CLEC-1 is a death sensor that limits antigen cross-presentation by dendritic cells and represents a target for cancer immunotherapy

Tumors exploit numerous immune checkpoints, including those deployed by myeloid cells to curtail antitumor immunity. Here, we show that the C-type lectin receptor CLEC-1 expressed by myeloid cells senses dead cells killed by programmed necrosis. Moreover, we identified Tripartite Motif Containing 21 (TRIM21) as an endogenous ligand overexpressed in various cancers. We observed that the combination of CLEC-1 blockade with chemotherapy prolonged mouse survival in tumor models. Loss of CLEC-1 reduced the accumulation of immunosuppressive myeloid cells in tumors and invigorated the activation state of dendritic cells (DCs), thereby increasing T cell responses. Mechanistically, we found that the absence of CLEC-1 increased the cross-presentation of dead cell-associated antigens by conventional type-1 DCs. We identified antihuman CLEC-1 antagonist antibodies able to enhance antitumor immunity in CLEC-1 humanized mice. Together, our results demonstrate that CLEC-1 acts as an immune checkpoint in myeloid cells and support CLEC-1 as a novel target for cancer immunotherapy.

SIRPγ-CD47 Interaction Positively Regulates the Activation of Human T Cells in Situation of Chronic Stimulation

A numerous number of positive and negative signals via various molecules modulate T-cell activation. Within the various transmembrane proteins, SIRPγ is of interest since it is not expressed in rodents. SIRPγ interaction with CD47 is reevaluated in this study. Indeed, we show that the anti-SIRPγ mAb clone LSB2.20 previously used by others has not been appropriately characterized. We reveal that the anti-SIRPα clone KWAR23 is a Pan anti-SIRP mAb which efficiently blocks SIRPα and SIRPγ interactions with CD47. We show that SIRPγ expression on T cells varies with their differentiation and while being expressed on Tregs, is not implicated in their suppressive functions. SIRPγ spatial reorganization at the immune synapse is independent of its interaction with CD47. In vitro SIRPα-γ/CD47 blockade with KWAR23 impairs IFN-γ secretion by chronically activated T cells. In vivo in a xeno-GvHD model in NSG mice, the SIRPγ/CD47 blockade with the KWAR23 significantly delays the onset of the xeno-GvHD and deeply impairs human chimerism. In conclusion, we have shown that T-cell interaction with CD47 is of importance notably in chronic stimulation.

794 Long-term anti-tumor preclinical efficacy of an optimized anti PD-1/IL-7 bifunctional antibody sustaining activation of progenitor stem-like CD8 TILs and disarming Treg suppressive activity

Background

Despite the PD-(L)1 therapy success, a majority of patients remain resistant. PD-1+IL7R+ progenitors CD8 TILs is a key T-cell subset associated with durable PD-(L)1 therapy response. However, this subset may rapidly undergo apoptosis and/or being fully exhausted after PD-(L)1 blockade. Some cytokines have the potential to strengthen PD-(L)1 therapy by promoting T cell survival, however, their clinical developments are limited by a shortened half-life and systemic toxicity. To redirect immunotherapy to tumor-specific T cells, expressing PD1, we propose to selectively deliver the pro-survival IL-7 to PD-1+ T cells using a bifunctional anti-PD1/IL-7 mutein antibody. We previously described that the anti-PD1/IL-7v abrogated suppressive activity of human Treg. Here we evaluated its preclinical anti-tumor efficacy and how it promotes the response of PD1+IL7R+ tumor-specific T cells.

Methods

Proliferation, IFN-γ, IL-7R signaling, and NFAT assays were tested to determine the mechanism of this antibody. For the suppressive assay, CD4 Treg and autologous CD8 Teff were co-cultured. In vivo experiments were performed in hPD-1 KI immunocompetent or humanized immunodeficient mice.

