Scoping Review of Factors Associated with Stem Cell Mobilization and Collection in Allogeneic Stem Cell Donors

There is wide interindividual variation in the efficacy of CD34+ cell mobilization and collection in healthy allogenic hematopoietic stem cell donors. Donor characteristics, blood cell counts, and various factors related to mobilization and collection have been associated with blood CD34+ cell count and CD34+ cell yield after granulocyte colony-stimulating factor (G-CSF) mobilization and collection. Given the heterogenous nature of the literature reporting these associations, in this scoping review we clarify the determinants of CD34+ count and yield. Studies published between 2000 and 2023 reporting allogeneic donors undergoing G-CSF mobilization and peripheral blood stem cell (PBSC) collection were evaluated. Eligible studies were those that assessed blood CD34+ cell count or CD34+ cell yield in the first PBSC collection after mobilization with 4 or 5 days of G-CSF treatment. Associations were recorded between these outcomes and donor factors (age, sex, weight, ethnicity), mobilization factors (G-CSF scheduling or dose), collection factors (venous access, processed blood volume [PBV]) or laboratory factors (blood cell counts at baseline or after mobilization). The 52 studies evaluated between 15 and 20,884 donors. Forty-three studies were retrospective, 33 assessed blood CD34+ cell counts, and 39 assessed CD34+ cell yield from PBSCs. Blood CD34+ cell counts consistently predicted CD34+ cell yield. Younger donors usually had higher blood CD34+ cell counts and CD34+ cell yield. Most studies that investigated the effect of donor ancestry found that donors of non-European ancestry had higher blood CD34+ cell counts after mobilization and higher CD34+ cell yields from collection. The poor consensus about the best predictors of blood CD34+ cell count and yield necessitates further prospective studies, particularly of the role of donor ancestry. The current focus on donor sex as a major predictor requires re-evaluation.

Improving cellular therapy operations through pre-harvest measurement of peripheral CD34-positive cell counts in allogeneic stem cell harvest

INTRODUCTION

Previously, our institution measured peripheral blood CD34 cell counts both pre- and post-peripheral blood stem cell harvest (PBSCH), with both samples analyzed simultaneously post-PBSCH. Since 2021, we have measured pre-CD34 cell counts during PBSCH, adjusting the processed blood volume based on these results. We retrospectively evaluated how this change impacted cellular therapy.

METHODS

Related healthy donors were included and divided into 1-day and 2-day harvest cohorts. Donors with CD34 cell counts measured post- and during PBSCH were categorized into the previous and current sub-cohorts, respectively.

RESULTS

Regarding the 1-day cohort (n = 212), the current sub-cohort had a significantly shorter average harvest duration (151 [standard deviation, SD = 45.1] vs. 180 [SD = 27.8] minutes, respectively) and higher average infusion rates (87.6% [SD = 21.1] vs. 78.1% [SD = 25.7], respectively) than the previous sub-cohort.

CONCLUSION

Adjusting the processed blood volume based on pre-PBSCH CD34 cell counts measured during the harvest may reduce donor burden and enhance workflow efficiency.

Sysmex XN-HPC: study of reference intervals and clinical decision limits in healthy allogeneic donors mobilised with G-CSF

