Optimization of fibronectin-assisted retroviral gene transfer into human CD34+ hematopoietic cells

Generation of Retrogenic Mice to Investigate T Cell Development

T cells develop in the thymus from bone marrow precursors, and genetic manipulation is an indispensable tool to explore their development in vivo. Retroviral transduction of T cell precursors in the bone marrow can be used to specifically eliminate or enforce gene expression. Here, we describe a fast and efficient method to ectopically express a gene in T cell precursors through retroviral transduction and transplant into recipient mice, which will enable laboratories to evaluate gene function in T cell development in vivo.

Gene Engineering T Cells with T-Cell Receptor for Adoptive Therapy

Prior to clinical testing of adoptive T-cell therapy with T-cell receptor (TCR)-engineered T cells, TCRs need to be retrieved, annotated, gene-transferred, and extensively tested in vitro to accurately assess specificity and sensitivity of target recognition. Here, we present a fundamental series of protocols that cover critical preclinical parameters, thereby enabling the selection of candidate TCRs for clinical testing.

Genetic Engineering and Enrichment of Human NK Cells for CAR-Enhanced Immunotherapy of Hematological Malignancies

The great clinical success of chimeric antigen receptor (CAR) T cells has unlocked new levels of immunotherapy for hematological malignancies. Genetically modifying natural killer (NK) cells as alternative CAR immune effector cells is also highly promising, as NK cells can be transplanted across HLA barriers without causing graft-versus-host disease. Therefore, off-the-shelf usage of CAR NK cell products might allow to widely expand the clinical indications and to limit the costs of treatment per patient. However, in contrast to T cells, manufacturing suitable CAR NK cell products is challenging, as standard techniques for genetically engineering NK cells are still being defined. In this study, we have established optimal lentiviral transduction of primary human NK cells by systematically testing different internal promoters for lentiviral CAR vectors and comparing lentiviral pseudotypes and viral entry enhancers. We have additionally modified CAR constructs recognizing standard target antigens for acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) therapy—CD19, CD33, and CD123—to harbor a CD34-derived hinge region that allows efficient detection of transduced NK cells in vitro and in vivo and also facilitates CD34 microbead-assisted selection of CAR NK cell products to >95% purity for potential clinical usage. Importantly, as most leukemic blasts are a priori immunogenic for activated primary human NK cells, we developed an in vitro system that blocks the activating receptors NKG2D, DNAM-1, NKp30, NKp44, NKp46, and NKp80 on these cells and therefore allows systematic testing of the specific killing of CAR NK cells against ALL and AML cell lines and primary AML blasts. Finally, we evaluated in an ALL xenotransplantation model in NOD/SCID-gamma (NSG) mice whether human CD19 CAR NK cells directed against the CD19+ blasts are relying on soluble or membrane-bound IL15 production for NK cell persistence and also in vivo leukemia control. Hence, our study provides important insights into the generation of pure and highly active allogeneic CAR NK cells, thereby advancing adoptive cellular immunotherapy with CAR NK cells for human malignancies further.

The murine cytomegalovirus immunoevasin gp40/m152 inhibits NKG2D receptor RAE-1γ by intracellular retention and cell surface masking

NKG2D (also known as KLRK1) is a crucial natural killer (NK) cell-activating receptor, and the murine cytomegalovirus (MCMV) employs multiple immunoevasins to avoid NKG2D-mediated activation. One of the MCMV immunoevasins, gp40 (m152), downregulates the cell surface NKG2D ligand RAE-1γ (also known as Raet1c) thus limiting NK cell activation. This study establishes the molecular mechanism by which gp40 retains RAE-1γ in the secretory pathway. Using flow cytometry and pulse-chase analysis, we demonstrate that gp40 retains RAE-1γ in the early secretory pathway, and that this effect depends on the binding of gp40 to a host protein, TMED10, a member of the p24 protein family. We also show that the TMED10-based retention mechanism can be saturated, and that gp40 has a backup mechanism as it masks RAE-1γ on the cell surface, blocking the interaction with the NKG2D receptor and thus NK cell activation.

Optimizing lentiviral vector transduction of hematopoietic stem cells for gene therapy

Autologous gene therapy using lentiviral vectors (LVs) holds promise for treating monogenetic blood diseases. However, clinical applications can be limited by suboptimal hematopoietic stem cell (HSC) transduction and insufficient quantities of available vector. We recently reported gene therapy for X-linked severe combined immunodeficiency using a protocol in which patient CD34+ cells were incubated with two successive transductions. Here we describe an improved protocol for LV delivery to CD34+ cells that simplifies product manipulation, reduces vector consumption, and achieves greater vector copy number (VCN) of repopulating HSCs in mouse xenotransplantation assays. Notable findings include the following: (1) the VCN of CD34+ cells measured shortly after transduction did not always correlate with the VCN of repopulating HSCs after xenotransplantation; (2) single-step transduction at higher CD34+ cell concentrations (2-4 × 106/ml) conserved LV without compromising HSC VCN; (3) poloxamer F108 (LentiBOOST) increased HSC VCN by two- to threefold (average from three donors); (4) although LentiBOOST + prostaglandin E2 combination further increased VCN in vitro, the VCN observed in vivo were similar to LentiBOOST alone; (5) cyclosporine H increased the HSC VCN to a similar or greater extent with LentiBOOST in vivo. Our findings delineate an improved protocol to increase the VCN of HSCs after CD34+ cell transduction with clinically relevant LVs.

T cell gene therapy to treat immunodeficiency

The application of therapeutic T cells for a number of conditions has been developed over the past few decades with notable successes including donor lymphocyte infusions, virus-specific T cells and more recently CAR-T cell therapy. Primary immunodeficiencies are monogenetic disorders leading to abnormal development or function of the immune system. Haematopoietic stem cell transplantation and, in specific candidate diseases, haematopoietic stem cell gene therapy has been the only definitive treatment option so far. However, autologous gene-modified T cell therapy may offer a potential cure in conditions primarily affecting the lymphoid compartment. In this review we will highlight several T cell gene addition or gene-editing approaches in different target diseases with a focus on what we have learnt from clinical experience and promising preclinical studies in primary immunodeficiencies. Functional T cells are required not only for normal immune responses to infection (affected in CD40 ligand deficiency), but also for immune regulation [disrupted in IPEX syndrome (immune dysregulation, polyendocrinopathy, enteropathy, X-Linked) due to dysfunctional FOXP3 and CTLA4 deficiency] or cytotoxicity [defective in X-lymphoproliferative disease and familial haemophagocytic lymphohistiocytosis (HLH) syndromes]. In all these candidate diseases, restoration of T cell function by gene therapy could be of great value.

