Dendritic cells infected with poxviruses encoding MART-1/Melan A sensitize T lymphocytes in vitro.

Dendritic cells (DC) are potent professional antigen-presenting cells that can activate naive T lymphocytes and initiate cellular immune responses. As adjuvants, DC may be useful in enhancing the immunogenicity of tumor antigens and mediating tumor regression. Endogenous expression of antigen by DC offers the potential advantage of allowing prolonged constitutive presentation of endogenously processed epitopes and exploitation of multiple restriction elements for the presentation of the same antigen. In this report, we show that human DC are (a) capable of infection by recombinant poxviruses encoding melanoma-associated antigen (MAA) genes and (b) capable of efficiently processing and presenting these MAA to cytotoxic T cells. In 6/6 HLA A*0201-expressing melanoma patients tested, the virally driven expression of MART-1/Melan A MAA by DC was sufficient to generate CD8+ T lymphocytes that could recognize naturally processed epitopes on tumor cells. In most cases, specific anti-MART-1 reactivity could be detected after a single stimulation. Analysis of epitope dominance revealed that the amino acid sequence recognized by these cytotoxic T lymphocytes (CTL) corresponded to the MART-1(27-35) residues previously shown to be most commonly recognized by cytotoxic T lymphocytes expanded from metastatic melanoma lesions. These data show that the virally driven expression of MAA by DC can be exploited for the efficient induction of clinically relevant cytotoxic T-cell responses. This has clinical implications for active immunization therapy, and currently vaccine trials have been proposed for patients with metastatic melanoma.

Enhancement of cellular immunity in melanoma patients immunized with a peptide from MART-1/Melan A.

PURPOSE: In this study, we tested the effectiveness of a melanoma-associated antigen-derived peptide, MART-1(27-35), in eliciting cellular immune responses in vivo in the context of a phase I active immunization protocol. This peptide (AAGIGILTV) corresponds to residues 27-35 from the nonmutated melanoma-associated antigen MART-1/Melan A and is recognized by most melanoma-specific, HLA-A*0201-restricted, tumor-infiltrating lymphocytes. To test the in vivo induction of cytotoxic T lymphocyte (CTL) sensitization, we compared CTL reactivity in vitro from peripheral blood mononuclear cell (PBMC) pools obtained before and after vaccination. PATIENTS AND METHODS: MART-1(27-35) was administered to HLA-A*0201 melanoma patients subcutaneously in an emulsification with incomplete Freund's adjuvant. A vaccination course included four inoculations of peptide at 3-week intervals. PBMC collected by leukapheresis and separated by Ficoll-Hypaque gradient before and after vaccination were analyzed in 18 patients by in vitro sensitization with MART-1(27-35). To induce MART-1(27-35)-specific CTL, PBMC were incubated with 1 microM peptide (on day 0) and interleukin-2 (IL-2) (300 IU/mL, on days 1 and 4 after each stimulation). At weekly intervals, cells were harvested and an aliquot was cryopreserved for later analysis. The remaining cells were replated and restimulated using irradiated autologous PBMC pulsed with 1 microM of relevant peptide. After three restimulations, all samples from one patient were tested simultaneously for HLA-A*0201-restricted anti-MART-1(27-35) reactivity by microcytotoxicity and cytokine (IFN-gamma) release assays. RESULTS: Toxicities were minimal and consisted of local irritation at the site of vaccine administration. None of the patients sustained a clinical response. The first eight patients were monitored by inducing CTL reactivity from PBMC obtained preimmunization and after two and four vaccinations. Only two prevaccination cultures were reactive to MART-1, compared with five and seven cultures from PBMC obtained after two and four vaccinations, respectively. Thus, an enhancement in cytotoxic activity could be detected in postvaccination CTL cultures, and serial vaccine administrations appeared to boost the detectability of cytotoxicity in vitro. For completeness, the analysis compared prevaccination with postvaccination PBMC cultures. Specific anti-MART-1(27-35) cytotoxicity (> or = 10 lytic units) could be detected in two prevaccination and 12 postvaccination cultures after two in vitro stimulations. In 15 postvaccination CTL cultures, a more than threefold increase in specific release of IFN-gamma was noted, compared with prevaccination. DISCUSSION: In vivo administration of a melanoma-associated antigen peptide, emulsified in incomplete Freund's adjuvant, could safely augment CTL reactivity against epitopes commonly expressed by melanoma cells. Although the enhancement of CTL reactivity did not achieve tumor regression, it is possible that the use of recombinant immunogens with increased immunomodulatory capabilities in future clinical trials could reach the threshold of CTL activation necessary for tumor regression.

Ligand occupancy of the alpha-V-beta3 integrin is necessary for smooth muscle cells to migrate in response to insulin-like growth factor.

