Gene-modified T cells for adoptive immunotherapy of renal cell cancer maintain transgene-specific immune functions in vivo

Background We have treated three patients with carboxy-anhydrase-IX (CAIX) positive metastatic renal cell cancer (RCC) by adoptive transfer of autologous T-cells that had been gene-transduced to express a single-chain antibody-G250 chimeric receptor [scFv(G250)], and encountered liver toxicity necessitating adaptation of the treatment protocol. Here, we investigate whether or not the in vivo activity of the infused scFv(G250)⁺ T cells is reflected by changes of selected immune parameters measured in peripheral blood. Methods ScFv(G250)-chimeric receptor-mediated functions of peripheral blood mononuclear cells (PBMC) obtained from three patients during and after treatment were compared to the same functions of scFv(G250)⁺ T lymphocytes prior to infusion, and were correlated with plasma cytokine levels. Results Prior to infusion, scFv(G250)⁺ T lymphocytes showed in vitro high levels of scFv(G250)-chimeric receptor-mediated functions such as killing of CAIX⁺ RCC cell lines and cytokine production upon exposure to these cells. High levels of IFN-γ were produced, whilst production of TNF-α, interleukin-4 (IL-4), IL-5 and IL-10 was variable and to lower levels, and that of IL-2 virtually absent. PBMC taken from patients during therapy showed lower levels of in vitro scFv(G250)-receptor-mediated functions as compared to pre-infusion, whilst IFN-γ was the only detectable cytokine upon in vitro PBMC exposure to CAIX. During treatment, plasma levels of IFN-γ increased only in the patient with the most prominent liver toxicity. IL-5 plasma levels increased transiently during treatment in all patients, which may have been triggered by the co-administration of IL-2. Conclusion ScFv(G250)-receptor-mediated functions of the scFv(G250)⁺ T lymphocytes are, by and large, preserved in vivo upon administration, and may be reflected by fluctuations in plasma IFN-γ levels.     

Manufacturing of gene-modified cytotoxic T lymphocytes for autologous cellular therapy for lymphoma

BACKGROUND: The production of therapeutic T-cell populations for adoptive immunotherapy of cancer requires extensive ex vivo cell processing, including the isolation or creation of Ag-specific T cells and their subsequent propagation to clinically relevant numbers. These procedures must be performed according to the principles of current good manufacturing practices (cGMP) for phase I clinical trials to ensure the identity, purity potency and safety of the cellular product. In this report we describe our approach to manufacturing and characterizing bulk populations of gene-modified autologous T cells for use in treating follicular lymphoma. METHODS: PBMC from healthy donors, obtained after informed consent, were stimulated in vitro with Ab to CD3epsilon (OKT3) and recombinant human IL-2 and then electroporated with plasmid DNA containing a human CD19-specific chimeric Ag receptor (CAR) gene and HSV-1 thymidine kinase (TK) gene. Stably transfected cells were selected in cytocidal concentrations of hygromycin B over multiple 14-day stimulation culture cycles and then cryopreserved. Vials of cryopreserved/selected T cells were used to initiate T-cell expansion cultures to produce cell products for clinical infusion. These cultures were characterized for phenotype, function and suitability for use in adoptive immunotherapy studies. RESULTS: Our results demonstrate that bulk populations of gene-modified T cells derived from peripheral blood of healthy donors express CD19+ chimeric Ag receptor at low levels and can specifically lyse CD19+ target cells in vitro. These cells display a differentiated T-effector phenotype, are sensitive to ganciclovir-mediated killing and display a non-transformed phenotype. TCR Vbeta usage indicated that all populations tested were polyclonal. Ex vivo cell expansion from cryopreserved cell banks is sufficient to produce doses of between 5 x 10(9) and 1 x 10(10) cells/run. One of three transductions resulted in a population of cells that was not suitable for infusion but was identified during release testing. No populations displayed any evidence of bacterial, fungal or mycoplasma contamination. DISCUSSION: We have established a manufacturing strategy that is being used to produce T cells for a phase I clinical trial for follicular lymphoma. Genetically modified T cells have been characterized by cell-surface marker phenotype, functional activity against CD19+ targets and requisite safety testing. These pre-clinical data confirm the feasibility of this approach to manufacturing T-cell products.     

