This is an exploratory study with an open-label, single-arm, single-center design. It plans to enroll subjects with refractory/relapsed acute B-cell lymphoblastic leukemia (B-ALL), or treatment-naive or previously treated B-ALL subjects who achieved complete remission (CR) after induction chemotherapy but still have positive minimal residual disease (MRD). The primary objectives are to preliminarily evaluate the safety, tolerability, pharmacokinetics, biology, preliminary efficacy, and immunogenicity of A-319 subcutaneous injection.