G-CSF Improves Stable Engraftment in Adults with Sickle Cell Disease Undergoing Nonmyeloablative Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is curative in patients with sickle cell disease (SCD). HSCT using nonmyeloablative conditioning leads to a mixed chimerism that improves the SCD phenotype but may be complicated by the continued need for immunosuppression and graft loss. Granulocyte colony stimulating factor (G-CSF) may stimulate progenitor cells and is used post-HSCT to reduce the duration of neutropenia and the risk of neutropenic fever. G-CSF has been generally avoided in patients with SCD due to its risk of promoting vaso-occlusion (PMID 19513902).

Starting in 7/2016, our institution administered G-CSF after day +5 post-HSCT on the days when the ANC was < 500 x10³/µL. In this study, we evaluated whether G-CSF is safe and can improve the duration of neutropenia, infection risk, and donor chimerisms in adults with SCD undergoing non-myeloablative HSCT. We included 34 adults with SCD that underwent allogeneic HSCT from an HLA-matched sibling donor in our institution and were conditioned with alemtuzumab and total body irradiation (TBI) (PMID 33534948) between 11/2011 and 8/2021. Medical records were individually reviewed for data extraction. Linear and categorical outcomes were compared by G-CSF use with the Kruskal-Wallis and chi-square test, respectively. We also compared the Kaplan-Meier curves for discontinuation of immunosuppression with the log-rank method. Median and interquartile range (IQR) are provided.

The median age of our cohort was 33 years (IQR, 26 - 45 years), 18 (53%) patients were female, and 30 (88%) had hemoglobin SS genotype. We did not observe statistically significant differences in baseline characteristics between the SCD patients that received G-CSF versus did not receive G-CSF for median age (37 years vs. 32 years), female gender (69% vs. 43%), hemoglobin SS genotype (85% vs. 90%) or median CD34+ dose (8.6 vs. 8.1 x 10⁶/kg), respectively. In the 13 SCD patients that received G-CSF, the median day when it was initiated was day +10 (IQR, 7 - 17) and for a median of 3 days (IQR, 2 - 7 days). The maximum pain score during hospitalization was not significantly different in the SCD group that received G-CSF (median 8, IQR, 7 - 10) compared to those that did not receive G-CSF (median 10, IQR, 9 - 10). Median time to neutrophil engraftment (G-CSF: day 16 vs. no G-CSF: day 22) and duration of neutropenia (G-CSF: 7 days vs. no G-CSF: 9 days) were relatively similar between the 2 groups, while the incidence of neutropenic fevers trended lower with G-CSF treatment (8% vs. 29%, respectively, P=0.1).

Whole blood or myeloid chimerism values were significantly higher in the SCD patients that received G-CSF at day +30, +90, +180, and 1 year post-HSCT (Figure 1A). Secondary graft loss was not observed after we implemented G-CSF while 4 out of 21 (19%) of patients experienced secondary graft failure who did not receive post-HSCT G-CSF. Furthermore, in those patients with stable engraftment, we observed a trend for more patients who received G-CSF being successfully tapered off immunosuppression (11/13, 85%) versus those that did not receive G-CSF (10/17, 59%) (Figure 1B).

In conclusion, administration of G-CSF to patients with SCD undergoing HSCT conditioned with alemtuzumab/TBI was associated with significantly higher whole blood or myeloid donor chimerism values. This benefit was achieved without a significant increase in pain scores during the hospitalization for HSCT and was associated with trends for a greater proportion of patients discontinuing immunosuppression and less secondary graft loss. Future studies investigating the effects of G-CSF on donor myeloid progenitor cells and on T-cell clearance may guide strategies to improve outcomes for curative therapies in adults with SCD.

Patel:Exelixis: Current Employment. Gordeuk:Forma: Consultancy; GSK: Consultancy; GBT: Consultancy, Research Funding; CSL Behring: Consultancy, Research Funding. Saraf:FORMA Therapeutics: Consultancy, Research Funding; Global Blood Therapeutics: Consultancy, Research Funding, Speakers Bureau; Agios: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; ORIC: Consultancy.