therapeutic peptide vaccines for melanoma continue to only demonstrate anecdotal success. We set out to evaluate the impact of low-dose GM-CSF emulsified in Montanide ISA-51 on the immunogenicity of HLA-A2 restricted melanoma differentiation antigen peptide vaccines (MART-1, gp100 and tyrosinase) administered in separate subcutaneous injections. We conducted a randomized phase II clinical trial of HLA-A2+ patients with metastatic melanoma that were immunized every 3 weeks with one of the following vaccine preparations: (A) peptides + Montanide ISA-51; (B) peptides + Montanide ISA-51 + GM-CSF (10 microg); (C) peptides + Montanide ISA-51 + GM-CSF (50 microg). Immunization efficacy was determined by quantification of vaccine specific tetramer positive cytotoxic T cells in peripheral blood. Global assessment of immune competence was ascertained using DTH testing to common recall antigens as well as peripheral blood immunophenotyping. Twenty-five eligible patients were equally distributed across all 3 treatment groups. Only 9 patients demonstrated evidence of immunization. Most commonly, immune response was achieved to the gp100 peptide. The addition of low-dose GM-CSF did not impact immunization efficacy. DTH reactivity to Candida appeared predictive of successful immunization. Successful immunization with the peptide vaccines was associated with improved clinical outcomes. The addition of low dose GM-CSF to peptide vaccines did not enhance immunogenicity. Higher doses of GM-CSF may be needed to achieve this effect and this is a testable hypothesis. Likewise, better patient selection based on immunologic status (DTH reactivity) may be helpful to better understand the clinical impact of therapeutic cancer vaccines.

θ-Defensins Prevent HIV-1 Env-mediated Fusion by Binding gp41 and Blocking 6-Helix Bundle Formation

Retrocyclin-1, a -defensin, protects target cells from human immunodeficiency virus, type 1 (HIV-1) by preventing viral entry. To delineate its mechanism, we conducted fusion assays between susceptible target cells and effector cells that expressed HIV-1 Env. Retrocyclin-1 (4 microm) completely blocked fusion mediated by HIV-1 Envs that used CXCR4 or CCR5 but had little effect on cell fusion mediated by HIV-2 and simian immunodeficiency virus Envs. Retrocyclin-1 inhibited HIV-1 Env-mediated fusion without impairing the lateral mobility of CD4, and it inhibited the fusion of CD4-deficient cells with cells bearing CD4-independent HIV-1 Env. Thus, it could act without cross-linking membrane proteins or inhibiting gp120-CD4 interactions. Retrocyclin-1 acted late in the HIV-1 Env fusion cascade but prior to 6-helix bundle formation. Surface plasmon resonance experiments revealed that retrocyclin bound the ectodomain of gp41 with high affinity in a glycan-independent manner and that it bound selectively to the gp41 C-terminal heptad repeat. Native-PAGE, enzyme-linked immunosorbent assay, and CD spectroscopic analyses all revealed that retrocyclin-1 prevented 6-helix bundle formation. This mode of action, although novel for an innate effector molecule, resembles the mechanism of peptidic entry inhibitors based on portions of the gp41 sequence.

Clinical and immunological analysis of melanoma patients receiving immunization using particle-mediated gene transfer of genes for gp100 and GM-CSF into uninvolved skin

