The Efficacy of Same Day Plerixafor Dosing on CD34+ Haematopoietic Stem Cell Collection: A Single Centre Australian Experience

Introduction: Haematopoietic stem cell (HSC) transplantation is an important therapeutic option for many haematological conditions, as well as, some solid organ cancers. Plerixafor (a selective inhibitor of CXCR4) can be used in patients for primary stem cell mobilisation; those who have previously failed stem cell mobilisation ("rescue" or "Planned"); or in patients with a poor peripheral CD34+ response to GCSF and/or chemotherapy mobilisation ("on demand", "just in time" or "pre-emptive"). In Australia, Plerixafor is funded for patients with CD34+ count <10 cells/µl on day of collection or if first apheresis has yielded CD34+ <1 x 106cells/kg. In these patients, Plerixafor is administered the evening prior to the planned morning collection but this presents logistical issues as it has to be given after hours. Therefore, it was proposed to administer Plerixafor followed by same day HSC collection to improve the logistics of these "just in time" collections. Methods: A retrospective case note audit identified 96 patients who received Plerixafor for HSC collection between 03/2017 and 06/2021. Patients were categorised into PM (late afternoon/evening dosing) and AM (morning dosing). Transplant HSC dose target was >2 x 106/kg. Results: Of the 96 patients, 17 received 2 doses of plerixafor with 4 of these patients receiving both an AM and PM dose. These 4 patients were excluded from the final analysis. Of the 92 patients remaining, 57% (n=52) of patients received PM and 43% (n=40) AM dosing. Median age was 64 years (range 23 to 78). 58% were male (n=53) and 42% female (n=39). Underlying malignancy included Myeloma (n=51), Lymphoma (n=37) and Solid malignancy (n=4). Median pre plerixafor blood CD34+ count was 8.7x10^6/kg (range 0.3-35.5) in the PM group and 9.2 (range 1.6-38.2) in AM group prior to collection. Median number of HSCs collected post-plerixafor administration was 4.97 x106/kg (range 0.91-34.97) for PM group vs 4.16 x106/kg (range 0.71-9.52) AM group. Total median HSC number collected for patients in the PM group was 6.6x106cells/kg (range 3.14-8.18) vs 5.16x106/kg (range = 2.46-6.45) in the AM group. The AM group had an increased median HSC collected post plerixafor of 83% vs PM median of 75%. A transplantable HSC dose was collected in 97% of those in the AM group and 96% in the PM group. Median number of apheresis procedures with PM dosing was 2 (range 1-5) vs 2.4 with AM dosing (range 1-4). Conclusion: While post plerixafor HSC collection doses were higher with PM dosing this is countered by the total median HSC collection being higher in the AM group. These findings show that same day plerixafor dosing is a feasible option with similar numbers of patients achieving their target HSC collection.