Functional Analysis of an Inducible Promoter Driven by Activation Signals from a Chimeric Antigen Receptor

Adoptive transfer of T cells expressing a chimeric antigen receptor (CAR) is a promising cell-based anticancer therapy. Although clinical studies of this approach show therapeutic efficacy, additional genetic modification is necessary to enhance the efficacy and safety of CAR-T cells. For example, production of an antitumor cytokine from CAR-T cells can potentially enhance their tumor-killing activity, but there are concerns that constitutive expression of anticancer molecules will cause systemic side effects. Therefore, it is important that exogenous gene expression is confined to the tumor locality. Here, we aimed to develop an inducible promoter driven by activation signals from a CAR. Transgene expression in T cells transduced with the CD19-targeted CAR and an inducible promoter, including inducible reporter genes (CAR-T/iReporter), was only induced strongly by co-culture with CD19-positive target cells. CAR-T/iReporter cells also showed redirected cytolysis toward CD19-positive, but not CD19-negative, tumor cells. Overall, our study indicated that the inducible promoter was selectively driven by activation signals from the CAR, and transduction with the inducible promoter did not affect original effector activities including interleukin-2 and interferon-γ production and the antitumor activity of CAR-redirected cytotoxic T lymphocytes. Moreover, this inducible promoter permits visualization and quantification of the activation status in CAR-T cells.

Fanconi anemia with sun-sensitivity caused by a Xeroderma pigmentosum-associated missense mutation in XPF

BACKGROUND

Fanconi anemia (FA) is an inherited genomic instability disorder with congenital and developmental abnormalities, bone marrow failure and predisposition to cancer early in life, and cellular sensitivity to DNA interstrand crosslinks.

CASE PRESENTATION

A fifty-one-year old female patient, initially diagnosed with FA in childhood on the basis of classic features and increased chromosomal breakage, and remarkable sun-sensitivity is described. She only ever had mild haematological abnormalities and no history of malignancy. To identify and characterise the genetic defect in this lady, who is one of the oldest reported FA patients, we used whole-exome sequencing for identification of causative mutations, and functionally characterized the cellular phenotype. Detection of the novel splice site mutation c.793-2A > G and the previously described missense mutation c.1765C > T (p.Arg589Trp) in XPF/ERCC4/FANCQ assign her as the third individual of complementation group FA-Q. Ectopic expression of wildtype, but not mutant, XPF/ERCC4/FANCQ, in patient-derived fibroblasts rescued cellular resistance to DNA interstrand-crosslinking agents. Patient derived FA-Q cells showed impaired nuclear excision repair capacity. However, mutated XPF/ERCC4/FANCQ protein in our patient's cells, as in the two other patients with FA-Q, was detectable on chromatin, in contrast to XP-F cells, where missense-mutant protein failed to properly translocate to the nucleus.

CONCLUSIONS

Patients with FA characteristics and UV sensitivity should be tested for mutations in XPF/ERCC4/FANCQ. The missense mutation p.Arg589Trp was previously detected in patients diagnosed with Xeroderma pigmentosum or Cockayne syndrome. Hence, phenotypic manifestations associated with this XPF/ERCC4/ FANCQ mutation are highly variable.

Retroviral Transduction of Quiescent Murine Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) represent an important target cell population in bone marrow transplantation, cell and gene therapy applications, and the development of leukemia models for research. Because the hematopoietic progeny carries the genetic information of HSCs and replenishes the blood and immune system, corrective gene transfer into HSCs provides an ideal therapeutic approach for many monogenic hematological diseases and a useful tool for studies of HSC function and blood formation in normal and malignant hematopoiesis. However, the efficiency of gene transfer into HSCs has been limited by several features of viral vectors, viral titer, methods of viral transduction, and the property of stem cell quiescence. In this chapter, we describe the production of retrovirus using murine stem cell virus (MSCV)-based retroviral vectors and purification and transduction of murine HSCs.

Improving the Transduction of Bone Marrow-Derived Cells with an Integrase-Defective Lentiviral Vector

In lentiviral vector (LV) applications where transient transgene expression is sufficient, integrase-defective lentiviral vectors (IDLVs) are beneficial for reducing the potential for off-target effects associated with insertional mutagenesis. It was previously demonstrated that human RPE65 mRNA expression from an integrating lentiviral vector (ILV) induces endogenous Rpe65 and Cralbp mRNA expression in murine bone marrow–derived cells (BMDCs), initiating programming of the cells to retinal pigment epithelium (RPE)-like cells. These cells regenerate RPE in retinal degeneration models when injected systemically. As transient expression of RPE65 is sufficient to activate endogenous RPE-associated genes for programming BMDCs, use of an ILV is an unnecessary risk. In this study, an IDLV expressing RPE65 (IDLV3-RPE65) was generated. Transduction with IDLV3-RPE65 is less efficient than the integrating vector (ILV3-RPE65). Therefore, IDLV3-RPE65 transduction was enhanced with a combination of preloading 20 × -concentrated viral supernatant on RetroNectin at a multiplicity of infection of 50 and transduction of BMDCs by low-speed centrifugation. RPE65 mRNA levels increased from ∼12-fold to ∼25-fold (p < 0.05) after modification of the IDLV3-RPE65 transduction protocol, achieving expression similar to the ∼27-fold (p < 0.05) increase observed with ILV3-RPE65. Additionally, the study shows that the same preparation of RetroNectin can be used to coat up to three wells with no reduction in transduction. Critically, IDLV3-RPE65 transduction initiates endogenous Rpe65 mRNA expression in murine BMDCs and Cralbp/CRALBP mRNA in both murine and human BMDCs, similar to expression observed in ILV3-RPE65-transduced cells. Systemic administration of ILV3-RPE65 or IDLV3-RPE65 programmed BMDCs in a mouse model of retinal degeneration is sufficient to retain visual function and reduce retinal degeneration compared to mice receiving no treatment or naïve BMDC. It is concluded that IDLV3-RPE65 is appropriate for programming BMDCs to RPE-like cells.

Protein A Functionalized Polyelectrolyte Microcapsules as a Universal Platform for Enhanced Targeting of Cell Surface Receptors

Targeted delivery systems recognizing specific receptors are a key element in personalized medicine. Such systems allow the delivery of therapeutics to desired sites of the body, increasing their local concentration and thus reducing the side effects. In this study, we fabricate chemically cross-linked (PAH/PAA)₂ microcapsules coated with specific cell-targeting antibodies in random (via direct covalent coupling to the surface) or optimized (via supporting layer of protein A) orientation. We use these antibody-functionalized capsules to target major histocompatibility complex (MHC) class I receptors in living cells and quantify the efficiency of targeting by flow cytometry. We show for the first time the selective binding of polyelectrolyte microcapsules to MHC class I receptors, and confirm that targeting is allotype-specific. Remarkably, protein A assisted immobilization of antibodies enhances targeting efficiency by 40-50% over capsules with randomly attached antibodies. Moreover, biofunctionalized capsules reveal low levels of cytotoxicity and nonspecific binding, excluding the need of additional modification with poly(ethylene glycol). Thus, protein A coated (PAH/PAA)₂ microcapsules represent a unique example of universal targeting tools providing high potential for selective binding to a broad range of cell surface receptors.

