To assess whether consolidation therapy with elranatamab and lenalidomide is superior to standard of care, in terms of MRD negativity rate.

To assess whether maintenance therapy with elranatamab is superior to standard of care, in terms of PFS.

To assess whether consolidation therapy with elranatamab and lenalidomide is superior, in terms of PFS

To assess whether consolidation therapy with elranatamab and lenalidomide is superior to standard of care, in terms of OS

From date of randomization to date of progressive disease, discontinuation from study, death, or censoring, whichever occurs first

Progression Free Survival assessed by Blinded Independent Central review per IMWG response criteria

Evaluation of completion of (Elra) consolidation following definitive therapy in patients with PBL, defined as the proportion of patients completing at least 3 cycles

Estimate the complete response (CR) rate (per 2014 LUGANO criteria)Ref . in HIV-positive and HIV-negative patients after 6 months of consolidation.

To evaluate the safety and tolerability of Elra consolidation, including the incidence, severity, and management of cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), assessed by ASTCT consensus criteria.

Evaluate the number of participants with events of CRS during Cycle 1 of study treatment. CRS events will be graded per the American Society for Transplantation and Cellular Therapy grading (ASTCT 2019).

Rate of participants with MRD negativity (defined as \<10-5) after completion of the Maintenance 1 portion of the study.

Hospitalization rate, defined as the number of patients who are hospitalized within the first 2 weeks of Cycle 1 of treatment, due to any cause, divided by the number of patients who are treated with elranatamab.

Rate of grade 3+ infections as grade by NCI CTCAE v5 within the first 24 months of treatment, defined as the number of patients who experience a grade 3+ infection within 24 months of treatment, divided by the number of patients who are treated with elranatamab.

Grade(G)4 neutropenia \>5 day; febrile neutropenia (absolute neutrophil count \[ANC\] \<1000/millimeter cube (mm\^3) with single temperature \>38.3 degree Celsius (deg C) or sustained temp\>=38 deg C for \>1 hour(H); G\>=3 neutropenia with infection; G4 thrombocytopenia (unless baseline count \>=25,000/mm\^3 and \<50,000/mm\^3, in which case G4 thrombocytopenia to be accompanied by \>=G2 bleeding); Platelet count \<10,000/mm\^3; G3 thrombocytopenia with \>=G2 bleeding; G\>=4 AE; G3 cytokine release syndrome(CRS) except CRS not maximally treated/improved to \<=G1 within 48H; G3 AE except AE attributed to CRS, G3 nausea,vomiting,diarrhea improved to G\<=2 within 72H after medical management, G3 fatigue \<1 week, G3 AE recovered to baseline/G1 within 5 day; confirmed drug-induced liver injury; G3-4 laboratory (lab) abnormality except G3-4 lab abnormality improved to G\<=2 within 72H after medical management \& without sequelae;G3 injection site reaction; G2/other clinically important AE may be considered DLT.

ORR: Percentage of participants with best overall response of confirmed stringent complete response (sCR), CR, very good partial response (VGPR) or PR per IMWG criteria. sCR: CR \& normal serum free light chain (sFLC) ratio \& absence of clonal cells in BMB/BMA by IH, IF, or flow cytometry. CR: negative immunofixation on serum \& urine, disappearance of any soft tissue plasmacytoma \& \<5% plasma cells in BMA, if disease measurable by sFLC only, preceding criteria plus normal sFLC ratio. VGPR: Serum \& urine M-protein detectable by immunofixation but not on electrophoresis; or \>=90% reduction in serum M-protein \& urine M-protein level \<100mg/24h. PR: \>=50% reduction in serum M-protein \& reduction in 24h urinary M-protein by \>=90% or \<200 mg/24h. If serum \& urine M-protein were unmeasurable, VGPR \& PR: \>=90% \& \>=50% decrease in difference respectively between involved \& uninvolved sFLC levels \& if present at baseline, \>=90% \& \>=50% reduction in soft tissue plasmacytomas' size.

CRS: supraphysiologic response following any immune therapy that results in the activation or engagement of endogenous or infused T-cells and/or other immune effector cells. Symptoms must include fever at the onset, and may include hypotension, hypoxia and end organ dysfunction. As per ASTCT criteria, Grade (G) 1: fever (temperature \>=38 degree Celsius), hypotension and/or hypoxia none; G 2: fever, hypotension not requiring vasopressors, hypoxia requiring low-flow nasal cannula/ facemask or blow-by; G 3: fever, hypotension requiring a vasopressor with or without vasopressin, hypoxia requiring high-flow nasal cannula/ facemask, nonrebreather mask, or Venturi mask; G 4: fever, hypotension requiring multiple vasopressors (excluding vasopressin), hypoxia requiring positive pressure. Organ toxicities associated with CRS graded according to CTCAE v5.0. G 1: Mild, G 2: Moderate, G 3: severe, and G 4: life-threatening consequences; urgent intervention indicated. G 5: death related to AE.

