The Master Regulator Protein BAZ2B Can Reprogram Human Hematopoietic Lineage-Committed Progenitors into a Multipotent State.

Bi-species, fusion-mediated, somatic cell reprogramming allows precise, organism-specific tracking of unknown lineage drivers. The fusion of Tcf7l1-/- murine embryonic stem cells with EBV-transformed human B cell lymphocytes, leads to the generation of bi-species heterokaryons. Human mRNA transcript profiling at multiple time points permits the tracking of the reprogramming of B cell nuclei to a multipotent state. Interrogation of a human B cell regulatory network with gene expression signatures identifies 8 candidate master regulator proteins. Of these 8 candidates, ectopic expression of BAZ2B, from the bromodomain family, efficiently reprograms hematopoietic committed progenitors into a multipotent state and significantly enhances their long-term clonogenicity, stemness, and engraftment in immunocompromised mice. Unbiased systems biology approaches let us identify the early driving events of human B cell reprogramming.

Controlled ploidy reduction of pluripotent 4n cells generates 2n cells during mouse embryo development.

Cells with high ploidy content are common in mammalian extraembryonic and adult tissues. Cell-to-cell fusion generates polyploid cells during mammalian development and tissue regeneration. However, whether increased ploidy can be occasionally tolerated in embryonic lineages still remains largely unknown. Here, we show that pluripotent, fusion-derived tetraploid cells, when injected in a recipient mouse blastocyst, can generate diploid cells upon ploidy reduction. The generated diploid cells form part of the adult tissues in mouse chimeras. Parental chromosomes in pluripotent tetraploid cells are segregated through tripolar mitosis both randomly and nonrandomly and without aneuploidy. Tetraploid-derived diploid cells show a differentiated phenotype. Overall, we discovered an unexpected process of controlled genome reduction in pluripotent tetraploid cells. This mechanism can ultimately generate diploid cells during mouse embryo development and should also be considered for cell fusion-mediated tissue regeneration approaches.

Reprogramming Müller glia via in vivo cell fusion regenerates murine photoreceptors.

Vision impairments and blindness caused by retinitis pigmentosa result from severe neurodegeneration that leads to a loss of photoreceptors, the specialized light-sensitive neurons that enable vision. Although the mammalian nervous system is unable to replace neurons lost due to degeneration, therapeutic approaches to reprogram resident glial cells to replace retinal neurons have been proposed. Here, we demonstrate that retinal Müller glia can be reprogrammed in vivo into retinal precursors that then differentiate into photoreceptors. We transplanted hematopoietic stem and progenitor cells (HSPCs) into retinas affected by photoreceptor degeneration and observed spontaneous cell fusion events between Müller glia and the transplanted cells. Activation of Wnt signaling in the transplanted HSPCs enhanced survival and proliferation of Müller-HSPC hybrids as well as their reprogramming into intermediate photoreceptor precursors. This suggests that Wnt signaling drives the reprogrammed cells toward a photoreceptor progenitor fate. Finally, Müller-HSPC hybrids differentiated into photoreceptors. Transplantation of HSPCs with activated Wnt functionally rescued the retinal degeneration phenotype in rd10 mice, a model for inherited retinitis pigmentosa. Together, these results suggest that photoreceptors can be generated by reprogramming Müller glia and that this approach may have potential as a strategy for reversing retinal degeneration.

NKG2C zygosity influences CD94/NKG2C receptor function and the NK-cell compartment redistribution in response to human cytomegalovirus.

