In Vivo Murine-Matured Human CD3+ Cells as a Preclinical Model for T Cell-Based Immunotherapies

Choosing the right mouse model: comparison of humanized NSG and NBSGW mice for in vivo HSC gene therapy

ABSTRACT

In vivo hematopoietic stem cell (HSC) gene therapy is an emerging and promising area of focus in the gene therapy field. Humanized mouse models are frequently used to evaluate novel HSC gene therapy approaches. Here, we comprehensively evaluated 2 mouse strains, NSG and NBSGW. We studied human HSC engraftment in the bone marrow (BM), mobilization of BM-engrafted HSCs into circulation, in vivo transduction using vesicular stomatitis virus glycoprotein-pseudotyped lentiviral vectors (VSV-G LVs), and the expression levels of surface receptors needed for transduction of viral vectors. Our findings reveal that the NBSGW strain exhibits superior engraftment of human long-term HSCs compared with the NSG strain. However, neither model resulted in a significant increase in circulating human HSCs after mobilization. We show that time after humanization as well as human chimerism levels and platelet counts in the peripheral blood can be used as surrogates for human HSC engraftment in the BM. Furthermore, we observed low expression of the low-density lipoprotein receptor, a requirement for VSV-G LV transduction, in the human HSCs present in the murine BM. Our comprehensive characterization of humanized mouse models highlights the necessity of proper validation of the model and methods to study in vivo HSC gene therapy strategies.

Impact of Betamethasone Pretreatment on Engrafment of Cord Blood-Derived Hematopoietic Stem Cells

Hematopoietic stem cell (HSC) transplantation is crucial to cure hematologic malignancies. Umbilical cord blood (UCB) is a source of stem cells, but 90% of UCB units are discarded due to low cellularity. Improving the engraftment capacities of CD34⁺ stem cells would allow the use of UCB that were so far rejected. Betamethasone induces long-term transcriptomic and epigenomic changes in immune cells through glucocorticoid receptor. We hypothesize that discarded UCB could be used owing to improvements induced by betamethasone. Isolated CD34⁺ HSC from UCB were exposed to the synthetic glucocorticoids betamethasone and fluticasone for 20 h, and cell phenotype was determined before transplantation. NSG mice were sub-lethally irradiated (1 Gy or 2 Gy) 6 h before intravenously transferring 2-5 × 10⁵ CD34⁺ HSC. The peripheral blood engraftment levels and the leukocyte subsets were followed up for 20 weeks using flow cytometry. At end point, the engraftment and leukocyte subsets were determined in the spleen and bone marrow. We demonstrated that betamethasone has surprising effects in recovering immune system homeostasis. Betamethasone and fluticasone increase CXCR4 and decrease HLA class II and CD54 expression in CD34⁺ HSCs. Both glucocorticoids-exposed cells showed a similar engraftment in 2 Gy-irradiated NSG mice. Interestingly, betamethasone-exposed cells showed enhanced engraftment in 1 Gy-irradiated NSG mice, with a trend to increase regulatory T cell percentage when compared to control. Betamethasone induces alterations in CD34⁺ HSCs and improve the engraftment, leading to a faster immune system recovery, which will contribute to engrafted cells survival.

Advances in Human Immune System Mouse Models for Studying Human Hematopoiesis and Cancer Immunotherapy

Immunotherapy has established itself as a promising tool for cancer treatment. There are many challenges that remain including lack of targets and some patients across various cancers who have not shown robust clinical response. One of the major problems that have hindered the progress in the field is the dearth of appropriate mouse models that can reliably recapitulate the complexity of human immune-microenvironment as well as the malignancy itself. Immunodeficient mice reconstituted with human immune cells offer a unique opportunity to comprehensively evaluate immunotherapeutic strategies. These immunosuppressed and genetically modified mice, with some overexpressing human growth factors, have improved human hematopoietic engraftment as well as created more functional immune cell development in primary and secondary lymphoid tissues in these mice. In addition, several new approaches to modify or to add human niche elements to further humanize these immunodeficient mice have allowed a more precise characterization of human hematopoiesis. These important refinements have opened the possibility to evaluate not only human immune responses to different tumor cells but also to investigate how malignant cells interact with their niche and most importantly to test immunotherapies in a more preclinically relevant setting, which can ultimately lead to better success of these drugs in clinical trials.