Specific Capture of Peptide-Receptive Major Histocompatibility Complex Class I Molecules by Antibody Micropatterns Allows for a Novel Peptide-Binding Assay in Live Cells

Binding assays with fluorescently labeled ligands and recombinant receptor proteins are commonly performed in 2D arrays. But many cell surface receptors only function in their native membrane environment and/or in a specific conformation, such as they appear on the surface of live cells. Thus, receptors on live cells should be used for ligand binding assays. Here, it is shown that antibodies preprinted on a glass surface can be used to specifically array a peptide receptor of the immune system, i.e., the major histocompatibility complex class I molecule H-2K^b , into a defined pattern on the surface of live cells. Monoclonal antibodies make it feasible to capture a distinct subpopulation of H-2K^b and hold it at the cell surface. This patterned receptor enables a novel peptide-binding assay, in which the specific binding of a fluorescently labeled index peptide is visualized by microscopy. Measurements of ligand binding to captured cell surface receptors in defined confirmations apply to many problems in cell biology and thus represent a promising tool in the field of biosensors.

Characterization of an Additional Splice Acceptor Site Introduced into CYP4B1 in Hominoidae during Evolution

CYP4B1 belongs to the cytochrome P450 family 4, one of the oldest P450 families whose members have been highly conserved throughout evolution. The CYP4 monooxygenases typically oxidize fatty acids to both inactive and active lipid mediators, although the endogenous ligand(s) is largely unknown. During evolution, at the transition of great apes to humanoids, the CYP4B1 protein acquired a serine instead of a proline at the canonical position 427 in the meander region. Although this alteration impairs P450 function related to the processing of naturally occurring lung toxins, a study in transgenic mice suggested that an additional serine insertion at position 207 in human CYP4B1 can rescue the enzyme stability and activity. Here, we report that the genomic insertion of a CAG triplet at the intron 5–exon 6 boundary in human CYP4B1 introduced an additional splice acceptor site in frame. During evolution, this change occurred presumably at the stage of Hominoidae and leads to two major isoforms of the CYP4B1 enzymes of humans and great apes, either with or without a serine 207 insertion (insSer207). We further demonstrated that the CYP4B1 enzyme with insSer207 is the dominant isoform (76%) in humans. Importantly, this amino acid insertion did not affect the 4-ipomeanol metabolizing activities or stabilities of the native rabbit or human CYP4B1 enzymes, when introduced as transgenes in human primary cells and cell lines. In our 3D modeling, this functional neutrality of insSer207 is compatible with its predicted location on the exterior surface of CYP4B1 in a flexible side chain. Therefore, the Ser207 insertion does not rescue the P450 functional activity of human CYP4B1 that has been lost during evolution.

[Construction of CD19-CAR retroviral vector and modification of its transduction of human T-lymphocytes]

OBJECTIVE

To improve the MigR1-CD19-CAR (chimeric antigen receptor) that contains a single chain variable region (scFv) which targeted to CD19 through a retroviral vector transduction efficiency of T-lymphocytes.

METHODS

Insert the CD19-CAR fragment into the retroviral vector (MigR1) through recombinant DNA technology, after transfecting plat-A packaging cell lines, viral supernatant was collected to transduce K562 cell line and activated human T-lymphocytes. We used flow cytometry to determine the transduction efficiency and RT-PCR to confirm the transcription of CD19-CAR gene. The ability of the transduced T cells to produce IFN-γ and TNF-α in a CD19-specific manner was measured in an enzyme-linked immunosorbent (ELISA) assay.

RESULTS

(1)Using MigR1-CD19-CAR retroviral vector to produce the high titer retrovirus. (2)MigR1-CD19-CAR transduction efficiency of K562 cell line was significantly higher than human T-lymphocytes (P<0.01). (3)120 min centrifugation could significantly improve transduction efficiency of T-lymphocytes to (54.5±14.6)%. (4)Transduction efficiency could be improved by deciding transduce time according to T-lymphocytes proliferation fold in vitro individually, and the highest transduction efficiency in the study was 69.3%. The CD19-CAR gene sequence was transcripted specificly with high efficiency. (5) IFN-γ and TNF-α released by CD19-CAR transduced T-lymphocytes significantly increased to (13 230±1 543) pg/ml and (4 217±211) pg/ml when coculture with CD19-K562 cells.

CONCLUSION

We have successfully constructed a second generation CAR which targeted to CD19 through a retroviral vector called MigR1 (MigR1-CD19-CAR). Deciding transduce time according to T-lymphocytes proliferation fold in vitro individually and 120 min centrifugation could improve the CAR transduction efficiency of T-lymphocytes. RT-PCR confirmed that the CD19-CAR gene was specificly transcripted with high efficiency. IFN-γ and TNF-α released by CD19-CAR transduced T-lymphocytes significantly increased when activated by target cells.

Identification of amino acid determinants in CYP4B1 for optimal catalytic processing of 4-ipomeanol

Mammalian CYP4B1 enzymes are cytochrome P450 mono-oxygenases that are responsible for the bioactivation of several exogenous pro-toxins including 4-ipomeanol (4-IPO). In contrast with the orthologous rabbit enzyme, we show here that native human CYP4B1 with a serine residue at position 427 is unable to bioactivate 4-IPO and does not cause cytotoxicity in HepG2 cells and primary human T-cells that overexpress these enzymes. We also demonstrate that a proline residue in the meander region at position 427 in human CYP4B1 and 422 in rabbit CYP4B1 is important for protein stability and rescues the 4-IPO bioactivation of the human enzyme, but is not essential for the catalytic activity of the rabbit CYP4B1 protein. Systematic substitution of native and p.S427P human CYP4B1 with peptide regions from the highly active rabbit enzyme reveals that 18 amino acids in the wild-type rabbit CYP4B1 protein are key for conferring high 4-IPO metabolizing activity. Introduction of 12 of the 18 amino acids that are also present at corresponding positions in other human CYP4 family members into the p.S427P human CYP4B1 protein results in a mutant human enzyme (P+12) that is as stable and as active as the rabbit wild-type CYP4B1 protein. These 12 mutations cluster in the predicted B-C loop through F-helix regions and reveal new amino acid regions important to P450 enzyme stability. Finally, by minimally re-engineering the human CYP4B1 enzyme for efficient activation of 4-IPO, we have developed a novel human suicide gene system that is a candidate for adoptive cellular therapies in humans.

