Repopulating activities of human cord blood cells separated by a stem cell collection filter in NOD/SCID mice: a comparative study of filter method and HES method

A simple filtration system for red blood cell depletion and volume reduction in routine processing of human umbilical cord blood

BACKGROUND AND OBJECTIVES

Currently, stem cells and other progenitor cells are obtained from human umbilical cord blood (HUCB) using a variety of methods that are designed primarily for red blood cell depletion and volume reduction prior to freezing and storage. Some of these methods are very cumbersome and involve several steps that may result in significant cell loss. Therefore, processes that minimize the loss of haematopoietic stem and progenitor cells (HSPC) remains very critical. In the present study, we describe a simple filtration process for achieving both volume reduction and red blood cell depletion in a 'closed sterile system' with significant recovery of viable HSPC.

MATERIALS AND METHODS

About 80-100 ml of HUCB were collected into citrate-phosphate-dextrose-adenine 1 anticoagulant. Each HUCB was divided into 25-70-ml aliquots and then either diluted with isotonic saline or filtered without any prior dilution with an experimental Red Cell Volume Reduction System (RCVRS). The HSPCs were recovered by retrograde rinsing of the filter with an isotonic stem cell recovery solution. The viability, colony forming properties, leucocytes and CD34+ cells recoveries were determined.

RESULTS

The mean volume of the HUCB before processing was reduced from 43.9 +/- 7.9 ml to 11.8 +/- 0.7 ml (n = 55) with red blood cell depletion of 85.2 +/- 3.7%. Diluting the HUCB with isotonic saline prior to processing with RCVRS increased the red blood cell depletion to 91.9 +/- 3.0% (n = 7) without any significant loss in viability or cell recovery. The mean viability of the RCVRS-processed HUCB was not significantly different from the control unprocessed blood (96.60 +/- 1.90 vs. 96.63 +/- 2.12%; P > 0.05). The mean recoveries of the CD34+ and the haematopoietic clonogenic progenitor cells with the filter were 83.9 +/- 26.8 (n = 40) and 99.9 +/- 27.9% (n = 35), respectively.

CONCLUSION

The present results show that the RCVRS provides a simple and easy-to-use process for obtaining red blood cell depletion and volume reduction of HUCB with good cell viability and recoveries.

SCID-repopulating activity of human umbilical cord blood-derived hematopoietic stem and/or progenitor cells in a nonobese diabetic/Shi-SCID mice serial xenotransplantation model and immune cell activities in vitro: a comparative study of the filter method and the hydroxyethyl starch method

BACKGROUND

A novel filter system was developed for umbilical cord blood (UCB) volume reduction. The aim of this study was to compare the functions of cryopreserved UCB cells processed by the filter and by the hydroxyethyl starch (HES) sedimentation method from the aspect of the graft quality.

STUDY DESIGN AND METHODS

UCB specimens were divided into two portions, processed in parallel by the filter or HES, and then cryopreserved in the clinical setting. The thawed UCB specimens containing 1 x 10(5) CD34+ cells were injected into nonobese diabetic/Shi-SCID mice, and the engraftment capacity in primary and secondary transplants was assessed. The functions of natural killer (NK) cells and monocyte-derived dendritic cells (DCs) were also assayed in vitro.

RESULTS

The percentage of recovery of CD34+ cells by both methods was equivalent. In the marrow of the primary transplant recipients, the percentage of hCD45+ cells in the filter group and HES group was 58.2 +/- 31.6 and 46.5 +/- 28.4 percent, respectively (p = 0.016). The engraftment capacity and multilineage differentiation in the secondary transplantations were equal in both groups. The cytotoxic activity of the NK cells and phagocytosis activity of the DCs from both the groups were similar.

CONCLUSION

The filter yielded a desirable percentage of recovery of hematopoietic cells with engraftment ability in the clinical setting. Thus, it is considered that the filter system may be useful for UCB banking for cord blood transplantation.