AMD3100 redosing fails to repeatedly mobilize hematopoietic stem cells in the nonhuman primate and humanized mouse

AMD3100 (plerixafor) is a vital component of many clinical and preclinical transplant protocols, facilitating harvest of hematopoietic stem and progenitor cells through mobilization into the peripheral blood circulation. Repeat mobilization with AMD3100 is also necessary for many patients with suboptimal first stem cell collection or those requiring repeat transplantation. In this study we investigated the mobilization efficacy of repeated AMD3100 dosages in the nonhuman primate and humanized mouse models. In nonhuman primates, we observed effective mobilization after the first AMD3100 administration but a significantly poorer response in CD34⁺ and hematopoietic stem cell-enriched CD90⁺ cells with subsequent doses of the drug. A similar loss of efficacy with repeated administration was noted in immunodeficient mice engrafted with human CD34⁺ cells, in whom the total human white cell population, and particularly human hematopoietic stem and progenitor cells, mobilized significantly less effectively following a second AMD3100 administration when compared with the first dose. Together, our results are expected to inform future mobilization protocols for the purposes of peripheral blood hematopoietic stem cell extraction or for applications in which hematopoietic stem cells must be made accessible for in vivo-delivered gene targeting agents.

Engineering a Humanised Niche to Support Human Haematopoiesis in Mice: Novel Opportunities in Modelling Cancer

Despite the bone marrow microenvironment being widely recognised as a key player in cancer research, the current animal models that represent a human haematopoietic system lack the contribution of the humanised marrow microenvironment. Here we describe a murine model that relies on the combination of an orthotopic humanised tissue-engineered bone construct (ohTEBC) with patient-specific bone marrow (BM) cells to create a humanised bone marrow (hBM) niche capable of supporting the engraftment of human haematopoietic cells. Results showed that this model supports the engraftment of human CD34⁺ cells from a healthy BM with human haematopoietic cells migrating into the mouse BM, human BM compartment, spleen and peripheral blood. We compared these results with the engraftment capacity of human CD34⁺ cells obtained from patients with multiple myeloma (MM). We demonstrated that CD34⁺ cells derived from a diseased BM had a reduced engraftment potential compared to healthy patients and that a higher cell dose is required to achieve engraftment of human haematopoietic cells in peripheral blood. Finally, we observed that hematopoietic cells obtained from the mobilised peripheral blood of patients yields a higher number of CD34⁺, overcoming this problem. In conclusion, this humanised mouse model has potential as a unique and patient-specific pre-clinical platform for the study of tumour–microenvironment interactions, including human bone and haematopoietic cells, and could, in the future, serve as a drug testing platform.

Humanized Mice Are Precious Tools for Preclinical Evaluation of CAR T and CAR NK Cell Therapies

Chimeric antigen receptor (CAR) T-cell therapy represents a revolutionary treatment for hematological malignancies. However, improvements in CAR T-cell therapies are urgently needed since CAR T cell application is associated with toxicities, exhaustion, immune suppression, lack of long-term persistence, and low CAR T-cell tumor infiltration. Major efforts to overcome these hurdles are currently on the way. Incrementally improved xenograft mouse models, supporting the engraftment and development of a human hemato-lymphoid system and tumor tissue, represent an important fundamental and preclinical research tool. We will focus here on several CAR T and CAR NK therapies that have benefited from evaluation in humanized mice. These models are of great value for the cancer therapy field as they provide a more reliable understanding of sometimes complicated therapeutic interventions. Additionally, they are considered the gold standard with regard to assessment of new CAR technologies in vivo for safety, efficacy, immune response, design, combination therapies, exhaustion, persistence, and mechanism of action prior to starting a clinical trial. They help to expedite the critical translation from proof-of-concept to clinical CAR T-cell application. In this review, we discuss innovative developments in the CAR T-cell therapy field that benefited from evaluation in humanized mice, illustrated by multiple examples.

