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Human cerebral organoids are unique in their development of progenitor-rich zones akin to ventricular zones from which neuronal progenitors differentiate and migrate radially. Analyses of cerebral organoids thus far have been performed in sectioned tissue or in superficial layers due to their high scattering properties. Here, we demonstrate label-free three-photon imaging of whole, uncleared intact organoids (~2 mm depth) to assess early events of early human brain development. Optimizing a custom-made three-photon microscope to image intact cerebral organoids generated from Rett Syndrome patients, we show defects in the ventricular zone volumetric structure of mutant organoids compared to isogenic control organoids. Long-term imaging live organoids reveals that shorter migration distances and slower migration speeds of mutant radially migrating neurons are associated with more tortuous trajectories. Our label-free imaging system constitutes a particularly useful platform for tracking normal and abnormal development in individual organoids, as well as for screening therapeutic molecules via intact organoid imaging.

Cerebral organoids generated from human pluripotent stem cells (hiPSCs) are unique in their ability to recapitulate human-specific neurodevelopmental events. They are capable of modeling the human brain and its cell composition, including human-specific progenitor cell types; ordered laminar compartments; and both cell-specific transcriptional signatures and the broader telencephalic transcriptional landscape. The serine/threonine kinase, GSK3β, plays a critical role in neurodevelopment, controlling processes as varied as neurogenesis, morphological changes, polarization, and migration. In the generation of cerebral organoids, inhibition of GSK3β at low doses has been used to increase organoid size and decrease necrotic core. However, little is known of the effects of GSK3β inhibition on organoid development. Here, we demonstrate that while low dose of GSK3β inhibitor CHIR 99021 increases organoid size, higher dose actually reduces organoid size; with the highest dose arresting organoid growth. To examine the mechanisms that may contribute to the phenotypic size differences observed in these treatment groups, we show that low dose of CHIR 99021 increases cell survival, neural progenitor cell proliferation and neuronal migration. A higher dose, however, decreases not only apoptosis but also proliferation, and arrests neural differentiation, enriching the pool of neuroepithelial cells, and decreasing the pools of early neuronal progenitors and neurons. These results reveal new mechanisms of the pleiotropic effects of GSK3β during organoid development, providing essential information for the improvement of organoid production and ultimately shedding light on the mechanisms of embryonic brain development.

BackgroundPatients with platinum-resistant/refractory ovarian cancer (PROC) experience suboptimal outcomes, highlighting an immediate need for novel therapies. This phase 1b study investigated the safety and efficacy of botensilimab (BOT), a fragment crystallizable (Fc)-enhanced anti–cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) antibody with differentiated mechanisms of action from first-generation CTLA-4 inhibitors, plus balstilimab (BAL; anti–programmed cell death protein 1 antibody), in an expanded cohort of patients with treatment-refractory ovarian cancer.MethodsBOT was administered intravenously at 1 mg/kg or 2 mg/kg every 6 weeks in combination with BAL intravenously at 3 mg/kg every 2 weeks (up to 2 years). The primary objectives were to assess safety and tolerability. Efficacy end points included objective response rate (ORR), duration of response (DOR), and progression-free survival (PFS) by Response Evaluation Criteria in Solid Tumors (RECIST) V.1.1. Overall survival (OS) was an exploratory end point.ResultsOverall, 44 patients were evaluable for safety (with a median of 3 prior lines of therapy; median follow-up 9.6 months (range, 0.6—36.6)), and 35 for efficacy. The most common treatment-related adverse event was diarrhea/colitis (43%; 16% grade 3) with no treatment-related deaths. RECIST-confirmed ORR was 23% (8/35; 95% CI 10% to 40%; one complete (CR), seven partial responses (PRs)) and clinical benefit rate (CR, PR, or stable disease ≥24 weeks) was 31% (11/35; 95% CI 17% to 49%). Median DOR was 9.7 months (95% CI 2.8 to not reached (NR)), median PFS was 2.8 months (95% CI 1.4 to 5.5), median OS was 14.8 months (95% CI 12.1 to NR), and 12-month OS was 75% (95% CI 55% to 86%). Immune phenotypic analyses and biomarker data revealed significantly higher FcγRIIIA+CD11c+ cells and higher programmed death-ligand 1 expression in responding patients, a strong association between T-cell infiltrated tumors and clinical benefit, and differences in immune architecture across histologic subtypes.ConclusionThe BOT/BAL combination demonstrated deep, durable responses and complete remissions in patients with treatment-refractory ovarian cancer where no standard treatments are currently available. RECIST under-represented clinical benefit with 11 patients achieving prolonged/clinically meaningful stable disease (or better) for ≥24 weeks. Toxicities were manageable and reversible. The encouraging clinical activity of BOT/BAL in heavily pretreated patients, as well as biomarker associations, warrants further investigation of this combination.