Peptide nanofibrils as enhancers of retroviral gene transfer

Amyloid fibrils are polypeptide-based polymers that are typically associated with neurodegenerative disorders such as Alzheimer's disease. More recently, it has become clear that amyloid fibrils also fulfill functional roles in hormone storage and biosynthesis. Furthermore, it has been demonstrated that semen contains abundant levels of polycationic amyloid fibrils. The natural role of these seminal amyloids remains elusive. Strikingly, however, they drastically enhance HIV-1 infection and may be exploited by the virus to increase its sexual transmission rate. Their strong activity in enhancing HIV-1 infection suggests that seminal amyloid might also promote transduction by retroviral vectors. Indeed, SEVI (semen-derived enhancer of virus infection), the best characterized seminal amyloid, boosts retroviral gene transfer more efficiently than conventional additives. However, the use of SEVI as laboratory tool for efficient retroviral gene transfer is limited because the polypeptide monomers are relatively expensive to produce. Furthermore, standardized production of SEVI fibrils with similar high activities is difficult to achieve because of the stochastic nature of the amyloid assembly process. These obstacles can be overcome by recently identified smaller peptides that spontaneously self-assemble into nanofibrils. These nanofibrils increase retroviral gene transfer even more efficiently than SEVI, are easy to produce and to handle, and seem to be safe as assessed in an ex vivo gene transfer study. Furthermore, peptide-based nanofibrils allow to concentrate viral particles by low-speed centrifugation. Specific adaption and customization of self-assembling peptides might lead to novel nanofibrils with versatile biological functions, e.g., targeted retroviral gene transfer or drug delivery.

An efficient large-scale retroviral transduction method involving preloading the vector into a RetroNectin-coated bag with low-temperature shaking

In retroviral vector-mediated gene transfer, transduction efficiency can be hampered by inhibitory molecules derived from the culture fluid of virus producer cell lines. To remove these inhibitory molecules to enable better gene transduction, we had previously developed a transduction method using a fibronectin fragment-coated vessel (i.e., the RetroNectin-bound virus transduction method). In the present study, we developed a method that combined RetroNectin-bound virus transduction with low-temperature shaking and applied this method in manufacturing autologous retroviral-engineered T cells for adoptive transfer gene therapy in a large-scale closed system. Retroviral vector was preloaded into a RetroNectin-coated bag and incubated at 4°C for 16 h on a reciprocating shaker at 50 rounds per minute. After the supernatant was removed, activated T cells were added to the bag. The bag transduction method has the advantage of increasing transduction efficiency, as simply flipping over the bag during gene transduction facilitates more efficient utilization of the retroviral vector adsorbed on the top and bottom surfaces of the bag. Finally, we performed validation runs of endoribonuclease MazF-modified CD4(+) T cell manufacturing for HIV-1 gene therapy and T cell receptor-modified T cell manufacturing for MAGE-A4 antigen-expressing cancer gene therapy and achieved over 200-fold (≥ 10(10)) and 100-fold (≥ 5 × 10(9)) expansion, respectively. In conclusion, we demonstrated that the large-scale closed transduction system is highly efficient for retroviral vector-based T cell manufacturing for adoptive transfer gene therapy, and this technology is expected to be amenable to automation and improve current clinical gene therapy protocols.

A unique carboxyl-terminal insert domain in the hematopoietic-specific, GTPase-deficient Rho GTPase RhoH regulates post-translational processing

RhoH is a hematopoietic-specific, GTPase-deficient member of the Rho GTPase family that was first identified as a hypermutable gene in human B lineage lymphomas. RhoH remains in a constitutively active state and thus its effects are regulated by expression levels or post-translational modifications. Similar to other small GTPases, intracellular localization of RhoH is dependent upon the conserved "CAAX" box and surrounding sequences within the carboxyl (C) terminus. However, RhoH also contains a unique C-terminal "insert" domain of yet undetermined function. RhoH serves as adaptor molecule in T cell receptor signaling and RhoH expression correlates with the unfavorable prognostic marker ZAP70 in human chronic lymphocytic leukemia. Disease progression is attenuated in a Rhoh(-/-) mouse model of chronic lymphocytic leukemia and treatment of primary human chronic lymphocytic leukemia cells with Lenalidomide results in reduced RhoH protein levels. Thus, RhoH is a potential therapeutic target in B cell malignancies. In the current studies, we demonstrate that deletion of the insert domain (LFSINE) results in significant cytoplasmic protein accumulation. Using inhibitors of degradation pathways, we show that LFSINE regulates lysosomal RhoH uptake and degradation via chaperone-mediated autophagy. Whereas the C-terminal prenylation site is critical for ZAP70 interaction, subcellular localization and rescue of the Rhoh(-/-) T cell defect in vivo, the insert domain appears dispensable for these functions. Taken together, our findings suggest that the insert domain regulates protein stability and activity without otherwise affecting RhoH function.

In vivo selection of CD4(+) T cells transduced with a gamma-retroviral vector expressing a single-chain intrabody targeting HIV-1 tat

We evaluated the potential of an anti-human immunodeficiency virus (HIV) Tat intrabody (intracellular antibody) to promote the survival of CD4(+) cells after chimeric simian immunodeficiency virus (SIV)/HIV (SHIV) infection in rhesus macaques. Following optimization of stimulation and transduction conditions, purified CD4(+) T cells were transduced with GaLV-pseudotyped retroviral vectors expressing either an anti-HIV-1 Tat or a control single-chain intrabody. Ex vivo intrabody-gene marking was highly efficient, averaging four copies per CD4(+) cell. Upon reinfusion of engineered autologous CD4(+) cells into two macaques, high levels of gene marking (peak of 0.6% and 6.8% of peripheral blood mononuclear cells (PBMCs) and 0.3% or 2.2% of the lymph node cells) were detected in vivo. One week post cell infusion, animals were challenged with SHIV 89.6p and the ability of the anti-HIV Tat intrabody to promote cell survival was evaluated. The frequency of genetically modified CD4(+) T cells progressively decreased, concurrent with loss of CD4(+) cells and elevated viral loads in both animals. However, CD4(+) T cells expressing the therapeutic anti-Tat intrabody exhibited a relative survival advantage over an 8- and 21-week period compared with CD4(+) cells expressing a control intrabody. In one animal, this survival benefit of anti-Tat transduced cells was associated with a reduction in viral load. Overall, these results indicate that a retrovirus-mediated anti-Tat intrabody provided significant levels of gene marking in PBMCs and peripheral tissues and increased relative survival of transduced cells in vivo.

Peptide nanofibrils boost retroviral gene transfer and provide a rapid means for concentrating viruses

Inefficient gene transfer and low virion concentrations are common limitations of retroviral transduction. We and others have previously shown that peptides derived from human semen form amyloid fibrils that boost retroviral gene delivery by promoting virion attachment to the target cells. However, application of these natural fibril-forming peptides is limited by moderate efficiencies, the high costs of peptide synthesis, and variability in fibril size and formation kinetics. Here, we report the development of nanofibrils that self-assemble in aqueous solution from a 12-residue peptide, termed enhancing factor C (EF-C). These artificial nanofibrils enhance retroviral gene transfer substantially more efficiently than semen-derived fibrils or other transduction enhancers. Moreover, EF-C nanofibrils allow the concentration of retroviral vectors by conventional low-speed centrifugation, and are safe and effective, as assessed in an ex vivo gene transfer study. Our results show that EF-C fibrils comprise a highly versatile, convenient and broadly applicable nanomaterial that holds the potential to significantly facilitate retroviral gene transfer in basic research and clinical applications.

