CAR-NK Cells: A Chimeric Hope or a Promising Therapy?

Immunotherapy with chimeric antigen receptor-engineered T cells (CAR-T) has revolutionized the treatment landscape of relapsed/refractory B-cell malignancies. Nonetheless, the use of autologous T cells has certain limitations, including the variable quality and quantity of collected effector T cells, extended time of cell processing, limited number of available CAR cells, toxicities, and a high cost. Thanks to their powerful cytotoxic capabilities, with proven antitumor effects in both haploidentical hematopoietic stem cell transplantation and adoptive cell therapy against solid tumors and hematological malignancies, Natural Killer cells could be a promising alternative. Different sources of NK cells can be used, including cellular lines, cord blood, peripheral blood, and induced pluripotent stem cells. Their biggest advantage is the possibility of using them in an allogeneic context without major toxic side effects. However, the majority of the reports on CAR-NK cells concern preclinical or early clinical trials. Indeed, NK cells might be more difficult to engineer, and the optimization and standardization of expansion and transfection protocols need to be defined. Furthermore, their short persistence after infusion is also a major setback. However, with recent advances in manufacturing engineered CAR-NK cells exploiting their cytolytic capacities, antibody-dependent cellular cytotoxicity (ADCC), and cytokine production, "off-the-shelf" allogeneic CAR-NK cells can provide a great potential in cancer treatments.

FLAMSA-Busulfan-Melphalan as a Sequential Conditioning Regimen in HLA-Matched or Haploidentical Hematopoietic Stem Cell Transplantation for High-Risk Myeloid Diseases.

Given the poor prognosis of relapsed/refractory myeloid malignancies, the concept of sequential conditioning before allogeneic hematopoietic stem cell transplantation (allo-HSCT) has proven to be an effective approach. We sought to evaluate a sequential scheme combining fludarabine, amsacrine, and cytarabine (FLAMSA) for cytoreduction, followed by reduced-intensity conditioning with busulfan and melphalan (FLAMSA-BuMel), which was designed to be suitable for both HLA-matched and haploidentical HSCT. This single-center retrospective study included 36 adult patients with high-risk myeloid malignancies who underwent allo-HSCT from HLA-matched (n = 19) or haploidentical (n = 17) donors. Along with the standard prophylaxis for graft-versus-host disease (GVHD), patients with a haploidentical donor received post-transplantation high-dose cyclophosphamide. A post-transplantation consolidation treatment with low-dose 5-azacytidine and prophylactic donor lymphocyte infusions was provided whenever possible. Thirty patients (83%) achieved complete remission on day +30. With a median follow-up of 30.0 months, the 2-year overall survival was 89% in the HLA-matched group versus 34% in the haploidentical group (P = .0018). The 2-year disease-free survival in these 2 groups was 68% and 34%, respectively (P = .013). At 2 years, the probability of relapse was 32% and 20%, respectively, and nonrelapse mortality was 0% and 58%, respectively (P = .0003). The leading cause of death was relapse in the HLA-matched group (3 of 19) and hemorrhagic events (5 of 17) in the haploidentical group, favored by significantly delayed platelet reconstitution and a severe GVHD context. These data confirm the feasibility of FLAMSA-BuMel as a sequential conditioning in allo-HSCT for high-risk myeloid malignancies. The use of bone marrow as the preferred graft source might reduce the incidence of acute GVHD and nonrelapse mortality in the haploidentical transplantation setting.

Combination of IL-2, rapamycin, DNA methyltransferase and histone deacetylase inhibitors for the expansion of human regulatory T cells.

FOXP3+ regulatory T cell (Treg) based cellular therapies represent promising therapeutic options in autoimmunity, allergy, transplantation and prevention of Graft Versus Host (GVH) Disease. Among human FOXP3-expressing CD4+T cells, only the CD45RA+ naïve Treg (nTreg) subset is suitable for in vitro expansion. However, FoxP3 expression decays in cells using currently described culture protocols. Rapamycin alone was not able to prevent FOXP3 loss in nTregs cells, as only a half of them maintained FOXP3 expression after 14 days of culture. In contrast we report a novel combined drug regimen that can drastically stabilize FOXP3 expression in cultured Tregs. IL-2, rapamycin, histone deacetylase and DNA methyltransferase inhibitors act in synergy to allow expansion of human regulatory T cells with sustained high expression of FOXP3 and CD15s with potent suppressive capacities in vitro and control of murine xeno-GVH reactions. Of note, an additional subsequent infusion of expanded nTreg cells did not improve survival of mice. Combination of IL-2, rapamycin, histone deacetylase and DNA methyltransferase inhibitors is optimal for the expansion in vitro of pure effective nTreg maintaining high levels of FOXP3 for therapeutic purposes.