Effective Multi-lineage Engraftment in a Mouse Model of Fanconi Anemia Using Non-genotoxic Antibody-Based Conditioning

Conditioning chemotherapy is used to deplete hematopoietic stem cells in the recipient’s marrow, facilitating donor cell engraftment. Although effective, a major issue with chemotherapy is the systemic genotoxicity that increases the risk for secondary malignancies. Antibody conjugates targeting hematopoietic cells are an emerging non-genotoxic method of opening the marrow niche and promoting engraftment of transplanted cells while maintaining intact marrow cellularity. Specifically, this platform would be useful in diseases associated with DNA damage or cancer predisposition, such as dyskeratosis congenita, Schwachman-Diamond syndrome, and Fanconi anemia (FA). Our approach utilizes antibody-drug conjugates (ADC) as an alternative conditioning regimen in an FA mouse model of autologous transplantation. Antibodies targeting either CD45 or CD117 were conjugated to saporin (SAP), a ribosomal toxin. FANCA knockout mice were conditioned with either CD45-SAP or CD117-SAP prior to receiving whole marrow from a heterozygous healthy donor. Bone marrow and peripheral blood analysis revealed equivalent levels of donor engraftment, with minimal toxicity in ADC-treated groups as compared with cyclophosphamide-treated controls. Our findings suggest ADCs may be an effective conditioning strategy in stem cell transplantation not only for diseases where traditional chemotherapy is not tolerated, but also more broadly for the field of blood and marrow transplantation.

Mouse models in hematopoietic stem cell gene therapy and genome editing

Gene therapy has become an important treatment option for a variety of hematological diseases. The biggest advances have been made with CAR T cells and many of those studies are now FDA approved as a routine treatment for some hematologic malignancies. Hematopoietic stem cell (HSC) gene therapy is not far behind with treatment approvals granted for beta-hemoglobinopathies and adenosine deaminase severe combined immune deficiency (ADA-SCID), and additional approbations currently being sought. With the current pace of research, the significant investment of biotech companies, and the continuously growing toolbox of viral as well as non-viral gene delivery methods, the development of new ex vivo and in vivo gene therapy approaches is at an all-time high. Research in the field of gene therapy has been ongoing for more than 4 decades with big success stories as well as devastating drawbacks along the way. In particular, the damaging effect of uncontrolled viral vector integration observed in the initial gene therapy applications in the 90s led to a more comprehensive upfront safety assessment of treatment strategies. Since the late 90s, an important read-out to comprehensively assess the quality and safety of cell products has come forward with the mouse xenograft model. Here, we review the use of mouse models across the different stages of basic, pre-clinical and translational research towards the clinical application of HSC-mediated gene therapy and editing approaches.

Targeted homology-directed repair in blood stem and progenitor cells with CRISPR nanoformulations

Ex vivo CRISPR gene editing in haematopoietic stem and progenitor cells has opened potential treatment modalities for numerous diseases. The current process uses electroporation, sometimes followed by virus transduction. While this complex manipulation has resulted in high levels of gene editing at some genetic loci, cellular toxicity was observed. We have developed a CRISPR nanoformulation based on colloidal gold nanoparticles with a unique loading design capable of cellular entry without the need for electroporation or viruses. This highly monodispersed nanoformulation avoids lysosomal entrapment and localizes to the nucleus in primary human blood progenitors without toxicity. Nanoformulation-mediated gene editing is efficient and sustained with different CRISPR nucleases at multiple loci of therapeutic interest. The engraftment kinetics of nanoformulation-treated primary cells in humanized mice are better relative to those of non-treated cells, with no differences in differentiation. Here we demonstrate non-toxic delivery of the entire CRISPR payload into primary human blood progenitors.

