Dirk Schadendorf

NCRs and DNAM-1 mediate NK cell recognition and lysis of human and mouse melanoma cell lines in vitro and in vivo

NK cells use a variety of receptors to detect abnormal cells, including tumors and their metastases. However, in the case of melanoma, it remains to be determined what specific molecular interactions are involved and whether NK cells control metastatic progression and/or the route of dissemination. Here we show that human melanoma cell lines derived from LN metastases express ligands for natural cytotoxicity receptors (NCRs) and DNAX accessory molecule-1 (DNAM-1), two emerging NK cell receptors key for cancer cell recognition, but not NK group 2 member D (NKG2D). Compared with cell lines derived from metastases taken from other anatomical sites, LN metastases were more susceptible to NK cell lysis and preferentially targeted by adoptively transferred NK cells in a xenogeneic model of cell therapy. In mice, DNAM-1 and NCR ligands were also found on spontaneous melanomas and melanoma cell lines. Interference with DNAM-1 and NCRs by antibody blockade or genetic disruption reduced killing of melanoma cells. Taken together, these results show that DNAM-1 and NCRs are critical for NK cell-mediated innate immunity to melanoma cells and provide a background to design NK cell-based immunotherapeutic strategies against melanoma and possibly other tumors.

Vaccination with IL-12 gene-modified autologous melanoma cells: preclinical results and a first clinical phase I study

Cytokine gene transfer into tumor cells has been shown to mediate tumor regression and antimetastatic effects in several animal models via immunomodulation. Therefore, clinical protocols have been developed to treat cancer patients with cytokine gene-modified tumor cells. We inserted the genes coding for the p35 and p40 chain of interleukin-12 (IL-12) in two independent eukaryotic expression vectors and transduced melanoma cells of 15 different primary tumor cultures with both plasmids by a ballistic gene transfer approach. Secreted IL-12 demonstrated strong bioactivity by inducing interferon-γ release from peripheral blood lymphocytes upon coculture with cell culture supernatants after IL-12 gene transfer which could at least partly be blocked by IL-12-specific antisera. Further enrichment of transduced tumor cells by magnetic separation directly after gene transfer increased cytokine secretion from a mean of 119 pg in the unsorted to 507 pg IL-12 (24 h/106 cells) in the magnetically enriched cell fraction. Irradiation of these cells led to a further elevation of secreted IL-12 (mean 987 pg). Elevated IL-12 levels were detected over 7 days after irradiation in vitro. In a subsequent first clinical phase I study six patients with metastatic melanoma were vaccinated with autologous, interleukin-12 gene-modified tumor cells. Melanoma cells were expanded in vitro from surgically removed metastases, transduced by ballistic gene transfer, irradiated and were then injected subcutaneously (s.c.) at weekly intervals. Clinically, there was no major toxicity except for mild fever. All patients completed more than four s.c. vaccinations over 6 weeks and were eligible for immunological evaluation. Post-vaccination, peripheral mononuclear cells were found to contain an increased number of tumor-reactive proliferative as well as cytolytic cells as determined by a limiting dilution analysis in two patients. Two patients developed DTH reactivity against autologous melanoma cells and one had a minor clinical response. Biopsies taken from that patient’s metastases revealed a heavy infiltration of CD4+ and CD8+ T lymphocytes. In conclusion, vaccination induced immunological changes even in a group of advanced, terminally ill patients. These changes can be interpreted as an increased antitumor immune response.

Drug-resistance in human melanoma

Advanced malignant melanoma has a poor prognosis since chemotherapy is mostly ineffective due in part to the intrinsic and/or extrinsic resistance of melanoma cells to systemic treatment with anti‐neoplastic agents. The reasons for the chemoresistant phenotype are unknown. The relevance of well‐analyzed drug‐resistance mechanisms, e.g., intracellular/extracellular transport and induction of certain enzyme systems, is reviewed. Most anti‐cancer drugs kill susceptible cells through induction of apoptosis. Therefore, it appears that differences in the apoptotic pathways which lead to apoptotic deficiency may account for the ability of some tumor cells to resist drug therapy. Human melanomas, which are characteristically drug‐resistant, are more likely to have altered apoptotic pathways and fewer pro‐apoptotic molecules. Tumor cells with these characteristics are seldom sensitive to drugs. The complexity of the molecular variants involved in signal transduction along apoptotic pathways suggests that the cell may have a variety of possibilities for regulating apoptosis and generating apoptotic deficiency. Thus, apoptosis and apoptotic deficiency should be analyzed to better clarify the mechanisms of melanoma resistance.

