Guidelines for the development and validation of new potency assays for the evaluation of umbilical cord blood

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.

Multicenter evaluation of the IL-3-pSTAT5 assay to assess the potency of cryopreserved stem cells from cord blood units: The BEST Collaborative study

BACKGROUND

The IL-3-pSTAT5 assay, a new, rapid, and standardized flow-cytometry-based assay may compensate for several limitations of the colony-forming unit (CFU) assay typically used for stem cell potency assessments of cord blood units (CBU). We performed an inter-laboratory evaluation of the performance of this new assay.

STUDY DESIGN AND METHODS

This Biomedical Excellence for Safer Transfusion (BEST) Collaborative multicenter, international study included 15 participants from public cord blood banks (CBBs), CBB-supporting research laboratories, and stem cell laboratories. To perform the IL-3-pSTAT5 assay, participating centers received reagents, instructions, and 10 blind CBU samples, including eight normal samples and two samples exposed to a transient warming event. We measured inter-laboratory agreement qualitatively (proportion of correctly classified samples) and quantitatively (coefficient of variation [CV], correlation coefficients, receiver operating characteristics (ROC) curve, and intraclass correlation coefficient [ICC]).

RESULTS

The qualitative agreement was 97.3% (i.e., 107/110; Fleiss' kappa = 0.835). The average CV on a per-sample basis was 11.57% among all samples, 8.99% among normal samples, and on a per-center basis was 9.42% among normal samples. In a correlation matrix that compared results across centers, the mean Pearson's correlation coefficient was 0.88 (standard deviation = 0.04). The ICC was 0.83 (95% confidence interval = 0.68-0.95). The area under the curve (AUC) from the ROC curve was 0.9974.

DISCUSSION

Excellent qualitative and quantitative agreement was exhibited across laboratories. The IL-3-pSTAT5 assay may therefore be implemented in flow cytometry laboratories to rapidly and reliably provide standardized measures of stem cell potency in CBUs.

Combined impact of HLA-allele matching and the CD34-positive cell dose on optimal unit selection for single-unit cord blood transplantation in adults

The combined effects of HLA-allele matching at six-loci (HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1) and CD34⁺ cell dose on clinical outcomes were analyzed in 1,226 adult cases with single-unit unrelated cord blood transplantation. In the six-loci analysis, low HLA-allele matches did not significantly increase the overall mortality compared to higher matches, whereas in the five-loci analysis excluding HLA-DPB1, they caused a higher overall mortality (HR 1.42, p = .002), possibly due to the graft-versus-leukemia effect of HLA-DPB1 mismatches. A lower CD34⁺ cell dose (<.50 × 10⁵/kg) resulted in higher mortality and lower engraftment; these inferior outcomes were offset by high HLA-allele matches (7-10/10 match), while the inferior outcomes of low HLA-allele matches were improved by increasing the CD34⁺ cell dose. Consideration of the combined effects of the CD34⁺ cell dose and HLA matching may expand the options for transplantable units when HLA matching or the CD34⁺ cell dose is inadequate.

Guidelines for Cord Blood Unit Selection

Optimal cord blood (CB) unit selection is critical to maximize the likelihood of successful engraftment and survival after CB transplantation (CBT). However, unit selection can be complex because multiple characteristics must be considered including unit cell dose, donor-recipient human leukocyte antigen (HLA) match, and unit quality. This review provides evidence-based and experience-based comprehensive guidelines for CB unit selection. Topics addressed include the use of both the TNC and the CD34⁺ cell dose, as well as the CD34⁺ cell to TNC content ratio to evaluate unit progenitor cell content and engraftment potential, the acceptable TNC and CD34⁺ cell dose criteria that define an adequate single-unit graft, and the indication and acceptable cell dose criteria for double-unit grafts. The acceptable criteria for 6-loci (HLA-A, -B antigen, -DRB1 allele) and 8-allele (HLA-A, -B, -C, -DRB1) donor-recipient HLA match, the evaluation of patients with donor-specific HLA antibodies, and the multiple determinants of unit quality are also reviewed in detail. Finally, a practical step-by-step guide to CB searches and the principles that guide ultimate graft selection are outlined.

