Post-thaw viability of cryopreserved peripheral blood stem cells (PBSC) does not guarantee functional activity: important implications for quality assurance of stem cell transplant programmes

Quality Assessment of Cryopreserved Peripheral Blood Stem Cell Products: Evaluation of Two Methods for Flow Cytometric Viability Testing

INTRODUCTION

The standard flow cytometry method for viability testing using 7-aminoactinomycin D (7-AAD) determines cells in necrosis and late apoptosis. The colony-forming unit (CFU) assay, which evaluates the proliferation ability of HSCs, is also used in graft quality assessment despite known deficiencies that make this assay impractical in routine clinical settings. The aim was to compare the effectiveness of the flow cytometry 7-AAD/annexin V method with the 7-AAD method in assessing the quality of HSCs in autologous and allogeneic peripheral blood stem cell (PBSC) products.

METHODS

Thirty autologous and 30 allogeneic fresh and thawed cryopreserved PBSC products were included in this study. The viability of HSCs was determined using the 7-AAD method and 7-AAD/annexin V method on a flow cytometer, while their clonogenic capacity was assessed by CFU assay.

RESULTS

There was an excellent correlation for CD34+ cell viability between the 7-AAD and the 7-AAD/annexin V method for fresh samples (Rs = 0.930, p < 0.001) and a good correlation for thawed PBSC samples (Rs = 0.739, p < 0.001). Excellent correlation was observed for post-thaw CD34+ cell recovery between the two methods for viability (Rs = 0.980, p < 0.001). Statistical analysis showed a weak correlation between CFU-GM recovery and CD34+ cell recovery, regardless of which viability testing method was used (7-AAD method p = 0.021, Rs = 0.298; 7-AAD/annexin V method p = 0.029, Rs = 0.282).

CONCLUSIONS

Results of this study showed that in the quality assessment of cryopreserved PBSC product viability, the 7-AAD/annexin V method had no added value compared to the 7-AAD method, which was suitable enough for routine quality control of cryopreserved autologous and allogeneic PBSC samples.

Orthobiologic Products: Preservation Options for Orthopedic Research and Clinical Applications

The biological products used in orthopedics include musculoskeletal allografts-such as bones, tendons, ligaments, and cartilage-as well as biological therapies. Musculoskeletal allografts support the body's healing process by utilizing preserved and sterilized donor tissue. These allografts are becoming increasingly common in surgical practice, allowing patients to avoid more invasive procedures and the risks associated with donor site morbidity. Bone grafting is one of the most frequently used procedures in orthopedics and traumatology. Biologic approaches aim to improve clinical outcomes by enhancing the body's natural healing capacity and reducing inflammation. They serve as an alternative to surgical interventions. While preliminary results from animal studies and small-scale clinical trials have been promising, the field of biologics still lacks robust clinical evidence supporting their efficacy. Biological therapies include PRP (platelet-rich plasma), mesenchymal stem cells (MSCs)/stromal cells/progenitor cells, bone marrow stem/stromal cells (BMSCs), adipose stem/stromal cells/progenitor cells (ASCs), cord blood (CB), and extracellular vesicles (EVs), including exosomes. The proper preservation and storage of these cellular therapies are essential for future use. Preservation techniques include cryopreservation, vitrification, lyophilization, and the use of cryoprotective agents (CPAs). The most commonly used CPA is DMSO (dimethyl sulfoxide). The highest success rates and post-thaw viability have been achieved by preserving PRP with a rate-controlled freezer using 6% DMSO and storing other cellular treatments using a rate-controlled freezer with 5% or 10% DMSO as the CPA. Extracellular vesicles (EVs) have shown the best results when lyophilized with 50 mM or 4% trehalose to prevent aggregation and stored at room temperature.

Assessment and comparison of viability assays for cellular products

BACKGROUND AIMS

Accurate assessment of cell viability is crucial in cellular product manufacturing, yet selecting the appropriate viability assay presents challenges due to various factors. This study compares and evaluates different viability assays on fresh and cryopreserved cellular products, including peripheral blood stem cell (PBSC) and peripheral blood mononuclear cell (PBMC) apheresis products, purified PBMCs and cultured chimeric antigen receptor and T-cell receptor-engineered T-cell products.

METHODS

Viability assays, including manual Trypan Blue exclusion, flow cytometry-based assays using 7-aminoactinomycin D (7-AAD) or propidium iodide (PI) direct staining or cell surface marker staining in conjunction with 7-AAD, Cellometer (Nexcelom Bioscience LLC, Lawrence, MA, USA) Acridine Orange/PI staining and Vi-CELL BLU Cell Viability Analyzer (Beckman Coulter, Inc, Brea, CA, USA), were evaluated. A viability standard was established using live and dead cell mixtures to assess the accuracy of these assays. Furthermore, precision assessment was conducted to determine the reproducibility of the viability assays. Additionally, the viability of individual cell populations from cryopreserved PBSC and PBMC apheresis products was examined.