The Sysmex XN series haematopoietic progenitor cell (XN-HPC) is a novel tool for assessing stem cell yield before allogeneic haematopoietic stem cell transplantation. This study aimed to establish a reference interval (RI) for XN-HPC in peripheral blood allogeneic transplant donors following granulocyte colony-stimulating factor (G-CSF) stimulation and determine its clinical significance. All specimens were analysed using Sysmex XN-20. Samples were collected and analysed using non-parametric percentile methods to define the RIs. Quantile regression was used to explore the dependency of the RIs on sex and age. Samples were included in clinical decision limits for apheresis based on receiver operating characteristic curve analysis. The non-parametrically estimated RI for XN-HPC was 623.50 (90% confidence interval [CI90%] 510.00-657.00) to 4,144.28 (CI90% 3,761.00-4,547.00). The RIs for the XN-HPC were not age-dependent but were sex-dependent. The RI for males was 648.40 (CI90% 582.00-709.00)-4,502.60 (CI90% 4,046.00-5,219.00) and for females was 490.90 (CI90% 311.00-652.00)-3,096.90 (CI90% 2,749.00-3,782.00). Comparisons based on XN-HPC values between the poor and less-than-optimal groups, good and less-than-optimal groups, and good and non-good groups had areas under the curve of 0.794 (P < 0.001), 0.768 (P < 0.001), and 0.806 (P < 0.001), respectively, indicating a good predictive value for mobilisation effectiveness. XN-HPC data exceeding 3974 × 106/L suggested that a sufficient number of stem cells could be collected clinically. Values > 5318 < 106/L indicated 100% mobilisation effectiveness. We established an RI for XN-HPC in peripheral blood allogeneic transplant donors following G-CSF stimulation and determined clinical decision thresholds for mobilisation efficiency.

Lactate dehydrogenase as a hematopoietic stem cell mobilization biomarker in autologous transplantation

INTRODUCTION

Pre-apheresis peripheral blood CD34+ cell count (PBCD34+) is the most important predictor of good cell mobilization before hematopoietic stem cell transplantation, albeit flow cytometry is not always immediately available. Identification of surrogate markers can be useful. The CD34+ cells proliferate after mobilization, resulting in elevated lactate dehydrogenase (LDH) activity and correlating with the PBCD34+ count.

OBJECTIVE

To determine the LDH cut-off value at which adequate CD34+ cell mobilization is achieved and its diagnostic yield.

MATERIALS AND METHODS

A total of 103 patients who received an autologous stem cell transplantation (ASCT) between January 2015 and January 2020 were included. Demographic and laboratory characteristics were obtained, including complete blood count, pre-apheresis PBCD34+ and LDH levels. Receiver operating characteristic (ROC) curves were performed to identify the optimal serum LDH activity cut-off points for ≥ 2 and ≥ 4 × 106 cells/kg post-mobilization CD34+ count and their diagnostic yield.

RESULTS

A post-mobilization serum LDH cut-off value of 462 U/L yielded a sensitivity (Se) = 86.8% (positive predictive value [PPV] = 72.7%), a pre- and post-mobilization serum LDH difference cut-off value of 387 U/L, an Se = 45.7% (PPV = 97%) and an LDH ratio of 2.46, with an Se = 47.1% (PPV = 97%) for an optimal mobilization count (CD34+ ≥ 4 × 106).

CONCLUSION

The LDH measurement represents a fast and affordable way to predict PBCD34+ mobilization in cases where flow cytometry is not immediately available. According to the LDH diagnostic yield, it could be used as a surrogate marker in transplant centers, supporting the CD34+ count, which remains the gold standard.

Peripheral Blood Allogeneic Stem Cell Mobilization: Can We Predict a Suboptimal Mobilization?

Allogeneic peripheral blood stem cells mobilization is now the basis of most stem cell transplants. In a very limited number of cases, mobilization is suboptimal leading to further collection procedures, to suboptimal cell doses infusion with delayed engraftment time, increased risks of transplant procedure and of related costs. To date we have no recognized and shared criteria for early estimating the probability of poor mobilization in healthy donors. We then analyzed allogeneic peripheral blood stem cell donations performed at the Fondazione Policlinico Universitario A.Gemelli IRCCS Hospital from January 2013 to December 2021 in order to identify premobilization factors associated with successful mobilization. The following data were collected: age, gender, weight, complete blood cell count at baseline, G-CSF dose, number of collection procedures, CD34+ cell count in peripheral blood on the first day of collection, CD34+ cell dose per kg body weight of recipient. Mobilization efficacy was defined according to the number of CD34+ cells in peripheral blood on day +5 of G-CSF administration. We classified donors as sub-optimal mobilizers or good mobilizers according to the achievement of the 50 CD34+ cell/μL threshold. We observed 30 suboptimal mobilizations in 158 allogeneic peripheral blood stem cell donations. Age and baseline white blood cell count were factors significantly associated with negative or positive impact on mobilization, respectively. We did not find significant differences in mobilization based on gender or G-CSF dose. Using cut-off values of 43 years and 5.5×10⁹/L WBC count, we built a suboptimal mobilization score: donors who reach 2, 1 or 0 points have a 46%, 16% or 4% probability of suboptimal mobilization, respectively. Our model explains 26% of the variability of mobilization confirming that most of the mobilization magnitude depends on genetically determined factors; however, suboptimal mobilization score is a simple tool providing an early assessment of mobilization efficacy before G-CSF administration begins in order to support allogeneic stem cells selection, mobilization and collection. Through a systematic review, we looked for confirmation of our findings. According to the published articles, all the variables we included in our model are confirmed to be strongly related to the success of mobilization. We believe that score system approach could be applied in clinical practice to assess the risk of mobilization failure at baseline allowing for a priori intervention.