Smooth muscle cells (SMCs) have been shown to migrate in response to insulin-like growth factor I (IGF-I). However, the mechanism mediating this response has not been determined. The migration rates of porcine and human vascular SMCs were assessed in a monolayer wounding assay. IGF-I and IGF-II induced increases of 141% and 97%, respectively, in the number of cells that migrated in 4 days. The presence of 0.2% fetal bovine serum in the culture medium was necessary for the IGFs to stimulate migration over uncoated plastic surfaces. However, if vitronectin was used as the substratum, IGF-I stimulated migration by 162% even in the absence of serum. To determine the role of integrins in mediating this migration, SMC surface proteins were labeled with 125I and immunoprecipitated with specific anti-integrin antibodies. Integrins containing alpha-V (vitronectin receptor), alpha5 (fibronectin receptor), and alpha3 (collagen/laminin receptor) subunits were the most abundant. IGF-I treatment caused a 73% reduction in alpha5-integrin subunit protein and a 25% increase in alpha-V subunit. More importantly, ligand binding of alpha-V-beta3 was increased by 2.4-fold. We therefore examined whether the function of the alpha-V-beta3 integrin was important for IGF-I-mediated migration. The disintegrin kistrin was shown by affinity crosslinking to specifically bind with high affinity to alpha-V-beta3 and not to alpha5-beta1 or other abundant integrins. The related disintegrin echistatin specifically inhibited 125I-labeled kistrin binding to alpha-V-beta3, while a structurally distinct disintegrin, decorsin, had 1000-fold lower affinity. The addition of increasing concentrations of either kistrin or echistatin inhibited IGF-I-induced migration, whereas decorsin had a minimal effect. The potency of these disintegrins in inhibiting IGF-I-induced migration paralleled their apparent affinity for the alpha-V integrin. Furthermore, an alpha-V-beta3 blocking antibody inhibited SMC migration by 80%. In summary, vitronectin receptor activation is a necessary component of IGF-I-mediated stimulation of smooth muscle migration, and alpha-V-beta3 integrin antagonists appear to be important reagents for modulating this process.

Insulin-like growth factor-I (IGF-I) regulates IGF-binding protein-5 synthesis through transcriptional activation of the gene in aortic smooth muscle cells.

Previous studies have shown that porcine aortic smooth muscle cells (SMCs) secrete two insulin-like growth factor-binding proteins (IGFBP), IGFBP-2 and -4, and that these IGFBPs modulate IGF-I-stimulated SMC proliferation and migration. In this study we demonstrate that porcine SMCs express IGFBP-5 mRNA and synthesize and secrete the protein. In this cell type, the biosynthesis of IGFBP-5 is up-regulated by IGF-I. This increase in IGFBP-5 synthesis is accompanied by an increase in the steady-state mRNA levels. The induction of IGFBP-5 mRNA by IGF-I is time- and dose-dependent and requires de novo protein synthesis. IGF-II and insulin also increase IGFBP-5 mRNA levels at high doses. An IGF-I analog with normal affinity for the IGF-I receptor but reduced affinity for IGFBPs evokes a similar increase. Another analog that binds to IGFBPs but not to the receptor has no effect, indicating that this effect of IGF-I is mediated through the IGF-I receptor. The IGF-I-induced IGFBP-5 gene expression is cell type-specific because IGF-I had no such effect in other cell types examined. Nuclear run-on assays revealed that IGF-I increased transcription rate of the IGFBP-5 gene, while IGF-I did not change the IGFBP-5 mRNA stability. Furthermore, the IGFBP-5 promoter was 3.5-fold more active in directing expression of the luciferase reporter gene in IGF-I-treated aortic SMCs as compared to control cells, whereas the luciferase activity remained the same in control- and IGF-I-treated fibroblasts. These results suggest that IGF-I up-regulates IGFBP-5 synthesis by transcriptionally activating the IGFBP-5 gene in aortic SMCs.

Insulin-like growth factor (IGF)-binding proteins inhibit the smooth muscle cell migration responses to IGF-I and IGF-II.

Smooth muscle cells have been shown to migrate in response to insulin-like growth factor I (IGF-I). However, the role of IGF-binding proteins (IGFBPs) in this process has not been determined. As IGFBPs are synthesized and secreted by smooth muscle cells and bind to IGFs with high affinity, this study was undertaken to determine the ability of IGFBP-1 and -2 to modulate cellular migration in response to IGF-I and -II. Confluent monolayers of porcine vascular smooth muscle cells were wounded with a razor blade. After wounding, IGF-I and -II induced increases of 159 +/- 49% (mean +/- SD) and 108 +/- 33%, respectively, above control values in the number of cells migrating over a fixed distance in 4 days. The addition of IGFBP-1 caused a 19-21% inhibition of IGF-I- or IGF-II-stimulated migration, whereas the addition of IGFBP-2 inhibited the effect of both by greater than 60%. The addition of IGFBP-2 alone had no effect, whereas IGFBP-1 addition was associated with a 42 +/- 12% increase. In contrast, [Trp221]IGFBP-1 in which the RGD sequence was changed to WGD, thus eliminating its capacity to bind to the alpha 5 beta 1 integrin, inhibited IGF-I-stimulated migration by 67 +/- 17%. An IGF analog that has a reduced affinity for IGFBP-2-stimulated migration equally well as IGF-I alone even in the presence of IGFBP-2. Likewise, the addition of insulin, which cannot bind to IGFBPs, at supraphysiological concentrations that are adequate to activate the IGF-I receptor resulted in a similar increase in migration. In summary, IGF-I and -II stimulate smooth muscle cell migration after wounding. This migratory response is modulated by IGFBPs. Both IGFBP-1 and IGFBP-2 appear to neutralize the effects of the IGFs by inhibiting their interaction with IGF receptors, but IGFBP-1 also has a direct stimulatory effect that requires an intact RGD integrin recognition sequence.