This study is a single-center, prospective, double-blind, randomized controlled clinical trial (RCT). Employing a parallel-group design, the trial plans to enroll 30 clinically diagnosed AD patients, who will be randomly assigned via a computerized randomization tool into three equal groups: low-dose, high-dose, and control (10 patients per group). The blinded clinical trial consists of three phases: \*\*Screening Phase\*\*: All enrolled patients must provide fully informed consent and meet inclusion criteria while avoiding exclusion criteria. Baseline assessments will be recorded, and single-cell omics samples will be collected. Patients may voluntarily opt for cerebrospinal fluid (CSF) sampling. The umbilical cord blood (UCB) used clinically is sourced from the Shandong Cord Blood Hematopoietic Stem Cell Bank. Following erythrocyte and granulocyte depletion via lymphocyte separation and density gradient centrifugation, the UCB is purified to reduce immunogenicity and undergoes genetic screening to exclude the APOE4 risk allele. \*\*Treatment Phase\*\*: In addition to standard care, patients will receive intravenous infusions at weekly intervals for four sessions. A fifth infusion will be administered one month after the fourth. The low-dose group receives 1×10⁸ UCB-derived mononuclear cells (UCB-MNCs) per infusion, the high-dose group receives 3×10⁸ UCB-MNCs, and the control group receives an equivalent volume of saline placebo. All clinically administered UCB-MNCs undergo genetic screening to exclude the APOE4 risk allele. \*\*Follow-up Phase\*\*: Assessments will be conducted at 30 days (1 month), 60 days (2 months), 90 days (3 months), and 180 days (6 months) post-initial infusion, including: 1. CDR-SB scale scoring; 2. Total and subdomain scores of the Activities of Daily Living (ADL) scale; 3. Serum inflammatory cytokines (IL-1, IL-2, IL-6, IL-8, IL-10, TNF-α), AD biomarkers (P-tau181, P-tau217), and other relevant markers; 4. Single-cell omics sample collection; 5. Optional CSF sampling per patient preference. After database lock, unblinding will occur for subsequent analysis.