Hematopoietic progenitor cells are resistant to dimethyl sulfoxide toxicity

Pros and Cons of Cryopreserving Allogeneic Stem Cell Products

The COVID-19 pandemic has precipitously changed the practice of transplanting fresh allografts. The safety measures adopted during the pandemic prompted the near-universal graft cryopreservation. However, the influence of cryopreserving allogeneic grafts on long-term transplant outcomes has emerged only in the most recent literature. In this review, the basic principles of cell cryopreservation are revised and the effects of cryopreservation on the different graft components are carefully reexamined. Finally, a literature revision on studies comparing transplant outcomes in patients receiving cryopreserved and fresh grafts is illustrated.

Safety of Cryopreserved Stem Cell Infusion through a Peripherally Inserted Central Venous Catheter

The management of patients undergoing stem cell transplantation requires a multipurpose central venous catheter (CVC) to facilitate drug administration, parenteral nutrition, transfusion of blood products, and collection of blood samples. Peripherally inserted central venous catheters (PICCs) appear to meet these requirements but are rarely used for stem cell infusion. We aimed to retrospectively assess the safety and feasibility of stem cell infusion through PICC and to evaluate its impact on transplantation kinetics. We retrospectively analyzed the outcomes of peripheral blood stem cell (PBSC) transplantation in patients receiving cryopreserved autologous or allogeneic PBSC by PICCs and compared the results with patients receiving transplants through a conventionally inserted central venous catheter (CICC). Despite statistically significant differences in CD34⁺ dose, infusion rate, and total length of administration, the clinical outcomes of transplantation, exemplified by platelet and neutrophil engraftment, along with the length of hospitalization, were not affected by the prolonged infusion time and lower infusion velocity in the PICC group. Our study showed that the clinical outcomes of PBSC transplantation did not differ between the PICC and CICC groups, suggesting that both types of catheters can be implemented in a PBSC transplantation setting.

Reduced dimethyl sulfoxide concentrations successfully cryopreserve human hematopoietic stem cells with multi-lineage long-term engraftment ability in mice

BACKGROUND AIMS

The cryopreservation of hematopoietic stem cells (HSCs) in dimethyl sulfoxide (DMSO) is used widely, but DMSO toxicity in transplant patients and the effects of DMSO on the normal function of cryopreserved cells are concerns. To address these issues, in vitro and clinical studies have explored using reduced concentrations of DMSO for cryopreservation. However, the effect of reducing DMSO concentration on the efficient cryopreservation of HSCs has not been directly measured.

METHODS

Cryopreservation of human bone marrow using 10%, 7.5% and 5% DMSO concentrations was examined. Cell counting, flow cytometry and colony assays were used to analyze different cell populations. The recovery of stem cells was enumerated using extreme limiting dilution analysis of long-term multi-lineage engraftment in immunodeficient mice. Four different methods of analyzing human engraftment were compared to ascertain stem cell engraftment: (i) engraftment of CD33⁺ myeloid, CD19⁺ B-lymphoid, CD235a⁺ erythroid and CD34⁺ progenitors; (ii) engraftment of the same four populations plus CD41⁺CD42b⁺ platelets; (iii) engraftment of CD34⁺⁺CD133⁺ cells; and (iv) engraftment of CD34⁺⁺CD38^- cells.

RESULTS

Hematopoietic colony-forming, CD34^++/+, CD34⁺⁺CD133⁺ and CD34⁺⁺CD38^- cells were as well preserved with 5% DMSO as they were with the higher concentrations tested. The estimates of stem cell frequencies made in the xenogeneic transplant model did not show any significant detrimental effect of using lower concentrations of DMSO. Comparison of the different methods of gauging stem cell engraftment in mice led to different estimates of stem cell numbers, but overall, all measures found that reduced concentrations of DMSO supported the cryopreservation of HSCs.

CONCLUSION

Cryopreservation of HSCs in DMSO concentrations as low as 5% is effective.

