Immunodeficient Mouse Strains Research Articles

Abstract 1334: Evaluation of NK cell combination therapies in mouse models of cancer

Abstract Adoptive immunotherapy with natural killer (NK) cells has emerged as a promising innovative approach against hematological malignancies and solid tumors. To enhance the functional aspects of NK cells and to achieve stronger, sustained anti-tumor responses, combination strategies are under development. They are focused on optimization of NK cell potency, persistence and tumor targeting using monoclonal antibodies, multi-specific NK cell engagers and immune modulators like cytokines. SAR445419 is a universal off-the-shelf allogeneic human NK cell (hNK) product made using Sanofi’s proprietary platform with potential broad application across hematologic and solid tumor indications. We evaluated the therapeutic potential of these NK cells in combination with internal assets and standard of care treatments in preclinical mouse models. The studies were performed in immunodeficient NOG mouse strains transgenic for hIL-15, supporting long-term engraftment of functional hNK cells. We demonstrated the therapeutic advantage of NK cell combination with an anti-CD20 monoclonal antibody (mAb) in a disseminated lymphoma model. We also reported prolonged lifespan of leukemia-bearing animals treated with NK cells and pegenzileukin, a PEGylated non-alpha rhIL-2 variant engineered to preferentially bind to the IL-2 βγ receptors and promote NK cell function. The anti-tumor response correlated with pegenzileukin-induced increase in NK cell numbers in the blood. A combination of CD38KO NK cells with an anti-CD38 mAb was also investigated in a model of multiple myeloma (MM). FcγR-KO immunodeficient mice were used in these studies to limit the confounding contribution of residual murine immune cells engaging with the Fc-competent therapeutic antibody and to specifically detect hNK-cell mediated activity. The comparison of CD38KO versus WT NK cell numbers in the blood of animals treated with an anti-CD38 mAb showed a significant decrease in CD38-expressing NK cell count that was mitigated by the genetic deletion of CD38. Obtained results suggest that CD38KO NK cells are resistant to anti-CD38 mAb-mediated fratricide and provide a rationale for the combination of CD38KO NK cells with anti-an CD38 mAb against MM. Overall, these preclinical in vivo studies have a pivotal role in the evaluation of NK cell combination therapies against cancer and reveal their therapeutic potential. Citation Format: Katarzyna Franciszkiewicz, Pauline Rettman, Beatrice Gauthier, Laurence Noblet, Celine Nicolazzi, Andre Kunert, Rob Igarashi, Loreley Calvet, Valeria Fantin, Sukhvinder Sidhu. Evaluation of NK cell combination therapies in mouse models of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1334.

Immunodeficient NBSGW mouse strain allows chemotherapy modeling in AML patient-derived xenografts.

Immunodeficient NBSGW mouse strain allows chemotherapy modeling in AML patient-derived xenografts.

Abstract A005: Preclinical evaluation of novel immune cell therapies, check point inhibitors, and immune cell engagers in humanized mouse models

Abstract Background The preclinical evaluation of novel immune therapies requires humanized mouse models with functional human immune cells. In previous studies we have demonstrated, that either peripheral blood mononuclear cells (PBMC), subsets of PBMCs like T- and NK-cells or hematopoietic stem cells (HSC) can be used to establish a humanized immune system with functional T-, B-, and NK cells, as well as monocytes and dendritic cells in immunodeficient mice. By xenotransplantation of cell-line-derived (CDX) or patient-derived (PDX) tumors on humanized mice, we successfully generated a full human tumor-immune-cell model for different disease entities. Finally, we validated the functionality of these models using checkpoint inhibitors like Ipilimumab (Ipi), Nivolumab (Nivo), Pembrolizumab (Pembro), cell therapies, and immune cell engagers. Methods HSC-humanized mice were generated by i.v. transplantation of CD34+ stem cells to immunodeficient 1st and 2nd generation NOG mice. Engraftment of immune cells was monitored by FACS analysis of blood samples. PBMC or isolated T- or NK-cell preparations were used to humanize mice by single or multiple i.v. injections. CDX and PDX from different entities were s.c. (i.e. lymphoma) and/or i.v. (leukemia) transplanted on those humanized mice. Tumor growth of orthotopic models was followed up by BLI measurement. Blood and tumor samples were analysed by for immune cell infiltration and activation. Results The transplanted HSCs engrafted in mice and established a functional human immune system with proliferation and differentiation. The 2nd generation NOG mice are showing an increased total engraftment and lineage specific differentiation of cells. The selected CDX and PDX tumors successfully engrafted on humanized mice without significant differences in tumor growth compared to non-humanized mice. Check point inhibitor treatments (Ipi, Nivo, or Pembro) induced tumor growth delay in selected models. BLI measurement is a suitable method to follow up systemic disease models and treatment effects over time. We identified a set of CDX and PDX models without interference with parallel injection of PBMC, T- or NK-cell preparations for the evaluation of immune cell engagers and other cell therapies. Conclusions We established human tumor-immune-cell models of different entities using CDX or PDX in combination with different donor derived immune cell subsets as effector cells. We demonstrated successful engraftment of HSC on different immunodeficient mouse strains, generating mice with a functional human hematopoiesis. These models have been successfully used for preclinical evaluation of novel check point inhibitors, cell therapies and immune cell engagers. Our human tumor-immune-cell models allow preclinical translational research on tumor immune biology as well as evaluation of new therapies, drug combinations, as well as biomarker identification and validation in subcutaneous and orthotopic models. Citation Format: Maria Stecklum, Annika Wulf-Goldenberg, Bernadette Brzezicha, Joshua Alcaniz, Glenn Smits, Wolfgang Walther, Jens Hoffmann. Preclinical evaluation of novel immune cell therapies, check point inhibitors, and immune cell engagers in humanized mouse models [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A005.

