Neurofibromatosis Type 1 Mutations Research Articles

Identification of Pathogenic Missense Mutations of NF1 Using Computational Approaches

Neurofibromatosis type 1 (NF1) is a prevalent autosomal dominant disorder caused by mutations in the NF1 gene, leading to multisystem disorders. Given the critical role of cysteine residues in protein stability and function, we aimed to identify key NF1 mutations affecting cysteine residues that significantly contribute to neurofibromatosis pathology. To identify the most critical mutations in the NF1 gene that contribute to the pathology of neurofibromatosis, we employed a sophisticated computational pipeline specifically designed to detect significant mutations affecting the NF1 gene. Our approach involved an exhaustive search of databases such as the Human Gene Mutation Database (HGMD), UniProt, and ClinVar for information on missense mutations associated with NF1. Our search yielded a total of 204 unique cysteine missense mutations. We then employed in silico prediction tools, including PredictSNP, iStable, and Align GVGD, to assess the impact of these mutations. Among the mutations, C379R, R1000C, and C1016Y stood out due to their deleterious effects on the biophysical properties of the neurofibromin protein, significantly destabilizing its structure. These mutations were subjected to further phenotyping analysis using SNPeffect 4.0, which predicted disturbances in the protein’s chaperone binding sites and overall structural stability. Furthermore, to directly visualize the impact of these mutations on protein structure, we utilized AlphaFold3 to simulate both the wild-type and mutant NF1 structures, revealing the significant effects of the R1000C mutation on the protein’s conformation. In conclusion, the identification of these mutations can play a pivotal role in advancing the field of precision medicine and aid in the development of effective drugs for associated diseases.

7694 Characterizing NF1 Germline Pathogenic Variants In A Cohort Of Patients With Pheochromocytomas And Neurofibromatosis Type 1

Abstract Disclosure: T. Hristova: None. S. Parisien-La Salle: None. S. Lapointe: None. D. Tremblay: None. N. Dumas: None. M. Labidi: None. Z. El Haffaf: None. I. Bourdeau: None. Introduction: Pheochromocytomas and paragangliomas (PPGLs) are the tumors with the highest heritability in adult patients, with identification of a germline mutation in more than 30% of cases. Up to 20 susceptibility genes for PPGLs are known, including NF1. Neurofibromatosis type 1 (NF1) is an inherited disease affecting approximately 1 in 3000 people that predisposes to the development of tumors, such as pheochromocytomas (PHEO). Up to recently, the diagnosis of NF1 was mainly based on clinical manifestations and NF1 genetic characterization was not systematically performed. Objectives: To characterize germline pathogenic variants in the NF1 gene in patients with NF1 developing and PHEO. Methods: We reviewed the charts of patients with a pathology-proven diagnosis of PHEOs that were investigated at Centre hospitalier de l’Université de Montréal (CHUM) between 2000 and May 2023. Genetic analysis included gene sequencing by Sanger method or multigene sequencing by NGS with a panel (Invitae, CA) Results: In our cohort of 220 PHEOs, 15 patients (6.8%) (Males: 6, Females: 9) had a diagnosis of NF1. Mean age at diagnosis of PHEO in NF1 patients was 48 ± 13.6 years, contrasting to the mean age of 38,7 ± 15.2 years in patients carrying germline mutations in non-NF1 genes, most likely reflecting lack of systematic biochemically screening of PHEO in NF1. Urinary metanephrines were elevated in 9/15 patients. 2/15 (15.4%) NF1 patients had bilateral PHEO and 1/15 (7,7%) metastatic disease. Mean tumour diameter was 4.64cm (min-max 1.5 – 12.5 cm). Eight out of 15 NF1 patients underwent NF1 genetic analysis. Heterozygous NF1 germline pathogenic variants were found in all of them: 3 deletions (c.7379delG, c.5844_5845delAA and one encompassing the entire gene), 3 premature stop codons leading to truncated proteins or loss of function (c.7549C>T, c.3916C>T, c.1246C>T), and 2 splicing defects (c.4269+1 G>A, c.1885G>A). Conclusions: We report a large cohort of patients with NF1 and PHEO. The older age at diagnosis of PHEO in NF1 is expected based on lack of systematic biochemical screening for PHEO in NF1 clinical guidelines. We report 8 germline NF1 mutations associated with PHEOs. Further studies are required to fully understand the impact of genetic pathogenic variants in this population and to unravel a possible genotype-phenotype correlation. Presentation: 6/2/2024

Concurrent multiple cerebral cavernous malformations and cauda equina paraganglioma: illustrative case.

