Michael Aigner

Hypomorphic mutations in PGAP2, encoding a GPI-anchor-remodeling protein, cause autosomal-recessive intellectual disability.

PGAP2 encodes a protein involved in remodeling the glycosylphosphatidylinositol (GPI) anchor in the Golgi apparatus. After synthesis in the endoplasmic reticulum (ER), GPI anchors are transferred to the proteins and are remodeled while transported through the Golgi to the cell membrane. Germline mutations in six genes (PIGA, PIGL, PIGM, PIGV, PIGN, and PIGO) in the ER-located part of the GPI-anchor-biosynthesis pathway have been reported, and all are associated with phenotypes extending from malformation and lethality to severe intellectual disability, epilepsy, minor dysmorphisms, and elevated alkaline phosphatase (ALP). We performed autozygosity mapping and ultra-deep sequencing followed by stringent filtering and identified two homozygous PGAP2 alterations, p.Tyr99Cys and p.Arg177Pro, in seven offspring with nonspecific autosomal-recessive intellectual disability from two consanguineous families. Rescue experiments with the altered proteins in PGAP2-deficient Chinese hamster ovary cell lines showed less expression of cell-surface GPI-anchored proteins DAF and CD59 than of the wild-type protein, substantiating the pathogenicity of the identified alterations. Furthermore, we observed a full rescue when we used strong promoters before the mutant cDNAs, suggesting a hypomorphic effect of the mutations. We report on alterations in the Golgi-located part of the GPI-anchor-biosynthesis pathway and extend the phenotypic spectrum of the GPI-anchor deficiencies to isolated intellectual disability with elevated ALP. GPI-anchor deficiencies can be interpreted within the concept of a disease family, and we propose that the severity of the phenotype is dependent on the location of the altered protein in the biosynthesis chain.

Effective elimination of acute myeloid leukemic cells by recombinant bispecific antibody derivatives directed against CD33 and CD16.

Single-chain Fv triplebodies (sctb), consisting of a single polypeptide chain with 3 single-chain antibody variable fragments connected in tandem, were generated as antileukemic agents. A CD19-specific sctb of this format has previously been shown to be superior to a bispecific single-chain Fv antibody fragment (bsscFv) for the elimination of leukemic B-lineage cells, but corresponding targeted agents for the treatment of acute myeloid leukemia are still lacking. For this purpose, both a bsscFv and a sctb specific for CD33 and the trigger molecule CD16 (FcγRIII) were produced. The sctb displayed 3.5-fold greater avidity for CD33 than the bsscFv 33xds16, whereas both had close to equal affinity for CD16. In antibody-dependent cellular cytotoxicity (ADCC) reactions with human mononuclear cells as effectors, both the bsscFv 33xds16 and the sctb induced lysis of tumor cells with half maximum effective concentrations (EC50) in the low picomolar range. It is interesting to note that the sctb promoted equal lysis of human leukemia-derived cell lines at 10 to 200-fold lower concentrations than the bsscFv. Both molecules mediated ADCC of primary patient cells. In conclusion, both the bsscFv 33xds16 and the sctb 33xds16x33 eliminated acute myeloid leukemia cells in ADCC reactions, but the novel sctb format showed significantly greater specific activity.

Null mutation in PGAP1 impairing Gpi-anchor maturation in patients with intellectual disability and encephalopathy.

Many eukaryotic cell-surface proteins are anchored to the membrane via glycosylphosphatidylinositol (GPI). There are at least 26 genes involved in biosynthesis and remodeling of GPI anchors. Hypomorphic coding mutations in seven of these genes have been reported to cause decreased expression of GPI anchored proteins (GPI-APs) on the cell surface and to cause autosomal-recessive forms of intellectual disability (ARID). We performed homozygosity mapping and exome sequencing in a family with encephalopathy and non-specific ARID and identified a homozygous 3 bp deletion (p.Leu197del) in the GPI remodeling gene PGAP1. PGAP1 was not described in association with a human phenotype before. PGAP1 is a deacylase that removes an acyl-chain from the inositol of GPI anchors in the endoplasmic reticulum immediately after attachment of GPI to proteins. In silico prediction and molecular modeling strongly suggested a pathogenic effect of the identified deletion. The expression levels of GPI-APs on B lymphoblastoid cells derived from an affected person were normal. However, when those cells were incubated with phosphatidylinositol-specific phospholipase C (PI-PLC), GPI-APs were cleaved and released from B lymphoblastoid cells from healthy individuals whereas GPI-APs on the cells from the affected person were totally resistant. Transfection with wild type PGAP1 cDNA restored the PI-PLC sensitivity. These results indicate that GPI-APs were expressed with abnormal GPI structure due to a null mutation in the remodeling gene PGAP1. Our results add PGAP1 to the growing list of GPI abnormalities and indicate that not only the cell surface expression levels of GPI-APs but also the fine structure of GPI-anchors is important for the normal neurological development.

