RecruitingBiological interventionA Clinical Trial of MK-1045 in People With B-cell Acute Lymphoblastic Leukemia (MK-1045-005)Researchers are looking for new ways to treat people with relapsed or refractory B-cell acute lymphoblastic leukemia (R/R B-ALL) that is CD19 positive using a medicine called MK-1045. MK-1045 is an immunotherapy, which is a treatment that helps the immune system fight cancer. This trial will compare MK-1045 to a standard immunotherapy called blinatumomab. The goals of this trial are to learn if more people who receive MK-1045 have no cancer cells in their bone marrow compared to people who receive blinatumomab and if people who receive MK-1045 live longer compared to people who receive blinatumomab.