Multi-laboratory evaluation of procedures for reducing the volume of cord blood: influence on cell recoveries

BACKGROUND

Various procedures can be used to isolate stem and progenitor cells from cord blood. This study evaluated the hydroxyethyl starch sedimentation (HES) with two centrifugation steps, and the top and bottom (T&B) isolation of buffy coat following a single centrifugation, and two filter systems for processing cord blood, one developed by Asahi Kasei Medical (filter A) and the second by Terumo (filter B).

METHODS

Each of seven laboratories was randomly assigned the evaluation of either the HES or T&B method and one of the filter methods (n=8 cord blood units, per laboratory, for each method). The leukocyte-containing fraction with the stem/progenitor cells was recovered from the filters by reverse flushing. Utilizing the routine traditional processing and testing procedures of each laboratory, in vitro parameters were determined, with samples obtained after collection, after processing and after freezing/thawing. The results were expressed as the percentage recovery of viable cells in processed vs. collected samples (performance 1; PF1) and in thawed vs. processed samples (performance 2; PF2). The composite results obtained by the seven laboratories were summarized.

RESULTS

The median PF1 percentage recovery of total nucleated cells (TNC) was comparable with both traditional methods (HES 79%, T&B 86%) and statistically reduced with both filtration procedures (filter A 58%, filter B 61%). Mononuclear cell (MNC) PF1 recovery was highest statistically with the T&B method (91%) and reduced on using filter A (77%) and filter B (70%) and the HES method (72%). CD34+ cell recovery was judged to be essentially comparable with the four methods, although the range of unit recoveries differed. The percentage recovery of TNC and MNC in PF1 was influenced by the volume of the collected cord blood, especially with use of the filtration procedures. This correlated with TNC content. A greater percentage of red cells and platelets was removed during processing with both filter methods. The time to process cord blood preparations with filter A was significantly shorter than the other methods. Processing with the HES method took the longest time. The recoveries for TNC, MNC and CD34+ cells in PF2 did not appear to be influenced by the specific processing procedure.

DISCUSSION

These data indicate that filters that capture stem and progenitor cells may be an appropriate methodology for processing cord blood collected for banking.

Analysis of leukocyte binding to depletion filters: role of passive binding, interaction with platelets, and plasma components

Since limited knowledge exists on the mechanisms which regulate cell binding to leukocyte removal filter surfaces, we investigated the binding patterns of leukocytes to individual layers of leukocyte depletion filters. After passage of 1 unit of whole blood, blotting of isolated filter layers on glass slides or elution of cells from filter layers revealed that most leukocytes were located within the first 10 of a total of 28 filter layers, peaking at layers 6 to 8, with granulocytes binding on average to earlier filter layers than lymphocytes. Leukocytes preincubated with inhibitors of actin activation showed unchanged distribution between filter layers, suggesting that cytoskeletal activation does not significantly contribute to their binding. When leukocytes were directly incubated with single filter layers, binding of up to 30% of input cells was recorded in the absence of Ca(2+). Immunohistological analyses showed colocalization of platelets and leukocytes, with co-clustering of platelets and leukocytes. Monocytes and to some degree lymphocytes but not granulocytes competed with platelets for filter binding. Precoating of filter layers with individual plasma components showed that hyaluronic acid, plasma type fibronectin, and fibrinogen all increased the binding of leukocytes compared with albumin coating. In conclusion, leukocytes can bind passively to filters in a process which does not require Ca(2+), which is independent of cytoskeletal activation and which may depend on individual plasma components. These results are of importance when new selective cell enrichment or depletion strategies through specific filters are envisaged.

