Immune-regulatory properties carried by human amnion epithelial cells: Focus on the role of HLA-G and adenosinergic ectoenzymes

Human amnion epithelial cells (hAEC) can be efficiently isolated from full-term amnion membrane and have been gaining recognition as advanced medical products. Such cells originate directly from the embryo during the early phase of development and exert a crucial function in the establishment of a tolerogenic environment, to avoid maternal immune rejection. Amnion cell immuno-modulation may be exploited, but additional efforts are required to establish the mechanisms underlying such capacity. The way to fully clarify such an issue is so far long. Here we overview current knowledge on the effects on innate or adaptive immune cells offered by intact hAEC or secreted mediators, pinpointing the mechanisms to date elucidated by our group and others. We move from the description of hAEC general features to molecular intermediaries generating effects directly or indirectly on immune cells. We focus on the role of non-canonical HLA class I molecules, with emphasis on HLA-G, but expand such analysis on adenosinergic mediators, cytokines, and hAEC-derived microvesicles. Finally, we report the ongoing clinical trials exploiting hAEC multipotency and immune modulation.

Microvesicles released from multiple myeloma cells are equipped with ectoenzymes belonging to canonical and non-canonical adenosinergic pathways and produce adenosine from ATP and NAD. Oncoimmunology 2018;7:e1458809. [PMID: 30221054 DOI: 10.1080/2162402x.2018.1458809]

Multiple myeloma (MM) derives from malignant transformation of plasma cells (PC), which accumulate in the bone marrow (BM), where microenvironment supports tumor growth and inhibits anti-tumor immune responses. Adenosine (ADO), an immunosuppressive molecule, is produced within MM patients' BM by adenosinergic ectoenzymes, starting from ATP (CD39/CD73) or NAD⁺ [CD38/CD203a(PC-1)/CD73]. These ectoenzymes form a discontinuous network expressed by different BM cells. We investigated the expression and function of ectoenzymes on microvesicles (MVs) isolated from BM plasma samples of patients with MM, using asymptomatic forms of monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM (SMM) as controls. The percentage of MVs expressing ectoenzymes at high levels was higher when derived from MM patients than controls. BM CD138⁺ PC from MM patients expressed high levels of all ectoenzymes. Paired MVs samples confirmed a higher percentage of MVs with high ectoenzymes expression in MM patients than controls. Pooled MVs from MM patients or controls were tested for ADO production. The catabolism of ATP, NAD⁺, ADPR and AMP to ADO was higher in MVs from MM patients than in those from controls. In conclusion, our results confirmed the hypothesis that MVs in MM niche are main contributor of ADO production. The ability of MVs to reach biological fluids strongly support the view that MVs may assume diagnostic and pathogenetic roles.

Anti-GD2 monoclonal antibody immunotherapy: a promising strategy in the prevention of neuroblastoma relapse

In spite of the satisfactory frequency of clinical response to first-line therapy in neuroblastoma (NB), complete eradication of NB cells is rarely achieved. As a consequence, the majority of patients with advanced stage NB undergo relapse, which is often resistant to conventional treatment and rapidly overwhelming. Thus, after induction of the apparent remission, new therapeutic strategies are needed to completely eradicate the small number of surviving NB cells and to prevent relapse. We explored the potential of different doses of the anti-GD2 monoclonal antibody (mAb) 14G2a in an experimental metastatic model where a limited number of HTLA-230 human NB cells are injected i.v. into nude mice, leading to extensive metastases and death of animals within 7-8 weeks. Treatment with 14G2a mAb (1-4 mg/kg cumulative dose given as five i.v. daily administrations) dramatically reduced the metastatic spread of NB cells and prolonged the long-term survival of treated mice in a dose-dependent manner. Neither macrophages nor NK cells appeared to contribute to the protective effect of antibody treatment in vivo, suggesting either an involvement of granulocytes or a complement-mediated cytotoxicity towards NB cells. Whatever the effecting mechanism(s) involved, these results strongly support the clinical use of anti-GD2 mAbs after first-line induction regimens.

Immunoliposomal fenretinide: a novel antitumoral drug for human neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid tumor of childhood. In advanced disease stages, prognosis is poor and treatments have limited efficacy, thus novel strategies are warranted. The synthetic retinoid fenretinide (HPR) induces apoptosis in NB and melanoma cell lines. We reported an in vitro potentiation of HPR effects on melanoma cells when the drug is incorporated into GD2-targeted immunoliposomes (anti-GD2-SIL-HPR). Here, we investigated the antitumor activity of anti-GD2-SIL-HPR against NB cells, both in vitro and in vivo. Anti-GD2-immunoliposomes (anti-GD2-SIL) showed specific, competitive binding to, and uptake by, various NB cell lines. Moreover, anti-GD2-SIL-HPR presented increased selectivity and efficacy in inhibiting NB cell proliferation through the induction of apoptosis, compared to free drug and SL-HPR. In an in vivo NB metastatic model, we demonstrated that anti-GD2-SIL-HPR completely inhibited the development of macroscopic and microscopic metastases in comparison to controls. However, similar, but significantly less potent antitumor effect was observed also in mice treated with anti-GD2 immunoliposomes without HPR (anti-GD2-SIL-blank) or anti-GD2 mAb alone (P=0.0297 and P=0.0294, respectively, vs. anti-GD2-SIL-HPR). Moreover, our results clearly demonstrated that, although anti-GD2 mAb had a strong antitumor effect in this in vivo NB model, 100% curability was obtained only following treatment with anti-GD2-SIL-HPR (P<0.0001). Anti-GD2 liposomal HPR should receive clinical evaluation as adjuvant therapy of neuroblastoma.

