Obtaining of CD34+ cells from healthy blood donors: development of a rapid and efficient procedure using leukoreduction filters

Differential composition and yield of leukocytes isolated from various blood component leukoreduction filters

In Flanders, an estimated 300,000 leukoreduction filters are discarded as biological waste in the blood establishment each year. These filters are a possible source of fresh donor leukocytes for downstream purposes including research. We investigated leukocyte isolation from two types of filters either used for the preparation of platelet concentrates (PC-LRF) or erythrocyte concentrates (EC-LRF). Outcome parameters were leukocyte yield, differential count, turnaround time and effect of storage conditions. Leukocytes were harvested by reverse flow of a buffer solution. Control was the gold standard density gradient centrifugation of buffy coats. Total leukocyte number isolated from PC-LRF (1049 (± 40) x 106) was almost double that of control (632 (± 66) x 106) but the differential count was comparable. Total leukocyte number isolated from EC-LRF (78 (± 9) x 106) was significantly lower than control, but the sample was specifically enriched in granulocytes (81 ± 4%) compared to control (30 ± 1%). Isolation of leukocytes from either PC- or EC-LRF takes 20 min compared to 240 min for control density gradient centrifugation. Leukocyte viability is optimal when harvested on day 1 post donation (95 ± 0.9%) compared to day 3 (76.4 ± 2.4%). In conclusion, our study demonstrates that leukoreduction filters from specific blood component processing are easy to use and present a valuable source for viable leukocytes of all types.

Preparation of clinical-grade WBCs using leukocyte reduction filters

OBJECTIVE

Our goal was to develop a simpler and less expensive method of obtaining human clinical-grade WBCs using an alternative method to continuous leukapheresis. Our purpose for the WBCs is to arm them with rabbit anticancer antibodies for a phase I clinical trial.

METHODS

Using leukocyte reduction filters (LRFs) discarded from the blood bank, we evaluated multiple variables to maximize recovery of WBCs with the lowest contamination of RBCs. Using an optimized protocol, full-scale runs according to FDA current Good Manufacturing Practice (cGMP) standards were completed with immediate filtration of blood obtained from donors participating in our study.

RESULTS

Forward flushing of the filter removed 85% to 95% of residual RBCs and platelets. When backward flushed with 800 mL, 95% of the WBCs recovered were contained in the first 400 mL. The number of recovered WBCs was in the range of 166-211 million/100 mL filtered blood. Subpopulations of WBCs recovered from the LRFs were in the same proportion as the donors' whole blood. Viability of recovered WBCs was 96-99%. Exogenous rabbit antibodies bound well to the recovered WBCs and were retained for at least 5 h without significant reduction. Three full scale runs of WBCs recovered from donor blood filtered through the LRF met all FDA specification of sterility, endotoxin levels, viability and stability.

CONCLUSION

Using LRFs, high quality clinical grade WBCs are readily obtained in quantities of 0.2 to 1.2 billion cells from 100 mL to 450 mL (1 unit) of whole blood.

Leukocyte reduction filters as an alternative source of peripheral blood leukocytes for research

INTRODUCTION

Peripheral blood leukocytes are a suitable cell model for science research. However, blood samples from healthy volunteers are limited in volume and difficult to obtain due to the complexity of volunteer recruitment.

OBJECTIVE

Therefore, it is urgent to find an alternative source of peripheral blood leukocytes.

METHOD

One of the possibilities is the use of leukocyte reduction filters (LRFs) in blood banks that is used for preparation of leukoreduced blood products. More than 90% of the leukocytes are trapped in the leukofilters allowing the desired blood product to pass through.

RESULTS

It has been reported that the biological function of leukocytes collected from the filters are no different from those isolated from buffy coats, leukapheresis products and whole blood (WB) cells. Moreover, LRFs are waste products that are discarded after leukoreduction.

CONCLUSION

Thus, leukofilters represent an economic source of human cell populations that can be used for a variety of investigative purposes, with no cost. In the present study, we reviewed the different usage of LRFs in the research, clinical and commercial applications.

Optimizing the recovery of peripheral blood mononuclear cells trapped in leukoreduction filters - A comparison study

Introduction

The isolation of captured peripheral blood mononuclear cells (PBMNCs) from leukoreduction filters (LRFs) can be of great importance in terms of bringing the lost cells back into use.

