Autologous melanoma vaccine induces inflammatory responses in melanoma metastases: relevance to immunologic regression and immunotherapy

Immune responses to malignancies

Immune responses to tumor-associated antigens (TAs) are often detectable in tumor-bearing hosts, but they fail to eliminate malignant cells or prevent the development of metastases. Patients with cancer generate robust immune responses to infectious agents (bacteria and viruses) perceived as a "danger signal" but only ineffective weak responses to TAs, which are considered as "self." This fundamental difference in responses to self versus nonself is further magnified by the ability of tumors to subvert the host immune system. Tumors induce dysfunction and apoptosis in CD8(+) antitumor effector cells and promote expansion of regulatory T cells, myeloid-derived suppressor cells, or both, which downregulate antitumor immunity, allowing tumors to escape from the host immune system. The tumor escape is mediated by several distinct molecular mechanisms. Recent insights into these mechanisms encourage expectations that a more effective control of tumor-induced immune dysfunction will be developed in the near future. Novel strategies for immunotherapy of cancer are aimed at the protection and survival of antitumor effector cells and also of central memory T cells in the tumor microenvironment.

Vaccination with irradiated autologous melanoma cells engineered to secrete human granulocyte-macrophage colony-stimulating factor generates potent antitumor immunity in patients with metastatic melanoma

We conducted a Phase I clinical trial investigating the biologic activity of vaccination with irradiated autologous melanoma cells engineered to secrete human granulocyte-macrophage colony-stimulating factor in patients with metastatic melanoma. Immunization sites were intensely infiltrated with T lymphocytes, dendritic cells, macrophages, and eosinophils in all 21 evaluable patients. Although metastatic lesions resected before vaccination were minimally infiltrated with cells of the immune system in all patients, metastatic lesions resected after vaccination were densely infiltrated with T lymphocytes and plasma cells and showed extensive tumor destruction (at least 80%), fibrosis, and edema in 11 of 16 patients examined. Antimelanoma cytotoxic T cell and antibody responses were associated with tumor destruction. These results demonstrate that vaccination with irradiated autologous melanoma cells engineered to secrete granulocyte-macrophage colony-stimulating factor stimulates potent antitumor immunity in humans with metastatic melanoma.

Rapid Extracellular Degradation of Synthetic Class I Peptides by Human Dendritic Cells

Dendritic cells (DCs) effectively process exogenous and endogenous Ag and present peptide in the context of both class I and class II molecules. We have demonstrated that peripheral blood DCs efficiently degrade synthetic class I peptides at their cell surface within minutes as determined by analyzing DC supernatants by HPLC. Fragments were verified as bona fide cleavage products by direct sequencing using collision-induced dissociation tandem mass spectrometry. The predominant degradative activities were 1) not secreted but associated with activity at the plasma membrane, 2) ecto-orientated, 3) not induced by peptide-specific interactions, and 4) not associated with nonspecific uptake. Sequence analysis indicated that both N- and C-terminal as well as endoproteolytic events were occurring at the cell surface. The primary exoproteolytic event was identified as CD13 or CD13-like activity through inhibition studies and could be inhibited by ubiquitin and metal-chelating agents. Endoproteolytic events could be inhibited in the presence of DTT, but the precise nature of this enzyme is still undetermined. Compared with the starting monocyte population, DCs cultured in the presence of granulocyte-macrophage CSF/IL-4 exhibited the highest degradative rate (4.3 nmol/min), followed by cultured monocytes (2.9 nmol/min) and freshly isolated monocytes (1.0 nmol/min). In addition to increased enzymatic activity, a change in substrate specificity was noted. Results are discussed with respect to APC loading, and alternatives are offered for circumventing such degradation.

