New tools for quantifying and visualizing adoptively transferred cells in recipient mice

The murine DCs transfected with DNA-plasmid encoding CCR9 demonstrate the increased migration to CCL25 and thymic cells in vitro and to the thymus in vivo

BACKGROUND

B220+CD11c+plasmacytoid DCs(pDCs) are known to participate in the negative selection and central tolerance induction by the capturing of self-antigens in peripheral tissues and further migration to the thymus using the CCL25-CCR9 chemotaxis axis.

AIM

Here we investigate the possibility of DCs migration stimulation to the thymus by the transfection with plasmid DNA-constructs encoding CCR9(pmaxCCR9) to develop a system for desired antigen delivery to the thymus for central tolerance induction.

METHODS

Dendritic cells(DCs) cultures were generated from UBC-GFP mice bone marrow cells expressing green fluorescent protein using the rmFlt3-L. DCs cultures were transfected with pmaxCCR9 by electroporation. The efficiency of electroporation was confirmed by RT-qPCR and flow cytometry. The migration of electroporated DCs was assessed in vitro and in vivo.

RESULTS

Dendritic cells(DCs) cultures obtained from UBC-GFP mice contained both B220+pDCs and SIRPa+cDC2. According to the RT-qPCR assay, the electroporation of obtained DCs cultures with pmaxCCR9 resulted in a 94.4-fold increase of RNA encoding CCR9 compared with non-electroporated cultures. Flow cytometry data showed that DCs cultures electroporated with pmaxCCR9 contained a significantly higher frequency of DCs carrying significantly higher levels of surface CCR9. Migration dynamics of obtained DCs analyzed in vitro showed that pmaxCCR9 electroporated DCs migrated significantly more active to CCL25 and thymic cells than non-electroporated and mock-electroporated DCs. In vivo, 30 days after injection, the relative amount of the DCs electroporated with pmaxCCR9 and pmaxMHC encoding antigenic determinants in the mice thymuses was 2.02-fold higher than the relative amount of the DCs electroporated with control plasmid.

CONCLUSION

Thus, the electroporation of murine DCs with pmaxCCR9 stimulated its migration to CCL25 and thymic cells in vitro as well as to the thymus in vivo. The obtained DCs loaded with a desired antigen may be suggested for further evaluation of central tolerance induction ability in in vivo models of autoimmune diseases and transplantation.

Cxcr6-Based Mesenchymal Stem Cell Gene Therapy Potentiates Skin Regeneration in Murine Diabetic Wounds

Mesenchymal stem cell (MSC) therapies for wound healing are often compromised due to low recruitment and engraftment of transplanted cells, as well as delayed differentiation into cell lineages for skin regeneration. An increased expression of chemokine ligand CXCL16 in wound bed and its cognate receptor, CXCR6, on murine bone-marrow-derived MSCs suggested a putative therapeutic relevance of exogenous MSC transplantation therapy. Induction of the CXCL16-CXCR6 axis led to activation of focal adhesion kinase (FAK), Src, and extracellular signal-regulated kinases 1/2 (ERK1/2)-mediated matrix metalloproteinases (MMP)-2 promoter regulation and expression, the migratory signaling pathways in MSC. CXCL16 induction also increased the transdifferentiation of MSCs into endothelial-like cells and keratinocytes. Intravenous transplantation of allogenic stable MSCs with Cxcr6 gene therapy potentiated skin tissue regeneration by increasing recruitment and engraftment as well as neovascularization and re-epithelialization at the wound site in excisional splinting wounds of type I and II diabetic mice. This study suggests that activation of the CXCL16-CXCR6 axis in bioengineered MSCs with Cxcr6 overexpression provides a promising therapeutic approach for the treatment of diabetic wounds.