Objective

The aim of this study was to evaluate various methods based on their potential to recover the peripheral blood cells from LRFs with a focus on mononuclear cells (MNCs).

Method

For cell isolation from LRFs, three distinct methods (back-flushing, direct and vacuum pump) were compared through the calculation of the yield of isolated MNCs. The viability of extracted cells was determined by the flow cytometry technique. Moreover, the recovered MNCs were characterized regarding the presence of blood stem cell purification. The cell culture, microscopic observation, and immunophenotyping were employed to characterize the blood stem cells (hematopoietic, mesenchymal and progenitor endothelial stem cells).

Results

The yield of isolation obtained in the back-flushing, direct and vacuum pump methods were 17.7 ± 1.28, 17.3 ± 0.96 and 21.2 ± 0.90 percent, respectively. Although the highest potential for total blood cell recovery belonged to the vacuum pump method, the lowest cell viability (85.73 ± 4.84%) was observed in this method. However, the isolation process of the back-flushing and direct methods had less effect on cell viability. The characterization of the isolated MNCs displayed that the dominant positive phenotype was for CD34/CD45, indicating hematopoietic stem cells. In addition, the endothelial stem/progenitor cells were significantly detected as CD31/CD133 positive cells.

Conclusion

According to our results and considering the safety and efficiency potential of each of the applied methods, the back-flushing in comparison with the other methods can be considered a suitable procedure for MNC isolation from LRFs.

Characterization of peripheral blood mononuclear cells isolated using two kinds of leukocyte filters

OBJECTIVE

The objective of this study was to compare the activity and biological function of leukocytes isolated using apheresis platelet leukoreduction system chambers (LRSC), whole blood leukoreduction filters (LRF), and leukocytes in unfiltered peripheral whole blood (WB).

METHODS

Peripheral blood mononuclear cells (PBMCs) and granulocytes were obtained by density gradient centrifugation using recovery filters and WB. Flow cytometry was used to detect the activity, phenotype, and apoptosis ratio of each cell subtype.

RESULTS

The proportion of lymphocytes obtained from PBMCs was similar when using the two different filters as compared to traditional isolation; however, there were significant differences between the monocytes and granulocytes. The phenotypic frequency of lymphocytes was similar, but the apoptosis rate of lymphocytes from the two filters was slightly higher. Additionally, monocytes isolated via the three sources were able to be induced into dendritic cells expressing specific molecules; Granulocytes isolated from the LRF showed a lower purity and a higher level of apoptosis than granulocytes isolated from the WB.

CONCLUSION

Compared with WB, the PBMCs isolated from the filters used in our blood center had no statistical difference in their activity and biological function, but they did differ in the proportion and quantity of monocytes and granulocytes. Our results show that the two filters can be used as an alternative method to collect leukocytes, which solves the problem of an insufficient blood supply for clinical and basic science research. Thus, these filters have significant value beyond their practical use in clinics.

Evaluation of anticancer activity of α-defensins purified from neutrophils trapped in leukoreduction filters

AIMS

The α-defensins or human neutrophil peptides (HNP 1-3) that exist in azurophilic granules are found to have anticancer activity. The pattern of disulfide bonds in α-defensins is crucial for the functional properties. Therefore, synthesis using the chemical and recombinant approaches is a challenging. A safe source for the production of α-defensins can be the use of leukoreduction filters in blood banks that contain large quantities of neutrophils and are discarded after use. The aim of this study was to purify α-defensins from neutrophils trapped in leukofilters and to investigate its anticancer activity.

MATERIALS AND METHODS

Immunoprecipitation was performed to purify α-defensins and the presence of protein was confirmed by Western Blot. The Jurkat T-cell line was incubated with different concentrations (5, 10 and 15 μg/ml) of purified HNP1-3 for 16 h. Cell viability was measured using a WST-1 assay and apoptosis was analyzed for Annexin V/PI markers. Caspase-3/7 activity was determined using fluorescence assay. The effects of purified α-defensins were compared to commercial HNP 1-3.

KEY FINDINGS

Purified HNP 1-3 decreased the viability at 10 and 15 μg/ml and commercial HNP 1-3 at 15 μg/ml concentrations. Following to the purified HNP1-3 treatment, the percentage of Annexin V positive population and caspase-3 activity were significantly increased compared to control (p = 0.000 and p = 0.001, respectively) and commercial HNP1-3 (p = 0.034 and p = 0.018, respectively).