Peptide-pulsed dendritic cells induce antigen-specific CTL-mediated protective tumor immunity

Cytotoxic T lymphocytes (CTLs) are a critical component of the immune response to tumors. Tumor-derived peptide antigens targeted by CTLs are being defined for several human tumors and are potential immunogens for the induction of specific antitumor immunity. Dendritic cells (DC) are potent antigen-presenting cells (APCs) capable of priming CTL responses in vivo. Here we show that major histocompatibility complex class I-presented peptide antigen pulsed onto dendritic APCs induces protective immunity to lethal challenge by a tumor transfected with the antigen gene. The immunity is antigen specific, requiring expression of the antigen gene by the tumor target, and is eliminated by in vivo depletion of CD8+ T cells. Furthermore, mice that have rejected the transfected tumor are protected from subsequent challenge with the untransfected parent tumor. These results suggest that immunization strategies using antigen-pulsed DC may be useful for inducing tumor-specific immune responses.

Activation markers on T cells infiltrating melanoma metastases after therapy with dinitrophenyl-conjugated vaccine

Treatment of metastatic melanoma patients with an autologous vaccine modified by the hapten, dinitrophenyl (DNP), produces a striking immunological effect: the induction of clinically evident inflammatory responses in metastatic tumors. Histological examination shows these tumors to be infiltrated with T lymphocytes. We studied the expression of activation markers on those cells and compared them with matched peripheral blood lymphocytes (PBL) and with lymphocytes extracted from metastases before treatment with DNP-conjugated vaccine. The median fraction of cells that were T cells in post-vaccine tumors was 41%, as compared with 9% in pre-treatment tumors, and those T cells were predominantly CD8+ (mean CD8/CD4 ratio = 5.0). A high proportion of both pre- and post-treatment infiltrating T cells expressed HLA-DR (mean +/- SE = 48% +/- 4%), CD69 (56% +/- 7%), and ganglioside GD3 (68% +/- 5%). This distinguished them from matched PBL in which expression of those markers was significantly lower (HLA-DR = 10% +/- 2%; CD69 = 2% +/- 0.4%; GD3 = 49% +/- 4%). These changes were not accompanied by increased cell-surface expression of interleukin-2 (IL-2) receptors, either CD25 or p75, which were expressed by 1%-2% and 12% of tumor-infiltrating lymphocytes (TIL), respectively. The pattern of activation marker expression that we identified appears to be characteristic of tissue T cells with the memory phenotype. The low expression of IL-2 receptors could indicate functional impairment of TIL in situ, perhaps because of inhibitory molecules produced by melanoma cells.

Expression of platelet-endothelial cell adhesion molecule-1 (PECAM-1) during melanoma-induced angiogenesis in vivo

Recent ultrastructural data indicate that tumor-induced angiogenesis involves polarized outgrowth of endothelial cells from established vessels into tumor parenchyma and interstitium. Efforts to define the cytoarchitecture of the angiogenic response and to ascertain molecular determinants of polarized endothelial migration have been impeded by lack of sensitive and specific immunologic markers for endothelium and vessel wall components. In this study, we utilized monoclonal antibody to platelet-endothelial cell adhesion molecule-1 (PECAM-1), a cell-cell adhesion molecule belonging to the immunoglobulin superfamily, to determine extent and patterns of angiogenesis in metastatic melanomas before (N = 7) and after (N = 3) induction of tumor-infiltrating lymphocyte responses provoked by administration of experimental melanoma vaccine. PECAM-1 proved to be a more reliable marker for angiogenesis than antibodies to von Willebrand Factor. Although both normal and tumor vessels exhibited prominent staining for PECAM-1, different patterns of endothelial reactivity were observed. Formation of new vessels was associated with i) PECAM-1 redistribution from a constitutive circumferential membrane pattern to a pattern restricted to cell-cell junctions; ii) formation of endothelial cords formed by cell-cell interactions; and iii) eventual development of open lumens. Vessels within inflamed (vaccine-treated) and non-inflamed melanomas did not differ with regard to patterns of PECAM-1 expression. Forming vessels of inflamed melanomas failed to express the cytokine-inducible activation marker, E-selectin. Although normal microvessels and reactive vessels of healing wounds demonstrated prominent staining for alpha 6 laminin receptor, vessels within melanomas showed apparently diminished expression.(ABSTRACT TRUNCATED AT 250 WORDS)