Cryoimmunology: Opportunities and challenges in biomedical science and practice

Autologous and allogeneic cryoimmunological medicine is a brand new branch of biomedical science and clinical practice that examines the features and formation of the immune response to immunogenic properties of normal and malignant biological structures altered by ultralow temperature, as well as specific changes in the structural and functional characteristics of immune cells and tissues after cryopreservation. Cryogenic protein denaturation phenomenon provides important insights into the mechanisms underlying the damage to cryogenic lesions immediately after freeze-thawing sessions in bioscience and medicine applications. The newly formed cryocoagulated protein components (cryomodified protein components) are crucial in cryoimmunology from the perspective of the formation of immunological substances at ultralow temperatures. Dendritic cells and cryocell detritus (cryocell debris) formed in living biological tissue after exposure to ultralow temperature in vivo may be an indication of one of the essential mechanisms involved in the cryoimmunological response of living structures to the impact of ultralow temperature exposure. Hence, the formation of new autologous and allogeneic cryoinduced immunogenic substances is a novel concept in biomedical research globally. Accordingly, this review focuses on issues concerning the peculiarities of the interaction of the immune system with a dominant malignant neoplasm tissue after exposure to subzero temperatures, considering the original cryogenic technical approaches. We present an overview of the state-of-the-art methods of cryoimmunology, and their major developments, past and present. The need for the delineation of structural and functional characteristics of the biological substrates of the immune system after cryopreservation that can be used in adoptive cell therapy, especially in cancer patients, is emphasized.

Dimethyl sulfoxide: a central player since the dawn of cryobiology, is efficacy balanced by toxicity?

Dimethyl sulfoxide (DMSO) is the cryoprotectant of choice for most animal cell systems since the early history of cryopreservation. It has been used for decades in many thousands of cell transplants. These treatments would not have taken place without suitable sources of DMSO that enabled stable and safe storage of bone marrow and blood cells until needed for transfusion. Nevertheless, its effects on cell biology and apparent toxicity in patients have been an ongoing topic of debate, driving the search for less cytotoxic cryoprotectants. This review seeks to place the toxicity of DMSO in context of its effectiveness. It will also consider means of reducing its toxic effects, the alternatives to its use and their readiness for active use in clinical settings.

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.

Cryopreservation and Enumeration of Human Endothelial Progenitor and Endothelial Cells for Clinical Trials

Background

Endothelial progenitor cells (EPC) are markers of endothelial injury and may serve as a surrogate marker for vascular repair in interventional clinical trials. Objectives of this study were to modify a method of isolation of peripheral blood mononuclear cells (PBMC) and enumeration of EPC and mature endothelial cells (EC) from peripheral blood and to evaluate influence of cryopreservation on viability of PBMC and on numbers of EPC and EC.

Patients/Methods

EPC and EC were analyzed in healthy volunteers in freshly isolated PBMC collected in CPT (cell preparation tubes) and in PBMC cryopreserved with: 1) Gibco Recovery^™ Cell Culture Freezing Medium, 2) custom freezing medium. Viability of PBMC was tested using DAPI. EPC were gated for CD45⁻ CD34⁺CD133^+/−VEGFR2^+/− and EC were gated for CD45⁻CD146⁺CD34^+/−VEGFR2^+/−.

Results

Cryopreservation for 7 days at −80°C decreased viable PBMC from 94 ± 0.5% (fresh) to 84 ± 4% (the custom medium) and to 69 ± 8% (Gibco medium), while cryopreservation at −65°C decreased viability to 60 ± 6% (p<0.001, the custom medium) and 49 ± 5% (p<0.001, Gibco medium). In fresh samples early EPC (CD45⁻ CD34⁺CD133⁺VEGFR2⁺) were enumerated as 0.2 ± 0.06%, late EPC(CD45⁻CD146⁺CD34⁺VEGFR²⁺) as 0.6 ± 0.1% and mature EC (CD45⁻CD146⁺CD34⁻VEGFR2⁺) as 0.8 ± 0.3%of live PBMC. Cryopreservation with Gibco and the custom freezing medium at −80°C for 7 days decreased numbers EPC and EC, however, this decrease was not statistically significant.