Questionable relevance of gamma delta T lymphocytes in renal cell carcinoma

Adoptive gammadelta T cell immunotherapy has moved briskly into clinical trials prompted by several small studies suggesting abundant accumulation of gammadelta T cells within renal cell carcinoma (RCC). In this study, we re-examined levels of gammadelta T cells within RCC tumors and correlated levels of these cells with pathologic features and outcome associated with this form of cancer. Tissues from 248 consecutive clear cell RCC tumors obtained from 2000 to 2003 were stained and quantified for total CD3+ and gammadelta T cells per mm2. Wilcoxon rank sum and Kruskal-Wallis tests were used to evaluate associations between T cell amounts and prognostic factors (age, gender, tumor size, stage, grade, tumor necrosis). Cox models were used to assess associations with RCC-specific death. Median numbers of total CD3+ and gammadelta T cells were 281/mm2 (interquartile range (IQR): 149-536) and 2.6/mm2 (IQR: 1.3-4.6), respectively. The median percentage of CD3+ T cells that were gammadelta T cells was 1.0% (IQR: 0.4-1.9). This low percentage of intratumoral gammadelta T cells was diluted even further with rising CD3+ T cell infiltration. Percentages of gammadelta T cells were not associated with even one single clinicopathologic feature examined. Median follow-up for this study was 3.1 years (48 patients died of RCC) and Cox analysis failed to demonstrate that gammadelta T cells (hazard ratio=1.02, p=0.25) were predictive of RCC-specific death. gammadelta T cells are rare and not recruited nor expanded within RCC tumors. Percentages of gammadelta T cells fail to correlate with any prognostic features of RCC nor specific death. As such, the role of gammadelta T cells in RCC immunobiology remains questionable.     

Genetic engineering of cytolytic T lymphocytes for adoptive T-cell therapy of neuroblastoma

BACKGROUND: Disease relapse is the leading cause of mortality for children diagnosed with disseminated neuroblastoma. The adoptive transfer of tumor-specific T cells is an attractive approach to target minimal residual disease following conventional therapies. We describe here the genetic engineering of human cytotoxic T lymphocytes (CTL) to express a chimeric immunoreceptor for re-directed HLA-independent recognition of neuroblastoma. METHODS: The CE7R chimeric immunoreceptor was constructed by PCR splice overlap extension and is composed of a single-chain antibody extracellular domain (scFv) derived from the L1-CAM-specific murine CE7 hybridoma fused to human IgG1 hinge-Fc, the transmembrane portion of human CD4, and the cytoplasmic tail of huCD3-zeta chain (scFvFc:zeta). Primary human T cells were genetically modified by naked DNA electrotransfer of plasmid expression vector CE7R-pMG then analyzed by Western blotting, flow cytometry for CE7R expression and cell surface trafficking, 4-h chromium release assay for re-directed neuroblastoma lysis, and ELISA for tumor-specific activation of cytokine production. RESULTS: CE7R is expressed as an intact chimeric protein that trafficks to the cell surface as a type I transmembrane protein. Primary human CE7R-expressing CD8(+) CTL clones specifically recognize human neuroblastoma tumor cells and are activated for tumor cell lysis and T(c)1 cytokine production. CONCLUSIONS: These data demonstrate the utility of CE7R for re-directing the effector function of CTL to neuroblastoma and have provided the rationale to initiate a FDA-authorized (BB-IND#9149) pilot clinical trial to establish the feasibility and safety of adoptive transfer of autologous CE7R(+)CD8(+) CTL clones to children with recurrent/refractory neuroblastoma.     

