Retrovirus-mediated gene transfer into T cells: 95% transduction efficiency without further in vitro selection

Split genome-based retroviral replicating vectors achieve efficient gene delivery and therapeutic effect in a human glioblastoma xenograft model

The murine leukemia virus-based semi-retroviral replicating vectors (MuLV-based sRRV) had been developed to improve safety and transgene capacity for cancer gene therapy. However, despite the apparent advantages of the sRRV, improvements in the in vivo transduction efficiency are still required to deliver therapeutic genes efficiently for clinical use. In this study, we established a gibbon ape leukemia virus (GaLV) envelopepseudotyped semi-replication-competent retrovirus vector system (spRRV) which is composed of two transcomplementing replication-defective retroviral vectors termed MuLV-Gag-Pol and GaLV-Env. We found that the spRRV shows considerable improvement in efficiencies of gene transfer and spreading in both human glioblastoma cells and pre-established human glioblastoma mouse model compared with an sRRV system. When treated with ganciclovir after intratumoral injection of each vector system into pre-established U-87 MG glioblastomas, the group of mice injected with spRRV expressing the herpes simplex virus type 1-thymidine kinase (HSV1-tk) gene showed a survival rate of 100% for more than 150 days, but all control groups of mice (HSV1-tk/PBS-treated and GFP/GCV-treated groups) died within 45 days after tumor injection. In conclusion, these findings sug-gest that intratumoral delivery of the HSV1-tk gene by the spRRV system is worthy of development in clinical trials for the treatment of malignant solid tumors. [BMB Reports 2022; 55(12): 615-620].

Chimeric antigen receptors for T-cell based therapy

The Chimeric Antigen Receptor (CAR) consists of an antibody-derived targeting domain fused with T-cell signaling domains that, when expressed by a T-cell, endows the T-cell with antigen specificity determined by the targeting domain of the CAR. CARs can potentially redirect the effector functions of a T-cell towards any protein and nonprotein target expressed on the cell surface as long as an antibody or similar targeting domain is available. This strategy thereby avoids the requirement of antigen processing and presentation by the target cell and is applicable to nonclassical T-cell targets like carbohydrates. This circumvention of HLA-restriction means that the CAR T-cell approach can be used as a generic tool broadening the potential of applicability of adoptive T-cell therapy. Proof-of-principle studies focusing upon the investigation of the potency of CAR T-cells have primarily focused upon the genetic modification of human and mouse T-cells for therapy. This chapter focuses upon methods to modify T-cells from both species to generate CAR T-cells for functional testing.

Reduced cell death, invasive and angiogenic features conferred by BRCA1-deficiency in mammary epithelial cells transformed with H-Ras

To investigate the role of tumor suppressors BRCA1 and p53 proteins in human breast tumorigenesis, we transformed immortalized human mammary epithelial cells, MCF10A, with or without BRCA1/p53 gene-specific knockdowns. Stable knockdown of BRCA1 alone in MCF10A cells led to centrosome amplification, impaired p53 protein stability, increased sensitivity towards DNA-damaging agents, defective chromosomal condensation at mitosis and elevated protein levels of cyclin D1 and c-myc. While over-expression of mutant H-Ras transformed MCF10A cells, depletion of BRCA1 dramatically enhanced the in vivo tumorigenesis that was associated with higher levels of VEGF, enhanced vascularization and less apoptosis in the BRCA1-deficient Ras-transformed tumors. The Ras-transformed BRCA1-deficient tumors exhibited features of the epithelial-to-mesenchymal transition, appeared to secrete matrix metalloproteases as visualized by in vivo bio-imaging of tumors using fluorescent probe MMP680, and were locally metastatic to lymph nodes. Our results suggest that loss of BRCA1 function may contribute to the aggressiveness of Ras-MAPK driven human breast cancer with associated increase in levels of cyclin D1 and c-myc, enhanced MAPK activity, angiogenic potential & invasiveness. This mammary xenograft tumor model may be useful as a tool to understand human breast tumor angiogenesis and metastasis, as well as to test candidate therapeutics.

Loss of T cell-mediated antitumor immunity after construct-specific downregulation of retrovirally encoded T-cell receptor expression in vivo

Adoptive T-cell therapy is clinically efficacious in the treatment of select cancers. However, it is often difficult to obtain adequate numbers of tumor-specific T cells for therapy. One method for overcoming this limitation is to generate tumor-specific T cells by retrovirally mediated T-cell-receptor (TCR) gene transfer. However, despite instances of therapeutic success, major obstacles remain, including attaining the survival of retrovirally modified T cells in vivo as well as inducing long-term and multi-gene retroviral expression. Using a murine model of adoptively transferred retrovirally modified CD8(+) T cells, where antitumor immunity was dependent on sustained, multigene expression, we found that in vitro assays are poor indicators of in vivo efficacy. Despite persisting for over 9 months in a nonlymphopenic environment, genetically modified T cells exhibited discordant retrovirally mediated gene expression in vivo not readily evident from initial in vitro assays. In particular, one of the two TCR subunit genes necessary for antigen specificity was selectively lost in vivo. As this discordant gene expression was associated with the loss of antitumor immunity, consideration of these findings may provide guidance in the design, evaluation and application of retroviral vectors for use in the treatment of cancer and other human disease.

Retroviral gene transfer into primary human natural killer cells

Modulation of intracellular signaling pathways or receptor expression in natural killer (NK) cells by genetic manipulation is an attractive possibility in studies of NK cell specificity and function. Moreover, feasible applications of these genetic manipulations in the context of gene and NK cell therapy regimens may be considered. However, efficient gene modification of primary NK cells has been largely hampered by the absence of an efficient gene-transfer protocol.A retrovirus-based easy-to-use transduction protocol that can insert the gene of interest permanently into primary NK cells would be an important tool to advance our studies in NK cell biology and NK cell-mediated therapies. We have recently described a protocol for efficient expansion of NK cells under good manufacturing practice (GMP) conditions from the healthy donors and from patients with hematological malignancies. As the active division of cells is a prerequisite for efficient retroviral insertion, the high rate of expansion in this protocol provides more efficient transduction by retroviral vectors. We hereby present this simple and efficient retroviral vector-based gene-transfer protocol for such ex vivo cultured primary human NK cells.

Immunotherapy for gastrointestinal cancer: current status and strategies for improving efficacy

BACKGROUND

Despite improvement in conventional strategies for treating gastrointestinal (GI) carcinoma, large numbers of patients still suffer from incurable or progressive disease.

OBJECTIVE

Here we consider the prospects for circumventing limitations and maximising the efficacy of different immunotherapies.

METHODS

We summarise different cancer vaccines and targeted drugs and highlight the scientific rationale of using immunotherapy for targeting GI cancers, in addition to the potential strategies for improving immunotherapeutic efficacy.

