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)

Following enrollment, patients will be CD34+ stem cell mobilized at the discretion of the treating attending physician with the plerixafor for the achievement of \>6 x10\^6 CD34+ cells/kg. The patients that fail to mobilize \>6 x10\^6 CD34+ cells/kg will not be randomized and will subsequently be followed for disease progression and overall survival.. Patients with \>6 x10\^6 CD34+ cells/kg cryopreserved on study will be admitted to the hospital for planned ASCT. Patients will be randomly infused with either 3-4 x 10\^6 CD34+ stem cells/kg or 6-8 x10\^6 CD34+ stem cells/kg on d0 per study randomization. The cell dose ranges within the two groups allows variability within aliquots of cells at the time of cryopreservation. Patients will receive standard supportive measures (including: growth factor support post-HDT/ASCT, antimicrobial prophylaxis, red blood cell and platelet transfusion and treatment for neutropenic fever) as per institutional guideline practices.