Immune-privileged tissues formed from immunologically cloaked mouse embryonic stem cells survive long term in allogeneic hosts.

The immunogenicity of transplanted allogeneic cells and tissues is a major hurdle to the advancement of cell therapies. Here we show that the overexpression of eight immunomodulatory transgenes (Pdl1, Cd200, Cd47, H2-M3, Fasl, Serpinb9, Ccl21 and Mfge8) in mouse embryonic stem cells (mESCs) is sufficient to immunologically 'cloak' the cells as well as tissues derived from them, allowing their survival for months in outbred and allogeneic inbred recipients. Overexpression of the human orthologues of these genes in human ESCs abolished the activation of allogeneic human peripheral blood mononuclear cells and their inflammatory responses. Moreover, by using the previously reported FailSafe transgene system, which transcriptionally links a gene essential for cell division with an inducible and cell-proliferation-dependent kill switch, we generated cloaked tissues from mESCs that served as immune-privileged subcutaneous sites that protected uncloaked allogeneic and xenogeneic cells from rejection in immune-competent hosts. The combination of cloaking and FailSafe technologies may allow for the generation of safe and allogeneically accepted cell lines and off-the-shelf cell products.

Cell-based passive immunization for protection against SARS-CoV-2 infection.

BACKGROUND: Immunologically impaired individuals respond poorly to vaccines, highlighting the need for additional strategies to protect these vulnerable populations from COVID-19. While monoclonal antibodies (mAbs) have emerged as promising tools to manage infectious diseases, the transient lifespan of neutralizing mAbs in patients limits their ability to confer lasting, passive prophylaxis from SARS-CoV-2. Here, we attempted to solve this problem by combining cell and mAb engineering in a way that provides durable immune protection against viral infection using safe and universal cell therapy. METHODS: Mouse embryonic stem cells equipped with our FailSafe™ and induced allogeneic cell tolerance technologies were engineered to express factors that potently neutralize SARS-CoV-2, which we call 'neutralizing biologics' (nBios). We subcutaneously transplanted the transgenic cells into mice and longitudinally assessed the ability of the cells to deliver nBios into circulation. To do so, we quantified plasma nBio concentrations and SARS-CoV-2 neutralizing activity over time in transplant recipients. Finally, using similar cell engineering strategies, we genetically modified FailSafe™ human-induced pluripotent stem cells to express SARS-CoV-2 nBios. RESULTS: Transgenic mouse embryonic stem cells engineered for safety and allogeneic-acceptance can secrete functional and potent SARS-CoV-2 nBios. As a dormant, subcutaneous tissue, the transgenic cells and their differentiated derivatives long-term deliver a supply of protective nBio titers in vivo. Moving toward clinical relevance, we also show that human-induced pluripotent stem cells, similarly engineered for safety, can secrete highly potent nBios. CONCLUSIONS: Together, these findings show the promise and potential of using 'off-the-shelf' cell products that secrete neutralizing antibodies for sustained protective immunity against current and future viral pathogens of public health significance.

Soluble CX3CL1-expressing retinal pigment epithelium cells protect rod photoreceptors in a mouse model of retinitis pigmentosa.