Engraftment capacity of umbilical cord blood cells processed by either whole blood preparation or filtration

Umbilical cord blood (UCB) preparation needs to be optimized in order to develop more simplified procedures for volume reduction, as well as to reduce the amount of contaminating cells within the final stem cell transplant. We evaluated a novel filter device (StemQuick((TM))E) and compared it with our routine buffy coat (BC) preparation procedure for the enrichment of hematopoietic progenitor cells (HPCs). Two groups of single or pooled UCB units were filtered (each n = 6), or equally divided in two halves and processed by filtration and BC preparation in parallel (n = 10). The engraftment capacity of UCB samples processed by whole blood (WB) preparation was compared with paired samples processed by filtration in the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse animal model. Filtration of UCB units in the two groups with a mean volume of 87.8 and 120.7 ml, respectively, and nucleated cell (NC) content of 9.7 and 23.8 x 10(8) resulted in a sufficient mean cell recovery for mononucleated cells ([MNCs] 74.2%-77.5%), CD34(+) cells (76.3%-79.0%), and colony-forming cells (64.1%-86.3%). Moreover, we detected a relevant depletion of the transplants for RBCs (89.2%-90.0%) and platelets ([PLTs] 77.5%-86.1%). In contrast, the mean depletion rate using BC processing proved to be significantly different for PLTs (10%, p = 0.03) and RBCs (39.6%, p < 0.01). The NC composition showed a highly significant increase in MNCs and a decrease in granulocytes after filtration (p < 0.01), compared with a less significant MNC increase in the BC group (p < 0.05). For mice transplanted with WB-derived progenitors, we observed a mean of 15.3% +/- 15.5% of human CD45(+) cells within the BM compared with 19.9% +/- 16.8% for mice transplanted with filter samples (p = 0.03). The mean percentage of human CD34(+) cells was 4.2% +/- 3.1% for WB samples and 4.5% +/- 3.2% for filter samples (p = 0.68). As the data of NOD/SCID mice transplantation demonstrated a significant engraftment capacity of HPCs processed by filtration, no negative effect on the engraftment potential of filtered UCB cells versus non-volume-reduced cells from WB transplants was found. The StemQuick((TM))E filter devices proved to be a useful tool for Good Manufacturing Practices conform enrichment of HPCs and MNCs out of UCB. Filtration enables a quick and standardized preparation of a volume-reduced UCB transplant, including a partial depletion of granulocytes, RBCs, and PLTs without the need for centrifugation. Therefore, it seems very probable that filter-processed UCB transplants will also result in sufficient hematopoietic reconstitution in humans.

Nonobese diabetic-severe combined immunodeficient mice transplantation of volume-reduced and thawed umbilical cord blood transplants following closed-system immunomagnetic cell selection

BACKGROUND

Protocols for the expansion of human umbilical cord blood (UCB) progenitors begin with the selection of CD34+ cells from stored frozen and thawed units. Use of an immunomagnetic selection procedure within a closed blood bag system for volume-reduced UCB transplants was evaluated, and the influence of CD34 cell selection on in vivo engraftment potential was studied.

STUDY DESIGN AND METHODS

Eleven thawed buffy coat-processed UCB units were processed within a standard blood bag with a washing solution. In six independent experiments, the same dosage of 2 x 104 CD34+ cells from paired selected and nonselected samples was transplanted into NOD-SCID mice. In two experiments, cells from the negative fraction were also transplanted.

RESULTS

The purity of CD34+ cells after selection was correlated with the removal of supernatant after the first washing step and therefore with adequate removal of damaged or dead cells (r=0.86, p < 0.01). Mice transplanted with unselected UCB cells had more human cells within their marrow than animals transplanted with selected cells (8.6 +/- 5.9% selected group vs. 19.8 +/- 14.2% unselected group; p=0.04), whereas no engraftment could be observed transplanting cells from the two negative fractions. A higher percentage of human CD45+ cells in the unselected group were found to be positive for CD38, CD14, CD33, and CD19, indicating a higher potential for these unselected progenitors to differentiate into myeloid cells and B cells.

CONCLUSIONS

Processing of volume-reduced and thawed UCB transplants within a closed-bag system before immunomagnetic CD34+ cell selection allows for the preparation of CD34+ cells of significant purity at technically useful cell recoveries. However, these experiments indicate a potential impairment of engraftment capacity for the CD34+ cell-enriched fraction.