Effect of Phosphorylation of CM2 Protein on Influenza C Virus Replication

CM2 is the second membrane protein of the influenza C virus and has been demonstrated to play a role in the uncoating and genome packaging processes in influenza C virus replication. Although the effects of N-linked glycosylation, disulfide-linked oligomerization, and palmitoylation of CM2 on virus replication have been analyzed, the effect of the phosphorylation of CM2 on virus replication remains to be determined. In this study, a phosphorylation site(s) at residue 78 and/or 103 of CM2 was replaced with an alanine residue(s), and the effects of the loss of phosphorylation on influenza C virus replication were analyzed. No significant differences were observed in the packaging of the reporter gene between influenza C virus-like particles (VLPs) produced from 293T cells expressing wild-type CM2 and those from the cells expressing the CM2 mutants lacking the phosphorylation site(s). Reporter gene expression in HMV-II cells infected with VLPs containing the CM2 mutants was inhibited in comparison with that in cells infected with wild-type VLPs. The virus production of the recombinant influenza C virus possessing CM2 mutants containing a serine-to-alanine change at residue 78 was significantly lower than that of wild-type recombinant influenza C virus. Furthermore, the virus growth of the recombinant viruses possessing CM2 with a serine-to-aspartic acid change at position 78, to mimic constitutive phosphorylation, was virtually identical to that of the wild-type virus. These results suggest that phosphorylation of CM2 plays a role in efficient virus replication, probably through the addition of a negative charge to the Ser78 phosphorylation site.IMPORTANCE It is well-known that many host and viral proteins are posttranslationally modified by phosphorylation, which plays a role in the functions of these proteins. In influenza A and B viruses, phosphorylation of viral proteins NP, M1, NS1, and the nuclear export protein (NEP), which are not integrated into the membranes, affects the functions of these proteins, thereby affecting virus replication. However, it was reported that phosphorylation of the influenza A virus M2 ion channel protein, which is integrated into the membrane, has no effect on virus replication in vitro or in vivo We previously demonstrated that the influenza C virus CM2 ion channel protein is modified by N-glycosylation, oligomerization, palmitoylation, and phosphorylation and have analyzed the effects of these modifications, except phosphorylation, on virus replication. This is the first report demonstrating that phosphorylation of the influenza C virus CM2 ion channel protein, unlike that of the influenza A virus M2 protein, plays a role in virus replication.

Adipose lineage specification of bone marrow-derived myeloid cells

We have reported the production of white adipocytes in adipose tissue from hematopoietic progenitors arising from bone marrow. However, technical challenges have hindered detection of this adipocyte population by certain other laboratories. These disparate results highlight the need for sensitive and definitive techniques to identify bone marrow progenitor (BMP)-derived adipocytes. In these studies we exploited new models and methods to enhance detection of this adipocyte population. Here we showed that confocal microscopy with spectrum acquisition could effectively identify green fluorescent protein (GFP) positive BMP-derived adipocytes by matching their fluorescence spectrum to that of native GFP. Likewise, imaging flow cytometry made it possible to visualize intact unilocular and multilocular GFP-positive BMP-derived adipocytes and distinguished them from non-fluorescent adipocytes and cell debris in the cytometer flow stream. We also devised a strategy to detect marker genes in flow-enriched adipocytes from which stromal cells were excluded. This technique also proved to be an efficient means for detecting genetically labeled adipocytes and should be applicable to models in which marker gene expression is low or absent. Finally, in vivo imaging of mice transplanted with BM from adipocyte-targeted luciferase donors showed a time-dependent increase in luciferase activity, with the bulk of luciferase activity confined to adipocytes rather than stromal cells. These results confirmed and extended our previous reports and provided proof-of-principle for sensitive techniques and models for detection and study of these unique cells.

Reliable transgene-independent method for determining Sleeping Beauty transposon copy numbers

Background

The transposon-based gene delivery technique is emerging as a method of choice for gene therapy. The Sleeping Beauty (SB) system has become one of the most favored methods, because of its efficiency and its random integration profile. Copy-number determination of the delivered transgene is a crucial task, but a universal method for measuring this is lacking. In this paper, we show that a real-time quantitative PCR-based, transgene-independent (qPCR-TI) method is able to determine SB transposon copy numbers regardless of the genetic cargo.

Results

We designed a specific PCR assay to amplify the left inverted repeat-direct repeat region of SB, and used it together with the single-copy control gene RPPH1 and a reference genomic DNA of known copy number. The qPCR-TI method allowed rapid and accurate determination of SB transposon copy numbers in various cell types, including human embryonic stem cells. We also found that this sensitive, rapid, highly reproducible and non-radioactive method is just as accurate and reliable as the widely used blotting techniques or the transposon display method. Because the assay is specific for the inverted repeat region of the transposon, it could be used in any system where the SB transposon is the genetic vehicle.

Conclusions

We have developed a transgene-independent method to determine copy numbers of transgenes delivered by the SB transposon system. The technique is based on a quantitative real-time PCR detection method, offering a sensitive, non-radioactive, rapid and accurate approach, which has a potential to be used for gene therapy.