Cauda equina neuroendocrine tumors (CENETs), previously known as cauda equina paragangliomas, and multiple cerebral cavernous malformations (CCMs) are uncommon conditions affecting the central nervous system. To the authors' knowledge, they have not been reported in the same patient. The authors present the case of a 45-year-old male with CENET and concurrent incidental MRI findings of multiple CCMs. Familial CCMs are associated with mutations in the KRIT1 (CCM1), MGC4607 (CCM2), and PDCD10 (CCM3) genes. Peripheral paragangliomas have been associated with mutations in succinate dehydrogenase (SDHx), RET (multiple endocrine neoplasia 2), VHL (von Hippel-Lindau syndrome), and NF1 (neurofibromatosis type 1) genes. Except for a single case, cauda equina paragangliomas have not been associated with any underlying genetic mutations. It is unclear whether the co-occurrence of these two rare conditions in the same patient is coincidental or suggests a possible shared pathogenesis. https://thejns.org/doi/10.3171/CASE24102.

The molecular biology of NF2/Merlin on tumorigenesis and development.

The neurofibromatosis type 2 (NF2) gene, known for encoding the tumor suppressor protein Merlin, is central to the study of tumorigenesis and associated cellular processes. This review comprehensively examines the multifaceted role of NF2/Merlin, detailing its structural characteristics, functional diversity, and involvement in various signaling pathways such as Wnt/β-catenin, Hippo, TGF-β, RTKs, mTOR, Notch, and Hedgehog. These pathways are crucial for cellular growth, proliferation, and differentiation. NF2 mutations are specifically linked to the development of schwannomas, meningiomas, and ependymomas, although the precise mechanisms of tumor formation in these specific cell types remain unclear. Additionally, the review explores Merlin's role in embryogenesis, highlighting the severe developmental defects and embryonic lethality caused by NF2 deficiency. The potential therapeutic strategies targeting these genetic aberrations are also discussed, emphasizing inhibitors of mTOR, HDAC, and VEGF as promising avenues for treatment. This synthesis of current knowledge underscores the necessity for ongoing research to elucidate the detailed mechanisms of NF2/Merlin and develop effective therapeutic strategies, ultimately aiming to improve the prognosis and quality of life for individuals with NF2 mutations.

A Comprehensive Overview of NF1 Mutations in Iranian Patients.

Neurofibromatosis type 1 (NF1) is a genetic disorder caused by mutations in the NF1 gene. This disorder shows nearly complete penetrance and high phenotypic variability. We used the whole-exome sequencing technique to identify mutations in 32 NF1 cases from 22 Iranian families. A total of 31 variants, including 30 point mutations and one large deletion, were detected. In eight cases, variants were inherited, while they were sporadic in the remaining. Seven novel variants, including c.5576T > G, c.6658_6659insC, c.2322dupT, c.92_93insAA, c.4360C > T, c.3814C > T, and c.4565_4566delinsC, were identified. The current study is the largest in terms of the sample size of Iranian NF1 cases with identified mutations. The results can broaden the spectrum of NF1 mutations and facilitate the process of genetic counseling in the affected families.

NFS-13. UNUSUAL NEUROFIBROMATOSIS TYPE 1-ASSOCIATED PILOCYTIC ASTROCYTOMAWITH MALIGNANT TRANSFORMATION IN A 7-YEAR-OLD GIRL

