A Study of JNJ-68284528, a Chimeric Antigen Receptor T Cell (CAR-T) Therapy Directed Against B-Cell Maturation Antigen (BCMA) in Participants With Relapsed or Refractory Multiple Myeloma

The purpose of the study is to characterize safety of JNJ-68284528 and establish the recommended Phase 2 dose (RP2D) (Phase 1b) and to evaluate the efficacy of JNJ-68284528 (Phase 2).

This study will evaluate the safety and efficacy of JNJ-68284528. The study will include two phases. In Phase1b the study will enroll adults with multiple myeloma with interval assessments for potential dose escalation or de-escalation in subsequent participants. The dose selected at the completion of phase 1b will be used in Phase 2. Following consent, enrolled participants will undergo an apheresis procedure to collect cells for manufacture of investigational drug product (JNJ-68284528). Following manufacture of the drug product, participants will undergo lymphodepletion prior to infusion of JNJ-68284528. Participants will be followed for at least 2 years after study drug infusion, with long-term 15 year follow-up on a separate study. The study will evaluate safety, biomarkers, pharmacokinetic/pharmacodynamic evaluations and efficacy.

Eligibility Criteria:
Inclusion Criteria:

* Have documented diagnosis of multiple myeloma according to International Myeloma Working Group (IMWG) diagnostic criteria
* Have measurable disease at Screening as defined by any of the following a) Serum monoclonal paraprotein (M-protein) level more than or equal to (\>=) 1.0 gram per deciliter(g/dL) or urine M-protein level \>=200 milligram per 24 hours (mg/24hr); or b) Light chain multiple myeloma without measurable disease in the serum or the urine: Serum immunoglobulin free light chain 10 mg/dL and abnormal serum immunoglobulin kappa lambda free light chain ratio
* Have received at least 3 prior multiple myeloma treatment lines of therapy or are double refractory to an immunomodulatory drug (IMiD) and proteasome inhibitor (PI) (refractory multiple myeloma as defined by IMWG consensus criteria). Note: induction with or without hematopoietic stem cell transplant and with or without maintenance therapy is considered a single lines of therapy a) Undergone at least 1 complete cycle of treatment for each line of therapy, unless progressive disease (PD) was the best response to the regimen
* Have received as part of previous therapy a PI, an IMiD, and an anti-CD38 antibody
* Participant must have documented evidence of progressive disease based on investigator's determination of response by the IMWG criteria on or within 12 months of their last line of therapy. Confirmation may be from either central or local testing. Also, participants with documented evidence of progressive disease (as above) within the previous 6 months and who are refractory or non-responsive to their most recent line of therapy afterwards are eligible
* Have Eastern Cooperative Oncology Group (ECOG) Performance Status grade of 0 or 1

Exclusion Criteria:

* Have received prior treatment with chimeric antigen receptor T (CAR-T) therapy directed at any target
* Have received any therapy that is targeted to B-cell maturation antigen (BCMA)
* Have following cardiac conditions: a) New York Heart Association (NYHA) stage III or IV congestive heart failure b) Myocardial infarction or coronary artery bypass graft (CABG) less than or equal to (\<=) 6 months prior to enrollment c) History of clinically significant ventricular arrhythmia or unexplained syncope, not believed to be vasovagal in nature or due to dehydration d) History of severe non-ischemic cardiomyopathy e) Impaired cardiac function (left ventricular ejection fraction \[LVEF\] less than \[\<\]45%) as assessed by echocardiogram or multiple-gated acquisition (MUGA) scan (performed less than or equal to (\<=) 8 weeks of apheresis)
* Received a cumulative dose of corticosteroids equivalent to \>= 70 mg of prednisone within the 7 days prior to apheresis
* Have received either of the following: a) An allogenic stem cell transplant within 6 months before apheresis. Participants who received an allogeneic transplant must be off all immunosuppressive medications for 6 weeks without signs of graft-versus-host disease (GVHD) b) An autologous stem cell transplant less than or equal to (\<=) 12 weeks before apheresis
* Have known active, or prior history of central nervous system (CNS) involvement or exhibits clinical signs of meningeal involvement of multiple myeloma