Severe short-term adverse events in related bone marrow or peripheral blood stem cell donors

The incidence of severe adverse events (SAEs) and associated risk factors in hematopoietic cell transplantation donors needs to be clarified for related donors (relatives of the transplant recipient), whose criteria for donation are more lenient than for unrelated donors. Data from related donors registered in the Japanese national data registry database between 2005 and 2021 were evaluated to determine the association of short-term SAE incidence with donor characteristics at registration.Fourteen of 4339 bone marrow (BM) donors (0.32%) and 54 of 10,684 peripheral blood stem cell (PBSC) donors (0.51%) experienced confirmed SAEs during the short donation period. No deaths were observed. Past medical history was a common risk factor for SAEs in both BM and PBSC donors. Age of 60 years or older and female sex were identified as risk factors for SAEs in PBSC donors. Female sex was also a risk factor for poor mobilization, which resulted in discontinuation of PBSC collection.Although donors should be selected carefully, a certain level of safety is ensured for related donors in Japan. Donor safety should be further increased by improving the selection method for related donors and extending the follow-up period.

Premobilization of CD133+ progenitors is associated with attenuated inflammation-induced pulmonary dysfunction following extracorporeal circulation in mice

OBJECTIVES

Progenitor cells mobilized by granulocyte colony-stimulating factor (G-CSF) have been shown to lessen acute kidney injury induced by extracorporeal circulation (ECC). Both acute kidney injury and lung injury are characterized by endothelial dysfunction. Our goal was to examine whether and how G-CSF-mobilized progenitors with endothelial capacity may help mitigate ECC-induced pulmonary dysfunction.

METHODS

G-CSF (10 μg/kg/day) was administered subcutaneously to C57BL/6 mice before or at the initiation of the ECC process, after which lung injury was assessed by measuring neutrophils in the fluid from bronchoalveolar lavage and determining the pathological score in lung tissue. CD133+ progenitors were isolated and injected into C57BL/6 mice before ECC in vivo. We incubated the CD133+ cells with pulmonary monocytes or neutrophils isolated from naïve mice in vitro.

RESULTS

Pretreatment with G-CSF for 2 days significantly decreased the number of neutrophils in the bronchoalveolar lavage fluid, and the pathological score (P < 0.01; n = 5) improved the PaO2/FiO2 ratio [193.4 ± 12.7 (ECC without G-CSF) vs 305.6 ± 22.6 mmHg (ECC with G-CSF); P = 0.03, n = 5] and suppressed neutrophil elastase and tumour necrosis factor-α levels in the circulation; we also observed increases in both circulating and pulmonary populations of CD133+ progenitors. Similar effects were observed in animals pretreated with CD133+ progenitors instead of G-CSF before ECC. The majority of CD133+/CD45- and CD133+/CD45+ progenitors were mobilized in the lung and in the circulation, respectively. Incubating CD133+ progenitors with neutrophils or pulmonary monocytes blocked lipopolysaccharide-induced release of inflammatory factors.