Validation of a semi automatic device to standardize quantification of Colony-Forming Unit (CFU) on hematopoietic stem cell products

Accurate characterization of hematopoietic stem cells (HSC) products is needed to better anticipate the hematopoietic reconstitution and the outcome in patients. Although CD34+ viable cells enumeration is a key predictor of time to correction of aplasia, it does not fully inform about functionality of cells contained in the graft. CFU assay is the gold standard in vitro potency assay to assess clonogenicity of HSC and consists on the count and identification of colonies several days after culture in a semi solid media. Manual count of colonies with optic microscope is the most commonly used method but its important variability and subjectivity hinders the universal implementation of this potency assay. The aim of this study is to validate a standardized method using the STEMvision™ system, the first semi-automated instrument for imaging and scoring hematopoietic colonies, according to French and European recommendations. Results obtained highlight better performance criteria with STEMvision™ system than the manual method. This semi-automatic device tends to reduce the coefficients of variation of repeatability, inter-operator variability and intermediate precision. This newly available platform could represent an interesting option, significantly improving performances of CFU assays used for the characterization of hematopoietic progenitors.

The influence of temperature treatment before cryopreservation on the viability and potency of cryopreserved and thawed CD34+ and CD45+ cord blood cells

BACKGROUND

Hematopoietic stem cell (HSC) viability and potency is crucial for qualified cord blood (CB) transplants. This study analyzes time and temperature condition before cryopreservation for the viability of CD34⁺/CD45⁺ cells after cryopreservation.

METHODS

Cell viabilities were determined by antibody co-staining with 7-aminoactinomycin D detecting necrotic cells, and subsequent flow cytometric analysis. Additionally, Annexin V staining for determination of apoptotic cells and colony-forming unit (CFU) assays for testing functional potency of HSCs were performed.

RESULTS

For all cell types assessed (CD45⁺/CD34⁺ cells, lymphocytes and granulocytes), the highest viabilities were obtained for CB maintained at 4°C or room temperature (RT; 22 ± 4°C) and cryopreserved directly after collection. Starting material were CB units with an age of 24.7 ± 3.5 h after birth. Post-thaw CD34⁺ cell results were > 90% after temperature treatment of t = 24 h (48 h total age) and > 70% after t = 48 h (72 h total age) at 4°C (48 h, 91.4 ± 5.5%; 72 h, 75.0 ± 12.0%) and RT (48 h, 84.2 ± 9.7%; 72 h, 72.6 ± 0.6%). Viabilities for 30°C samples were < 80% after t = 24 h (48 h total age, 79.8 ± 3.1%) and < 50% after t = 48 h of treatment (72 h total age, 46.8 ± 14.3%). Regarding CFU recovery of pre-freeze (without volume reduction) and thawed CB, a trend toward the highest recoveries was observed at 4°C/RT. The difference between 4°C (77.5 ± 12.0%) and 30°C samples (53.9 ± 4.8%) was shown to be significant in post-thaw samples after t = 24 h treatment (48 h total age; P = 0.0341).

DISCUSSION

Delays between collection and cryopreservation should be minimized because increasing time reduces numbers of viable cells and CFUs before/after cryopreservation. CB units should be maintained at 4°C/RT to retain the highest possible potency of the cells after thawing.

Quality and exploitation of umbilical cord blood for cell therapy: Are we beyond our capabilities?

There is increasing interest in identifying novel stem cell sources for application in emerging cell therapies. In this context, umbilical cord blood (UCB) shows great promise in multiple clinical settings. The number of UCB banks has therefore increased worldwide, with the objective of preserving potentially life-saving cells that are usually discarded after birth. After a rather long and costly processing procedure, the resultant UCB-derived cell products are cryopreserved until transplantation to patients. However, in many cases, only a small proportion of administered cells engraft successfully. Thus, can we do any better regarding current UCB-based therapeutic approaches? Here we discuss concerns about the use of UCB that are not critically pondered by researchers, clinicians, and banking services, including wasting samples with small volumes and the need for more reliable quality and functional controls to ensure the biological activity of stem cells and subsequent engraftment and treatment efficacy. Finally, we appeal for collaborative agreements between research institutions and UCB banks in order to redirect currently discarded small-volume UCB units for basic and clinical research purposes. Developmental Dynamics 245:710-717, 2016. © 2016 Wiley Periodicals, Inc.

Cord blood collection and processing with hydroxyethyl starch or non-hydroxyethyl starch

BACKGROUND

Collection and processing characteristics influencing quality of cord blood (CB) units play an essential role to cord blood banks (CBBs). At many CBBs, volume reduction is performed using hydroxyethyl starch (HES) and the Sepax (Biosafe) automated cell processing system. Due to the withdrawal of HES from the European market, a validation of the nonHES protocol was performed.