Warburg phenotype in renal cell carcinoma: high expression of glucose-transporter 1 (GLUT-1) correlates with low CD8(+) T-cell infiltration in the tumor.

Many tumor cells are characterized by a dysregulated glucose metabolism associated with increased glycolysis in the presence of oxygen (“Warburg Effect”). Here, we analyzed for the first time a possible link between glucose metabolism and immune cell infiltration in renal cell carcinoma (RCC). RCC specimens revealed a highly significant increase in the expression of lactate dehydrogenase A (LDHA) and glucose‐transporter 1 (GLUT‐1) compared to the corresponding normal kidney tissue on mRNA level. Accordingly, tumor cell lines of different origin such as RCC, melanoma and hepatocellular carcinoma strongly expressed LDHA and GLUT‐1 compared to their nonmalignant counterparts. In line with this finding, tumor cells secreted high amounts of lactate. High expression of GLUT‐1 and LDH5, a tetramer of 4 LDHA subunits, was confirmed by tissue microarray analysis of 249 RCC specimens. Overall, 55/79 (69.6%) and 46/71 (64.7%) cases of clear cell carcinoma showed a constitutive, but heterogeneous expression of GLUT‐1 and LDH5, respectively. The number of CD3+, CD8+ and FOXP3+ T cells was significantly elevated in RCC lesions compared to normal kidney epithelium, but effector molecules such as granzyme B and perforin were decreased in tumor infiltrating T cells. Of interest, further analysis revealed an inverse correlation between GLUT‐1 expression and the number of CD8+ T cells in RCC lesions. Together, our data suggest that an accelerated glucose metabolism in RCC tissue is associated with a low infiltration of CD8+ effector T cells. Targeting the glucose metabolism may represent an interesting tool to improve the efficacy of specific immunotherapeutic approaches in RCC.

Moonlighting osteoclasts as undertakers of apoptotic cells.

Rapid clearance of apoptotic cells, frequently referred to as efferocytosis, is crucial for the maintenance of tissue homeostasis and the prevention of autoimmunity. The common model of apoptotic cell clearance involves a system of released “Find me” and exposed “Eat me” signals on apoptotic cells, detected and recognized by matching receptors on macrophages or dendritic cells (DC), referred to as the phagocytic synapse. Osteoclasts share the monocyte lineage with these professional mononuclear phagocytes, thus raising the question if, in addition to bone resorption, osteoclasts can act as scavengers for apoptotic cells. Our qPCR data clearly show that osteoclasts express most of the genes required for dying cell clearance at mRNA levels similar to or even higher than those observed in M1-macrophages, M2-macrophages or DC. Our microscopical analyses reveal that osteoclasts in fact can bind and/or engulf apoptotic cells in an essentially serum-independent fashion. Together with our data on the abundance of the respective mRNAs, these results identify the vitronectin receptor (integrin ανβ3)/milk fat globule-EGF factor 8 protein (MFG-E8) axis, the scavenger receptors (CD36, CD68 and class A macrophage scavenger receptor (SR-A)), the complement/complement receptor axis, the Mer/Tyro3/Protein S axis, and the phosphatidylserine (PS) receptor brain-specific angiogenesis inhibitor 1 (BAI1) as the most promising candidates to be involved in osteoclast-mediated efferocytosis.

IFN-γ-driven intratumoral microenvironment exhibits superior prognostic effect compared with an IFN-α-driven microenvironment in patients with colon carcinoma.