MODL-10. SEVERELY IMMUNODEFICIENT NOG-EXL MICE ALLOW FOR HUMANIZATION AND DEVELOPMENT OF A HUMAN GLIOBLASTOMA-DERIVED TUMOR MICROENVIRONMENT

Abstract Cellular immunotherapy has resulted in tremendous therapeutic advances across liquid tumors. However, for solid tumors, including glioblastoma (GBM), significant limitations still exist in successfully translating immune-based adoptive cell therapeutics from the bench to the clinic. The majority of preclinical in vivo GBM models either use human cell lines grown in immunodeficient animals or syngeneic tumors grown in immunocompetent animals. Both approaches lack critical immune components of the tumor microenvironment (TME), thus inherently limiting the ability to adequately model immunotherapies. Here, we demonstrate the ability of hematopoietic stem cells (HSCs) from a GBM patient to successfully engraft in the severely immunodeficient NOG-EXL mouse strain and generate a patient-derived immune system. Intraosseous injections of a low number (10,000) of CD34+ HSCs, obtained from a bone marrow draw from the patient at the time of tumor resection, resulted in an average of 20% human CD45+ cells in peripheral blood 17 weeks post-transplant. GBM organoids, established from the same patient, were implanted intracranially at Week 18 and allowed to grow for 5 weeks without significant clinical evidence of graft-vs-host disease or macrophage activation syndrome. Immunohistochemical and flow cytometry analyses of mouse brains, with and without tumors, revealed infiltration of human-derived, CD45+/CD33+ cells, in proximity to the tumor engraftment site. These results demonstrate the ability of patient-obtained CD34+ HSCs to engraft and form a TME in severely immunodeficient mice. Subsequent work will focus on the differences between autologous and allogeneic humanized tumor-bearing mice in the context of the originating tumor. Additional future work will focus on testing cellular therapies directed towards the relevant areas of the autologous model.

A humanized orthotopic mouse model for preclinical evaluation of immunotherapy in Ewing sarcoma.

The advent of novel cancer immunotherapy approaches is revolutionizing the treatment for cancer. Current small animal models for most cancers are syngeneic or genetically engineered mouse models or xenograft models based on immunodeficient mouse strains. These models have been limited in evaluating immunotherapy regimens due to the lack of functional human immune system. Development of animal models for bone cancer faces another challenge in the accessibility of tumor engraftment sites. Here, we describe a protocol to develop an orthotopic humanized mouse model for a bone and soft tissue sarcoma, Ewing sarcoma, by transplanting fresh human cord blood CD34+ hematopoietic stem cells into young NSG-SGM3 mice combined with subsequent Ewing sarcoma patient derived cell engraftment in the tibia of the humanized mice. We demonstrated early and robust reconstitution of human CD45+ leukocytes including T cells, B cells, natural killer cells and monocytes. Ewing sarcoma xenograft tumors successfully orthotopically engrafted in the humanized mice with minimal invasive procedures. We validated the translational utility of this orthotopic humanized model by evaluating the safety and efficacy of an immunotherapy antibody, magrolimab. Treatment with magrolimab induces CD47 blockade resulting in significantly decreased primary tumor growth, decreased lung metastasis and prolonged animal survival in the established humanized model. Furthermore, the humanized model recapitulated the dose dependent toxicity associated with the CD47 blockade as observed in patients in clinical trials. In conclusion, this orthotopic humanized mouse model of Ewing sarcoma represents an improved platform for evaluating immunotherapy in bone and soft tissue sarcoma, such as Ewing sarcoma. With careful design and optimization, this model is generalizable for other bone malignancies.

Microenvironment-dependent growth of Sezary cells in humanized IL-15 mice.

Sezary syndrome (SS) is a rare, aggressive leukemic variant of cutaneous T-cell lymphoma (CTCL) that lacks adequate therapeutic options and representative small-animal models. Here, we demonstrate that IL-15 is a critical CTCL growth factor. Importantly, an immunodeficient knock-in mouse model genetically engineered to express human IL-15 uniquely supported the growth of SS patient samples relative to conventional immunodeficient mouse strains. SS patient-derived xenograft (PDX) models recapacitated key pathological features of the human disease, including skin infiltration and spread of leukemic cells to the periphery, and maintained the dependence on human IL-15 upon serial in vivo passaging. Detailed molecular characterization of the engrafted cells by single-cell transcriptomic analysis revealed congruent neoplastic gene expression signatures but distinct clonal engraftment patterns. Overall, we document an important dependence of Sezary cell survival and proliferation on IL-15 signaling and the utility of immunodeficient humanized IL-15 mice as hosts for SS - and potentially other T and NK cell-derived hematologic malignancies - PDX model generation. Furthermore, these studies advocate the thorough molecular understanding of the resultant PDX models to maximize their translational impact.