Rett syndrome (RTT) is a devastating neurodevelopmental disorder without effective treatments. Attempts at developing targeted therapies have been relatively unsuccessful, at least in part, because the genotypical and phenotypical variability of the disorder. Therefore, identification of biomarkers of response and patients’ stratification are high priorities. Administration of Insulin-like Growth Factor 1 (IGF-1) and related compounds leads to significant reversal of RTT-like symptoms in preclinical mouse models. However, improvements in corresponding clinical trials have not been consistent. A 20-weeks phase I open label trial of mecasermin (recombinant human IGF-1) in children with RTT demonstrated significant improvements in breathing phenotypes. However, a subsequent randomised controlled phase II trial did not show significant improvements in primary outcomes although two secondary clinical endpoints showed positive changes. To identify molecular biomarkers of response and surrogate endpoints, we used RNA sequencing to measure differential gene expression in whole blood samples of participants in the abovementioned phase I mecasermin trial. When all participants (n=9) were analysed, gene expression was unchanged during the study (baseline vs. end of treatment, T0 to T3). However, when participants were subclassified in terms of breathing phenotype improvement, specifically by their plethysmography-based apnoea index, individuals with moderate-severe apnoea and breathing improvement (Responder group) displayed significantly different transcript profiles compared to the other participants in the study (Mecasermin Study Reference group, MSR). Many of the differentially expressed genes are involved in the regulation of cell cycle processes and immune responses, as well as in IGF-1 signalling and breathing regulation. While the Responder group showed limited gene expression changes in response to mecasermin, the MSR group displayed marked differences in the expression of genes associated with inflammatory processes (e.g., neutrophil activation, complement activation) throughout the trial. Our analyses revealed gene expression profiles associated with severe breathing phenotype and its improvement after mecasermin administration in RTT, and suggest that inflammatory/immune pathways and IGF-1 signalling contribute to treatment response. Overall, these data support the notion that transcript profiles have potential as biomarkers of response to IGF-1 and related compounds.

Human cerebral organoids derived from induced pluripotent stem cells can recapture early developmental processes and reveal changes involving neurodevelopmental disorders. Mutations in the X-linked methyl-CpG binding protein 2 (MECP2) gene are associated with Rett syndrome, and disease severity varies depending on the location and type of mutation. Here, we focused on neuronal activity in Rett syndrome patient-derived organoids, analyzing two types of MECP2 mutations-a missense mutation (R306C) and a truncating mutation (V247X)-using calcium imaging with three-photon microscopy. Compared to isogenic controls, we found abnormal neuronal activity in Rett organoids and altered network function based on graph theoretic analyses, with V247X mutations impacting functional responses and connectivity more severely than R306C mutations. These changes paralleled EEG data obtained from patients with comparable mutations. Labeling >/>DLX promoter-driven inhibitory neurons demonstrated differences in activity and functional connectivity of inhibitory and excitatory neurons in the two types of mutations. Transcriptomic analyses revealed HDAC2-associated impairment in R306C organoids and decreased GABA receptor expression in excitatory neurons in V247X organoids. These findings demonstrate mutation-specific mechanisms of vulnerability in Rett syndrome and suggest targeted strategies for their treatment.