13033 Background: To investigate a new method of activating melanoma-specific immune responses, we examined in vivo particle-mediated gene transfer (PMGT) of cDNAs for gp100 and GM-CSF into uninvolved skin of melanoma patients (pts). We now report the analysis of a completed Phase I clinical study. Methods: Two treatment groups of 6 pts each were evaluated. Group I received PMGT with cDNA for gp100 during each 3 week cycle; Group II received PMGT with cDNA for GM-CSF followed 3 days later by PMGT for gp100 at the same site. PMGT used 0.25 ug DNA and 250 ug gold/treatment. Endpoints included vaccine toxicity, transgene expression, immunological activation, and antitumor effects. Results: No systemic toxicity could be attributed to the vaccines, while local toxicity in both groups included mild erythema and induration which resolved within 2 weeks. Monitoring for autoimmunity showed no induction of pathologic autoantibodies. Biopsies of vaccine sites obtained 2 days after the gp100 PMGT showed 16% of gold beads to be in the dermis in Group I vs 3% in Group II, suggesting the prior GM-CSF PMGT inhibited bead penetration (p < 0.001 by chi-square; each bead penetration was analyzed as an independent event). Biopsies in Group I obtained 2 days after vaccination showed 16% of beads in the dermis vs 22% after 4 days (p < 0.001 by chi-square; each bead penetration was analyzed as an independent event). Transgene expression in vaccinated skin sites was detected by ELISA (GM-CSF) and IHC (gp100). One of 4 HLA-A2+ subjects showed a 5 × 5-mm DTH response to gp100 peptide 210M after Cycle 1. Preliminary in vitro studies suggest minimal immunological activation. Of 4 pts who enrolled with no evidence of disease, 2 remain disease-free after 61–73 months of follow-up. Conclusions: PMGT with cDNA for gp100 and GM-CSF yields transgene expression in normal human skin with minimal local or systemic toxicity. Pathologic autoimmunity was not demonstrated. Bead concentration in the dermis increases over time, suggesting persistence of beads in this skin level. Conclusions related to melanoma-specific immune induction await T-cell and antibody studies. Supported in part by the UW General Clinical Research Center (M01 RR03186). No significant financial relationships to disclose.

The HIV-Neutralizing Monoclonal Antibody 4E10 Recognizes N-Terminal Sequences on the Native Antigen

Characterization of the epitope recognized by the broadly neutralizing anti-HIV Ab 4E10 has, heretofore, focused on a linear sequence from the gp41 pretransmembrane region (PTMR). Attempts to generate neutralizing Abs based on this linear epitope sequence have been unsuccessful. We have characterized the antigenic determinants on recombinant glycosylated full-length Ags, and nonglycosylated and truncated Ags recognized by 4E10 using epitope extraction and excision assays in conjunction with MALDI mass spectrometry. The mAb recognized the peptides (34)LWVTVYYGVPVWK(46) and (512)AVGIGAVFLGFLGAAGSTMGAASMTLTVQAR(542) located at the N-terminal region of gp120 and gp41, respectively. Immunoassays verified AV(L/M)FLGFLGAA as the gp41 epitope core. Recognition of the peptide from the gp41 PTMR was detected only in constructs in which the N termini of the mature envelope proteins were missing. In this region, the epitope core is located in the sequence (672)WFDITNWLWY(681). We hypothesize that the hydrophobic surface of the paratope functions as a "trap" for the viral sequences, which are responsible for insertion into the host cell membrane. As the N-terminal region of gp120, the fusogenic peptide of gp41, and the PTMR of gp41 show high sequence homology among various HIV strains, this model is consistent with the broadly neutralizing capabilities of 4E10.

Ocular Infiltrating CD4+T Cells from Patients with Vogt-Koyanagi-Harada Disease Recognize Human Melanocyte Antigens

