The purpose of this study is to assess the safety, tolerability, and preliminary efficacy of SYNCAR-100 in patients with CD19-positive relapsed or refractory B-cell acute lymphoblastic leukemia (R/R B-ALL). Participants who have signed the informed consent form will undergo screening against the inclusion and exclusion criteria. Eligible participants will receive study drug administration once weekly for a total of four doses, followed by a 1-year safety and efficacy follow-up observation period. After the completion of the study, long-term follow-up may be required for participants to monitor their health and survival status until 15 years post-treatment, or until the occurrence of patient death, loss to follow-up, or withdrawal of consent.