Establishing the Median Infectious Dose and Characterizing the Clinical Manifestations of Mouse, Rat, Cow, and Human Corynebacterium bovis Isolates in Select Immunocompromised Mouse Strains.

Corynebacterium bovis (Cb), the cause of hyperkeratotic dermatitis in various immunocompromised mouse strains, significantly impacts research outcomes if infected mice are used. Although Cb has been isolated from a variety of species, including mice, rats, cows, and humans, little is known about the differences in the infectivity and clinical disease that are associated with specific Cb isolates. The infectious dose that colonized 50% of the exposed population (ID50 ) and any associated clinical disease was determined in athymic nude mice (Hsd:Athymic Nude-Foxn1 nu ) inoculated with Cb isolates collected from mice (n = 5), rat (n = 1), cow (n = 1), and humans (n = 2) The same parameters were also determined for 2 of the mouse isolates in 2 furred immunocompromised mouse strains (NSG [NOD. Cg-Prkdcscid Il2rgtm1Wjl /Sz] and NSG-S [NOD. Cg-Prkdcscid Il2rgtm1Wjl Tg(CMV-IL3, CSF2, KITLG)1Eav/MloySzJ]). To determine the ID 50, mice (n= 6/dose; 3 of each sex) were inoculated topically in 10-fold increments ranging from 1 to 10 8 bacteria. Mice were scored daily for 14 days for the severity of clinical signs. On days 7 and 14 after inoculation, buccal and dorsal skin swabs were evaluated by aerobic culture to determine infection status. The mouse isolates yielded lower ID50values (58 to 1000 bacteria) than did the bovine (6460 to 7498 bacteria) and rat (10,000 bacteria) isolates. Human isolates did not colonize mice or cause disease. Mouse isolates produced clinical disease of vary- ing severity in nude mice. Despite significant immunodeficiency, furred NSG and NSG-S mice required a 1000- to 3000-fold higher inoculum for colonization than did athymic nude mice. Once colonized, clinically detectable hyperkeratosis did not develop in the haired strains until 18 to 22 d after inoculation, whereas athymic nude mice that developed clinically detect- able disease showed hyperkeratosis between 6 and 14 d after inoculation. In conclusion, there are significant differences in Cb's ID 50, disease course, and severity of clinical signs between Cb isolates and among immunodeficient mouse strains.

Production of Humanized Mice through Stem Cell Transfer.

The development of "humanized" mice has become a prominent tool for translational animal studies of human diseases. Immunodeficient mice can be humanized by injections of human umbilical cord stem cells. The engraftment of these cells and their development into human lymphocytes has been made possible by the development of novel severely immunodeficient mouse strains. Proven protocols for the generation and analysis of humanized mice in the NSG mouse background are presented here. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Human umbilical stem cell engraftment of neonatal immunodeficient mice Basic Protocol 2: Human umbilical stem cell engraftment of 4-week-old immunodeficient mice Support Protocol 1: Preparation of human umbilical stem cells Support Protocol 2: Submandibular blood collection from humanized mice and analysis of peripheral blood via flow cytometry.

NCG-MHC-dKO mice - an excellent model for PBMC reconstitution and pharmacodynamic evaluation in the absence of GvHD

Abstract Human immune cell reconstitution (Peripheral Blood Mononuclear Cells; PBMC or CD34 +hematopoietic stem cell; HSC) is commonly performed in immunodeficient mouse strains, such as NCG, NSG, or NOG. Human immune reconstitution utilizing PBMCs is a much more rapid model, allowing for T-cell reconstitution within 2 weeks. Due to the occurrence of xenogeneic graft-versus-host disease (xGvHD) around 4 weeks post-engrafment, the application of PBMC-reconstituted NCG mice is relatively limited. xGvHD is mainly induced by T cells derived from donor PBMC engraftment recognizing the murine host MHC class I and class II as foreign and attacking the host cells and organs. Deleting the β2m (NCG-β2m-KO) could reduce the occurrence of xGvHD; however, β2m is not only in the MHC class I subunit but also in the FcRn subunit, of which deletion shortens the half-life of IgG, making it unsuitable for IgG antibody agent evaluation. In addition, the deletion of MHC class I or class II alone results in an imbalanced CD4/CD8 ratio. To solve these problems, we developed the NCG-MHC-dKO mouse model by knocking out the H2K1, H2D1, and H2Ab1genes. Compared with the existing NCG-B2m-KO mouse model, the NCG-MHC-dKO significantly prolonged survival, reduced xGvHD occurrence, and did not affect the CD4/CD8 ratio when reconstituted with PBMC. Furthermore, treatment with anti-PD-L1 antibodies significantly inhibited MDA-MB-231 tumor cell growth in PBMC-reconstituted NCG-MHC-dKO mice, similar to NCG mice. Based on our preliminary data, the NCG-MHC-dKO mouse is a promising model for evaluating antibody and cell therapy agents, assessing treatment-related cytokine release syndrome, and evaluating long-term toxicities of cell therapies.