METHODS

This partially retrospective study identified CB characteristics such as gestational age and CB volume/cell count correlated with higher quality. For the nonHES validation, CB was analyzed for total nucleated cell (TNC), mononuclear cell (MNC) recovery, hematocrit (HCT) and colony-forming units (CFUs). Viabilities of CD34(+) and CD45(+) cells were determined by 7-aminoactinomycin D (7-AAD) and AnnexinV (AnnV) staining and compared for 21 mL and 42 mL buffy coat (BC) samples applying the HES/nonHES protocol.

RESULTS

Factors affecting the potency of CB transplants were the gestational age and the volume reduction to a defined BC volume. High initial cell counts and CB volumes correlated negatively with post-processing TNC recovery for lower BC volumes. Post-processing HES and nonHES results were comparable, but nonHES revealed a significantly lower post-thaw recovery of viable CD34(+) cells measured by 7-AAD/AnnV (21 mL: 45.4 ± 16.4%; 42 mL: 67.3 ± 14.5%) as compared with HES (21 mL: 72.7 ± 14.4%, P = 0.0164; 42 mL: 83.4 ± 14.7%, P = 0.0203).

DISCUSSION

Due to the lower post-thaw CD34(+) cell viability (AnnV(-)/7-AAD(-)) for nonHES samples, the use of HES is recommended, ideally combined with a high BC volume. The post-processing HCT has no statistically significant impact on the post-thaw CD34(+) cell viability (AnnV(-)/7-AAD(-)).

Relevance of flow cytometric enumeration of post-thaw leucocytes: influence of temperature during cell staining on viable cell recovery

BACKGROUND AND OBJECTIVES

Our post-thaw cell recovery rates differed substantially in interlaboratory comparisons of identical samples, potentially due to different temperatures during cell staining.

MATERIALS AND METHODS

Viable CD34(+) cells and leucocyte (WBC) subtypes were quantified by multiparameter single-platform flow cytometry in leucapheresis products collected from 30 adult lymphoma and myeloma patients, and from 10 paediatric patients. After thawing, cells were prepared for analysis within 30 min between thawing and acquisition, at either 4°C or at room temperature.

RESULTS

For cell products cryopreserved in conventional freezing medium (10% final DMSO), viable cell recovery was clearly lower after staining at 4°C than at RT. Of all WBC subtypes analysed, CD4(+) T cells showed the lowest median recovery of 4% (4°C) vs. 25% (RT), followed by CD3, CD34 and CD8 cells. The recovery was highest for CD3γδ cells with 44% (4°C) vs. 71% (RT). In the 10 samples cryopreserved in synthetic freezing medium (5% final DMSO), median recovery rates were 89% for viable CD34 (both at 4°C and RT) and 79% (4°C) vs 68% (RT) for WBC.

CONCLUSIONS

The post-thaw environment and, potentially, the cryoprotectant impact the outcome of cell enumeration, and results from the analysis tube may not be representative of the cells infused into a patient.

Improving Quality and Potency Testing for Umbilical Cord Blood: A New Perspective

This article critically reviews current methods to test and characterize umbilical cord blood (UCB) for hematopoietic stem cell transplantation. These tests include total nucleated cell (TNC) count, viability, viable CD34-positive content, and the colony-forming unit assay. It is assumed that the data obtained are sufficient to perform a UCB stem cell transplant without actually determining the quality and potency of the stem cells responsible for engraftment. This assumption has led not only to a high graft failure rate attributed to low or lack of potency, but also to noncompliance with present statutes that require UCB stem cells to be of high quality and, indeed, potency for a transplant to be successful. New evidence now calls into question the quality of the data, based on the UCB processed TNC fraction because using this impure fraction masks and significantly underestimates the functionality of the stem cells in both the segment and the unit. It is proposed that UCB units should be processed to the mononuclear cell fraction and that new cost-effective technology that measures the quality and potency of UCB stem cells be implemented to achieve better practices in UCB testing. These changes would provide the transplant physician with the assurance that the stem cells will perform as intended and would reduce risk and increase safety and efficacy for the patient.

SIGNIFICANCE

Current stem cell transplantation of umbilical cord blood cells requires testing that includes four basic parameters that do not determine whether the stem cells are of high quality, as required by the Stem Cell Therapeutic and Research Act of 2005. No cord blood units collected or transplanted so far have been tested for stem cell quality or potency. New scientific evidence calls into question cord blood processing and testing practices required by regulatory agencies and standards organizations. A new perspective is described that includes stem cell quality and potency testing that could reduce graft failure rates.

