Human embryonic stem cell (hES) derived dendritic cells are functionally normal and are susceptible to HIV-1 infection
© Bandi and Akkina; licensee BioMed Central Ltd. 2008
Received: 31 October 2007
Accepted: 23 January 2008
Published: 23 January 2008
Human embryonic stem (hES) cells hold considerable promise for cell replacement and gene therapies. Their remarkable properties of pluripotency, self-renewal, and tractability for genetic modification potentially allows for the production of sizeable quantities of therapeutic cells of the hematopoietic lineage. Dendritic cells (DC) arise from CD34+ hematopoietic progenitor cells (HPCs) and are important in many innate and adaptive immune functions. With respect to HIV-1 infection, DCs play an important role in the efficient capture and transfer of the virus to susceptible cells. With an aim of generating DCs from a renewable source for HIV-1 studies, here we evaluated the capacity of hES cell derived CD34+ cells to give rise to DCs which can support HIV-1 infection.
Undifferentiated hES cells were cultured on S17 mouse bone marrow stromal cell layers to derive CD34+ HPCs which were subsequently grown in specific cytokine differentiation media to promote the development of DCs. The hES derived DCs (hES-DC) were subjected to phenotypic and functional analyses and compared with DCs derived from fetal liver CD34+ HPC (FL-DC). The mature hES-DCs displayed typical DC morphology consisting of veiled stellate cells. The hES-DCs also displayed characteristic phenotypic surface markers CD1a, HLA-DR, B7.1, B7.2, and DC-SIGN. The hES-DCs were found to be capable of antigen uptake and stimulating naïve allogeneic CD4+ T cells in a mixed leukocyte reaction assay. Furthermore, the hES-DCs supported productive HIV-1 viral infection akin to standard DCs.
Phenotypically normal and functionally competent DCs that support HIV-1 infection can be derived from hES cells. hES-DCs can now be exploited in applied immunology and HIV-1 infection studies. Using gene therapy approaches, it is now possible to generate HIV-1 resistant DCs from anti-HIV gene transduced hES-CD34+ hematopoietic progenitor cells.
Human embryonic stem (hES) cells are endowed with pluripotential and self-renewal properties [1, 1]. In addition, they are tractable for stable genetic modification. These attributes qualify them as potential candidates to derive an unlimited supply of any cell type for transplantation, gene therapy, drug screening and functional genomic applications. A number of previous studies have demonstrated the ability of hES cells to differentiate into a myriad of cell types that include neurons, hematopoietic cells, cardiomyocytes, and insulin-secreting cells, to name a few [3–9]. Many new studies are currently directed towards expanding the use of hES cells for novel applications.
In this regard, the ability to generate cells of the hematopoietic system has considerable potential in several areas of clinical and experimental medicine as they can reconstitute the entire blood system and can serve as primary targets in gene therapy in treating infectious diseases such as AIDS and inherited diseases [9, 10]. Given the present lack of effective vaccines and the ineffectiveness of drug based therapies for a complete cure with regard to HIV/AIDS, new and innovative approaches are essential [10, 11]. Gene therapy through intracellular immunization offers a promising alternative approach and possible supplement to current HAART therapy. A primary goal of many ongoing studies is to introduce an effective anti-HIV gene into hematopoietic progenitor cells . As these cells possess the ability to self-renew, they have the potential to continually produce HIV resistant T cells, macrophages, and dendritic cells in the body thus providing long term immune reconstitution. These approaches use CD34+ hematopoietic stem cells for anti-HIV gene transduction via integrating viral vectors such as lentiviral vectors. Current sources of CD34+ cells are restricted to human umbilical cord blood (CB), adult bone marrow (BM), mobilized peripheral blood, (MPB), and fetal liver . hES cells are a good viable alternative for the generation of an unlimited supply of CD34+ cells thus paving the way for utilization of these cells for hematopoietic cell therapy . Recently we demonstrated derivation of phenotypically and functionally normal macrophages from hES-CD34+ cells and established that they could support HIV-1 infection. These studies laid the ground work for utilizing hES-CD34+ cells in HIV research and for testing anti-HIV genes in a gene/cell therapy setting .
