The dose of cells expressing the surface antigen CD34 (CD34+) has been show
n to be a reliable predictor of the time to engraftment following transplan
tation of PBPC to support high-dose chemotherapy. However, evaluation of ra
re cells is complicated by a number of factors, including the variability i
n operator and technical procedures. Recently, Becton Dickinson Immunocytom
etry Systems introduced a new CD34+ cell analysis system, the ProCOUNT cell
enumeration kit, which automates the analysis of CD34+ cells and minimizes
the variabilities of this procedure. We have evaluated the ProCOUNT system
in comparison to a standard CD34 cell analysis (based on the Milan approac
h) using leukapheresis products from patients and normal donors mobilized w
ith chemotherapy plus recombinant human G-CSF (rhG-CSF) or with rhG-CSF alo
ne. In addition, we compared these analyses using CD34+ cell-selected mobil
ized leukapheresis products with purities of 75% or greater. The standard C
D34 cell analysis methodology quantitated the frequency of cells identified
as CD45+, low side scatter, and CD34+. A high correlation coefficient was
obtained between the ProCOUNT methodology and the standard CD34 cell analys
is methodology for cells obtained from leukapheresis products mobilized wit
h chemotherapy plus rhG-CSF (r = 0.98), rhG-CSF alone (r = 0.96), and CD34-selected mobilized leukapheresis products (r = 0.83). A comparison was als
o made between technicians using both analysis methods. Whereas the correla
tion coefficient between two technicians using the standard methodology was
r = 0.77, the correlation coefficient was much higher when using ProCOUNT
(r = 0.99). These data demonstrate that the use of ProCOUNT is associated w
ith less variability between data analyzed by different operators. Also, Pr
oCOUNT is consistent with existing CD34+ cellular analysis methodologies. A
n additional advantage is the ability to determine the absolute concentrati
on of CD34+ cells, thereby allowing calculation of total CD34+ cell numbers
without using WBC counts, which also have inherent errors. The ProCOUNT sy
stem provides an automated analysis procedure that minimizes the variables
in CD34+ cell analysis and may be useful for standardization of methodology
between laboratories.