Inclusion Criteria:

* Age: Part 1: 18-90 years of age, Part 2: 13-90 years of age
* Relapsed B-cell ALL with bone marrow blasts \>= 5%
* Refractory B-cell ALL as defined in the protocol
* Bone marrow blasts requirement (flow cytometry): Part 1: \>0.01% to \<5% prior to VNX-101 dosing, Part 2: \>0.01% to \<50% prior to VNX-101 dosing.
* Ineligible or declined CAR-T therapy or failed to respond or relapsed after such therapy
* If prior blinatumomab treatment, cells remain CD19+ and not refractory to blinatumomab
* AAV specified capsid total antibody \<1:400
* Protocol-specified ranges for renal, liver, cardiac and pulmonary function
* Protocol-specified ranges for hematology parameters

Exclusion Criteria:

* Hepatoxicity (AST or ALT \> 2x upper limit of normal)
* History of thrombotic microangiopathy or cardiomyopathy, or evidence of sensory neuropathy
* Pregnant or nursing (lactating) women
* Acute Graft versus Host Disease (GvHD): Grade 2-4 or chronic GvHD of any grade
* History of hypersensitivity to corticosteroids or history of corticosteroid-related toxicity
* Chemotherapy given within the protocol-specified discontinuation timelines

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 3/20/2025. Questions regarding updates should be directed to the study team contact.