Inclusion Criteria:

* ≥18 years of age at the time of signing informed consent.
* Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2.
* Diagnosis of B-cell NHL according to WHO 2017 classification or WHO 2016 classification where applicable:

1. DLBCL (germinal center B cell \[GCB\] or activated B cell \[ABC\] type or not otherwise specified \[NOS\])
2. HGBCL (with MYC and BCL2 and/or BCL6 rearrangements or NOS)
3. PMBCL
4. FL 3b
5. DLBCL transformed from FL
* Participants must have relapsed or refractory (r/r) B cell NHL after autologous stem cell transplant (ASCT) or at least 2 prior lines of therapy including an anti-CD20 monoclonal antibody and an anthracycline containing chemotherapy regimen. Note: participants with DLBCL transformed from FL must have r/r disease after ASCT or at least 2 prior therapies following transformation irrespective of therapeutic agents.
* At least 1 FDG-avid lesion per Lugano Classification criteria at time of enrollment.

Exclusion Criteria:

* Treatment with any investigational cellular therapy prior to enrollment. Treatment with an approved anti-CD19 CAR T cell therapy in an investigational setting may be permitted after discussion with and approval of the Sponsor.
* Progression within 6 weeks of prior anti-CD19 CAR T cell therapy.
* Residual toxicities or end-organ damage to vital organs from prior therapy that could put a subject at undue risk based on Investigator's assessment. Toxicities related to prior cytokine release syndrome (CRS) or neurotoxicity must be resolved.
* If a subject has received prior anti-CD19 CAR T therapy, development of ≥ Grade 3 CAR T related CRS or ≥ Grade 3 neurotoxicity that in the opinion of the Investigator would cause unacceptable risk of toxicity to the subject upon treatment with bbT369.
* Primary central nervous system (CNS) lymphoma or a history or presence of clinically relevant CNS pathology.
* Active autoimmune disease requiring systemic immunosuppressive and/or cytotoxic therapy within the past two years.
* Treatment with any prior anti-CD79a therapy.
* Previous history of an allogeneic bone marrow transplantation. Autologous stem cell transplantation (ASCT) is permitted.