Human fetal brain self-organizes into long-term expanding organoids

Human brain development involves an orchestrated, massive neural progenitor expansion while a multi-cellular tissue architecture is established. Continuously expanding organoids can be grown directly from multiple somatic tissues, yet to date, brain organoids can solely be established from pluripotent stem cells. Here, we show that healthy human fetal brain in vitro self-organizes into organoids (FeBOs), phenocopying aspects of in vivo cellular heterogeneity and complex organization. FeBOs can be expanded over long time periods. FeBO growth requires maintenance of tissue integrity, which ensures production of a tissue-like extracellular matrix (ECM) niche, ultimately endowing FeBO expansion. FeBO lines derived from different areas of the central nervous system (CNS), including dorsal and ventral forebrain, preserve their regional identity and allow to probe aspects of positional identity. Using CRISPR-Cas9, we showcase the generation of syngeneic mutant FeBO lines for the study of brain cancer. Taken together, FeBOs constitute a complementary CNS organoid platform.

Temporal morphogen gradient-driven neural induction shapes single expanded neuroepithelium brain organoids with enhanced cortical identity

Pluripotent stem cell (PSC)-derived human brain organoids enable the study of human brain development in vitro. Typically, the fate of PSCs is guided into subsequent specification steps through static medium switches. In vivo, morphogen gradients are critical for proper brain development and determine cell specification, and associated defects result in neurodevelopmental disorders. Here, we show that initiating neural induction in a temporal stepwise gradient guides the generation of brain organoids composed of a single, self-organized apical-out neuroepithelium, termed ENOs (expanded neuroepithelium organoids). This is at odds with standard brain organoid protocols in which multiple and independent neuroepithelium units (rosettes) are formed. We find that a prolonged, decreasing gradient of TGF-β signaling is a determining factor in ENO formation and allows for an extended phase of neuroepithelium expansion. In-depth characterization reveals that ENOs display improved cellular morphology and tissue architectural features that resemble in vivo human brain development, including expanded germinal zones. Consequently, cortical specification is enhanced in ENOs. ENOs constitute a platform to study the early events of human cortical development and allow interrogation of the complex relationship between tissue architecture and cellular states in shaping the developing human brain.

Pyroptosis-inducing active caspase-1 as a genetic adjuvant in anti-cancer DNA vaccination

Pyroptosis is a recently discovered form of inflammatory programmed necrosis characterized by caspase-1-mediated and gasdermin D-dependent cell death leading to the release of pro-inflammatory cytokines such as Interleukin-1 beta (IL-1β). Here, we evaluated whether pyroptosis could be exploited in DNA vaccination by incorporating a constitutively active variant of caspase-1 to the antigen-expressing DNA. In vitro, transfection with constitutively active caspase-1 DNA induced pro-IL-1β maturation and IL-1β release as well as gasdermin D-dependent cell death. To test active caspase-1 as a genetic adjuvant for the induction of antigen-specific T cell responses, mice were vaccinated intradermally with a DNA vaccine consisting of the active caspase-1 plasmid together with a plasmid encoding an ovalbumin-derived CD8 T cell epitope. Active caspase-1 accelerated and amplified antigen-specific CD8 T cell responses when administered simultaneously with the DNA vaccine at an equimolar dose. Moreover, upon challenge with melanoma cells expressing ovalbumin, mice vaccinated with the antigen vaccine adjuvanted with active caspase-1 showed significantly better survival compared to the non-adjuvanted group. In conclusion, we have developed a novel genetic adjuvant that for the first time employs the pyroptosis pathway to improve DNA vaccination against cancer.

770 Personalized synthetic polyepitope DNA cancer vaccines encoding a novel pyroptotic adjuvant to generate effective anti-tumor T cell immunity

Background

As every tumor carries its unique set of neoantigens distinguishing it from healthy tissue, cancer vaccines need to be produced quickly and on an individual basis to swiftly induce a broad immune response targeting multiple antigens. DNA provides an ideal platform to achieve this, as a single polyepitope vaccine can encode multiple (>20) antigens. However, standard plasmid DNA vaccines take months to produce and tend to be poorly immunogenic in humans.