Microsatellite stable metastatic colorectal cancer (MSS mCRC; mismatch repair proficient) has previously responded poorly to immune checkpoint blockade. Botensilimab (BOT) is an Fc-enhanced multifunctional anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) antibody designed to expand therapy to cold/poorly immunogenic solid tumors, such as MSS mCRC. BOT with or without balstilimab (BAL; anti-PD-1 antibody) is being evaluated in an ongoing expanded phase 1 study. The primary endpoint is safety and tolerability, which was evaluated separately in the dose-escalation portion of the study and in patients with MSS mCRC (using combined dose-escalation/dose-expansion data). Secondary endpoints include investigator-assessed RECIST version 1.1–confirmed objective response rate (ORR), disease control rate (DCR), duration of response (DOR) and progression-free survival (PFS). Here we present outcomes in 148 heavily pre-treated patients with MSS mCRC (six from the dose-escalation cohort; 142 from the dose-expansion cohort) treated with BOT and BAL, 101 of whom were considered response evaluable with at least 6 months of follow-up. Treatment-related adverse events (TRAEs) occurred in 89% of patients with MSS mCRC (131/148), most commonly fatigue (35%, 52/148), diarrhea (32%, 47/148) and pyrexia (24%, 36/148), with no grade 5 TRAEs reported and a 12% discontinuation rate due to a TRAE (18/148; data fully mature). In the response-evaluable population ( n  = 101), ORR was 17% (17/101; 95% confidence interval (CI), 10–26%), and DCR was 61% (62/101; 95% CI, 51–71%). Median DOR was not reached (NR; 95% CI, 5.7 months–NR), and median PFS was 3.5 months (95% CI, 2.7–4.1 months), at a median follow-up of 10.3 months (range, 0.5–42.6 months; data continuing to mature). The combination of BOT plus BAL demonstrated a manageable safety profile with no new immune-mediated safety signals and encouraging clinical activity with durable responses. ClinicalTrials.gov identifier: NCT03860272 . In an ongoing phase 1 trial, the combination of two new immunotherapies targeting CTLA-4 and PD-1 was overall well tolerated and elicited encouraging clinical responses in patients with relapsed/refractory microsatellite stable colorectal cancer, a tumor type typically unresponsive to immune checkpoint blockade.

Rett syndrome (RTT) is a severe neurodevelopmental disease caused by mutations in methyl-CpG-binding protein 2 (MECP2), which encodes a transcriptional modulator of many genes including BDNF. BDNF comprises nine distinct promoter regions, each triggering the expression of a specific transcript. The role of this diversity of transcripts remains unknown. MeCP2 being highly expressed in neurons, RTT was initially considered as a neuronal disease. However, recent studies have shown that MeCP2 was also expressed in astrocytes. Though several studies explored Bdnf IV expression in Mecp2-deficient mice, the differential expression of Bdnf isoforms in Mecp2-deficient neurons and astrocytes was never studied. By using TaqMan technology and a mouse model expressing a truncated Mecp2 (Mecp2 super(308/y)), we firstly showed in neurons that Bdnf transcripts containing exon I, IIb, IIc, IV, and VI are prominently expressed, whereas in astrocytes, Bdnf transcript containing exon VI is preferentially expressed, suggesting a specific regulation of Bdnf expression at the cellular level. Secondly, we confirmed the repressive role of Mecp2 only on the expression of Bdnf VI in neurons. Our data suggested that the truncated Mecp2 protein maintains its function on Bdnf expression regulation in neurons and in astrocytes. Interestingly, we observed that Bdnf transcripts (I and IXA), regulated by neural activity induced by bicuculline in Mecp2 super(308/y) neurons, were not affected by histone deacetylase inhibition. In contrast, Bdnf transcripts (IIb, IIc, and VI), regulated by histone deacetylation, were not affected by bicuculline treatment in wild-type and Mecp2 super(308/y) neurons. All these results reflect the complexity of regulation of Bdnf gene.