Minimal conditioning in Fanconi anemia promotes multi-lineage marrow engraftment at 10-fold lower cell doses

BACKGROUND

Gene therapy approaches for the treatment of Fanconi anemia (FA) hold promise for patients without a suitably matched donor for an allogeneic bone marrow transplant. However, significant limitations include the collection of sufficient stem cell numbers from patients, the fragility of these cells during ex vivo manipulation, and clinically meaningful engraftment following transplantation. With these challenges in mind, we were interested in determining (i) whether gene-corrected cells at progressively lower numbers can successfully engraft in FA; (ii) whether low-dose conditioning facilitates this engraftment; and (iii) whether these cells can be selected for post-transplant.

METHODS

Utilizing a well characterized mouse model of FA, we infused donor bone marrow from healthy heterozygote littermates that are unaffected carriers of the FANCA mutation to mimic a gene-corrected product, after administering low-dose conditioning. Once baseline engraftment was observed, we administered a second, very-low selective dose to determine whether gene-corrected cells could be selected for in vivo.

RESULTS

We demonstrate that upfront low-dose conditioning greatly increases successful engraftment of hematopoietic corrected cells in a pre-clinical animal model of FA. Additionally, without conditioning, cells can still engraft and demonstrate a selective advantage in vivo over time following transplantation, and these corrected cells can be directly selected for in vivo after engraftment.

CONCLUSIONS

Minimal conditioning prior to bone marrow transplant in Fanconi anemia promotes the multi-lineage engraftment of 10-fold fewer cells compared to nonconditioned controls. These data provide important insights into the potential of minimally toxic conditioning protocols for FA gene therapy applications.

Long-Term Persistence of Anti-HIV Broadly Neutralizing Antibody-Secreting Hematopoietic Cells in Humanized Mice

Broadly neutralizing antibodies (bNAbs) are among the most promising strategies to achieve long-term control of HIV-1 in the absence of combination antiretroviral therapy. Passive administration of such antibodies in patients efficiently decreases HIV-1 viremia, but is limited by the serum half-life of the protein. Here, we investigated whether antibody-secreting hematopoietic cells could overcome this problem. We genetically modified human CD34⁺ hematopoietic stem and progenitor cells (HSPCs) to secrete bNAbs and transplanted them into immunodeficient mice. We found that the gene-modified cells engraft and stably secrete antibodies in the peripheral blood of the animals for the 9 months of the study. Antibodies were predominantly expressed by human HSPC-derived T- and B cells. Importantly, we found that secreted PGT128 was able to delay HIV-1 viremia in vivo and also prevent a decline in CD4⁺ cells. Gene-modified cells were maintained in bone marrow and were also detected in spleen, thymus, lymph nodes, and gut-associated lymphoid tissue. These data indicate that the bNAb secretion from HSPC-derived cells in mice is functional and can affect viral infection and CD4⁺ cell maintenance. This study paves the way for potential applications to other diseases requiring long-lasting protein or antibody delivery.

HIV infection results in clonal expansions containing integrations within pathogenesis-related biological pathways

The genomic integration of HIV into cells results in long-term persistence of virally infected cell populations. This integration event acts as a heritable mark that can be tracked to monitor infected cells that persist over time. Previous reports have documented clonal expansion in people and have linked them to proto-oncogenes; however, their significance or contribution to the latent reservoir has remained unclear. Here, we demonstrate that a directed pattern of clonal expansion occurs in vivo, specifically in gene pathways important for viral replication and persistence. These biological processes include cellular division, transcriptional regulation, RNA processing, and posttranslational modification pathways. This indicates preferential expansion when integration events occur within genes or biological pathways beneficial for HIV replication and persistence. Additionally, these expansions occur quickly during unsuppressed viral replication in vivo, reinforcing the importance of early intervention for individuals to limit reservoir seeding of clonally expanded HIV-infected cells.