Production and purification of melanoma gp100 antigen and polyclonal antibodies

CD122-targeted interleukin-2 and αPD-L1 treat bladder cancer and melanoma via distinct mechanisms, including CD122-driven natural killer cell maturation

Bladder cancer (BC) and melanoma are amenable to immune checkpoint blockade (ICB) therapy, yet most patients with advanced/metastatic disease do not respond. CD122-targeted interleukin (IL)-2 can improve ICB efficacy, but mechanisms are unclear. We tested αPD-L1 and CD122-directed immunotherapy with IL-2/αIL-2 complexes (IL-2c) in primary and metastatic bladder and melanoma tumors. IL-2c treatment of orthotopic MB49 and MBT-2 BC generated NK cell antitumor immunity through enhanced activation, reduced exhaustion, and promotion of a mature, effector NK cell phenotype. By comparison, subcutaneous B16-F10 melanoma, which is IL-2c sensitive, requires CD8⁺ T and not NK cells, yet we found αPD-L1 efficacy requires both CD8⁺ T and NK cells. We then explored αPD-L1 and IL-2c mechanisms at distinct metastatic sites and found intraperitoneal B16-F10 metastases were sensitive to αPD-L1 and IL-2c, with IL-2c but not αPD-L1, increasing CD122⁺ mature NK cell function, confirming conserved IL-2c effects in distinct cancer types and anatomic compartments. αPD-L1 failed to control tumor growth and prolong survival in B16-F10 lung metastases, yet IL-2c treated B16-F10 lung metastases effectively even in T cell and adaptive immunity deficient mice, which was abrogated by NK cell depletion in wild-type mice. Flow cytometric analyses of NK cells in B16-F10 lung metastases suggest that IL-2c directly boosts NK cell activation and effector function. Thus, αPD-L1 and IL-2c mediate nonredundant, immune microenvironment-specific treatment mechanisms involving CD8⁺ T and NK cells in primary and metastatic BC and melanoma. Mechanistic differences suggest effective treatment combinations including in other tumors or sites, warranting further studies.

In silico approach of modified melanoma peptides and their immunotherapeutic potential

Melanoma is a type of skin cancer with increasing incidence worldwide and high lethality. Conventional forms of treatment are not effective in advanced cancer stages. Hence, immunotherapeutic approaches have been tested to modulate immune response against tumor cells. Some vaccine models using tumor-associated antigens (TAAs) such as glycoprotein 100 (gp100) have been studied, but their expected effectiveness has not been shown until now. Antigen immunogenicity is a crucial point to improve the immune response, and therefore mutations are inserted in peptide sequences. It is possible to understand the interactions which occur between peptides and immune system molecules through computer simulation, and this is essential in order to guide efficient vaccine models. In this work, we have calculated the interaction binding energies of crystallographic data based on modified gp100 peptides and HLA-A*0201 using density functional theory (DFT) and the molecular fractionation with conjugated caps (MFCC) approach. Our results show the most relevant residue-residue interactions, the impact of three mutations in their binding sites, and the main HLA-A*0201 amino acids for peptide-HLA binding.

Sensitive Multiplexed Quantitative Analysis of Autoantibodies to Cancer Antigens with Chemically S-Cationized Full-Length and Water-Soluble Denatured Proteins

Humoral immune responses against tumor-associated antigens (TAAs) or cancer/testis antigens (CTAs) aberrantly expressed in tumor cells are frequently observed in cancer patients. Recent clinical studies have elucidated that anticancer immune responses with increased levels of anti-TAA/CTA antibodies improve cancer survival rates. Thus, these antibody levels are promising biomarkers for diagnosing the efficiency of cancer immunotherapy. Full-length antigens are favored for detecting anti-TAA/CTA antibodies because candidate antigen proteins contain multiple epitopes throughout their structures. In this study, we developed a methodology to prepare purified water-soluble and full-length antigens by using cysteine sulfhydryl group cationization (S-cationization) chemistry. S-Cationized antigens can be prepared from bacterial inclusion bodies, and they exhibit improved protein solubility but preserved antigenicity. Anti-TAA/CTA antibodies detected in cancer patients appeared to recognize linear epitopes, as well as conformational epitopes, and because the frequency of cysteine side-residues on the epitope-paratope interface was low, any adverse effects of S-cationization were virtually negligible for antibody binding. Furthermore, S-cationized antigen-immobilized Luminex beads could be successfully used in highly sensitive quantitative-multiplexed assays. Indeed, patients with a more broadly induced serum anti-TAA/CTA antibody level showed improved progression-free survival after immunotherapy. The comprehensive anti-TAA/CTA assay system, which uses S-cationized full-length and water-soluble recombinant antigens, may be a useful diagnostic tool for assessing the efficiency of cancer immunotherapy.