Human cytomegalovirus (HCMV) infection promotes a persistent expansion of a functionally competent NK-cell subset expressing the activating CD94/NKG2C receptor. Factors underlying the wide variability of this effect observed in HCMV-seropositive healthy individuals and exacerbated in immunocompromized patients are uncertain. A deletion of the NKG2C gene has been reported, and an apparent relation of NKG2C genotype with circulating NKG2C(+) NK-cell numbers was observed in HCMV(+) children. We have assessed the influence of NKG2C gene dose on the NK-cell repertoire in a cohort of young healthy adults (N = 130, median age 19 years). Our results revealed a relation of NKG2C copy number with surface receptor levels and with NKG2C(+) NK-cell numbers in HCMV(+) subjects, independently of HLA-E dimorphism. Functional studies showed quantitative differences in signaling (i.e. iCa(2+) influx), degranulation, and IL-15-dependent proliferation, in response to NKG2C engagement, between NK cells from NKG2C(+/+) and hemizygous subjects. These observations provide a mechanistic interpretation on the way the NKG2C genotype influences steady-state NKG2C(+) NK-cell numbers, further supporting an active involvement of the receptor in the HCMV-induced reconfiguration of the NK-cell compartment. The putative implications of NKG2C zygosity over viral control and other clinical variables deserve attention.

Wnt/ß-catenin signaling triggers neuron reprogramming and regeneration in the mouse retina.

Cell-fusion-mediated somatic-cell reprogramming can be induced in culture; however, whether this process occurs in mammalian tissues remains enigmatic. Here, we show that upon activation of Wnt/ß-catenin signaling, mouse retinal neurons can be transiently reprogrammed in vivo back to a precursor stage. This occurs after their spontaneous fusion with transplanted hematopoietic stem and progenitor cells (HSPCs). Moreover, we demonstrate that retinal damage is essential for cell-hybrid formation in vivo. Newly formed hybrids can proliferate, commit to differentiation toward a neuroectodermal lineage, and finally develop into terminally differentiated neurons. This results in partial regeneration of the damaged retinal tissue, with functional rescue. Following retinal damage and induction of Wnt/ß-catenin signaling, cell-fusion-mediated reprogramming also occurs after endogenous recruitment of bone-marrow-derived cells in the eyes. Our data demonstrate that in vivo reprogramming of terminally differentiated retinal neurons after their fusion with HSPCs is a potential mechanism for tissue regeneration.

Functional impact of A91V mutation of the PRF1 perforin gene.

Perforin (PRF1) gene mutations have been associated with Familial Hemophagocytic Lymphohistiocytosis type 2 (FHL2). Substitution p.A91V (c.272C>T) in exon 2 was first described as a neutral polymorphism. Nonetheless, recent clinical evidence and functional assays, suggest a potential pathogenic role for p.A91V, especially in compound heterozygous individuals. Moreover, p.A91V homozygosity has been linked to various pathological states including FHL and lymphocytic leukaemias. In the present report we evaluated the impact of this mutation in a compound heterozygous A91V/G149S 31 year-old asymptomatic female. Functional assays revealed low perforin expression levels, as well as an impaired NK cell-mediated cytotoxicity, partially reconstituted after incubation with IL-2. These results support that p.A91V mutation, associated to another mutated PRF1 allele, may potentially predispose seemingly healthy carriers to suffer a milder FHL2 clinical phenotype, including later onset of the disease. Thus, clinical monitoring of p.A91V carrier individuals bearing another mutation in PRF1 is warranted.

Association of atherosclerosis with expression of the LILRB1 receptor by human NK and T-cells supports the infectious burden hypothesis.

OBJECTIVE: The contribution of human cytomegalovirus (HCMV) to vascular disease may depend on features of the immune response not reflected by the detection of specific antibodies. Persistent HCMV infection in healthy blood donors has been associated with changes in the distribution of NK cell receptors (NKR). The putative relationship among HCMV infection, NKR distribution, subclinical atherosclerosis, and coronary heart disease was assessed. METHODS AND RESULTS: NKR expression was compared in acute myocardial infarction (AMI) patients (n=70) and a population-based control sample (n=209). The relationship between NKR expression and carotid intima-media thickness (CIMT) in controls (n=149) was also studied. HCMV infection was associated with higher proportions of NKG2C+ and LILRB1+ NK and T-cells. In contrast, only LILRB1+ NK and CD56+ T-cells were found to be increased in AMI patients, independent of age, sex, conventional vascular risk factors, and HCMV seropositivity. Remarkably, LILRB1 expression in NK and T-cells significantly correlated with CIMT in controls. CONCLUSIONS: The association of overt and subclinical atherosclerotic disease with LILRB1+ NK and T-cells likely reflects a relationship between the immune challenge by infections and cardiovascular disease risk, without attributing a dominant role for HCMV. Our findings may lead to the identification of novel biomarkers of vascular disease.

