Muscle-directed AAV gene therapy rescues the maple syrup urine disease phenotype in a mouse model.

Maple syrup urine disease (MSUD) is a rare, inherited metabolic disorder characterized by a dysfunctional mitochondrial enzyme complex, branched-chain alpha-keto acid dehydrogenase (BCKDH), which catabolizes branched-chain amino acids (BCAAs). Without functional BCKDH, BCAAs and their neurotoxic alpha-keto intermediates can accumulate in the blood and tissues. MSUD is currently incurable and treatment is limited to dietary restriction or liver transplantation, meaning there is a great need to develop new treatments for MSUD. We evaluated potential gene therapy applications for MSUD in the intermediate MSUD (iMSUD) mouse model, which harbors a mutation in the dihydrolipoamide branched-chain transacylase E2 (DBT) subunit of BCKDH. Systemic delivery of an adeno-associated virus (AAV) vector expressing DBT under control of the liver-specific TBG promoter to the liver did not sufficiently ameliorate all aspects of the disease phenotype. These findings necessitated an alternative therapeutic strategy. Muscle makes a larger contribution to BCAA metabolism than liver in humans, but a muscle-specific approach involving a muscle-specific promoter for DBT expression delivered via intramuscular (IM) administration only partially rescued the MSUD phenotype in mice. Combining the muscle-tropic AAV9 capsid with the ubiquitous CB7 promoter via IM or IV injection, however, substantially increased survival across all assessed doses. Additionally, near-normal serum BCAA levels were achieved and maintained in the mid- and high-dose cohorts throughout the study; this approach also protected these mice from a lethal high-protein diet challenge. Therefore, administration of a gene therapy vector that expresses in both muscle and liver may represent a viable approach to treating patients with MSUD.

TCRß Combinatorial Immunoreceptor Expression by Neutrophils Correlates with Parasite Burden and Enhanced Phagocytosis during a Plasmodium berghei ANKA Malaria Infection.

Recent studies have demonstrated that a subpopulation of neutrophils express the TCRαß combinatorial immunoreceptor in humans and mice. Here, we report that a Plasmodium berghei ANKA murine malaria infection induces expansion of TCRß expressing CD11b+ Ly6G+ neutrophils in the spleen during the early phase of infection. Measurement of TCRß transcript and protein levels of neutrophils in wild-type versus nude and Rag1 knockout mice establishes that the observed expression is not a consequence of nonspecific antibody staining or passive receptor expression due to phagocytosis or trogocytosis of peripheral T cells. Remarkably, on day 3 postinfection, we observed a highly significant correlation between the proportion of neutrophils that express TCRß and peripheral blood parasite burden. In addition, TCRß+ neutrophils phagocytose parasitized erythrocytes with 4-fold greater efficiency than TCRß- neutrophils. Together these results signify that TCR expression by the neutrophil plays an important role in the regulation of parasite burden by enhancing the phagocytic capacity of the neutrophil.

A Novel Gametocyte Biomarker for Superior Molecular Detection of the Plasmodium falciparum Infectious Reservoirs.

Background: Complete malaria eradication and optimal use of transmission-reducing interventions require knowledge of submicroscopic infectious reservoirs among asymptomatic individuals. Even submicroscopic levels of Plasmodium falciparum gametocytes can infect mosquitoes and promote onward transmission. Most efforts to identify gametocyte carriers use polymerase chain reaction amplification of the gametocyte-specific transcript Pfs25. Methods: To expand the repertoire of biomarkers available for superior gametocyte detection, we compared the gene expression profiles of gametocytes and asynchronous blood-stage P. falciparum parasites by microarray technology. This allowed the identification of 56 molecules abundantly expressed in the gametocyte stage of the parasite. The analytical sensitivity for gametocyte detection was evaluated for 25 genes with the highest expression levels. Results: One candidate, Pfg17, exhibited superior analytical sensitivity against a panel of gametocyte-spiked whole blood, detecting 10 gametocytes/mL; in comparison, Pfs25 detected only 25.3 gametocytes/mL. Pfg17 also exhibited superior clinical sensitivity, identifying 19.1% more samples from blood-film microscopy-negative Ghanaian children and 40% more samples from asymptomatic adults as gametocyte positive. Conclusions: Cumulatively, our results suggest Pfg17 is an excellent biomarker for detecting asymptomatic infectious reservoirs otherwise missed by the most sensitive molecular method available. Our study has also improved the repertoire of transmission-stage antigens available for evaluation as candidate vaccines.