Adoptive immuno-gene therapy of cancer with single chain antibody [scFv(Ig)] gene modified T lymphocytes

Adoptive transfer of antigen-specific T cells has recently shown therapeutic successes in the treatment of viral infections and tumors. T cells specific for the antigen of interest can be generated in vitro, and adoptively transferred back to provide patients with large numbers of immune-competent T cells. Adoptive T cell therapy, however, is a patient-tailored treatment that unfortunately is not universally applicable to treat viral infections and tumors. We and others have demonstrated that the transfer of genes encoding antigen-specific receptors into T cells (i.e., genetic retargeting) represents an attractive alternative to induce antigen-specific immunity. Currently, we evaluate this concept in a clinical protocol to treat patients with metastatic renal cell cancer (RCC) using autologous RCC-specific gene-modified T lymphocytes.     

Immunolabeling of CD3-positive lymphocytes with a recombinant single-chain antibody/alkaline phosphatase conjugate

G3(3) is a novel murine monoclonal antibody directed against the CD3 antigen of human T lymphocytes which could be used to analyze lymphoid malignancies. We have produced and characterized a recombinant colorimetric immunoconjugate with the antigen-binding specificity of antibody G3(3). A gene encoding a single-chain antibody variable fragment (scFv) was assembled using the original hybridoma cells as a source of antibody variable heavy (VH) and variable light (VL) chain genes. The chimeric gene was introduced into a prokaryotic expression vector in order to produce a soluble scFv fused to bacterial alkaline phosphatase. DNA sequencing and Western blotting analyses demonstrated the integrity of the soluble immunoconjugate recovered from induced recombinant bacteria. The scFv/AP protein was bifunctional and similar in immunoreactivity to the parent G3(3) antibody. Flow cytometry and immunostaining experiments confirmed that the activity of the scFv/AP protein compares favourably with that of the parent antibody. The scFv/AP conjugate was bound to CD3 antigen at the surface of T cells and was directly detected by its enzymatic activity. Thus this novel fusion protein has potential applications as an immunodiagnostic reagent.     

CD8<Superscript>+</Superscript> T lymphocytes isolated from renal cancer patients recognize tumour cells through an HLA- and TCR/CD3-independent pathway

PURPOSE: The aim of this study was to characterize the immune response of patients affected by renal cell carcinoma (RCC). METHODS: Long-term RCC lines were established by retroviral-mediated transfer of the large T-antigen of SV40 into fresh carcinoma cells. Reactive T cell effectors were generated by iterative stimulations of patients' PBMC with autologous tumour cells. RESULTS: This protocol led to the induction of CD8(+) T cell clones reactive against the autologous tumour, but not against NK-sensitive cell lines. However, some of these effectors recognize normal renal cells, allogeneic renal carcinoma cell lines and colon and non-small cell lung carcinomas but not melanomas and lymphoblastoid lines, without evidence of shared classical HLA class I (HLA-I) molecules. Further characterization performed on the CD8(+) TCR alpha/beta(+) clone, CTL30, demonstrated that neither expression of CD1, HLA-Ia nor HLA-Ib, correlated with the T cells' recognition. Moreover, beta2m expression by target cells was not required to achieve interaction of tumour-effector cells. In agreement with this observation, the lytic activity of CTL30 was not inhibited by anti-HLA-I Ab, and antigen expression was not affected by inhibitors of antigen processing. Lytic activity of CTL30, while partially inhibited by anti-NKG2D, could not be abolished by anti-CD3 Abs. Moreover, growth and expansion of CTL30 was sustained only by T cell interaction with antigen-expressing tumour cells; unspecific mitogenic stimuli, such as anti-CD3 and PHA, did not allow T cell expansion. These results demonstrated the existence of an alpha/beta T cell population, recognizing epithelial tumour cells through an HLA-unrestricted, CD3-independent mechanism.     