Results

The anti-PD1/IL-7v antibody design has been optimized with a monovalent approach to enhance its biological activity: (1) preserved PD-1 antagonist activity, (2) improved pSTAT5 IL7R signaling, and (3) enhanced in vivo drug exposure and antitumor efficacy. An IL7 mutein has been designed to improve activity on PD1+ T cells while sparing PD1neg T cells.Using a chronic antigen stimulation model, anti-PD1/IL-7v restores the proliferation & survival of both early and fully exhausted CD8+ or CD4+ T cells. Similarly, anti-PD1/IL-7v, but not anti-PD1 alone, reactivates exhausted TILs isolated from human resected tumors. Gene expression analysis by Nanostring showed increase cytotoxicity, antigen presentation, and chemokines signatures. In vivo, anti-PD1/IL-7v demonstrated high monotherapy efficacy (90%) in a PD-1 sensitive orthotopic immunocompetent mouse tumor model as well as in a PD-1 refractory tumor model with 70% of CR vs 15% for anti-PD-1 alone. A selective higher expansion of stem-like/progenitors CD8 TILs was observed after therapy with anti-PD1/IL-7v compared to anti-PD1. Memory immune response was demonstrated in 100% of cured mice after tumor rechallenge in the absence of new treatment in 3 different tumor models. Finally, using two different humanized mouse models implanted with human tumors (A549 or MDA-MB231), we confirmed significant preclinical monotherapy efficacy of the anti-PD-1/IL7v.

Conclusions

These data highlight the potential of anti-PD1/IL-7 bifunctional drug to overcome immunotherapy resistance and to promote durable anti-tumor efficacy by preferentially reinvigorating PD-1+IL7R+ stem-like progenitors CD8 T cells.

Abstract 692: Optimized antagonist anti-PD-1/IL-7 bispecific antibody to sustain exhausted T cell function and to disarm Treg suppressive activity

Although anti PD(L)-1 therapy lead to impressive responses, the majority of patient are unresponsive or fail to develop a durable response after treatment. Immunocytokines have the potential to strengthen PD-(L)1 therapy by promoting T cell survival, however, their clinical developments are limited by a shortened half-life and systemic toxicity. To redirect immunotherapy to tumor specific T cells, we propose to selectively deliver IL-7 to PD1+ T cells using a bispecific anti-PD1 fused to IL-7 (BiCKI®IL-7). Intratumoral progenitor exhausted CD8+ T cells (Tpex) coexpressing PD1/IL-7R+ were described as the key subset responsive to anti PD-(L)1; but their efficacies are transient as Tpex rapidly undergo apoptosis limiting the full efficacy of anti-PD-(L)1. BICKI®IL7 was specifically designed to preferentially reinvigorate effector functions of PD1+IL-7R+ tumor-specific T cells, to sustain long-term anti-tumor response and counteract immune resistance in refractory patients.

BICKI®IL7 was created by the fusion of a flexible linker and human IL-7 to the Fc portion of a high affinity antagonist anti-PD1 antibody. BICKI®IL7 constructed with wild-type IL-7 exhibited a high binding and potency (pSTAT5 IL-7 signaling) irrespective of PD1 expression. As our goal is to selectively activate the IL-7 signaling into PD1+ T cells but not PD1 negative cells, we fused different IL-7 muteins having 2 to 30,000-fold lower affinity for CD127/CD132 complex. One BICKI®IL7 mutein construction was selected for its loss of potency on PD1- cells and its optimal cis-binding/redirection and cis-activity on PD1+ cells. Furthermore, BICKI®IL7 mutein fully antagonized the PD-L1/2 interactions and inhibitory signaling to a similar extent to the naked anti PD1. Interestingly, BICKI®IL7 mutein synergistically activates TCR signaling while IL-7+anti-PD1 combo has no additive effect. Using a chronic antigen stimulation model, we demonstrated that BICKI®IL-7 efficiently activates and sustains the proliferation of early and fully exhausted T cells, and also confirmed the synergy. In parallel, we also explored the effect of the BICKI®IL7 mutein on Tregs in coculture assay. BICKI®IL7 mutein preferentially stimulated CD8 Teff over Treg as opposed to IL-2 & IL-15 and, also abrogated Treg suppression by restoring Teff IFN-γ secretion and proliferation. In vivo, BICKI®IL-7 mutein enhanced anti-tumor responses in mesothelioma model and promoted the proliferation and generation of memory CD8 T cells to higher extent to anti-PD1 treatment. Taken together, our data validate the therapeutic potential of providing IL-7 signal to strengthen PD1 therapy and prevent immunoresistance by sustaining T cell response and overcoming Treg suppression. The bispecific BiCKI®IL-7 mutein can preferentially deliver and activate IL-7 into PD1+ tumor-specific T cells limiting the risk of I-O/I-O immunotoxicity.