RESULTS/CONCLUSION

Many cancer vaccines and antibody-directed therapies have been tested in early phase clinical trials and demonstrated proof of concept and safety. As yet few have been properly evaluated for clinical efficacy; although adoptive transfer of tumour-associated-antigen-specific T cells has shown dramatic clinical responses in some patients. The recognition of a role for T regulatory cells in limiting anti-tumour immunity has provided momentum for developing strategies to over-ride such immunoinhibitory effects. There is some evidence that conventional therapies may work by influencing these negative factors and allowing expression of immune control mechanisms. An important developing area for clinical evaluation is the testing of combined conventional and immunotherapeutic modalities which may provide for synergy; thereby circumventing the limitations of individualised treatments and generating additional clinical benefits.

Multifactorial optimization of gammaretroviral gene transfer into human T lymphocytes for clinical application

The ability to genetically modify human T cells to target tumor antigens through retroviral gene transfer constitutes a potentially powerful approach to cancer immunotherapy. However, low transduction efficiencies may hamper the efficacy of such therapeutic strategies in the clinical setting. Most commonly, gammaretroviral gene transfer into T cells is conducted through spinoculation, that is, centrifugation of retroviral particles and T cells on RetroNectin-coated non-tissue culture vessels. Here we present data investigating the impact of temperature, speed, and frequency of spinoculation on T cell transduction efficiencies. We found that all three variables independently impacted gene transfer, with increasing temperature, speed, and frequency of spinoculation all enhancing the transduction of T cells. These improved conditions were additive, with the greatest proportion of transduced T cells being generated at the highest tested temperature and speed, after daily spinoculation for 2 to 3 days. Under these conditions, enhanced gene transfer was observed in T cells derived from healthy donors, using research-grade vector stocks. Whereas both RetroNectin and spinoculation were critical to optimal gene transduction, preloading of gammaretroviral particles before spinoculation did not enhance gene transfer. Significantly, application of these enhanced transduction conditions to T cells derived from previously treated patients with chronic lymphocytic leukemia allowed for adequate gene transfer under both small-scale and large-scale clinically applicable conditions using either preclinical or current Good Manufacturing Practice-grade gammaretroviral vector stocks.

OuaSelect, a novel ouabain-resistant human marker gene that allows efficient cell selection within 48 h

Efficient selection of gene-modified cells is required for a number of potential gene therapy applications, as well as molecular biology studies. Ideally, a clinical selection regimen would combine high selection speed, efficiency and efficacy, in addition to clinical grade selection techniques and low immunogenicity. To our knowledge, a selection marker satisfying all these features is so far not available. Ouabain is a clinically used cardiac glycoside and selective Na(+)/K(+)-ATPase inhibitor. On the basis of the high sensitivity of human Na(+)/K(+)-ATPase proteins to ouabain, and rapid killing of cells upon exposure, we have screened the ubiquitously expressed Na(+)/K(+)-ATPase alpha1 subunit for mutations that could greatly increase its resistance to ouabain. Two amino-acid substitutions, Q118R and N129D were sufficient to confer a two log greater resistance to ouabain in HeLa, Jurkat, U2OS cells and in primary cells. Furthermore, following transduction of primary lymphocytes with the alpha1(Q118R/N129D) gene, >99% pure populations of gene-modified cells were achieved with a recovery rate of >80% after 48 h of exposure to ouabain. These results identify the human alpha1(Q118R/N129D) (OuaSelect) as a promising selection marker gene for safe, rapid and cost-effective selection in clinical gene therapy and molecular biology research.

Adaptive evolution of a tagged chimeric gammaretrovirus: identification of novel cis-acting elements that modulate splicing

Retroviruses are well known for their ability to incorporate envelope (Env) proteins from other retroviral strains and genera, and even from other virus families. This characteristic has been widely exploited for the generation of replication-defective retroviral vectors, including those derived from murine leukemia virus (MLV), bearing heterologous Env proteins. We investigated the possibility of "genetically pseudotyping" replication-competent MLV by replacing the native env gene in a full-length viral genome with that of another gammaretrovirus. Earlier, we developed replication-competent versions of MLV that stably transmit and express transgenes inserted into the 3' untranslated region of the viral genome. In one such tagged MLV expressing green fluorescent protein, we replaced the native env sequence with that of gibbon ape leukemia virus (GALV). Although the GALV Env protein is commonly used to make high-titer pseudotypes of MLV vectors, we found that the env replacement greatly attenuated viral replication. However, extended cultivation of cells exposed to the chimeric virus resulted in selection of mutants exhibiting rapid replication kinetics and different variants arose in different infections. Two of these variants had acquired mutations at or adjacent to the splice acceptor site, and three others had acquired dual mutations within the long terminal repeat. Analysis of the levels of unspliced and spliced viral RNA produced by the parental and adapted viruses showed that the mutations gained by each of these variants functioned to reverse an imbalance in splicing caused by the env gene substitution. Our results reveal the presence of previously unknown cis-acting sequences in MLV that modulate splicing of the viral transcript and demonstrate that tagging of the retroviral genome with an easily assayed transgene can be combined with in vitro evolution as an approach to efficiently generating and screening for replicating mutants of replication-impaired recombinant viruses.

Tumorigenic conversion of primary human esophageal epithelial cells using oncogene combinations in the absence of exogenous Ras

To investigate pathways of human esophageal squamous cell transformation, we generated esophageal tumor cells using human telomerase- and SV40-immortalized primary esophageal epithelial cells (EPC2) by overexpression of selected combinations of oncogenes. H-Ras, c-Myc, or Akt, but not epidermal growth factor receptor (EGFR), induced transformed colonies in soft agar. By contrast, bioluminescence imaging of genetically altered immortalized esophageal cells revealed that Akt, EGFR, or H-Ras, but not c-Myc, resulted in tumor formation in immunodeficient mice. H-Ras-driven tumors showed highly tumorigenic phenotypes with 2.6 +/- 0.6 days for doubling, whereas Akt and EGFR tumors doubled every 9.5 +/- 1.6 and 6.1 +/- 1.2 days, respectively. H-Ras-driven tumors expressed the hypoxia-inducible factor target Glut1, whereas Akt- or EGFR-driven tumors had evidence of angiogenesis and no detectable Glut1 expression. Proliferation rates among these tumors were similar, but there was reduced apoptosis in the more aggressive H-Ras-driven tumors that also developed aneuploidy and multiple centrosomes. c-Myc overexpression did not result in tumorigenic conversion but introduction of Bcl-XL into c-Myc-expressing cells generated tumors. Although cytokeratin expression was typical of squamous carcinoma, gene expression profiling was done to compare the four different types of engineered tumors with human esophageal squamous cell carcinomas and adenocarcinomas. Interestingly, c-Myc plus Bcl-XL transformants mimicked squamous carcinomas, whereas H-Ras-, EGFR-, and Akt-driven tumors were similar to adenocarcinomas in their molecular profiles. These genetically engineered models may provide new platforms for understanding human esophagus cancer and may assist in the evaluation of new therapies.

