A NYLON WOOL FILTER COATED WITH HUMAN-IMMUNOGLOBULIN FOR RAPID DEPLETION OF MONOCYTES AND MYELOID CELLS FROM PERIPHERAL-BLOOD STEM-CELL TRANSPLANTS

The aim of this study was to develop an inexpensive method for reducin g the number of differentiated cells from granulocyte colony-stimulati ng factor-mobilized leukocytapheresis products (LPs) containing periph eral blood stem cells. Analysis of LPs showed the presence of signific ant numbers of monocytes and myeloid cells. The myeloid cells represen ted largely immature stages of the granulocyte lineage (myelocytes and metamyelocytes). We investigated whether these cells could be selecti vely depleted by filtration over nylon wool. Filtration of LP samples over nylon wool in a medium containing fetal calf serum resulted in va riable but on average lo cv yields of CD34(+) cells (48 +/- 30%; n=13) and strongly variable depletions of myeloid cells. The adherence of C D34(+) cells to the polyamide fiber was partially mediated by activate d platelets that were present in the LPs. Removal of platelets by coun terflow centrifugal elutriation before filtration resulted in increase d yields of CD34(+) cells in the filtrates (65 +/- 13%; n=10). The yie ld of progenitor cells was similarly enhanced when trisodium citrate, a chelating substance, was added to the filtration medium. Adherence o f the myeloid cells to the nylon fiber was promoted by preincubation o f the columns with human immunoglobulin (Ig) (2 mg/mL). Small-scale fi ltrations of LP samples in the presence of trisodium citrate over colu mns with Ig-coated nylon wool resulted in removal of 96 +/- 4% of the monocytes and 74 +/- 18% of the myeloid cells, with a yield of 71 +/- 15% CD34(+) cells and 67 +/- 10% granulocyte-monocyte colony-forming u nits (CFU-GM) (n=23). There was no loss of primitive stem cells during the procedure: the yield of late-appearing cobblestone area-forming c ells (CAFCs, week 6) was 110 +/- 30% (n=4). CFU-GM production per CAFC -derived clone was unchanged upon filtration, indicating that the qual ity of stem cells was not affected. Moreover, the proportions of CD34( +) cells expressing a primitive immunophenotype (CD38(low) or Thy-1(+) ) were unchanged after filtration. Further enrichment of progenitor ce lls was obtained by separation of LP samples by elutriation before fil tration. The combination of these two techniques resulted in complete removal of platelets, 89 +/- 7% depletion of erythrocytes, and 91 +/- 6% reduction of leukocytes, with a 50% yield of CD34(+) cells (n=14). In conclusion, we have developed a rapid filtration technique by which monocytes and myeloid cells can be depleted from LP samples, with onl y minor loss of colony-forming cells and complete recovery of primitiv e stem cells.