Synergistic cytotoxic effect of macrophages and normal mouse serum on neuraminidase-treated murine leukaemia cells

Tools to study and target the Siglec-sialic acid axis in cancer

Siglecs are widely expressed on leucocytes and bind to ubiquitously presented glycans containing sialic acids (sialoglycans). Most Siglecs carry an immunoreceptor tyrosine-based inhibition motif (ITIM) and elicit an inhibitory intracellular signal upon ligand binding. A few Siglec receptors can, however, recruit immunoreceptor tyrosine-based activation motif (ITAM)-containing factors, which activate cells. The role of hypersialylation (the enhanced expression of sialoglycans) has recently been explored in cancer progression. Mechanistic studies have shown that hypersialylation on cancer cells can engage inhibitory Siglecs on the surface of immune cells and induce immunosuppression. These recent studies strongly suggest that the Siglec-sialic acid axis can act as a potential target for cancer immunotherapy. Moreover, the use of new tools and techniques is facilitating these studies. In this review, we summarise techniques used to study Siglecs, including different mouse models, monoclonal antibodies, Siglec fusion proteins, and sialoglycan arrays. Furthermore, we discuss the recent major developments in the study of Siglecs in cancer immunosuppression, tools, and techniques used in targeting the Siglec-sialic acid axis and the possibility of clinical intervention.

The sialoglycan-Siglec glyco-immune checkpoint - a target for improving innate and adaptive anti-cancer immunity

Introduction: During cancer progression, tumor cells develop several mechanisms to prevent killing and to shape the immune system into a tumor-promoting environment. One of such regulatory mechanism is the overexpression of sialic acid (Sia) on carbohydrates of proteins and lipids on tumor cells. Sia-containing glycans or sialoglycans were shown to inhibit immune effector functions of NK cells and T cells by engaging inhibitory Siglec receptors on the surface of these cells. They can also modulate the differentiation of myeloid cells into tumor-promoting M2 macrophages. Areas covered: We review the role of sialoglycans in cancer and introduce the Siglecs, their expression on different immune cells and their interaction with cancer-associated sialoglycans. The targeting of this sialoglycan-Siglec glyco-immune checkpoint is discussed along with potential therapeutic approaches. Pubmed was searched for publications on Siglecs, sialic acid, and cancer. Expert opinion: The targeting of sialoglycan-Siglec interactions has become a major focus in cancer research. New approaches have been developed that directly target sialic acids in tumor lesions. Targeted sialidases that cleave sialic acid specifically in the tumor, have already shown efficacy; efforts targeting the sialoglycan-Siglec pathway for improvement of CAR T cell therapy are ongoing. The sialoglycan-Siglec immune checkpoint is a promising new target for cancer immunotherapy.

Therapeutic effectiveness of neuraminidase-treated allogeneic myeloblasts as immunogen in acute myelocytic leukemia

Our chemoimmunotherapy study shows significantly longer remission and survival in acute myelocytic leukemia (AML) patients who have been immunized with neuraminidase-treated allogeneic myeloblasts as compared to patients who received chemotherapy alone or neuraminidase-treated myeloblasts plus MER. MER impairs the immunotherapeutic effectiveness of neuraminidase-treated allogeneic myeloblasts in AML patients. The in vivo and in vitro immunologic status in each arm of the protocol correlate well with the duration of remission and survival of the patient.

Specific immunotherapy with neuraminidase-modified leukemic cells: experimental and clinical trials

The data presented establish the therapeutic effectiveness of immunotherapy with neuraminidase-treated allogeneic myeloblasts in combination with sustaining chemotherapy in patients with acute myelocytic leukemia. The in vivo and in vitro immunologic tests indicate normal immunocompetence in patients receiving immunotherapy versus control patients treated with chemotherapy alone. These findings correlate well with the improved duration of remission as the direct result of the immunotherapy.

Neuraminidase and tumor immunotherapy

Preliminary results of first clinical studies with the enzyme neuraminidase call attention to a new kind of cancer treatment. This promising approach to tumor immunotherapy was entered into the clinical phase as a consequence of successful experimental studies in tumor-bearing mice, rats and dogs. In this review, the presently known and essential results of experimental and clinical studies on tumor immunotherapy by means of neuraminidase are presented as well as some necessary and critical considerations in this context. Moreover, out of a broad variety of results of biochemical and biological in vitro studies, it was attempted to select the more essential knowledge which could contribute to a better understanding of the still rather unclear in vivo mode of action of the enzyme neuraminidase. In a first brief paragraph (1.0), the biochemically characteristic data of the enzyme neuraminidase is presented. In the second section (2.0), the basic knowledge about the effects of neuraminidase on cell behavior is rather amply contained. Here, on the one hand, the biophysical and biochemical alterations are mentioned, the so-called ""unmasking'' effects are reconsidered and, on the other hand, the effects on the immunologically responding cell are discussed. In a third section (3.0), the diverse findings from animal experiments using neuraminidase-treated tumor cells are confronted, whereby tumor transplantation experiments and tumor therapy experiments are dealt with separately. The last section (4.0) reports about the first clinical studies with neuraminidase-treated autologous as well as homologous tumor cells, which partly brought about rather surprising and astonishing success. On the basis of recent findings by the study group of the authors, the more prior and sometimes discrepant results of various groups are critically considered. The problems of alteration of antigenicity and of other properties of cells through splitting off membrane-bound neuraminic acid, the facts of adjuvanticity of neuraminidase itself, the relation of successful therapy to dose dependency as well as the relation of undesirable methods for tumor mass reduction to the immunological responsiveness of the tumor bearer were especially looked into.

The effects of cell density, incubation temperature, syngeneic serum, and syngeneic red blood cells on mouse lymphocyte responses in vitro

Various parameters affecting the quantitative assessment of mouse mixed lymphocyte response (MLR) in microplates were investigated. In agreement with the findings of others cell density was found to be particularly critical, maximal proliferative efficiency occurring at 3 X 10(6) viable cells/cm2. Slight reduction in the degree of viable cell--cell interaction caused by either reduction in cell density or insertion of irradiated cells into the cultures greatly reduced the efficiency of the proliferation. An incubation temperature of 33-34 degrees C was found to have distinct advantages over 37 degrees C, there being improved cell survival and reproducibility at this lower temperature. Transformation of mouse lymphocytes was strongly inhibited by low concentrations of normal syngeneic serum, the degree of inhibition depending on the concentration of foetal calf serum (FCS) in culture and on the method of preparation of serum. Inhibition of mouse cell responses was also caused by syngeneic red blood cells (RBC), in contrast to the pronounced enhancement of guinea pig lymphocyte responses to phytohaemagglutinin (PHA) in the presence of syngeneic RBC.