This is a Phase 1b Extension Trial to allow repeat intracerebroventricular injections of RB-ADSCs in subjects previously treated in and successfully completed RBI Protocol RB-ADSC-02. In the previous Phase 1 clinical trial, RB-ADSC-02, subjects with mild to moderate Alzheimer's disease (AD) received a single intraventricular injection of RB-ADSC. RB-ADSC will be delivered intracerebroventricularly every 2 months via the previously implanted Ommaya reservoir for up to 6 injections in total. The primary objective of safety is performed 2 months after the last dose administration at the month 12 follow-up visit. The secondary objective endpoint evaluations of efficacy are performed at the month 6 and 12 visits.

This is a Phase 1b Extension Trial to allow repeat intracerebroventricular injections of RB-ADSCs in subjects previously treated in and successfully completed RBI Protocol RB-ADSC-02. In the previous Phase 1 clinical trial, RB-ADSC-02, subjects with mild to moderate Alzheimer's disease (AD) received a single intraventricular injection of RB-ADSC.

RB-ADSC will be delivered intracerebroventricularly every 2 months via the previously implanted Ommaya reservoir for up to 6 injections in total. Participants will be followed for 2 months after the last administration. The primary objective is safety and tolerability of repeated dosing of RB-ADSC. Adverse events (AEs) and serious adverse events (SAEs) will be assessed by the incidence and severity of dose-limiting toxicity (DLT) and other AEs, incidence and severity of cytokine response syndrome, vital sign measurements, clinical laboratory tests and physical examination. Preliminary efficacy of repeated dosing will be evaluated with clinical assessments (MMSE, FAST, ADAS-Cog), volumetric MRI (NeuroQuant), CSF biomarkers (phosphor-Tau, total-Tau,AB-42), and diagnostic imaging comparison (Amyloid-PET).

Inclusion Criteria:

1. Successful completion of the Phase 1 single dose administration study of RB-ADSC, Protocol RB-ADSC-02.
2. Written informed consent to participate in this Phase 1b Extension Study either provided by the participant or a legal representative
3. The participant must have a relative/caregiver who is alert for possible side effects.
4. The caregiver must separately meet the specified inclusion/exclusion criteria for caregivers for this Phase 1b Extension Study.

Exclusion Criteria:

1. Participant experienced treatment related SAE or DLT in Protocol RB-ADSC-02
2. Participants who, in the opinion of the Investigator, are unsuitable for this Phase 1 Extension Study