SIGNIFICANCE

Results indicated the anticancer activity of HNP1-3 which can be used as future chemotherapeutic drugs. Furthermore, leukofilters can be considered as economic source for purifying these peptides.

Repopulating hematopoietic stem cells from steady-state blood before and after ex vivo culture are enriched in the CD34+CD133+CXCR4low fraction

The feasibility of ex vivo expansion allows us to consider the steady-state peripheral blood as an alternative source of hematopoietic stem progenitor cells for transplantation when growth factor-induced cell mobilization is contraindicated or inapplicable. Ex vivo expansion dramatically enhances the in vivo reconstituting cell population from steady-state blood. In order to investigate phenotype and the expression of homing molecules, the expression of CD34, CD133, CD90, CD45RA, CD26 and CD9 was determined on sorted CD34⁺ cells according to CXCR4 (“neg”, “low” “bright”) and CD133 expression before and after ex vivo expansion. Hematopoietic stem cell activity was determined in vivo on the basis of hematopoietic repopulation of primary and secondary recipients - NSG immuno-deficient mice. In vivo reconstituting cells in the steady-state blood CD34⁺ cell fraction before expansion belong to the CD133⁺ population and are CXCR4^low or, to a lesser extent, CXCR4^neg, while after ex vivo expansion they are contained only in the CD133⁺CXCR4^low cells. The failure of the CXCR4^bright population to engraft is probably due to the exclusive expression of CD26 by these cells. The limiting-dilution analysis showed that both repopulating cell number and individual proliferative capacity were enhanced by ex vivo expansion. Thus, steady-state peripheral blood cells exhibit a different phenotype compared to mobilized and cord blood cells, as well as to those issued from the bone marrow. These data represent the first phenotypic characterization of steady-state blood cells exhibiting short- and long-term hematopoietic reconstituting potential, which can be expanded ex vivo, a sine qua non for their subsequent use for transplantation.

Fully reduced HMGB1 accelerates the regeneration of multiple tissues by transitioning stem cells to GAlert

While stem cell therapy has become the standard of care for hematological disorders, challenges remain for the treatment of solid organ injuries. Targeting endogenous cells would overcome many hurdles associated with exogenous stem cell therapy. Alarmins are released upon tissue damage, and here we describe how upregulation of a physiological pathway by exogenous administration of a single dose of HMGB1, either locally or systemically, promotes tissue repair by targeting endogenous stem cells. We show that HMGB1 complexed with CXCL12 transitions stem cells that express CXCR4 from G₀ to G_Alert. These primed cells rapidly respond to appropriate activating factors released upon injury. HMGB1 promotes healing even if administered 2 wk before injury, thereby expanding its translational benefit for diverse clinical scenarios.

A major discovery of recent decades has been the existence of stem cells and their potential to repair many, if not most, tissues. With the aging population, many attempts have been made to use exogenous stem cells to promote tissue repair, so far with limited success. An alternative approach, which may be more effective and far less costly, is to promote tissue regeneration by targeting endogenous stem cells. However, ways of enhancing endogenous stem cell function remain poorly defined. Injury leads to the release of danger signals which are known to modulate the immune response, but their role in stem cell-mediated repair in vivo remains to be clarified. Here we show that high mobility group box 1 (HMGB1) is released following fracture in both humans and mice, forms a heterocomplex with CXCL12, and acts via CXCR4 to accelerate skeletal, hematopoietic, and muscle regeneration in vivo. Pretreatment with HMGB1 2 wk before injury also accelerated tissue regeneration, indicating an acquired proregenerative signature. HMGB1 led to sustained increase in cell cycling in vivo, and using Hmgb1^−/− mice we identified the underlying mechanism as the transition of multiple quiescent stem cells from G₀ to G_Alert. HMGB1 also transitions human stem and progenitor cells to G_Alert. Therefore, exogenous HMGB1 may benefit patients in many clinical scenarios, including trauma, chemotherapy, and elective surgery.