Conclusions

Our data indicate that cryopreservation at −80°C for 7 days decreases, although not significantly, viability of PBMC and numbers of subsets of EC and EPC. This method may provide an optimized approach to isolation and short-term cryopreservation of subsets of EPC and of mature EC suitable for multicenter trials.

Automated washing of human progenitor cells: evaluation of apoptosis and cell necrosis

BACKGROUND

High-dose chemotherapy followed by reinfusion of autologous stem cells harvested from peripheral blood has been increasingly applied for a variety of disorders. The critical importance of cell dose in the clinical outcome, after transplant, has motivated the need to develop techniques aimed at reducing cell losses and increasing reproducibility.

OBJECTIVES

The aim of this study is to evaluate the efficacy of the Sepax S-100 device to process thawed HPC-A products in comparison with manual procedure.

METHODS/MATERIALS

We have analysed viability, total nucleated cells (TNC), haematopoietic progenitors and CD34+ cells recovery.

RESULTS

The TNC and CD34+ cells recovery in the automatic procedure was of 91.9% (73-100; SD ± 12.60) and 86.7% (69-100; SD ± 10.21), respectively. Instead the recovery of TNC and CD34+ cells using the manual method was of 84.7% (47-100; SD ± 22.9) and 80.29% (23-100; SD ± 25.96). The results, obtained from the assessment of viability of CD34+ both 7-AAD)+ and AnnV+ showed a high percentage of necrosis and apoptosis in this cell subset by using the manual procedure in respect to the Sepax automated system.

CONCLUSION

Overall, our data suggest that the automated washing procedure is safe and suitable for processing of thawed HPC-A products and can be daily used in clinical routine.

The viability of cryopreserved PBPC depends on the DMSO concentration and the concentration of nucleated cells in the graft

BACKGROUND

DMSO is widely used as a cryoprotectant for PBPC. It is desirable to reduce the amount of DMSO without jeopardizing the quality of the stem cell product. The present study was undertaken to investigate whether recovery and survival of CD34+ cells would be significantly altered when PBPC used for autologous transplantations were cryopreserved with four different DMSO concentrations.

METHODS

Apheresis samples of PBPC from 20 consecutive patients were mixed in parallel with 2%, 4%, 5% and 10% DMSO, frozen with identical cell concentrations at a controlled rate, and stored in liquid nitrogen for 6-8 weeks. PBPC samples from 11 consecutive patients were also cryopreserved with two different cell concentrations (150 and 300 x 10(6) nucleated cells/mL) to investigate the effect of increasing the cell concentrations while decreasing the DMSO concentration. The flow cytometric absolute count method, based on ISHAGE guidelines, was used to measure the absolute count of total and viable CD34+ cells in the post-thaw samples.

RESULTS

PBPC cryopreserved at 150 x 10(6) cells/mL with 2% DMSO yielded significantly inferior CD34+ cell recovery (P < 0.001) and survival (P < 0.001) compared with cryopreservation with 4% and 5% DMSO. This was also observed when comparing higher cell concentrations. However, a reduced cell survival (P = 0.02) was observed when the nucleated cell concentration was increased from 150 to 300 x 10(6) cells/mL in samples cryopreserved with 5% DMSO.

DISCUSSION

We conclude that 5% DMSO may be the optimal dose for cryopreserving PBPC as long as the cells have not been concentrated at much more than 200 x 10(6) nucleated cells/mL.