Unique Biological Properties of Catalytic Domain Directed Human Anti-CAIX Antibodies Discovered through Phage-Display Technology

Carbonic anhydrase IX (CAIX, gene G250/MN-encoded transmembrane protein) is highly expressed in various human epithelial tumors such as renal clear cell carcinoma (RCC), but absent from the corresponding normal tissues. Besides the CA signal transduction activity, CAIX may serve as a biomarker in early stages of oncogenesis and also as a reliable marker of hypoxia, which is associated with tumor resistance to chemotherapy and radiotherapy. Although results from preclinical and clinical studies have shown CAIX as a promising target for detection and therapy for RCC, only a limited number of murine monoclonal antibodies (mAbs) and one humanized mAb are available for clinical testing and development. In this study, paramagnetic proteoliposomes of CAIX (CAIX-PMPLs) were constructed and used for anti-CAIX antibody selection from our 27 billion human single-chain antibody (scFv) phage display libraries. A panel of thirteen human scFvs that specifically recognize CAIX expressed on cell surface was identified, epitope mapped primarily to the CA domain, and affinity-binding constants (KD) determined. These human anti-CAIX mAbs are diverse in their functions including induction of surface CAIX internalization into endosomes and inhibition of the carbonic anhydrase activity, the latter being a unique feature that has not been previously reported for anti-CAIX antibodies. These human anti-CAIX antibodies are important reagents for development of new immunotherapies and diagnostic tools for RCC treatment as well as extending our knowledge on the basic structure-function relationships of the CAIX molecule.     

Streamlined production of genetically modified T cells with activation,transduction and expansion in closed-system G-Rex bioreactors

BackgroundGas Permeable Rapid Expansion (G-Rex) bioreactors have been shown to efficiently expand immune cells intended for therapeutic use, but do not address the complexity of the viral transduction step required for many engineered T-cell products. Here we demonstrate a novel method for transduction of activated T cells with Vectofusin-1 reagent. Transduction is accomplished in suspension, in G-Rex bioreactors. The simplified transduction step is integrated into a streamlined process that uses a single bioreactor with limited operator intervention.MethodsPeripheral blood mononuclear cells (PBMCs) from healthy donors were thawed, washed and activated with soluble anti-CD3 and anti-CD28 antibodies either in cell culture bags or in G-Rex bioreactors. Cells were cultured in TexMACS GMP medium with interleukin (IL)-7 and IL-15 and transduced with RetroNectin in bags or Vectorfusin-1 in the G-Rex. Total viable cell number, fold expansion, viability, transduction efficiency, phenotype and function were compared between the two processes.ResultsThe simplified process uses a single vessel from activation through harvest and achieves 56% transduction with 29-fold expansion in 11 days. The cells generated in the simplified process do not differ from cells produced in the conventional bag-based process functionally or phenotypically.DiscussionThis study demonstrates that T cells can be transduced in suspension. Further, the conventional method of generating engineered T cells in bags for clinical use can be streamlined to a much simpler, less-expensive process without compromising the quality or function of the cell product.     

Clinical-grade generation of active NK cells from cord blood hematopoietic progenitor cells for immunotherapy using a closed-system culture process

Natural killer (NK) cell-based adoptive immunotherapy is a promising treatment approach for many cancers. However, development of protocols that provide large numbers of functional NK cells produced under GMP conditions are required to facilitate clinical studies. In this study, we translated our cytokine-based culture protocol for ex vivo expansion of NK cells from umbilical cord blood (UCB) hematopoietic stem cells into a fully closed, large-scale, cell culture bioprocess. We optimized enrichment of CD34(+) cells from cryopreserved UCB units using the CliniMACS system followed by efficient expansion for 14 days in gas-permeable cell culture bags. Thereafter, expanded CD34(+) UCB cells could be reproducibly amplified and differentiated into CD56(+)CD3(-) NK cell products using bioreactors with a mean expansion of more than 2,000 fold and a purity of >90%. Moreover, expansion in the bioreactor yielded a clinically relevant dose of NK cells (mean: 2×10(9) NK cells), which display high expression of activating NK receptors and cytolytic activity against K562. Finally, we established a versatile closed washing procedure resulting in optimal reduction of medium, serum and cytokines used in the cell culture process without changes in phenotype and cytotoxic activity. These results demonstrate that large numbers of UCB stem cell-derived NK cell products for adoptive immunotherapy can be produced in closed, large-scale bioreactors for the use in clinical trials.     