Detecting primitive hematopoietic stem cells in total nucleated and mononuclear cell fractions from umbilical cord blood segments and units

BACKGROUND

Rare hematopoietic stem cell populations are responsible for the transplantation engraftment process. Umbilical cord blood (UCB) is usually processed to the total nucleated cell (TNC), but not to the mononuclear cell (MNC) fraction. TNC counts are used to determine UCB unit storage, release for transplantation and correlation with time to engraftment. However, the TNC fraction contains varying concentrations of red blood cells, granulocytes, platelets and other cells that dilute and mask the stem cells from being detected. This does not allow the quality and potency of the stem cells to be reliably measured.

METHODS

63 UCB segments and 10 UCB units plus segments were analyzed for the response of both primitive lympho-hematopoietic and primitive hematopoietic stem cells in both the TNC and MNC fractions. The samples were analyzed using a highly sensitive, standardized and validated adenosine triphosphate (ATP) bioluminescence stem cell proliferation assay verified against the colony-forming unit (CFU) assay. Dye exclusion and metabolic viability were also determined.

RESULTS

Regardless of whether the cells were derived from a segment or unit, the TNC fraction always produced a significantly lower and more variable stem cell response than that derived from the MNC fraction. Routine dye exclusion cell viability did not correspond with metabolic viability and stem cell response. Paired UCB segments produced highly variable results, and the UCB segment did not produce similar results to the unit.

DISCUSSION

The TNC fraction underestimates the ability and capacity of the stem cells in both the UCB segment and unit and therefore provides an erroneous interpretation of the of the results. Dye exclusion viability can result in false positive values, when in fact the stem cells may be dead or incapable of proliferation. The difference in response between the segment and unit calls into question the ability to use the segment as a representative sample of the UCB unit. It is apparent that present UCB processing and testing methods are inadequate to properly determine the quality and potency of the unit for release and use in a patient.

Dominant unit CD34+ cell dose predicts engraftment after double-unit cord blood transplantation and is influenced by bank practice

We investigated the unit characteristics associated with engraftment after double-unit cord blood (CB) transplantation (dCBT) and whether these could be reliably identified during unit selection. Cumulative incidence of neutrophil engraftment in 129 myeloablative dCBT recipients was 95% (95% confidence interval: 90-98%). When precryopreservation characteristics were analyzed, the dominant unit CD34(+) cell dose was the only characteristic independently associated with engraftment (hazard ratio, 1.43; P = .002). When postthaw characteristics were also included, only dominant unit infused viable CD34(+) cell dose independently predicted engraftment (hazard ratio, 1.95; P < .001). We then examined the determinants of infused viable CD34(+) cell dose (precryopreservation count, postthaw recovery, and postthaw viability) in 402 units thawed at our center. This revealed close correlation between precryopreservation and postthaw CD34(+) cell counts (r(2) = 0.73). Median CD34(+) cell recovery was 101%, although it ranged from 12% to 1480%. Notably, units from non-Netcord Foundation for the Accreditation of Cellular Therapy (Netcord-FACT)-accredited banks were more likely to have low recovery (P < .001). Furthermore, although median postthaw CD34(+) cell viability was 92%, 33 (8%) units had <75% viable CD34(+) cells. Units from non-Netcord-FACT-accredited banks and units with cryovolumes other than 24.5 to 26.0 mL were more likely to have poor postthaw viability. Precryopreservation CD34(+) cell dose and banking practices should be incorporated into CB unit selection.

Current practices and prospects for standardization of the hematopoietic colony-forming unit assay: a report by the cellular therapy team of the Biomedical Excellence for Safer Transfusion (BEST) Collaborative

BACKGROUND AIMS

Wide acceptance of the colony-forming unit (CFU) assay as a reliable potency test for stem cell products is hindered by poor inter-laboratory reproducibility. The goal of this study was to ascertain current laboratory practices for performing the CFU assay with an eye towards identifying practices that could be standardized to improve overall reproducibility.

METHODS

A survey to evaluate current laboratory practices for performing CFU assays was designed and internationally distributed.

RESULTS

There were 105 respondents to the survey, of whom 68% performed CFU assays. Most survey recipients specified that an automated rather than a manual cell count was performed on pre-diluted aliquots of stem cell products. Viability testing methods employed various stains, and when multiple sites used the same viability stain, the methods differed. Cell phenotype used to prepare working cell suspensions for inoculating the CFU assay differed among sites. Most respondents scored CFU assays at 14-16 days of incubation, but culture plates were read with various microscopes. Of 57 respondents, 42% had not performed a validation study or established assay linearity. Only 63% of laboratories had criteria for determining if a plate was overgrown with colonies.