Cryopreservation of hematopoietic stem cells

Stem cell transplantation represents a critical approach for the treatment of many malignant and non-malignant diseases. The foundation for these approaches is the ability to cryopreserve marrow cells for future use. This technique is routinely employed in all autologous settings and is critical for cord blood transplantation. A variety of cryopreservatives have been used with multiple freezing and thawing techniques as outlined in the later chapters. Freezing efficiency has been proven repeatedly and the ability of long-term stored marrow to repopulate has been established. Standard approaches outlined here are used in many labs as the field continues to evolve.

Cryopreservation of hematopoietic and non-hematopoietic stem cells

Recent studies illustrate the potential for improving the cryopreservation of stem cells. Reduced DMSO concentrations in the cryopreservation medium, post thaw washing of cells and increased cell concentration have been actively studied. Standardization of cell processing has led to the study of liquid storage prior to cryopreservation, validation of mechanical (uncontrolled rate freezing) freezing, and cryopreservation bag failure. Finally, the need for the systematic study and optimization of preservation processes has not been fulfilled. As the sources and applications of stem cells (hematopoietic and non-hematopoietic) continue to be developed, the need for effective preservation methods will only grow.

Cell loss and recovery in umbilical cord blood processing: a comparison of postthaw and postwash samples

BACKGROUND

Engraftment after umbilical cord blood (UCB) transplantation is highly dependent on nucleated cell (NC) and CD34+ cell content. Current standard postthaw (PT) processing includes a wash step to remove dimethyl sulfoxide (DMSO), lysed red cells, and stroma. The contribution of the wash step to cell loss and ultimately the dose of cells available for transplant have yet to be systematically reported. This study examines the effect of the wash step as well as that of PT storage on various quality control variables of UCB units.

STUDY DESIGN AND METHODS

Ten units were thawed and washed based on the New York Blood Center method. Samples were removed from each unit at six time points: prefreeze (PF), immediately PT, immediately postwash (PW), and 1, 2, and 5 hours PW. On each sample, total nucleated cell (TNC) count, CD34+ cell enumeration, colony-forming unit (CFU)-granulocyte-macrophage, and viability assays (fluorescence microscopy [acridine orange/propidium iodide, or AO/PI] and flow cytometry [7-aminoactinomycin]) were obtained.

RESULTS

TNC counts decreased PT and at subsequent time points; the PT TNC recovery was 89 percent compared to 82 percent PW (p < 0.01). TNC recovery decreased to 90 percent of PW (82% of PT) values (p < 0.01) and 83 percent of PW (76% of PT) values (p < 0.001), at 2 and 5 hours PW, respectively. CD34+ cell loss PT was not significant. Viability by AO/PI decreased PT and plateaued over time. In contrast, viability by flow cytometry remained higher and increased slightly over time. CFUs were significantly lower PT, recovering PW.

CONCLUSIONS

Our data indicate that the thawing and washing results in a substantial loss of cells, with TNC loss approaching 20 percent when compared with PF counts; the wash step was responsible for nearly half of the cell loss. The reduced PT viability was expected. Elapse of time PW resulted in further loss of NCs but no detectable significant changes in CD34+ cell content and viability and/or CFU.

Evaluation of an automated cell processing device to reduce the dimethyl sulfoxide from hematopoietic grafts after thawing

BACKGROUND

The direct transfusion of thawed hematopoietic progenitor cells (HPCs) is associated to transfusion-related side effects that are thought to be dose-dependent on the infused dimethyl sulfoxide (DMSO). Both the effectiveness of a fully automated cell processing device to washing out DMSO and the effects of DMSO elimination over the recovered cells were evaluated.

STUDY DESIGN AND METHODS

Twenty cryopre-served peripheral blood HPC bags (HPC apheresis [HPC-A]) were thawed and processed for washing with an automated cell-processing device. Viability, colony-forming units (CFUs), and absolute count of recovered cells were evaluated by flow cytometry immediately after washing as well as at different times after washing and compared with a sample taken just after thawing (control) but maintained at 4 degrees C. DMSO content was measured by high-performance liquid chromatography and the osmolarity with an osmometer.