RESULTS

All methods provided accurate viability measurements and generated consistent and reproducible viability data. The assessed viability assays were demonstrated to be reliable alternatives when evaluating the viability of fresh cellular products. However, cryopreserved products exhibited variability among the tested assays. Additionally, analyzing the viability of each subset of the cryopreserved PBSC and PBMC apheresis products revealed that T cells and granulocytes were more susceptible to the freeze-thaw process, showing decreased viability.

CONCLUSIONS

The study demonstrates the importance of careful assay selection, validation and standardization, particularly for assessing the viability of cryopreserved products. Given the complexity of cellular products, choosing a fit-for-purpose viability assay is essential.

Validation of a rapid potency assay for cord blood stem cells using phospho flow cytometry: The IL-3-pSTAT5 assay

INTRODUCTION

Public cord blood banks (CBBs) are required to measure cord blood units (CBUs) potency before their release, allowing for the identification of units that may be unsuitable for haematopoietic transplantation. We have developed a rapid flow cytometry assay based on the measurement of STAT-5 phosphorylation of CD34+ stem cells in response to IL-3 stimulation.

METHOD

To adapt the assay from a research setting to its implementation within our CBB regulated operations, we proceded with a full method validation and a correlation comparison of the IL-3-pSTAT5 assay results with the colony-forming unit assay (CFU) results. A total of 60 CBUs cryopreserved in vials were analysed by flow cytometry to determine the sensitivity, specificity, intra-assay precision, robustness, reproducibility, and inter-laboratory agreement of the assay. The CFU assay was also done on the same samples for comparison purposes.

RESULTS

The assay threshold was established at 50% CD34+CD45+pSTAT5+, which provides a 100% sensitivity and a 98.3% specificity. An average intra-assay CV of 7.3% was determined. All results met our qualitative results acceptance criteria regarding the inter-user and inter-laboratory agreements, IL-3 stimulation time, post-thaw incubation delay and staining time. The IL-3-pSTAT5 assay results correlated well with the total CFU determined using the CFU assay (r²  = 0.82, n = 56).

CONCLUSION

This study shows that our rapid flow cytometry assay can be successfully validated and that the potency data obtained display good sensitivity, specificity and robustness. These results demonstrate the feasibility of implementing this assay within CBB operations, as a validated potency assay.

The Evolving Landscape of Potency Assays

There is a "goldilocks" aspect to potency assays. On the one hand, a comprehensive evaluation of the cell product with detailed quantitative measurement of the critical quality attribute/s of the desired biological activity is required. On the other hand, the potency assay benefits from simplification and lean approaches that avoid unnecessary complication and enhance robustness, to provide a reproducible and scalable product. There is a need to balance insightful knowledge of complex biological healing processes with straightforward manufacture of an advanced therapeutic medicinal product (ATMP) that can be administered in a trustworthy cost-effective manner. While earlier chapters within this book have highlighted numerous challenges facing the potency assay conundrum, this chapter offers a forward-looking perspective regarding the many recent advances concerning acellular products, cryopreservation, induced MSC, cell priming, nanotechnology, 3D culture, regulatory guidelines and evolving institutional roles, that are likely to facilitate potency assay development in the future.

Development and clinical translation considerations for the next wave of gene modified hematopoietic stem and progenitor cells therapies

INTRODUCTION

Consistent and reliable manufacture of gene modified hematopoietic stem and progenitor cell (HPSC) therapies will be of the utmost importance as they become more mainstream and address larger populations. Robust development campaigns will be needed to ensure that these products will be delivered to patients with the highest quality standards.

AREAS COVERED

Through publicly available manuscripts, press releases, and news articles - this review touches on aspects related to HSPC therapy, development, and manufacturing.

EXPERT OPINION

Recent advances in genome modification technology coupled with the longstanding clinical success of HSPCs warrants great optimism for the next generation of engineered HSPC-based therapies. Treatments for some diseases that have thus far been intractable now appear within reach. Reproducible manufacturing will be of critical importance in delivering these therapies but will be challenging due to the need for bespoke materials and methods in combination with the lack of off-the-shelf solutions. Continued progress in the field will manifest in the form of industrialization which currently requires attention and resources directed toward the custom reagents, a focus on closed and automated processes, and safer and more precise genome modification technologies that will enable broader, faster, and safer access to these life-changing therapies.

Sustained Hematopoietic Engraftment Potential after Prolonged Storage of Cryopreserved Hematopoietic Stem Cells (HSC) Used in Salvage Autologous Stem Cell Transplantation: Prolonged Storage of HSCs Sustains Hematological Reconstitution Potential

BACKGROUND

Salvage autologous hematopoietic stem cell transplantation (HSCT) is an effective treatment for patients with relapsed multiple myeloma (MM). Peripheral blood stem cells (PBSCs), a source of hematopoietic stem cells (HSCs), are collected prior to first transplant and adequate quantities of PBSCs can be collected and stored potentially for years to support at least two transplants for eligible patients. To ensure the safety of salvage HSCT used in the treatment of patients in subsequent relapse, PBSCs must retain the potential to engraft even after several years of cryopreservation. Although PBSC viability has been extensively studied using in vitro techniques, few publications describe the most rigorous functional potency measure: of patients receiving a myeloablative conditioning regimen. This study describes a large single-institution experience evaluating the engraftment kinetics of PBSCs used in salvage transplantation after multiple years of storage in comparison to first transplantation of the same patients in the treatment of MM.