A self-inactivating retrovector incorporating the IL-2 promoter for activation-induced transgene expression in genetically engineered T-cells

Background

T-cell activation leads to signaling pathways that ultimately result in induction of gene transcription from the interleukin-2 (IL-2) promoter. We hypothesized that the IL-2 promoter or its synthetic derivatives can lead to T-cell specific, activation-induced transgene expression. Our objective was to develop a retroviral vector for stable and activation-induced transgene expression in T-lymphocytes.

Results

First, we compared the transcriptional potency of the full-length IL-2 promoter with that of a synthetic promoter composed of 3 repeats of the Nuclear Factor of Activated T-Cells (NFAT) element following activation of transfected Jurkat T-cells expressing the large SV40 T antigen (Jurkat TAg). Although the NFAT3 promoter resulted in a stronger induction of luciferase reporter expression post stimulation, the basal levels of the IL-2 promoter-driven reporter expression were much lower indicating that the IL-2 promoter can serve as a more stringent activation-dependent promoter in T-cells. Based on this data, we generated a self-inactivating retroviral vector with the full-length human IL-2 promoter, namely SINIL-2pr that incorporated the enhanced green fluorescent protein (EGFP) fused to herpes simplex virus thymidine kinase as a reporter/suicide "bifunctional" gene. Subsequently, Vesicular Stomatitis Virus-G Protein pseudotyped retroparticles were generated for SINIL-2pr and used to transduce the Jurkat T-cell line and the ZAP-70-deficient P116 cell line. Flow cytometry analysis showed that EGFP expression was markedly enhanced post co-stimulation of the gene-modified cells with 1 μM ionomycin and 10 ng/ml phorbol 12-myristate 13-acetate (PMA). This activation-induced expression was abrogated when the cells were pretreated with 300 nM cyclosporin A.

Conclusion

These results demonstrate that the SINIL-2pr retrovector leads to activation-inducible transgene expression in Jurkat T-cell lines. We propose that this design can be potentially exploited in several cellular immunotherapy applications.

RhoH GTPase recruits and activates Zap70 required for T cell receptor signaling and thymocyte development

RhoH is a hematopoietic-specific, GTPase-deficient member of the Rho GTPase family with unknown physiological function. Here we demonstrate that Rhoh-/- mice have impaired T cell receptor (TCR)-mediated thymocyte selection and maturation, resulting in T cell deficiency. RhoH deficiency resulted in defective CD3zeta phosphorylation, impaired translocation of the signaling molecule Zap70 to the immunological synapse and reduced activation of Zap70-mediated signaling in thymic and peripheral T cells. Proteomic analyses demonstrated that RhoH is a component of TCR signaling and is required for recruitment of Zap70 to the TCR through interaction with RhoH noncanonical immunoreceptor tyrosine-based activation motifs (ITAMs). In vivo reconstitution studies also demonstrated that RhoH function depends on phosphorylation of the RhoH ITAMs. These findings suggest that RhoH is a critical regulator of thymocyte development and TCR signaling by mediating recruitment and activation of Zap70.

Efficient gene transfer into primary human natural killer cells by retroviral transduction

OBJECTIVE

To optimize retroviral gene transfer into primary human natural killer (NK) cells.

MATERIALS AND METHODS

NK cells from healthy donors were expanded ex vivo for a period of 21 days. Retroviral transductions were carried out by replacing culture media with retrovirus-containing supernatant during 2-hour incubations on days 3, 4, 5, 6, 10, 15, or 20. In some experiments, NK cells were transduced on 2 consecutive days (days 5 and 6). Green fluorescent protein served as a marker for detection of transduced cells.

RESULTS

NK cells showed a median of 27.2% transduction efficiency after a single transduction round (transduction on day 5) and a median of 47.1% transduction efficiency after two rounds of transduction (transduction on days 5 and 6), 24 hours after exposure to retrovirus-containing supernatants. On day 21 after initial culture, 51.9% of NK cells were transduced after a single transduction round (transduction on day 5) and 75.4% after two rounds of transduction (transduction on days 5 and 6). Gene transfer did not change the function or phenotype of NK cells as determined by phenotypical analysis, nor did the proliferative ability or cytotoxic function change.

CONCLUSION

The results show that NK cells can successfully be transduced with retroviral vectors, without any detectable changes in phenotype or function. This may open up new possibilities in the studies of NK cell biology and the development of NK cells for immunotherapy regimens.

Initial depletion of regulatory T cells: the missing solution to preserve the immune functions of T lymphocytes designed for cell therapy

We investigated the causes of the altered functionality of T cells cultured under conditions designed for cell and gene therapy and the strategies to prevent their defects. We first showed that human T cells cultured for 6 days with anti-CD3 ± anti-CD28 antibodies and interleukin-2 presented a 50% decrease of their proliferative responses to allogeneic or recall antigens. Similarly, day-6 cultured murine T cells completely lost their capacity to reject allogeneic skin grafts and to provoke graft-versus-host disease (GVHD) when infused into irradiated semi-allogeneic mice. Interestingly, injection of higher amounts of cultured T cells restored GVHD induction. Moreover, depletion of CD25+ cells prior to T-cell cultures can prevent these deficiencies both in mice and humans. Therefore, we demonstrated that culture conditions used for T-cell therapy preferentially activated and expanded regulatory T cells (Treg's). Thus, we showed that dividing cells sorted from T-cell cultures strongly suppressed the proliferation of autologous T cells in response to allogeneic stimulation. An increased detection of Foxp3 at mRNA and protein levels in the cultures confirmed the Treg expansion. Overall, we demonstrate that T-cell cultures promote Treg expansion over effector T cells, leading to deleterious immune functions, and that this imbalance can be prevented by an initial depletion of CD25+ cells.

Engineering T cells for cancer therapy

It is generally accepted that the immune system plays an important role in controlling tumour development. However, the interplay between tumour and immune system is complex, as demonstrated by the fact that tumours can successfully establish and develop despite the presence of T cells in tumour. An improved understanding of how tumours evade T-cell surveillance, coupled with technical developments allowing the culture and manipulation of T cells, has driven the exploration of therapeutic strategies based on the adoptive transfer of tumour-specific T cells. The isolation, expansion and re-infusion of large numbers of tumour-specific T cells generated from tumour biopsies has been shown to be feasible. Indeed, impressive clinical responses have been documented in melanoma patients treated with these T cells. These studies and others demonstrate the potential of T cells for the adoptive therapy of cancer. However, the significant technical issues relating to the production of natural tumour-specific T cells suggest that the application of this approach is likely to be limited at the moment. With the advent of retroviral gene transfer technology, it has become possible to efficiently endow T cells with antigen-specific receptors. Using this strategy, it is potentially possible to generate large numbers of tumour reactive T cells rapidly. This review summarises the current gene therapy approaches in relation to the development of adoptive T-cell-based cancer treatments, as these methods now head towards testing in the clinical trial setting.