Targeting rare populations of murine antigen-specific T lymphocytes by retroviral transduction for potential application in gene therapy for autoimmune disease

CD4+ T cells are important mediators in the pathogenesis of autoimmunity and would therefore provide ideal candidates for lymphocyte-based gene therapy. However, the number of Ag-specific T cells in any single lesion of autoimmunity may be quite low. Successful gene transfer into autoantigen-specific CD4+ T cells would serve as an ideal vehicle for site-targeted gene therapy if it were possible to transduce preferentially the small number of autoantigen-specific T cells. In this study we have demonstrated that retroviral infection of CD4+ lymphocytes from either autoantigen-stimulated TCR transgenic mice, or Ag-activated immunized nontransgenic mice, with a retroviral vector (pGCIRES), resulted in the transduction of only the limited number of Ag-reactive CD4+ T cells. In contrast, polyclonal activation of the same cultures resulted in transduction of non-antigen-specific lymphocytes. Transduction of Ag-reactive CD4+ T cells with pGCIRES retrovirus encoding the regulatory genes IL-4 (IL4) and soluble TNF receptor (STNFR) resulted in stable integration and long-term expression of recombinant gene products. Moreover, expression of the pGCIRES marker protein, GFP, directly correlated with the expression of the upstream regulatory gene. Retroviral transduction of CD4+ T cells targeted specifically Ag-reactive cells and was cell cycle-dependent and evident only during the mitosis phase. These studies suggest that retroviral transduction of autoantigen-specific murine CD4+ T cells, using the pGCIRES retroviral vector, may provide a potential method to target and isolate the low frequency of autoantigen-specific murine CD4+ T cells, and provides a rational approach to gene therapy in animal models of autoimmunity.     

A new way to generate cytolytic tumor-specific T cells: electroporation of RNA coding for a T cell receptor into T lymphocytes

Effective T cell receptor (TCR) transfer until now required stable retroviral transduction. However, retroviral transduction poses the threat of irreversible genetic manipulation of autologous cells. We, therefore, used optimized RNA transfection for transient manipulation. The transfection efficiency, using EGFP RNA, was >90%. The electroporation of primary T cells, isolated from blood, with TCR-coding RNA resulted in functional cytotoxic T lymphocytes (CTLs) (>60% killing at an effector to target ratio of 20:1) with the same HLA-A2/gp100-specificity as the parental CTL clone. The TCR-transfected T cells specifically recognized peptide-pulsed T2 cells, or dendritic cells electroporated with gp100-coding RNA, in an IFNγ-secretion assay and retained this ability, even after cryopreservation, over 3 days. Most importantly, we show here for the first time that the electroporated T cells also displayed cytotoxicity, and specifically lysed peptide-loaded T2 cells and HLA-A2⁺/gp100⁺ melanoma cells over a period of at least 72 h. Peptide-titration studies showed that the lytic efficiency of the RNA-transfected T cells was similar to that of retrovirally transduced T cells, and approximated that of the parental CTL clone. Functional TCR transfer by RNA electroporation is now possible without the disadvantages of retroviral transduction, and forms a new strategy for the immunotherapy of cancer.Niels Schaft and Jan Dörrie contributed equally     

Enhanced receptor expression and in vitro effector function of a murine-human hybrid MART-1-reactive T cell receptor following a rapid expansion

Peripheral blood lymphocytes (PBL) genetically modified to express T cell receptors (TCR) specific to known melanoma antigens, such as melanoma antigen recognized by T cells-1 (MART-1), and gp100 can elicit objective tumor regression when administered to patients with metastatic melanoma. It has also been demonstrated that modifications within the constant regions of a fully human TCR can enhance surface expression and stability without altering antigen specificity. In this study, we evaluated the substitution of murine constant regions for their human counterpart within the DMF5 MART-1-specific TCR. Unlike previous studies, all modified TCRs were inserted into retroviral vectors and analyzed for expression and function following a clinical transduction protocol. PBL were transduced with retroviral supernatant generated from stable packaging lines encoding melanoma-specific TCRs. This protocol resulted in high levels of antigen-specific T cells without the need for additional peptide stimulation and selection. Both the human and murinized TCR efficiently transduced PBL; however, the murinized TCR exhibited significantly higher tetramer binding, mean fluorescence intensity, as well as, increased in vitro effector function following our clinical transduction and expansion protocol. Additional TCR modifications including insertion of a second disulfide bond or the linker modifications evaluated herein did not significantly enhance TCR expression or subsequent in vitro effector function. We conclude that the substitution of a human constant region with a murine constant region was sufficient to increase receptor expression and tetramer binding as well as antitumor activity of the DMF5 TCR and could be a tool to augment other antigen-specific TCR.     