Mutations in the gene encoding the transcriptional modulator methyl-CpG binding protein 2 (MeCP2) are responsible for the neurodevelopmental disorder Rett syndrome which is one of the most frequent sources of intellectual disability in women. Recent studies showed that loss of Mecp2 in astrocytes contributes to Rett-like symptoms and restoration of Mecp2 can rescue some of these defects. The goal of this work is to compare gene expression profiles of wild-type and mutant astrocytes from Mecp2(308/y) mice (B6.129S-MeCP2/J) by using Affymetrix mouse 2.0 microarrays. Results were confirmed by quantitative real-time RT-PCR and by Western blot analysis. Gene set enrichment analysis utilizing Ingenuity Pathways was employed to identify pathways disrupted by Mecp2 deficiency. A total of 2152 genes were statistically differentially expressed between wild-type and mutated samples, including 1784 coding transcripts. However, only 257 showed fold changes >1.2. We confirmed our data by replicative studies in independent primary cultures of cortical astrocytes from Mecp2-deficient mice. Interestingly, two genes known to encode secreted proteins, chromogranin B and lipocalin-2, showed significant dysregulation. These proteins secreted from Mecp2-deficient glia may exert negative non-cell autonomous effects on neuronal properties, including dendritic morphology. Moreover, transcriptional profiling revealed altered Nr2f2 expression which may explain down- and upregulation of several target genes in astrocytes such as Ccl2, Lcn2 and Chgb. Unraveling Nr2f2 involvement in Mecp2-deficient astrocytes could pave the way for a better understanding of Rett syndrome pathophysiology and offers new therapeutic perspectives.

Rett syndrome (RTT) is a severe neurodevelopmental disease caused by mutations in methyl-CpG-binding protein 2 (MECP2), which encodes a transcriptional modulator of many genes including BDNF. BDNF comprises nine distinct promoter regions, each triggering the expression of a specific transcript. The role of this diversity of transcripts remains unknown. MeCP2 being highly expressed in neurons, RTT was initially considered as a neuronal disease. However, recent studies have shown that MeCP2 was also expressed in astrocytes. Though several studies explored Bdnf IV expression in Mecp2-deficient mice, the differential expression of Bdnf isoforms in Mecp2-deficient neurons and astrocytes was never studied. By using TaqMan technology and a mouse model expressing a truncated Mecp2 (Mecp2(308/y)), we firstly showed in neurons that Bdnf transcripts containing exon I, IIb, IIc, IV, and VI are prominently expressed, whereas in astrocytes, Bdnf transcript containing exon VI is preferentially expressed, suggesting a specific regulation of Bdnf expression at the cellular level. Secondly, we confirmed the repressive role of Mecp2 only on the expression of Bdnf VI in neurons. Our data suggested that the truncated Mecp2 protein maintains its function on Bdnf expression regulation in neurons and in astrocytes. Interestingly, we observed that Bdnf transcripts (I and IXA), regulated by neural activity induced by bicuculline in Mecp2(308/y) neurons, were not affected by histone deacetylase inhibition. In contrast, Bdnf transcripts (IIb, IIc, and VI), regulated by histone deacetylation, were not affected by bicuculline treatment in wild-type and Mecp2(308/y) neurons. All these results reflect the complexity of regulation of Bdnf gene.

Mutations in the gene encoding the tran1.2. We confirmed our data by replicative studies in independent primary cultures of cortical astrocytes from Mecp2-deficient mice. Interestingly, two genes known to encode secreted proteins, chromogranin B and lipocalin-2, showed significant dysregulation. These proteins secreted from Mecp2-deficient glia may exert negative non-cell autonomous effects on neuronal properties, including dendritic morphology. Moreover, transcriptional profiling revealed altered Nr2f2 expression which may explain down- and upregulation of several target genes in astrocytes such as Ccl2, Lcn2 and Chgb. Unraveling Nr2f2 involvement in Mecp2-deficient astrocytes could pave the way for a better understanding of Rett syndrome pathophysiology and offers new therapeutic perspectives.