Interferon (IFN)-α and IFN-γ are cytokines with potent immunomodulating and anti-tumor activities. It is unknown which of the two IFNs may be more potent in the regulation of an anti-tumorigenic response in colorectal carcinoma or whether both cytokines cooperate. We, therefore, established human myxovirus resistance protein A and human guanylate-binding protein-1 as markers for the differential detection of IFN-α- and IFN-γ-driven tumor micromilieus, respectively. In vitro studies with different cultures of tumor cells from colorectal carcinoma and stroma cells showed that the expression of myxovirus resistance protein A was exclusively induced by IFN-α, whereas guanylate-binding protein-1 was strongly induced by IFN-γ and only weakly by IFN-α. This expression pattern was used to distinguish cell activation caused by the two cytokines in a clinical cohort of patients with colon carcinoma (n = 378). Patients with primary tumors expressing only guanylate-binding protein-1 exhibited the highest cancer-specific 5-year survival (94.0%, P = 0.006) compared with those expressing both factors (90.3%, P = 0.006), myxovirus resistance protein A alone (83.5%, P = 0.096), or none (72.8%). Our study describes a successful proof-of-principle approach that complex cytokine interaction networks can be dissected in human tissues and demonstrates that an IFN-γ-driven tumor microenvironment exhibits a superior prognostic effect compared with an IFN-α-driven tumor microenvironment in colon carcinoma.

Suppressive effects of tumor cell-derived 5′-deoxy-5′-methylthioadenosine on human T cells

ABSTRACT The immunosuppressive tumor microenvironment represents one of the main obstacles for immunotherapy of cancer. The tumor milieu is among others shaped by tumor metabolites such as 5′-deoxy-5′-methylthioadenosine (MTA). Increased intratumoral MTA levels result from a lack of the MTA-catabolizing enzyme methylthioadenosine phosphorylase (MTAP) in tumor cells and are found in various tumor entities. Here, we demonstrate that MTA suppresses proliferation, activation, differentiation, and effector function of antigen-specific T cells without eliciting cell death. Conversely, if MTA is added to highly activated T cells, MTA exerts cytotoxic effects on T cells. We identified the Akt pathway, a critical signal pathway for T cell activation, as a target of MTA, while, for example, p38 remained unaffected. Next, we provide evidence that MTA exerts its immunosuppressive effects by interfering with protein methylation in T cells. To confirm the relevance of the suppressive effects of exogenously added MTA on human T cells, we used an MTAP-deficient tumor cell-line that was stably transfected with the MTAP-coding sequence. We observed that T cells stimulated with MTAP-transfected tumor cells revealed a higher proliferative capacity compared to T cells stimulated with Mock-transfected cells. In conclusion, our findings reveal a novel immune evasion strategy of human tumor cells that could be of interest for therapeutic targeting.

Abstract 5621: MCSP/CD3-bispecific single-chain antibody construct engages CD4+ and CD8+ T cells for lysis of MCSP-expressing human uveal melanoma cells