Abstract INTRODUCTION Neurofibromatosis type 1(NF1) is a tumor predisposition syndrome with germline NF 1 gene aberrations with overactivation of the RAS–MAPK signaling pathway. NF1-associated gliomas in children are usually low-grade Glioma with indolent course. Malignant transformation in NF1 associated LGG is predominated in adults is scarce in children METHOD A 7-year-old girl diagnosed as NF1-based on diagnostic criteria and germline NF1 gene mutation, presented with progressive RT side hemiplegia, Brain MRI showed a large left thalamic cystic and solid mass and obstructive hydrocephalus she had VPS insertion and stereotactic biopsy.pathological examination revealed aggressive High-grade Glioma HGG features diffuse brain infiltration, endothelial hyperplasia, increased mitotic activity necrosis, and High Ki67. Immunohistochemically and molecular analysis showed NF1 mutation in addition to TP53 mutation, retained ATRX, negative CDKN2A/B, and high tumor mutational burden (6 Muts/Mb). Tumor methylation profiling (DKFZ CNS v12.5) classified as Supratentorial midline pilocytic astrocytoma (score 0.6878). debulking of the tumor and ommaya reservoir insertion was done with recurrent aspiration of the cystic component. The second biopsy demonstrated low-grade pilocytic astrocytoma, confirmed by methylation profiling (score 0.9377). Immunohistochemically and molecular analysis showed NF1 mutation, negative TP53, and Retained ATRX RESULT She was treated with low-grade glioma chemotherapy carboplatin/ vincristine, with improved clinical and neurological condition and stable MRI evaluation. One year after diagnosis while on maintenance LGG chemotherapy MRI imaging showed tumor progression Subtotal resection of the mass was performed, morphology and molecular studies confirmed HGG, and she received focal radiation therapy. Up till now, the patient is currently stable clinically and by imaging surveillance. CONCLUSION Our case characterized a transformed glioma in a child with NF1 illustrating the intratumoral heterogeneity and presence of transformed/anaplastic clone within NF1-associated pilocytic astrocytoma and demonstrate the complexity of molecular genetics of gliomas in children with NF1.

NF1 with 47,XYY mosaicism diagnosed by mandibular neurofibromas.

Neurofibromatosis type 1 (NF1) is an autosomal dominant nevus disease characterized by multiple manifestations, primarily café-au-lait macules and neurofibromas. Here, we present the case of an NF1 patient with 47,XYY mosaicism whose diagnosis was prompted by café-au-lait macules on the skin and mandibular neurofibromas. Targeted next-generation sequencing of the patient's blood sample revealed a novel frameshift mutation in NF1 (NM_000267.3:c.6832dupA:p.Thr2278Asnfs*8) that is considered a pathogenic variant.

Susceptibility-Weighted MRI for Predicting NF-2 Mutations and S100 Protein Expression in Meningiomas.

S100 protein expression levels and neurofibromatosis type 2 (NF-2) mutations result in different disease courses in meningiomas. This study aimed to investigate non-invasive biomarkers of NF-2 copy number loss and S100 protein expression in meningiomas using morphological, radiomics, and deep learning-based features of susceptibility-weighted MRI (SWI). This retrospective study included 99 patients with S100 protein expression data and 92 patients with NF-2 copy number loss information. Preoperative cranial MRI was conducted using a 3T clinical MR scanner. Tumor volumes were segmented on fluid-attenuated inversion recovery (FLAIR) and subsequent registration of FLAIR to high-resolution SWI was performed. First-order textural features of SWI were extracted and assessed using Pyradiomics. Morphological features, including the tumor growth pattern, peritumoral edema, sinus invasion, hyperostosis, bone destruction, and intratumoral calcification, were semi-quantitatively assessed. Mann-Whitney U tests were utilized to assess the differences in the SWI features of meningiomas with and without S100 protein expression or NF-2 copy number loss. A logistic regression analysis was used to examine the relationship between these features and the respective subgroups. Additionally, a convolutional neural network (CNN) was used to extract hierarchical features of SWI, which were subsequently employed in a light gradient boosting machine classifier to predict the NF-2 copy number loss and S100 protein expression. NF-2 copy number loss was associated with a higher risk of developing high-grade tumors. Additionally, elevated signal intensity and a decrease in entropy within the tumoral region on SWI were observed in meningiomas with S100 protein expression. On the other hand, NF-2 copy number loss was associated with lower SWI signal intensity, a growth pattern described as "en plaque", and the presence of calcification within the tumor. The logistic regression model achieved an accuracy of 0.59 for predicting NF-2 copy number loss and an accuracy of 0.70 for identifying S100 protein expression. Deep learning features demonstrated a strong predictive capability for S100 protein expression (AUC = 0.85 ± 0.06) and had reasonable success in identifying NF-2 copy number loss (AUC = 0.74 ± 0.05). In conclusion, SWI showed promise in identifying NF-2 copy number loss and S100 protein expression by revealing neovascularization and microcalcification characteristics in meningiomas.

