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 study for DS-2325a will evaluate the safety, tolerability, and pharmacokinetics of multiple ascending doses of DS-2325a in healthy participants. DS-2325a will be evaluated after subcutaneous (SC) injections.

Inclusion Criteria:

• Must be able to understand a written informed consent, which must be obtained prior to initiation of study procedures.
• Must be willing and able to comply with all study requirements.
• Healthy males or non-pregnant, non-lactating healthy females.
• Aged 18 to 50 years of age (inclusive) at the time of signing informed consent.
• BMI of 18.0 kg/m^2 to 30.0 kg/m^2 (inclusive) as measured at Screening.
• Women of childbearing potential who are sexually active with a male partner must practice effective contraception during the study treatment period and for 90 days after last IMP administration. They must agree to use 2 different means of nonhormonal contraceptive methods.
• Women of non-childbearing potential must be either surgically sterile or in menopausal state confirmed as follows: 1 year of spontaneous amenorrhea without an alternative medical cause and a serum follicle stimulating hormone (FSH) level ≥40 mIU/mL.
• Male participants who are sexually active with a female partner of childbearing potential must use, with their partner, a condom plus an approved method of highly effective contraception from the time of informed consent until 90 days after last IMP administration.
• Women should not donate eggs and men should not donate sperm during the study treatment period and for at least 90 days after last IMP administration.
• All female participants must have a negative serum pregnancy test at Screening and Admission (Day -2).

Exclusion Criteria:

• History or presence of clinically significant cardiovascular, pulmonary, hepatic, renal, hematologic, metabolic, endocrine, immunologic, infectious, dermatologic, neurologic, oncologic, psychological, psychiatric, ophthalmologic, or gastrointestinal disease (except cholecystectomy), as judged by the Investigator.
• History or presence of chronic lung or respiratory disease, including clinically significant asthma (as judged by the Investigator) and chronic obstructive pulmonary disease (COPD).
• History, or presence in the average of triplicate ECGs at Screening and Admission (Day -2).
• Laboratory results (serum chemistry, hematology, coagulation, and urinalysis) outside the normal range, if considered clinically significant by the Investigator at Screening or Admission (Day -2).
• Creatinine clearance (CrCl) <80 mL/mina t Screening.
• History or presence of any other clinically significant condition, including laboratory abnormality, that in the opinion of the Investigator, would jeopardize the safety of the participant, obtaining informed consent, compliance to the study procedures, or the validity of the study results.

De-identified individual participant data (IPD) 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/

Studies 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 from 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.