Optimization of therapeutic T cell expansion in G-Rex device and applicability to large-scale production for clinical use

Our center performs experimental clinical studies with advanced therapy medicinal products (ATMPs) based on polyclonal T cells, all of which are currently expanded in standard T-flasks. Given the need to increase the efficiency and safety of large-scale T cell expansion for clinical use, we have optimized the method to expand in G-Rex devices both cytokine-induced killer cells (CIKs) from peripheral or cord blood and blinatumomab-expanded T cells (BETs). We show that the G-Rex reproducibly allowed the expansion of >30 × 10⁶ CD3⁺ cells/cm² of gas-permeable membrane in a mean of 10 to 11 days in a single unit, without manipulation, except for addition of cytokines and sampling of supernatant for lactate measurement every 3 to 4 days. In contrast, 21 to 24 days, twice-weekly cell resuspension and dilution into 48 to 72 T-flasks were required to complete expansions using the standard method. We show that the CIKs produced in G-Rex (CIK-G) were phenotypically very similar, for a large panel of markers, to those expanded in T-flasks, although CIK-G products had lower expression of CD56 and higher expression of CD27 and CD28. Functionally, CIK-Gs were strongly cytotoxic in vitro against the NK cell target K562 and the REH pre-B ALL cell line in the presence of blinatumomab. CIK-Gs also showed therapeutic activity in vivo in the Ph⁺ pre-B ALL-2 model in mice. The expansion of both CIKs and BETs in G-Rex was validated in good manufacturing practices (GMP) conditions, and we plan to use G-Rex for T cell expansion in future clinical studies.     

不同培养基对流式细胞仪分选外周血T细胞的影响

摘要 目的：通过探讨用于流式分选的T细胞体外扩增的无血清培养基，提高过继细胞的增殖能力和活性。方法：采用人外周血淋巴细胞分离管制备外周血单个核细胞，再用流式细胞分选仪从6例健康志愿者的外周血单个核细胞中分选CD3+T细胞到4种常用的培养基中：X-VIVO 15、KBM 581、TexMACS GMP和10 % FBS/1640，观察并记录培养细胞的状态和体外增殖能力。于第3天，第6天和第8天，通过胎盼蓝染色后进行活细胞计数。于第8天用凋亡试剂盒检测扩增细胞的凋亡情况，并用流式细胞分析仪检测细胞的免疫表型。结果：X-VIVO 15、TexMACS GMP和10 % FBS/1640作为流式细胞分选的接收液仅少量细胞碎片，而分选在KBM 581的细胞大量死亡，显著高于X-VIVO 15组（P<0.05）。X-VIVO 15中扩增的细胞数量最多，增殖检测结果显示活细胞在X-VIVO 15中快速增殖且细胞凋亡率显著低于KBM 581 和 TexMACS GMP（P<0.05）。4种培养基扩增的细胞主要呈现效应记忆型。其中，X-VIVO 15中效应记忆型T细胞比例显著高于TexMACS GMP（P<0.05）。TexMACS中效应细胞比例显著高于10 % FBS/1640（P<0.05）。结论：X-VIVO 15无血清培养基扩增流式分选的T细胞具有高增殖能力、细胞活性和记忆表型，适用于经流式分选后细胞的体外扩增。     

Improvement of in vitro potency assays by a resting step for clinical-grade chimeric antigen receptor engineered T cells