Role of the CM2 protein in the influenza C virus replication cycle

CM2 is the second membrane protein of influenza C virus. Although its biochemical characteristics, coding strategy, and properties as an ion channel have been extensively studied, the role(s) of CM2 in the virus replication cycle remains to be clarified. In order to elucidate this role, in the present study we generated CM2-deficient influenza C virus-like particles (VLPs) and examined the VLP-producing 293T cells, VLPs, and VLP-infected HMV-II cells. Quantification of viral RNA (vRNA) in the VLPs by real-time PCR revealed that the CM2-deficient VLPs contain approximately one-third of the vRNA found in wild-type VLPs although no significant differences were detected in the expression levels of viral components in VLP-producing cells or in the number and morphology of the generated VLPs. This finding suggests that CM2 is involved in the genome packaging process into VLPs. Furthermore, HMV-II cells infected with CM2-deficient VLPs exhibited significantly reduced reporter gene expression. Although CM2-deficient VLPs could be internalized into HMV-II cells as efficiently as wild-type VLPs, a smaller amount of vRNA was detected in the nuclear fraction of CM2-deficient VLP-infected cells than in that of wild-type VLP-infected cells, suggesting that the uncoating process of the CM2-deficient VLPs in the infected cells did not proceed in an appropriate manner. Taken together, the data obtained in the present study indicate that CM2 has a potential role in the genome packaging and uncoating processes of the virus replication cycle.

An adoptive transfer method to detect low-dose radiation-induced bystander effects in vivo

The potential for irradiated cells to induce biological effects in their unirradiated neighbors (known as the bystander effect) has been observed repeatedly in vitro. However, whether bystander effects occur in vivo under the specific conditions relevant to low-dose radiation protection is still unclear. To test this, the fate of bystander cells in the mouse spleen was examined using an adoptive transfer method designed to replicate the rare, irradiated cells in an organ that might be expected after a low-dose-rate, low-LET radiation exposure. Splenic lymphocytes radiolabeled with low activities of (3)H-thymidine were introduced into the spleens of unirradiated recipient mice. In this study, the apoptotic and proliferative response of the neighboring bystander spleen cells was compared to the response of spleen cells in parallel control recipients that received sham-irradiated cells. Neither the local area surrounding lodged radiolabeled cells nor the spleen as a whole showed a change in apoptosis or proliferation either 1 or 3 days after adoptive transfer. Increasing the irradiated cell numbers, increasing the mean (3)H-thymidine activity per cell, or exposing cells ex vivo to an acute X-ray dose also had no effect. Possible reasons for the absence of a bystander effect in the spleen under these conditions are discussed.

Adhesion of T and B lymphocytes to mouse atherosclerotic aortas: Association with lesion topology and VCAM‐1 expression

OBJECTIVE

Although T and B lymphocytes accumulate in atherosclerotic lesions and play a key role in their growth, the mechanisms involved in the adhesion and recruitment of T and B lymphocytes by the lesions have not been resolved. The aim of this study was to compare T and B lymphocyte adhesion to atherosclerotic arteries and to test the role of VCAM-1 and ICAM-1.

MATERIAL AND METHODS

T and B lymphocytes were labelled with red and green fluorescent dyes and incubated with freshly isolated aortas from apolipoprotein-E-deficient mice. In some experiments the aortas were pre-incubated with specific monoclonal antibodies. After washing, the adhering cells were detected by confocal laser scanning microscopy.

RESULTS

The number of T and B lymphocytes that adhered to the aortic intimal surface was similar in both lesioned and non-lesioned areas and in the shoulder region of the lesions. However, the adhesion of T and B lymphocytes was significantly higher in the shoulder regions compared with the lesioned (p<0.0001) and non-lesioned areas of the aorta (p<0.0001). After pre-incubation of the aortas with antibodies against VCAM-1 or ICAM-1, the lymphocyte adhesions in lesioned areas were 42 % (p = 0.04) and 55 % (p = 0.17), respectively, of those in lesioned areas that had been pre-incubated with a control antibody. However, although VCAM-1 protein expression was most pronounced in the shoulder region, the lymphocyte adhesions in the shoulder region and in non-lesioned areas were unaffected by pre-incubation with VCAM-1 antibodies.

CONCLUSIONS

The results suggest that adhesion of T and B lymphocytes to mouse aortic endothelium is similar, is affected by lesion topology and is dependent on VCAM-1 expression over the core of atherosclerotic lesions.

Real-time PCR to determine transgene copy number and to quantitate the biolocalization of adoptively transferred cells from EGFP-transgenic mice

