Bone marrows are harvested from the patient's iliac depending on the patient's body weight as follows: 8 ml/kg for patients under 10 kg; [80 ml + (body weight in kg - 10) × 7 ml] for patients above 10 kg. Mononuclear cells from collected bone marrow are infused intrathecally through a space between number vertebrae 4th and 5th. Two transplantations will be conducted at an interval of 6 months. The educational intervention will be developed based on the Early Start Denver Model for 6 months after the first infusion.

Evaluation: The efficacy outcomes will be measured using the CARS, Vineland Adaptive Behavior Scales - second Edition (VABS), Autism Behavior Checklists (ABC), and Clinical Global Impression (CGI). In addition, Health-related quality of life (HRQoL) in patients will be evaluated at baseline, two months, six months, and 12 months with those in the control group (educational intervention only) using the Pediatric Quality of Life Inventory (PedsQL)

The educational intervention will be developed based on the Early Start Denver Model for six months after enrollment.

Evaluation: The efficacy outcomes will be measured using the CARS, Vineland Adaptive Behavior Scales - second Edition (VABS), Autism Behavior Checklists (ABC), and Clinical Global Impression (CGI). In addition, Health-related quality of life (HRQoL) in patients will be evaluated at baseline, two months, six months, and 12 months with those in the control group (educational intervention only) using the Pediatric Quality of Life Inventory (PedsQL)

Biological/ Vaccine: Autologous bone marrow-derived mononuclear cell infusion (BM-MNCs) will be administrated at baseline, and the second infusion will be performed six months after the first administration. For each transplantation, the bone marrow will be harvested through an anterior iliac crest puncture under general anesthesia in the operating theatre. The volume collected depends on the patient's body weight based on our experience from a previous study as follows: 8 ml/kg for patients under 10 kg; [80 ml + (body weight in kg - 10) x 7 ml] for patients above 10 kg but no more than 250 ml in total.

Educational intervention: 6 months based on the Early Start Denver Model

The Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5). DSM-5 describes three levels of increasing severity of ASD.DSM-5 describes three levels of increasing severity of ASD, from (1) ("requiring support") to (2) ("requiring substantial support"), and finally to (3) ("requiring very substantial support").

The Childhood Autism Rating Scale (CARS) consists of 14 domains assessing behaviors associated with ASD, with a 15th domain rating general impressions of ASD. Each domain is scored on a scale ranging from one to four; higher scores are associated with a higher level of impairment. Total scores can range from a low of 15 to a high of 60; scores below 30 indicate that the individual is in the non-autistic range, scores between 30 and 36.5 indicate mild to moderate autism, and scores from 37 to 60 indicate severe autism.

The Vineland Adaptive Behaviour Scale second version (VABS-2) is a semi-structured interview measuring adaptive behavior with standard scores (M = 100, SD = 15). We define proficiency as a standard score of 85 or above (i.e., 1 SD below the mean). This metric for "not impaired" is used in other optimal outcome studies and the learning disability literature. We define growth as an improvement of at least 1 SD in standard scores (15 points) from T1 to T2. Improvement of 1 SD in clinical trials is considered a large effect size.

The Pediatric Quality of Life Inventory™ 4.0 Generic Core Scales - Parent Report (PedsQL) is a tool for assessing the HRQoL of children aged 2-18.

PedsQL includes four domains (physical functioning, emotional functioning, social functioning, and school functioning) and is scored using three levels: no problems (1), some problems (2), or many problems (3). The PedsQL has 23 items, and scores on the standard portion range from 0 to 100, with 100 representing the best possible quality of life.