STING activation reprograms the microenvironment to sensitize NF1-related malignant peripheral nerve sheath tumors for immunotherapy.

Neurofibromatosis type 1 (NF1) is caused by mutations in the NF1 gene that encodes neurofibromin, a RAS GTPase-activating protein. Inactivating NF1 mutations cause hyperactivation of RAS-mediated signaling, resulting in the development of multiple neoplasms, including malignant peripheral nerve sheath tumors (MPNSTs). MPNSTs are an aggressive tumor and the main cause of mortality in patients with NF1. MPNSTs are difficult to resect and refractory to chemo- and radiotherapy, and no molecular therapies currently exist. Immune checkpoint blockade (ICB) is an approach to treat inoperable, undruggable cancers like MPNST, but successful outcomes require an immune cell-rich tumor microenvironment. While MPNSTs are noninflamed "cold" tumors, here, we converted MPNSTs into T cell-inflamed "hot" tumors by activating stimulator of IFN genes (STING) signaling. Mouse genetic and human xenograft MPNST models treated with a STING agonist plus ICB exhibited growth delay via increased apoptotic cell death. This strategy offers a potential treatment regimen for MPNSTs.

SOX9 Promotes Collagen VI Secretion by Upregulating PCOLCE in Neurofibroma.

Neurofibromatosis type 1 (NF1) is caused by NF1 gene mutations. Patients with NF1 often have complications with tumors, such as neurofibroma. In order to investigate the pathogenesis of human neurofibroma, a systematic comparison of protein expression levels between Schwann cell-like sNF96.2 cells, which originated from malignant peripheral nerve sheath tumors (MPNST), and normal Schwann cells was performed using 4-D label-free proteomic analysis. In addition, the expression levels and localization of dysregulated proteins were confirmed using a Gene Expression Omnibus (GEO) transcriptomic dataset, Western blot analysis, and immunofluorescence labeling. The effects of SRY-box transcription factor 9 (SOX9) in the neurofibroma and surrounding microenvironment were evaluated in vivo using a tumor transplantation model. The present study observed that SOX9 and procollagen C-endopeptidase enhancer (PCOLCE) were significantly altered. NF1 mutation promoted the nuclear translocation and transcriptional activity of SOX9 in neurofibromas. SOX9 increased collagen VI secretions by enhancing the activation of PCOLCE in neurofibroma cells. These findings might provide new perspectives on the pathophysiological significance of SOX9 in neurofibromas and elucidate a novel molecular mechanism underlying neurofibromas.

Generation of heterozygous and homozygous NF1 lines from human-induced pluripotent stem cells using CRISPR/Cas9 to investigate bone defects associated with neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is one of the most common genetic disorders caused by heterozygous germline NF1 mutations. NF1 affects many systems, including the skeletal system. To date, no curative therapies are available for skeletal manifestations such as scoliosis and tibial dysplasia, mainly due to the lack of knowledge about the mechanisms that underlie this process. By using CRISPR/Cas9-mediated gene editing in human-induced pluripotent stem cells (hiPSCs) to minimize the variability due to genetic background and epigenetic factors, we generated isogenic heterozygous and homozygous NF1-deficient hiPSC lines to investigate the consequences of neurofibromin inactivation on osteoblastic differentiation. Here, we demonstrate that loss of one or both copies of NF1 does not alter the potential of isogenic hiPSCs to differentiate into mesenchymal stem cells (hiPSC-MSCs). However, NF1 (+/-) and NF1 (-/-) hiPSC-MSCs show a defect in osteogenic differentiation and mineralization. In addition, we show that a mono-allelic deletion in NF1 in an isogenic context is sufficient to impair cell differentiation into osteoblasts. Overall, this study highlights the relevance of generating isogenic lines, which may help in genotype-phenotype correlation and provide a human cellular model to understand the molecular mechanisms underlying NF1 and, thus, discover new therapeutic strategies.

Pulmonary Arterial Hypertension in Neurofibromatosis Type 1: A Case with a Novel NF1 Gene Mutation.

Neurofibromatosis type 1 (NF1) is an autosomal dominant multi-organ disease. The clinical manifestations include not only skin lesions and malignant tumors but also lung complications, including pulmonary arterial hypertension (PAH). However, the association between gene mutations in NF1 and the occurrence of PAH has not yet been elucidated. We herein report a case of isolated PAH in a 67-year-old woman with NF1, presumably caused by a novel heterozygous mutation, c.4485_4486delinsAT (p.Lys1496Ter), in the NF1 gene.

