Although CD34 ϩ cell counts from peripheral blood have been shown to be useful in predicting whether stem cell mobilization will result in the collection of sufficient cells for transplantation, it remains difficult to estimate the number of leukaphereses required to obtain such levels. Here, we examine the relationship between the pre-leukapheresis CD34 ϩ cell levels from peripheral blood and the efficiency of the leukapheresis procedure in 30 oncology patients (16 breast, 2 ovarian, and 12

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... atological malignancies) with a total of 102 leukapheresis products using the Cobe Spectra (COBE BCT, Lakewood, CO). Peripheral blood stem cells were mobilized with chemotherapy followed by G-CSF (5 u/kg/day) with a target value for transplant of 1ϫ10 7 CD34 ϩ cells/kg collected from each patient. Samples for CD34 ϩ estimation (per L) were taken before leukapheresis, at 2 hours during the procedure (approximately 6-8 L processed) and from the final product (approximately 25-30 L processed). When these CD 34 ϩ cell counts were compared, a strong correlation was found between the pre-leukapheresis CD34 ϩ cell count and those obtained at both 2 hours (r ϭ 0.90) and from the final product (r ϭ 0.98). On the other hand, no correlation was found between the final CD34 ϩ cell count of the product and either the pre-leukapheresis WBC, MNC count, or platelet count of the patient. Similarly, no correlation was found between CD34 ϩ cell counts and the hematocrit of the final product. In spite of the strong correlation between pre-CD34 ϩ cell counts and those of the final product, it remains difficult to predict with accuracy the number of leukapheresis procedures to reach the required CD34 ϩ cell target for transplant. To examine this further, we investgated the field of each leukapheresis procedure by dividing the actual CD34 ϩ cell count of the product by the theoretical value obtained from the pre-CD34 ϩ cell count from the peripheral blood expressed as a percentage. The mean overall efficiency of collection for all leukaphereses was 39% (median 37%) and no correlation between the efficiency of the collection and the pre-CD34 ϩ cell count was observed. When the pheresis collections were divided into 3 groups, however, according to pre-CD34 ϩ cell counts (Gp 1 ϭ 0.02 to 0.19%; Gp 2 ϭ 0.20 to 0.99%; Gp 3 ϭ 1% and above), the efficiency of collection in both Group 2 (44%) and Group 3 (49%) was significantly lower than that of Group 1 (25%) patients (p ϭ 0.05). In these 3 leukapheresis groups, the median number of procedures to reach a target of 1ϫ10 7 CD34 + cells for tranaplant was 0.45 for Gp 3 (ϳ12 L processed), 1.0 for Gp 2 (ϳ25 L processed) and 4.5 for Gp 1 (ϳ112 L processed). Therefore, although pre-leukapheresis CD34 + cell counts appear to be useful predictors for stem cell leukapheresis transplant targets, other factors influencing the yield efficiency of these procedures must be further investigated to reliably determine the number of procedures to be carried out in these patients.