RESULTS

The median recovery of viable total nucleated cells, viable CD34+ cells, and CFU colonies was 89 (range, 74-115), 103 (range, 62-126), and 91 percent (range, 46%-196%), respectively, in the washing group. Recovery of viable CD3+ cells was 97 percent (range, 42%-131%) and CD14+ cells was 82 percent (54%-119%). The percentages of DMSO elimination and osmolarity reduction were 98 (range, 96-99) and 90 percent (range 86%-95%), respectively. Moreover, elimination of the cryoprotectant improved CFU count, viability, and cell recoveries along the time when compared with the control group.

CONCLUSION

Washing out DMSO in thawed HPC-A by use of this approach is safe and efficient in terms of recovery and viability of nucleated and progenitor cells. Additionally, the removal degree of DMSO is very high and therefore might ameliorate the transfusion-related side effects.

A theoretically optimized method for cord blood stem cell cryopreservation

The objective of this study was to develop an optimal cryopreservation method for human umbilical cord blood hematopoietic progenitor cells as evidenced by improved retention of in vivo engraftment ability and multilineage differentiation. An extended understanding of the osmometric/permeability characteristics of cord blood stem cells was accomplished by measuring permeability of the cryoprotectant dimethyl sulfoxide (DMSO) at below-ambient temperatures (10 degrees and 3 degrees C). These data were combined with previously published osmotic and permeability data and the water-NaCl-DMSO phase diagram in conjunction with a mathematical model to determine an optimal initial DMSO concentration, cooling rate, and liquid nitrogen plunging temperature. Cells cryopreserved with the theoretically optimized procedure were then compared with cells frozen using standard methods for the ability to engraft in irradiated NOD/SCID mice. The optimal procedure was determined to include a 0.7 molal (approximately 5%) DMSO concentration at a cooling rate of 4 degrees C/min, and a plunging temperature of -44 degrees C. The optimized protocol resulted in significantly higher engraftment of human CD45(+) cells (17.2 +/- 1.6% vs. 8.4 +/- 1.6%), CD19(+) B lymphocytes (11.3 +/- 1.2% vs. 5.8 +/- 1.2%), and CD34(+) cells (1.9 +/- 0.09% vs. 0.6 +/- 0.09%) compared to cells frozen using a standard method. Engraftment of CD33(+) cells was not significantly different (4.0 +/- 0.3 vs. 3.2 +/- 0.6, respectively). This study demonstrated that the use of a theoretically determined optimal cryopreservation method is superior to standard methods for maintaining UCB PCBs with multilineage repopulation potential in NOD/SCID mice.

No differences in colony formation of peripheral blood stem cells frozen with 5% or 10% dimethyl sulfoxide

High-dose chemotherapy with autologous stem cell rescue usually requires cryopreservation of the cells. For several years, 10% dimethyl sulfoxide (DMSO) has been used as the standard cryoprotectant. Because DMSO infusion can lead to toxic clinical complications in a dose-related manner, we wanted to evaluate if reduction to 5% DMSO would be possible. We have compared colony formation in the myeloid, erythropoietic, and megakaryocyte lineages in peripheral blood progenitor cell (PBPC) samples cryopreserved in parallel with 5% and 10% DMSO. Twenty-seven PBPC samples from patients with malignant diseases were investigated after 3 months of cryopreservation in liquid N(2), and samples from 14 of these patients were investigated after 1 year. A significantly higher colony formation was demonstrated for colony-forming units-erythrocyte (CFU-E) and CFU-granulocyte, erythrocyte, macrophage, megakaryocyte (GEMM) both at 3 months and at 1 year in the 5% samples. For CFU-granulocyte-macrophage (GM) and CFU-megakaryocyte (Mk) no significant difference was demonstrated neither at 3 months nor at 1 year in samples frozen with 5% and 10% DMSO. Also, there was a statistically significant correlation between the CFU-total and CFU-Mk-total, indicating that the CFU-total might be used as an evaluation of megakaryocyte progenitors. Viability testing with the Trypan Blue exclusion test showed that cells cryopreserved in 5% DMSO had significantly higher viability than the cells cryopreserved in 10% DMSO. We conclude that 5% DMSO is at least as good for cryopreservation of small-volume PBPC samples as the conventional 10% DMSO, and our results suggest that the possibility of using 5% DMSO for cryopreservation of autologous PBPC grafts should be further investigated in clinical studies.