BackgroundChimeric antigen receptor engineered T (CAR-T) cell therapy is a promising approach currently revolutionizing the field of cancer immunotherapy. However, data concerning clinical-grade CAR-T cell stability and functionality after months of cryopreservation have not been released by companies so far. To investigate the effect of cryopreservation on CAR-T cells and to further optimize the potency assays, we performed this study.MethodsA third generation of CD19 CAR-T cells was manufactured according to Good Manufacturing Practice (GMP) requirements, which is applied to patients in an ongoing clinical phase 1 study. Quality control tests for sterility, endotoxin and mycoplasma were performed for each batch. Stability in terms of viability, recovery, transduction efficiency and functional capacity was determined using microscopy, multiparametric flow cytometry as well as chromium-51 release tests.ResultsUp to 90days of cryopreservation had no influence on viability, recovery and transduction efficiency of CAR-T cells. However, higher cell concentration for cryopreservation could alter the cell viability and recovery but not the transduction efficiency. Moreover, directly after thawing, both the quantity and quality of the functionality of CAR-T cells were transiently hampered by the negative effects of cryopreservation. Notably, the impaired functionality could be fully restored and even strengthened after an overnight resting process.DiscussionCryopreservation is a challenge for the functional activity of CAR-T cells. However, CAR-T cells regain their potency by overnight incubation at 37°C, which mimics the clinical application setting. Therefore, an overnight resting step should be included in in vitro potency assays.     

Highly efficient gene transfer into antigen-specific primary mouse lymphocytes with replication-deficient retrovirus expressing the 10A1 envelope protein

Background

Introduction of recombinant genes in the genome of primary lymphocytes by virtue of a replication‐deficient retrovirus can be used in immunological studies and for cell‐based gene therapy.

Methods

Packaging cells GP+E86 producing replication‐deficient retrovirus incorporating the genes of enhanced green fluorescent protein (eGFP), C2γ or C2ξ, were generated by calcium phosphate‐mediated transfection. Clones with the highest titres of retrovirus vector were isolated from them and their supernatants were used for transduction of PT67 cells. Primary mouse lymphocytes and T‐cell hybridoma MD.45 were transduced by centrifugation with retroviral stock. The retroviral content of packaging cell supernatants was determined by dot blotting and hybridization with a DNA probe.

Results

PT67 cells produced ～50 times more retrovirus vector than the original GP+E86 clones. When retroviral stocks of PT67 and GP+E86 cells were used at 1/50 dilution and undiluted, respectively (to normalize them forretroviral RNA content), the transduction efficiency of mouse T‐cell hybridoma was 40% and 5%, respectively. Centrifugation of target cells with retroviral stock at 2000 g for 60 min increased the percentage of transduced cells two‐ to three‐fold. Within a population of cells isolated from the draining lymph nodes of an immunized mouse and reactivated with an antigen, up to 60% of CD4⁺ T cells and up to 80% of B cells could be transduced with a transgene in replication‐deficient retrovirus packaged by PT67 cells using the optimized gene transfer protocol.

Conclusions

This protocol allows for the generation of packaging cells producing high titres of retrovirus vector. The 10A1 envelope protein is superior to the ecotropic one for the transduction of mouse lymphocytes. Copyright © 2002 John Wiley & Sons, Ltd.

     

Quantitative analysis of retroviral and lentiviral gene transfer to murine embryonic stem cells

The effectiveness of retrovirus or lentivirus transduction of embryonic stem (ES) cells is often limited because transgene expression is silenced or variegated. We wondered if other steps of transduction, in addition to gene expression, were restricted in ES cells. We quantitatively compared (1) the amount of virus binding, (2) the number of integrated transgenes, and (3) the resulting level of gene expression. We found that three- to fourfold fewer retroviruses and lentiviruses bound to R1 mES cells than to NIH 3T3 cells, suggesting that both types of viruses bind less efficiently to mES cells. Retroviruses and lentiviruses differed in the efficiency with which they completed post-binding steps of transduction. In R1 mES cells, we detected 3-fold fewer integrated retrovirus transgenes and 11-fold lower expression levels than in NIH 3T3 cells, which suggests that the primary limitation to retrovirus transduction may be low levels of transgene expression. In contrast, we detected 10-fold fewer integrated lentivirus transgenes and 8-fold lower expression levels in R1 mES cells than in NIH 3T3 cells, which suggests that lentivirus transduction may be limited by inefficient intracellular post-binding steps of transduction. The implications of our findings for developing improved viral vectors for transducing mES cells are discussed.     

