Factors influencing platelet clumping during peripheral blood hematopoietic stem cell collection

Aggregates in apheresis-derived platelet concentrates: A 5-year single-centre experience

BACKGROUND AND OBJECTIVES

The phenomenon of aggregates in apheresis-derived platelet concentrates (APCs) has not yet been fully elucidated. Initially, visible aggregates (IVA) usually dissolve within 24 h after collection, but some persist till the end of the shelf life (persistent aggregates, PA). A study conducted at the Croatian Institute of Transfusion Medicine aimed to identify factors that influence the aggregate occurrence in APCs.

MATERIALS AND METHODS

We conducted a cross-sectional study for the 2018-2022 period and collected data on APCs with IVA. We analysed APCs discarded due to PA separately for two apheresis technologies and compared them to the control group.

RESULTS

Significantly more donations were discarded in the IVA group compared with the control group and total number of discarded APCs. A total of 205 APCs were discarded due to PA (14.7% of IVA APCs and 1.27% of all APCs collected). Amicus APCs with PA had a significantly lower platelet count and mean platelet volume. They were obtained by procedures with less anticoagulant used. In contrast to Amicus APCs, Haemonetics APCs with PA had a significantly higher platelet count. None of the donor-related factors examined was predictive of PA.

CONCLUSION

APCs with IVA are more often discarded, not only due to aggregates, but also for impairment of other quality control parameters. Type of apheresis technology, being one of the most common risk factors for IVA, was not confirmed as the main risk factor for PA. There seem to be some donor-related causal factors.

Hematopoietic stem cell collection for sickle cell disease gene therapy

PURPOSE OF REVIEW

Gene therapy for sickle cell disease (SCD) is advancing rapidly, with two transformative products recently approved by the US Food and Drug Administration and numerous others under study. All current gene therapy protocols require ex vivo modification of autologous hematopoietic stem cells (HSCs). However, several SCD-related problems impair HSC collection, including a stressed and damaged bone marrow, potential cytotoxicity by the major therapeutic drug hydroxyurea, and inability to use granulocyte colony stimulating factor, which can precipitate severe vaso-occlusive events.

RECENT FINDINGS

Peripheral blood mobilization of HSCs using the CXCR4 antagonist plerixafor followed by apheresis collection was recently shown to be safe and effective for most SCD patients and is the current strategy for mobilizing HSCs. However, exceptionally large numbers of HSCs are required to manufacture an adequate cellular product, responses to plerixafor are variable, and most patients require multiple mobilization cycles, increasing the risk for adverse events. For some, gene therapy is prohibited by the failure to obtain adequate numbers of HSCs.

SUMMARY

Here we review the current knowledge on HSC collection from individuals with SCD and potential improvements that may enhance the safety, efficacy, and availability of gene therapy for this disorder.

PAR4-Mediated PI3K/Akt and RhoA/ROCK Signaling Pathways Are Essential for Thrombin-Induced Morphological Changes in MEG-01 Cells

Thrombin stimulates platelets via a dual receptor system of protease-activated receptors (PARs): PAR1 and PAR4. PAR1 activation induces a rapid and transient signal associated with the initiation of platelet aggregation, whereas PAR4 activation results in a prolonged signal, required for later phases, that regulates the stable formation of thrombus. In this study, we observed differential signaling pathways for thrombin-induced PAR1 and PAR4 activation in a human megakaryoblastic leukemia cell line, MEG-01. Interestingly, thrombin induced both calcium signaling and morphological changes in MEG-01 cells via the activation of PAR1 and PAR4, and these intracellular events were very similar to those observed in platelets shown in previous studies. We developed a novel image-based assay to quantitatively measure the morphological changes in living cells, and observed the underlying mechanism for PAR1- and PAR4-mediated morphological changes in MEG-01 cells. Selective inhibition of PAR1 and PAR4 by vorapaxar and BMS-986120, respectively, showed that thrombin-induced morphological changes were primarily mediated by PAR4 activation. Treatment of a set of kinase inhibitors and 2-aminoethoxydiphenyl borate (2-APB) revealed that thrombin-mediated morphological changes were primarily regulated by calcium-independent pathways and PAR4 activation-induced PI3K/Akt and RhoA/ROCK signaling pathways in MEG-01 cells. These results indicate the importance of PAR4-mediated signaling pathways in thrombin-induced morphological changes in MEG-01 cells and provide a useful in vitro cellular model for platelet research.

Process and procedural adjustments to improve CD34+ collection efficiency of hematopoietic progenitor cell collections in sickle cell disease

BACKGROUND

Adequate CD34+ collection efficiency (CE) is critical to achieve target CD34+ cell doses in hematopoietic progenitor cell (HPC) collections. Autologous HPC collection in sickle cell disease (SCD) is associated with unstable collection interfaces and low CD34+ CEs. We hypothesized that variables specific to SCD, activation of blood cells and elevated viscosity, might contribute to these issues and made adjustments to the collection process and procedure to address our hypothesis.

STUDY DESIGN AND METHODS

In two patients with SCD undergoing autologous HPC collection on our clinical trial (NCT02193191), we therefore implemented adjustments to the process and procedure in the following areas: proximity of RBC exchange to HPC collection, the type of anticoagulation, and the packing factor setting.

RESULTS

There was no collection interface instability. Our CD34+ CE1s were high at 70% and 51%, and granulocyte CE, platelet CE, and product granulocyte % were remarkably low. Product hematocrits were not as high as previously reported to be required to obtain adequate CEs. Interestingly, one HPC product showed a hemoglobin S (HbS) of 91% at the same time that the peripheral blood (PB) showed a HbS of 22%.

DISCUSSION

Adjustments to the HPC collection process and procedure were associated with adequate CD34+ CEs and low granulocyte and platelet contamination in HPC products from SCD patients. Given the discrepancy in the percentage of sickle RBCs in the product versus the PB, we hypothesize that CD34+ cells and RBCs may aggregate. Our interventions and hypothesis should be further investigated in larger studies.