Abstract 41: Subcutaneous growth and immune cell profiling of BT-474 human breast carcinoma in four strains of triple immunodeficient mice

Abstract Triple immunodeficient mouse models, that lack functional T cells, B cells, and natural killer cells, are necessary when evaluating human cancer cell growth and cell-based therapy activity, allowing for assessment without innate mouse immune system involvement. Due to limited colony sizes at any given vendor, study timelines can sometimes become compromised unless a sufficient alternative is validated. Site location can also be a factor, as licensing restrictions may be an issue for international corporations. In an effort to prove overall similarities across four strains of triple immunodeficient mice, the growth characteristics of BT-474 were compared in female NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice, NOD.CB17-Prkdcscid IL2rgtm1/BcgenHsd (B-NDG) mice, NOD-Prkdcem26Cd52Il2rgem26Cd22/NjuCrl (NCG) mice, and NOD.Cg-Prkdcscid Il2rgtm1Sug/JicTac (CIEA NOG) mice. An immune cell profile was also performed across these four mouse strains and evaluated via flow cytometry to observe any immune cell subset differences in blood, spleen, and tumor samples. Samples analyzed post implant were collected when subcutaneous tumors were ~500 mm3. Model development studies were completed previously to optimize tumor growth kinetics. Historic growth conditions were BT-474 cells implanted at 1.0E+07 cells/implant in the presence of an extracellular matrix into the high right axilla of female NSG mice. Using the same optimized growth conditions, NSG, B-NDG, NCG, and CIEA NOG mice were implanted with BT-474 cells. BT-474 grew well in all the tested mouse strains, producing 100% take rate. Compared to NSG mice, median tumor volume doubling times differed by 1-5 days, median times to an evaluation size of 150 mm3 (typical study enrollment tumor volume) differed by +/- ~4 days and median time to an evaluation size of 1250 mm3 (tumor volume at the end of life) differed by +/- ~10 days. BT-474 did not induce body weight loss in any of the tested mouse strains and all clinical observations were similar. Flow cytometry was performed to quantify lymphocyte and myeloid immune subsets in blood, spleen, and tumor. Overall, compared to NSG mice, the absolute counts were similar for all immune subsets measured except for regulatory T cells (Tregs). B-NDG, NCG, and CIEA NOG mice had reduced Treg numbers in the spleen of tumor-bearing mice. In the tumor, Treg numbers were lower in the B-NDG and CIEA NOG mice. No differences were observed for any immune subset in the blood. Overall, the tumor growth kinetics of BT-474 in B-NDG mice was most similar to historical data using NSG mice. The flow data also confirmed that each strain’s immune cell population generally looked very similar, with limited differences between the four strains of triple immunodeficient mice. Citation Format: Justin Snider, Derrik Germain, Lauren Kucharczyk, Anita Zaitouna, Erin Trachet, Scott Wise. Subcutaneous growth and immune cell profiling of BT-474 human breast carcinoma in four strains of triple immunodeficient mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 41.

Abstract 38: PBMC donor selection affects engraftment rates and onset of graft versus host disease in humanized NCG mice for use in cancer studies

Abstract Preclinical studies examining tumor biology and immunity are limited by differences between the mouse and human immune systems. Humanized mouse models offer a unique tool to assess the anti-tumor response by recapitulating aspects of human tumor biology. Humanized mice are created by injecting either human CD34+ hematopoietic stem cells or peripheral blood mononuclear cells (PBMCs) into an immunodeficient mouse strain. Here we utilized a PBMC humanized NCG mouse model to investigate human T-cell mediated anti-tumor response (>95% CD3+ T-cells by day 21). The challenges encountered with this model include the onset of graft versus host disease (GvHD) and donor variability leading to donor specific engraftment rates. Consistency is required with humanized PBMC models to ensure their use as an appropriate research model. Therefore, we examined the relationship between donor selection and engraftment rates as well as the onset of GvHD. Inter-donor variability was assessed by collecting PBMCs from multiple healthy donors. Intra-donor consistency was assessed by collecting PBMCs from the same donors at subsequent collections and comparing to initial human immune cell profiling by flow cytometry. NCG mice were injected with 1 × 107 PBMCs from individual donors. Animals were weighed three times a week to monitor for changes in body weight and general health status. Peripheral blood was collected at day 9, 21 and 42 for flow cytometry screening of human immune cell engraftment (hCD45+, hCD3+, hCD4+ and hCD8+) at the initial collection. Human PBMCs isolated from additional collections from the same donors were also injected into NCG mice and flow cytometry was performed on the new cell lots at day 21. Donors were grouped into categories based on engraftment rates, which were donor dependent. Donor variability is an important aspect to consider when humanizing mice with human PBMCs. PBMC humanized models are important for the study of pre-clinical therapeutics, but donor engraftment rates must be considered when engrafting the mice to create a consistently humanized mouse. Citation Format: Steven Bronson, Jenny Rowe, Christoph Eberle, Stephen Festin. PBMC donor selection affects engraftment rates and onset of graft versus host disease in humanized NCG mice for use in cancer studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 38.