Transcutaneous immunization with hydrophilic recombinant gp100 protein induces antigen-specific cellular immune response

The objective of this study was to evaluate the potential of transcutaneous immunization with tumor antigen to induce cell-mediated immunity. For this purpose, hydrophilic recombinant gp100 protein (HR-gp100) was topically applied on human intact skin in vitro, and used as a vaccine in a mouse model. We demonstrate that HR-gp100 permeates into human skin, and is processed and presented by human dendritic cells. In a mouse model, an HR-gp100-based vaccine triggered antigen-specific T cell responses, as shown by proliferation assays, ELISA and intracellular staining for IFN-γ. Transcutaneous antigen delivery may provide a safe, simple and effective method to elicit cell-mediated immunity.

A melanoma multiepitope polypeptide induces specific CD8+ T-cell response

Strategies using epitope-based vaccination are being considered for melanoma immunotherapy, in an attempt to overcome failure of other modalities. In the present study, we designed and produced a multiepitope polypeptide for melanoma (MEP-mel), which contains three repeats of four antigenic epitopes (gp100: 209-217 (210M); gp100: 280-288 (288V); Mart1: 26-35 (27L); tyrosinase: 368-376 (370D). The peptides were attached to each other by linkers containing sequences recognized by the proteasome, to improve protein cleavage and antigen presentation. The results show that peptide-specific T cells produced IFN-gamma when stimulated with MEP-mel-transfected dendritic cells. The presentation of peptides by MEP-mel-transfected dendritic cells was proteasome-dependent and was more long-lasting than the presentation of exogenously delivered native peptides. When dendritic cells were loaded with MEP-mel protein, weak cross presentation was induced. The production of multiepitope molecules based on several peptides linked by sequences sensitive to proteasomal cleavage represents a promising new tool for the improvement of cancer immunotherapy.

Immunological activation following transcutaneous delivery of HR-gp100 protein

Transcutaneous immunization aims at taking advantage of the skin's immune system for the purpose of immunoprotection. In the present study, we evaluated the potential of topical delivery of a recombinant melanoma protein, HR-gp100, derived from a shortened sequence of the native gp100 gene. The protein was applied on the skin, with and without the addition of two forms of heat labile enterotoxin (nLT and LTB). HR-gp100 fused to Haptide, a cell penetrating 20mer peptide (HR-gp100H) was also tested. Topical HR-gp100 and HR-gp100H application on the ears of mice elicited the production of specific antibodies, and transcutaneous delivery to intact human skin induced dose-dependent LC activation. nLT and LTB also activated LC, but did not further increase the activation induced by HR-gp100. These results show that HR-gp100, an antigenic tumor-derived protein, activates the immune system following transcutaneous delivery, as shown by both Langerhans cell activation and induction of antibody production.

Heat labile enterotoxin of E. coli: a potential adjuvant for transcutaneous cancer immunotherapy

Escherichia coli heat labile enterotoxin (LT) has been shown to penetrate intact skin and to activate adaptive immunity. A nontoxic mutant, nLT, and its B subunit (LTB), have been evaluated separately for their potential use as a tool for transcutaneous delivery of antigens for cancer immunotherapy. We have shown that FITC-labeled nLT is taken up by human dendritic cells (hDC) in vitro and in mouse skin, and induces maturation and activation of hDC in vitro. hDC matured with nLT enhanced nonspecific melanoma antigen uptake and presentation to autologous CD8+ T cells. In mouse in vivo studies, nLT or LTB were applied on the skin either mixed with recombinant gp100 or genetically fused with a multiepitope polypeptide (MEP). Fused LTB-MEP induced antibody production that was dependent on LTB cell binding. We conclude that LT derivatives may be useful for the transcutaneous delivery of tumor antigens for cancer immunotherapy.

Recombinant hydrophilic human gp100: uptake by dendritic cells and stimulation of autologous CD8+ lymphocytes from melanoma patients

Native gp100, a glycoprotein highly expressed in the majority of melanomas, contains several immunogenic peptides that are recognized by cytotoxic lymphocytes (CTLs) in the context of major histocompatibility complex (MHC) class I molecules. The objective of this study was to evaluate the ability of dendritic cells (DCs) from melanoma patients to take up gp100 protein and stimulate specific autologous CTL. The gp100 used in this study was a recombinant molecule with diminished hydrophobicity, HR-gp100, produced in Escherichia coli bacteria and in Pichia pastoris yeast. Stimulation of CD8+ T cells from melanoma patients with HR-gp100-loaded DC was visualized by confocal microscopy using stained target cells, and was quantitatively measured by the production of IFN-gamma using an ELISPOT assay. The results showed that HR-gp100 protein, produced either in bacteria or in yeast, when loaded on DC from melanoma patients, stimulated autologous CD8+ lymphocytes. By direct visualization, these lymphocytes were found in close contact with dead melanoma cells, and to contain membrane material transferred from stained melanoma cells; in cultures containing control lymphocytes stimulated with unloaded DC, no melanoma cell killing was observed. In ELISPOT assays, increased number of IFN-gamma-producing CD8+ T lymphocytes from patients, but not from healthy controls, were measured upon stimulation with HR-gp100-loaded DC. HR-gp100 could represent a useful tool to load DC with multiple immunogenic epitopes/antigen-derived epitopes for the immunotherapy of melanoma.