Genetic characterization and mutational profiling of foramen magnum meningiomas: a multi-institutional study.

Foramen magnum (FM) meningiomas pose significant surgical challenges and have high morbidity and mortality rates. This study aimed to investigate the distribution of clinically actionable mutations in FM meningiomas and identify clinical characteristics associated with specific mutational profiles. The authors conducted targeted next-generation sequencing of 62 FM meningiomas from three international institutions, covering all relevant meningioma genes (AKT1, KLF4, NF2, POLR2A, PIK3CA, SMO, TERT promoter, and TRAF7). Patients with a radiation-induced meningioma or neurofibromatosis type 2 (NF2) were excluded from the study. Additionally, patient and tumor characteristics, including age, sex, radiological features, and tumor location, were retrospectively collected and evaluated. The study cohort consisted of 46 female and 16 male patients. Clinically significant driver mutations were detected in 58 patients (93.5%). The most commonly observed alteration was TRAF7 mutations (26, 41.9%), followed by AKT1E17K mutations (19, 30.6%). Both mutations were significantly associated with an anterolateral tumor location relative to the brainstem (p = 0.0078). NF2 mutations were present in 11 cases (17.7%) and were associated with posterior tumor location, in contrast to tumors with TRAF7 and AKT1E17K mutations. Other common mutations in FM meningiomas included POLR2A mutations (8, 12.9%; 6 POLR2AQ403K and 2 POLR2AH439_L440del), KLF4K409Q mutations (7, 11.3%), and PIK3CA mutations (4, 6.5%; 2 PIK3CAH1047R and 2 PIK3CAE545K). POLR2A and KLF4 mutations exclusively occurred in female patients and showed no significant association with specific tumor locations. All tumors harboring AKT1E17K and POLR2A mutations displayed meningothelial histology. Ten tumors exhibited intratumoral calcification, which was significantly more frequent in NF2-mutant compared with AKT1-mutant FM meningiomas (p = 0.047). These findings provide important insights into the molecular genetics and clinicopathological characteristics of FM meningiomas. The identification of specific genetic alterations associated with tumor location, volume, calcification, histology, and sex at diagnosis may have implications for personalized treatment strategies in the future.

Neurofibromin 1 mutations impair the function of human induced pluripotent stem cell-derived microglia.

Neurofibromatosis type 1 (NF1) is an autosomal dominant condition caused by germline mutations in the neurofibromin 1 (NF1) gene. Children with NF1 are prone to the development of multiple nervous system abnormalities, including autism and brain tumors, which could reflect the effect of NF1 mutation on microglia function. Using heterozygous Nf1-mutant mice, we previously demonstrated that impaired purinergic signaling underlies deficits in microglia process extension and phagocytosis in situ. To determine whether these abnormalities are also observed in human microglia in the setting of NF1, we leveraged an engineered isogenic series of human induced pluripotent stem cells to generate human microglia-like (hiMGL) cells heterozygous for three different NF1 gene mutations found in patients with NF1. Whereas all NF1-mutant and isogenic control hiMGL cells expressed classical microglia markers and exhibited similar transcriptomes and cytokine/chemokine release profiles, only NF1-mutant hiMGL cells had defects in P2X receptor activation, phagocytosis and motility. Taken together, these findings indicate that heterozygous NF1 mutations impair a subset of the functional properties of human microglia, which could contribute to the neurological abnormalities seen in children with NF1.

Econazole selectively induces cell death in NF1-homozygous mutant tumor cells

Cutaneous neurofibromas (cNFs) are tumors that develop in more than 99% of individuals with neurofibromatosis type 1 (NF1). They develop in the dermis and can number in the thousands. cNFs can be itchy and painful and negatively impact self-esteem. There is no US Food and Drug Administration (FDA)-approved drug for their treatment. Here, we screen a library of FDA-approved drugs using a cNF cell model derived from human induced pluripotent stem cells (hiPSCs) generated from an NF1 patient. We engineer an NF1 mutation in the second allele to mimic loss of heterozygosity, differentiate the NF1+/- and NF1-/- hiPSCs into Schwann cell precursors (SCPs), and use them to screen a drug library to assess for inhibition of NF1-/- but not NF1+/- cell proliferation. We identify econazole nitrate as being effective against NF1-/- hiPSC-SCPs. Econazole cream selectively induces apoptosis in Nf1-/- murine nerve root neurosphere cells and human cNF xenografts. This study supports further testing of econazole for cNF treatment.

