The main objective of this prospective, observational, long-term follow-up (LTFU) study is to evaluate the long-term safety profile of the gene therapy products evaluated by Krystal Biotech, Inc. which have a shared backbone of HSV-1, in participants who received at least one dose of investigational product (IP).

Due to the guidelines for gene therapy for vectors which may undergo latency/ reactivation, Krystal Biotech, Inc. has established a Long-Term Follow-up Protocol which will identify and mitigate the long-term risks to the participants receiving their gene therapy products and capture delayed adverse events in participants, annually, for 5-years following the last study visit. Additionally, it will allow the Sponsor to further understand the persistence of the gene therapy products used in their parent treatment protocols.

Inclusion Criteria:

• All adult and pediatric participants who received at least one gene therapy treatment in a previous Krystal Biotech, Inc. sponsored study, and have discontinued or completed the parent treatment protocol (which do not have the LTFU embedded into the parent protocol), as applicable.
• Consent/Assent must be obtained by the participants (and, parental/legal representative, when applicable) prior to any study-related data being collected.
• Participant is willing and able to adhere to the protocol requirements.

Exclusion Criteria:

• Participants who enroll into a non-Krystal Biotech, Inc. interventional gene therapy clinical trial will be excluded from the study.

Participants who received at least one treatment of gene therapy from a Krystal Biotech, Inc. sponsored study, will be asked to roll-over to this LTFU protocol upon either premature discontinuation from, or completion of a prior parent treatment protocol. However, if a participant enrolls in a different Sponsor gene therapy trial during the LTFU phase this participant will be dropped out from the study.