CD34-FORMING-UNITS GRANULOCYTE-MACROPHAGE ARE RECRUITED DURING LARGE-VOLUME LEUKAPHERESIS AND CONCENTRATED BY COUNTERFLOW CENTRIFUGAL ELUTRIATION( PROGENITORS AND COLONY)

The recruitment of mononuclear cells (MNCs), colony-forming units-gran ulocyte macrophage (CFU-GM), lymphocyte subpopulations, and CD34+ prog enitor cells was studied during large-volume (15-25 L blood processed) peripheral blood stem cell (PBSC) harvests. Normal donors (n = 13) un derwent a 4-hour leukapheresis designed to maximize PBSC yield (blood flow rate, 85 mL/min). Mean (+/- SD) volume processed was 17.7 +/- 0.4 L, and yield was 2.4 +/- 0.7 x 10(10) white cells containing 99 perce nt MNCs and 1.3 mL red cells per L of blood processed. Postapheresis h ematocrit, platelets, and MNCs were reduced from preapheresis values b y 7, 35, and 23 percent, respectively (p<0.05). In nine donors, the co mponent was collected as four 1-hour samples, and culturing of CFU-GM and flow cytometric analysis of lymphocyte subpopulations and CD34+/HL A-DR+ cells were done in individual samples. Total CFU-GM were 2.4 +/- 1.4 x 10(6) (3.0 +/- 1.8 x 10(4) CFU-GM/kg) and lymphocytes were 20.8 x 10(9), with 75 percent CD3+ T cells, 10 percent CD19/CD20+ B cells, and 17 percent natural killer cells. A more than twofold increase in CFU-GM and CD34+ cells was noted over the course of the 4-hour procedu re (p<0.05). In four donors, the leukapheresis component underwent cou nterflow centrifugal elutriation (CCE), which separated it into four f ractions in an attempt to concentrate CD34+ and CFU-GM progenitors and to deplete T-lymphocytes on a large scale. There was a 1.8-, 4.6-, 3. 9-, and 0.32-fold increase in CFU-GM in the four fractions relative to the unseparated component. CD34+ cells represented 0.09, 0.23, 0.66, and 0.41 percent of the fractions, respectively, while there was a rel ative depletion of CD3+ T-lymphocytes by 61.4, 78.7, 85.1, and 98.1 pe rcent. Thus, MNCs, CFU-GM, and CD34+ cells are recruited during large- volume leukapheresis, which may generate adequate mean CFU-GM per kg-t o allow PBSC bone marrow rescue in fewer procedures. CD34+ and CFU-GM progenitors are concentrated by CCE, and T cells are modestly depleted by CCE.