To determine whether patients with Vogt-Koyanagi-Harada (VKH) disease have immune responses specific to the melanocyte antigens tyrosinase and gp100. T-cell clones (TCCs) were established from cells infiltrating the aqueous humor and from peripheral blood mononuclear cells (PBMCs) of patients with VKH. The target cells were LDR4-transfected cells (HLA-DRB1*0405). The TCCs were cocultured with LDR4 in the presence of tyrosinase (tyrosinase450-462: SYLQDSDPDSFQD), gp100 (gp100(44-59): WNRQLYPEWTEAQRLD), or a control peptide. The immune response was evaluated by cytokine production. The responding melanocyte peptide-specific VKH-TCCs were characterized by an immunofluorescence method with flow cytometry. A search was made for molecular mimicry among tyrosinase450-462, gp100(44-59), and exogenous antigens, such as viruses, by database screening. Cells infiltrating the eye and PBMCs in HLA-DR4+ (HLA-DRB1*0405, 0410) patients with VKH contained a population of CD4+ T lymphocytes that recognized tyrosinase and gp100 peptides and produced RANTES and IFN-gamma in response to the two peptides. The T cells were active memory Th1-type lymphocytes, and they recognized the tyrosinase peptide and produced IFN-gamma in response to HLA-DRB1*0405+ melanoma cells. Cytomegalovirus envelope glycoprotein H (CMV-egH290-302) had high amino acid homology with the tyrosinase peptide. In addition, some of the VKH-TCCs recognized CMV-egH290-302 peptide, as well as the tyrosinase peptides. In VKH there are tyrosinase and gp100 peptide-specific T cells that can mediate an inflammatory response. Such melanocyte antigen-specific T cells could be associated with the cause and pathology of VKH disease.

Evaluation of the HER2/neu‐derived peptide GP2 for use in a peptide‐based breast cancer vaccine trial

E75 and GP2 are human leukocyte antigen (HLA)-A2-restricted immunogenic peptides derived from the HER2/neu protein. In a E75 peptide-based vaccine trial, preexisting immunity and epitope spreading to GP2 was detected. The purpose of this study was to further investigate GP2 for potential use in vaccination strategies. Importantly, a naturally occurring polymorphism (I-->V at position 2, 2VGP2) associated with increased breast cancer risk was addressed. Prevaccination peripheral blood samples (PBMC) from HLA-A2 breast cancer patients and CD8+ T cells from HLA-A2 healthy donors were stimulated with autologous dendritic cells (DC) pulsed with GP2 and tested in standard cytotoxicity assays with HER2/neu+ tumor cells or GP2- or 2VGP2-loaded T2 targets. Additional cytotoxicity experiments used effectors stimulated with DC pulsed with E75, GP2, or the combination of E75+GP2. GP2-stimulated prevaccination PBMC from 28 patients demonstrated killing of MCF-7, SKOV3-A2, and the HLA-A2- control target SKOV3 of 28.8+/-3.7% (P<.01), 29.5+/-4.0% (P<.01), and 16.9+/-2.7%, respectively. When compared with E75, GP2-stimulated CD8+ T cells lysed HER2/neu+ targets at 43.8+/-5.2% versus 44.2+/-5.7% for E75 (P=.87). When combined, an additive effect was noted with 58.6+/-5.4% lysis (P=.05). GP2-stimulated CD8+ T cells specifically recognized both GP2-loaded (19.6+/-5.7%) and 2VGP2-loaded T2 targets (17.7+/-5.2%). GP2 is a clinically relevant HER2/neu-derived peptide with immunogenicity comparable to that of E75. Importantly, GP2-specific effectors recognize 2VGP2-expressing targets; therefore, a GP2 vaccine should be effective in patients carrying this polymorphism. GP2 may be most beneficial used in a multiepitope vaccine.

Immunization of Stage IV Melanoma Patients with Melan-A/MART-1 and gp100 Peptides plus IFN-α Results in the Activation of Specific CD8+ T Cells and Monocyte/Dendritic Cell Precursors