Similar to monocytes/macrophages, dendritic cells (DCs) also originate from hematopoietic progenitor cells and spread via the bloodstream and lymphatics [12, 13]. They are found in almost every organ as sentinels of the immune system. In innate immunity, DCs function via type-1 interferon activation of both macrophges and NK cells. In adaptive immunity, DCs constitute the most powerful antigen presenting cells (APCs) that prime naïve T lymphocytes and sensitize cytotoxic T lymphocytes to the antigens they present . Thus, efficient generation of these cells from renewable sources such as hES cells would have great potential for immunotherapy applications. However in HIV-1 infection, in addition to being infected and functionally compromised, paradoxically they are also culprits in the efficient transfer of the virus to susceptible cells . Thus in gene therapy applications for HIV infections they are also among principal cells that need to be protected. For such efforts to proceed further, it is important to evaluate if hES derived DCs are functionally normal and support HIV-1 infection. As a first step towards this goal, here we show that hES-CD34+ cells can give rise to normal DCs which are capable of supporting HIV-1 infection.
Hematopoietic differentiation of human ES cells and derivation of dendritic cells
hES derived DCs (hES-DC) express normal DC surface markers
hES-DC express Dendritic Cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN)
DC-SIGN (CD209) is a DC-specific C-type lectin which is expressed by mature DCs. DC-SIGN plays a vital role in establishing the initial contact between DCs and resting T cells through its recognition of ICAM-3 receptor [13–15]. In addition, with regard to HIV infection, it was found that DC-SIGN bound virus is more stable and is more efficiently transferred to susceptible target cells [13, 14]. We therefore examined the hES-DCs for its presence by staining with anti-DC-SIGN-PE and anti-CD1a-PECY5 conjugated antibodies. Results showed that a significant percentage of hES-DC (14.4%) express DC-SIGN similar to FL-DCs (14.3%) (Figure 3). We also observed cell populations single positive for CD1a and DC-SIGN which could represent other DC subtypes.
hES-DCs are capable of allogeneic T cell stimulation
hES-DCs are capable of antigen uptake
hES-DCs can support productive HIV-1 infection
Towards the goal of exploiting hES cells for novel hematopoietic cell reconstitution and HIV gene therapies, here we have shown that phenotypically normal and functionally competent dendritic cells could be differentiated from hES-CD34+ cells. Moreover, we also have demonstrated for the first time that hES-DCs can be productively infected with HIV-1 thus allowing future testing of anti-HIV therapeutic genes such as siRNAs for efficacy in these cells.
In these studies, we induced hES derived CD34+ cells to differentiate into myeloid DCs in the presence of cytokines SCF, GM-CSF, Flt3, IL-3, TNF-α, and IL-4. CD34+ cells derived from human fetal liver were also evaluated in parallel for comparison. Based on FACS analysis for surface markers during culture, CD34+ cells differentiated into mature myeloid DCs showing the typical CD1a phenotype similar to those derived from FL CD34+ cells. The morphology and phenotypic characteristics of hES-DCs were found to be similar to that of DCs derived from fetal liver CD34+ cells cultured in parallel.
It is important that hES-DCs are also functionally normal for future applications. Therefore we analyzed the functional markers HLA-DR (MHC-II), B7.1 (CD80), and B7.2 (CD86) typically expressed by mature DCs. The antigen presenting cell surface marker, HLA-DR present on mature DCs is critical for antigen presentation to CD4+ T cells and the co-stimulatory molecules B7.1 and B7.2 are needed to activate T cells. The mature hES-DCs expressed HLA-DR, B7.1, and B7.2 surface molecules which were comparable with levels expressed in FL-DCs. Consistent with the DCs' ability, the hES-DCs also showed normal capacity for antigen capture as evidenced by dextran uptake. We further analyzed the capacity of hES-DCs to induce proliferation of allogeneic T cells in a mixed leukocyte reaction. Our results showed that hES-DCs indeed are capable of mediating this allogeneic response. We also evaluated the expression of another cell surface molecule, DC-SIGN (CD209) which is a DC-specific adhesion receptor belonging to the C-type lectin family involved in the interactions with T cells [13, 14]. Our results showed similar levels of DC-SIGN in hES-DCs and FL-DCs. The above data taken together showed that hES-DCs are phenotypically and functionally normal.
It is known that HIV-1 can infect DCs with the virus remaining stable for long periods. DCs transmit the virus efficiently to CD4 T cells and therefore play an important role in HIV-1 infection. Our results showed that hES-DCs were susceptible to HIV-1 infection similar to that of FL-DCs. However, not all the cells in the culture were productively infected and the levels of viral production are low. This is consistent with previous findings that DCs support only a low level replication and fully mature DCs may have a block in viral replication [13, 14]. A recent report has also demonstrated the derivation of physiologically normal DCs from hES-CD34+ cells using a different protocol and compared these to those derived from adult human CD34+ cells and peripheral blood monocytes . Our results are in agreement and confirmed these previous findings, and additionally extended them further by demonstrating that hES-DCs are also susceptible to HIV-1 infection.