Quantitative real-time PCR (qPCR) is a sensitive technique for the detection and quantitation of specific DNA sequences. Here we describe a Taqman qPCR assay for quantification of tissue-localized, adoptively transferred enhanced green fluorescent protein (EGFP)-transgenic cells. A standard curve constructed from serial dilutions of a plasmid containing the EGFP transgene was (i) highly reproducible, (ii) detected as few as two copies, and (iii) was included in each qPCR assay. qPCR analysis of genomic DNA was used to determine transgene copy number in several mouse strains. Fluorescent microscopy of tissue sections showed that adoptively transferred vascular endothelial cells (VEC) from EGFP-transgenic mice specifically localized to tissue with metastatic tumors in syngeneic recipients. VEC microscopic enumeration of liver metastases strongly correlated with qPCR analysis of identical sections (Pearson correlation 0.81). EGFP was undetectable in tissue from control mice by qPCR. In another study using intra-tumor EGFP-VEC delivery to subcutaneous tumors, manual cell count and qPCR analysis of alternating sections also strongly correlated (Pearson correlation 0.82). Confocal microscopy of the subcutaneous tumor sections determined that visual fluorescent signals were frequently tissue artifacts. This qPCR methodology offers specific, objective, and rapid quantitation, uncomplicated by tissue autofluorescence, and should be readily transferable to other in vivo models to quantitate the biolocalization of transplanted cells.

Differential influence of chemokine receptors CCR2 and CXCR3 in development of atherosclerosis in vivo

BACKGROUND

Recruitment of mononuclear leukocytes within atherosclerotic lesions is a critical step in atherogenesis. Mice lacking the chemokine receptor CCR2, highly expressed on macrophages but also on T lymphocytes, show a striking reduction of atherosclerotic lesion formation. The chemokine receptor CXCR3 is a marker of activated T helper type 1 lymphocytes, the principal T lymphocyte type detected within atheroma. We investigated whether the deletion of both of these 2 important receptors expressed on the principal inflammatory cells present in atheroma would further affect atherogenesis in vivo.

METHODS AND RESULTS

We crossed ApoE(-/-) mice with either CCR2(-/-) or CXCR3- mice and crossed ApoE(-/-) CCR2(-/-) mice with the ApoE(-/-) CXCR3- mice to generate a triple knockout strain. Analysis of atherosclerosis development after 10 weeks of high-cholesterol diet revealed differential effects on early atherosclerotic lesions in the abdominal aorta and on advanced lesions in aortic roots. ApoE(-/-) CXCR3- mice, but not the triple knockout mice, displayed significantly reduced atherosclerotic lesion development within abdominal aortas compared with ApoE(-/-) CCR2(-/-) and ApoE(-/-) mice. This reduction of lesion formation correlated with an upregulation of antiinflammatory molecules such as interleukin-10, interleukin-18BP, and endothelial nitric oxide synthase and with an increased number of regulatory T lymphocytes within atherosclerotic lesions. In contrast, lesion size development within the aortic roots was more enhanced in ApoE(-/-) and ApoE(-/-) CXCR3- mice compared with ApoE(-/-) CCR2(-/-) and triple knockout mice.

CONCLUSIONS

Blocking chemokine signaling in vivo through deletion of the chemokine receptors CCR2 and CXCR3 has differential effects during atherogenesis. In addition, our results point to an important role of regulatory T lymphocytes during early atherogenesis.

G-CSF-primed hematopoietic stem cells or G-CSF per se accelerate recovery and improve survival after liver injury, predominantly by promoting endogenous repair programs

OBJECTIVE

On the basis of the recently recognized potential of bone marrow (BM) cells to give rise to hepatocytes, we investigated the possibility that granulocyte colony-stimulating factor (G-CSF)-mobilized BM cells could home to the injured liver and promote tissue repair. We also examined the origin of cells (endogenous or BM) reconstituting liver after damage.

METHODS

Acute and chronic liver injury models were generated by injecting CCl4 in C57Bl6 mice and G-CSF was administered in hematopoietic stem cell (HSC) mobilization doses. After sex-mismatched BM transplantation into lethally irradiated recipients and treatment with CCl4 +/- G-CSF, sry (sex-determining region for Y chromosome) protein was detected by immunohistochemistry in liver sections. Double immunohistochemistry for sry and ki-67 protein was used to define the origin of proliferating cells reconstituting liver after injury.

RESULTS

In both acute and chronic liver injury model, G-CSF administration ameliorated the histological damage and accelerated the regeneration process. This was accompanied by a strong survival benefit in G-CSF-treated group vs CCl4 group. Quantitative analysis showed higher percentage of BM-origin hepatocytes in the CCl4+G-CSF group compared with the CCl4 group, although the liver engraftment rate still remained rather low. Double staining for ki-67 and sry demonstrated that the recovery acceleration after chemical injury and G-CSF treatment was mainly mediated by increased proliferation of host hepatocytes (ki-67(+)/sry(-)) with less support from BM-origin cells (ki-67(+)/sry(+)).

CONCLUSION

G-CSF treatment significantly improved survival and liver histology in chemically injured mice, predominantly by promoting endogenous repair mechanisms. Therefore, mobilization with G-CSF might offer a novel therapeutic approach for the treatment of acute and chronic liver diseases in humans.