The use of IFN-alpha in clinical oncology has generally been based on the rationale of exploiting its antiproliferative and antiangiogenic activities. However, IFN-alpha also exhibits enhancing effects on T-cell and dendritic cell functions, which may suggest a novel use as a vaccine adjuvant. We have carried out a pilot phase I-II trial to determine the effects of IFN-alpha, administered as an adjuvant of Melan-A/MART-1:26-35(27L) and gp100:209-217(210M) peptides, on immune responses in stage IV melanoma patients. In five of the seven evaluable patients, a consistent enhancement of CD8(+) T cells recognizing modified and native MART-1 and gp100 peptides and MART-1(+)gp100(+) melanoma cells was observed. Moreover, vaccination induced an increase in CD8(+) T-cell binding to HLA tetramers containing the relevant peptides and an increased frequency of CD45RA(+)CCR7(-) (terminally differentiated effectors) and CD45RA(-)CCR7(-) (effector memory) cells. In all patients, treatment augmented significantly the percentage of CD14(+) monocytes and particularly of the CD14(+)CD16(+) cell fraction. An increased expression of CD40 and CD86 costimulatory molecules in monocytes was also observed. Notably, postvaccination monocytes from two of the three patients showing stable disease or long disease-free survival showed an enhanced antigen-presenting cell function and capability to secrete IP10/CXCL10 when tested in mixed leukocyte reaction assays, associated to a boost of antigen and melanoma-specific CD8(+) T cells. Although further clinical studies are needed to show the adjuvant activity of IFN-alpha, the present data represent an important starting point for considering a new clinical use of IFN-alpha and new immunologic end points, potentially predictive of clinical response.

Comparison of Common γ-Chain Cytokines, Interleukin-2, Interleukin-7, and Interleukin-15 for the In Vitro Generation of Human Tumor-Reactive T Lymphocytes for Adoptive Cell Transfer Therapy

The adoptive transfer of human tumor-reactive T lymphocytes into autologous patients can mediate the regression of metastatic melanoma. Here, the in vitro generation of melanoma-reactive T lymphocytes was compared using 3 common gamma-chain cytokines, interleukin (IL)-2, IL-7, and IL-15, alone or in combination. The proliferation, function, and phenotype were evaluated for tumor-reactive T cells derived from peripheral blood mononuclear cells (PBMCs) from patients previously immunized with the melanoma-associated peptide gp100:209-217(210M) and PBMCs transduced with a retrovirus encoding the alpha and beta chains of a gp100-reactive T-cell receptor (TCR). IL-7 alone did not induce significant proliferation of any tumor-reactive T-cell population, whereas IL-2 and IL-15 induced significant proliferation of tumor-reactive T lymphocytes from both sources. Cells cultured in the presence of IL-2 or IL-15 secreted comparable amounts of interferon-gamma and IL-2 in response to melanoma cells in vitro and were phenotypically similar in terms of costimulatory molecules (CD27 and CD28), cytokine receptors (CD25, CD122, and CD127), and a lymphoid homing molecule (CD62L). In addition, the proliferation, function, and phenotype of T cells cultured with combinations of IL-2, IL-7, and IL-15 were similar to those grown with IL-2 alone. The effects of these cytokines on TCR stimulation of CD45RA+ naive cells derived from adult patients and from human umbilical cord blood were also compared. Similar to the data with activated tumor-reactive T lymphocytes, IL-7 alone did not support significant proliferation of naive T cells after TCR stimulation with anti-CD3, although IL-2 and IL-15 induced comparable proliferation of T lymphocytes with similar phenotypic attributes.

Development of 111In-labeled tumor-associated antigen peptides for monitoring dendritic-cell-based vaccination

