Netherton syndrome (NS) is a rare autosomal recessive disease and no systemic treatment or standard of care currently exists for patients with NS. DS-2325a, a specific and potent inhibitor of kallikrein 5, is expected to treat NS by replacing a defective gene.

This first-in-human study for DS-2325a will evaluate the safety, tolerability, and pharmacokinetics of single ascending doses of DS-2325a in healthy participants. DS-2325a will be evaluated after both subcutaneous (SC) injections and intravenous (IV) infusions, as it may have to be given intravenously to young patients and as loading dose.

Inclusion Criteria:

• Participants must give written informed consent to participation in the study prior to Screening
• Healthy men and women 18 to 45 years of age (inclusive), with a BMI of 18 kg/m2 to 30 kg/m^2 (inclusive) at Screening
• All women must have a negative serum pregnancy test at Screening and all women of childbearing potential must have a negative urine pregnancy test on Day -1
• Women must not be lactating during the study treatment period and for 3 months after the last dose of study treatment
• Women of childbearing potential must practice effective contraception during the study treatment period and for 3 months after the last dose of study treatment. They must agree to use 2 different means of nonhormonal contraceptive methods
• Women of non-childbearing potential must be either surgically sterile (ie, bilateral tubal ligation at least 3 months prior to dosing) or in menopausal state confirmed as follows: 1 year of spontaneous amenorrhea without an alternative medical cause and a serum FSH level ≥40 mIU/mL
• Men must agree to use contraception (condom with spermicide) during the study treatment period and for at least 3 months after the last dose of study treatment or be surgically sterile (vasectomy at least 3 months prior to dosing)
• Women should not donate eggs and men should not donate sperm during the study treatment period and for at least 3 months after the last dose of study treatment
• Participants must be in good health as determined by Screening medical history, physical examination, vital signs, ECGs, serum chemistry, hematology, virology, and urinalysis performed at Screening and on Day -1

Exclusion Criteria:

• History or current chronic lung disease including asthma, chronic obstructive pulmonary disease (COPD), or heavy smoking of >10 pack years
• Previous or current treatment with systemic corticosteroids or any immunosuppressive agents
• Participants who have received a transfusion or any blood products within the last year prior to dosing
• Participants who have made any blood donation or have had a loss of blood of ≥500 mL within 56 days prior to the dose of study drug
• Participants who consume more than 21 units of alcohol per week (1 unit of alcohol equals 1/2 pint of beer, 4 ounces of wine, or 1 ounce of spirits) or those participants who have a significant history of alcoholism or drug/chemical abuse within the last 2 years.
• Participants with positive results on tests for drugs of abuse, cotinine, or alcohol at Screening and/or Day -1.

De-identified individual participant data (IPD) on completed studies and applicable supporting clinical trial documents may be available upon request at https://vivli.org/. In cases where clinical trial data and supporting documents are provided pursuant to our company policies and procedures, Daiichi Sankyo will continue to protect the privacy of our clinical trial participants. Details on data sharing criteria and the procedure for requesting access can be found at this web address: https://vivli.org/ourmember/daiichi-sankyo/

Completed studies that has reached a global end or completion with all data set collected and analyzed, and for which the medicine and indication have received European Union (EU) and United States (US), and/or Japan (JP) marketing approval on or after 01 January 2014 or by the US or EU or JP Health Authorities when regulatory submissions in all regions are not planned and after the primary study results have been accepted for publication.

Formal request from qualified scientific and medical researchers on IPD and clinical study documents on completed clinical trials supporting products submitted and licensed in the United States, the European Union and/or Japan from 01 January 2014 and beyond for the purpose of conducting legitimate research. This must be consistent with the principle of safeguarding study participants' privacy and consistent with provision of informed consent.