Hemophagocytic lymphohistiocytosis following gene replacement therapy in a child with type 1 spinal muscular atrophy

Gene-based therapies for neuromuscular disorders

Neuromuscular diseases (NMD) include a broad group of medical conditions with both acquired and genetic causes. In recent years, important advances have been made in the treatment of genetically caused NMD, and most of these advances are due to the implementation of therapies aimed at gene regulation. Among these therapies, gene replacement, small interfering RNA (siRNA), and antisense antinucleotides are the most promising approaches. More importantly, some of these therapies have already gained regulatory approval or are in the final stages of approval. The review focuses on motor neuron diseases, neuropathies, and Duchenne muscular dystrophy, summarizing the most recent developments in gene-based therapies for these conditions.

Deciphering conundrums of adeno-associated virus liver-directed gene therapy: focus on hemophilia

Adeno-associated virus gene therapy has been the subject of intensive investigation for monogenic disease gene addition therapy for more than 25 years, yet few therapies have been approved by regulatory agencies. Most have not progressed beyond phase 1/2 due to toxicity, lack of efficacy, or both. The liver is a natural target for adeno-associated virus since most serotypes have a high degree of tropism for hepatocytes due to cell surface receptors for the virus and the unique liver sinusoidal geometry facilitating high volumes of blood contact with hepatocyte cell surfaces. Recessive monogenic diseases such as hemophilia represent promising targets since the defective proteins are often synthesized in the liver and secreted into the circulation, making them easy to measure, and many do not require precise regulation. Yet, despite initiation of many disease-specific clinical trials, therapeutic windows are often nonexistent, resulting in excess toxicity and insufficient efficacy. Iterative progress built on these attempts is best illustrated by hemophilia, with the first regulatory approvals for factor IX and factor VIII gene therapies eventually achieved 25 years after the first gene therapy studies in humans. Although successful gene transfer may result in the production of sufficient transgenic protein to modify the disease, many emerging questions on durability, predictability, reliability, and variability of response have not been answered. The underlying biology accounting for these heterogeneous responses and the interplay between host and virus is the subject of intense investigation and the subject of this review.

Improved gene therapy for spinal muscular atrophy in mice using codon-optimized hSMN1 transgene and hSMN1 gene-derived promotor

Physiological regulation of transgene expression is a major challenge in gene therapy. Onasemnogene abeparvovec (Zolgensma®) is an approved adeno-associated virus (AAV) vector gene therapy for infants with spinal muscular atrophy (SMA), however, adverse events have been observed in both animals and patients following treatment. The construct contains a native human survival motor neuron 1 (hSMN1) transgene driven by a strong, cytomegalovirus enhancer/chicken β-actin (CMVen/CB) promoter providing high, ubiquitous tissue expression of SMN. We developed a second-generation AAV9 gene therapy expressing a codon-optimized hSMN1 transgene driven by a promoter derived from the native hSMN1 gene. This vector restored SMN expression close to physiological levels in the central nervous system and major systemic organs of a severe SMA mouse model. In a head-to-head comparison between the second-generation vector and a benchmark vector, identical in design to onasemnogene abeparvovec, the 2nd-generation vector showed better safety and improved efficacy in SMA mouse model.

HLH Syndrome in a Community Hospital: The Challenge of an Early Diagnosis

Introduction

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal hyperinflammatory cytokine storm. It can be secondary to infections, malignancies, autoimmune diseases, or the manifestation of genetic disorders, including primary immune deficiency. HLH requires a high index of suspicion and is challenging for community hospitals.

Methods

Medical records of children with HLH admitted to the Meir Medical Center in Israel between 2014 and 2017 were reviewed.

Results

Nine children met ≥5/8 HLH-2004 criteria. The median age was 1.1 year, and 78% of the patients were aged <2 years. All patients had prolonged fever, cytopenia, and elevated soluble interleukin-2 receptor, and 89% had elevated ferritin levels. Of three children who underwent gene panel evaluation, one had heterozygote genetic variants of UNC13D and STXBP2 of unclear significance, whereas the other two had no variants. Infection was identified in 8 of 9 patients: adenovirus, HHV6, EBV, and Streptococcus Group A. Only 2 patients received HLH-2004 therapy (dexamethasone, etoposide, cyclosporin-A) and the others received dexamethasone and/or intravenous gamma globulins (IVIG), with rapid resolution of fever (median 2 days). One patient (11%) died of Pseudomonas septicemia and multiorgan failure. At a median follow-up of 7 years (range 2.6-8.1 years), all others (8/9) are long-term survivors with no recurrent HLH, but 2 patients developed adenovirus-related bronchiolitis obliterans.

Conclusion

Children presenting with prolonged fever and abnormal blood counts should be evaluated with ferritin, triglycerides, and fibrinogen levels which indicate possible HLH. Early intervention with corticosteroids and/or IVIG may prevent deterioration, spare them from chemotherapy and provide time for more elaborate testing to identify true HLH. Unfortunately, mortality remains a significant risk for these children.

Thrombotic microangiopathy following systemic AAV administration is dependent on anti-capsid antibodies

BACKGROUNDSystemic administration of adeno-associated virus (AAV) can trigger life-threatening inflammatory responses, including thrombotic microangiopathy (TMA), acute kidney injury due to atypical hemolytic uremic syndrome-like complement activation, immune-mediated myocardial inflammation, and hepatic toxicity.METHODSWe describe the kinetics of immune activation following systemic AAV serotype 9 (AAV9) administration in 38 individuals following 2 distinct prophylactic immunomodulation regimens. Group 1 received corticosteroids and Group 2 received rituximab plus sirolimus in addition to steroids to prevent anti-AAV antibody formation.RESULTSGroup 1 participants had a rapid increase in immunoglobulin M (IgM) and IgG. Increase in D-dimer, decline in platelet count, and complement activation are indicative of TMA. All Group 1 participants demonstrated activation of both classical and alternative complement pathways, as indicated by depleted C4 and elevated soluble C5b-9, Ba, and Bb antigens. Group 2 patients did not have a significant change in IgM or IgG and had minimal complement activation.CONCLUSIONSThis study demonstrates that TMA in the setting of AAV gene therapy is antibody dependent (classical pathway) and amplified by the alternative complement pathway. Critical time points and interventions are identified to allow for management of immune-mediated events that impact the safety and efficacy of systemic gene therapy.

261st ENMC International Workshop: Management of safety issues arising following AAV gene therapy. 17th-19th June 2022, Hoofddorp, The Netherlands

Adeno-associated virus (AAV) gene therapies are demonstrating much promise in the area of neuromuscular disorders. There are now therapies in clinical trials or real-world use for several disorders including spinal muscular atrophy and Duchenne muscular dystrophy. However, there have been several concerning reports of serious adverse events, including deaths. Reporting and monitoring of these is not consistent between trials. Therefore, a group of clinicians, investigators, industry and patient representatives met the weekend of 17th-19th June 2022 to discuss safety issues arising from the use of these therapies. The group shared information on safety events across a spectrum of AAV gene therapy products, both in clinical trials and commercial use. Patterns of serious adverse events were identified and the group discussed methods of identification and management of these as well as new ways of improving information sharing across industry in order to improve the safety of these promising treatments.

Lethal immunotoxicity in high-dose systemic AAV therapy

High-dose systemic gene therapy with adeno-associated virus (AAV) is in clinical trials to treat various inherited diseases. Despite remarkable success in spinal muscular atrophy and promising results in other diseases, fatality has been observed due to liver, kidney, heart, or lung failure. Innate and adaptive immune responses to the vector play a critical role in the toxicity. Host factors also contribute to patient death. This mini-review summarizes clinical findings and calls for concerted efforts from all stakeholders to better understand the mechanisms underlying lethality in AAV gene therapy and to develop effective strategies to prevent/treat high-dose systemic AAV-gene-therapy-induced immunotoxicity.

Immunogenicity of Recombinant Adeno-Associated Virus (AAV) Vectors for Gene Transfer

Recombinant adeno-associated viruses (AAVs) have emerged as promising gene delivery vehicles resulting in three US Food and Drug Administration (FDA) and one European Medicines Agency (EMA)-approved AAV-based gene therapies. Despite being a leading platform for therapeutic gene transfer in several clinical trials, host immune responses against the AAV vector and transgene have hampered their widespread application. Multiple factors, including vector design, dose, and route of administration, contribute to the overall immunogenicity of AAVs. The immune responses against the AAV capsid and transgene involve an initial innate sensing. The innate immune response subsequently triggers an adaptive immune response to elicit a robust and specific response against the AAV vector. AAV gene therapy clinical trials and preclinical studies provide important information about the immune-mediated toxicities associated with AAV, yet studies suggest preclinical models fail to precisely predict the outcome of gene delivery in humans. This review discusses the contribution of the innate and adaptive immune response against AAVs, highlighting the challenges and potential strategies to mitigate these responses, thereby enhancing the therapeutic potential of AAV gene therapy.

The Treatment Based on Ruxolitinib and Amphotericin B is Effective for Relapsed Leishmaniasis-Related Hemophagocytic Lymphohistiocytosis: A Case Report and Literature Review

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is known as a life-threatening syndrome, and Leishmania is the most common protozoan that triggers infection-related HLH. It is thus important to find the root cause and treat it effectively.

CASE REPORT

This paper reports a 44-year-old man who developed antisynthetase antibody syndrome previously. The patient progressed rapidly to the extent of meeting the HLH-2004 diagnostic criteria, despite the unknown etiology. Although the patient was promptly treated in line with the HLH-1994 protocol to achieve remission, he still relapsed after glucocorticoid reduction. Afterwards, it was found out that HLH was secondary to Leishmania infection. The symptoms of HLH were alleviated quickly by the treatment with Ruxolitinib and Amphotericin B.

CONCLUSION

Etiological screening plays a crucial role in leishmaniasis-related HLH. An experienced pathologist and real-time PCR are essential for treating Leishmania. The treatment of Ruxolitinib and Amphotericin B proved effective in alleviating the relapse of visceral leishmaniasis-related HLH.