Dose limiting toxicity rate based on dose limiting toxicity evaluable participants

Number of participants with AE among participants who take at least 1 dose of study intervention. AEs are categorized by seriousness and relationship to treatment. Relatedness to study drug is assessed by investigator.

Dose limiting toxicity rate based on dose limiting toxicity evaluable participants.

Dose limiting toxicity based on dose limiting toxicity evaluable participants.

Dose limiting toxicity rate based on dose limiting toxicity evaluable participants.

DLT was defined as any of the following: Treatment Emergent Adverse Events (AEs) occurring in Cycle 0 and Cycle 1 (total 4 weeks): Grade (G) 4 neutropenia lasting greater than (\>)7 days; febrile neutropenia (absolute neutrophil count \[ANC\] less than (\<)1,000 per millimeter cube (/mm\^3) with single temperature \>38.3 degree Celsius (deg C), or sustained temperature of greater than or equal to (\>=) 38deg C for \>1 hour \[h\]); G\>=3 neutropenia with infection; G4 thrombocytopenia (unless the baseline count was \>=25,000/mm\^3 and \<50,000/mm\^3, in which case G4 thrombocytopenia was to be accompanied by \>=G2 bleeding), Platelet count \<10,000/mm\^3 was considered a DLT irrespective of other factors; G3 thrombocytopenia with \>=G2 bleeding; G4 AEs; G3 AE \>=5 days despite optimal supportive care (except AEs attributed to cytokine release syndrome \[CRS\]); G3 CRS (except CRS that have not been maximally treated or improved to \<=G1 within 48h); confirmed drug induced liver injury.

Hematological: Grade 4 neutropenia lasting \>5 days; Febrile neutropenia \<1000/mm\^3 with a single temperature of \>38.3 degree Celsius (C) or a sustained temperature of \>=38 degree C for more than one hour; grade \>=3 neutropenia with infection; grade 4 thrombocytopenia; grade 3 thrombocytopenia with \>= Grade 2 bleeding. Non-hematological: grade 4 adverse events (AEs); Grade 3 AE lasting \>=5 days despite optimal supportive care, with exception of AE attributed to cytokine release syndrome (CRS) event; grade 3 CRS, except those CRS that had a) not been maximally treated or b) improved to \<=grade 1 within 48 hours; grade 4 CRS; confirmed drug-induced liver injury (DILI) meeting Hy's law criteria; grade 4 laboratory abnormalities deemed clinically significant by the investigator reported Grade 4 AE; clinically important or persistent toxicities that were not included in above criteria were also be considered a DLT following review by the investigators and the sponsor.

ORR per IMWG criteria: percentage of participants with best overall response (BOR) of stringent complete response (sCR), complete response (CR), very good partial response (VGPR) or partial response (PR). sCR: complete response plus normal free light chain (FLC) ratio and absence of clonal cells in bone marrow biopsy by immunohistochemistry; CR: negative immunofixation on serum and urine and disappearance of any soft tissue plasmacytomas and \<5% plasma cells in bone marrow aspirates. VGPR: serum and urine M-protein detectable by immunofixation but not on electrophoresis or \>=90% reduction in serum M-protein plus urine M-protein level \<100 mg/24 hr. PR: \>=50% reduction of serum M-protein and reduction in 24 hrs urinary M-protein by \>=90% or to \<200 mg/24 hr. If serum and urine M-protein were unmeasurable, \>=50% decrease in difference between involved and uninvolved FLC levels required in place of the M-protein criteria.

DOR per IMWG criteria:time from first documentation of objective tumor (OT)response to first documentation of OTprogression or to death due to any cause, whichever occurred first.sCR: CR plus normal FLC ratio \& absence of clonal cells in bone marrow biopsy by immunohistochemistry;CR:Negative immunofixation on serum \& urine \& disappearance of any soft tissue plasmacytomas\&\<5% plasma cells in bone marrow aspirates.VGPR: serum \& urine M-protein(Mp) detectable by immunofixation but not on electrophoresis or \>=90% reduction in serum Mp plus urine Mp level \<100 mg/24 hr. PR: \>=50% reduction of serum Mp \& reduction in 24 hrs urinary Mp by \>=90% or to \<200 mg/24 hr.If serum \& urine Mp were unmeasurable, \>=50% decrease in difference between involved \& uninvolved FLC levels required in place of Mp criteria. Progression: appearance of local, regional or distant disease of same type after CR or progression of pre-existing lesions. It did not include second primary malignancies of unrelated types.