A Phase 1 Study of BLKR201 in Healthy Adult Participants

Inclusion Criteria: * Are a healthy man or woman 18 to 55 years old * Weigh at least 50 kilograms (110 pounds) * Have a body mass index (BMI) between 18 and 30 * Are willing to stay at the research unit for the required study visits * Are willing to follow study rules about diet, alcohol, tobacco, and medications * Are able to understand and sign the informed consent form Women who can become pregnant must: * Have a negative pregnancy test before starting * Use a highly effective form of birth control during the study and for a period after the last dose Men with partners who can become pregnant must: * Use highly effective birth control during the study and for a period after the last dose * Not donate sperm during that time Exclusion Criteria: * Have any significant medical condition involving the heart, lungs, liver, kidneys, stomach, intestines, brain, blood, or immune system * Have abnormal laboratory test results at screening that the study doctor considers important * Have a history of heart rhythm problems or abnormal electrocardiogram (ECG) results * Have high blood pressure at screening * Have had a serious infection within the past 6 months * Test positive for HIV, hepatitis B, hepatitis C, or tuberculosis * Have a history of cancer in the past 5 years (with limited exceptions for certain treated skin cancers) * Have a history of serious stomach problems such as ulcers, stomach surgery, or stomach bleeding * Use tobacco, nicotine, or marijuana products * Test positive for drugs or alcohol at screening * Have taken another investigational drug within the required time before this study * Have received a live vaccine within 30 days before study start * Are pregnant or breastfeeding * Have a known allergy to the study drug or similar medicines Additional exclusions: * Regular heavy alcohol use * Regular use of certain medications such as anti-inflammatory drugs, steroids, or blood thinners * Donation of more than 500 milliliters (about one pint) of blood within 1 month before screening For the spinal fluid (CSF) portion of the study, you cannot take part if you: * Take blood-thinning medications * Have bleeding or clotting problems * Have medical conditions that make a spinal tap unsafe