Reenacting Neuroectodermal Exposure of Hematopoietic Progenitors Enables Scalable Production of Cryopreservable iPSC-Derived Human Microglia

Ice recrystallization inhibitors enable efficient cryopreservation of induced pluripotent stem cells: A functional and transcriptomic analysis

The successful use of human induced pluripotent stem cells (iPSCs) for research or clinical applications requires the development of robust, efficient, and reproducible cryopreservation protocols. After cryopreservation, the survival rate of iPSCs is suboptimal and cell line-dependent. We assessed the use of ice recrystallization inhibitors (IRIs) for cryopreservation of human iPSCs. A toxicity screening study was performed to assess specific small-molecule carbohydrate-based IRIs and concentrations for further evaluation. Then, a cryopreservation study compared the cryoprotective efficiency of 15 mM IRIs in 5 % or 10 % DMSO-containing solutions and with CryoStor® CS10. Three iPSC lines were cryopreserved as single-cell suspensions in the cryopreservation solutions and post-thaw characteristics, including pluripotency and differential gene expression were assessed. We demonstrate the fitness-for-purpose of 15 mM IRI in 5 % DMSO as an efficient cryoprotective solution for iPSCs in terms of post-thaw recovery, viability, pluripotency, and transcriptomic changes. This mRNA sequencing dataset has the potential to be used for molecular mechanism analysis relating to cryopreservation. Use of IRIs can reduce DMSO concentrations and its associated toxicities, thereby improving the utility, effectiveness, and efficiency of cryopreservation.

Standardized generation of human iPSC-derived hematopoietic organoids and macrophages utilizing a benchtop bioreactor platform under fully defined conditions

BACKGROUND

There is a significant demand for intermediate-scale bioreactors in academic and industrial institutions to produce cells for various applications in drug screening and/or cell therapy. However, the application of these bioreactors in cultivating hiPSC-derived immune cells and other blood cells is noticeably lacking. To address this gap, we have developed a xeno-free and chemically defined intermediate-scale bioreactor platform, which allows for the generation of standardized human iPSC-derived hematopoietic organoids and subsequent continuous production of macrophages (iPSC-Mac).

METHODS

We describe a novel method for intermediate-scale immune cell manufacturing, specifically the continuous production of functionally and phenotypically relevant macrophages that are harvested on weekly basis for multiple weeks.

RESULTS

The continuous production of standardized human iPSC-derived macrophages (iPSC-Mac) from 3D hematopoietic organoids also termed hemanoids, is demonstrated. The hemanoids exhibit successive stage-specific embryonic development, recapitulating embryonic hematopoiesis. iPSC-Mac were efficiently and continuously produced from three different iPSC lines and exhibited a consistent and reproducible phenotype, as well as classical functionality and the ability to adapt towards pro- and anti-inflammatory activation stages. Single-cell transcriptomic analysis revealed high macrophage purity. Additionally, we show the ability to use the produced iPSC-Mac as a model for testing immunomodulatory drugs, exemplified by dexamethasone.

CONCLUSIONS

The novel method demonstrates an easy-to-use intermediate-scale bioreactor platform that produces prime macrophages from human iPSCs. These macrophages are functionally active and require no downstream maturation steps, rendering them highly desirable for both therapeutic and non-therapeutic applications.

An adapted protocol to derive microglia from stem cells and its application in the study of CSF1R-related disorders

BACKGROUND

Induced pluripotent stem cell-derived microglia (iMGL) represent an excellent tool in studying microglial function in health and disease. Yet, since differentiation and survival of iMGL are highly reliant on colony-stimulating factor 1 receptor (CSF1R) signaling, it is difficult to use iMGL to study microglial dysfunction associated with pathogenic defects in CSF1R.

METHODS

Serial modifications to an existing iMGL protocol were made, including but not limited to changes in growth factor combination to drive microglial differentiation, until successful derivation of microglia-like cells from an adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) patient carrying a c.2350G > A (p.V784M) CSF1R variant. Using healthy control lines, the quality of the new iMGL protocol was validated through cell yield assessment, measurement of microglia marker expression, transcriptomic comparison to primary microglia, and evaluation of inflammatory and phagocytic activities. Similarly, molecular and functional characterization of the ALSP patient-derived iMGL was carried out in comparison to healthy control iMGL.