Retrovirus-based mRNA transfer for transient cell manipulation

Retrovirus-mediated mRNA transfer (RMT) combines the advantageous features of retrovirus-mediated cell targeting and entry with the controlled transfer of mRNAs. We have recently exploited this strategy for the dose-controlled transfer of recombinases and DNA transposases, avoiding cytotoxicity and potential insertional mutagenesis. Further applications can be envisaged, especially when low expression levels are sufficient to modify cell fate or function. Here we describe a step-by-step protocol for the generation of RMT vector particles, their titration and their application in a model cell line.

Development of defective and persistent Sendai virus vector: a unique gene delivery/expression system ideal for cell reprogramming

The ectopic expression of transcription factors can reprogram differentiated tissue cells into induced pluripotent stem cells. However, this is a slow and inefficient process, depending on the simultaneous delivery of multiple genes encoding essential reprogramming factors and on their sustained expression in target cells. Moreover, once cell reprogramming is accomplished, these exogenous reprogramming factors should be replaced with their endogenous counterparts for establishing autoregulated pluripotency. Complete and designed removal of the exogenous genes from the reprogrammed cells would be an ideal option for satisfying this latter requisite as well as for minimizing the risk of malignant cell transformation. However, no single gene delivery/expression system has ever been equipped with these contradictory characteristics. Here we report the development of a novel replication-defective and persistent Sendai virus (SeVdp) vector based on a noncytopathic variant virus, which fulfills all of these requirements for cell reprogramming. The SeVdp vector could accommodate up to four exogenous genes, deliver them efficiently into various mammalian cells (including primary tissue cells and human hematopoietic stem cells) and express them stably in the cytoplasm at a prefixed balance. Furthermore, interfering with viral transcription/replication using siRNA could erase the genomic RNA of SeVdp vector from the target cells quickly and thoroughly. A SeVdp vector installed with Oct4/Sox2/Klf4/c-Myc could reprogram mouse primary fibroblasts quite efficiently; ∼1% of the cells were reprogrammed to Nanog-positive induced pluripotent stem cells without chromosomal gene integration. Thus, this SeVdp vector has potential as a tool for advanced cell reprogramming and for stem cell research.

Correct mRNA processing at a mutant TT splice donor in FANCC ameliorates the clinical phenotype in patients and is enhanced by delivery of suppressor U1 snRNAs

The U1 small nuclear RNA (U1 snRNA) as a component of the major U2-dependent spliceosome recognizes 5' splice sites (5'ss) containing GT as the canonical dinucleotide in the intronic positions +1 and +2. The c.165+1G>T germline mutation in the 5'ss of exon 2 of the Fanconi anemia C (FANCC) gene commonly predicted to prevent correct splicing was identified in nine FA patients from three pedigrees. RT-PCR analysis of the endogenous FANCC mRNA splicing pattern of patient-derived fibroblasts revealed aberrant mRNA processing, but surprisingly also correct splicing at the TT dinucleotide, albeit with lower efficiency. This consequently resulted in low levels of correctly spliced transcript and minute levels of normal posttranslationally processed FANCD2 protein, indicating that this naturally occurring TT splicing might contribute to the milder clinical manifestations of the disease in these patients. Functional analysis of this FANCC 5'ss within splicing reporters revealed that both the noncanonical TT dinucleotide and the genomic context of FANCC were required for the residual correct splicing at this mutant 5'ss. Finally, use of lentiviral vectors as a delivery system to introduce expression cassettes for TT-adapted U1 snRNAs into primary FANCC patient fibroblasts allowed the correction of the DNA-damage-induced G2 cell-cycle arrest in these cells, thus representing an alternative transcript-targeting approach for genetic therapy of inherited splice-site mutations.

Efficient and stable MGMT-mediated selection of long-term repopulating stem cells in nonhuman primates

HSC transplantation using genetically modified autologous cells is a promising therapeutic strategy for various genetic diseases, cancer, and HIV. However, for many of these conditions, the current efficiency of gene transfer to HSCs is not sufficient for clinical use. The ability to increase the percentage of gene-modified cells following transplantation is critical to overcoming this obstacle. In vivo selection with mutant methylguanine methyltransferase (MGMTP140K) has been proposed to overcome low gene transfer efficiency to HSCs. Previous studies have shown efficient in vivo selection in mice and dogs but only transient selection in primates. Here, we report efficient and stable MGMTP140K-mediated multilineage selection in both macaque and baboon nonhuman primate models. Treatment consisting of both O6-benzylguanine (O6BG) and N,N'-bis(2-chloroethyl)-N-nitroso-urea (BCNU) stably increased the percentage of transgene-expressing cells from a range of initial levels of engrafted genetically modified cells, with the longest follow-up after drug treatment occurring over 2.2 years. Drug treatment was well tolerated, and selection occurred in myeloid, lymphoid, and erythroid cells as well as platelets. Retrovirus integration site analysis before and after drug treatments confirmed the presence of multiple clones. These nonhuman primate studies closely model a clinical setting and should have broad applications for HSC gene therapy targeting human diseases of malignant, genetic, and infectious nature, including HIV.

The influence of semen-derived enhancer of virus infection on the efficiency of retroviral gene transfer

BACKGROUND

An improvement of retroviral infection has been postulated using a naturally occurring fragment of the abundant semen marker prostatic acidic phosphatase. This peptide, termed semen-derived enhancer of virus infection (SEVI), promotes HIV attachment to the target cells.

METHODS

In the present study, we examined whether SEVI would also enhance the infectivity of other viruses with different envelope proteins. We focused on retroviruses pseudotyped with envelopes that are commonly used for the genetic modification of cells, in particular, T cells and hematopoietic progenitor cells. Because the effect of SEVI is considered to be a result of its cationic properties, we compared SEVI with other cationic agents such as protamine sulfate and Polybrene.

RESULTS

We found that SEVI increases the efficiency of gene transfer for lentiviral and gammaretroviral vector constructs pseudotyped with VSV-G, GALV, RD114 or foamy viral envelopes on hematopoietic and nonhematopoietic cell lines. On T cells, the transduction efficiency of GALV and RD114 pseudotyped vectors was significantly increased by SEVI. A significant increase of the gene transfer rate was also detected for foamy virally pseudotyped lentivirus on murine hematopoietic progenitor cells. No toxic effect of SEVI treatment was detected on any cell type tested, including human and murine hematopoietic stem/progenitor cells. When directly comparing the effect of SEVI with Polybrene or protamine sulfate, we show that the semen-derived protein is more efficient in increasing the gene transfer rate.

CONCLUSIONS

SEVI is a promising agent for promoting and improving gene transfer and may also be useful for clinical gene therapy studies.

Germline mutations in breast and ovarian cancer pedigrees establish RAD51C as a human cancer susceptibility gene

Germline mutations in a number of genes involved in the recombinational repair of DNA double-strand breaks are associated with predisposition to breast and ovarian cancer. RAD51C is essential for homologous recombination repair, and a biallelic missense mutation can cause a Fanconi anemia-like phenotype. In index cases from 1,100 German families with gynecological malignancies, we identified six monoallelic pathogenic mutations in RAD51C that confer an increased risk for breast and ovarian cancer. These include two frameshift-causing insertions, two splice-site mutations and two nonfunctional missense mutations. The mutations were found exclusively within 480 pedigrees with the occurrence of both breast and ovarian tumors (BC/OC; 1.3%) and not in 620 pedigrees with breast cancer only or in 2,912 healthy German controls. These results provide the first unambiguous evidence of highly penetrant mutations associated with human cancer in a RAD51 paralog and support the 'common disease, rare allele' hypothesis.