Abstract 5192: NCG-MHC-dKO mice: an excellent model for PBMC reconstitution and pharmacodynamic evaluation in the absence of GvHD

Abstract Human immune cell reconstitution (PBMC or CD34+ hematopoietic stem cell; HSC) is commonly performed in immunodeficient mouse strains such as NCG, NSG, or NOG. The use of PBMC is preferred for multiple reasons, including faster engraftment, lower cost, and the presence of mature immune cell populations. Although there are donor-to-donor variations in GvHD occurrence, and specific donors can be screened, the symptoms of GvHD typically occur within 4 weeks. GvHD significantly limits the study window required to evaluate the efficacy of therapeutic agents, such as cancer immunotherapies. GvHD is an immune reaction triggered mainly by donor T cells identifying the mouse MHC class I and class II as foreign and attacking the host cells and organs. Deletion of β2m (NCG- β2m-KO) reduces the occurrence of GvHD; however, β2m is not only in the MHC class I subunit but also in the FcRn subunit, of which deletion shortens the half-life of IgG, making it unsuitable for IgG antibody agent evaluation. In addition, the deletion of MHC class I or class II alone results in an imbalanced CD4/CD8 ratio. To solve these problems, we developed the NCG-MHC-dKO mouse model by knocking out the H2K1, H2D1, and H2Ab1 genes. Compared with the existing NCG- β2m-KO or other β2m null mouse models, the NCG-MHC-dKO significantly prolonged survival, reduced GvHD occurrence, and did not affect the CD4/CD8 ratio when reconstituted with PBMC. Furthermore, treatment with anti-PD-L1 antibodies significantly inhibited MDA-MB-231 tumor cell growth in PBMC-reconstituted NCG-MHC-dKO mice, similar to NCG mice. Based on our preliminary data, the NCG-MHC-dKO mouse is a promising model for antibody and cell therapy agent evaluation, assessing treatment-related cytokine release syndrome, and evaluating long-term toxicities of cell therapies. Citation Format: Huiyi Wang, Jun Xing, Jialu Fan, Huanhuan Hou, Santi Suryani Chen, Zhiying Li, Mark Wade Moore, Jing Zhao, Xiang Gao, Cunxiang Ju. NCG-MHC-dKO mice: an excellent model for PBMC reconstitution and pharmacodynamic evaluation in the absence of GvHD. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5192.

Abstract 2940: Use of NK humanized mouse models for the in vivo evaluation of anti-tumor NK-cell therapies

Abstract Novel immunotherapeutic strategies targeting human Natural Killer (huNK) cells using monoclonal or multi-specific antibodies and immune modulator molecules are under development and there is a pressing need to have suitable mouse models for the evaluation of these therapeutics. Existing humanized mouse models have limitations and do not show an optimal development of innate immune cells such as NK, dendritic or other myeloid cells. We previously described the development of robust mouse models that allow the engraftment and maintenance of fully functional huNK cells using several strains of immunodeficient transgenic mice for human cytokines (IL-15). The optimal parameters (source of immune cells, pre-conditioning regimen, route of administration) were identified, and the models were validated by flow cytometry and in vivo efficacy studies using an anti-CD20 Ab. Here, we report further development and characterization of these models and highlight their value to evaluate a variety of NK based therapeutics. We show that huNK cells can infiltrate a subcutaneous B-cell lymphoma model after treatment with an anti-CD20 Ab. We show that SAR444245 (non-alpha IL2) can activate huNK cells in vivo in all developed huIL-15 transgenic models and confirmed the minimal effective dose by flow-cytometry PD studies. We show the efficacy of both reference and internal ADCC-enhanced antibodies in disseminated tumor models in our humanized huIL-15 transgenic mice. In addition, we performed a deep characterization of huNK cells in huIL-15 transgenic models, using a 28-color flow cytometry panel centered on NK cell biology and profiled them transcriptionally by single cell RNA Seq in a disseminated B-cell lymphoma model. Overall, we have developed robust models sustaining fully functional huNK cells that can be proficiently recruited in vivo by various NK-based therapeutics and can be used to evaluate the efficacy of combination therapies. Citation Format: Pauline Rettman, Laure-Marie Meyer, Ravi Rangara, Anna Ponchet-Lac, Nicolas Moindrot, Angélique Biancotto, Céline Lefranc, Fabien Delahaye, Emilia Rabia, Matteo Cesaroni, Sukhvinder Sidhu, Céline Nicolazzi. Use of NK humanized mouse models for the in vivo evaluation of anti-tumor NK-cell therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2940.