STUDY DESIGN AND METHODS

A retrospective chart review of patients with MM undergoing HSCT from 2000 to 2021, identified 89 patients who received salvage autologous PBSC stored > 1 year after first HSCT. PBSC were cryopreserved and stored in vapor-phase liquid nitrogen refrigerators at a temperature of ≤ -150°C. All patients received a PBSC product for both transplants from the same collection cycle. Differences in CD34⁺ cell doses and days to engraftment between the first and salvage transplant were tested using a paired 2-tailed t-test and Wilcoxon signed-rank test. Univariate and multivariable linear regressions were used to determine association between storage time and days to engraftment, adjusting for CD34+ cell dose and conditioning regimen in the multivariable model.

RESULTS

The median storage time between day of initial collection and salvage transplant was 5.4 years (range, 1.0 - 19.7). Engraftment kinetics demonstrated a sustained neutrophil engraftment (absolute neutrophil count (ANC) > 0.5 × 10⁹ cells/L) at a median of 11 days after both the first and salvage transplant (ranges, 8 - 15 and 8 - 19 respectively, p<0.05). The median time to sustained platelet engraftment (> 20 × 10⁹ cells/L without transfusion support) was 13.5 days after first HSCT and 14 days after salvage HSCT (ranges, 9 - 27 and 10 - 56 respectively, p = 0.616). After adjusting for CD34+ cell doses and conditioning regimens, there was no association between the duration of cryopreservation and days to neutrophil (r = 0.178, p = 0.130) or platelet (r = 0.244, p = 0.100) engraftments.

CONCLUSION

Engraftment kinetics of the salvage HSCT are comparable to the first HSCT even when products are stored in vapor-phase nitrogen refrigerators for a median time of 5.4 years. There is no association between storage duration and time to engraftment when controlling for CD34+ dose and conditioning regimens. Prolonged storage of cryopreserved HSC products is a safe practice for MM patients undergoing salvage autologous HSCT.

Effects of cell concentration, time of fresh storage, and cryopreservation on peripheral blood stem cells: PBSC fresh storage and cryopreservation

INTRODUCTION

Peripheral blood stem cells are widely used in autologous or allogeneic transplantation. The quality of the product directly impacts clinical outcomes, and the cell quality and/or functionality may be influenced by the storage conditions as time, temperature, total nucleated cells (TNC) concentration and cryopreservation requirement.

OBJECTIVE

To verify the effects of time, cell concentration, and cryopreservation/thawing in the viability and functionality of stem cells for transplantation.

METHODS

We evaluated TNC, CD45⁺ viable cells, CD34⁺ viable cells, and cell viability and functionality of 11 samples. Measurements were performed immediately and 24 h, 48 h, 72 h, and 96 h after sample collection at high and low TNC concentrations. The same parameters were also evaluated after cryopreservation and thawing of the samples.

RESULT

Duration of storage and TNC concentration exhibited a negative effect on cell quality (CD45⁺ viable cells, CD34⁺ viable cells and functionality). Moreover, the association of these parameters increased the negative effect on graft quality. Cryopreservation and thawing also negatively affected the collected sample regarding viable CD34⁺ cells (recovery 66.2 %), viable CD45⁺ cells (recovery 56.8 %), and 7-AAD viability. No significant losses in viable CD45⁺/CD34⁺ cells and functionality were observed in the first 24 h in both TNC conditions.

CONCLUSION

These results emphasize the importance to consider carefully the storage conditions until transplantation, measuring TNC/μL until 24 h after collection (diluting the product when TNC > 300 × 10³/μL) and infusing fresh graft as soon as possible.

Cell Viability Assessment Using Fluorescence Vital Dyes and Confocal Microscopy in Evaluating Freezing and Thawing Protocols Used in Cryopreservation of Allogeneic Venous Grafts

The authors present their contribution to the improvement of methods suitable for the detection of the freezing and thawing damage of cells of cryopreserved venous grafts used for lower limb revascularization procedures. They studied the post-thaw viability of cells of the wall of cryopreserved venous grafts (CVG) immediately after thawing and after 24 and 48 h culture at +37 °C in two groups of six CVG selected randomly for slow thawing in the refrigerator and rapid thawing in a water bath at +37 °C. The grafts were collected from multi-organ and tissue brain-dead donors, cryopreserved, and stored in a liquid nitrogen vapor phase for five years. The viability was assessed from tissue slices obtained by perpendicular and longitudinal cuts of the thawed graft samples using in situ staining with fluorescence vital dyes. The mean and median immediate post-thaw viability values above 70% were found in using both thawing protocols and both types of cutting. The statistically significant decline in viability after the 48-h culture was observed only when using the slow thawing protocol and perpendicular cutting. The possible explanation might be the “solution effect damage” during slow thawing, which caused a gentle reduction in the graft cellularity. The possible influence of this phenomenon on the immunogenicity of CVG should be the subject of further investigations.