Mutation of the RAD51C gene in a Fanconi anemia-like disorder

Fanconi anemia (FA) is a rare chromosomal-instability disorder associated with a variety of developmental abnormalities, bone marrow failure and predisposition to leukemia and other cancers. We have identified a homozygous missense mutation in the RAD51C gene in a consanguineous family with multiple severe congenital abnormalities characteristic of FA. RAD51C is a member of the RAD51-like gene family involved in homologous recombination-mediated DNA repair. The mutation results in loss of RAD51 focus formation in response to DNA damage and in increased cellular sensitivity to the DNA interstrand cross-linking agent mitomycin C and the topoisomerase-1 inhibitor camptothecin. Thus, biallelic germline mutations in a RAD51 paralog are associated with an FA-like syndrome.

Effect of cell lysates on retroviral transduction efficiency of cells in suspension culture

Recombinant retroviruses are effective vectors able to integrate transgenes into the target cell's genome to achieve longer-term expression. This study investigates the effect of cell lysis products, a common cell culture by-product, on the transduction of suspension cells by gammaretroviral vectors. Cell lysates derived from human and murine suspension cell lines significantly increased the transduction of human TF-1 and K-562 cell lines by gibbon ape leukemia virus-pseudotyped retroviral vectors without altering tropism. The transduction efficiency of TF-1 cells increased as a function of lysate concentration and decreased with increasing target cell concentrations. This was adequately predicted using a saturation equation based on the lysed-to-target cell concentration ratio, R, where: Fold increase = 1+Fold_(Max) (R/(K_(L)+R)). Lysate completely masked the effects of fibronectin when the two were added in combination. With protamine sulfate, the transduction efficiency was increased by lysate to 58% from 20% for protamine sulfate alone. Overall, the presence of cell lysate significantly influenced the outcome of the transduction process, either alone or in the presence of protamine sulfate or fibronectin.

Kinetics and effect of integrin expression on human CD34(+) cells during murine leukemia virus-derived retroviral transduction with recombinant fibronectin for stem cell gene therapy

The CH-296 recombinant fragment of human fibronectin is essential for murine leukemia virus (MLV)-derived retroviral transduction of CD34(+) cells for the purpose of stem cell gene therapy. Although the major effect of CH-296 is colocalization of the MLV-derived retrovirus and target cells at specific adhesion domains of CH-296 mediated by integrins expressed on CD34(+) cells, the precise roles of the integrins are unclear. We examined the kinetics of integrin expression on CD34(+) cells during the course of MLV-derived retrovirus-mediated gene transduction with CH-296. Flow cytometry revealed that the levels of both very late activation protein (VLA)-4 and VLA-5 on CD34(+) cells freshly isolated from cord blood were insufficient for effective MLV-derived retroviral transduction. However, increases were achieved during culture for preinduction and MLV-derived retrovirus-mediated gene transduction in the presence of a cocktail of cytokines. In addition, we confirmed by using specific antibodies that inhibition of the cell adhesion mediated by the integrins significantly reduced transduction efficiency, indicating that integrin expression is indeed important for CH-296-based MLV-derived retroviral transduction. Only a few cytokines are capable of inducing integrin expression, and stem cell factor plus thrombopoietin was found to be the minimal combination that was sufficient for effective transduction of an MLV-derived retrovirus based on CH-296. Our findings should be useful for improving the culture conditions for CH-296-based MLV-derived retroviral transduction in stem cell gene therapy.

Development of gene therapy: potential in severe combined immunodeficiency due to adenosine deaminase deficiency

The history of stem cell gene therapy is strongly linked to the development of gene therapy for severe combined immunodeficiencies (SCID) and especially adenosine deaminase (ADA)-deficient SCID. Here we discuss the developments achieved in over two decades of clinical and laboratory research that led to the establishment of a protocol for the autologous transplant of retroviral vector-mediated gene-modified hematopoietic stem cells, which has proved to be both successful and, to date, safe. Patients in trials in three different countries have shown long-term immunological and metabolic correction. Nevertheless, improvements to the safety profile of viral vectors are underway and will undoubtedly reinforce the position of stem cell gene therapy as a treatment option for ADA-SCID.

Transfection of myeloid leukaemia cell lines is distinctively regulated by fibronectin substratum

Gene transfer into haematopoietic cells is a challenging approach. The extracellular matrix component fibronectin has been known to modulate the cell cycle dynamics, viability and differentiation of leukaemia cells. Thus, our aim was to investigate the influence of fibronectin substratum on the liposomal transfection of myeloid leukaemia cell lines. Liposomal transfection was performed with K562 and HL-60 as representative lines of transfection-competent and -incompetent myeloid leukaemia cells, respectively. Flow cytometry analyses were performed to determine transfection efficiency monitored by green fluorescent protein (GFP) expression and to assess cell viability and cell cycle status. Quantitation of GFP gene expression and DNA uptake was assayed by real time PCR. The current data showed that the adhesion to fibronectin deteriorated the transfection of K562 cells. In contrary, it enhanced the delivery of plasmid DNA into HL-60 cells. Correspondingly, the adhesion to fibronectin influenced the transfection efficiency mainly by modulating the intracellular presence of plasmid DNA. The cell cycle and viability which is regulated by fibronectin had a minor impact on the success of gene delivery. This phenomenon may be considered as an important factor which may modulate the potential gene transfer approaches for myeloid leukaemia.

The evolution of gene therapy in X-linked severe combined immunodeficiency

OBJECTIVES

To review the evolution of gene therapy in infants with X-linked severe combined immunodeficiency (XL-SCID) and to evaluate the current challenges facing this evolving field.

DATA SOURCES

The MEDLINE, OVID, CINAHL, and HealthSTAR databases were searched to identify pertinent articles using the following keywords: gene therapy, XL-SCID, bone marrow transplant, and viral vectors.

STUDY SELECTION

Journal articles were selected for their relevance to human gene therapy in patients with XL-SCID.

RESULTS

Gene therapy with a retrovirus-derived vector has been used to treat 20 patients with XL-SCID internationally. Although most patients derived improvements in T- and B-cell immune numbers and function, severe adverse effects have occurred. After gene therapy, 5 of the 20 patients developed leukemia. This outcome has been associated with insertion of the corrected gene near the T-cell proto-oncogene LMO2. One of the 5 patients subsequently died.

CONCLUSIONS

Within the past decade, effective improvements in vectorology and cell culture conditions have resulted in clinical success in some infants with SCID and have revived interest after many years of setbacks. However, clinical success and significant adverse events have been reported in patients with XL-SCID who have undergone gene therapy using a retroviral vector. As extensive research into improving safety through vector development and monitoring of gene therapy continues, further progress in gene therapy development can be anticipated.