RESULTS

The newly devised protocol allowed the generation of iMGL with enhanced transcriptomic similarity to cultured primary human microglia and with higher scavenging and inflammatory competence at ~ threefold greater yield compared to the original protocol. Using this protocol, decreased CSF1R autophosphorylation and cell surface expression was observed in iMGL derived from the ALSP patient compared to those derived from healthy controls. Additionally, ALSP patient-derived iMGL presented a migratory defect accompanying a temporal reduction in purinergic receptor P2Y12 (P2RY12) expression, a heightened capacity to internalize myelin, as well as heightened inflammatory response to Pam3CSK4. Poor P2RY12 expression was confirmed to be a consequence of CSF1R haploinsufficiency, as this feature was also observed following CSF1R knockdown or inhibition in mature control iMGL, and in CSF1RWT/KO and CSF1RWT/E633K iMGL compared to their respective isogenic controls.

CONCLUSIONS

We optimized a pre-existing iMGL protocol, generating a powerful tool to study microglial involvement in human neurological diseases. Using the optimized protocol, we have generated for the first time iMGL from an ALSP patient carrying a pathogenic CSF1R variant, with preliminary characterization pointing toward functional alterations in migratory, phagocytic and inflammatory activities.

Therapeutic potential to target sialylation and SIGLECs in neurodegenerative and psychiatric diseases

Sialic acids, commonly found as the terminal carbohydrate on the glycocalyx of mammalian cells, are pivotal checkpoint inhibitors of the innate immune system, particularly within the central nervous system (CNS). Sialic acid-binding immunoglobulin-like lectins (SIGLECs) expressed on microglia are key players in maintaining microglial homeostasis by recognizing intact sialylation. The finely balanced sialic acid-SIGLEC system ensures the prevention of excessive and detrimental immune responses in the CNS. However, loss of sialylation and SIGLEC receptor dysfunctions contribute to several chronic CNS diseases. Genetic variants of SIGLEC3/CD33, SIGLEC11, and SIGLEC14 have been associated with neurodegenerative diseases such as Alzheimer's disease, while sialyltransferase ST8SIA2 and SIGLEC4/MAG have been linked to psychiatric diseases such as schizophrenia, bipolar disorders, and autism spectrum disorders. Consequently, immune-modulatory functions of polysialic acids and SIGLEC binding antibodies have been exploited experimentally in animal models of Alzheimer's disease and inflammation-induced CNS tissue damage, including retinal damage. While the potential of these therapeutic approaches is evident, only a few therapies to target either sialylation or SIGLEC receptors have been tested in patient clinical trials. Here, we provide an overview of the critical role played by the sialic acid-SIGLEC axis in shaping microglial activation and function within the context of neurodegeneration and synaptopathies and discuss the current landscape of therapies that target sialylation or SIGLECs.

Integrative Analysis of Single-Cell and Bulk Sequencing Data Depicting the Expression and Function of P2ry12 in Microglia Post Ischemia-Reperfusion Injury

P2ry12 is a microglial marker gene. Recently, increasing evidence has demonstrated that its expression levels can vary in response to different CNS disorders and can affect microglial functions, such as polarization, plasticity, and migration. However, the expression and function of P2ry12 in microglia during ischemia-reperfusion injury (IRI) remain unclear. Here, we developed a computational method to obtain microglia-specific P2ry12 genes (MSPGs) using sequencing data associated with IRI. We evaluated the change in comprehensive expression levels of MSPGs during IRI and compared it to the expression of P2ry12 to determine similarity. Subsequently, the MSPGs were used to explore the P2ry12 functions in microglia through bioinformatics. Moreover, several animal experiments were also conducted to confirm the reliability of the results. The expression of P2ry12 was observed to decrease gradually within 24 h post injury. In response, microglia with reduced P2ry12 expression showed an increase in the expression of one receptor-encoding gene (Flt1) and three ligand-encoding genes (Nampt, Igf1, and Cxcl2). Furthermore, double-labeling immunofluorescence staining revealed that inhibition of P2ry12 blocked microglial migration towards vessels during IRI. Overall, we employ a combined computational and experimental approach to successfully explore P2ry12 expression and function in microglia during IRI.