Different expression profiles of human cyclin B1 in normal PHA-stimulated T lymphocytes and leukemic T cells

BACKGROUND: In a previous work, we demonstrated with flow cytometry (FCM) methods that accumulation of human cyclin B1 in leukemic cell lines begins during the G(1) phase of the cell cycle (Viallard et al. , Exp Cell Res 247:208-219, 1999). In the present study, FCM was used to compare the localization and the kinetic patterns of cyclin B1 expression in Jurkat leukemia cell line and phytohemagglutinin (PHA)-stimulated normal T lymphocytes. METHODS: Cell synchronization was performed in G(1) with sodium n-butyrate, at the G(1)/S transition with thymidine and at mitosis with colchicine. Cells (leukemic cell line Jurkat or PHA-stimulated human T-lymphocytes) were stained for DNA and cyclin B1 and analyzed by FCM. Western blotting was used to confirm certain results. RESULTS: Under asynchronous growing conditions and for both cell populations, cyclin B1 expression was essentially restricted to the G(2)/M transition, reaching its maximal level at mitosis. When the cells were synchronized at the G(1)/S boundary by thymidine or inside the G(1) phase by sodium n-butyrate, Jurkat cells accumulated cyclin B1 in both situations, whereas T lymphocytes expressed cyclin B1 only during the thymidine block. The cyclin B1 fluorescence kinetics of PHA-stimulated T lymphocytes was strictly similar when considering T lymphocytes blocked at the G(1)/S phase transition by thymidine and in exponentially growing conditions. These FCM results were confirmed by Western blotting. The detection of cyclin B1 by Western blot in cells sorted in the G(1) phase of the cell cycle showed that cyclin B1 was present in the G(1) phase in leukemic T cells but not in normal T lymphocytes. Cyclin B1 degradation was effective at mitosis, thus ruling out a defective cyclin B1 proteolysis. CONCLUSIONS: We found that the leukemic T cells behaved quite differently from the untransformed T lymphocytes. Our data support the notion that human cyclin B1 is present in the G(1) phase of the cell cycle in leukemic T cells but not in normal T lymphocytes. Therefore, the restriction point from which cyclin B1 can be detected is different in the two models studied. We hypothesize that after passage through a restriction point differing in T lymphocytes and in leukemic cells, the rate of cyclin B1 synthesis becomes constant in the S and G(2)/M phases and independent from the DNA replication cycle.     

Thoracic duct lymphatic fluid harbors phenotypically naive T cells for use in adoptive T-cell therapy

Background aims: Manufacturing of potent chimeric antigen receptor (CAR) T cells requires phenotypically naive and early memory T cells. We hypothesized lymphatic fluid collected from the thoracic duct of children would serve as a unique reservoir for early T cells, which could then be used for CAR T-cell therapy. Methods: We evaluated lymphatic fluid collected from 25 pediatric patients undergoing thoracic duct cannulation for other clinical indications. Results: Lymphatic fluid in the thoracic duct was rich in T cells, with higher percentage of naive and stem central memory T-cell subsets compared with paired blood samples. T cells from lymphatic fluid showed decreased negative checkpoint regulators on the surface and increased rapid expansion with bead activation. Creation of CD19-directed CAR T cells from blood and lymphatic T cells showed similar lentiviral transduction properties, but CAR T cells generated from lymphatic fluid produced superior cytotoxicity in a murine leukemia model because they were able to achieve equivalent tumor eradication at lower doses. Conclusions: These results are the first characterization of T cells from the thoracic duct of pediatric patients and suggest an alternative approach for manufacturing of cellular therapy that will improve both expansion and cytotoxic effect.