Abstract 5207: Development of MHC I/II knock-out immunodeficient mouse strains for alleviating GvHD induced by human PBMC reconstitution

Abstract Severely immunodeficient mouse strains, such as B-NDG mice, lack B, T, and NK cells, and have been widely used as an in vivo model to evaluate human immune responses, including applications in immuno-oncology in recent years. However, when human peripheral blood mononuclear cells (PBMCs) are engrafted in these mice, severe acute xenogeneic graft-versus-host disease (GvHD) arises due to engagement of human T cell receptors (TCRs) with major histocompatibility complex (MHC) proteins I and II on the surface of murine immune cells. GvHD shortens the animal life span such that there is only a brief window of evaluation of human immune cell functions in these mouse models. Consequently, efforts have been undertaken to reduce human PBMC-induced GvHD and to subsequently extend the window of human immunity assessment in immunodeficient mouse strains by eliminating mouse MHC I and MHC II. We previously engineered a novel B2m gene knock-out strain on the B-NDG background (NOD.CB17-PrkdcscidIl2rgtm1/Bcgen), which is deficient in MHC I expression, but expresses the B2m gene fused into the FcRn gene to retain FcRn-mediated antibody metabolism. In order to eliminate MHC II expression, we also engineered an H2-Ab1 gene knock-out strain on the same B-NDG background and cross-bred the two strains together to obtain an MHC I/II double KO mouse model, termed B-NDG MHC I/II DKO mice plus. Splenocytes collected from the engineered strains were analyzed by flow cytometry. As expected, mouse H-2Kb/H-2Db was not detectable in B-NDG B2m KO plus mice or B-NDG MHC I/II DKO mice plus. While mouse I-Ak was detected in B-NDG mice and B-NDG B2m KO plus mice, it was not detected in B-NDG MHC I/II DKO mice plus. Pharmacokinetic assessments demonstrate that B-NDG mice and B-NDG B2m KO mice plus groups were able to recycle human IgG, with no differences when compared with wild-type C57BL/6 mice, indicating normal FcRn function. Finally, the three strains of mice were irradiated and engrafted with human PBMC from three donors to evaluate GvHD incidence. As expected, the reconstitution levels of CD45+ leukocytes, T cells, CD4+ T cells, CD8+ T cells, Tregs and NK cells were similar among the three strains. However, lack of MHC I/II in B-NDG MHC I/II DKO mice plus can significantly extend the life span and reduce GvHD induced by human PBMC engraftment compared to B-NDG mice and B-NDG B2m KO mice plus. These results indicate that B-NDG MHC I/II DKO mice plus provides a useful mouse model for reducing GvHD after human PBMC reconstitution in immunodeficient mice. This model may be a powerful preclinical tool for future in vivo evaluation of cell therapies and antibodies. Citation Format: Qiang Liu, Chengzhang Shang, Xiaofei Zhou, Jenna Frame, Zhiyuan Shen, Zhaoxue Yu. Development of MHC I/II knock-out immunodeficient mouse strains for alleviating GvHD induced by human PBMC reconstitution. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5207.

Use of Hu-PBL Mice to Study Pathogenesis of Human-Restricted Viruses.

Different humanized mouse models have been developed to study human diseases such as autoimmune illnesses, cancer and viral infections. These models are based on the use of immunodeficient mouse strains that are transplanted with human tissues or human immune cells. Among the latter, mice transplanted with hematopoietic stem cells have been widely used to study human infectious diseases. However, mouse models built upon the transplantation of donor-specific mature immune cells are still under development, especially in the field of viral infections. These models can retain the unique immune memory of the donor, making them suitable for the study of correlates of protection upon natural infection or vaccination. Here, we will review some of these models and how they have been applied to virology research. Moreover, the future applications and the potential of these models to design therapies against human viral infections are discussed.

Isolation and Characterization of a Novel Alpha-Hemolytic Streptococcus spp. from the Oral Cavity and Blood of Septicemic Periparturient Immunodeficient Mice.

MISTRG is an immunodeficient mouse strain that expresses multiple human cytokines that support hematopoietic stem cell maintenance and myelopoiesis. While establishing a breeding colony of MISTRG mice in a dedicated barrier room, 6 cases of death or disease occurred in pregnant or postpartum mice. Clinically, this manifested as hunched posture, dyspnea, and 1 case of emaciation with ataxia. Pathologic analysis of 7 mice revealed multisystemic necrosuppurative inflammation variably affecting the uterus and placenta, joints, meninges, inner and middle ears, kidneys, and small intestine. Bacteria cultured from the blood of septic mice were identified with 89% probability by the Vitek 2 identification system as Streptococcus sanguinuswith atypical biochemical parameters; the API 20E/NE system fully differentiated the isolates as a novel Streptococcusspecies. MALDI Biotyper-based mass spectrometry also indicated that the phenotype represented a novel Streptococcusspp. Sequencing revealed that the full-length 16S rRNA gene identity was below 97% with known Streptococcus species, including the 2 closest species Streptococcus acidominimus and Streptococcus azizii. We propose the name Streptococcus murisepticum spp. nov to our novel isolates. All male mice in this colony remained healthy despite their association with diseased female mice. Overall, 19% of the colony carried the novel Streptococcus in their oral cavity, but it could not be detected in feces. The organism was sensitive to amoxicillin, which was administered via drinking water throughout pregnancy and weaning to establish a colony of pathogen-negative future breeders. The colony remained disease-free and culture-negative for Streptococcus murisepticum spp. nov after treatment with amoxicillin. We suspect that oral colonization of MISTRG mice with the novel Streptococcus species and its associated unique pathology in periparturient mice is potentially the principal cause of loss of this strain at several institutions. Therefore, screening the oral cavity for α-hemolytic streptococci followed by targeted antibiotic treatment may be necessary when establishing MISTRG and allied immunodeficient mouse strains.

