Multiple Myeloma (MM) is a hematological cancer characterized by proliferation of malignant plasma cells in the bone marrow (BM). MM represents the second most frequent hematological malignancy, ...accounting 1% of all cancer and 13% of hematological tumors, with ~9,000 new cases per year. Patients with monoclonal gammopathy of undetermined significance (MGUS) and asymptomatic smoldering MM (SMM) usually evolve to active MM in the presence of increased tumor burden, symptoms and organ damage. Despite the role of high dose chemotherapy in combination with autologous stem cell transplantation and the introduction of new treatments, the prognosis of MM patients is still poor, and novel therapeutic approaches have been tested in the last years, including new immunomodulatory drugs, proteasome inhibitors and monoclonal antibodies (mAbs). CD38 is a glycoprotein with ectoenzymatic functions, which is expressed on plasma cells and other lymphoid and myeloid cell populations. Since its expression is very high and uniform on myeloma cells, CD38 is a good target for novel therapeutic strategies. Among them, immunotherapy represents a promising approach. Here, we summarized recent findings regarding CD38-targeted immunotherapy of MM in pre-clinical models and clinical trials, including (i) mAbs (daratumumab and isatuximab), (ii) radioimmunotherapy, and (iii) adoptive cell therapy, using chimeric antigen receptor (CAR)-transfected T cells specific for CD38. Finally, we discussed the efficacy and possible limitations of these therapeutic approaches for MM patients.
Laboratory of Immunogenetics, Department of Genetics, Biology, and Biochemistry and Centro di Ricerca in Medicina Sperimentale, University of Torino Medical School, Torino, Italy
The membrane ...proteins CD38 and CD157 belong to an evolutionarily conserved family of enzymes that play crucial roles in human physiology. Expressed in distinct patterns in most tissues, CD38 (and CD157) cleaves NAD + and NADP + , generating cyclic ADP ribose (cADPR), NAADP, and ADPR. These reaction products are essential for the regulation of intracellular Ca 2+ , the most ancient and universal cell signaling system. The entire family of enzymes controls complex processes, including egg fertilization, cell activation and proliferation, muscle contraction, hormone secretion, and immune responses. Over the course of evolution, the molecules have developed the ability to interact laterally and frontally with other surface proteins and have acquired receptor-like features. As detailed in this review, the loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications in mice. CD38 is a powerful disease marker for human leukemias and myelomas, is directly involved in the pathogenesis and outcome of human immunodeficiency virus infection and chronic lymphocytic leukemia, and controls insulin release and the development of diabetes. Here, the data concerning diseases are examined in view of potential clinical applications in diagnosis, prognosis, and therapy. The concluding remarks try to frame all of the currently available information within a unified working model that takes into account both the enzymatic and receptorial functions of the molecules.
Tumor microenvironments are rich in extracellular nucleotides that can be metabolized by ectoenzymes to produce adenosine, a nucleoside involved in controlling immune responses. Multiple myeloma, a ...plasma cell malignancy developed within a bone marrow niche, exploits adenosinergic pathways to customize the immune homeostasis of the tumor. CD38, a multifunctional protein that acts as both receptor and ectoenzyme, is overexpressed at all stages of myeloma. At neutral and acidic pH, CD38 catalyzes the extracellular conversion of NAD
to regulators of calcium signaling. The initial disassembly of NAD
is also followed by adenosinergic activity, if CD38 is operating in the presence of CD203a and CD73 nucleotidases. cAMP extruded from tumor cells provides another substrate for metabolizing nucleotidases to signaling adenosine. These pathways flank or bypass the canonical adenosinergic pathway subjected to the conversion of ATP by CD39. All of the adenosinergic networks can be hijacked by the tumor, thus controlling the homeostatic reprogramming of the myeloma in the bone marrow. In this context, adenosine assumes the role of a local hormone: cell metabolism is adjusted via low- or high-affinity purinergic receptors expressed by immune and bone cells as well as by tumor cells. The result is immunosuppression, which contributes to the failure of immune surveillance in cancer. A similar metabolic strategy silences immune effectors during the progression of indolent gammopathies to symptomatic overt multiple myeloma disease. Plasma from myeloma aspirates contains elevated levels of adenosine resulting from interactions between myeloma and other cells lining the niche and adenosine concentrations are known to increase as the disease progresses. This is statistically reflected in the International Staging System for multiple myeloma. Along with the ability to deplete CD38
malignant plasma cell populations which has led to their widespread therapeutic use, anti-CD38 antibodies are involved in the polarization and release of microvesicles characterized by the expression of multiple adenosine-producing molecules. These adenosinergic pathways provide new immune checkpoints for improving immunotherapy protocols by helping to restore the depressed immune response.