Natural killer cell-mediated response to human cytomegalovirus-infected macrophages is modulated by their functional polarization.

MΦ comprise a heterogeneous population of cells, which contribute to host defense and maintenance of immune homeostasis. MΦ may be infected by human cytomegalovirus (HCMV), which has evolved different strategies to subvert the immune response. In the present study, we comparatively analyzed the natural killer (NK) cell response against HCMV (TB40E)-infected proinflammatory (M1) and antinflammatory (M2) MΦ, derived from autologous monocytes, cultured in the presence of GM-CSF and M-CSF, respectively. M1 MΦ were more resistant to infection and secreted IL-6, TNF-α, IFN-α, and IL-12; by contrast, in HCMV-infected M2 MΦ, proinflammatory cytokines, IL-10, and IFN-α production were limited and IL-12 was undetectable. NK cell degranulation was triggered by interaction with HCMV-infected M1 and M2 MΦ at 48 h postinfection. The response was partially inhibited by specific anti-NKp46, anti-DNAM-1, and anti-2B4 mAb, thus supporting a dominant role of these activating receptors. By contrast, only HCMV-infected M1 MΦ efficiently promoted NK cell-mediated IFN-γ secretion, an effect partially related to IL-12 production. These observations reveal differences in the NK cell response triggered by distinct, HCMV-infected, monocyte-derived cell types, which may be relevant in the immunopathology of this viral infection.

NKp46 and DNAM-1 NK-cell receptors drive the response to human cytomegalovirus-infected myeloid dendritic cells overcoming viral immune evasion strategies.

Information on natural killer (NK)-cell receptor-ligand interactions involved in the response to human cytomegalovirus (HCMV) is limited and essentially based on the study of infected fibroblasts. Experimental conditions were set up to characterize the NK response to HCMV-infected myeloid dendritic cells (DCs). Monocyte-derived DCs (moDCs) infected by the TB40/E HCMV strain down-regulated the expression of human leukocyte antigen class I molecules and specifically activated autologous NK-cell populations. NKG2D ligands appeared virtually undetectable in infected moDCs, reflecting the efficiency of immune evasion mechanisms, and explained the lack of antagonistic effects of NKG2D-specific monoclonal antibody. By contrast, DNAM-1 and DNAM-1 ligands (DNAM-1L)-specific monoclonal antibodies inhibited the NK response at 48 hours after infection, although the impact of HCMV-dependent down-regulation of DNAM-1L in infected moDCs was perceived at later stages. moDCs constitutively expressed ligands for NKp46 and NKp30 natural cytotoxicity receptors, which were partially reduced on HCMV infection; yet, only NKp46 appeared involved in the NK response. In contrast to previous reports in fibroblasts, human leukocyte antigen-E expression was not preserved in HCMV-infected moDCs, which triggered CD94/NKG2A(+) NK-cell activation. The results provide an insight on key receptor-ligand interactions involved in the NK-cell response against HCMV-infected moDCs, stressing the importance of the dynamics of viral immune evasion mechanisms.

Natural killer cell receptor expression reflects the role of human cytomegalovirus in the pathogenesis of a subset of CD4+ T-cell large granular lymphocytosis.