Dendritic cells (DC) are professional antigen-presenting cells capable of inducing potent immune responses. In our ongoing clinical trials, human leukocyte antigen (HLA)-A2.1+ melanoma patients are vaccinated with mature DC, presenting tumor-derived peptides in major histocompatibility complexes (MHC) to naive T cells. Previously, we have shown that both intradermally and intranodally injected (111)In-labeled mature DC migrate to draining lymph nodes. However, little is known about the fate of the MHC-peptide complex after injection of these peptide-loaded DC. The aim of the present study was to develop radiolabeled, tumor-derived peptides to monitor their binding to MHC Class I. The HLA-A2.1 binding peptide gp100:154-162mod (gp100:154m) was conjugated with diethylenetriamine pentaacetic acid (DTPA) either at the N-terminus (alpha-DTPA-gp100:154m) or at the epsilon amino group of the Lys(154) residue (epsilon-DTPA-gp100:154m) and labeled with (111)In. The maximum specific activity for both peptides was 13 GBq/micromol. The IC50 of the alpha-[(111)In]DTPA-gp100:154m peptide was >75 microM. The IC50 of the (111)In-labeled epsilon-DTPA-gp100:154m was 3 microM, similar to the unconjugated peptide. MHC binding studies showed specific binding of the epsilon-[(111)In]DTPA-gp100:154m peptide to the JY cells at 4 degrees C. Interestingly, no specific binding was observed for the alpha-[(111)In]DTPA-gp100:154m peptide. In contrast to the alpha-[(111)In]DTPA-gp100:154m peptide, the epsilon-[(111)In]DTPA-gp100:154m peptide was recognized by cytotoxic T cells. When DTPA was conjugated to the epsilon NH2 group of the Lys(154) residue, MHC binding of the peptide was preserved and could still be recognized by cytotoxic T cells. These studies allow the noninvasive determination of the behavior of MHC-peptide complexes on DC in vivo.

The N-terminal 12 Residue Long Peptide of HIV gp41 is the Minimal Peptide Sufficient to Induce Significant T-cell-like Membrane Destabilization in Vitro

Here, we predicted the minimal N-terminal fragment of gp41 required to induce significant membrane destabilization using IMPALA. This algorithm is dedicated to predict peptide interaction with a membrane. We based our prediction of the minimal fusion peptide on the tilted peptide theory. This theory proposes that some protein fragments having a peculiar distribution of hydrophobicity adopt a tilted orientation at a hydrophobic/hydrophilic interface. As a result of this orientation, tilted peptides should disrupt the interface. We analysed in silico the membrane-interacting properties of gp41 N-terminal peptides of different length derived from the isolate BRU and from an alignment of 710 HIV strains available on the Los Alamos National Laboratory. Molecular modelling results indicated that the 12 residue long peptide should be the minimal fusion peptide. We then assayed lipid-mixing and leakage of T-cell-like liposomes with N-terminal peptides of different length as first challenge of our predictions. Experimental results confirmed that the 12 residue long peptide is necessary and sufficient to induce membrane destabilization to the same extent as the 23 residue long fusion peptide. In silico analysis of some fusion-incompetent mutants presented in the literature further revealed that they cannot insert into a modelled membrane correctly tilted. According to this work, the tilted peptide model appears to explain at least partly the membrane destabilization properties of HIV fusion peptide.

The effects of gp100 and tyrosinase peptide vaccinations on nevi in melanoma patients

A new approach to prevent disease recurrence in high-risk melanoma patients involves immunization with gp100 and tyrosinase peptides. This is the first study to examine the effects of such treatments on nevi. We studied biopsies of 'clinically atypical' nevi from 10 patients before and after peptide vaccination. All had a cutaneous melanoma measuring at least 1.5 mm in depth, satellite metastases, or at least one positive lymph node. We performed immunohistochemical stains for CD3, CD4, CD8, MHC-I, MHC-II, CD1a, HMB-45, MART-1, tyrosinase, bcl-2, p53, and Ki-67 (mib-1). Immunohistochemistry showed no differences in staining due to vaccination in either the immunologic or melanocytic markers. However, there was a significant increase in both p53 and bcl-2 staining, and a trend toward decreased Ki-67 staining, in the nevi post-treatment. The primary goal of peptide vaccinations with gp100 and tyrosinase is to activate melanoma-specific T cells in order to prevent melanoma recurrence. Nevi were studied in order to assess the effects on benign melanocytes. No significant changes in lymphocytes, langerhans cells, expression of MHC antigens, or melanocytic markers were found. The increase in p53 and bcl-2 raises the possibility that vaccination with melanocytic antigens stimulates a response in benign melanocytes.