In HIV-1 disease, infection of CD4 T cells leads to their eventual decline whereas infection of monocytes/macrophages and dendritic cells leads to continued viral spread and defects in antigenic presentation thus exacerbating the disease process . We previously demonstrated the derivation of macrophagres from hES-CD34+ cells whereas studies of Galic et al  derived functional T cells from hES-CD34+ cells in vivo using humanized mice. Whether the hES derived T cells support HIV-1 infection remains to be determined. Lentiviral vector transduction of hES cells and derivation of functional macrophages and T cells that retained the expression of the transgene established that hES cells are tractable for deriving gene modified end-stage primary hematopoietic cells [10, 20]. Moreover, our present results together with our previous findings that both hES derived DCs and macrophages are susceptible to HIV infection paved the way for testing anti-HIV constructs introduced into either hES cells or their derivative hematopoietic progenitor CD34+ cells. Thus far many previous studies including our own evaluated a variety of anti-HIV gene constructs in a hematopoietic stem cell setting using CD34+ cells from routine sources such as bone marrow and cord blood . Newer and more potent novel constructs such as siRNAs are currently being investigated some of which are currently entering clinical trials . In addition to anti-HIV genes with a direct inhibitory action on viral molecules, siRNAs and ribozymes that down regulate cellular molecules that aid in HIV-1 infection such as viral coreceptors CCR5 and CXCR4 also show considerable promise [22, 23]. Such constructs can now be introduced into hES cells and their efficacy tested in end-stage cells represented by DCs, macrophages, and T cells.
In summary, our data demonstrated the development of terminally differentiated DCs derived from hES cells. The hES-DCs display typical DC morphology, express normal phenotypical markers, are capable of antigenic stimulation, and support HIV-1 infection.
Phenotypically normal and functionally competent dendritic cells could be derived from hES-CD34+ cells. Large numbers of these hES-DCs cells can now be cultured from a renewable source for use in cell and immune-based therapies. Since these cells also support productive HIV-1 infection, they provide a uniform source of DCs for viral infection studies. It is also now feasible to gene transduce either hES cells themselves and/or hES derived CD34+ cells with anti-HIV genes such as inhibitory siRNAs and test their antiviral efficacy in down stream differentiated DCs which are among the primary target cells that need to be protected against HIV-1 infection.
hES cell growth and propagation
H1 human embryonic stem cell line (hES) was obtained from WiCell (Madison, Wisconsin). The undifferentiated cells were maintained by co-culture with mitomycin C treated mouse embryonic fibroblast (MEF) cells (Chemicon, Temecula, CA) in DMEM/F12 medium supplemented with 20% knockout serum replacer (Invitrogen), 1% MEM-non essential amino acids (Invitrogen), 1 mM L-glutamine, 0.1 mM β-mercaptoethanol (Invitrogen), 0.5% penicillin/streptomycin and 4 ng/ml human basic fibroblast growth factor (Invitrogen). Culture media was replaced daily with fresh complete medium. Mature colonies were subculture weekly by digesting with collagenase IV (Invitrogen) as previously described .
Differentiation of hES cells into DCs
The undifferentiated hES cells (H1) were harvested by treatment with 1 mg/ml collagenase IV (Invitrogen) and dispersed by scraping to maintain the cells in small clumps. The hES cells were added to irradiated (35 Gy) S17 mouse bone marrow derived cell layers and cultured with differentiation media composed of RPMI supplemented with 15% FBS (HyClone), 2 mM L-glutamine, 0.1 mM β-mercaptoethanol, and 1% MEM-nonessential amino acids, 1% penicillin/streptomycin. Media was changed every 2 to 3 days. After indicated days (14–17 days), the differentiated hES cystic bodies were harvested and digested into single cell suspension using collagenase type IV followed by 0.05% trypsin/EDTA supplemented with 2% chick serum (Invitrogen) for 20 minutes at 37°C. Cells were washed twice with phosphate-buffered saline (PBS), filtered through a 70-μM cell strainer (BD Biosciences). To assess the levels of CD34+ hematopoietic progenitor cells in the bulk cell suspension, cells were labeled with PE conjugated anti-CD34+ antibody (BD Biosciences, San Jose, CA) and analyzed by FACS. To purify the CD34+ cells, Direct CD34+ Progenitor Cell Isolation Kit (Miltenyi Biotech, Auburn, CA) was used as recommended by the manufacturer's protocol. Isolated CD34+ cell purity was determined by FACS like above. For comparative experiments, human CD34+ cells were also purified from fetal liver tissue as described above . To derive DCs, the purified CD34+ cells (~4 × 105 to 6 × 105 cells) were cultured in Iscove's media containing 10 ng/ml each of SCF, IL-3, TNF-α, IL-4 and 50 ng/ml each of GM-CSF and Flt-3. The differentiated mature dendritic cells were used for subsequent phenotypic and functional analysis.