Methods

To address the first issue, a GMP-compatible method (AmpliVax) was developed that allows the simultaneous production of milligram amounts of multiple DNA vaccines in single vessel reactions within two days. This method relies on a primer-free, isothermal, rolling-circle amplification using high fidelity DNA polymerase and RNA polymerase to amplify circular DNA templates into linear double-stranded concatemers. Concatemers are digested into single linear expression cassettes which are subsequently protected by nuclease-resistant caps. To improve DNA vaccine immunogenicity, two avenues were explored. First, neoantigen DNA vaccines were tested in a therapeutic setting together with a checkpoint inhibitor drug. Second, DNA vaccines were combined with a novel caspase-1-based genetic adjuvant (PyroVant) that induces pyroptosis by exploiting the inflammasome pathway.

Results

Upon intradermal injection in mice, synthetic AmpliVax DNA vaccines matched plasmid DNA vaccines in terms of in vivo expression, immunogenicity and tumor protection. While treatment of mice carrying an MC38 colorectal tumor with either a polyepitope neoantigen DNA vaccine or anti-PD-1 did not significantly delay tumor outgrowth compared to untreated mice (0% survival), the combination of the neoantigen vaccine and anti-PD1 resulted in up to 70% tumor-free survival. PyroVant DNA accelerated and amplified antigen-specific CD8 T cell responses when administered simultaneously with a polyepitope DNA vaccine. What's more, subsequent challenge with melanoma cells revealed that PyroVant also significantly improved tumor-free survival.

Conclusions

In conclusion, we have created a novel synthetic DNA vaccine platform suitable for the production of effective personalized cancer vaccines. Current efforts are aimed at testing combinations of therapeutic synthetic DNA vaccines, PyroVant and checkpoint inhibitors in multiple pre-clinical tumor models.

In vivo inactivation of glycosidases by conduritol B epoxide and cyclophellitol as revealed by activity-based protein profiling

Glucocerebrosidase (GBA) is a lysosomal β‐glucosidase‐degrading glucosylceramide. Its deficiency causes Gaucher disease (GD), a common lysosomal storage disorder. Carrying a genetic abnormality in GBA constitutes at present the largest genetic risk factor for Parkinson's disease (PD). Conduritol B epoxide (CBE), a mechanism‐based irreversible inhibitor of GBA, is used to generate cell and animal models for investigations on GD and PD. However, CBE may have additional glycosidase targets besides GBA. Here, we present the first in vivo target engagement study for CBE, employing a suite of activity‐based probes to visualize catalytic pocket occupancy of candidate off‐target glycosidases. Only at significantly higher CBE concentrations, nonlysosomal glucosylceramidase (GBA2) and lysosomal α‐glucosidase were identified as major off‐targets in cells and zebrafish larvae. A tight, but acceptable window for selective inhibition of GBA in the brain of mice was observed. On the other hand, cyclophellitol, a closer glucose mimic, was found to inactivate with equal affinity GBA and GBA2 and therefore is not suitable to generate genuine GD‐like models.

Enzymes

Glucocerebrosidase (http://www.chem.qmul.ac.uk/iubmb/enzyme/EC3/2/1/45.html), nonlysosomal β‐glucocerebrosidase (http://www.chem.qmul.ac.uk/iubmb/enzyme/EC3/2/1/45.html); cytosolic β‐glucosidase (http://www.chem.qmul.ac.uk/iubmb/enzyme/EC3/2/1/21.html); α‐glucosidases (http://www.chem.qmul.ac.uk/iubmb/enzyme/EC3/2/1/20.html); β‐glucuronidase (http://www.chem.qmul.ac.uk/iubmb/enzyme/EC3/2/1/31.html).