A Phase 1, Multicenter, Open-label, Dose-escalation Study Evaluating the Safety and Tolerability of Intravenous KK2269 Monotherapy and Combination Therapy With Docetaxel in Adult Participants With Solid Tumors

* Key Common Inclusion Criteria for Parts 1 and 2: * Patients who are ≥ 18 years old at the time of informed consent * Patients who have disease measurable by RECIST v1.1 * Patients with an ECOG PS of 0 or 1 * Patients with a life expectancy of at least 3 months in the judgement of the investigator or subinvestigator * The specified periods have passed respectively after the completion of previous cancer treatments as of the date of enrollment at the time of the first dose of KK2269 * Patients who agree to use a medically effective method of contraception * Key Additional Inclusion Criterion for Part 1: •Patients with histological or cytological evidence of at least one locally advanced or metastatic non-CNS solid tumor * Key Additional Inclusion Criteria for Part 2: •Patients with histological or cytological evidence of any of the following disease: Gastric adenocarcinoma, GEJ adenocarcinoma, or esophageal adenocarcinoma, NSCLC (Only patients with NSCLC will be enrolled in the expansion part) •Patients who are suitable for docetaxel treatment * Key Common Exclusion Criteria for Parts 1 and 2: * Patients with an uncontrolled or serious intercurrent illness * Patients with known active central nervous system metastasis * Patients with a history of ≥ Grade 3 allergic reaction to any antibody drug * Patients with a history of autoimmune disease * Patients with a history of HIV, HBV, or HCV at screening * Patients who have a history of primary immunodeficiency * Key Additional Exclusion Criterion For Part 2: * Patients with a history of treatment with docetaxel