Calcium-phosphate ceramics and polysaccharide-based hydrogel scaffolds combined with mesenchymal stem cell differently support bone repair in rats.

Research in bone tissue engineering is focused on the development of alternatives to autologous bone grafts for bone reconstruction. Although multiple stem cell-based products and biomaterials are currently being investigated, comparative studies are rarely achieved to evaluate the most appropriate approach in this context. Here, we aimed to compare different clinically relevant bone tissue engineering methods and evaluated the kinetic repair and the bone healing efficiency supported by mesenchymal stem cells and two different biomaterials, a new hydrogel scaffold and a commercial hydroxyapatite/tricalcium phosphate ceramic, alone or in combination.Syngeneic mesenchymal stem cells (5 × 105) and macroporous biphasic calcium phosphate ceramic granules (Calciresorb C35®, Ceraver) or porous pullulan/dextran-based hydrogel scaffold were implanted alone or combined in a drilled-hole bone defect in rats. Using quantitative microtomography measurements and qualitative histological examinations, their osteogenic properties were evaluated 7, 30, and 90 days after implantation. Three months after surgery, only minimal repair was evidenced in control rats while newly mineralized bone was massively observed in animals treated with either hydrogels (bone volume/tissue volume = 20%) or ceramics (bone volume/tissue volume = 26%). Repair mechanism and resorption kinetics were strikingly different: rapidly-resorbed hydrogels induced a dense bone mineralization from the edges of the defect while ceramics triggered newly woven bone formation in close contact with the ceramic surface that remained unresorbed. Delivery of mesenchymal stem cells in combination with these biomaterials enhanced both bone healing (>20%) and neovascularization after 1 month, mainly in hydrogel.Osteogenic and angiogenic properties combined with rapid resorption make hydrogels a promising alternative to ceramics for bone repair by cell therapy.

Fucoidan promotes early step of cardiac differentiation from human embryonic stem cells and long-term maintenance of beating areas.

Somatic stem cells require specific niches and three-dimensional scaffolds provide ways to mimic this microenvironment. Here, we studied a scaffold based on Fucoidan, a sulfated polysaccharide known to influence morphogen gradients during embryonic development, to support human embryonic stem cells (hESCs) differentiation toward the cardiac lineage. A macroporous (pore 200 µm) Fucoidan scaffold was selected to support hESCs attachment and proliferation. Using a protocol based on the cardiogenic morphogen bone morphogenic protein 2 (BMP2) and transforming growth factor (TGFß) followed by tumor necrosis factor (TNFα), an effector of cardiopoietic priming, we examined the cardiac differentiation in the scaffold compared to culture dishes and embryoid bodies (EBs). At day 8, Fucoidan scaffolds supported a significantly higher expression of the 3 genes encoding for transcription factors marking the early step of embryonic cardiac differentiation NKX2.5 (p<0.05), MEF2C (p<0.01), and GATA4 (p<0.01), confirmed by flow cytometry analysis for MEF2C and NKX2.5. The ability of Fucoidan scaffolds to locally concentrate and slowly release TGFß and TNFα was confirmed by Luminex technology. We also found that Fucoidan scaffolds supported the late stage of embryonic cardiac differentiation marked by a significantly higher atrial natriuretic factor (ANF) expression (p<0.001), although only rare beating areas were observed. We postulated that absence of mechanical stress in the soft hydrogel impaired sarcomere formation, as confirmed by molecular analysis of the cardiac muscle myosin MYH6 and immunohistological staining of sarcomeric α-actinin. Nevertheless, Fucoidan scaffolds contributed to the development of thin filaments connecting beating areas through promotion of smooth muscle cells, thus enabling maintenance of beating areas for up to 6 months. In conclusion, Fucoidan scaffolds appear as a very promising biomaterial to control cardiac differentiation from hESCs that could be further combined with mechanical stress to promote sarcomere formation at terminal stages of differentiation.

Heterozygous and homozygous JAK2(V617F) states modeled by induced pluripotent stem cells from myeloproliferative neoplasm patients.