Autophagy modulation alleviates cryoinjury in murine spermatogonial stem cell cryopreservation

BACKGROUND

Cryopreservation can expand the usefulness of spermatogonial stem cells (SSCs) in various fields. However, previous investigations that have attempted to modulate cryoinjury-induced mechanisms to increase cryoprotective efficiency have mainly focused on apoptosis and necrosis.

OBJECTIVES

This study aimed to establish an effective molecular-based cryoprotectant for SSC cryopreservation via autophagy modulation.

MATERIALS AND METHODS

To determine the efficacy of autophagy modulation, we assessed the recovery rate and relative proliferation rate and performed western blotting for the determination of autophagy flux, immunocytochemistry and real-time quantitative polymerase chain reaction (RT-qPCR) for SSC characterization, and spermatogonial transplantation for in vivo SSC functional activity.

RESULTS

The results showed that a basal level of autophagy caused a higher relative proliferation rate (pifithrin-μ 0.01 μM, 184.2 ± 11.2%; 3-methyladenine 0.01 μM, 175.3 ± 10.3%; pifithrin-μ 0.01 μM + 3-methyladenine 0.01 μM, P3, 224.6 ± 22.3%) than the DMSO control (100 ± 6.2%). All treatment groups exhibited normal characteristics, suggesting that these modulators could be used as effective cryoprotectants without changing the properties of the undifferentiated germ cells. According to the results of the in vivo spermatogonial transplantation assay, the colonies per total number of cultured SSCs was significantly higher in the pifithrin-μ 0.01 μM (1596.7 ± 172.5 colonies), 3-methyladenine 0.01 μM (1522.1 ± 179.2 colonies), and P3 (1727.5 ± 196.5 colonies) treatment groups than in the DMSO control (842.8 ± 110.08 colonies), which was comparable to that of the fresh control (1882.1 ± 132.1 colonies).

DISCUSSION

A basal level of autophagy is more essential for resilience in frozen SSCs after thawing, rather than the excessive activation or inhibition of autophagy.

CONCLUSION

A basal level of autophagy plays a critical role in the pro-survival response of frozen SSCs after thawing; herein, a new approach by which SSC cryoprotective efficiency can be improved was identified.

Long-Term Cryopreservation Does Not Affect Quality of Peripheral Blood Stem Cell Grafts: A Comparative Study of Native, Short-Term and Long-Term Cryopreserved Haematopoietic Stem Cells

Cryopreserved haematopoietic progenitor cells are used to restore autologous haematopoiesis after high dose chemotherapy. Although the cells are routinely stored for a long period, concerns remain about the maximum storage time and the possible negative effect of storage on their potency. We evaluated the effect of cryopreservation on the quality of peripheral stem cell grafts stored for a short (3 months) and a long (10 years) period and we compared it to native products.The viability of CD34+ cells remained unaffected during storage, the apoptotic cells were represented up to 10% and did not differ between groups. The clonogenic activity measured by ATP production has decreased with the length of storage (ATP/cell 1.28 nM in native vs. 0.63 in long term stored products, P < 0.05). Only borderline changes without statistical significance were detected when examining mitochondrial and aldehyde dehydrogenase metabolic activity and intracellular pH, showing their good preservation during cell storage. Our experience demonstrates that cryostorage has no major negative effect on stem cell quality and potency, and therefore autologous stem cells can be stored safely for an extended period of at least 10 years. On the other hand, long term storage for 10 years and longer may lead to mild reduction of clonogenic capacity. When a sufficient dose of stem cells is infused, these changes will not have a clinical impact. However, in products stored beyond 10 years, especially when a low number of CD34+ cells is available, the quality of stem cell graft should be verified before infusion using the appropriate potency assays.

Inhibition of Caspase-8 Activity Improves Freezing Efficiency of Male Germline Stem Cells in Mice

