of CD34+ cells from 0.05% before treatment to about 1.5% after 5 days [111–113]. This results in a yield of about 4.5 × 108 CD34+ cells from a single apheresis [112]. The usual dose of CD34+ cells considered suitable for transplantation is about 2.5–5 × 106/kg or about2 × 108 for a 70‐kg person. Thus, one such apheresis concentrate is usually adequate for a transplant.
Another approach to reducing the number of apheresis procedures necessary is large‐volume leukapheresis, in which 15 or more liters of donor blood is processed to increase the number of PBSCs obtained [114] or the use of the agent plerixafor for stem cell mobilization.
As a result of these factors, collection of PBSCs from normal donors now exceeds marrow in many hematopoietic transplant centers [73, 112, 115, 116], thus eliminating marrow collection in the operating suite, along with the attendant risks of anesthesia and the marrow collection process.
Collection procedures
PBSCs can be collected using the Terumo Spectra Optia, the Fresenius Kabi COM.TEC, or the Amicus Separator (Table 6.1). The procedures are the same or similar to those used for MNC collection. PBSCs can be collected from small children [117], but adjustments are necessary in priming the system and managing the patients. Studies comparing the CD34+ cell yield of different apheresis instruments found general equivalency between the collection devices [114, 118, 119].
For normal donors, the usual skin preparation, venous access, needles or catheters, solutions, and software are used. Blood flow rates of 40–80 mL/min are used depending on the donor’s venous access and blood flow tolerance. The MNC collection procedures involve processing 10–15 L of blood over 3 to 4 hours, although usually a larger volume of blood is processed to increase the PBSC yield [114]. There may be recruitment of CD34+ cells during extended apheresis up to 40 L over 5 hours. However, it is not clear that the CD34+ cell levels remain stable or increase (recruitment) during apheresis of normal donors, and so most centers process 15–18 L of blood, and this usually provides a suitable dose in one or two procedures.
Effects of peripheral blood stem cell collection on normal donors
The major clinical symptoms of PBSC collection on donors are caused by the G‐CSF the donors receive to mobilize the PBSCs. Almost all donors experience some side effect [73]. The most common of these is bone pain, but headache, fatigue, and flu‐like symptoms also occur. In response to G‐CSF, the donor’s leukocyte count increases to 30,000–40,000 per microliter, and the platelet count decreases by about 40% [120, 121]. The leukocyte and platelet counts return to normal by about day 16, or about 10 days after the apheresis donation and discontinuation of G‐CSF. There is an increase in alkaline phosphatase, alanine aminotransferase, lactate dehydrogenase, and sodium, and a decrease in glucose, potassium, bilirubin, and blood urea nitrogen. In donors who receive G‐CSF, the spleen size increases [122] and splenic rupture has been reported [123]. Although most donors experience some side effects, these are mild and should interfere with PBSC donation only rarely.
Recently, it has been suggested that platelet and MNC donors may experience prolonged lymphopenia after repeated donations [124]. It is unclear whether this effect is instrument dependent and/or related to other factors such as donor age, and studies are ongoing. Thus far, there appear to be no reports of medical complications associated with this apparent lymphopenia.
Characteristics of the peripheral blood stem cell concentrates
Large quantities of CD34+ cells can be collected from normal donors given G‐CSF for 5 days. G‐CSF doses of 7.5 or 10 mg/day provide a greater yield than 5 mg/day [115], but it is not clear whether there are statistically significant differences in the CD34+ cell yield between 7.5 and 10 mg/day. Because the donor side effects increase with increasing doses of G‐CSF, we recommend that donors be given 7.5 mg/kg/day of G‐CSF to mobilize peripheral blood CD34+ cells [115]. The composition of the PBSC component is shown in Tables 6.3 and 6.4. Most PBSC components contain only a small volume of red cells (mean, 7 mL) but a rather large total number of neutrophils and platelets [115]. This number of platelets is similar to the number of platelets ordinarily provided in a platelet transfusion, and if transfused fresh (i.e., allogeneic transplant) this may provide an additional benefit from the PBSC transfusion. The PBSC concentrate usually has a volume of about 200 mL and contains approximately 3 × 1010 MNCs and 4 × 108 CD34+ cells.
Quality control of peripheral blood stem cell concentrates
Because there is no definitive test for the primordial hematopoietic stem cell, quality control of these PBSC concentrates is not standardized. Cell culture techniques can be used to determine CFU‐GM, BFU‐E, and CFU‐MIX colonies, and the number of CD34+ cells can be determined by flow cytometry. In practice, the dose for transplantation is usually based on cell counting to obtain at least 3 × 108 mononuclear or 5 × 106 CD34+ cells per kilogram of the recipient’s body weight. The results of progenitor assays are not available for about 2 weeks and thus can be used only in retrospect for research purposes. Many centers do not even determine progenitor content because they do not believe there is a correlation with engraftment, although we believe this can be a valuable quality‐control test.
Table 6.3 Effects of 10 μg/kg G‐CSF dose on the quantity of cells collected by one apheresis procedure from healthy people treated with G‐CSF for 5 days (number of cells collected).
Source: Stroncek DF, Clay ME, Smith J, et al. Composition of peripheral blood progenitor cell components collected from healthy donors. Transfusion 1997; 37:411–417. © 1997 John Wiley & Sons. Reproduced with permission of John Wiley & Sons.
| All components (n = 150) | |||
|---|---|---|---|
| Cell type | Mean ± SD | Median | Range |
| WBCs (× 109) | 39.8 ± 21.8 | 36.0 | 15.6–163.3 |
| MNCs (× 109) | 38.1 ± 19.4 | 34.5 | 15.6–139.7 |
| CD34+ cells (× 108) | 452 ± 294 | 383 | 78–1,380 |
| CD34+ cells (× 106 per L processed) | 53.2 ± 33.1 | 46.5 | 9.3–146.3 |
| RBC (mL) | 7.2 ± 3.5 | 7.6 | 0–15.5 |
| Neutrophils (× 109) | 1.77 ± 3.37 | 1.05 | 0–23.68 |
| Platelets (× 1011) | 490 ± 100 | 490 | 250–740 |
MNC, mononuclear cell; RBC, red blood cell; WBC, white blood cell.