Retrovirus mediated gene transduction of human T-cell subsets

PURPOSE

Allogeneic bone marrow transplantation (AlloBMT) can be curative for patients with leukaemia. Graft versus host disease (GVHD) is a potentially life threatening complication of AlloBMT mediated by the T cells contained within the graft. In order to be able to control GVHD, the allogeneic T cells may be transduced with a suicide gene such as herpes simplex virus thymidine kinase (HSV-tk). For this strategy to be successful, all subsets of T cells should be transduced to a similar extent. Also, the transduction protocol should not induce expression of unwanted homing receptors, nor should it lead to unwanted skewing of the T-cell receptor repertoire. We have studied the transduction efficiency of naïve and memory subsets of CD4+ and CD8+ T cells, and examined the transduced T-cell subsets for possible changes in T-cell receptor (TCR) repertoire and homing receptor expression.

METHODS

The cells were transduced using a Moloney murine retroviral vector carrying a conjugate of the genes encoding the truncated form of the cell surface marker, low affinity nerve growth factor receptor (DeltaLNGFR) and HSV-tk. Transduction efficiency and homing receptor expression were quantified by flow cytometry. TCR repertoire was determined by spectratyping.

RESULTS

We obtained a transduction efficiency of 30-50% of the cells, with no difference between the T-cell subsets. Cell surface receptors responsible for homing to skin, gastrointestinal tract or lymph nodes were practically absent at the end of 2 weeks in culture. The activation procedure seemed to favour the expansion of certain T-cell clones over polyclonal populations. However, there was no difference in the TCR repertoire between transduced and non-transduced cells.

CONCLUSION

Changes in the composition of the T-cell subsets at the end of the cell culture were the results of the activation, and not the suicide gene transduction. The transduced T cells did not express unwanted homing receptors.

T cell repertoire in patients with stable scleroderma

At onset of systemic sclerosis (SSc), T cells have been found to oligoclonally expand in the skin, presumably in response to auto-antigens, but the T cell repertoire has not been evaluated at a later stage. To determine whether a perpetuating immune response contributes to the pathogenesis of stable SSc, the T cell repertoire was analysed in patients with diffuse (d) or limited (l) SSc, and compared to patients with primary Raynaud's phenomenon (RP) or healthy volunteers (Ctrl). The T cell repertoire (total, CD4 or CD8 sorted blood T cells) was analysed by qualitative and quantitative immunoscope (14 BV families analysed) in 11 untreated dSSc and 11 untreated lSSc, 10 RP and 11 Ctrl. To better detect in vivo activated cells, repertoire analysis was also performed on sorted CD4 T cells after in vitro culture with IL-2. In parallel, 6 skin biopsies from SSc patients were analysed. After 7-8 years of disease evolution, SSc patients did not show detectable clonal T cell expansions in the skin, even after tentative expansion from the biopsy with IL-2. Total T cell, sorted CD4 and CD8 T cell repertoires from the blood of patients with SSc did not show significant perturbation as compared to patients with RP and Ctrl. After IL-2 culture for 7 days, blood CD4 T cells from the patients did not preferentially expand as compared to RP and Ctrl. These findings suggest that antigen-driven immune responses may play a lesser role in established SSc than at disease onset.

Lentiviral transduction of human hematopoietic cells by HIV-1- and SIV-based vectors containing a bicistronic cassette driven by various internal promoters

BACKGROUND

Lentiviral gene transfer into hematopoietic cells has been mostly optimized with vectors carrying a single reporter gene. For many clinical applications, lentiviral vectors should contain more than one gene because transduced cells should be enriched by a selectable marker or killed for safety reasons after use. Thus, we compared various vectors containing a bicistronic cassette driven by different ubiquitous promoters for their ability to transduce human T-lymphocytes, CD34+-cells, and dendritic cells (DCs) derived from CD34+-cells or monocytes.

METHODS

We designed HIV or SIV constructs containing a bicistronic cassette composed of two reporter genes (thy1/GFP) linked by an internal ribosome entry site sequence and driven by the cytomegalovirus (CMV) or elongation factor 1alpha (EF1alpha) promoters. The woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) was or not inserted within the constructs, the Vpx accessory protein was or not used for SIV vectors. Target cells were infected at the same multiplicity of infection, transduction efficiency was analyzed both by flow cytometry and vector integration.

RESULTS

For T-cells, HIV-based vectors/WPRE+ in which the thy1/GFP cassette was driven by the EF1alpha promoter were more efficient than SIV-based vectors. For CD34+-cells and CD34+-derived DCs, better thy1/GFP expression was achieved when the CMV promoter drove the cassette inserted into HIV-based vectors/WPRE+. Conversely, for monocyte-derived DCs, the cassette yielded better thy1/GFP expression when inserted into SIV-based vectors/WPRE+ and driven by the CMV or EF1alpha promoters, the use of Vpx significantly improving the expression levels.

CONCLUSIONS

Our results provide guidelines for improving the transduction of T-cells, CD34+-cells or DCs with lentiviral bicistronic vectors designed for clinical applications.

Optimization of Human T-Cell Expansion Ex Vivo Using Magnetic Beads Conjugated with Anti-CD3 and Anti-CD28 Antibodies

T-cell receptor engagement and accompanying costimulatory signals control the level of activation and functional potential of individual T cells. The authors previously developed a novel technology in which human T cells are activated and expanded in culture ex vivo using anti-CD3 and anti-CD28 monoclonal antibodies covalently linked to superparamagnetic beads (Xcyte Dynabeads). In this study the addition of N-acetyl L-cysteine (NAC) to the cultures markedly increased the expansion of T cells from human peripheral blood mononuclear cells without diminishing cell function. NAC increased the rate of T-cell division, reduced apoptosis, and increased the percentage of antigen-specific memory T cells in the cultures. The effect of varying the ratio of beads to T cells (1:10-10:1) at culture initiation was also evaluated. Polyclonal T cells were expanded at all bead-to-T cell ratios tested (range 1:10-10:1). While high bead-to-T cell ratios (5:1 and 10:1) deleted, low ratios (1:10 and 1:5) preserved memory T cells directed against cytomegalovirus, Epstein-Barr virus, and influenza virus antigens. Adding more anti-CD3/anti-CD28 beads during the culture led to further expansion of T cells. Experiments also revealed that reducing the amount of anti-CD3 antibodies relative to the amount of anti-CD28 antibodies on the beads favored the proliferation of antigen-specific T cells. In summary, these data indicate that T cell-stimulating effects of anti-CD3/anti-CD28 beads can be further manipulated to control the expansion of antigen-specific memory T cells and can be used to rapidly expand antigen-specific T cells ex vivo for potential clinical applications.