Identification of novel proteins associated with the development of chemoresistance in malignant melanoma using two-dimensional electrophoresis.

A model system for studying chemoresistance in human melanoma cells (MeWo) has been established utilizing the four commonly used cytotoxic drugs vindesine, cisplatin, fotemustine and etoposide to yield stable drug‐resistant sublines. We analyzed phenotypical differences between MeWo cells and their chemoresistant counterparts using two‐dimensional electrophoresis. Proteins that were overexpressed in chemoresistant cell lines were purified and identified using matrix assisted laser desorption/ionization‐time of flight — mass spectrometry (MALDI‐TOF‐MS) and microsequencing. Here we show that four proteins, namely the translationally controlled tumor protein, the human elongation factor 1‐δ, tetratricopeptide repeat protein and the isoform 14‐3‐3‐γ of the 14‐3‐3‐family are overexpressed in chemoresistant melanoma cell lines. The significance of these findings is now being verified using transfection experiments with the aim of developing more effective chemotherapy protocols.

The role of the proteasome activator PA28 in MHC class I antigen processing

The proteasome system is the major source for the generation of viral antigens and tumor antigens presented by major histocompatibility complex class I (MHC class I) molecules. A specific feature of the proteasomal antigen processing machinery is that five of its components are inducible by IFN-gamma. Two of these are the alpha and beta subunits of the proteasome activator PA28. Our results show that PA28 selectively up-regulates the presentation of viral MHC class I epitopes and that down regulation PA28 in tumor cells results in impaired presentation of a human TRP2 tumor antigen.

Interferon-γ down-regulates NKG2D ligand expression and impairs the NKG2D-mediated cytolysis of MHC class I-deficient melanoma by natural killer cells

NKG2D operates as an activating receptor on natural killer (NK) cells and costimulates the effector function of αβ CD8+ T cells. Ligands of NKG2D, the MHC class I chain‐related (MIC) and UL16 binding protein (ULBP) molecules, are expressed on a variety of human tumors, including melanoma. Recent studies in mice demonstrated that NKG2D mediates tumor immune surveillance, suggesting that antitumor immunity in humans could be enhanced by therapeutic manipulation of NKG2D ligand (NKG2DL) expression. However, signals and mechanisms regulating NKG2DL expression still need to be elucidated. Here, we asked whether the proinflammatory cytokine Interferon‐γ (IFN‐γ) affects NKG2DL expression in melanoma. Cell lines, established from MHC class I‐negative and ‐positive melanoma metastases, predominantly expressed MICA and ULBP2 molecules on their surface. Upon IFN‐γ treatment, expression of MICA, in some cases, also of ULBP2 decreased. Besides melanoma, this observation was made also for glioma cells. Down‐regulation of NKG2DL surface expression was dependent on the cytokine dose and the duration of treatment, but was neither due to an intracellular retention of the molecules nor to an increased shedding of ligands from the tumor cell surface. Instead, quantitative RT‐PCR revealed a decrease of MICA‐specific mRNA levels upon IFN‐γ treatment and siRNA experiments pointed to an involvement of STAT‐1 in this process. Importantly, IFN‐γ‐treated MHC class I‐negative melanoma cells were less susceptible to NKG2D‐mediated NK cell cytotoxicity. Our study suggests that IFN‐γ, by down‐regulating ligand expression, might facilitate escape of MHC class I‐negative melanoma cells from NKG2D‐mediated killing by NK cells.

Functional HLA-DM on the surface of B cells and immature dendritic cells

HLA‐DM (DM) plays a critical role in antigen presentation through major histocompatibility complex (MHC) class II molecules. DM functions as a molecular chaperone by keeping class II molecules competent for antigenic peptide loading and serves as an editor by favoring presentation of high‐stability peptides. Until now, DM has been thought to exert these activities only in late endosomal/lysosomal compartments of antigen‐presenting cells. Here we show that a subset of DM resides at the cell surface of B cells and immature dendritic cells. Surface DM engages in complexes with putatively empty class II molecules and controls presentation of those antigens that rely on loading on the cell surface or in early endosomal recycling compartments. For example, epitopes derived from myelin basic protein that are implicated in the autoimmune disease multiple sclerosis are down‐modulated by DM, but are presented in the absence of DM. Thus, this novel concept of functional DM on the surface may be relevant to both protective immune responses and autoimmunity.