Immunological and Antitumor Effects of IL-23 as a Cancer Vaccine Adjuvant

The promising, but modest, clinical results of many human cancer vaccines indicate a need for vaccine adjuvants that can increase both the quantity and the quality of vaccine-induced, tumor-specific T cells. In this study we tested the immunological and antitumor effects of the proinflammatory cytokine, IL-23, in gp100 peptide vaccine therapy of established murine melanoma. Neither systemic nor local IL-23 alone had any impact on tumor growth or tumor-specific T cell numbers. Upon specific vaccination, however, systemic IL-23 greatly increased the relative and absolute numbers of vaccine-induced CD8(+) T cells and enhanced their effector function at the tumor site. Although IL-23 specifically increased IFN-gamma production by tumor-specific T cells, IFN-gamma itself was not a primary mediator of the vaccine adjuvant effect. The IL-23-induced antitumor effect and accompanying reversible weight loss were both partially mediated by TNF-alpha. In contrast, local expression of IL-23 at the tumor site maintained antitumor activity in the absence of weight loss. Under these conditions, it was also clear that enhanced effector function of vaccine-induced CD8(+) T cells, rather than increased T cell number, is a primary mechanism underlying the antitumor effect of IL-23. Collectively, these results suggest that IL-23 is a potent vaccine adjuvant for the induction of therapeutic, tumor-specific CD8(+) T cell responses.

IFN-Induced Attrition of CD8 T Cells in the Presence or Absence of Cognate Antigen during the Early Stages of Viral Infections

Profound lymphopenia has been observed during many acute viral infections, and our laboratory has previously documented a type I IFN-dependent loss of CD8 T cells immediately preceding the development of the antiviral T cell response. Most memory (CD44(high)) and some naive (CD44(low)) CD8 T cells are susceptible to IFN-induced attrition, and we show in this study that the IFN-induced attrition of CD8(+)CD44(high) T cells is associated with elevated activation of caspase-3 and caspase-8. We questioned whether TCR engagement by Ag would render CD8 T cells resistant to attrition. We tested whether a high concentration of Ag (GP33 peptide) would protect lymphocytic choriomeningitis (LCMV)-specific naive CD8 T cells (TCR transgenic P14 cells specific for the GP33 epitope of LCMV) and memory CD8 T cells (GP33-specific LCMV-immune cells) from depletion. Both naive P14 and memory GP33-specific donor CD8 T cells decreased substantially 16 h after inoculation with the Toll receptor agonist and IFN inducer, poly(I:C), regardless of whether a high concentration of GP33 peptide was administered to host mice beforehand. Moreover, donor naive P14 and LCMV-specific memory cells were depleted from day 2 LCMV-infected hosts by 16 h posttransfer. These results indicate that Ag engagement does not protect CD8 T cells from the IFN-induced T cell attrition associated with viral infections. In addition, computer models indicated that early depletion of memory T cells may allow for the generation for a more diverse T cell response to infection by reducing the immunodomination caused by cross-reactive T cells.

Enhanced viral and tumor immunity with intranodal injection of canary pox viruses expressing the melanoma antigen, gp100

The route of administration and extent of helper T-cell activation are factors that are likely to be important for the development of effective cancer vaccines. In order to optimize CD8(+) cytotoxic T-lymphocyte (CTL) responses, the immunologic effects of direct lymph node (LN) injections of canary pox virus (ALVAC) vectors (expressing the melanoma antigen, gp100) and immunogenic gp100 peptides, along with concomitant injections of the helper adjuvant, tetanus toxoid, were studied in high-risk HLA-A*0201(+) patients. Forty-two patients were vaccinated using six different protocols. Twenty-three patients were 'primed' with ALVAC(2)-gp100m and 'boosted' with gp100 peptides, either subcutaneously or into an LN. Intranodal (IN) peptides, alone, were administered to six patients. Thirteen patients were given tetanus toxoid initially, and with each gp100 vaccination. Toxicity was recorded and immunologic responses were determined in 35 patients by enzyme-linked immunospot (ELISPOT) and gp100-tetramer binding assays and anti-ALVAC(2) enzyme-linked immunosorbent assays (ELISAs). All vaccine protocols were tolerated well. Using stringent criteria for immunologic response, 8 of 18 patients responded to the viral vaccines, in striking contrast to peptides only (0 of 6 patients) or with help in trans from tetanus-reactive T-cells (1 of 11 patients). Changes in gp100-reactive CTL frequencies and ALVAC antibodies were greatest when viruses were injected directly into LNs. IN injections of ALVAC(2)-gp100m viruses are feasible, safe, and may be a superior method of vaccination in humans. CTL responses to this vaccine were not enhanced by tetanus toxoid.