Suicide gene therapy and the control of graft-vs-host disease

Allogeneic bone marrow transplantation as a cure for leukaemia and lymphoma is limited by the development of graft-vs-host disease (GVHD), an immunological reaction of the donor's T lymphocytes against the host's normal tissues. One therapeutic option to treat GVHD is the transfer of 'suicide' genes into the donor's T lymphocytes to render them susceptible to prodrug administration. This procedure should permit the elimination of unwanted T lymphocytes in GVHD. The main genes proposed for such a strategy will be described in this chapter, together with the advantages and limitations found during preclinical and clinical studies to date.

Toward gene therapy for human CD3 deficiencies

The CD3 subunits of the T cell receptor-CD3 complex (TCR-CD3) help to regulate surface TCR-CD3 expression, and participate in signal transduction leading to intrathymic selection and peripheral antigen recognition by T lymphocytes. Humans who lack individual CD3 chains show impairments in the expression and activation-induced downregulation of TCR-CD3, and the defective immune responses that result may be lethal. We have investigated delivery of a normal CD3 chain to treat disorders of this type. Retroviral transduction of CD3gamma into CD3gamma-deficient peripheral blood T lymphocytes from two unrelated patients selectively corrected the observed TCR-CD3 expression and downregulation defects, but unexpectedly seemed to cause adverse effects that can be explained by an autoreactive recognition mechanism. These data support the feasibility of gene therapy for human CD3 deficiencies, but also suggest that gene transfer into postthymic lymphocytes carrying mutations on T cell recognition or activation pathways may disrupt their intrathymic calibration and become harmful to the host.

Retrovirus-mediated gene transfer in human primary T lymphocytes induces an activation- and transduction/selection-dependent TCR-B variable chain repertoire skewing of gene-modified cells

In a clinical trial that we recently reported, a suicide gene transfer in human primary T cells required 12 days of ex vivo culture, including activation of peripheral blood mononuclear cells (PBMC) with CD3 monoclonal antibody (CD3 mAb), retrovirus-mediated transduction, and selection of gene-modified cells (GMC) by G418. The aim of the present study was to determine the impact of the initial T cell activation and of the transduction/selection on T cell receptor beta variable chain (TCRBV) repertoire of GMC by using the spectratyping method. The TCRBV repertoires of nontransduced, nonselected control (Co) cells and of GMC generated after an initial stimulation with CD3 mAb, CD3/CD28 beads, or allogeneic PBMC or Epstein-Barr virus-transformed B (B-EBV) cells were compared to the ones of their corresponding PBMC. The TCRBV repertoires were skewed in Co cells generated after CD3 mAb or after allogeneic stimulation, and even more so in their corresponding GMC, demonstrating that both culture-dependent and transduction/selection-dependent events led to TCRBV repertoire alterations. However, TCRBV repertoires were not altered, or to a lesser extent, in Co cells or GMC produced after CD3/CD28 bead activation, demonstrating a protective effect on both culture-dependent and transduction/selection-dependent repertoire alterations. Thus, we suggest to replace the initial CD3 mAb stimulation by CD3/CD28 beads for the production of clinical-grade GMC in the setting of future gene therapy trials.

Preparation of Genetically Homogeneous Antigen-Specific Thymidine Kinase Positive T-Lymphocyte Clones for the Control of Alloreactivity Post-Bone Marrow Transplantation

We have previously proposed the use of HLA-specific T-cell clones transduced with a suicide gene to produce an allogeneic effect that can be controlled after allogeneic bone marrow transplantation. Procedures described so far to obtain specific T-cells transduced with a suicide gene have led to the recovery of heterogeneous polyclonal T-cells with a limited level of purity. We have therefore developed an approach to select specific T-cell clones in which the suicide transgene is inserted at a unique site of the genome, and used it to produce CD(+)-cytotoxic HLA-DP-specific T-cell clones. Immunization was performed by a one-way mixed lymphocyte culture and responder T lymphocytes were transduced at day 16, 6 days after the second stimulation. Transductions were carried out using gibbon ape leukemia virus (GALV)-pseudotyped retroviral particles harboring a bicistronic Thy-1/TK vector produced by TEFLY GA16-pKM4 clone 34 packaging cells. Three to 5 days later, CD90 immunomagnetic selection and cloning were performed on the transduced T cells. Our results demonstrate that this procedure led to the recovery of T-cell clones, the majority of which had the expected specificity and a single site of transgene insertion. Such clonotransgenic T-cell populations represent suitable tools to drive a defined alloreaction that can be controlled after bone marrow transplantation.

Gene therapy in the treatment of intestinal inflammation

BACKGROUND

Local expression of anti-inflammatory or immunoregulatory genes may offer an alternative treatment of gastrointestinal inflammation.

DISCUSSION

We review the basic requirements for gene therapy, the possible routes of delivery, and the different strategies for specific targeting focusing on gastrointestinal inflammation.

The impact of retroviral suicide gene transduction procedures on T cells

Retroviral vectors encoding the herpes simplex thymidine kinase gene have been used to render T cells sensitive to the prodrug ganciclovir. Such genetically modified T cells have been used in clinical trials for their graft-versus-leukaemia effects following allogeneic haematopoietic stem cell transplantation. In the event of graft-versus-host disease (GVHD) the cells were susceptible to elimination through exposure to ganciclovir. We have investigated the impact of T-cell activation, required for successful retrovirus-mediated gene transfer, on T-cell receptor repertoire profile, subset distribution and antiviral potential. Using a combination of antibodies against CD3 and CD28, T cells were transduced at high efficiency when exposed to retrovirus between 48 and 72 h later. Lymphocytes had undergone up to seven cycles of cell division by the end of the procedure. Although the T-cell receptor Vbeta repertoire was not altered after retroviral transduction, there were notable shifts in subset profiles with an increased proportion of CD45RO cells in transduced populations. T cells continued to proliferate for several days after transduction and were difficult to sustain under the extended culture conditions required to generate virus-specific T cells. These observations may explain the lower than expected levels of GVHD and poor antiviral immunity reported in recent trials.

Novel interfering bifunctional molecules against the CCR5 coreceptor are efficient inhibitors of HIV-1 infection

CCR5 is the major coreceptor for the HIV-1 strains responsible for primary infection. Individuals homozygous for a 32-bp deletion in the CCR5 coding region are resistant to HIV-1 infection. Strategies to delete CCR5 functionally could thus be of substantial benefit in preventing HIV-1 infection or delaying disease. We evaluated new molecules for their ability to inhibit cell membrane CCR5 expression and to prevent HIV-1 infection. These inhibitors include several truncated forms of CCR5 that may act as negative transdominants, as well as bifunctional molecules resulting from the combination of a previously described anti-CCR5 ribozyme or a truncated CCR5 variant with an intracellular chemokine (RANTES-KDEL). These constructs efficiently blocked membrane CCR5 expression when cotransfected into HEK 293 cells. When expressed by retroviral transduction, some of these molecules significantly inhibited CCR5-dependent chemotaxis in the MCF-7 cell line and reduced CCR5 expression and HIV-1 infection in human T cells. Analysis of inhibitors with different efficiencies showed a strong linear correlation between CCR5 expression inhibition and prevention of HIV-1 infection. This study indicates the potential clinical application of several new CCR5 inhibitory molecules for HIV-1 gene therapy.