Cryopreservation of male germline stem cells (GSCs) is an essential technique for their long-term preservation and utilization in various fields. However, the specific apoptosis pathways involved in cryoinjury during freezing remain unclear. Therefore, our study sought to identify the pathways involved in cryoinjury-induced apoptosis and thereby to improve freezing efficiency during GSC cryopreservation through the creation of a specific molecular-based cryoprotectant. The activities of caspase-8, caspase-9, caspase-3, and caspase-7 were assessed by Western blot analyses to determine the role of specific apoptosis pathways in GSC cryoinjury. Specifically, the role of a specific caspase was identified by recovery rate, relative proliferation rate, Annexin V/propidium iodide co-staining, and caspase activity using its inhibitor and activator. Moreover, the safety of the cryoprotectant was assessed by immunofluorescence and quantitative real-time polymerase chain reaction (qRT-PCR). Furthermore, the efficacy of the molecular-based cryoprotectant was assessed using frozen cells in the presence of dimethyl sulfoxide (DMSO) (control), trehalose, a caspase-8 inhibitor Z-IETD-FMK [ZIF], or a mixture of the aforementioned compounds, after which the changes in Src signaling were measured. Our results demonstrated that caspase-8 plays a major role in cryoinjury-induced apoptosis and therefore its inhibition improves freezing efficiency. Specifically, a significantly higher relative proliferation rate was observed in the Z-IETD-FMK 0.01 μM-treated cells than in the DMSO control (100% ± 6.2% vs. 189.8% ± 9.5%), with decreases in both early apoptosis (16.6% ± 2.2% vs. 7.5% ± 1.0%) and caspase-8 activity (1.0-fold vs. 0.4-fold). The relative proliferation rate was significantly higher in the cryoprotectant mixture (246.0% ± 12.2%) than other individual treatment groups (trehalose 200 mM, 189.8% ± 9.5%; Z-IETD-FMK 0.01 μM, 189.7% ± 2.2%) with no significant differences in Src signaling. Therefore, our findings provide novel insights into the development of freezing protocols to enhance GSC freezing efficiency, thereby facilitating the wider adoption of GSCs in the livestock industry and/or clinical trials.

Automated dry thawing of cryopreserved haematopoietic cells is not adversely influenced by cryostorage time, patient age or gender

Cell therapies are becoming increasingly widely used, and their production and cryopreservation should take place under tightly controlled GMP conditions, with minimal batch-to-batch variation. One potential source of variation is in the thawing of cryopreserved samples, typically carried out in water baths. This study looks at an alternative, dry thawing, to minimise variability in the thawing of a cryopreserved cell therapy, and compares the cellular outcome on thaw. Factors such as storage time, patient age, and gender are considered in terms of cryopreservation and thawing outcomes. Cryopreserved leukapheresis samples from 41 donors, frozen by the same protocol and stored for up to 17 years, have been thawed using automated, water-free equipment and by conventional wet thawing using a water bath. Post-thaw viability, assessed by both trypan blue and flow cytometry, showed no significant differences between the techniques. Similarly, there was no negative effect of the duration of frozen storage, donor age at sample collection or donor gender on post-thaw viability using either thawing method. The implication of these results is that the cryopreservation protocol chosen initially remains robust and appropriate for use with a wide range of donors. The positive response of the samples to water-free thawing offers potential benefits for clinical situations by removing the subjective element inherent in water bath thawing and eliminating possible contamination issues.

Cryopreservation of hematopoietic cells using a pre-constituted, protein-free cryopreservative solution with 5% dimethyl sulfoxide

BACKGROUND AIMS

Adequate cryopreservation techniques are critical to ensure optimal recovery of functional progenitor cells in hematopoietic cell (HC) transplantation, minimize risk of contamination and prevent infusion-related adverse events (irAEs). In this article, we provide graft function and infusion safety results observed by decreasing the concentration of dimethyl sulfoxide (DMSO) in cryopreservative media and by minimizing processor-dependent formulation.

METHODS

Ten HC products, collected after standard mobilization of multiple myeloma patients, were cryopreserved with PRIME-XV FreezIS (FreezIS) and compared with products previously cryopreserved with media formulated in-house to achieve a final DMSO concentration of 10% (Std10) and 5% (Std5). At infusion, HCs were analyzed for recovery of CD34+ cells and viability; irAEs and time to engraftment of neutrophils and platelets were also monitored.

RESULTS

Median CD34+ cell recovery for HC cryopreserved with Std10, Std5 and FreezIS was 38%, 78% and 68%, respectively (P = 0.0002). There were less frequent irAEs with Std5 and FreezIS (10%) compared with Std10 (80%) (P ≤ 0.0001). Median time to neutrophil engraftment was comparable (11 days) for all three groups, while platelet engraftment occurred at a median of 20, 19 and 17 days, respectively (p-values not significant).

CONCLUSIONS

FreezIS, a Good Manufacturing Practice-grade, pre-constituted cryopreservative with low DMSO content, maintains functional viability of the HC product while reducing the incidence of irAEs compared with 10% DMSO solutions. The pre-constituted nature of this agent also decreases processor-dependent handling, hence decreasing the risk of variability and infection.

A novel method to evaluate prethawing viability of cryopreserved CD34+ hematopoietic stem cells for autologous transplantation

BACKGROUND

Cryopreservation of CD34+ hematopoietic stem cells (HSCs) is associated with variable loss of viability. Although postfreezing CD34+ cell viability can be assessed on the sampling tube (bag tail) directly connected to the main bag (mother bag), results often underestimate the actual viability observed when the mother bag is thawed and reinfused. We assessed a novel method to measure postfreezing CD34+ cell viability, based on small bag (minibag) samples; results were compared with those obtained on the corresponding mother bags and bag tails.