Evaluation of the cytotoxicity effect of dimethyl sulfoxide (DMSO) on Caco2/TC7 colon tumor cell cultures

Dimethyl sulfoxide (DMSO) is usually used to solubilize poorly soluble drugs in permeation assays such as that using Caco2 enterocyte-like cells. The objective of this study was to evaluate the toxicity of DMSO on Caco2/TC7 cells and determinate the maximal concentration usable in permeation experiments. Caco2/TC7 cells were cultured for 21 d on 96-well plates for evaluation of toxicity. The determination of lactate dehydrogenase (LDH) release in cell supernatant and the measurement of Neutral Red (NR) uptake are used for cytotoxicity assays. DMSO solutions (0-100%) in Hank's balanced salt solution containing HEPES (25 mM), pH 7.4, were incubated with Caco-2/TC7 cells on 96 well plates. Caco2/TC7 cells were cultured on Transwell-Clear inserts to evaluate the influence of DMSO on the apparent permeability of the paracellular marker mannitol. DMSO 10% did not induce any significant increase in LDH release whereas a significant increase in LDH activity (ANOVA, p<0.05) occurred at a DMSO concentration of 20 to 50%. NR incorporation in viable cells was statistically reduced by 27 to 36% at DMSO concentration of 20% up to 100% (ANOVA, p>0.05). No statistical difference (p<0.05) in apparent mannitol permeability was observed between the control and 10% DMSO groups. In conclusion, at concentrations of up to 10%, DMSO did not produce any significant alteration in apical membrane permeability or on cell-to-cell tight junctional complexes.

Uncontrolled-rate freezing and storage at -80 degrees C, with only 3.5-percent DMSO in cryoprotective solution for 109 autologous peripheral blood progenitor cell transplantations

BACKGROUND

Although controlled-rate freezing and storage in liquid nitrogen are the standard procedure for peripheral blood progenitor cell (PBPC) cryopreservation, uncontrolled-rate freezing and storage at -80 degrees C have been reported.

STUDY DESIGN AND METHODS

The prospective evaluation of 109 autologous PBPC transplantations after uncontrolled-rate freezing and storage at -80 degrees C of apheresis products is reported. The cryoprotectant solution contained final concentrations of 1-percent human serum albumin, 2.5-percent hydroxyethyl starch, and 3.5-percent DMSO.

RESULTS

With in vitro assays, the median recoveries of nucleated cells (NCs), CD34+ cells, CFU-GM, and BFU-E were 60.8 percent (range, 11.2-107.1%), 79.6 percent (6.3-158.1%), 35.6 percent (0.3-149.5%), and 32.6 percent (1.7-151.1%), respectively. The median length of storage was 7 weeks (range, 1-98). The median cell dose, per kg of body weight, given to patients after the preparative regimen was 6.34 x 10(8) NCs (range, 0.02-38.3), 3.77 x 10(6) CD34+ cells (0.23-58.5), and 66.04 x 10(4) CFU-GM (1.38-405.7). The median time to reach 0.5 x 10(9) granulocytes per L, 20 x 10(9) platelets per L, and 50 x 10(9) reticulocytes per L was 11 (range, 0-37), 11 (0-129), and 17 (0-200) days, respectively. Hematopoietic reconstitution did not differ in patients undergoing myeloablative or nonmyeloablative conditioning regimens before transplantation.

CONCLUSION

This simple and less expensive cryopreservation procedure can produce successful engraftment, comparable to that obtained with the standard storage procedure.