Human myeloma cells express CD38 at high levels and grow in hypoxic niches inside the bone marrow. Myeloma cells respond to hypoxia with metabolic changes leading to aerobic glycolysis, thus reducing ...ATP and increasing NAD
. Our hypothesis is that these conditions favor the enzymatic pathways involved in the production of adenosine in the niche. Within the niche, NAD
is able to activate a discontinuous adenosinergic pathway that relies upon CD38, CD203a, and CD73 or TRACP, according to the environmental pH. The observed variability in adenosine concentrations in bone marrow aspirates is a result of the interactions taking place among myeloma and other cells in the bone marrow niche. A pilot study showed that adenosine profiles differ during disease progression. Adenosine levels were significantly higher in the bone marrow plasma of patients with symptomatic myeloma and correlated with ISS staging, suggesting that adenosine is produced in the myeloma niche at micromolar levels by an ectoenzymatic network centered on CD38. Adenosine levels increase with disease aggressiveness, a finding that supports adenosine as a potential marker of myeloma progression.
The tumor microenvironment is characterized by of high levels of extracellular nucleotides that are metabolized through the dynamic and sequential action of cell surface enzymes (ectoenzymes). These ...ectoenzymes operate according to their spatial arrangement, as part of (1) continuous (molecules on the same cell) or (2) discontinuous (molecules on different cells) pathways, the latter being facilitated by restricted cellular microenvironment. The outcome of this catabolic activity is an increase in the local concentration of adenosine, a nucleoside involved in the control of inflammation and immune responses. The aim of the work presented here was to demonstrate that a previously unexplored enzymatic pathway may be an alternate route to produce extracellular adenosine. Our data show that this new axis is driven by the nucleotide-metabolizing ectoenzymes CD38 (an NAD
+
nucleosidase), the ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1, also known as CD203a or PC-1) and the 5′ ectonucleotidase (5′-NT) CD73, while bypassing the canonical catabolic pathway mediated by the nucleoside tri- and diphosphohydrolase (NTPDase) CD39. To determine the relative contributions of these cell surface enzymes to the production of adenosine, we exploited a human T-cell model allowing for the modular expression of the individual components of this alternative pathway upon activation and transfection. The biochemical analysis of the products of these ectoenzymes by high-performance liquid chromatography (HPLC) fully substantiated our working hypothesis. This newly characterized pathway may facilitate the emergence of an adaptive immune response in selected cellular contexts. Considering the role for extracellular adenosine in the regulation of inflammation and immunogenicity, this pathway could constitute a novel strategy of tumor evasion, implying that these enzymes may represent ideal targets for antibody-mediated therapy.
This medical review addresses the hypothesis that CD38/NADase is at the center of a functional axis (i.e., intracellular Ca
mobilization/IFNγ response/reactive oxygen species burst) driven by severe ...acute respiratory syndrome coronavirus 2 infection, as already verified in respiratory syncytial virus pathology and CD38 activity in other cellular settings. Key features of the hypothesis are that
) the substrates of CD38 (e.g., NAD
and NADP
) are depleted by viral-induced metabolic changes;
) the products of the enzymatic activity of CD38 e.g., cyclic adenosine diphosphate-ribose (ADPR)/ADPR/nicotinic acid adenine dinucleotide phosphate and related enzymes e.g., poly(ADP-ribose)polymerase, Sirtuins, and ADP-ribosyl hydrolase are involved in the anti-viral and proinflammatory response that favors the onset of lung immunopathology (e.g., cytokine storm and organ fibrosis); and
) the pathological changes induced by this kinetic mechanism may be reduced by distinct modulators of the CD38/NAD
axis (e.g., CD38 blockers, NAD
suppliers, among others). This view is supported by arrays of associative basic and applied research data that are herein discussed and integrated with conclusions reported by others in the field of inflammatory, immune, tumor, and viral diseases.