Sodium butyrate modulates cell cycle-related proteins in HT29 human colonic adenocarcinoma cells

Sodium butyrate (NaB), a product of colonic fermentation of dietary fibre, has been shown to inhibit cell proliferation by blocking cells in the G0/G1 phase of the cell cycle through a mechanism of action still not completely understood. We investigated the effect of NaB on the level of some G1 phase-related proteins in a colon carcinoma cell line (HT29). In particular, we addressed our attention to cyclin D1 (the key regulator of G1S progression), p21waf1/cip1 (the main inactivator of the cyclin D/cdk complex), and p53 (the most important regulator of p21waf1/cip1 gene transcription). At inhibitory concentrations (higher than 1 mM) NaB reduced cyclin D1 and p53 level in a dose-dependent manner and sustained the synthesis of p21waf1/cip1, probably in a p53-independent way, accounting for the G0/G1 block observed by flow cytometry. Present results provide further evidence on the molecular mechanism at the basis of the physiological role of NaB and support the hypothesis that an unbalanced diet, poor in carbohydrates and therefore in NaB, could result in functional alterations with clinical and carcinogenic implications.

Inhibition of neuroblastoma-induced angiogenesis by fenretinide

Retinoids are a class of natural or synthetic compounds that participate in the control of cell proliferation, differentiation and fetal development. The synthetic retinoid fenretinide (HPR) inhibits carcinogenesis in various animal models. Retinoids have also been suggested to be effective inhibitors of angiogenesis. The effects of HPR on certain endothelial cell functions were investigated in vitro, and its effects on angiogenesis was studied in vivo, by using the chorioallantoic membrane (CAM) assay. HPR inhibited vascular endothelial growth factor- (VEGF-) and fibroblast growth factor-2- (FGF-2)-induced endothelial cell proliferation without affecting endothelial motility; moreover, HPR inhibited growth factor-induced angiogenesis in the CAM assay. Furthermore, a significant antiangiogenic potential of HPR has also been observed in neuroblastoma (NB) biopsy-induced angiogenesis in vivo. We previously demonstrated that supernatants derived from NB cell lines stimulated endothelial cell proliferation. In the present study, we found that this effect was abolished when NB cells were incubated in the presence of HPR. VEGF- and FGF-2-specific ELISA assays, performed on both NB cells derived from conditioned medium and cellular extracts, indicated no consistent effect of HPR on the level of these angiogenic cytokines. Moreover, RT-PCR analysis of VEGF and FGF-2 gene expression confirmed the above lack of effect. HPR was also able to significantly repress the spontaneous growth of endothelial cells, requiring at least 48-72 hr of treatment with HPR, followed by a progressive accumulation of cells in G(1) at subsequent time points. Finally, immunohistochemistry experiments performed in the CAM assay demonstrated that endothelial staining of both VEGF receptor 2 and FGF-2 receptor-2 was reduced after implantation of HPR-loaded sponges, as compared to control CAMs. These data suggest that HPR exerts its antiangiogenic activity through both a direct effect on endothelial cell proliferative activity and an inhibitory effect on the responsivity of the endothelial cells to the proliferative stimuli mediated by angiogenic growth factors.

Tissue transglutaminase is a caspase substrate during apoptosis. Cleavage causes loss of transamidating function and is a biochemical marker of caspase 3 activation

Tissue transglutaminase (tTG) is a Ca2+-dependent cross-linking enzyme that participates in the apoptotic machinery by irreversibly assembling a protein scaffold that prevents the leakage of intracellular components. In the present study a single-chain antibody fragment (scFv) detecting tTG is described. We demonstrate that TG/F8 scFv, selected from a phase display library of human V-gene segments by binding to guinea-pig liver tTG, can react with human tTG both in Western blot and in immunohistochemistry. The specific detection of tTG by TG/F8 in human thymocytes is verified by mass spectrometric analysis of the purified protein. Furthermore, we demonstrate that in lymphoid cells tTG is cleaved by caspase 3 during the late phase of apoptotic death, concomitant to DNA fragmentation, and that such cleavage causes loss of cross-linking function. We propose tTG cleavage as a valuable biochemical marker of caspase 3 activation during the late execution phase of apoptosis.

Biochemical characterization and membrane expression of an antigen shared by activated and neoplastic cells of neuroectodermal origin

The reactivity of a mAb (M16) raised against a small cell lung carcinoma line is described. M16 identifies a surface antigen expressed on cells of neuroectodermal origin following activation, as well as neoplastic transformation. M16 antigen expression is increased on retinoblastoma and neuroblastoma cell lines upon 'in vitro' stimulation and it is induced 'in vivo' on glial cells activated following brain injury. Furthermore, glial tumors show levels of M16 molecule expression increasing with the degree of malignancy, and in a retinoblastoma cell line, the expression of M16 was inversely related to the level of HLA-Class I and N-CAM antigens. The M16 antigen may represent a marker of both activation and neoplastic progression for neuroectodermal cells.