Cases of Mixed Schwannoma-Meningioma With and Without Neurofibromatosis 2 with Emphasis on Tumorigenesis.

Concurrent occurrence of schwannoma and meningiomas are rare, and are found especially in association with neurofibromatosis type 2 (NF2). Occurrence of mixed tumor without the aforementioned conditions is extremely rare. We present three cases of mixed tumor in different locations, including two with NF2 and one without NF2. We analyse the relationship of mixed tumor with NF2 and its clinical implications. Presence of mixed schwannoma-meningioma should prompt screening for NF2. Thus aids in early diagnosis of unsuspected NF2 cases. We observed that irrespective of different locations, cases with NF2 showed frequent recurrence of schwannoma as compared to case who did not fit in the existing clinical criteria for NF2. Collision tumor and thereby NF2 mutations indicates the prognosis and recurrence of the tumor, thereby guides in deciding the management.

Combining nonsense mutation suppression therapy with nonsense-mediated decay inhibition in neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) results from germline mutations in the tumor-suppressor gene NF1 and predisposes patients to developing nervous system tumors. Twenty percent of NF1 patients harbor nonsense mutations resulting in premature termination codons (PTCs). Nonsense suppression therapies can facilitate ribosomal readthrough of PTCs to restore full-length protein, but their potential in NF1 is underexplored. We developed a minipig model of NF1 carrying a PTC to test whether nonsense suppression could restore expression of the NF1-encoded protein neurofibromin invitro and invivo. Nonsense suppression did not reliably increaseneurofibromin in primary NF1-/- Schwann cells isolated from minipig neurofibromas but could reduce phosphorylated ERK. Gentamicin invivo produced a similar plasma pharmacokinetic profile to humans and was detectable in clinicallyrelevant tissues, including cerebral cortex, sciatic nerve,optic nerve, and skin. In gentamicin-treated animals, increased neurofibromin expression was seen in the optic nerve. Nonsense-mediated decay (NMD) causes degradation of transcripts with PTCs, which could impede nonsense suppressiontherapies. Nonsense suppression in combination with NMD inhibition restored neurofibromin protein expression in primary NF1-/- Schwann cells isolated from minipig neurofibromas. Thus, the effectiveness of nonsense suppression therapies can be improved in NF1 by the concurrent use of NMD inhibitors.

Topical delivery of mitogen-activated protein kinase inhibitor binimetinib prevents the development of cutaneous neurofibromas in neurofibromatosis type 1 mutant mice

Cutaneous neurofibromas (cNFs) are a hallmark of patients with the neurofibromatosis type 1 (NF1) genetic disorder. These benign nerve sheath tumors, which can amount to thousands, develop from puberty onward, often cause pain and are considered by patients to be the primary burden of the disease. Mutations of NF1, encoding a negative regulator of the RAS signaling pathway, in the Schwann cell (SCs) lineage are considered to be at the origin of cNFs. The mechanisms governing cNFs development are poorly understood, and therapeutics to reduce cNFs are missing, mainly due to the lack of appropriate animal models. To address this, we designed the Nf1-KO mouse model that develops cNFs. Using this model, we found that cNFs development is a singular event and goes through 3 successive stages: initiation, progression, and stabilization characterized by changes in the proliferative and MAPK activities of tumor SCs. We found that skin trauma accelerated the development of cNFs and further used this model to explore the efficacy of the MEK inhibitor binimetinib to cure these tumors. We showed that while topically delivered binimetinib has a selective and minor effect on mature cNFs, the same drug prevents their development over long periods.

Germline Neurofibromin 1 mutation enhances the anti-tumour immune response and decreases juvenile myelomonocytic leukaemia tumourigenicity.