A randomised, phase II study of intetumumab, an anti-αv-integrin mAb, alone and with dacarbazine in stage IV melanoma

Background:αv integrins are involved in angiogenesis and melanoma tumourigenesis. Intetumumab (CNTO 95) is a fully human anti-αv-integrin monoclonal antibody.Methods:In a multicentre, randomised, phase II study, stage IV melanoma patients were randomised 1 : 1 : 1 : 1 to 1000 mg m−2 dacarbazine+placebo (n=32), 1000 mg m−2 dacarbazine+10 mg kg−1 intetumumab (n=32), 10 mg kg−1 intetumumab (n=33), or 5 mg kg−1 intetumumab (n=32) q3w. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall survival (OS), objective response rate (ORR), adverse events, and pharmacokinetics.Results:No statistically significant differences in efficacy were observed between groups. In the dacarbazine+placebo, dacarbazine+intetumumab, 10 mg kg−1 intetumumab, and 5 mg kg−1 intetumumab groups, median PFS was 1.8, 2.5, 1.4, and 1.4 months; median OS was 8, 11, 15, and 9.8 months; and ORR of complete+partial response was 10, 3, 6, and 0%. Nonlinear intetumumab pharmacokinetics and potential intetumumab–dacarbazine interactions were observed. Transient, asymptomatic, nonrecurring, grade 1–2, uveitic reactions that resolved spontaneously or with topical steroids were seen in 22–30% of intetumumab-treated patients. Low-grade infusion-reaction symptoms (headache, fatigue, nausea, vomiting, fever, chills) were observed, as expected, in 16–73% of dacarbazine-treated patients. No intetumumab-related myelosuppression, laboratory/electrocardiogram abnormalities, or deaths occurred.Conclusion:With its favourable safety profile and a nonsignificant trend towards improved OS, intetumumab merits further investigation in advanced melanoma.

Effects of granulocyte-macrophage colony-stimulating factor and foreign helper protein as immunologic adjuvants on the T-cell response to vaccination with tyrosinase peptides

Immunologic adjuvants are used to augment the immunogenicity of MHC class I–restricted peptide vaccines, but this effect has rarely been systematically evaluated in a clinical trial. We have investigated, in a phase I study, whether addition of the 2 adjuvants GM‐CSF and KLH can enhance the T‐cell response to MHC class I peptide vaccines. Forty‐three high‐risk melanoma patients who were clinically free of disease received 6 vaccinations with MHC class I–restricted tyrosinase peptides alone, with either GM‐CSF or KLH or with a combination of both adjuvants. The primary end point was induction of tyrosinase‐specific T cells, and serial T‐cell monitoring was performed in unstimulated peripheral blood samples before and after the second, fourth and sixth vaccinations by ELISPOT assay. Tyrosinase‐specific IFN‐γ‐producing T cells were detected as early as 2 weeks after the second vaccination in 5 of 9 patients vaccinated with tyrosinase peptides in combination with GM‐CSF and KLH but not in any patient vaccinated with tyrosinase peptides without adjuvants or in combination with either adjuvant alone. After 6 vaccinations, tyrosinase‐specific T cells were found in patients immunized with peptides either without adjuvants (3 of 9 patients) or in combination with the single adjuvant GM‐CSF (4 of 9 patients) but not with KLH (0 of 10 patients). Our results suggest that addition of either GM‐CSF or KLH as a single adjuvant has little impact on the immunogenicity of tyrosinase peptides. The combined application of GM‐CSF and KLH was associated with early induction of T‐cell responses.

Enhanced expression of human ABC-transporter tap is associated with cellular resistance to mitoxantrone

Multidrug resistance (MDR) phenotypes have been associated with the overexpression of various members of the superfamily of ATP binding cassette (ABC) transporters. Here we demonstrate that a member of the ABC‐transporter family, the heterodimer ‘transporter associated with antigen processing’ (TAP), physiologically involved in major histocompatibility complex class I‐restricted antigen presentation, is significantly overexpressed in the human gastric carcinoma cell line EPG85‐257RNOV exhibiting a mitoxantrone‐resistant phenotype. This tumor cell line shows an atypical MDR phenotype in the absence of ‘P‐glycoprotein’ or ‘MDR‐associated protein’ overexpression but with an enforced ‘breast cancer resistance protein’ expression level. Transfection of both TAP subunits encoding cDNA molecules, TAP1 and TAP2, into the drug‐sensitive parental gastric carcinoma cell line EPG85‐257P conferred a 3.3‐fold resistance to mitoxantrone but not to alternative anti‐neoplastic agents. Furthermore, cell clones transfected with both, but not singularly expressed TAP1 or TAP2, reduced cellular mitoxantrone accumulation. Taken together, the data suggest that the heterodimeric TAP complex possesses characteristics of a xenobiotic transporter and that the TAP dimer contributes to the atypical MDR phenotype of human cancer cells.