Chronic myeloid leukemia progenitor cells require autophagy when leaving hypoxia-induced quiescence

Albeit tyrosine kinase inhibitors anti-Abl used in Chronic Myeloid Leukemia (CML) block the deregulated activity of the Bcr-Abl tyrosine kinase and induce remission in 90% of patients, they do not eradicate immature hematopoietic compartments of leukemic stem cells. To elucidate if autophagy is important for stem cell survival and/or proliferation, we used culture in low oxygen concentration (0.1% O₂ for 7 days) followed back by non-restricted O₂ supply (normoxic culture) to mimic stem cell proliferation and commitment. Knockdown of Atg7 expression, a key player in autophagy, in K562 cell line inhibited autophagy compared to control cells. Upon 7 days at 0.1% O₂ both K562 and K562 shATG7 cells stopped to proliferate and a similar amount of viable cells remained. Back to non-restricted O₂ supply K562 cells proliferate whereas K562 shATG7 cells exhibited strong apoptosis. Using immunomagnetic sorted normal and CML CD34⁺ cells, we inhibited the autophagic process by lentiviral infection expressing shATG7 or using a Vps34 inhibitor. Both, normal and CML CD34⁺ cells either competent or deficient for autophagy stopped to proliferate in hypoxia. Surprisingly, while normal CD34⁺ cells proliferate back to non restricted O₂ supply, the CML CD34⁺ cells deficient for autophagy failed to proliferate. All together, these results suggest that autophagy is required for CML CD34⁺ commitment while it is dispensable for normal CD34 cells.

Steady state peripheral blood provides cells with functional and metabolic characteristics of real hematopoietic stem cells

Hematopoietic stem cells (HSCs), which are located in the bone marrow, also circulate in cord and peripheral blood. Despite high availability, HSCs from steady state peripheral blood (SSPB) are little known and not used for research or cell therapy. We thus aimed to characterize and select HSCs from SSPB by a direct approach with a view to delineating their main functional and metabolic properties and the mechanisms responsible for their maintenance. We chose to work on Side Population (SP) cells which are highly enriched in HSCs in mouse, human bone marrow, and cord blood. However, no SP cells from SSBP have as yet been characterized. Here we showed that SP cells from SSPB exhibited a higher proliferative capacity and generated more clonogenic progenitors than non-SP cells in vitro. Furthermore, xenotransplantation studies on immunodeficient mice demonstrated that SP cells are up to 45 times more enriched in cells with engraftment capacity than non-SP cells. From a cell regulation point of view, we showed that SP activity depended on O₂ concentrations close to those found in HSC niches, an effect which is dependent on both hypoxia-induced factors HIF-1α and HIF-2α. Moreover SP cells displayed a reduced mitochondrial mass and, in particular, a lower mitochondrial activity compared to non-SP cells, while they exhibited a similar level of glucose incorporation. These results provided evidence that SP cells from SSPB displayed properties of very primitive cells and HSC, thus rendering them an interesting model for research and cell therapy.

The early secreted antigenic target of 6 kD of Mycobacterium tuberculosis inhibits the proliferation and differentiation of human peripheral blood CD34+ cells

Abnormalities in hematopoiesis are common in tuberculosis patients and highly prevalent in AIDS patients with tuberculosis coinfection. To explore the potential role of the early secreted antigenic target of 6-kD (ESAT-6) of Mycobacterium tuberculosis (Mtb) in abnormal hematopoiesis in tuberculosis, we studied the effect of ESAT-6 on proliferation and differentiation of in vitro-expanded CD34⁺ cells isolated from the peripheral blood of the healthy donors. ESAT-6 but not control protein antigen 85A (Ag85A) of Mtb inhibited the proliferation of CD34⁺ cell derived peripheral blood stem/progenitor cells (PBSPC) in a dose dependent manner when determined by MTT-assay. ESAT-6 but not Ag85A reduced the number of colony forming cells (CFC) of PBSPC by 60-90% as determined by CFC assay by incubation of CD34⁺ cells in a semi-solid cellulose media in the presence of cytokine cocktail for two weeks. ESAT-6 but not Ag85A increased the percentages of the Annexin-V positive cells and enhanced the cleavage of caspase-3 in PBSPC in a time and dose dependent manner as determined by flow cytometry and Western blot analysis, respectively. ESAT-6 also inhibited murine bone marrow derived non-adherent cell proliferation in response to granulocyte-macrophage colony stimulating factor treatment. We conclude that ESAT-6, an essential virulence factor of Mtb, may contribute to the abnormal hematopoiesis of tuberculosis patients by inhibiting the proliferation and differentiation of hematopoietic cells via apoptosis.