Osmometric and permeability characteristics of human placental/umbilical cord blood CD34+ cells and their application to cryopreservation

The transplantation of placental/cord blood-derived HPC (e.g., CD34+ cells) has become a useful treatment for a broad spectrum of malignant and nonmalignant diseases. The ability to cryopreserve this cell type with high efficiency adds considerable flexibility to cord blood transplantation. The purpose of this study was to develop an understanding of the fundamental cryobiologic factors of these cells, including the osmotic/permeability characteristics, and to use a theoretical approach to optimize freezing procedures. To that end, biophysical parameters, including the osmotically inactive cell volume (Vb), hydraulic conductivity (Lp), and cryoprotectant permeability coefficient (P(CPA)) for DMSO and propylene glycol were measured using a modified Coulter Counter (Coulter Electronics, Inc., Hialeah, FL) at 22 degrees C. In addition, the osmotic tolerance of PCB CD34+ cells was assessed using a colony-forming assay. These experimentally determined parameters were used in a mathematical model to predict optimal cryoprotectant addition and removal procedures. The results demonstrate a Vb of 0.32 x V(iso), an average Lp of 0.17 +/- 0.03 (microm/min/atm +/- SD), and a PCPA of 0.94 +/- 0.004 or 1.0 +/- 0.004 cm/min (x10(-3)) for DMSO or propylene glycol, respectively. No significant difference was determined between the two cryoprotectants used. The osmotic tolerance limits were determined to be 200 and 600 mOsm/kg (1.29 and 0.62 x V(iso), respectively). These results indicate potential benefits of modifications to the widely used method of Rubinstein et al. Proc Natl Acad Sci USA 92:10119-10122, 1995) for cord blood CD34+ cell cryopreservation. As opposed to Rubinstein's method in which DMSO is added to cooled cell suspensions over a 15-min interval, our data indicate that better results may be obtained by introducing and removing the cryoprotectant at ambient temperature over 5 min both to increase viability by avoiding unnecessary risks from osmotic shock and to simplify the protocol. In addition, substitution of propylene glycol for DMSO may be of benefit during the actual freezing and thawing process.

Quantification of residual dimethyl sulfoxide in supernatants of haematopoietic stem cells by capillary zone electrophoresis

Dimethyl sulfoxide (DMSO) is a chemical compound that is used to preserve haematopoietic stem cells during freezing at -180 degrees C. As DMSO is largely removed by washing before reinjection of cells into a patient, accidents (notably cardiovascular) are infrequent. The lack of a method for evaluating the residual quantities of this product led us to develop a technique for assaying DMSO by capillary zone electrophoresis without extraction. This simple, rapid and precise technique was applied to the supernatant of cell pellets of thirteen patients before and after washing.

Ex vivo expansion of frozen/thawed CD34+ cells isolated from frozen human apheresis products

Human CD34+ cells purified from frozen mobilized peripheral blood apheresis products (n = 7) were studied immediately (freshly isolated) or refrozen and studied after > 30 days storage in liquid nitrogen (refrozen/thawed). The proliferation and differentiation of freshly isolated or refrozen/thawed CD34+ cells were examined after 10 days of serum-supplemented suspension culture with recombinant human hematopoietic growth factors. The proliferative capacity (fold increase) of the refrozen/thawed CD34+ cells (mean +/- SD, 54.3 +/- 34.3) was comparable to the freshly isolated CD34+ cell cultures (49.0 +/- 42.4). Two-color flow cytometry of the CD34+ cultured cell populations, fresh and refrozen/thawed, displayed typical patterns of neutrophil differentiation into CD15/CD11b neutrophil precursors. The colony-forming ability of freshly isolated and refrozen/thawed CD34+ cells showed no significant differences (p > 0.05) in the total number or type of colony-forming units (CFU-GM, CFU-M, BFU-E, CFU-GEMM) obtained. In addition, the cloning efficiencies of freshly isolated (19.5 +/- 7.6%) and refrozen/thawed CD34+ cells (21.9 +/- 12.7%) were comparable (p = 0.366). These data suggest that CD34+ cells enriched from frozen apheresis blood products can be either used immediately or stored in liquid nitrogen and thawed with minimal effect on their ability to proliferate and differentiate in liquid culture.