Citation Format: Aurore Morello, Justine Durand, Margaux Seite, Virginie Thepenier, Géraldine Teppaz, Emmanuelle Wilhelm, Arianne Desselle, Caroline Mary, Nicolas Poirier. Optimized antagonist anti-PD-1/IL-7 bispecific antibody to sustain exhausted T cell function and to disarm Treg suppressive activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 692.

Agonist anti-ChemR23 mAb reduces tissue neutrophil accumulation and triggers chronic inflammation resolution

Resolution of inflammation is elicited by proresolving lipids, which activate GPCRs to induce neutrophil apoptosis, reduce neutrophil tissue recruitment, and promote macrophage efferocytosis. Transcriptional analyses in up to 300 patients with Inflammatory Bowel Disease (IBD) identified potential therapeutic targets mediating chronic inflammation. We found that ChemR23, a GPCR targeted by resolvin E1, is overexpressed in inflamed colon tissues of severe IBD patients unresponsive to anti-TNFα or anti-α4β7 therapies and associated with significant mucosal neutrophil accumulation. We also identified an anti-ChemR23 agonist antibody that induces receptor signaling, promotes macrophage efferocytosis, and reduces neutrophil apoptosis at the site of inflammation. This ChemR23 mAb accelerated acute inflammation resolution and triggered resolution in ongoing chronic colitis models, with a significant decrease in tissue lesions, fibrosis and inflammation-driven tumors. Our findings suggest that failure of current IBD therapies may be associated with neutrophil infiltration and that ChemR23 is a promising therapeutic target for chronic inflammation.

Selective SIRPα blockade reverses tumor T cell exclusion and overcomes cancer immunotherapy resistance

T cell exclusion causes resistance to cancer immunotherapies via immune checkpoint blockade (ICB). Myeloid cells contribute to resistance by expressing signal regulatory protein-α (SIRPα), an inhibitory membrane receptor that interacts with ubiquitous receptor CD47 to control macrophage phagocytosis in the tumor microenvironment. Although CD47/SIRPα-targeting drugs have been assessed in preclinical models, the therapeutic benefit of selectively blocking SIRPα, and not SIRPγ/CD47, in humans remains unknown. We report a potent synergy between selective SIRPα blockade and ICB in increasing memory T cell responses and reverting exclusion in syngeneic and orthotopic tumor models. Selective SIRPα blockade stimulated tumor nest T cell recruitment by restoring murine and human macrophage chemokine secretion and increased anti-tumor T cell responses by promoting tumor-antigen crosspresentation by dendritic cells. However, nonselective SIRPα/SIRPγ blockade targeting CD47 impaired human T cell activation, proliferation, and endothelial transmigration. Selective SIRPα inhibition opens an attractive avenue to overcoming ICB resistance in patients with elevated myeloid cell infiltration in solid tumors.

Abstract 2287: Bispecific anti-PD1 checkpoint inhibitors antibodies (BiCKI), an optimized platform designed to tackle anti-PD-(L)1 primary and secondary resistance mechanisms