CONCLUSIONS

Our results suggest that pretreatment of G-CSF attenuates ECC-induced pulmonary dysfunction through inhibiting the inflammatory response in lung tissue and in the circulation with associated premobilization of CD133+ progenitors.

Plerixafor-based mobilization in pediatric healthy donors with unfavorable donor/recipient body weight ratio resulted in a better CD34+ collection yield: A retrospective analysis

INTRODUCTION

In order to propose risk-adapted mobilization algorithms, several authors have tried to look for predictive factors of the CD34⁺ yield in healthy pediatric donors. Donor recipient body weight ratio (D/R ratio) was identified as one of the main variables related with the success to achieve the target cell dose for transplantation. According to this variable we modified the mobilization schedule.

MATERIAL AND METHODS

We report the results of 46 mobilizations and apheresis procedures performed in our center with unfavorable D/R ratio. Mobilization was attempted by the standard regime of G-CSF (10 mcg/kg/24 hours) in 28 cases (60.9%), with high dose G-CSF (10 mcg/kg/12 hours) in 9 cases (19.6%), and with plerixafor and G-CSF single dose regime in 9 cases (19.6%).

RESULTS

CD34⁺ cell quantification before apheresis is closely related to CD34⁺ yield, being the only factor related to collected CD34⁺ cells (beta .71; P < .0001). The mobilization efficiency was higher in plerixafor group compared to the other two schedules (P < .0001). By using plerixafor for mobilization, we achieved the target CD34⁺ cell dose of ≥2 × 10⁶ /kg per recipient body weight in all cases with unfavorable D/R ratio. It was observed that 17.4% of cases that not reached the established target cell dose were located in the standard or high-dose mobilization regimes. This difference is even greater for optimal collections (≥5 × 10⁶ /kg), since of the 54.3% cases that did not reach this goal none was mobilized by plerixafor.

CONCLUSION

Tailoring the mobilization regime we can reach the target cell dose, even in those cases with the worst D/R ratio.

Seasonal variation of human physiology does not influence the harvest of peripheral blood CD34+ cells from unrelated hematopoietic stem cell donors

There are many reports on factors predicting the outcome of PBSC (peripheral blood stem cell) mobilization, such as the donor's gender, age, weight, white blood cell count, platelets pre apheresis, LDH and iron status. Although there are reports of seasonal variation in the physiology of the human immune system and hematopoiesis there are no data that such differences play a role in the response to G-CSF in healthy hematopoietic stem cell donors. The response to G-CSF could also impact the collection results during different seasons. To assess the possible impact of seasonal variation we performed a retrospective, single-center analysis of mobilization and harvest of PBSC in 330 healthy unrelated donors. We found no significant differences in the number of CD34+ cells in peripheral blood after G-CSF mobilization and in collection results when all donors were analyzed. In the subgroup of male donors the number of CD34+ stem cells after G-CSF mobilization was higher than average in summer and autumn (p = 0.036), however, it did not translate into clinically relevant differences in stem cell harvest. We conclude that although there is possible seasonal variation in the response to G-CSF in male donors there is no impact on PBSC harvest in healthy unrelated donors.

Clinical outcomes of multiple myeloma patients who undergo autologous hematopoietic stem cell transplant with G-CSF or G-CSF and plerixafor mobilized grafts