Uveal melanoma is the most common cancer of the eye and metastasizes in approximately 50% of patients. None of the current therapies prevents the development of metastases or extends the survival time of these patients. Bi-specific T cell engager (BiTE) are based on recombinant single-chain antibody constructs. These molecules can transiently connect T cells to tumor cells, leading to concomitant T cell activation and serial lysis of tumor cells. Recently, a BiTE antibody bi-specific for CD19 and CD3 (blinatumomab) has shown very high response rates in patients with refractory non-Hodgkin9s B cell lymphoma (100%) and B-precursor acute lymphocytic leukemia (80%). These findings suggest that the mode of BiTE antibody action may also be useful for treatment of solid tumors. Human melanoma-associated chondroitin sulfate proteoglycan (MCSP, also known as HMW-MAA, gp240, or CSPG4), is expressed on the surface of >90% of human cutaneous melanoma lesions and cell lines, with restricted distribution in normal tissues. MCSP expression has also been detected in uveal melanoma tumor-tissue sections and could serve as a target antigen for immunotherapeutic approaches. Here we report that primary and metastatic uveal melanoma cell lines express MCSP and that CD4+ and CD8+ T cells are activated to lyse MCSP-expressing uveal melanoma cells by a novel BiTE antibody, which is bispecific for MCSP and CD3 (MCSP-BiTE). The surface of uveal melanoma cells was stained by anti-MCSP monoclonal antibodies when analyzed by flow cytometry. Seven out of 9 primary and 1 out of 3 metastatic uveal melanoma cell lines expressed MCSP at various expression levels. For functional analysis, CD4+ and CD8+ T cells were isolated from peripheral blood mononuclear cells (PBMC) of healthy donors using magnetic bead sorting. Both PBMC and unstimulated CD8+ T cells specifically lysed MCSP+ uveal melanoma cells in the presence of MCSP-BiTE as determined by 51Cr-release assays. As detected by ELISA, unstimulated CD4+ T cells produced IFNγ in response to MCSP-expressing uveal melanoma cells in the presence of MCSP-BiTE, and redirected lysis was evident by microscopy. In contrast, co-culture of T cells with MCSP-expressing uveal melanoma cells alone, or in the presence of a control BiTE, did not result in cytolytic activity or IFNγ release. Furthermore, naive CD4+ and CD8+ T cells upregulated expression of T cell activation markers CD25 and CD137 solely in response to MCSP-expressing uveal melanoma cells decorated with MCSP-BiTE. BiTE-induced T cell activation required the expression of MCSP, as co-culture of T cells with MCSP-negative uveal melanoma cells in combination with MCSP-BiTE did not result in T cell activation. In conclusion, MCSP-BiTE can induce CD4+ and CD8+ T cells against MCSP-expressing uveal melanoma cells and should therefore be tested as a novel immunotherapy for uveal melanoma patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5621.

Visualizing Single-Cell Secretion Dynamics with Single-Protein Sensitivity

Cellular secretion of proteins into the extracellular environment is an essential mediator of critical biological mechanisms, including cell-to-cell communication, immunological response, targeted delivery, and differentiation. Here, we report a novel methodology that allows for the real-time detection and imaging of single unlabeled proteins that are secreted from individual living cells. This is accomplished via interferometric detection of scattered light (iSCAT) and is demonstrated with Laz388 cells, an Epstein-Barr virus (EBV)-transformed B cell line. We find that single Laz388 cells actively secrete IgG antibodies at a rate of the order of 100 molecules per second. Intriguingly, we also find that other proteins and particles spanning ca. 100 kDa-1 MDa are secreted from the Laz388 cells in tandem with IgG antibody release, likely arising from EBV-related viral proteins. The technique is general and, as we show, can also be applied to studying the lysate of a single cell. Our results establish label-free iSCAT imaging as a powerful tool for studying the real-time exchange between cells and their immediate environment with single-protein sensitivity.

Advances in cellular therapy: 6th international symposium on the clinical use of cellular products, March 24 and 25, 2011, Erlangen, Germany

‘‘Cellular Therapy 2011’’: The 6th International Symposium on the Clinical Use of Cellular Products was held in Erlangen, Germany, on March 24–25, 2011. Twelve years ago, the conference took place for the first time in Regensburg and was originally initiated by Andreas Mackensen. Over the past years, it gained reputation and attracted leading researchers in the field from all over the world. This year’s conference was jointly organized at the University of Erlangen by the Department of Hematology & Oncology (Andreas Mackensen), the Department of Dermatology (Gerold Schuler), Erlangen, and the Department of Hematology & Oncology, Regensburg (Reinhard Andreesen). In principal, the ‘‘Cellular Therapy Meeting’’ aims at providing a multidisciplinary forum for basic and clinical researchers to communicate and to learn about the broad scope of cell therapy from different perspectives. The two-day meeting was attended by approximately 400 international participants and included sessions in the field of immune effector cells (T cells and NK cells), regulatory cells (Treg and MSC), antigen-presenting cells, cancer vaccination, gene-based cellular therapy, metabolism as well as regulatory issues and clinical applications of cellular therapy. These topics were presented by talks from 23 invited international experts. In addition, 20 short talks selected from abstracts of highest scientific quality and almost 130 posters were presented at the meeting. In this report, we summarize the most important research findings and highlight the main discussion topics of the plenary sessions.