Recombinant Sendai virus vectors for activated T lymphocytes

T-lymphocyte-directed gene therapy has potential as a treatment of subjects with immunological disorders. One current limitation of this therapeutic strategy is low gene transfer efficiency, even when complex procedures are used. We report herein that a recombinant Sendai virus vector (SeV) was able to overcome this issue. Using jellyfish enhanced green fluorescent protein gene (EGFP), we found that SeV was able to transduce and express a foreign gene specifically and efficiently in activated murine and human T cells, but not in naive T cells, without centrifugation or reagents including polybrene and protamine sulfate; the present findings were in clear contrast to those demonstrated with the use of retroviruses. The transduction was selective in antigen-activated T cells, while antigen-irrelevant T cells were not transduced, even under bystander activation from specific T-cell responses by antigens ex vivo. Receptor saturation studies suggested a possible mechanism of activated T-cell-specific gene transfer, ie, SeV might attach to naive T cells but might be unable to enter their cytoplasm. We therefore propose that the SeV vector system may prove to be a potentially important alternative in the area of T-cell-directed gene therapy used in the clinical setting.

Transduction and selection of human T cells with novel CD34/thymidine kinase chimeric suicide genes for the treatment of graft-versus-host disease

Clinical trials evaluating the herpes simplex virus thymidine kinase (HSV-tk)/ganciclovir (GCV) suicide gene therapy system for the control of graft-versus-host disease (GVHD) have been limited by low transduction efficiencies and inefficient selection procedures. In this study, we designed and evaluated a novel chimeric suicide gene consisting of the extracellular and transmembrane domains of human CD34 and full-length HSV-tk (DeltaCD34-tk). High-efficiency transfer of DeltaCD34-tk to primary human T cells was accomplished after a single exposure to VSV-G-pseudotyped, Moloney murine leukemia virus-based retrovirus 48 h after activation of human PBMCs with anti-CD3 and anti-CD28 antibodies immobilized on magnetic beads. Using an optimized 5-day transduction and selection procedure, transduction efficiencies averaged 71%, with isolation purities greater than 95% and yields exceeding 90%. The immunoselected T cells were selectively eliminated by GCV (IC(50) approximately 3 nM), maintained a normal subset composition, exhibited a polyclonal TCR Vbeta family repertoire, and contained 5 or 6 vector copies per transduced cell when optimally transduced. No increase in GCV sensitivity was observed upon incorporation of highly active mutant HSV-tk enzymes into the DeltaCD34-tk suicide gene. T cells modified with the DeltaCD34-tk gene using the optimized protocol should improve the overall efficacy of the HSV-tk/GCV suicide gene therapy method of GVHD control.

TCR dynamics in human mature T lymphocytes lacking CD3 gamma

The contribution of CD3gamma to the surface expression, internalization, and intracellular trafficking of the TCR/CD3 complex (TCR) has not been completely defined. However, CD3gamma is believed to be crucial for constitutive as well as for phorbol ester-induced internalization. We have explored TCR dynamics in resting and stimulated mature T lymphocytes derived from two unrelated human congenital CD3gamma-deficient (gamma(-)) individuals. In contrast to gamma(-) mutants of the human T cell line Jurkat, which were selected for their lack of membrane TCR and are therefore constitutively surface TCR negative, these natural gamma(-) T cells constitutively expressed surface TCR, mainly through biosynthesis of new chains other than CD3gamma. However, surface (but not intracellular) TCR expression in these cells was less than wild-type cells, and normal surface expression was clearly CD3gamma-dependent, as it was restored by retroviral transduction of CD3gamma. The reduced surface TCR expression was likely caused by an impaired assembly or membrane transport step during recycling, whereas constitutive internalization and degradation were apparently normal. Ab binding to the mutant TCR, but not phorbol ester treatment, caused its down-modulation from the cell surface, albeit at a slower rate than in normal controls. Kinetic confocal analysis indicated that early ligand-induced endocytosis was impaired. After its complete down-modulation, TCR re-expression was also delayed. The results suggest that CD3gamma contributes to, but is not absolutely required for, the regulation of TCR trafficking in resting and Ag-stimulated mature T lymphocytes. The results also indicate that TCR internalization is regulated differently in each case.

T lymphocytes isolated from patients with advanced colorectal cancer are suitable for gene immunotherapy approaches

Despite improvements in treatment, the 5-year survival for metastatic colorectal cancer remains poor. Novel approaches such as gene immunotherapy are being investigated to improve treatment. Retroviral gene transfer methods have been shown to transduce primary human T lymphocytes effectively resulting in the expression of therapeutic genes. However, a number of defects have been identified in T lymphocytes isolated from patients bearing tumour, which may have critical implications for the development of gene-targeted T cells as an anticancer therapy. To address this issue, primary T lymphocytes were isolated from patients with advanced colorectal cancer and tested for their ability to be transduced and to express subsequently a chimeric immune receptor consisting of a single-chain antibody fragment antigen-binding moiety specific for carcinoembryonic antigen (CEA) fused to the T cell receptor (TCR) CD3zeta chain. In 10 out of 10 patients, T lymphocytes were transduced, expanded in the absence of selection and tested for functional activity against CEA-expressing tumour cells. In each case, functional-specific cytotoxic activity was observed. Negligible activity was found in control cultures. This study highlights the feasibility of patient-derived T lymphocytes as a source of immune cells for autologous gene immunotherapy approaches.

CD28 costimulation and immunoaffinity-based selection efficiently generate primary gene-modified T cells for adoptive immunotherapy

The introduction of an inducible suicide gene has been proposed as a strategy to exploit the antitumor reactivity of donor T cells after allogeneic hematopoietic stem cell transplantation but permit control of graft-versus-host disease. However, there are several obstacles to this approach that may impair the ability of T cells to function and survive in vivo. These include the requirement for in vitro activation or long-term culture to introduce the transgene and obtain therapeutic cell numbers, the toxicity of drug selection to enrich transduced cells, and the immunogenicity of the transgene-encoded products. Here we have developed a transduction and selection strategy for generating large numbers of polyclonal T cells transduced with a retroviral vector encoding the human low-affinity nerve growth factor receptor (LNGFR) for selection and a Fas-based suicide construct (LV'VFas). Ligation of CD28 in conjunction with a T-cell receptor signal permitted efficient transduction, substantially promoted T-cell growth, and contributed to the generation of gene-modified T cells that retained clonal diversity, functional properties, and a homing receptor profile similar to untransduced peripheral blood lymphocytes. Microbeads conjugated directly to antibody specific to LNGFR significantly improved the immunomagnetic selection of LV'VFas-modified T cells and assisted in scaling of the selection procedure to therapeutic cell numbers. Thus, these studies identified a strategy that requires only a brief ex vivo culture and does not use drug selection to obtain large numbers of functional gene-modified polyclonal T cells that can be used for adoptive immunotherapy.