Although Anti PD(L)1 therapy lead to impressive therapeutic responses by reinvigorating T cells, primary and secondary resistances occur de novo or during treatment impeding the full efficacy of the drug. To tackle this resistance mechanisms and reduced the immunotoxicity of combination therapy, we designed a 2nd generation of anti-PD1 antibody by fusing immune protein to the Fc portion of the antibody, named BiCKI®. The anti PD1 will more selectively drive the immune active drug on antigen-experienced (PD1+) T cells, through cis-targeting mechanism. These bifunctional molecules were designed with an optimized anti-PD1 backbone for bispecific format, fused to an active protein domain to the C-ter of heavy and/or light chains. Different protein candidate were successfully fused to the optimized anti-PD1, such as cytokines, costimulatory molecules, or dominant negative receptors with PD1/PDL1 full antagonistic activity. In contrast to combination, BiCKI® antibodies enable the simultaneous dual-binding specificity in a single drug allowing a synergistic activation. Each BiCKI® is selected on its synergistic capacity to re-activate of anti-tumor T cell responses or TCR signaling in cell-based assays. Bispecific antibody development in clinic has been hampered by difficult manufacturing process, reduced pharmacokinetic (PK) and drug exposure. Both anti PD-1 CDRs and VH/VL framework sequences were carefully selected and optimized for bioproductivity and biostability of the molecule. A 2 to 15-fold increased productivity in mammalian cells was observed versus the non-optimized anti-PD1 antibody or other anti-PD-1 bispecific backbones as Pembrolizumab or Nivolumab. We also evaluated the impact of the Fc isotype,linker flexibility and affinity of the fused compound on the PK profile of different bispecifics fused to costimulatory molecules or cytokines. The IgG isotype with reduced FcgR binding property, of the anti-PD-1 backbone was associated with a better PK profile with some exceptions for cytokine. The presence or length of a linker between Fc domain and the fused protein has a small impact the PK and drug efficacy. More importantly, the affinity of the fused compound has an impact the PK profile of BiCKI® For example, the anti-PD-1 fused to wild-type IL-7 cytokine possesses a high affinity for the CD127/CD132 receptors but display a reduced drug exposure both in mouse and cynomolgus. This potential difficulty was solved with further improved products including IL-7 mutants having reduced affinity for CD127 and/or CD132. While significant correlation between IL7 affinity and PK has been observed, increased PK and drug exposure could be achieved using optimized combination of Fc isotype a linker length design and BiCKI-IL7 mutants retaining significant IL7R signaling. Conclusion: Our BICKI® platform was designed to overcome major hurdles of bispecific antibody development, we improved its manufacturability and drug exposure by selectively designing the structure of bispecific antibodies. By fusing costimulatory molecule, cytokines or dominant negative receptor to the anti PD-1 blocking antibody, we can generate and select various efficient bispecific molecules acting in synergy to counteract primary and secondary resistance mechanisms of anti-PD(L)1 therapies.

Citation Format: Caroline Mary, Aurore Morello, Virginie Thepenier, Géraldine Teppaz, Justine Durand, Nicolas Poirier. Bispecific anti-PD1 checkpoint inhibitors antibodies (BiCKI), an optimized platform designed to tackle anti-PD-(L)1 primary and secondary resistance mechanisms [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2287.

Abstract 910: A novel bifunctional anti-PD-1 IL-7 fusion protein to reinvigorate exhausted T cell and disarms Treg suppressive activity

Despite the clinical success of anti-PD(L)1 therapy, the majority of patient remain unresponsive or fail to develop a durable response. We explored a second generation of PD-1 antibody by fusing IL-7 cytokine to the Fc portion, called BiCKI® IL-7. The high affinity of the anti PD-1 antibody will allow the concentration/retention of the drug into the tumor microenvironment and preferentially deliver IL-7 in cis-dependent manner to PD-1+ cells. IL-7 is an optimal target for immunotherapy to preferentially stimulate effector T-cell (Teff) functions over regulatory T-cells (Treg)due to the differential expression of IL-7R and poor capacity of IL-7 to stimulate Treg proliferation. Moreover, It has been published that PD-1 blockades increase IL-7R expression and improve IL-7 signaling in exhausted T-cells rationalizing our combinatorial approach.