JAK2(V617F) is the predominant mutation in myeloproliferative neoplasms (MPN). Modeling MPN in a human context might be helpful for the screening of molecules targeting JAK2 and its intracellular signaling. We describe here the derivation of induced pluripotent stem (iPS) cell lines from 2 polycythemia vera patients carrying a heterozygous and a homozygous mutated JAK2(V617F), respectively. In the patient with homozygous JAK2(V617F), additional ASXL1 mutation and chromosome 20 allowed partial delineation of the clonal architecture and assignation of the cellular origin of the derived iPS cell lines. The marked difference in the response to erythropoietin (EPO) between homozygous and heterozygous cell lines correlated with the constitutive activation level of signaling pathways. Strikingly, heterozygous iPS cells showed thrombopoietin (TPO)-independent formation of megakaryocytic colonies, but not EPO-independent erythroid colony formation. JAK2, PI3K and HSP90 inhibitors were able to block spontaneous and EPO-induced growth of erythroid colonies from GPA(+)CD41(+) cells derived from iPS cells. Altogether, this study brings the proof of concept that iPS can be used for studying MPN pathogenesis, clonal architecture, and drug efficacy.

Mesenchymal stem cell delivery into rat infarcted myocardium using a porous polysaccharide-based scaffold: a quantitative comparison with endocardial injection.

The use of mesenchymal stem cells (MSCs) for tissue regeneration is often hampered by modest engraftment in host tissue. This study was designed to quantitatively compare MSCs engraftment rates after delivery using a polysaccharide-based porous scaffold or endocardial (EC) injection in a rat myocardial infarction model. Cellular engraftment was measured by quantitative reverse transcription-polymerase chain reaction using MSCs previously transduced with a lentiviral vector that expresses green fluorescent protein (GFP). The use of a scaffold promoted local cellular engraftment and survival. The number of residual GFP(+) cells was greater with the scaffold than after EC injection (9.7% vs. 5.1% at 1 month and 16.3% vs. 6.1% at 2 months, respectively [n=5]). This concurred with a significant increase in mRNA vascular endothelial growth factor level in the scaffold group (p<0.05). Clusters of GFP+ cells were detected in the peri-infarct area, mainly phenotypically consistent with immature MSCs. Functional assessment by echocardiography at 2 months postinfarct also showed a trend toward a lower left ventricular dilatation and a reduced fibrosis in the scaffold group in comparison to direct injection group (n=10). These findings demonstrate that using a porous biodegradable scaffold is a promising method to improve cell delivery and engraftment into damaged myocardium.

Infusion of allogeneic natural killer cells in a patient with acute myeloid leukemia in relapse after haploidentical hematopoietic stem cell transplantation.

BACKGROUND: Allogeneic donor natural killer (NK)-cell infusion (NK-DLI) is a promising immunotherapy for patients with hematologic disorders. CASE REPORT: This report describes the case of a patient who received a single haploidentical NK-DLI for a relapse of acute myeloid leukemia (AML) after haploidentical hematopoietic stem cell transplantation. He underwent a cytoreductive, immunosuppressive regimen before NK-DLI and received high-dose interleukin-2 in vivo for 8 weeks afterward. RESULTS: No major adverse effect was observed. Prospective phenotypic and functional studies of the NK cells showed major expansion of infused NK cells and, more importantly, of the alloreactive KIR2DL1+KIR2DL2/DL3-NKG2A- subset, which reached 117×10(6) cells/L on Day +14 after NK-DLI, the greatest expansion of infused alloreactive NK cells reported so far. Infused NK cells conserved their lytic capacities against K562 target cells and primary AML-mismatched blasts. CONCLUSION: We review the literature to clarify these data and to detail the indications for allogeneic NK-DLI, the criteria for determining the most suitable donor, the types of conditioning regimens, and the procedures for selecting and activating NK cells.

Monocytic cells derived from human embryonic stem cells and fetal liver share common differentiation pathways and homeostatic functions.