Functional impairment of human T-lymphocytes following PHA-induced expansion and retroviral transduction: implications for gene therapy

The immune function of retrovirus-mediated gene modified (GM) T cells is critical for a beneficial effect to follow their adoptive transfer into patients. Recent clinical data show that GM T cells expanded with PHA have reduced function in vivo. However, little functional analysis of PHA stimulation is available. Our results show that expansion of T cells with PHA impairs their ability to respond (proliferation, cytotoxicity and IFN gamma and perforin expression) to allogeneic stimulation or viral antigens in vitro. Conversely, CD3/CD28-based protocols can preserve this immune function. Retroviral transduction did not alter the functional profile induced by polyclonal stimulation. We investigated the mechanisms leading to this functional effect, and identified differential effects of PHA and CD3/CD28 on the distribution of CCR7/CD45RA T cell functional subsets, which may explain the functional differences observed. While CD3/CD28 stimulation parallels the lineage differentiation pattern induced by antigens in physiological conditions, PHA induces a skewed distribution of the CCR7/CD45RA functional T cell subsets, with near disappearance of the subpopulations that display the effector phenotype. Overall, this study demonstrates a functional disadvantage for transduction protocols based on PHA, uncovers mechanisms that may explain this functional effect, and provides us with information to design and select transduction protocols with an improved functional outcome.

Hepatic fibrosis--role of hepatic stellate cell activation

Hepatic fibrosis is a reversible wound healing response characterized by accumulation of extracellular matrix (ECM), or "scar," that follows chronic but not self-limited liver disease. The ECM components in fibrotic liver are similar regardless of the underlying cause. Activation of hepatic stellate cells is the central event in hepatic fibrosis. These perisinusoidal cells orchestrate an array of changes including degradation of the normal ECM of liver, deposition of scar molecules, vascular and organ contraction, and release of cytokines. Not only is hepatic fibrosis reversible, but it is also increasingly clear that cirrhosis may be reversible as well. The exact stage at which fibrosis/cirrhosis becomes truly irreversible is not known. Antifibrotic therapies will soon be a clinical reality. Emerging therapies will be targeted to those patients with reversible disease. The paradigm of stellate cell activation provides an important framework for defining therapeutic targets.

Selective modification of antigen-specific CD4(+) T cells by retroviral-mediated gene transfer and in vitro sensitization with dendritic cells

Adoptive therapy with antigen-specific T cells is a potential treatment against cancers and viral diseases. To establish a system to modify the genes of these cells to increase their effectiveness, we examined whether the combined use of retroviral vector, which only infects dividing cells, and in vitro sensitization of T cells with antigen-loaded dendritic cells (DCs) could selectively modify antigen-specific T cells with a bcl-2 gene. Human CD4(+) T cells were used as target cells. Autologous DCs transfected with genes of hepatitis B virus (HBV) stimulated a specific T cell proliferation. Importantly, these proliferating T cells were selectively transduced by a bcl-2-retrovirus, and CD25(+) T cells isolated from them contained higher levels of integrated provirus. To select bcl-2-transduced, activated T cells, cells were subjected to interleukin-2 (IL-2) withdrawal. In contrast to CD25(-) and mock-infected CD25(+) T cells, 70% of CD25(+) T cells transduced with bcl-2-retrovirus survived IL-2 withdrawal. These surviving T cells were demonstrated to contain integrated bcl-2 provirus and exhibited HBV-specific proliferation and interferon-gamma secretion. In addition, bcl-2 overexpression protected HBV-specific T cells from transforming growth factor (TGF)-beta-induced cell death. These results demonstrate the feasibility of our strategy in the generation of genetically modified antigen-specific CD4(+) T cells and show that bcl-2-transduced antigen-specific T cells survive IL-2 withdrawal and TGF-beta-induced apoptosis.

Reduced graft-versus-host disease-inducing capacity of T cells after activation, culturing, and magnetic cell sorting selection in an allogeneic bone marrow transplantation model in rats

Graft-versus-host disease (GvHD), a major complication of allogeneic bone marrow transplantation, has been ascribed to mature T cells in the graft. Because T cells play an important role in engraftment of the bone marrow and decrease the probability of relapse of leukemia, a treatment strategy was developed to preserve the benefits of T cells in the graft and to control the severe complications of GvHD. This can be accomplished by the genetic modification of donor T cells with a suicide gene that allows their selective in vivo elimination and subsequently the abrogation of GvHD. For clinical benefit the alloreactivity of herpes simplex virus thymidine kinase (HSV-TK) gene-transduced T cells should be retained. Therefore, we investigated the influence of gene transduction and the selection procedure on T cells. We demonstrated that activation and culturing of T cells reduce their capacity to induce lethal GvHD in an allogeneic rat bone marrow transplantation model. Furthermore, positive immunomagnetic selection of gene-transduced T cells resulted in loss of the GvHD-inducing capacity of HSV-TK(+) T cells directly after MACS (magnetic cell sorting) selection; this loss could be recovered by a 1-day expansion of the selected T cells. No effect on alloreactivity was observed to be caused by the gene transduction procedure. Our study resulted in the development of an optimized culture and gene transduction protocol with preservation of T cell alloreactivity. Treatment of transplanted rats with ganciclovir resulted in a rapid reduction in the number of HSV-TK(+) T cells in the peripheral blood and in increased survival of the animals.

Gene therapy of HIV-1 infection using lentiviral vectors expressing anti-HIV-1 genes

The use of vectors based on primate lentiviruses for gene therapy of human immunodeficiency virus type 1 (HIV-1) infection has many potential advantages over the previous murine retroviral vectors used for delivery of genes that inhibit replication of HIV-1. First, lentiviral vectors have the ability to transduce dividing and nondividing cells that constitute the targets of HIV-1 infection such as resting T cells, dendritic cells, and macrophages. Lentiviral vectors can also transfer genes to hematopoietic stem cells with a superior gene transfer efficiency and without affecting the repopulating capacity of these cells. Second, these vectors could be potentially mobilized in vivo by the wild-type virus to secondary target cells, thus expanding the protection to previously untransduced cells. And finally, lentiviral vector backbones have the ability to block HIV-1 replication by several mechanisms that include sequestration of the regulatory proteins Tat and Rev, competition for packaging into virions, and by inhibition of reverse transcription in heterodimeric virions with possible generation of nonfunctional recombinants between the vector and viral genomes. The inhibitory ability of lentiviral vectors can be further increased by expression of anti-HIV-1 genes. In this case, the lentiviral vector packaging system has to be modified to become resistant to the anti-HIV-1 genes expressed by the vector in order to avoid self-inhibition of the vector packaging system during vector production. This review focuses on the use of lentiviral vectors as the main agents to mediate inhibition of HIV-1 replication and discusses the different genetic intervention strategies for gene therapy of HIV-1 infection.