STUDY DESIGN AND METHODS

Sixty-one apheresis procedures of 42 patients undergoing autologous HSC transplant were analyzed. Viable CD34+ cells were quantified with flow cytometry before controlled rate freezing (ICE-CUBE14M system, SY-LAB- IceCube, SIAD), after 10 days of storage (mini-bag and bag tail), and before reinfusion (aliquot from a thawed mother bag). Results were compared using Student's t test and Spearman's rho correlation test.

RESULTS

The mean CD34+ cell viability before cryopreservation was 99.3% (confidence interval [CI], 98.94-99.65%); the mean amount of CD34+ cells, white blood cells and neutrophils in the mother bag was 0.8 ± 1.1 × 10⁹ /L, 63.4 ± 23.5 × 10⁹ /L, and 25.7 ± 15.5 × 10⁹ /L, respectively. Mother bags postthawing CD34+ cell viability was 72.3% (CI, 67.74-76.85%; p < 0.01 compared to prefreezing); no difference was observed with respect to minibags (73.7%; CI, 69.80-77.59%; p = NS), whereas significantly lower values were found for bag tails (58.6%; CI, 54.19-63.00%; p < 0.01 vs. both mini- and mother bags).

CONCLUSION

Compared to bag tails, minibags represent a more accurate tool to measure the CD34+ cell viability of the apheresis mother bag prior to reinfusion; in addition, minibags may could be of help for case-by-case calculation of the amount of apheresis to be infused to patients undergoing autologous HSC transplant.

Adequate Engraftment With Lower Hematopoietic Stem Cell Dose

BACKGROUND

Adequate hematopoietic stem cell dose is required to proceed with autologous stem cell transplantation (ASCT).

PATIENTS AND METHODS

We conducted a retrospective analysis of 108 patients with multiple myeloma and lymphoma who underwent ASCT with noncryopreserved stem cells at our center. Data were compared for patients who received stem cell dose < 2 × 10⁶/kg with those who received a higher dose.

RESULTS

The median CD34 dose collected in the lesser dose group was 1.76 × 10⁶/kg (1.22 to 1.97 × 10⁶/kg). Mean CD34 dose of the whole group was 4.96 ± 4.2 × 10⁶/kg. Neutrophil engraftment was similar in both groups (12 vs. 11 days) (P = .065). Similarly, platelet engraftment occurred in 12 versus 11 days in both groups (P = .017). Length of hospital stay was similar in both groups. There was no significant difference in the incidence of proven bacterial infections between the 2 groups. There was no transplant-related mortality in lower dose group.

CONCLUSION

ASCT can be safely performed with lower hematopoietic stem cell dose in noncryopreserved setting.

Stem Cells from Human Trabecular Meshwork Hold the Potential to Develop into Ocular and Non-Ocular Lineages After Long-Term Storage

Stem cells from the eye hold a great potential for vision restoration and can also be used for regeneration in other tissues. In this study, we characterized the stem cell properties of Trabecular meshwork stem cells (TMSCs) after long-term cryopreservation (∼8 years). TMSCs derived from four donors were examined for their viability and proliferation, as well as stem cell marker expression. Spheroid formation, colony formation, and multipotency were investigated. We observed that TMSCs were fully viable with variable proliferation ability. They expressed the stem cell markers CD90, CD166, CD105, CD73, OCT4, SSEA4, Notch1, KLF4, ABCG2, Nestin, and HNK1 detected by flow cytometry, quantitative polymerase chain reaction, or immunofluorescent staining. They could form spheroids and colonies after thawing. All TMSCs were able to differentiate into osteocytes, neural cells, and trabecular meshwork (TM) cells, but not adipocytes. Differentiated TM cells responded to dexamethasone treatment with increased expression of myocilin and angiopoietin-like 7 (ANGPTL7). In a nutshell, our study demonstrated that TMSCs retain their stem cell properties after long-term cryopreservation and hence can be an effective cell therapy source for various clinical applications.

Intracellular delivery of mRNA to human primary T cells with microfluidic vortex shedding

Intracellular delivery of functional macromolecules, such as DNA and RNA, across the cell membrane and into the cytosol, is a critical process in both biology and medicine. Herein, we develop and use microfluidic chips containing post arrays to induce microfluidic vortex shedding, or μVS, for cell membrane poration that permits delivery of mRNA into primary human T lymphocytes. We demonstrate transfection with μVS by delivery of a 996-nucleotide mRNA construct encoding enhanced green fluorescent protein (EGFP) and assessed transfection efficiencies by quantifying levels of EGFP protein expression. We achieved high transfection efficiency (63.6 ± 3.44% EGFP + viable cells) with high cell viability (77.3 ± 0.58%) and recovery (88.7 ± 3.21%) in CD3 + T cells 19 hrs after μVS processing. Importantly, we show that processing cells via μVS does not negatively affect cell growth rates or alter cell states. We also demonstrate processing speeds of greater than 2.0 × 10⁶ cells s^-1 at volumes ranging from 0.1 to 1.5 milliliters. Altogether, these results highlight the use of μVS as a rapid and gentle delivery method with promising potential to engineer primary human cells for research and clinical applications.