Impact of Plerixafor (P) mobilized stem cells on immune reconstitution, such as absolute lymphocyte count at day 30 (ALC30), and on long-term outcomes of Multiple Myeloma (MM) patients undergoing autologous stem cell transplant (ASCT) has not been well established. We evaluated total of 469 patients mobilized with G-CSF (G) alone, and 141 patients mobilized with G-CSF plus plerixafor (G+ P). Patients only received plerixafor if they had peripheral blood CD34⁺   blood count <20/μL on first planned day of collection. Primary endpoint, ALC30, was 1.3 K/μL (range, 0.1-4.5) and 1.2 K/μL (range, 0.1-5.1) for G and G + P, respectively (P =. 61). The median PFS was 2.5 years (95% CI, 2.1-3.2) and 2.8 years (95% CI, 2.0-3.3) for G and G + P, respectively (HR: 1.13; 95% CI, 0.84-1.50; P = .42). The median OS was 6.1 years (95% CI, 4.6-NR) for G group compared to 3.7 years (95% CI, 3.2-NR) for the G + P group (HR: 1.64; 95% CI, 1.12-2.40; P = .01). The median follow-up time for OS was 2.53 years (95% CI, 2.13-2.99) and 1.59 years (95% CI, 1.17-2.02) for G and G+ P group, respectively. In this large retrospective analysis of MM patients mobilized with G-CSF vs G-CSF + P, there was no significant difference in lymphocyte recovery or PFS. There was an overall survival difference in patients who were poor mobilizers and could not be mobilized with G-CSF alone.

Smoking is an important factor that affects peripheral blood progenitor cells yield in healthy male donors

BACKGROUND

Smoking could reduce the CD34+ cells in peripheral blood of healthy individual. This study aimed to investigate the correlation between smoking load and the effect of peripheral blood hematopoietic progenitor cells (PBPCs) mobilization by granulocyte colony-stimulating factor (G-CSF) alone in healthy donors.

METHODS

Retrospective analysis was performed on 145 healthy adult PBPCs donors who underwent PBPCs mobilization and collection. Smoking factors were evaluated and correlated with mobilization responses, as indicated by the collected CD34+ cells concentration.

RESULTS

The collected CD34+ cells concentration was closely related to pre-CD34 (P < .001) and CD34+ cells collected per volume blood processed (P < .001) which suggested that collected CD34+ cells concentration was a reliable indicator of PBPCs mobilization efficiency. The heavy smoking donors revealed significantly lower collected CD34+ cells concentration, compared to that of the nonsmoking (P < .001) and light smoking donors (P < .05). The levels of collected CD34+ cells in light smoking were also obviously lower than that in nonsmoking donors (P < .05).There were no obvious differences in the collected CD34+ cells concentration, overall processed blood volume and total collected CD34+ cells between nonsmoking and smoking cessation groups (P = .490; P = .464; P = .819).

CONCLUSION

Cigarette smoking is an important factor that affects the yield of PBPCs in male donors, especially when the smoking load is more than five pack-years. Mobilization of PBMCs could be restored by smoking cessation in chronic smokers.

A matched-pair analysis reveals marginally reduced CD34+ cell mobilization on second occasion in 27 related donors who underwent peripheral blood stem cell collection twice at the same institution

BACKGROUND

In a small proportion of cases, hematopoietic function is insufficient after allogeneic hematopoietic stem cell transplantation, as a result of poor graft function or graft failure. These complications are common indications of re-mobilization of the initial donor, either for a second allograft or for an infusion of CD34+ Selected stem Cell Boost (SCB).

METHODS AND MATERIALS

We retrospectively reviewed the results of two cycles of CD34+ cell mobilization and collection. CD34+ cells mobilized and collected at each cycle were compared. When CD34+ cell selection from the collected allogeneic mononuclear cells was indicated, it was performed with the Clinimacs Plus® medical device, and results from in-process and final quality checks were analyzed. To assess the efficacy of CD34+ SCB, transfusion needs before and after the infusion of selected CD34+ cells were calculated.

RESULTS

The median peripheral blood concentration of CD34+ cells/μL was marginally reduced during the second cycle (35.6 vs 33.8, p < 0.05); results revealed a strong correlation between paired values (r = 0.85). The cumulative number of collected CD34+ cells were similar for both cycles; the total processed blood volume was higher during the second cycle (p = 0.023). For CD34+ immune-selection procedures, CD34+ cell recovery and purity were respectively 57% and 95%, with a median T-cell depletion of 6.7 log. Recipients' needs for platelet and red blood cell transfusions were significantly reduced after CD34+ SCB.

CONCLUSION

This study confirms the feasibility of a second cycle of mobilization in healthy related donors and the benefits of CD34+ SCB on hematopoietic reconstitution.