This is a Phase 1, single-center, open-label, single-arm, dose-escalation positron emission tomography study to assess the safety and tolerability, immunogenicity, Pharmacokinetics, dosimetry, and biodistribution after GEH200521 (18F) Injection is co-administered with GEH200520 Injection in healthy volunteers.

The estimated study duration for each subject is approximately 28 days in part A and 34 days in part B.

The primary study objective is to evaluate the safety and tolerability of the IMPs, the selected mass doses of GEH200520 Injection co-administered with a fixed dose of GEH200521 (18F) Injection.

Inclusion Criteria:

• The subject is able and willing to comply with all study procedures as described in the protocol, and has read, signed, and dated an informed consent form prior to any study procedures being performed.
• The subject is male or female ≥18 years of age.
• The subject has a body mass index (BMI) ≥18 and ≤35 kg/m2.
• The subject has no history of chronic medical illness or symptoms of active illness per Investigator's assessment.
• The subject has no clinically significant deviation from normal ranges in physical examination, ECG, and clinical laboratory parameters.
• Female and male contraception methods.

Exclusion Criteria:

• Subject is using prescribed and/or non-prescribed medication which in the Investigator's opinion might impact subject safety or the study results.
• Subject has a known or suspected allergy to IMP and/or IMP ingredients.
• Subject has had a surgery within 8 weeks prior to enrollment or a surgery is scheduled during the study.
• Subject has been enrolled in this or another interventional clinical study within the 30 days before screening for this study or is actively participating in another clinical study with IMP(s).
• Subject has been enrolled in another clinical study with radiation or exposed to radiation due to medical practice, which in the Investigator's opinion might impact subject safety or the study results.
• Subject is pregnant, planning to become pregnant, or is lactating.
• Creatinine and liver function laboratory values higher than 1.5x upper limit ranges per local site clinical practice.