Metastatic diffusion of Neuroblastoma (NB) cells in the bone marrow (BM) represents the most negative prognostic factors for NB patients. Multiple immune escape mechanisms are postulated as ...responsible. Our working hypothesis is that adenosine (ADO), an immunosuppressive molecule along with the ectoenzymatic pathways (CD39-CD73 and CD38-CD203a/PC-1-CD73) controlling its production, are involved in the dynamics of NB cells in the BM. The results indicate that ectonucleotidases are expressed by i) NB cell lines, ii) metastatic NB cells isolated from NB patients' BM, iii) microvesicles (MV) derived from both NB cell types and iv) resident BM cell populations. BM infiltration by NB cells increased CD203a/PC-1 and CD73 expression on lymphoid and myeloid cells, respectively. Expressions of ectoenzymes and GD2 (NB-associated marker) were higher on MV from NB patients' BM than in controls. Moreover, CD203a/PC-1 expression on BM-derived MV provide a basis for distinguishing NB patients with high or low BM infiltration. ADO production and consumption of related by-products were significantly higher when assessed on NB patients' MV than those from controls. MV isolated from NB patients' BM significantly downregulated in vitro T cell proliferation. Lastly, NB patients with worse prognosis are identified by a high percentage of CD38
+
or CD73
+
MV in the BM. In conclusion, ectonucleotidases are present and functional on NB cells, as well as in NB-infiltrated BM and in MV derived from BM. It is reasonable that MV are involved in BM infiltration by NB cells. Therefore, targeting these molecules may widen the therapeutic armamentarium for metastatic NB patients.
Ectoenzymes are cell surface molecules, which represent functional bridges between the environment and the cytoplasm. One set of ectoenzymes-CD39, CD38, CD203a, and CD73-leads to the generation of ...adenosine (ADO) by metabolizing ATP and NAD
. While ADO is known to control inflammation and suppress immune responses, other aspects of ADO function are still obscure, mainly due to its short half-life in biological fluids. Human multiple myeloma (MM) grows in the closed system of the bone marrow (BM) niche representing an ideal setting for studying ectoenzymes and their products. Another source of information on ectoenzyme function may derive from
results of anti-CD38 antibody therapy in MM. Current results, obtained from
models and from preliminary
findings, indicate that ectoenzymes produce ADO locally in the BM niche. Furthermore, MM cells release microvesicles (MV), which thanks to their molecular cargo and surface ectoenzymes may function as particulate communicators outside of the niche. During anti-CD38 antibody therapy, the MV carry therapeutic IgG, determining that the prevalent orientation of MV will be toward cells and tissues expressing receptors for the IgG Fc domain. The resulting picture is one where MM adopts an immune escape strategy based on reshaping the environmental niche. This adaptation is followed by actions of MV that are exerted in biological fluids and circulating immune cells. By coating FcRs
cells, MV modify pericellular spaces, reproducing the metabolic halo generated by ectoenzymes within closed systems.
Monoclonal antibodies (mAbs) were initially considered as a possible "magic bullet" for in vivo elimination of tumor cells. mAbs represented the first step: however, as they were murine in nature ...(the earliest experience on the field), they were considered unfit for human applications. This prompted the development of techniques for cloning the variable regions of conventional murine antibodies, genetically mounted on human IgG. The last step in this years-long process was the design for the preparation of fully human reagents. The choice of the target molecule was also problematic, since cancer-specific targets are quite limited in number. To overcome this obstacle in the planning phases of antibody-mediated therapy, attention was focused on a set of normal molecules, whose quantitative distribution may balance a tissue-dependent generalized expression. The results and clinical success obtained with anti-CD20 mAbs revived interest in this type of strategy. Using multiple myeloma (MM) as a tumor model was challenging first of all because the plasma cells and their neoplastic counterpart eluded the efforts of the Workshop on Differentiation Antigens to find a target molecule exclusively expressed by these cells. For this reason, attention was turned to surface molecules which fulfill the requisites of being reasonably good targets, even if not specifically restricted to tumor cells. In 2009, we proposed CD38 as a MM target in virtue of its expression: it is absent on early hematological progenitors, has variable but generalized limited expression by normal cells, but is extremely high in plasma cells and in myeloma. Further, regulation of its expression appeared to be dependent on a variety of factors, including exposure to all-trans retinoic acid (ATRA), a potent and highly specific inducer of CD38 expression in human promyelocytic leukemia cells that are now approved for in vivo use. This review discusses the history of human CD38, from its initial characterization to its targeting in antibody-mediated therapy of human myeloma.
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