Chemoprotection by transfer of resistance genes

Dose-limiting toxicity of chemotherapeutic agents, i.e., myelosuppression, can limit their effectiveness. The transfer and expression of drug-resistance genes might decrease the risks associated with acute hematopoietic toxicity. Protection of hematopoietic stem/progenitor cells by transfer of drug-resistance genes provides the possibility of intensification or escalation of antitumor drug doses and consequently an improved therapeutic index. This chapter reviews drug-resistance gene transfer strategies for either myeloprotection or therapeutic gene selection. Selecting candidate drug-resistance gene(s), gene transfer methodology, evaluating the safety and the efficiency of the treatment strategy, relevant in vivo models, and oncoretroviral transduction of human hematopoietic stem/progenitor cells under clinically applicable conditions are described.

Genetic modification of human hematopoietic cells: preclinical optimization of oncoretroviral-mediated gene transfer for clinical trials

This chapter provides information about the oncoretroviral transduction of human hematopoietic stem/ progenitor cells under clinically applicable conditions. We describe in detail a short -60 h transduction protocol which consistently yields transduction efficiencies in the range of 30-50% with five different oncoretroviral vectors. We discuss a number of parameters that affect transduction efficiency, including the oncoretroviral vector characteristics, the vector stock collection, the source of CD34+ cells and transduction conditions.

Murine hematopoietic stem cell transduction using retroviral vectors

Hematopoietic stem cells (HSCs) represent an important target cell population in bone marrow transplantation and gene therapy applications. Their progeny cells carry the genetic information of the HSCs and replenish the blood and immune system. Therefore, in the setting of inherited diseases, transduction of HSCs with retroviral vectors (including gammaretro- and lentiviral vectors) offers the possibility to correct the phenotype in all blood lineages as demonstrated in clinical trials for immunodeficiencies (e.g., X-SCID). In the process of developing gene therapy strategies for patient applications, suitable mouse models for the human gene therapy are important to validate the concept. Stem-cell-enriched populations such as lineage negative cells as the functional equivalent of human CD34(+) cells can be isolated from murine bone marrow and efficiently transduced using retroviral vectors. This chapter provides a step-by-step protocol for retroviral transduction of murine lineage negative cells.

Overnight transduction with foamyviral vectors restores the long-term repopulating activity of Fancc-/- stem cells

Fanconi anemia (FA) is a complex genetic disorder characterized by congenital abnormalities, bone marrow failure, and myeloid malignancies. Identification of 13 FA genes has been instrumental to explore gene transfer technologies aimed at correction of autologous FA-deficient stem cells. To date, 3 human FA stem cell gene therapy trials with standard 4-day transduction protocols using gammaretroviral vectors failed to provide clinical benefit. In addition, 2- to 4 day ex vivo manipulation of bone marrow from mice containing a disruption of the homologue of human FANCC (Fancc) results in a time-dependent increase in apoptosis and a risk for malignant transformation of hematopoietic cells. Here, we show that a 14-hour transduction period allows a foamyviral vector construct expressing the human FANCC cDNA to efficiently transduce murine FA stem cells with 1 to 2 proviral integrations per genome. Functionally, the repopulating activity of Fancc(-/-) stem cells from reconstituted mice expressing the recombinant FANCC transgene was comparable with wild-type controls. Collectively, these data provide evidence that short-term transduction of c-kit(+) cells with a foamyviral vector is sufficient for functional correction of a stem cell phenotype in a murine FA model. These data could have implications for future gene therapy trials for FA patients.

Human hematopoietic cell culture, transduction, and analyses

This unit provides methods for introducing genes into human hematopoietic progenitor cells. The Basic Protocol describes isolation of CD34(+) cells, transduction of these cells with a retroviral vector on fibronectin-coated plates, assaying the efficiency of transduction, and establishing long-term cultures. Support protocols describe methods for maintenance of vector-producing fibroblasts (VPF) and supernatant collection from these cells, screening medium components for the ability to support hematopoietic cell growth, and establishing colonies from long-term cultures. Other protocols provide PCR-based methods to analyze individual colonies for transduction, methods to analyze cells harvested from long-term cultures, and procedures for freezing and thawing of hematopoietic cells.

Transduction of primary hematopoietic cells by retroviral vectors

INTRODUCTIONNoncycling cells are relatively resistant to transduction with retroviral vectors. Because most immortalized cell lines are actively proliferating, this is not an issue. However, for many primary cells, especially quiescent populations such as primitive progenitor and stem cells, the gene-transfer rate can be particularly low. This protocol describes transduction of primary hematopoietic cells. Two interventions are combined to maximize gene transfer in hematopoietic progenitor cells: (1) cytokines and other growth factors are used to stimulate cell cycling in hematopoietic cells, and (2) matrix proteins such as fibronectin are used to mediate colocalization of target cells and vector.

Stem cell collection and gene transfer in Fanconi anemia

Fanconi anemia (FA) is a rare genetic syndrome characterized by progressive bone marrow failure (BMF), congenital anomalies, and a predisposition to malignancy. Successful gene transfer into hematopoietic stem cells (HSCs) could reverse BMF in this disease. We developed clinical trials to determine whether a sufficient number of CD34(+) stem cells could be collected for gene modification and to evaluate the safety and efficacy of HSC-corrective gene transfer in FA genotype A (FANCA) patients. Here, we report that FA patients have significant depletion of their BM CD34(+) cell compartment even before severe pancytopenia is present. However, oncoretroviral-mediated ex vivo gene transfer was efficient in clinical scale in FA-A cells, leading to reversal of the cellular phenotype in a significant percentage of CD34(+) cells. Re-infusion of gene-corrected products in two patients was safe and well tolerated and accompanied by transient improvements in hemoglobin and platelet counts. Gene correction was transient, likely owing to the low dose of gene-corrected cells infused. Our early experience shows that stem cell collection is well tolerated in FA patients and suggests that collection be considered as early as possible in patients who are potential candidates for future gene transfer trials.

Generation of HIV-1-based lentiviral vector particles

This unit presents protocols outlining the methodology and techniques involved in the construction and application of HIV-1-based lentiviral vector systems. Also described are procedures that can be used to concentrate and purify high-titer recombinant lentiviral vector preparations, as well as protocols for transduction of adherent and suspension cells.