Structural Basis of the Differential Stability and Receptor Specificity of H-2D b in Complex with Murine versus Human β 2-Microglobulin

beta(2)-Microglobulin (beta(2)m) is non-covalently linked to the major histocompatibility complex (MHC) class I heavy chain and interacts with CD8 and Ly49 receptors. Murine MHC class I heavy chains can bind human beta(2)m (hbeta(2)m) and peptide, and such hybrid molecules are often used in structural and functional studies. The replacement of mouse beta(2)m (mbeta(2)m) with hbeta(2)m has several functional consequences for MHC class I complex stability and specificity, but the structural basis for this is presently unknown. To investigate the impact of species-specific beta(2)m subunits on MHC class I conformation, we provide a crystallographic comparison of H-2D(b) in complex with LCMV-derived gp33 peptide and either hbeta(2)m or mbeta(2)m. The conformation of the gp33 peptide is not affected by the beta(2)m species. Comparison of the interface between beta(2)m and the alpha(1)alpha(2) domains of the heavy chain in these two crystal structures reveals a marked increase in both polarity and number of hydrogen bonds between hbeta(2)m and the alpha(1)alpha(2) domains of H-2D(b). We propose that the positioning of two hydrogen bond rich regions at the hbeta(2)m/alpha(1)alpha(2) interface plays a central role in the increased overall stability and peptide exchange capacity in the H-2D(b)/hbeta(2)m complex. These two regions act as bridges, holding and stabilizing the underside of the alpha(1) and alpha(2) helices, enabling a prolonged peptide-receptive conformation of the peptide binding cleft. Furthermore, analysis of H-2D(b) in complex with either mbeta(2)m or hbeta(2)m provides a structural explanation for the differential binding of H-2D(b)/hbeta(2)m to both Ly49A and Ly49C. Our comparative structural study emphasizes the importance of beta(2)m residues at positions 3, 6 and 29 for binding to Ly49A and suggests that sterical hindrance by residue K6 on hbeta(2)m impairs the recognition of Ly49C by H-2D(b)/gp33/hbeta(2)m. Finally, comparison of the two H-2D(b) crystal structures implies that the beta(2)m species may affect the strength of TCR recognition by affecting CD8 binding.

Expression, refolding and crystallization of murine MHC class I H-2Dbin complex with human β2-microglobulin

Beta2-microglobulin (beta2m) is non-covalently linked to the major histocompatibility (MHC) class I heavy chain and interacts with CD8 and Ly49 receptors. Murine MHC class I can bind human beta2m (hbeta2m) and such hybrid molecules are often used in structural and functional studies. The replacement of mouse beta2m (mbeta2m) by hbeta2m has important functional consequences for MHC class I complex stability and specificity, but the structural basis for this is unknown. To investigate the impact of species-specific beta2m subunits on MHC class I conformation, murine MHC class I H-2Db in complex with hbeta2m and the peptide gp33 derived from lymphocytic choriomeningitis virus (LCMV) has been expressed, refolded in vitro and crystallized. Crystals containing two complexes per asymmetric unit and belonging to the space group P2(1), with unit-cell parameters a = 68.1, b = 65.2, c = 101.9 A, beta = 102.4 degrees, were obtained.