A high frequency of CD4(+) T-cell large granular lymphocyte (T-LGL) lymphocytosis occurs in human leukocyte antigen (HLA) -DRB1*0701 individuals displaying monoclonal expansions of Vß13.1+ CD4(+) T-cell clones, which specifically respond to human cytomegalovirus (HCMV) antigens. We previously reported the expression of natural killer (NK)-cell associated receptors (NKR) by HCMV-specific cytolytic CD4(+) T cells from healthy donors. In the present study a high expression of different NKR (i.e., NKG2D, killer Ig-like receptors (KIR), CD94, ILT2) was observed in CD4(+) T cells from both Vß13.1- and Vß13.1+ CD4(+) T-LGL cases. Remarkably, elevated numbers of CD94/NKG2C+ NK cells, previously shown to expand in association to HCMV infection, were preferentially found in Vß13.1+ T-LGL, further supporting its role in the pathogenesis of a subset of CD4(+) T-LGL.

Influence of human cytomegalovirus infection on the NK cell receptor repertoire in children.

Human cytomegalovirus (hCMV) infection is usually asymptomatic but may cause disease in immunocompromised hosts. It has been reported that hCMV infection may shape the NK cell receptor (NKR) repertoire in adult individuals, promoting a variable expansion of the CD94/NKG2C+ NK cell subset. We explored the possible relationship between this viral infection and the expression pattern of different NKR including CD94/NKG2C, CD94/NKG2A, immunoglobulin-like transcript 2 (ILT2, CD85j), KIR2DL1/2DS1, KIR3DL1, and CD161 in peripheral blood lymphocytes from healthy children, seropositive (n=21) and seronegative (n=20) for hCMV. Consistent with previous observations in adults, a positive serology for hCMV was associated with increased numbers of NKG2C+ NK and T cells as well as with ILT2+ T lymphocytes. Moreover, the proportions of CD161+ and NKG2C+CD56-CD3- NK cells also tended to be increased in hCMV+ individuals. Excretion of the virus was associated with higher proportions of NKG2C+ NK cells. Altogether, these data reveal that hCMV may have a profound influence on the NKR repertoire in early childhood.

IL-12-dependent inducible expression of the CD94/NKG2A inhibitory receptor regulates CD94/NKG2C+ NK cell function.

The inhibitory CD94/NKG2A and activating CD94/NKG2C killer lectin-like receptors specific for HLA-E have been reported to be selectively expressed by discrete NK and T cell subsets. In the present study, minor proportions of NK and T cells coexpressing both CD94/NKG2A and CD94/NKG2C were found in fresh peripheral blood from adult blood donors. Moreover, CD94/NKG2A surface expression was transiently detected upon in vitro stimulation of CD94/NKG2C+ NK cells in the presence of irradiated allogeneic PBMC or rIL-12. A similar effect was observed upon coculture of NKG2C+ NK clones with human CMV-infected autologous dendritic cell cultures, and it was prevented by an anti-IL-12 mAb. NKG2A inhibited the cytolytic activity of NKG2C+ NK clones upon engagement either by a specific mAb or upon interaction with a transfectant of the HLA class I-deficient 721.221 cell line expressing HLA-E. These data indicate that beyond its constitutive expression by an NK cell subset, NKG2A may be also transiently displayed by CD94/NKG2C+ NK cells under the influence of IL-12, providing a potential negative regulatory feedback mechanism.

Evaluation of PARVG located on 22q13 as a candidate tumor suppressor gene for colorectal and breast cancer.

Colorectal cancer (CRC) and breast cancer constitute common neoplasms in Western countries and leading causes of cancer-related death. Development and progression of both malignancies occur as a multistep process, requiring the activation of oncogenes and the inactivation of several tumor suppressor genes. Our group has recently identified a minimal region of deletion on 22q13 involved in CRC and breast cancer patients, which is highly indicative of the existence of a tumor suppressor gene (or genes). We performed mutation analysis of the PARVG gene, one of the genes present on the 22q13 region of interest, which has been previously demonstrated to have a reduced expression in some cancer cell lines. We have identified several DNA variants that are not compatible with pathogenic mutations. Accordingly, PARVG appears not to be a tumor suppressor gene involved in CRC and breast cancer development and progression.