Results Our anti PD-1/IL-7 bispecific antibody efficiently blocks the PD-1/PD-L1 and PD-L2 interactions and the PD-1-mediated inhibitory signal (pSHP1) and in parallel activates IL-7R pSTAT5 signaling into T cells. Anti PD-1/IL-7 preferentially binds in cis to T cells coexpressing PD-1 and CD127 enabling a selective activation of primed antigen- experienced T cells over PD1-negative (e.g. naïve) cells. A high affinity/avidity of the molecule was observed using biosensor when both receptor CD127 and PD-1, supporting the cis-targeting activity of the drug. Using in vitro T cell activation bioassay, we observed that IL-7 portion fused to the anti-PD-1 synergizes to enhance TCR mediated signaling (NFAT) through activation of the non-canonical pathway while IL-7 in combination with anti-PD1 (two separates product) has no additive effect. Although IL-7R expression decrease over chronic stimulation of Teff cells, we demonstrated that IL-7 efficiently activates progenitor and some fully-exhausted human T-cells (pSTAT5) and maintain their proliferation and survival capacity. This IL-7R signaling activation was associated with a significant increased IFNγ secretion using ex-vivo fresh human tumor explant culture. A significant higher IFNγ production was obtained with anti PD-1/IL-7compared to anti PD-1 treatment alone, including in non-responder patients to anti-PD1, suggesting that the anti PD-1/IL-7 bispecific can reactivate TILs that are resistant to PD-1 therapy. Knowing that Tregs have a key suppressive function, we also explored the possibility that anti-PD-1/IL-7 affect Treg functions. In a human Treg/Teff coculture assay, anti PD-1/IL-7 abrogates the Treg capacity to inhibit proliferation and IFN-g secretion of CD8+ Teff. Moreover, IL-7 and anti-PD-1/IL-7 does not stimulate Treg proliferation, in contrast to IL-2 and IL-15.

Conclusion Our data validate the therapeutic potential of providing IL-7 signals to overcome PD-1 resistance. The bifunctional anti-PD1/IL-7 favors the T-cell effector over T-regulatory immune balance by stimulating Teff cells and exhausted T-cell, while disarming Tregs suppressive functions.

Citation Format: Aurore Morello, Justine Durand, Virginie Thepenier, Géraldine Teppaz, Margaux Seite, Sabrina Pengam, Caroline Mary, Nicolas Poirier. A novel bifunctional anti-PD-1 IL-7 fusion protein to reinvigorate exhausted T cell and disarms Treg suppressive activity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 910.

SIRPα/CD47 axis controls the maintenance of transplant tolerance sustained by myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature hematopoietic precursors known to suppress immune responses. Interaction of SIRP alpha (SIRPα), expressed by myeloid cells, with the ubiquitous receptor CD47 is an important immune checkpoint of the innate response regulating macrophages and dendritic cells functions. We previously described that MDSC expressing SIRPα accumulated after transplantation and maintained kidney allograft tolerance. However, the role of the SIRPα/CD47 axis on MDSC function remained unknown. Here, we found that blocking SIRPα or CD47 with monoclonal antibodies (mAbs) induced differentiation of MDSC into myeloid cells overexpressing MHC class II, CD86 costimulatory molecule and increased secretion of macrophage-recruiting chemokines (eg, MCP-1). Using a model of long-term kidney allograft tolerance sustained by MDSC, we observed that administration of blocking anti-SIRPα or CD47 mAbs induced graft dysfunction and rejection. Loss of tolerance came along with significant decrease of MDSC and increase in MCP-1 concentration in the periphery. Graft histological and transcriptomic analyses revealed an inflammatory (M1) macrophagic signature at rejection associated with overexpression of MCP-1 mRNA and protein in the graft. These findings indicate that the SIRPα-CD47 axis regulates the immature phenotype and chemokine secretion of MDSC and contributes to the induction and the active maintenance of peripheral acquired immune tolerance.

IL-7 receptor influences anti-TNF responsiveness and T cell gut homing in inflammatory bowel disease