Phenotypic analysis of hES-DCs
To determine if hES derived DCs were phenotypically normal, analysis of the characteristic cell surface markers was performed by FACS using respective conjugated antibodies against CD1a-PECY5, CD14-PE, HLA-DR-PE, B7.1-PE, B7.2-PE and DC-SIGN-PE. Fetal liver CD34+ cell derived DCs were also evaluated in parallel. Blocking step was first performed by incubating the cells with the respective isotype sera control for 30 minutes at 4°C before staining with the respective cell surface marker antibodies. Isotype control staining was used to determine background levels. FACS analysis was performed on Beckman-Coulter EPICS®XL-MCL flow cytometer with data analysis using EXPO 32 ADC software (Coulter Corporation, Miami, FL). A minimum of 10,000 cells were analyzed in each FACS evaluation.
Functional analysis of hES-DCs by Mixed Leukocyte Reaction (MLR) assay and antigen uptake assay
The T cell stimulatory capacity of DCs derived from hES cells CD34+ progenitor cells was assessed by co-incubating graded numbers of CD1a+ cells previously sorted on the basis of CD1a immunomagnetic labeling (Miltenyi Biotech, Auburn, CA), and irradiated (3500 rads) DCs for 5 days with 5 × 105 allogeneic peripheral T cells isolated from peripheral blood using a column purification method to isolate resting T cells per manufacturer's instruction (Cedarlane, Ontario, CA). BrdU (10 μM final concentration) was added 18 hr before harvest and incorporation was measured by permeabilizing the cells with ice cold 70% ethanol for 20 min followed by washing in PBS. The cells were resuspended in freshly prepared 2 N HCl and incubated for 20 min at room temperature to denature nuclear DNA. The cells were then neutralized with 0.2 M disodiumborate and washed with PBS twice. Cells were stained for 20 min with anti-BrdU antibody conjugated with PE (BD-Pharmingen, San Jose, CA). Cells were washed with PBS and analyzed by FACS to determine the percent incorporation of BrdU which is indicative of proliferation. The percent BrdU was determined as a function of input number of sorted DCs and plotted as percent BrdU staining vs. input numbers of DCs. Alexa-dextran was used to assess cell endocytosis as previously described . The antigen uptake capacity was determined using CD1a+ immunomagnetic purified hES-DCs and FL-DCs. Cells resuspended in 10% FBS Iscove's medium (~1 × 105 cells) were incubated with 1 mg/ml Alexa-dextran at 37°C and 0°C for 60 minutes. The cells were later washed with PBS five times prior to FACS analysis. The level of antigen uptake by DCs was expressed as the difference in percentages between the test (37°C) and control samples (0°C). Fetal liver derived CD34+ cells were also evaluated in parallel.
HIV-1 infection of hES cells derived dendritic cells
To determine if hES-DCs can be infected with HIV-1 and support viral replication, cells were incubated with a X4 tropic replication competent HIV-GFP reporter virus NLENG-IRES [10, 26]. An m.o.i of 0.2 in the presence of 4 μg/ml polybrene was used. Infected cells were visualized by fluorescence microscopy to identify GFP expressing cells. Infected culture supernatants were also assayed for p24 antigen by ELISA using a Coulter-p24 kit (Beckman Coulter, Fullerton, CA).
Work reported here was supported by NIH RO1 grants AI50492 and AI057066 to R.A. We thank Joseph Anderson for suggestions, William Wheat for help with MLR and antigen uptake assays, Sarah Akkina and Jennifer Quick for help with maintaining hES cells and culturing cystic bodies. We thank Leila Remling for isolating fetal CD34+ cells, and the NIH AIDS Research and Reference Reagents Program for HIV-1 related reagents used in this work.
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