Safety and Pharmacokinetics of Single Ascending Doses and Multiple Ascending Doses of CS6253 in Healthy Volunteers

* Phase 1A SAD: Five or more cohorts of 8 healthy volunteers (HVs) will receive a single IV bolus injection of study drug or placebo. The first 4 cohorts will be male only. The last cohort will be repeated with the max safe dose of the previous cohorts in healthy elderly subjects (male and female of non childbearing potential, \> 50years) * Phase 1B MAD: Two or more cohorts of 8 male and female HVs will receive multiple (4) IV bolus injections of study drug or placebo every 72 hours. * Phase 1 Subcutaneous SC Cohort: One cohort of 6 male and 6 female HVs will receive one SC injection of study drug.