Using point-of-care CD34 enumeration to optimize PBSC collection conditions

Background: A PBSC graft containing 4-5 × 10⁶ CD34⁺ cells/kg is considered optimal in terms of durable engraftment. Tracking CD34 kinetics via point-of-care testing during PBSC mobilization could determine which (and when) patients will yield an optimal product. We evaluated whether microvolume fluorimetry (MVF) would be useful in optimizing PBSC mobilization/harvest and if it will shorten our standard 6 b collection. Methods: Absolute CD34 values were obtained using the IMAGN 2000 and STELLer CD34 assay (50 μL sample volume). Peripheral blood (PB) CD34 values from 30 patients undergoing PBSC mobilization were used to generate a PB CD34-based algorithm that would predict collection day/duration of apheresis. The algorithm was then used prospectively to collect PBSC products on 50 hematologic malignancy (HM) patients. Results: Using the algorithm, patients were assigned to either a 6 (11-20 CD34/μL), 4 (21-49 CD34/ μL) or 2 (≥ 50 CD34/μL) h collection. Patients with a CD34 value ≤ 10/μL were re-tested. All patients (n = 43) predicted to mobilize reached the optimal CD34 (4-5 × 10⁶/kg) value with 1.0 apheresis procedure; seven patients had ≤ 10/μL (non-mobilizers). The majority (75%) had apheresis charges decreased by 33-66%; 47% only required a 2 h procedure and 28% required 4 h. All patients demonstrated rapid trilineage engraftment. Discussion: Absolute PB CD34 measurement using MVF offers a rapid and reliable approach to obtaining optimal PBSC products with minimal technical expertise. Although not a replacement for conventional flow cytometry, it meets the requirements for a point-of-care procedure.