BACKGROUND: Retinitis pigmentosa (RP) is an inherited retinal disease that results in photoreceptor degeneration, leading to severe vision loss or blindness. Due to its genetic heterogeneity, developing a new gene therapy to correct every genetic mutation contributing to its progression is infeasible. Photoreceptor transplantation can be harnessed to restore vision; however, this approach is limited by poor cell survival and synaptic integration into the neural retina. Thus, we developed a combined cell and gene therapy that is expected to protect photoreceptors in most, if not all, cases of RP. METHODS: Human embryonic stem cells (hESCs) modified with our FailSafe™ system were genetically engineered to overexpress sCX3CL1, an inhibitor of microglia activation that has been shown to preserve photoreceptor survival and function in mouse models of RP, independent of the genetic cause. These cells were differentiated into human retinal pigment epithelium (hRPE) cells and used as therapeutic cells due to their longevity and safety, both of which have been demonstrated in preclinical and clinical studies. Transgenic hRPE were delivered into the subretinal space of immunodeficient mice and the rd10 mouse model of RP to evaluate donor cell survival and retention of transgene expression. The outer nuclear layer was quantified to assess photoreceptor protection. RESULTS: Transgenic FailSafe™ hRPE (FS-hRPE) cells can survive for at least four months in the retina of immunodeficient mice and retain transgene expression. However, these cells do not persist beyond two weeks post-injection in the retina of immunocompetent rd10 recipients, despite Cyclosporine A treatment. Nevertheless, sCX3CL1-expressing FailSafe™ hRPE cells prevented photoreceptor degeneration in a local acting manner during the duration of their presence in the subretinal space. CONCLUSIONS: Transgenic hESCs differentiate into hRPE cells and retain sCX3CL1 transgene expression both in vitro and in vivo. Moreover, hRPE cells delivered to the subretinal space of rd10 mice prevented photoreceptor degeneration in a local-acting manner, suggesting that this approach could have applications for preserving photoreceptors in specific subregions of the retina, such as the macula. Overall, our study not only reveals the potential of a combined cell and gene therapy for the treatment of RP, but also the possibility of using hRPE cells to deliver therapeutic biologics in situ to treat diseases over long-term.

A Model-System to Address the Impact of Phenotypic Heterogeneity and Plasticity on the Development of Cancer Therapies.

The main challenges in developing effective anti-cancer therapies stem from the highly complex and heterogeneous nature of cancer, including the presence of multiple genetically-encoded and environmentally-induced cancer cell phenotypes within an individual. This diversity can make the development of successful treatments difficult as different phenotypes can have different responses to the same treatment. The lack of model-systems that can be used to simultaneously test the effect of therapies on multiple distinct phenotypic states further contributes to this problem. To mitigate these challenges, we suggest that in vitro model-systems that consist of several genetically-related but phenotypically distinct populations can be used as proxies for the several phenotypes (including adherent and circulating tumor cells) present in a patient with advanced disease. As proof of concept, we have developed such a model and showed that different phenotypes had different responses to the same challenge (i.e., a change in extracellular pH) both in terms of sensitivity and phenotypic plasticity. We suggest that similar model-systems could be developed and used when designing novel therapeutic strategies, to address the potential impact of phenotypic heterogeneity and plasticity of cancer on the development of successful therapies. Specifically, the effect of a therapy should be considered on more than one cancer cell phenotype (to increase its effectiveness), and both cell viability as well as changes in phenotypic state (to address potential plastic responses) should be evaluated. Although we are aware of the limitations of in vitro systems, we believe that the use of established cell lines that express multiple phenotypes can provide invaluable insights into the complex interplay between therapies and cancer's heterogeneous and plastic nature.

Jack of many trades: Multifaceted role of neuropilins in pancreatic cancer.

Neuropilins (NRPs) have been described as receptors for class 3 semaphorins and coreceptors for a plethora of ligands, such as members of the vascular endothelial growth factor (VEGF) family of angiogenic cytokines and transforming growth factor (TGF). Initial studies using genetic models have indicated that neuropilin-1 (NRP-1) is essential for axonal guidance during neuronal and cardiovascular development, regulated via semaphorins and VEGF, respectively, whereas the other homolog of neuropilin, NRP-2, has been shown to play a more specific role in neuronal patterning and lymphangiogenesis. Pancreatic ductal adenocarcinoma (PDAC) remains a significant cause of cancer mortality with the lowest five-year survival rate compared to other types of cancer. Recent findings have indicated that NRPs are abundantly expressed in pancreatic cancer cell lines and pancreatic tumor tissues, where they mediate several essential cancer-initiating and cancer-promoting functional responses through their unique ability to bind multiple ligands. Specifically, NRPs have been implicated in numerous biological processes such as cancer cell proliferation, survival, invasion, and tumor growth. More recently, several other protumorigenic roles mediated by NRPs have emerged, advocating NRPs as ideal therapeutic targets against PDAC.