Study of the Impact of CD34+ Cell Dose on Absolute Lymphocyte Count Following High-Dose Therapy and Autologous Stem Cell Transplantation for Relapsed and Refractory Diffuse Large B-cell Lymphoma (DLBCL)

Inclusion Criteria: * Age ≥ 18 years old * Diagnosed with relapsed or refractory de novo DLBCL or follicular lymphoma transformed to DLBCL to one previous line of anthracycline-containing chemotherapy * KPS ≥ 70 * Complete or partial response by IWG Working Group or ICML Criteria to maximum of one salvage line of chemotherapy without pre-HDT/ASCT salvage radiotherapy. * Eligible for high-dose therapy and autologous stem-cell rescue * Serum creatinine ≤ 1.5 mg/dL, or if creatinine \>1.5 mg/dL, calculated creatinine clearance of ≥50 mL/min by 24 hour creatinine clearance or CKD-EPI. * Last cycle of most recent salvage therapy within 8 weeks of enrollment * Total bilirubin \< 2.0 mg/dL o If Gilbert"s disease is suspected and total bilirubin \> 2.0 mg/dL, direct bilirubin must be \< 2.0 mg/dL * Females of childbearing potential and males must agree to use an acceptable form of contraception per institutional practices. Exclusion Criteria: * Disease progression by IWG Working Group or ICML Criteria since last therapy * Prior autologous or allogeneic stem cell transplantation * HIV infection * Comorbid condition(s) which, in the opinion of the attending physician and/or MSKCC Principal Investigator, will preclude stem cell mobilization and/or high-dose therapy with autologous stem cell rescue * Treatment plan that includes post-transplant maintenance therapy * Salvage therapy that includes involved field radiotherapy