It remains unknown what causes inflammatory bowel disease (IBD), including signaling networks perpetuating chronic gastrointestinal inflammation in Crohn's disease (CD) and ulcerative colitis (UC), in humans. According to an analysis of up to 500 patients with IBD and 100 controls, we report that key transcripts of the IL-7 receptor (IL-7R) pathway are accumulated in inflamed colon tissues of severe CD and UC patients not responding to either immunosuppressive/corticosteroid, anti-TNF, or anti-α4β7 therapies. High expression of both IL7R and IL-7R signaling signature in the colon before treatment is strongly associated with nonresponsiveness to anti-TNF therapy. While in mice IL-7 is known to play a role in systemic inflammation, we found that in humans IL-7 also controlled α4β7 integrin expression and imprinted gut-homing specificity on T cells. IL-7R blockade reduced human T cell homing to the gut and colonic inflammation in vivo in humanized mouse models, and altered effector T cells in colon explants from UC patients grown ex vivo. Our findings show that failure of current treatments for CD and UC is strongly associated with an overexpressed IL-7R signaling pathway and point to IL-7R as a relevant therapeutic target and potential biomarker to fill an unmet need in clinical IBD detection and treatment.

IL-7 receptor blockade blunts antigen-specific memory T cell responses and chronic inflammation in primates

Targeting the expansion of pathogenic memory immune cells is a promising therapeutic strategy to prevent chronic autoimmune attacks. Here we investigate the therapeutic efficacy and mechanism of new anti-human IL-7Rα monoclonal antibodies (mAb) in non-human primates and show that, depending on the target epitope, a single injection of antagonistic anti-IL-7Rα mAbs induces a long-term control of skin inflammation despite repeated antigen challenges in presensitized monkeys. No modification in T cell numbers, phenotype, function or metabolism is observed in the peripheral blood or in response to polyclonal stimulation ex vivo. However, long-term in vivo hyporesponsiveness is associated with a significant decrease in the frequency of antigen-specific T cells producing IFN-γ upon antigen restimulation ex vivo. These findings indicate that chronic antigen-specific memory T cell responses can be controlled by anti-IL-7Rα mAbs, promoting and maintaining remission in T-cell mediated chronic inflammatory diseases.

First-in-Human Study in Healthy Subjects with FR104, a Pegylated Monoclonal Antibody Fragment Antagonist of CD28

FR104 is a monovalent pegylated Fab' Ab, antagonist of CD28, under development for treatment of transplant rejection and autoimmune diseases. In contrast to CD80/86 antagonists (CTLA4-Ig), FR104 selectively blunts CD28 costimulation while sparing CTLA-4 and PD-L1 coinhibitory signals. In the present work, FR104 has been evaluated in a first-in-human study to evaluate the safety, pharmacokinetics, pharmacodynamics, and potency of i.v. administrations in healthy subjects. Sixty-four subjects were randomly assigned to four single ascending dose groups, two double dose groups and four single ascending dose groups challenged with keyhole limpet hemocyanin. Subjects were followed up over a maximum of 113 d. Overall, the pharmacokinetics of FR104 after a single and double infusions was approximately linear at doses ≥0.200 mg/kg. CD28 receptor occupancy by FR104 was saturated at the first sampling time point (0.5 h) at doses above 0.02 mg/kg and returned to 50% in a dose-dependent manner, by day 15 (0.020 mg/kg) to 85 (1.500 mg/kg). FR104 was well tolerated, with no evidence of cytokine-release syndrome and no impact on blood lymphocyte subsets. Inhibition of anti-keyhole limpet hemocyanin Ab response was dose-dependent in FR104 recipients and was already apparent at a dose of 0.02 mg/kg. Abs to FR104 were detected in 22/46 (48%) of FR104 recipients and only 1/46 (2.2%) was detected during drug exposure. In conclusion, selective blockade of CD28 with FR104 was safe and well tolerated at the doses tested. The observed immunosuppressive activity indicated that FR104 has potential to show clinical activity in the treatment of immune-mediated diseases.

Codon swapping of zinc finger nucleases confers expression in primary cells and in vivo from a single lentiviral vector

BACKGROUND

Zinc finger nucleases (ZFNs) are promising tools for genome editing for biotechnological as well as therapeutic purposes. Delivery remains a major issue impeding targeted genome modification. Lentiviral vectors are highly efficient for delivering transgenes into cell lines, primary cells and into organs, such as the liver. However, the reverse transcription of lentiviral vectors leads to recombination of homologous sequences, as found between and within ZFN monomers.