The early emergence of macrophages and their large pattern of tissue distribution during development suggest that they may play a critical role in the initial steps of embryogenesis. In the present study, we show that monocytic cells derived from human embryonic stem cells (hESCs) and from fetal liver follow a differentiation pathway different to that of adult cells, leading to specific functions. Embryonic and fetal monocytic cells differentiated from a CD14(low)CD16(-) precursor to form CD14(high)CD16(+) cells without producing the CD14(high)CD16(-) cell population that predominates in adult peripheral blood. Both demonstrated an enhanced expression of genes encoding tissue-degrading enzymes, chemokines, and scavenger receptors, as was previously reported for M2 macrophages. Compared with adult blood monocytes, embryonic and fetal monocytic cells secreted high amounts of proteins acting on tissue remodeling and angiogenesis, and most of them expressed the Tie2 receptor. Furthermore, they promoted vascular remodeling in xenotransplanted human tumors. These findings suggest that the regulation of human fetal and embryonic monocytic cell differentiation leads to the generation of cells endowed mainly with anti-inflammatory and remodeling functions. Trophic and immunosuppressive functions of M2-polarized macrophages link fetus and tumor development, and hESCs offer a valuable experimental model for in vitro studies of mechanisms sustaining these processes.

Regulatory T cell content in the bone marrow graft does not predict the occurrence of acute GVHD.

The subpopulation of regulatory T cells (Treg) was shown to play a key role in alloreactive responses. In allogeneic hematopoietic stem cell transplantation, several groups tested whether Treg content in transplants correlates with graft-versus-host disease (GVHD) with controversial results. In a retrospective study of 49 consecutive HLA-matched sibling transplantations, we studied the relationship between Treg content in bone marrow transplants and acute GVHD (aGVHD) occurrence. We observed a large variability in Treg in bone marrow grafts. However, contrary to previous observations in peripheral blood stem cells transplantation, we report that the Treg content of allogeneic bone marrow transplantation did not predict the occurrence of aGVHD.

Delayed recovery after autologous peripheral hematopoietic cell transplantation: potential effect of a high number of total nucleated cells in the graft.

BACKGROUND: Some patients demonstrate delayed recoveries after autologous hematopoietic stem cell transplantation despite infusion of an adequate number of CD34+ cells/kg and clinically stable status. Factors considered being possible predictors of this outcome in this context were explored. STUDY DESIGN AND METHODS: A total of 246 patients were evaluated in terms of engraftment. Delayed recovery was defined by white blood cell recovery time exceeding mean+1 SEM. Clinical factors and graft characteristics were examined. Comparisons between patients with normal or delayed engraftment were made. Proinflammatory cytokines and proteolytic enzyme quantification and CXCR4+ and CD44+ cell enumeration were performed on peripheral hematopoietic stem cells (PHSC) product samples of patients with delayed engraftment and patients with usual engraftment time. RESULTS: Sixteen patients, who received at least 3 × 10(6) CD34+ cells/kg without known clinical factors likely to affect engraftment, demonstrated a delayed recovery time of over 20 days. Some graft variables were found to be significantly increased in these patients by univariate analysis. One variable was the total number of nucleated cells cryopreserved and infused. Among the nucleated cells, the absolute number of granulocytes before and after cryopreservation also differed significantly between the two groups. A multivariate analysis showed that the main predictive factor for delayed recovery was the number of nucleated cells in the graft (p=0.0044). The influence of contaminating cells might be related to the release of elastase, matrix metalloproteinase-9, interleukin (IL)-1ß, and IL-6 involved in stem cell homing. CONCLUSION: Therefore, the numeration of total nucleated cells and granulocytes should be considered as a possible quality control variable of PHSCs submitted for cryopreservation.

A common bipotent progenitor generates the erythroid and megakaryocyte lineages in embryonic stem cell-derived primitive hematopoiesis.

The megakaryocytic (MK) and erythroid lineages are tightly associated during differentiation and are generated from a bipotent megakaryocyte-erythroid progenitor (MEP). In the mouse, a primitive MEP has been demonstrated in the yolk sac. In human, it is not known whether the primitive MK and erythroid lineages are generated from a common progenitor or independently. Using hematopoietic differentiation of human embryonic stem cells on the OP9 cell line, we identified a primitive MEP in a subset of cells coexpressing glycophorin A (GPA) and CD41 from day 9 to day 12 of coculturing. This MEP differentiates into primitive erythroid (GPA(+)CD41(-)) and MK (GPA(-)CD41(+)) lineages. In contrast to erythropoietin (EPO)-dependent definitive hematopoiesis, KIT was not detected during erythroid differentiation. A molecular signature for the commitment and differentiation toward both the erythroid and MK lineages was detected by assessing expression of transcription factors, thrombopoietin receptor (MPL) and erythropoietin receptor (EPOR). We showed an inverse correlation between FLI1 and both KLF1 and EPOR during primitive erythroid and MK differentiation, similar to definitive hematopoiesis. This novel MEP differentiation system may allow an in-depth exploration of the molecular bases of erythroid and MK commitment and differentiation.

