5-hydroxytryptophan (5-HTP), a precursor of serotonin, is produced in a microbial host cell. A modified bacterial phenylalanine 4-hydroxylase (P4H) catalyzes the tryptophan 5-hydroxylation reaction. Optionally the host cell includes a cofactor regeneration mechanism, allowing continuous production of 5-HTP without supplementation of exogenous cofactors.

Provided herein are recombinant adeno-associated virus (rAAV) compositions that can restore phenylalanine hydroxylase (PAH) gene function in cells, and methods for using the same to treat diseases associated with reduction of PAH gene function (e.g., PKU). Also provided are nucleic acids, vectors, packaging systems, and methods for making the adeno-associated virus compositions.

A lentiviral vector system for expressing a lentiviral particle is disclosed. The lentiviral vector system includes a therapeutic vector. The lentiviral vector system produces a lentiviral particle that encodes a codon-optimized PAH for upregulating PAH expression in the cells of a subject afflicted with phenylketonuria (PKU).

Provided are methods for reducing the risk of occurrence and/or the severity of pathogenic diseases (e.g., diseases associate with varicella zoster virus reactivation, influenza infection, and/or S. pneumoniae infection) in a subject that is receiving a gene therapy and an accompanying immunosuppressant regimen.

Provided are methods for reducing the risk of occurrence and/or the severity of transaminitis in a subject that is receiving a gene therapy.

Provided herein are methods of treating phenylketonuria by normalizing levels of amino acids, neurotransmitters, and neurotransmitter metabolites in a subject having phenylketonuria.

Provided herein are variant phenylalanine hydroxylase (PAH) polypeptides which are more stable and have greater activity than wild-type human PAH. Also provided are methods to treat phenylketonuria (PKU) and/or to reduce levels of phenylalanine in an individual in need thereof. Further provided herein are expression cassettes, vectors (e.g., rAAV vectors), viral particles, pharmaceutical compositions and kits for expressing the variant PAH polypeptide in an individual in need thereof.

The present disclosure provides expression constructs comprising a phenylalanine hydroxylase (PAH) transgene and methods of using the constructs for treating phenylketonuria (PKU).

Provided herein is a dual vector transfection system for the production of recombinant adeno-associated virus (rAAV). The dual vector transfection system generally comprises: (1) a first nucleic acid vector comprising a first nucleotide sequence encoding an AAV Rep protein, a second nucleotide sequence comprising an rAAV genome comprising a transgene, and a third nucleotide sequence encoding an AAV capsid protein; and (2) a second nucleic acid vector comprising a helper virus gene.

A lentiviral vector system for expressing a lentiviral particle is disclosed. The lentiviral vector system includes a therapeutic vector. The therapeutic vector comprises a phenylalanine hydroxylase (PAH) sequence for expressing at least one of PAH or a variant thereof, wherein the PAH sequence is truncated.