Juvenile myelomonocytic leukaemia (JMML) is an aggressive paediatric leukaemia characterized by mutations in five canonical RAS pathway genes, including the NF1 gene. JMML is driven by germline NF1 gene mutations, with additional somatic aberrations resulting in the NF1 biallelic inactivation, leading to disease progression. Germline mutations in the NF1 gene alone primarily cause benign neurofibromatosis type 1 (NF1) tumours rather than malignant JMML, yet the underlying mechanism remains unclear. Here, we demonstrate that with reduced NF1 gene dose, immune cells are promoted in anti-tumour immune response. Comparing the biological properties of JMML and NF1 patients, we found that not only JMML but also NF1 patients driven by NF1 mutations could increase monocytes generation. But monocytes cannot further malignant development in NF1 patients. Utilizing haematopoietic and macrophage differentiation from iPSCs, we revealed that NF1 mutations or knockout (KO) recapitulated the classical haematopoietic pathological features of JMML with reduced NF1 gene dose. NF1 mutations or KO promoted the proliferation and immune function of NK cells and iMacs derived from iPSCs. Moreover, NF1-mutated iNKs had a high capacity to kill NF1-KO iMacs. NF1-mutated or KO iNKs administration delayed leukaemia progression in a xenograft animal model. Our findings demonstrate that germline NF1 mutations alone cannot directly drive JMML development and suggest a potential cell immunotherapy for JMML patients.

Abstract 5170: STING inflames NF1 malignancies for immunotherapy

Abstract Introduction: Neurofibromatosis Type 1 (NF1) is caused by mutations in the NF1 gene that encodes neurofibromin, a RAS GTPase-Activating Protein. Inactivating NF1 mutations result in hyperactivation of RAS-mediated signaling. NF1 patients develop benign tumors on the skin and along nerves in the spinal cord and brain, and ~10% of these progress to Malignant Peripheral Nerve Sheath Tumors (MPNST). Attempts to inhibit RAS-signaling to treat MPNST have not worked in clinical trials. Surgical removal is the only cure for MPNST, which is challenging due to large tumor size and/or proximity to nerves. MPNSTs often recur, metastasize, and respond poorly to chemo- and radiotherapy. As a result, MPNSTs are the leading cause of death in NF1 patients. Immune Checkpoint Blockade (ICB) is an approach to treat inoperable, undruggable cancers. Immune checkpoint proteins (ICPs) terminate normal immune responses to prevent collateral tissue damage. Cancer cells hijack this mechanism and express ICPs to avoid immune detection. ICB disrupts this process, enhancing antitumor immunity. Monoclonal antibodies (mABs) that disrupt the interaction between Programmed Cell Death Receptor 1 (PD-1) and its ligand Programmed Cell Death Ligand 1 (PD-L1) are a widely used ICB therapy. Having a T cell-enriched hot tumor microenvironment (TME) is required for successful ICB. However, MPNSTs lack a T cell-inflamed TME and respond poorly to ICB therapy. Activation of the protein “stimulator of interferon genes” (STING) enhances anti-tumor immunity via induction of pro-inflammatory cytokines, thus increasing T cell infiltration into the TME. We hypothesized that reprogramming the MPNST TME by STING pathway activation would turn cold MPNSTs into hot tumors amenable to ICB. Methods: We treated mouse MPNSTs with STING agonist or STING agonist + anti-PD-1/anti-PD-L1 mAb. Tumor size was measured throughout treatment. The mice were sacrificed and tumor tissue was analyzed for STING pathway activation, T cell infiltration, cell proliferation, and apoptosis. MPNST allograft tumors in athymic mice were controls. Results: STING pathway activation and increased T cell presence was observed in STING agonist-treated MPNSTs compared to vehicle-treated. MPNSTs treated with STING agonist alone or STING agonist + PD-1/PD-L1 mAbs showed less tumor growth relative to vehicle. Importantly, STING agonist + PD-1/PD-L1 mAb-treated tumors showed significant cell death increase while cell proliferation remained unchanged. Interestingly, tumors in athymic mice continued to grow despite treatment suggesting the antitumor effects seen in immunocompetent mice were mediated by T cells. Conclusions: Our data show that MPNSTs can become T cell-rich tumors by activating STING signaling. Reprogramming the TME made MPNSTs susceptible to immune destruction by ICB therapy. Our studies support this novel treatment strategy for MPNST, an aggressive, deadly tumor for which no molecular therapy currently exists. Citation Format: Nipunika Somatilaka, Laasya Madana, Ali Sadek, Renee M. McKay, Lu Q. Le. STING inflames NF1 malignancies for immunotherapy. [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 5170.