CONCLUSIONS

Survey results revealed inconsistent inter-laboratory practices for performing the CFU assay. The relatively low number of centers with validated CFU assays raises concerns about assay accuracy and emphasizes a need to establish central standards. The survey results shed light on numerous steps of the methodology that could be targeted for standardization across laboratories.

The Assessment of Parameters Affecting the Quality of Cord Blood by the Appliance of the Annexin V Staining Method and Correlation with CFU Assays

The assessment of nonviable haematopoietic cells by Annexin V staining method in flow cytometry has recently been published by Duggleby et al. Resulting in a better correlation with the observed colony formation in methylcellulose assays than the standard ISHAGE protocol, it presents a promising method to predict cord blood potency. Herein, we applied this method for examining the parameters during processing which potentially could affect cord blood viability. We could verify that the current standards regarding time and temperature are sufficient, since no significant difference was observed within 48 hours or in storage at 4°C up to 26°C. However, the addition of DMSO for cryopreservation alone leads to an inevitable increase in nonviable haematopoietic stem cells from initially 14.8% ± 4.3% to at least 30.6% ± 5.5%. Furthermore, CFU-assays with varied seeding density were performed in order to evaluate the applicability as a quantitative method. The results revealed that only in a narrow range reproducible clonogenic efficiency (ClonE) could be assessed, giving at least a semiquantitative estimation. We conclude that both Annexin V staining method and CFU-assays with defined seeding density are reliable means leading to a better prediction of the final potency. Especially Annexin V, due to its fast readout, is a practical tool for examining and optimising specific steps in processing, while CFU-assays add a functional confirmation.

Cord blood banking activities at a university hospital in northeast Mexico: an 8-year experience

BACKGROUND

Umbilical cord blood (UCB) represents an alternative source of stem cells for transplantation for the treatment of hematologic malignancies and genetic disorders. There is scarce information detailing cord blood bank (CBB) collection and transplantation activities from developing countries. We documented our experience at a public university hospital in northeast Mexico.

STUDY DESIGN AND METHODS

We carried out a retrospective and descriptive analysis of our CBB activity during an 8-year period from May 2002 to September 2010. Collection, processing, and cryopreservation of CB were carried out following standard operating procedures. The minimum volume and total nucleated cell (TNC) content for cryopreservation were 80 mL and 8.0 × 10(8) , respectively.

RESULTS

A total of 1256 UCB units were collected; 428 (34%) were banked and 828 (66%) were discarded. The main reason for exclusion was biologic: low volume and/or low number of TNC accounted for 84% of the total discarded units. Cryopreserved cord blood units (CBUs) had a median volume of 113.8 mL (range, 80-213.2 mL) and 13.0 × 10(8) (range, 8 × 10(8) -36.6 × 10(8) ) TNCs. Cell viability was 99.3% (88-100%). The median CD34+ cell content was 4.0 × 10(6) (0.46 × 10(6) -19.38 × 10(6) ). Sixteen units have been released for transplantation, leading to a utilization rate of 3.7%.

CONCLUSION

CBB demands considerable human and financial resources; it is then essential for centers at developing countries to share their experience, results, and databases to increase the probability of finding matching units for their patients. Efforts to create and maintain CBBs allow to offer this therapeutic option at an affordable cost.

The use of back-up units to enhance the safety of unrelated donor cord blood transplantation

The inability to obtain additional stem cells is a disadvantage of unrelated donor cord blood transplantation (CBT). Moreover, in the event of problems with unit shipment, compromised unit quality, thaw mishaps, or graft failure, the time to secure a back-up graft could be unacceptable. Emergent shipment of 1 to 2 back-up units that have been previously typed and reserved could overcome this limitation. However, the advantages of this approach are not established. Therefore, we present our use of back-up units over a 5.5-year period. Six of 121 CBT recipients (5%) required back-up unit infusion. Indications included shipment mishaps (n = 2), poor unit viability (n = 2), significant infusion reaction (n = 1), and graft failure (n = 1). Lack of back-up units would have caused transplantation delay or infusion of inferior-quality units. Five of the 6 patients achieved sustained donor engraftment. We demonstrate that back-up units are emergently required in a significant minority of patients, supporting the incorporation of at least 1 back-up unit in cord blood (CB) selection algorithms to enhance CBT safety.