∙ \- To be eligible for leukapheresis, patients must have a CD19+ B-cell malignancy with relapsed or refractory disease, defined below. To be eligible for 131-I apamistamab conditioning and treatment with 19-28z CAR T-cells, patients must additionally have detectable evidence of residual malignancy at the time of assessment prior to CAR T-cell infusion (as defined below), regardless of therapy administered following leukapheresis.

∙ a. Patients with diffuse large B-cell lymphoma (de novo or DLBCL transformed from an indolent lymphoma (follicular lymphoma, chronic lymphocytic leukemia \[Richter syndrome\]) or high-grade B-cell lymphoma (HGBL): (DLBCL patients) i. Defined as relapsed or refractory DLBCL or high-grade B-cell lymphoma (HGBL) following 2 or more prior chemoimmunotherapy regimens (with at least one course including an anthracycline and CD20-directed therapy) following diagnosis of de novo DLBCL/HGBL or DLBCL arising from indolent lymphoma, and requiring further treatment. Exception: patients with Richter syndrome (DLBCL arising from CLL/small lymphocytic lymphoma) are eligible following 1 or more prior chemoimmunotherapy regimens (with at least one course including an anthracycline and CD20-directed therapy) and do not require a second course of chemoimmunotherapy to be eligible.

∙ ii. Patients must have at least one FDG-avid (PET-avid) measurable lesion iii. Biopsy confirmation of relapsed of refractory DLBCL is required iv. For patients who have received treatment for confirmed relapsed or refractory disease otherwise meeting criteria a.i.-a.iii. as above, within 6 weeks of study enrollment, active disease does not need to be re-confirmed or present immediately prior to Screening A for the patient to be eligible for leukapheresis. However, detectable evidence of residual malignancy must be present at Screening B in order for the patient to be eligible for 131-I apamistamab and CAR T-cell therapy.

∙ b. Patients with B-cell acute lymphoblastic leukemia or B lymphoblastic lymphoma (ALL) or chronic myeloid leukemia (CML) in lymphoid blast crisis: (B-ALL patients) i. Patients with Philadelphia chromosome-negative B-cell ALL must have been refractory to at least 1 line of multi-agent chemotherapy or relapsed following at least 1 prior multiagent systemic chemotherapy regimen that included induction and consolidation therapy ii. Patients with Philadelphia chromosome-positive ALL or CML in lymphoid blast crisis must have exhibited persistent disease following therapy with a second- or third-generation tyrosine kinase inhibitor iii. Patients must have ≥5% bone marrow involvement and/or at least one FDG-avid (PET-avid) measurable extramedullary lesion iv. For patients who have received treatment for confirmed relapsed or refractory disease otherwise meeting criteria b.i.-b.iii. as above, within 6 weeks of study enrollment, active disease does not need to be re-confirmed or present immediately prior to Screening A for the patient to be eligible for leukapheresis. However, detectable evidence of residual malignancy must be present at Screening B in order for the patient to be eligible for 131-I apamistamab and CAR T-cell therapy.

• While prior CD19-targeted therapies, including CAR T-cell therapy, do not exclude participation, CD19 expression by immunohistochemical staining or flow cytometry must be confirmed prior to enrollment.

• Age ≥ 18 years of age

• Creatinine clearance ≥50 mL/min as calculated by the Cockroft-Gault formula

• Direct bilirubin ≤2.0 mg/dL, AST and ALT ≤3.0x upper limit of normal (ULN), unless liver dysfunction is thought to be related to underlying malignancy

• Adequate pulmonary function as assessed by ≥92% oxygen saturation on room air by pulse oximetry.

• Adequate bone marrow function meeting the following criteria as defined below, without requiring blood product or granulocyte-colony stimulating factor support in the past 7 days, unless cytopenias are attributed to underlying malignancy in the opinion of the investigator:

‣ Absolute neutrophil count ≥0.5k/µL,

⁃ Platelets ≥30k/µL,

⁃ Hemoglobin ≥7g/dL.

• ECOG performance status 0-2.