The Kinetics of Etoposide (VP-16) Peripheral Blood Progenitor Cell (PBPC) Mobilization.

The kinetics of G-CSF PBPC mobilization are well described. CD34+cells in peripheral blood rise four days after G-CSF administration, and decline after the eighth day. VP-16 is increasingly used with G-CSF as a mobilizing regimen; however, the kinetics of mobilization are sparsely described. We retrospectively reviewed 275 patients (pts) with NHL or HD who received VP-16 plus G-CSF as a primary PBPC mobilizing regimen. 214 (78%) had NHL; 31% received prior radiation therapy; 63% were male; 85% had responsive disease. Pts received VP-16 (2 gm/m²) followed by daily G-CSF (10 mcg/kg). All pts experienced a significant WBC nadir. Pts began pheresis when their WBC recovered to 5,000. Pts were pheresed for at least 2 days or until 7.0 x 10⁶ CD34+ cells/kg were collected; pheresis continued until a minimum of 2.0 x 10⁶ CD34+ cells were collected. WBC nadir occurred day +6 after VP-16 and WBC recovery to 5,000 occurred day +13 (median) after VP-16. Pts were pheresed for a median of 3 days which yielded a median of 9.7 x 10⁶ CD34+ cells/kg (range, 2.0–100.1 x 10⁶). 72% of pts began collection on day +12, day +13, or day +14. The average CD34+ cell collection was maximal on the first 3 days of pheresis, but reasonable yields continued to be obtained for approximately 10 days of pheresis, as shown below:

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81% collected ≥ 5 x 10⁶ CD34+ cells/kg, and 72% collected ≥ 7 x 10⁶ CD34+ cells/kg. The platelet count on the first day of pheresis correlated with the ability to collect 5 and 7 x 10⁶ CD34+ cells/kg (p<0.001). 50 of 275 (18%) pts did not begin pheresis until day +15 or longer after VP-16 administration. The variables that correlated with these problematic pts was the platelet count at day 1 of pheresis and refractory disease at the time of mobilization; of 24 pts with refractory disease, 11 (46%) had poor WBC recovery after VP-16 and initiated mobilization on a median of day +16 (p<0.001). We conclude that VP-16 + G-CSF is a very effective mobilizing regimen. The majority of pts mobilize large numbers of CD34+ cells requiring only 3 days of leukopheresis for excellent yields. Unlike the kinetics of G-CSF for PBPC mobilization in which yields of CD34+ cells are optimal for only 3–4 days, CD34+ cell collection continues for approximately 10 days from the initiation of pheresis. A minority of pts have poor WBC recovery after VP-16 administration, and these pts tend to be those with refractory disease.