Cryopreservation of Hematopoietic Stem Cells: Emerging Assays, Cryoprotectant Agents, and Technology to Improve Outcomes

Hematopoietic stem cell (HSC) therapy is widely used to treat a growing number of hematological and non-hematological diseases. Cryopreservation of HSCs allows for cells to be transported from the site of processing to the site of clinical use, creates a larger window of time in which cells can be administered to patients, and allows sufficient time for quality control and regulatory testing. Currently, HSCs and other cell therapies conform to the same cryopreservation techniques as cells used for research purposes: cells are cryopreserved in dimethyl sulfoxide (DMSO) at a slow cooling rate. As a result, HSC therapy can result in numerous adverse symptoms in patients due to the infusion of DMSO. Efforts are being made to improve the cryopreservation of HSCs for clinical use. This review discusses advances in the cryopreservation of HSCs from 2007 to the present. The preclinical development of new cryoprotectants and new technology to eliminate cryoprotectants after thawing are discussed in detail. Additional cryopreservation considerations are included, such as cooling rate, storage temperature, and cell concentration. Preclinical cell assessment and quality control are discussed, as well as clinical studies from the past decade that focus on new cryopreservation protocols to improve patient outcomes.

Manufacturing chimeric antigen receptor T cells: issues and challenges

Clinical trials of adoptively transferred CD19 chimeric antigen receptor (CAR) T cells have delivered unprecedented responses in patients with relapsed refractory B-cell malignancy. These results have prompted Food and Drug Administration (FDA) approval of two CAR T-cell products in this high-risk patient population. The widening range of indications for CAR T-cell therapy and increasing patient numbers present a significant logistical challenge to manufacturers aiming for reproducible delivery systems for high-quality clinical CAR T-cell products. This review discusses current and novel CAR T-cell processing methodologies and the quality control systems needed to meet the increasing clinical demand for these exciting new therapies.

The value of the post-thaw CD34+ count with and without DMSO removal in the setting of autologous stem cell transplantation

BACKGROUND

CD34+ cell count correlates with engraftment potency after autologous stem cell transplantation. Assessment of CD34+ mainly occurs after apheresis and before cryopreservation with dimethyl sulfoxide (DMSO). The influence of postthaw CD34+ cell numbers over time to engraftment is not well studied, and determination of postthaw CD34+ cell counts is challenging for a variety of reasons. The aim of this retrospective study was to systematically assess the value of postthaw CD34+ cell counts in autologous grafts with and without DMSO removal.

STUDY DESIGN AND METHODS

Between January 2008 and December 2015, 236 adult patients underwent a total of 292 autologous stem cell transplantations. Median age at transplantation was 56 years, and the main indication was multiple myeloma (60%). DMSO removal was done in 96 grafts (33%), either by centrifugation or by Sepax method.

RESULTS

Patients receiving grafts containing DMSO showed a significantly faster platelet (p = 0.02) and RBC (p = 0.001) engraftment. DMSO removal was not associated with fewer infusion-related adverse events. We observed a good correlation between CD34+ cell count after apheresis and CD34+ cell count after thawing/washing (r = 0.931). Ninety grafts (31%) showed a significant loss of viable CD34+ cells, which translated into a delayed engraftment.

CONCLUSION

DMSO removal was associated with delayed platelet and RBC engraftment without preventing adverse events. CD34+ cell enumeration after thawing remains difficult to perform, but grafts showing higher cell loss during cryopreservation and thawing are associated with slower engraftment. Prospective studies on the role of DMSO removal and postthaw CD34+ enumeration using defined protocols are needed.

Peripheral Stem Cell Apheresis is Feasible Post 131Iodine-Metaiodobenzylguanidine-Therapy in High-Risk Neuroblastoma, but Results in Delayed Platelet Reconstitution

PURPOSE

Targeted radiotherapy with ¹³¹iodine-meta-iodobenzylguanidine (¹³¹I-MIBG) is effective for neuroblastoma (NBL), although optimal scheduling during high-risk (HR) treatment is being investigated. We aimed to evaluate the feasibility of stem cell apheresis and study hematologic reconstitution after autologous stem cell transplantation (ASCT) in patients with HR-NBL treated with upfront ¹³¹I-MIBG-therapy.

EXPERIMENTAL DESIGN

In two prospective multicenter cohort studies, newly diagnosed patients with HR-NBL were treated with two courses of ¹³¹I-MIBG-therapy, followed by an HR-induction protocol. Hematopoietic stem and progenitor cell (e.g., CD34⁺ cell) harvest yield, required number of apheresis sessions, and time to neutrophil (>0.5 × 10⁹/L) and platelet (>20 × 10⁹/L) reconstitution after ASCT were analyzed and compared with "chemotherapy-only"-treated patients. Moreover, harvested CD34⁺ cells were functionally (viability and clonogenic capacity) and phenotypically (CD33, CD41, and CD62L) tested before cryopreservation (n = 44) and/or after thawing (n = 19).