Transduction of an IL-2 gene into human melanoma-reactive lymphocytes results in their continued growth in the absence of exogenous IL-2 and maintenance of specific antitumor activity

IL-2-dependent activated cells undergo apoptotic death when IL-2 is withdrawn either in vitro or after in vivo cell transfer. To attempt to sustain their survival after IL-2 withdrawal, melanoma-reactive human T lymphocytes were retrovirally transduced with an exogenous human IL-2 gene. Transduced PBMC and cloned CD8+ T cells produced IL-2 and maintained viability after IL-2 withdrawal. Upon restimulation, IL-2 transductants proliferated in the absence of exogenous IL-2 and could be actively grown, and their survival could be maintained without added IL-2 for over 8 wk. PBMCs similarly transduced with a control vector did not produce IL-2 and failed to proliferate in the absence of IL-2. A CD8+ T cell clone, when transduced with an IL-2 gene, manifested the same phenotypes as PBMCs in the absence of exogenous IL-2. Furthermore, an Ab reactive with the alpha-chain of IL-2R complex reduced the viability mediated by IL-2 secretion of the IL-2 transductants. Moreover, transduction of an IL-2 gene did not affect the high degree of recognition and specificity of transductants against melanoma targets. These tumor-reactive IL-2 transductants may be valuable for in vitro studies and for improved adoptive transfer therapies for patients with metastatic melanoma.

Severe perturbations of the blood T cell repertoire in polymyositis, but not dermatomyositis patients

Polymyositis and dermatomyositis are diseases characterized by muscle weakness and muscle inflammatory infiltrates. Their pathogenesis remains unclear. A central role for endomysial autoaggressive CD8(+) T cells is suspected in polymyositis and for perivascular B cells in dermatomyositis. We compared the T cell repertoire of 10 polymyositis and 10 dermatomyositis patients by immunoscope, a method providing a global assessment of the T cell repertoire and a sensitive detection of clonal T cell expansions. Samples were analyzed qualitatively and quantitatively in the blood (unsorted cells and CD4(+) and CD8(+) cells) and in muscle infiltrates. Dramatic perturbations of the T cell repertoire were observed in the blood of polymyositis but not dermatomyositis patients (p < 0.0005), the latter being undistinguishable from controls. These perturbations were due to oligoclonal expansions of CD8(+) T cells and most blood clonal expansions were also found in muscle. These results indicate that the pathogenesis of polymyositis and dermatomyositis is different and reinforce the view that polymyositis but not dermatomyositis is an autoimmune CD8(+) T cell-mediated disease. Moreover, this method may be helpful for the differential diagnosis of polymyositis and dermatomyositis and for noninvasive follow-up of polymyositis patients.

Use of suicide gene-expressing donor T-cells to control alloreactivity after haematopoietic stem cell transplantation

Conditional ablation of alloreactive donor T-cells to prevent or treat graft-versus-host disease (GvHD) in the context of allogeneic haematopoietic stem cell transplantation could significantly contribute to expand the use of alloreactivity as a treatment modality. The prevention and treatment of GvHD induced by herpes simplex virus 1-thymidine kinase (HS-tk)-expressing donor T-cells by ganciclovir (GCV) has been demonstrated. Early clinical findings suggest that the use of such cells early or late after transplantation is associated with no acute toxicity, persistent circulation of the gene-modified cells (GMC) and GCV-sensitive GvHD. However, a number of limitations such as reduced immune function of gene-modified T-cells, immunogenicity of GMC as well as presence of a truncated HS-tk gene have emerged and need to be addressed.

Systematic analysis of clinically applicable conditions leading to a high efficiency of transduction and transgene expression in human T cells

BACKGROUND

The transduction of human peripheral blood T cells with retroviral vectors constitutes an attractive approach for the correction of a number of genetic diseases. In this study we have conducted a systematic analysis of the relevance of a large number of parameters currently considered to affect the transduction of, and transgene expression in, human T cells.

METHODS

Retroviral vectors encoding the human nerve growth factor receptor (NGFR) were used for transducing human T cells from normal volunteers. The proportion of T cells that expressed the marker transgene was determined by flow cytometry using anti-NGFR antibodies.

RESULTS

Spinoculation and static fibronectin (FN)-assisted infections improved to a similar extent the transduction efficiency of PHA/IL-2 stimulated T cells, when compared with samples subjected to standard static infections. When immobilized anti-CD3 (anti-CD3i) or anti-CD3i/28i-stimulated T cells were considered, static infections in FN-coated plates were reproducibly more efficient than spinoculation infections performed on FN-uncoated plates. Under optimized manipulation conditions (three infection cycles of anti-CD3i/28i-stimulated T cells in FN-coated plates) the total number of NGFR+ T cells harvested after 7 days of incubation represented, on average, twice the total number of T cells seeded at Day 0, and up to 95% of the human T cells efficiently expressed the marker transgene. Similar results were obtained regardless of whether samples were manipulated in medium supplemented with fetal bovine serum or with heat-inactivated autologous serum.

CONCLUSIONS

Our study offers new experimental conditions for the transduction of human T cells, with obvious implications for the development of gene therapy protocols.

Primary T lymphocytes as targets for gene therapy

Peripheral blood T lymphocytes have been considered an attractive target for gene therapy applications. They can be easily harvested and readily expanded ex vivo. The transduction efficiency of primary human lymphocytes with standard retroviral vectors approaches 50% or more using optimized methods of gene transfer. Other methods of gene transfer, including adenoviral, adeno-associated viral, and lentiviral vectors, or nonviral techniques, have also been used for gene transfer into primary lymphocytes. Despite encouraging results in vitro, human clinical trials using retroviral vectors to transduce primary lymphocytes have been hindered by low expression levels of transgenes and immune responses against transgene products. Strategies to overcome these problems need to be developed.

Transient control of a virus-induced immunopathology by genetic immunosuppression

The ability to control T cell reactivity using suicide genes opens new perspectives for the treatment of T cell-mediated diseases. The therapeutic effect is achieved by the selective killing of thymidine kinase gene-modified activated T cells by ganciclovir (GCV). This strategy has been shown to control T cell alloreactivity efficiently after bone marrow or solid organ transplantation. Here, we aimed to determine whether an immunopathological process induced by a viral infection could be controlled by GCV when T cells express a thymidine kinase transgene. When transgenic mice were infected with the lymphocytic choriomeningitis virus, administration of GCV resulted in an efficient, but only transient, control of the immunopathological immune response. Further analysis revealed the existence of a minute population of GCV-insensitive T cells. These cells expand in response to the virus despite the presence of GCV and cause immunopathology before viral elimination is finally obtained. Thus, when confronted with a replicative virus, the efficacy of this genetic immunosuppression strategy is highly dependent on the presence of even small numbers of GCV-insensitive cells. These results emphasize the need for sufficient preclinical investigations with regard to the pathology and the nature of the immune response if suicide gene transfer is envisioned for new therapeutic indications.