A semiautomated technique for volume reduction of stem cell suspensions for autotransplantation

Infusion of thawed cryopreserved autologous stem cells (SC) is associated with a variety of complications due to the presence of dimethyl sulfoxide (DMSO) and free hemoglobin and to volume overload. Commonly, the DMSO is not removed before infusion for fear that prolonged in vitro exposure of the cells to DMSO leads to loss of clonogenic activity. We describe a simple technique for the substantial reduction in volume and DMSO content of bone marrow (BM) and peripheral blood stem cell (PBSC) suspensions. Sixty-five patients were transplanted with thawed, volume-reduced SC cryopreserved according to Stiff et al. Semiautomated volume reduction was performed on a COBE 2991 cell processor. The median volumes of cryopreserved SC were 1152 ml and 933 ml for the pools of PBSC products and the mixed pools of BM and PBSC, respectively, whereas the volume of SC infused was 153 ml (78% reduction). There were no differences in cell recoveries between PBSC and BM (98%). Only 2 patients demonstrated minimal side effects during infusion. A cohort of 16 metastatic breast cancer patients underwent PBSC harvests following chemotherapy/G-CSF priming and subsequent autotransplantation. Median time to an absolute neutrophil count > 500/microliters was 8 days (range 6-14 days), and median time to a platelet count > 20,000/microliters was 11 days (range 6-18 days). Volume reduction of SC products without the risk of graft failure was performed simply and resulted in few complications during infusion.

Autologous peripheral blood progenitor cell transplantation

Harvesting of autologous peripheral blood stem cells (PBSCs) has been facilitated by using currently available, efficient apheresis technology at the time of rebound from chemotherapy while patients are receiving recombinant growth factors, i.e., granulocyte (G) or granulocyte-macrophage (GM) colony stimulating factor (CSF). Ideally pheresis should be done before patients have had extensive stem cell toxins, i.e., alkylating agents or nitrosoureas. This strategy has facilitated the use of high dose chemoradiotherapy given as a single regimen or in a divided dose for patients with solid tumors or hematologic malignancies and results in more rapid engraftment than bone marrow transplantation (BMT). Although there are no assays which measure repopulating stem cells, enumeration of CD34+ cells within PBSCs is a direct and rapid assay which provides an index of both early and late long-term reconstitutive capacity, since it correlates with colony-forming unit (CFU)-GMs, as well as pre-progenitor or delta assays and long-term culture-initiating cells (LTC-IC). A threshold of > or = 2 x 10(6) CD34+ cells/kg recipient body weight has been reported to be required for engraftment, but may vary depending upon the clinical setting. Strategies for mobilization of normal PBSCs also increase tumor cell contamination within PB in the setting of both hematologic malignancies and solid tumors, but the significance of these tumor cells in terms of patient outcome is unclear. Recently isolation of CD34+ cells from PBSCs has been done using magnetic beads or immunoabsorption on columns or rigid plates in order to enrich for normal hematopoietic progenitors and potentially decrease tumor cell contamination. As for other cellular blood components, standards have been developed to assure efficient collection and processing, thawing, and reinfusion, and to maintain optimal PBPC viability. Finally, future directions of clinical research include expansion of hematopoietic progenitor cells ex vivo; use of umbilical cord or placenta as rich sources of progenitor cells; syngeneic hematopoietic stem cell transplantation; related and unrelated allogeneic hematopoietic stem cell transplantation; treatment of infections, i.e., Epstein Barr virus, or tumor relapse after allogeneic BMT using donor PBSC infusions; and gene therapy approaches.