M2 Macrophages Drive Resistance to Phagocytosis and Improve Mitochondrial Metabolism in Acute Myeloid Leukemia Facilitating Leukemic Transformation and In Vivo Engraftment

Acute myeloid leukemia (AML) is a heterogeneous disease, which also extends to its tumor microenvironment (TME). Using single cell RNA-seq data (GSE116256), we performed differential gene expression analysis on macrophages from AML patients (AML-derived macrophages, AdMs) compared to healthy bone marrow macrophages. Thus, 306 upregulated genes in AdMs were identified as involved in different biological pathways such as proliferation, inflammation and cellular metabolism. Down-regulated genes (232) were mainly associated with the regulation of apoptosis. Single cell gene set enrichment analysis associated AdMs with an M2-like phenotype and an immunosuppression transcriptional program. We then investigated the macrophage landscape in a large cohort of AML patients by flow cytometry (n = 61) and immunohistochemistry, which revealed a large heterogeneity whereby AML patients with a predominant M2-like TME showed poor prognosis. Next, we evaluated the immune function of AdMs compared to healthy donor-derived macrophages. Thus, we showed that AdMs displayed decreased phagocytic capacity towards AML cells compared to healthy macrophages. Since AdMs might directly descend from the mutated leukemic clones we evaluated whether these mutations could affect the immune function of macrophages. Cord blood-derived CD34+ cells were lentivirally transduced with FLT3-ITD, differentiated towards macrophages, and these FLT3-ITD+ macrophages displayed decreased phagocytic activity. We questioned whether endogenous murine macrophages that are still present in immunodeficient mouse strains that are often used for human studies might form a barrier that needs to be taken to achieve efficient engraftment of human cells. Macrophages were isolated from NSG mice and were used in phagocytosis assays. The percentage of phagocytosed primary AML blasts by murine macrophages ranged between 3.2-51.4%, similar to phagocytosis levels observed when using human macrophages for the same AML samples. While performing these phagocytosis assays, we noted that the cells that remained and were not phagocytosed had an altered appearance and were very viable, as if these cells had gained fitness. We tested this further by exposing leukemic blasts to M2 macrophages for 48 h, after which the remaining cells were analyzed functionally. We observed that the 48 h "training" of primary leukemic blasts significantly enhanced their mitochondrial metabolism (in part mediated via mitochondrial transfer from macrophages to leukemic blasts), enhanced their in vitro and in vivo homing capacity and that they became resistant to phagocytosis. As a most striking example we used primary APL cells that are notoriously difficult to engraft in NSG mice, which we hypothesized could be in line with their high intrinsic susceptibility to macrophage-mediated phagocytosis. APL cells were exposed to M2 macrophages for 48h resulting in two cellular fates: 91.7% of cells were phagocytosed, but the remaining 8.3% APL blasts were able to induce fatal leukemia when transplanted into NSGS mice in all evaluated cases (n = 6), while prior to training these cells did not engraft long-term and were not able to confer disease. We also tested the tumor supportive capacity on M2 macrophages by performing intrafemoral injection in NSGS mice after which non-trained APL blasts were injected intravenously. Again, efficient engraftment and fatal leukemia development were observed, but only in mice co-injected with M2 macrophages. Strategies to target the supportive AdM subpopulation would be of interest. In our scRNA-seq analysis, we identified the metabolic enzyme Nicotinamide phosphoribosyltransferase (NAMPT) to be upregulated in AdMs. Ex vivo studies revealed that while conventional chemotherapeutics, AraC/venetoclax, efficiently target the AML blasts (CD34+/CD117+) with minimum effects on the AdMs, NAMPT inhibition with KPT-9274 was able to efficiently target both the AML blasts and the AdM fractions. Functionally, treatment of M2 macrophages with KPT-9274 shifted their polarization towards an M1 phenotype, with reduced support to AML cells in co-culture assays. In conclusion, we uncover the heterogeneity in the macrophage landscape in AML patients, show the functional relevance of M2-polarized macrophages for leukemic transformation, and provide alternative approaches for targeting aimed at the tumor-supportive microenvironment.

TMIC-51. SEX-SPECIFIC T CELL BEHAVIOR DRIVES DIFFERENTIAL IMMUNE RESPONSES IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) is the most common primary malignant brain tumor and shows poor outcomes as a median survival is 12-18 months with current standard-of-care of therapy. GBM exhibits sex differences in incidence and overall survival, with males experiencing a higher incidence and a worse prognosis compared to females. However, the role of immune cells in GBM sex differences outside of myeloid cells remains poorly understood. Using a syngeneic mouse GBM model, we recapitulated the sex differences observed in patients, with shortened survival in male hosts compared to female hosts. These findings were not recapitulated in immuno-deficient mouse strains such as NSG and RAG1KO mice, suggesting a role for immune system, specifically T cells, in GBM sex differences. Flow cytometry analysis of tumor-infiltrating leukocytes revealed that more T cells were found in female tumors, whereas male tumors were enriched in macrophages. Additionally, more T cells in male tumors exhibited high levels of inhibitory receptors, whereas most female T cells were more functional as measured by expression of anti-tumor cytokines such as TNF, IFN-gamma, and granzyme B. A bone marrow chimera model (BMC) revealed that male T cells retained their phenotype in female hosts, whereas female T cell behavior was affected by the male environment. Yet survival analysis on BMC model and adoptive transfer model suggests strong immune cell-intrinsic effect on controlling tumor progression, further supported by in vitro T cell exhaustion model. Lastly, we found that males have more progenitor exhausted T cells, which led to better response to anti-PD1 treatment. Collectively, these results suggest that both cell-intrinsic and cell-extrinsic factors regulate T cell activity in a sex-specific manner, providing insights to develop sex-specific therapeutic approaches.

