• ≥ 18 years old;

• Sign on the informed consent;

• Histologically confirmed large B-cell lymphoma that also meets the definition of high-risk large B-cell lymphoma as a lymphoma International Prognostic Index (IPI) score of 3-5 and/or high-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 rearrangement (double/triple-hit lymphoma) (DHL/THL) and must be treated with 2 cycles of CD20 monoclonal antibodies combined with anthracyclines. Presence of positive PET assessable lesions (DS score of 4 or 5) as determined by the Lugano criteria (Cheson et al., 2014)；

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1;

• Expected survival greater than 12 weeks；

• Adequate organ function：

‣ Absolute neutrophil count ≥ 1000/μL；Absolute lymphocyte count ≥ 100/μL； Platelet count ≥ 75,000/μL；Hb ≥ 80g/L；

⁃ Serum creatinine ≤ 1.5 × upper limit of normal (ULN) or creatinine clearance (Cockcroft-Gault formula) \> 50 mL/min (serum creatinine clearance due to lymphoma mass compression should be \> 30 mL/min)；

⁃ Serum alanine aminotransferase (ALT) ≤ 5 upper limit of normal (ULN) and total bilirubin ≤2ULN（or for subjects with Gilbert's syndrome or lymphoma invading the liver \< 3 ULN）；

⁃ Baseline oxygen saturation \> 92% on room air；

⁃ Left ventricular ejection fraction (LVEF) ≥50% assessed by echocardiography or radionuclide activity angiography (MUGA) within 1 month of enrollment；

• Adequate vascular access for leukapheresis procedure;

• Women of childbearing potential must agree to use highly effective methods of contraception for at least 28 days prior to lymphocyte clearance chemotherapy through 1 year after Relmacabtagene Autoleucel infusion; Males who have partners of childbearing potential must agree to use an effective barrier contraceptive method for 1 year after Relmacabtagene Autoleucel infusion.