This clinical study aims to evaluate whether a nasal spray containing exosomes derived from human umbilical cord mesenchymal stem cells (hUC-MSC-EXOs) can safely and effectively improve core symptoms in children aged 3-7 years with autism spectrum disorder (ASD). It is a 24-week, randomized, controlled, open-label trial. Forty pediatric patients with ASD will be randomly assigned at a 1:1 ratio to two groups: an active exosome nasal spray treatment group and a no-intervention control group. The treatment group will receive the nasal spray every other day, totaling 10 administrations throughout the study. The no-intervention control group will receive no experimental treatment but will undergo the same assessments and safety checks concurrently with the treatment group. This design aims to monitor the safety and efficacy of the hUC-MSC-EXOs nasal spray.

Inclusion Criteria:

• Diagnosis meets the ICD-11 ASD criteria or DSM-5 ASD clinical diagnostic standards.
• No significant improvement in core symptoms was observed after ≥3 months of standardized behavioral intervention.
• Score ≥30 on the CARS2, indicating mild-to-moderate or more severe autism.
• Aged 3 (inclusive) to 7 (inclusive) years, regardless of gender
• Voluntary participation in this clinical study, with written informed consent provided by the patient's legal guardian, and willingness to undergo examinations, treatment, and cooperate with follow-up visits.
• In the investigator's judgment, the patient is capable of understanding and complying with study requirements.

Exclusion Criteria:

• History of severe allergic reactions.
• Any severe mental disorder or other types of autism spectrum disorders.
• History of epileptic seizures within the past six months.
• Autism secondary to epilepsy, cerebrovascular disease, or traumatic brain injury.
• Disease severity rated as normal, borderline mental disorder, or mild mental disorder on the Clinical Global Impression scale.
• Moderate or severe extrapyramidal symptoms or tardive dyskinesia.
• Severe self-injurious behavior.
• Active systemic or severe localized infections, including human immunodeficiency virus, syphilis, and hepatitis.
• Autoimmune diseases.
• Major organ impairment.
• Severe pulmonary or hematological diseases, malignancies, or immunodeficiency.
• Concurrent treatments that may interfere with the safety and efficacy evaluation of stem cell therapy.
• Participation in other clinical trials within the past three months.
• Other clinical conditions deemed by investigators as unsuitable for study inclusion.