32 (PB022) - Humanized mouse models for preclinical evaluation of novel immune therapies, checkpoint inhibitors and immune cell engagers

Background: The preclinical evaluation of novel immune therapies demands humanized mouse models with functional human immune cells. In previous studies we have established a humanized immune system with functional T- B- and NK cells, as well as monocytes in immunodeficient mice by transfer of hematopoietic stem cells (HSCs) or peripheral blood mononuclear cells (PBMC). By transplantation of cell-line-derived (CDX) or patient-derived (PDX) tumor xenografts on humanized mice, we successfully generated a full human tumor-immune-cell model for different tumor entities. Finally, we validated the functionality of these models using checkpoint inhibitors or immune cell engagers. Methods: HSC-humanized mice were generated by single i.v. transplantation of CD34+ stem cells to immunodeficient NOG mice. Engraftment of immune cells was monitored by FACS analysis of blood samples. CDX and PDX from different entities were transplanted on the humanized mice. PBMC or isolated T- or NK-cell preparations were used to humanize mice by single or multiple i.v. injections into tumor-bearing mice or with simultaneous tumor cell transplantation. These models were used to evaluate immune checkpoint inhibitors. Blood and tumor samples were analysed by FACS and immunohistochemistry for immune cell infiltration and activation. Results: The transplanted HSCs engrafted in mice and established a functional human differentiated immune system with proliferating immune cells. Up to 20% of the human immune cells in the blood were functional T cells, characterized by a high PD-1 expression 14 weeks after HSC inoculation. Selected CDX and PDX tumors successfully engrafted on humanized mice without significant differences in tumor growth compared to non-humanized mice. Checkpoint inhibitor treatments induced tumor growth delay in selected models. FACS analysis of xenograft tumors revealed an increased percentage of tumor-infiltrating T cells. In addition, we identified a set of CDX and PDX models without interference with parallel injection of PBMC, T- or NK-cell preparations for the evaluation of immune cell engagers and other immune therapeutics. Conclusions: We established human tumor-immune-cell models of different entities using CDX or PDX in combination with different donor derived immune cell subsets as effector cells. We demonstrated successful engraftment of HSCs on immunodeficient mouse strains generating mice with a functional human hematopoiesis. These models have been employed for preclinical evaluation of novel checkpoint inhibitors and immune cell engagers. Our human tumor-immune-cell models allow preclinical, translational studies on tumor immune biology as well as evaluation of new therapies, drug combinations and biomarker identification and validation. No conflict of interest.

Efficacy of 3 Buprenorphine Formulations for the Attenuation of Hypersensitivity after Plantar Incision in Immunodeficient NSG Mice.

Buprenorphine is perhaps the most prescribed analgesic for management of postoperative pain in mice. Although various buprenorphine formulations are effective in commonly used immunocompetent mouse strains, a knowledge gap exists regarding its efficacy in immunodeficient mice. Here we used a plantar incision to evaluate the efficacy of 3 buprenorphine formulations for attenuating postoperative mechanical and thermal hypersensitivity in the immunodeficient NSG mouse strain. We also characterized the pharmacokinetics of these formulations over a 72-h period. We hypothesized that all 3 buprenorphine formulations evaluated-the standard preparation and 2 extended-release products (Bup-HCl, Bup-ER, and Bup-XR, respectively)-would attenuate postoperative mechanical and thermal hypersensitivity resulting from a plantar incision in NSG mice. Male and female NSG mice (n = 48) were allocated to 4 treatment groups: saline (0.9% NaCl, 5 mL/kg SC once); Bup-HCl (0.1 mg/kg SC, BID for 2 d); Bup-ER (1.0 mg/kg SC once); and Bup-XR (3.25 mg/kg SC once). Mechani- cal and thermal hypersensitivity assessments were conducted 24 h before surgery and at 4, 8, 24, 48, and 72 h afterward. All groups of mice showed mechanical and thermal hypersensitivity within the first 24 h after surgery. Behavioral pain indicators (guarding, toe-touching [intermittent partial weight bearing], licking the incision, vocalizations) were observed in some mice from each group at every postoperative time point. Plasma buprenorphine was measured in a separate group of mice and concentrations surpassed the suggested therapeutic level (1.0 ng/mL) for less than 4 h for Bup-HCl, for at least 24 h for Bup-ER, and for 72 h for Bup-XR. Our results indicate that at the dosages studied, these buprenorphine formulations do not adequately attenuate postoperative mechanical and thermal hypersensitivity in the plantar incisional model in NSG mice. These findings support the need for strain-specific analgesic protocols for mice used in research.