Lipid nanoparticle-encapsulated mRNA therapy corrects serum total bilirubin level in Crigler-Najjar syndrome mouse model.

Crigler-Najjar syndrome is a rare disorder of bilirubin metabolism caused by uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) mutations characterized by hyperbilirubinemia and jaundice. No cure currently exists; treatment options are limited to phototherapy, whose effectiveness diminishes over time, and liver transplantation. Here, we evaluated the therapeutic potential of systemically administered, lipid nanoparticle-encapsulated human UGT1A1 (hUGT1A1) mRNA therapy in a Crigler-Najjar mouse model. Ugt1 knockout mice were rescued from lethal post-natal hyperbilirubinemia by phototherapy. These adult Ugt1 knockout mice were then administered a single lipid nanoparticle-encapsulated hUGT1A1 mRNA dose. Within 24 h, serum total bilirubin levels decreased from 15 mg/dL (256 µmol/L) to <0.5 mg/dL (9 µmol/L), i.e., slightly above wild-type levels. This reduction was sustained for 2 weeks before bilirubin levels rose and returned to pre-treatment levels by day 42 post-administration. Sustained reductions in total bilirubin levels were achieved by repeated administration of the mRNA product in a frequency-dependent manner. We were also able to rescue the neonatal lethality phenotype seen in Ugt1 knockout mice with a single lipid nanoparticle dose, which suggests that this may be a treatment modality appropriate for metabolic crisis situations. Therefore, lipid nanoparticle-encapsulated hUGT1A1 mRNA may represent a potential treatment for Crigler-Najjar syndrome.

Treating Transthyretin Amyloidosis via Adeno-Associated Virus Vector Delivery of Meganucleases.

Transthyretin amyloidosis (ATTR) is a progressive and fatal disease caused by transthyretin (TTR) amyloid fibril accumulation in tissues, which disrupts organ function. As the TTR protein is primarily synthesized by the liver, liver transplantation can cure familial ATTR but is not an option for the predominant age-related wild-type ATTR. Approved treatment approaches include TTR stabilizers and an RNA-interference therapeutic, but these require regular re-administration. Gene editing could represent an effective one-time treatment. We evaluated adeno-associated virus (AAV) vector-delivered, gene-editing meganucleases to reduce TTR levels. We used engineered meganucleases targeting two different sites within the TTR gene. AAV vectors expressing TTR meganuclease transgenes were first tested in immunodeficient mice expressing the human TTR sequence delivered using an AAV vector and then against the endogenous TTR gene in rhesus macaques. Following a dose of 3 × 1013 genome copies per kilogram, we detected on-target editing efficiency of up to 45% insertions and deletions (indels) in the TTR genomic DNA locus and >80% indels in TTR RNA, with a concomitant decrease in serum TTR levels of >95% in macaques. The significant reduction in serum TTR levels following TTR gene editing indicates that this approach could be an effective treatment for ATTR.

TCRß-expressing macrophages induced by a pathogenic murine malaria correlate with parasite burden and enhanced phagocytic activity.

Macrophages express a wide array of invariant receptors that facilitate host defense and mediate pathogenesis during pathogen invasion. We report on a novel population of CD11bhighCD14+F4/80+ macrophages that express TCRß. This population expands dramatically during a Plasmodium berghei ANKA infection and sequesters in the brain during experimental cerebral malaria. Importantly, measurement of TCRß transcript and protein levels in macrophages in wildtype versus nude and Rag1 knockout mice establishes that the observed expression is not a consequence of passive receptor expression due to phagocytosis or trogocytosis of peripheral T cells or nonspecific antibody staining to an Fc receptor or cross reactive epitope. We also demonstrate that TCRß on brain sequestered macrophages undergoes productive gene rearrangements and shows preferential Vß usage. Remarkably, there is a significant correlation in the proportion of macrophages that express TCRß and peripheral parasitemia. In addition, presence of TCRß on the macrophage also correlates with a significant increase (1.9 fold) in the phagocytosis of parasitized erythrocytes. By transcriptional profiling, we identify a novel set of genes and pathways that associate with TCRß expression by the macrophage. Expansion of TCRß-expressing macrophages points towards a convergence of the innate and adaptive immune responses where both arms of the immune system cooperate to modulate the host response to malaria and possibly other infections.