Fluorophore-conjugated iron oxide nanoparticle labeling and analysis of engrafting human hematopoietic stem cells

The use of nanometer-sized iron oxide particles combined with molecular imaging techniques enables dynamic studies of homing and trafficking of human hematopoietic stem cells (HSC). Identifying clinically applicable strategies for loading nanoparticles into primitive HSC requires strictly defined culture conditions to maintain viability without inducing terminal differentiation. In the current study, fluorescent molecules were covalently linked to dextran-coated iron oxide nanoparticles (Feridex) to characterize human HSC labeling to monitor the engraftment process. Conjugating fluorophores to the dextran coat for fluorescence-activated cell sorting purification eliminated spurious signals from nonsequestered nanoparticle contaminants. A short-term defined incubation strategy was developed that allowed efficient labeling of both quiescent and cycling HSC, with no discernable toxicity in vitro or in vivo. Transplantation of purified primary human cord blood lineage-depleted and CD34(+) cells into immunodeficient mice allowed detection of labeled human HSC in the recipient bones. Flow cytometry was used to precisely quantitate the cell populations that had sequestered the nanoparticles and to follow their fate post-transplantation. Flow cytometry endpoint analysis confirmed the presence of nanoparticle-labeled human stem cells in the marrow. The use of fluorophore-labeled iron oxide nanoparticles for fluorescence imaging in combination with flow cytometry allows evaluation of labeling efficiencies and homing capabilities of defined human HSC subsets.

Biomaterial-mediated retroviral gene transfer using self-assembled monolayers

Biomaterial-mediated gene delivery has recently emerged as a promising alternative to conventional gene transfer technologies that focus on direct delivery of viral vectors or DNA-polymer/matrix complexes. However, biomaterial-based strategies have primarily targeted transient gene expression vehicles, including plasmid DNA and adenovirus particles. This study expands on this work by characterizing biomaterial properties conducive to the surface immobilization of retroviral particles and subsequent transduction of mammalian cells at the cell-material interface. Self-assembled monolayers (SAMs) of functionally-terminated alkanethiols on gold were used to establish biomaterial surfaces of defined chemical composition. Gene transfer was observed to be greater than 90% on NH(2)-terminated surfaces, approximately 50% on COOH-functionalized surfaces, and undetectable on CH(3)-terminated SAMs, similar to controls of tissue culture-treated polystyrene. Gene delivery via the NH(2)-SAM was further characterized as a function of retrovirus coating time, virus concentration, and cell seeding density. Finally, SAM-mediated gene delivery was comparable to fibronectin- and poly-l-lysine-based methods for gene transfer. This work is significant to establishing safe and effective gene therapy strategies, developing efficient methods for gene delivery, and supporting recent progress in the field of biomaterial-mediated gene transfer.

Hypomorphic mutations in the gene encoding a key Fanconi anemia protein, FANCD2, sustain a significant group of FA-D2 patients with severe phenotype

FANCD2 is an evolutionarily conserved Fanconi anemia (FA) gene that plays a key role in DNA double-strand-type damage responses. Using complementation assays and immunoblotting, a consortium of American and European groups assigned 29 patients with FA from 23 families and 4 additional unrelated patients to complementation group FA-D2. This amounts to 3%-6% of FA-affected patients registered in various data sets. Malformations are frequent in FA-D2 patients, and hematological manifestations appear earlier and progress more rapidly when compared with all other patients combined (FA-non-D2) in the International Fanconi Anemia Registry. FANCD2 is flanked by two pseudogenes. Mutation analysis revealed the expected total of 66 mutated alleles, 34 of which result in aberrant splicing patterns. Many mutations are recurrent and have ethnic associations and shared allelic haplotypes. There were no biallelic null mutations; residual FANCD2 protein of both isotypes was observed in all available patient cell lines. These analyses suggest that, unlike the knockout mouse model, total absence of FANCD2 does not exist in FA-D2 patients, because of constraints on viable combinations of FANCD2 mutations. Although hypomorphic mutations arie involved, clinically, these patients have a relatively severe form of FA.

Evaluation of different protocols for gene transfer into non-obese diabetes/severe combined immunodeficiency disease mouse repopulating cells

PURPOSE

Although gene transfer with retroviral vectors has shown distinct clinical success in defined settings, efficient genetic manipulation of hematopoietic progenitor cells remains a challenge. To address this issue we have evaluated different transduction protocols and retroviral constructs in the non-obese diabetes (NOD)/severe combined immunodeficiency disease (SCID) xenograft model.

METHODS

An extended transduction protocol requiring 144 h of in vitro manipulation was compared to a more conventional protocol requiring 96 h only.

RESULT

While pretransplantation analysis of cells transduced with a retroviral vector, expressing the enhanced green fluorescent protein (EGFP) marker gene, demonstrated significantly higher overall transduction rates for the extended protocol (33.6 +/- 2.3 vs. 22.1 +/- 3.8%), EGFP expression in CD34+ cells before transplantation (4.0 +/- 0.9 vs. 11.6 +/- 2.5%), engraftment of human cells in NOD/SCID bone marrow 4 weeks after transplantation (4.5 +/- 1.7 vs. 36.5 +/- 9.4%) and EGFP expression in these cells (0 +/- 0 vs. 11.3 +/- 2.8%) were significantly impaired. When the 96 h protocol was used in combination with the spleen focus forming virus (SFFV)/murine embryonic stem cell (MESV) hybrid vector SFbeta11-EGFP, high transduction rates for CD45+ (41.0 +/- 5.3%) and CD34+ (38.5 +/- 3.7%) cells prior to transplantation, as well as efficient human cell engraftment in NOD/SCID mice 4 weeks after transplantation (32.4 +/- 3.5%), was detected. Transgene expression was observed in B-lymphoid (15.9 +/- 2.0%), myeloid (36.5 +/- 3.5%) and CD34+ cells (10.1 +/- 1.5%).

CONCLUSION

Our data show that CD34+ cells maintained in cytokines for multiple days may differentiate and loose their capacity to contribute to the haematological reconstitution of NOD/SCID mice. In addition, the SFFV/MESV hybrid vector SFbeta11-EGFP allows efficient transduction of and gene expression in haematopoietic progenitor cells.

Gene-modified tissue-engineered skin: the next generation of skin substitutes

Tissue engineering combines the principles of cell biology, engineering and materials science to develop three-dimensional tissues to replace or restore tissue function. Tissue engineered skin is one of most advanced tissue constructs, yet it lacks several important functions including those provided by hair follicles, sebaceous glands, sweat glands and dendritic cells. Although the complexity of skin may be difficult to recapitulate entirely, new or improved functions can be provided by genetic modification of the cells that make up the tissues. Gene therapy can also be used in wound healing to promote tissue regeneration or prevent healing abnormalities such as formation of scars and keloids. Finally, gene-enhanced skin substitutes have great potential as cell-based devices to deliver therapeutics locally or systemically. Although significant progress has been made in the development of gene transfer technologies, several challenges have to be met before clinical application of genetically modified skin tissue. Engineering challenges include methods for improved efficiency and targeted gene delivery; efficient gene transfer to the stem cells that constantly regenerate the dynamic epidermal tissue; and development of novel biomaterials for controlled gene delivery. In addition, advances in regulatable vectors to achieve spatially and temporally controlled gene expression by physiological or exogenous signals may facilitate pharmacological administration of therapeutics through genetically engineered skin. Gene modified skin substitutes are also employed as biological models to understand tissue development or disease progression in a realistic three-dimensional context. In summary, gene therapy has the potential to generate the next generation of skin substitutes with enhanced capacity for treatment of burns, chronic wounds and even systemic diseases.