RESULTS

Thirty-eight patients (47%) were treated with ¹³¹I-MIBG-therapy, 43 (53%) only with chemotherapy. Median cumulative ¹³¹I-MIBG dose/kg was 0.81 GBq (22.1 mCi). Median CD34⁺ cell harvest yield and apheresis days were comparable in both groups. Post ASCT, neutrophil recovery was similar (11 days vs. 10 days), whereas platelet recovery was delayed in ¹³¹I-MIBG- compared with chemotherapy-only-treated patients (29 days vs. 15 days, P = 0.037). Testing of harvested CD34⁺ cells revealed a reduced post-thaw viability in the ¹³¹I-MIBG-group. Moreover, the viable CD34⁺ population contained fewer cells expressing CD62L (L-selectin), a marker associated with rapid platelet recovery.

CONCLUSIONS

Harvesting of CD34⁺ cells is feasible after ¹³¹I-MIBG. Platelet recovery after ASCT was delayed in ¹³¹I-MIBG-treated patients, possibly due to reinfusion of less viable and CD62L-expressing CD34⁺ cells, but without clinical complications. We provide evidence that peripheral stem cell apheresis is feasible after upfront ¹³¹I-MIBG-therapy in newly diagnosed patients with NBL. However, as the harvest of ¹³¹I-MIBG-treated patients contained lower viable CD34⁺ cell counts after thawing and platelet recovery after reinfusion was delayed, administration of ¹³¹I-MIBG after apheresis is preferred.

The relationship between CD34+ stem cell dose and time to neutrophil recovery in autologous haematopoietic stem cell recipients-A single centre experience

A retrospective, observational study was performed of 112 patients who underwent autologous haematopoietic stem cell transplantation (ASCT) to determine the relationship between CD34+ stem cell dose and neutrophil engraftment. Importantly, a novel approach to more accurately calculate time to neutrophil engraftment was employed. The results demonstrated that a higher CD34+ stem cell dose was associated with faster neutrophil recovery (P < 0.05). CD34+ stem cell dose using actual and ideal patient body weight were both equally predictive of neutrophil engraftment as were absolute and viable CD34+ measurements. The clinical implications for this relationship are limited with an increase in CD34+ stem cell dose by 1 × 10⁶/kg reducing the neutrophil engraftment time by only 3 h and 50 min. The median time to neutrophil recovery was 217 h (9 days and 1 h) and this relatively early engraftment time may be related to an early initiation of granulocyte colony-stimulating factor (G-CSF) on day +1 post-transplant. Female patients engrafted 17 h faster than their male counterparts on multi-variate analysis (P < 0.05). Conditioning chemotherapy, bacteraemia, G-CSF dose/kg body weight and increasing age had no impact on time to neutrophil recovery.

The importance of post-thaw subculture for standardizing cellular activity of fresh or cryopreserved mouse embryonic stem cells

Objective

Remarkable difference in cellular activity was found between early and late subpassaged embryonic stem cell (ESCs) lines, which can be created by subtle changes in cell manipulation protocol. This study subsequently examined whether post-thaw subculture of early subpassaged ESC lines could further affect the activity of the ESCs.

Methods

Fresh (as a control treatment) or cryopreserved F1 hybrid (B6CBAF1) early ESC lines (C57BL/6xCBA) of the 4 (P4) or the 19 passage (P19) were subcultured once, twice or six times under the same condition. The post-thaw survival of the ESCs was monitored after the post-treatment subculture and the ability of cell proliferation, reactive oxygen species (ROS) generation, apoptosis and mitochondrial ATP synthesis was subsequently examined.

Results

Regardless of the subculture number, P19 ESCs showed better (p<0.05) doubling time and less ATP production than P4 ESCs and such difference was not influenced by fresh or cryopreservation. The difference between P4 and P19 ESC lines became decreased as the post-treatment subculture was increased and the six times subculture eliminated such difference. Similarly, transient but prominent difference in ROS production and apoptotic cell number was detected between P4 and P19 ESCs only at the 1st subculture after treatment, but no statistical differences between two ESC lines was detected in other observations.

Conclusion

The results of this study suggest that post-thaw subculture of ESCs under the same environment is recommended for standardizing their cellular activity. The activity of cell proliferation ability and ATP synthesis can be used as parameters for quality control of ESCs.

Genetic Engineering and Manufacturing of Hematopoietic Stem Cells

The marketing approval of genetically engineered hematopoietic stem cells (HSCs) as the first-line therapy for the treatment of severe combined immunodeficiency due to adenosine deaminase deficiency (ADA-SCID) is a tribute to the substantial progress that has been made regarding HSC engineering in the past decade. Reproducible manufacturing of high-quality, clinical-grade, genetically engineered HSCs is the foundation for broadening the application of this technology. Herein, the current state-of-the-art manufacturing platforms to genetically engineer HSCs as well as the challenges pertaining to production standardization and product characterization are addressed in the context of primary immunodeficiency diseases (PIDs) and other monogenic disorders.