METHODS

We used a codon swapping strategy to both drastically disrupt sequence identity between ZFN monomers and to reduce sequence repeats within a monomer sequence. We constructed lentiviral vectors encoding codon-swapped ZFNs or unmodified ZFNs from a single mRNA transcript. Cell lines, primary hepatocytes and newborn rats were used to evaluate the efficacy of integrative-competent (ICLV) and integrative-deficient (IDLV) lentiviral vectors to deliver ZFNs into target cells.

RESULTS

We reduced total identity between ZFN monomers from 90.9% to 61.4% and showed that a single ICLV allowed efficient expression of functional ZFNs targeting the rat UGT1A1 gene after codon-swapping, leading to much higher ZFN activity in cell lines (up to 7-fold increase compared to unmodified ZFNs and 60% activity in C6 cells), as compared to plasmid transfection or a single ICLV encoding unmodified ZFN monomers. Off-target analysis located several active sites for the 5-finger UGT1A1-ZFNs. Furthermore, we reported for the first time successful ZFN-induced targeted DNA double-strand breaks in primary cells (hepatocytes) and in vivo (liver) after delivery of a single IDLV encoding two ZFNs.

CONCLUSION

These results demonstrate that a codon-swapping approach allowed a single lentiviral vector to efficiently express ZFNs and should stimulate the use of this viral platform for ZFN-mediated genome editing of primary cells, for both ex vivo or in vivo applications.

Characterization of dystrophin deficient rats: a new model for Duchenne muscular dystrophy

A few animal models of Duchenne muscular dystrophy (DMD) are available, large ones such as pigs or dogs being expensive and difficult to handle. Mdx (X-linked muscular dystrophy) mice only partially mimic the human disease, with limited chronic muscular lesions and muscle weakness. Their small size also imposes limitations on analyses. A rat model could represent a useful alternative since rats are small animals but 10 times bigger than mice and could better reflect the lesions and functional abnormalities observed in DMD patients. Two lines of Dmd mutated-rats (Dmdmdx) were generated using TALENs targeting exon 23. Muscles of animals of both lines showed undetectable levels of dystrophin by western blot and less than 5% of dystrophin positive fibers by immunohistochemistry. At 3 months, limb and diaphragm muscles from Dmdmdx rats displayed severe necrosis and regeneration. At 7 months, these muscles also showed severe fibrosis and some adipose tissue infiltration. Dmdmdx rats showed significant reduction in muscle strength and a decrease in spontaneous motor activity. Furthermore, heart morphology was indicative of dilated cardiomyopathy associated histologically with necrotic and fibrotic changes. Echocardiography showed significant concentric remodeling and alteration of diastolic function. In conclusion, Dmdmdx rats represent a new faithful small animal model of DMD.

Efficient gene targeting by homology-directed repair in rat zygotes using TALE nucleases

The generation of genetically modified animals is important for both research and commercial purposes. The rat is an important model organism that until recently lacked efficient genetic engineering tools. Sequence-specific nucleases, such as ZFNs, TALE nucleases, and CRISPR/Cas9 have allowed the creation of rat knockout models. Genetic engineering by homology-directed repair (HDR) is utilized to create animals expressing transgenes in a controlled way and to introduce precise genetic modifications. We applied TALE nucleases and donor DNA microinjection into zygotes to generate HDR-modified rats with large new sequences introduced into three different loci with high efficiency (0.62%–5.13% of microinjected zygotes). Two of these loci (Rosa26 and Hprt1) are known to allow robust and reproducible transgene expression and were targeted for integration of a GFP expression cassette driven by the CAG promoter. GFP-expressing embryos and four Rosa26 GFP rat lines analyzed showed strong and widespread GFP expression in most cells of all analyzed tissues. The third targeted locus was Ighm, where we performed successful exon exchange of rat exon 2 for the human one. At all three loci we observed HDR only when using linear and not circular donor DNA. Mild hypothermic (30°C) culture of zygotes after microinjection increased HDR efficiency for some loci. Our study demonstrates that TALE nuclease and donor DNA microinjection into rat zygotes results in efficient and reproducible targeted donor integration by HDR. This allowed creation of genetically modified rats in a work-, cost-, and time-effective manner.