GFP-transduced CD34+ and Lin- CD34- hematopoietic stem cells did not adopt a cardiac phenotype in a nonhuman primate model of myocardial infarct.

OBJECTIVE: Studies in mice have reported contradictory results on the contribution of bone marrow cells to myocardial regeneration. This study aims to evaluate their ability to differentiate into cells of cardiac lineage in a nonhuman primate mode of myocardial infarct. MATERIALS AND METHODS: Lin(-)CD34(-) and CD34(+)-enriched bone marrow cells or mobilized peripheral blood cells were transduced with green fluorescent protein (GFP) and injected directly into ischemic myocardium. The fate of the transplanted cells was evaluated using quantitative reverse transcription polymerase chain reaction (QRT-PCR) and immunohistology. Animals were followed-up using echocardiography. RESULTS: QRT-PCR analysis detected from 3% to 10% of the original number of administered GFP(+) cells after 7 days. These GFP(+) cells did not express cardiac tissue-specific markers, but were immunophenotypically consistent with undifferentiated hematopoietic cells. The local production of vascular endothelial growth factor, measured by QRT-PCR, was approximately doubled as compared to the untreated infarcted control heart. Three months after hematopoietic stem cell (HSC) administration, no GFP(+) cells were detected and no evidence of regeneration of the infarcted region was found by histological examination. In contrast, a high level of matrix metalloproteinase 2 was measured in infarct and peri-infarct area. At this time, an improved ejection fraction and decreased left ventricular chamber dimension, which might be also related to a natural course after reperfusion, were observed. CONCLUSIONS: Our data show that GFP(+) CD34(+) and Lin(-)CD34(-)-enriched HSC do not differentiate into cardiomyocytes or into endothelial cells in the infarcted myocardium and that the local production of some growth factors had no positive effect on myocardial regeneration after 3 months.

Lack of evidence of sustained hematopoietic reconstitution after transplantation of unmanipulated adult liver stem cells in monkeys.

The aim of this study was to search for hematopoietic potential in the liver of non-human primates. Lethally irradiated (2 x 5 Gy gamma) macaque monkeys were given autologous hepatic mononuclear cells (HMNC) isolated from a liver lobe by perfusion and digestion with 0.1% collagenase. Two monkeys were given intramedullary injections of HMNC (18.6 x 10(6)/kg, 20.4 x 10(6)/kg) and two others were co-transplanted with HMNC (14.35 x 10(6)/kg, 96.5 x 10(6)/kg) and bone marrow mesenchymal stem cells (0.42 x 10(6)/kg, 1.16 x 10(6)/kg). All monkeys exhibited a transient neutrophil recovery from day 22 for 10 days, but failed to produce platelets and remained transfusion-dependent. In conclusion, adult liver stem cells from a monkey model show a low level of in vivo hematopoietic potential, suggesting ex vivo manipulation will be required before clinical use of such cells.

Bone marrow mesenchymal stem cells suppress lymphocyte proliferation in vitro but fail to prevent graft-versus-host disease in mice.

Several reports have suggested that mesenchymal stem cells (MSCs) could exert a potent immunosuppressive effect in vitro, and thus may have a therapeutic potential for T cell-dependent pathologies. We aimed to establish whether MSCs could be used to control graft-vs-host disease (GVHD), a major cause of morbidity and mortality after allogeneic hemopoietic stem cell transplantation. From C57BL/6 and BALB/c mouse bone marrow cells, we purified and expanded MSCs characterized by the lack of expression of CD45 and CD11b molecules, their typical spindle-shaped morphology, together with their ability to differentiate into osteogenic, chondrogenic, and adipogenic cells. These MSCs suppressed alloantigen-induced T cell proliferation in vitro in a dose-dependent manner, independently of their MHC haplotype. However, when MSCs were added to a bone marrow transplant at a MSCs:T cells ratio that provided a strong inhibition of the allogeneic responses in vitro, they yielded no clinical benefit on the incidence or severity of GVHD. The absence of clinical effect was not due to MSC rejection because they still could be detected in grafted animals, but rather to an absence of suppressive effect on donor T cell division in vivo. Thus, in these murine models, experimental data do not support a significant immunosuppressive effect of MSCs in vivo for the treatment of GVHD.