This study is researching an experimental drug called ALN-APOC3 (called "study drug"). The study is focused on participants who have dyslipidemia (abnormal amounts of fats in the blood, including triglycerides and cholesterol), but who are otherwise healthy.

The aim of the study is to see how safe and effective the study drug is.

The study is looking at several other research questions, including:

• What side effects may happen from taking the study drug
• How much study drug is in the blood at different times
• How the study drug changes lipid levels in the blood

Key Inclusion Criteria:

1. Judged by the investigator to be in good health based on medical history, physical examination, vital signs, Electrocardiograms (ECG's) and laboratory safety testing, as defined in the protocol

2. Participants can enter the study under one of the following options, as defined in the protocol:

   1. Currently not taking statin and have not been on statin therapy for the 3 months prior to screening, or
   2. On a stable dose of statin, taken continuously for 3 months

3. Fasting triglycerides concentrations ≥100 and <500 mg/dL (1.13 to 5.65 mmol/L) during screening visit, as defined in the protocol

4. Fasting LDL-C ≥70 (1.81 mmol/L) if on stable statin therapy OR if not on statin treatment, as defined in the protocol

Key Exclusion Criteria:

1. History of clinically significant cardiovascular (other than dyslipidemia), respiratory, hepatic, renal, gastrointestinal, endocrine, hematological, psychiatric, or neurological disease, or any other concern, as assessed by the investigator that may confound the results of the study or poses an additional risk to the participant by study participation
2. Was hospitalized (ie, >24 hours) for any reason within 30 days of the screening visit
3. Is positive for Human Immunodeficiency Virus (HIV) or Hepatitis B surface Antigen (HBsAg) at the screening visit, as defined in the protocol
4. Is positive for hepatitis C antibody and positive for qualitative Hepatitis C Virus (HCV) Ribonucleic Acid (RNA) test at the screening visit
5. Any malignancy, except for non-melanoma skin cancer or cervical/anus in-situ, that have been resected with no evidence of metastatic disease for 3 years prior to the screening visit

NOTE: Other protocol defined inclusion/exclusion criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing.

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf