Primitive hematopoietic progenitors within mobilized blood are spared by uncontrolled rate freezing

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.

A Deeper Depth of Response After Salvage Therapy Improves Outcomes of Autologous Stem Cell Transplantation in Relapsed Lymphoma and the Feasibility of Non-controlled Rate Freezing of Peripheral Blood Stem Cells

Background High-dose chemotherapy followed by autologous stem cell transplantation is considered a standard treatment approach for patients with relapsed Hodgkin's lymphoma (HL) and non-Hodgkin lymphoma (NHL). The goal of autologous stem cell transplant in relapsed lymphoma is to achieve long-term disease control, i.e., cure, in contrast to disorders like multiple myeloma, where it only prolongs the duration of remission, progression-free survival, and improves the quality of life. Published outcomes of high-dose therapy and ASCT and the impact of different factors affecting survival in low- to middle-income countries are very limited. Our study analyzed all the autologous stem cell transplants performed in our center over a six-year period to ascertain engraftment, responses, outcomes, and variables that may have impacted transplant outcomes. Methods We conducted a retrospective study including 76 patients from January 2015 to December 2020. Data were retrieved from electronic medical records at Shaukat Khanum Memorial Cancer Hospital and Research Centre, Lahore, Pakistan. Results Out of a total of 82 autologous transplant patients, 76 were eligible for the study, out of which 50 (66%) had HL and 26 (34%) had NHL. The median age was 29 years (range 18-53) and 29 years (range 20-45) for HL and NHL, respectively. The male-to-female ratio was 5:2 and 4:1 for HL and NHL, respectively. The majority had advanced-stage disease, 85% in HL and 75% in NHL. The minimum cell dose infused was 2.5 million CD34+ cells/kg. Median days to platelets and ANC engraftment were 14 and 11 days, respectively. The 30-day transplant-related mortality was 8.9% and 7.4% in HL and NHL, respectively. The 100-day mortality was 15.2% and 11% in HL and NHL, respectively. The two-year disease-free survival (DFS) and overall survival (OS) were 83% and 83%, respectively, in HL patients. The two-year DFS and OS were 78% and 85%, respectively, in NHL patients. Conclusion High-dose therapy and autologous stem cell transplantation in low- to middle-income countries are limited to relatively younger patients, potentially curative conditions such as lymphoma, and predominantly after achieving a complete response to salvage therapy due to limited resources. Due to these factors, our study shows excellent response rates and survival outcomes compared to internationally published data. Engraftment was also excellent and comparable to published data despite the non-controlled rate freezing of peripheral blood stem cells.

Long-Term Cryopreservation of Peripheral Blood Stem Cell Harvest Using Low Concentration (4.35%) Dimethyl Sulfoxide with Methyl Cellulose and Uncontrolled Rate Freezing at -80 °C: An Effective Option in Resource-Limited Settings

Long-term cryopreservation of peripheral blood stem cells (PBSCs) is highly useful in the setting of tandem/multiple transplantations or treatment of relapse in the autologous hematopoietic stem cell transplantation (HSCT) setting. Even in allogeneic HSCT, donor lymphocyte infusions may be stored for months to years if excess stem cells are collected from donors. Cryopreservation is a delicate, complex, and costly procedure, and higher concentrations of dimethyl sulfoxide (DMSO), a commonly used cryoprotectant, can be toxic to cells and cause adverse effects in the recipient during infusions. In this study, we examined the effect of long-term cryopreservation using 4.35% DMSO (as final concentration) with methyl cellulose and uncontrolled rate freezing in a mechanical freezer (-80 °C) on the viability and colony-forming ability of CD34+ human PBSCs. For patients undergoing autologous HSCT, PBSCs were cryopreserved using DMSO (final concentration of 4.35%) with methyl cellulose. The post-thaw viability of PBSCs was determined using Trypan blue exclusion and flow cytometry-based 7-amino-actinomycin-D (FC-7AAD) methods. Concentrations of CD34+ stem cells and immune cell subsets in post-thaw PBSC harvest samples were assessed using multicolor flow cytometry, and the clonogenic potential of post-thaw stem cells was studied using a colony-forming unit (CFU) assay. CD34+ stem cell levels were correlated with the prestorage CD34 levels using the Pearson correlation test. The viability results in the Trypan blue dye exclusion method and the flow cytometry-based method were compared using Bland-Altman plots. We studied 26 PBSC harvest samples with a median cryopreservation duration of 6.6 years (range, 3.8 to 11.5 years). The median viability of post-thaw PBSCs was >80% using both methods, with a weak agreement between them (r = .03; P = .5). The median CD34+ stem cell count in the post-thaw samples was 9.13 × 106/kg (range, .44 to 26.27 × 106/kg). The CFU assay yielded a good proliferation and differentiation potential in post-thaw PBSCs, with a weak correlation between granulocyte macrophage CFU and CD34+ stem cell levels (r = .4; P = .05). Two samples that had been cryopreserved for >8 years showed low viability. Cryopreservation of PBSCs using 4.35% DMSO with methyl cellulose and uncontrolled freezing in a mechanical freezer at -80 °C allows the maintenance of long-term viability of PBSC for up to 8 years.

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.

A bioinspired and chemically defined alternative to dimethyl sulfoxide for the cryopreservation of human hematopoietic stem cells

The cryopreservation of hematopoietic cells using dimethyl sulfoxide (DMSO) and serum is a common procedure used in transplantation. However, DMSO has clinical and biological side effects due to its toxicity, and serum introduces variation and safety risks. Inspired by natural antifreeze proteins, a novel class of ice-interactive cryoprotectants was developed. The corresponding DMSO-, protein-, and serum-free cryopreservation media candidates were screened through a series of biological assays using human cell lines, peripheral blood cells, and bone marrow cells. XT-Thrive-A and XT-Thrive-B were identified as lead candidates to rival cryopreservation with 10% DMSO in serum based on post-thaw cell survival and short-term proliferation assays. The effectiveness of the novel cryopreservation media in freezing hematopoietic stem cells from human whole bone marrow was assessed by extreme limiting dilution analysis in immunodeficient mice. Stem cell frequencies were measured 12 weeks after transplant based on bone marrow engraftment of erythroid, myeloid, B-lymphoid, and CD34⁺ progenitors measured by flow cytometry. The recovered numbers of cryopreserved stem cells were similar among XT-Thrive A, XT-Thrive B, and DMSO with serum groups. These findings show that cryoprotectants developed through biomimicry of natural antifreeze proteins offers a substitute for DMSO-based media for the cryopreservation of hematopoietic stem cells.

Effect of serum replacement on murine spermatogonial stem cell cryopreservation

Cryopreservation of spermatogonial stem cells (SSCs) is a necessity to preserve the genetic information of valuable livestock herds and to produce transgenic animals. However, serum, a key component that allows efficient cryopreservation, has many limitations attributed to its undefined composition, inter-batch variations, and contamination potential. Therefore, we aimed to establish a method for serum-free cryopreservation of SSCs. To evaluate the cryopreservation efficiency of serum replacements, we assessed the recovery rate, relative proliferation potential, proliferation capacity, and apoptosis capacity. SSCs were characterized, and their functional activity was determined through immunofluorescence, RT-qPCR, and spermatogonial transplantation. The efficiency of each serum replacement was compared to that of the negative control (10% DMSO in DPBS) and positive control (10% DMSO and 40% FBS in DPBS). Our results indicated that cryopreservation with 5% human serum albumin (rHSA) exhibited a higher relative proliferation potential (274.0 ± 13.4%) than with DMSO control (100 ± 8.6%), with no significant difference from the 40% FBS (190.0 ± 20.1%). Moreover, early apoptosis also significantly decreased to a greater extent with 5% rHSA (5.1 ± 0.7%) than with DMSO control (12.9 ± 0.8%) and was at a level comparable to the 40% FBS (4.9 ± 0.8%). In addition, the SSCs cryopreserved with 5% rHSA exhibited normal self-renewal and differentiation abilities. In conclusion, 5% rHSA is a potential serum replacement for SSC cryopreservation, with properties comparable to that of serum. These results would contribute to the application of SSCs in improving livestock and in future clinical trials for human infertility treatment.

Cryopreservation of peripheral blood mononuclear cells using uncontrolled rate freezing

Peripheral blood mononuclear cells are widely used as source material for anticancer immunotherapies. The conventional cryopreservation method for peripheral blood mononuclear cells is time-consuming and expansive, which involves controlled rate freezing followed by storage in liquid nitrogen. Instead, the convenient uncontrolled rate freezing cryopreservation method had been reported successfully in peripheral blood hematopoietic stem cells and peripheral blood progenitor cells. Therefore, we hypothesized that uncontrolled rate freezing cooling method maybe also applied to peripheral blood mononuclear cells cryopreservation. In this study, we evaluated the performance of uncontrolled rate freezing and controlled rate freezing cooling methods through cell recovery rate, viability, differentiation potential into cytokine-induced killer cells and the cellular properties of the cultured cytokine-induced killer cells. The results showed similar post-thaw viability and recovery rate in both controlled rate freezing and uncontrolled rate freezing cryopreserved peripheral blood mononuclear cells. Importantly, the uncontrolled rate freezing cryopreserved peripheral blood mononuclear cells exhibited higher growth ratio and earlier cell clustering during ex-vivo cytokine-induced killer cell culture than the controlled rate freezing ones. These two groups of expanded cytokine-induced killer cells also exhibited similar effector cell subset ratio and tumoricidal activity. In general, the performance of cryopreserved peripheral blood mononuclear cells using uncontrolled rate freezing cooling method, with the commercial cryoprotective agent CellBanker 2, was equal or better than the controlled rate freezing method. Our study implied that the combined use of cryoprotective agent CellBanker 2 and uncontrolled rate freezing could be a convenient cryopreservation method for peripheral blood mononuclear cells.

Fetal bovine serum-free cryopreservation methods for clinical banking of human adipose-derived stem cells

The use of fetal bovine serum (FBS) as a cryopreservation supplement is not suitable for the banking of mesenchymal stem cells (MSCs) due to the risk of transmission of disease as well as xenogeneic immune reactions in the transplanted host. Here, we investigated if human serum albumin (HSA), human serum (HS), or knockout serum replacement (KSR) can replace FBS for the cryopreservation of MSCs. In addition, we examined the characteristics of MSCs after multiple rounds of cryopreservation. Human adipose-derived stem cells (ASCs) cryopreserved with three FBS replacements, 9% HSA, 90% HS, or 90% KSR, in combination with 10% dimethyl sulfoxide (Me₂SO) maintained stem cell properties including growth, immunophenotypes, gene expression patterns, and the potential to differentiate into adipogenic, osteogenic, and chondrogenic lineages, similar to ASCs frozen with FBS. Moreover, the immunophenotype, gene expression, and differentiation capabilities of ASCs were not altered by up to four freeze-thaw cycles. However, the performance of three or four freeze-thaw cycles significantly reduced the proliferation ability of ASCs, as indicated by the longer population doubling time and reduced colony-forming unit-fibroblast frequency. Together, our results suggest that HSA, HS, or KSR can replace FBS for the cryopreservation of ASCs, without altering their stemness, and should be processed with no more than two freeze-thaw cycles for clinical approaches.

Serum albumin as a local therapeutic agent in cell therapy and tissue engineering

Albumin is a major plasma protein that has become ubiquitous in regenerative medicine research. As such, many studies have examined its structure and advantageous properties. However, a systematic and comprehensive understanding of albumin's role, capabilities and therapeutic potential still eludes the field. In the present work, we review how albumin is applied in tissue engineering, including cell culture and storage, in vitro fertilization and transplantation. Furthermore, we discuss how albumin's physiological role extends beyond a carrier for metal ions, fatty acids, pharmacons and growth factors. Albumin acts as a bacteriostatic coating that simultaneously promotes attachment and proliferation of eukaryotic cells. These properties with the combination of free radical scavenging, neutrophil activation and as a buffer molecule already make the albumin protein beneficial in healing processes supporting functional tissue remodeling. Nevertheless, recent data revealed that albumin can be synthesized by osteoblasts and its local concentration is raised after bone trauma. Interestingly, by increasing the local albumin concentration in vivo, faster bone healing is achieved, possibly because albumin recruits endogenous stem cells and promotes the growth of new bone. These data also suggest an active role of albumin, even though a specific receptor has not yet been identified. Together, this discussion sheds light on why the extravascular use of the albumin molecule is in the scope of scientific investigations and why it should be considered as a local therapeutic agent in regenerative medicine. © 2016 BioFactors, 43(3):315-330, 2017.

Effect of trehalose on cryopreservation of pure peripheral blood stem cells

Stem cells are an important tool for the study of hematopoiesis. Despite developments in cryopreservation, post-thaw cell death remains a considerable problem. Cryopreservation protocol should limit cell damage due to freezing and ensure the recovery of the functional cell characteristics after thawing. Thus, the use of cryoprotectants is essential. In particular, the efficacy of trehalose has been reported for clinical purposes in blood stem cells. The aim of the current study was to establish an efficient method for biological research based on the use of trehalose, to cryopreserve pure peripheral blood stem cells. The efficacy of trehalose was assessed in vitro and the cell viability was evaluated. The data indicate that trehalose improves cell survival after thawing compared with the standard freezing procedure. These findings could suggest the potential for future trehalose application for research purposes in cell cryopreservation.

Storage of human biospecimens: selection of the optimal storage temperature

Millions of biological samples are currently kept at low tempertures in cryobanks/biorepositories for long-term storage. The quality of the biospecimen when thawed, however, is not only determined by processing of the biospecimen but the storage conditions as well. The overall objective of this article is to describe the scientific basis for selecting a storage temperature for a biospecimen based on current scientific understanding. To that end, this article reviews some physical basics of the temperature, nucleation, and ice crystal growth present in biological samples stored at low temperatures (-20°C to -196°C), and our current understanding of the role of temperature on the activity of degradative molecules present in biospecimens. The scientific literature relevant to the stability of specific biomarkers in human fluid, cell, and tissue biospecimens is also summarized for the range of temperatures between -20°C to -196°C. These studies demonstrate the importance of storage temperature on the stability of critical biomarkers for fluid, cell, and tissue biospecimens.

A policy for the disposal of autologous hematopoietic progenitor cells: report from an Italian consensus panel

BACKGROUND

Autologous stem cell transplantation (ASCT) requires collection and cryopreservation of hematopoietic progenitor cells (HPCs), which in turn may be partially or never reinfused. Thus, HPC storage has become a logistic, ethical, and economic issue. SIDEM, GITMO, and CNT/ISS endorsed a project aimed to define national criteria for HPC disposal aimed to guarantee appropriateness and equity.

STUDY DESIGN AND METHODS

A multidisciplinary panel was convened including HPC harvest and manipulation experts from apheresis units, hematologists with clinical expertise in ASCT, a representative of the national health authority, and a bioethicist. An analytic hierarchy process (AHP) was carried out to select disposal criteria.

RESULTS

The AHP selected two criteria for prompt disposal of freshly collected HPCs: an abnormal freezing procedure causing highly reduced viability or major microbiology contamination. Moreover, AHP selected six major criteria, each one of them allowing for the disposal of stored HPC units: patient death, withdrawal of consent to ASCT, contraindications or loss of indications to ASCT, a damaged label that prevents correct identification of the unit, and time elapsed since harvest longer than 10 years. Three minor criteria were additionally identified that allowed to anticipate disposal only provided that viability levels are below the limit of acceptance: a documented cold chain interruption, loss of bag integrity, and total amount of stored CD34+ cells lower than 1 × 10(6) /kg or lower than 2 × 10(6)/kg in patients with a successfully completed stem cell transplantation program.

CONCLUSIONS

A formal consensus process allowed SIDEM and GITMO to propose a policy for autologous HPC disposal that fulfills clinical, ethical, and economic criteria.

Relative recovery of haematopoietic stem cell products after cryogenic storage of up to 19 years

There is an increasing trend towards long-term frozen storage of haematopoietic stem cells. For such stem cells, harvested from peripheral blood (PB) or BM, it is not known if stem cell viability decreases with time. In this study, 31 separate bags of stem cell product (SCP) stored for 11-19 years (median 15 years) were assessed for total nucleated cell (TNC) count, colony forming unit-granulocyte/macrophage (CFU-GM), CD34⁺ cell count and cell viability. The results were compared with the initial results obtained for the products at the time of stem cell harvest, and the percentage recovery of each parameter was plotted against time. Recovery of TNC, CD34⁺ cell count and cell viability decreased with time (P=<0.01) but CFU-GM did not. This study shows that SCPs harvested from PB and BM do deteriorate with long-term storage. This could have an impact on rates of engraftment.

Long-term storage of peripheral blood stem cells frozen and stored with a conventional liquid nitrogen technique compared with cells frozen and stored in a mechanical freezer

BACKGROUND

Cryopreservation of hematopoietic progenitor cells using liquid nitrogen and controlled-rate freezing requires complex equipment and highly trained staff and is expensive. We compared the liquid nitrogen method with methods using a combination of dimethyl sulfoxide (DMSO) and hydroxyethyl starch (HES) for cryopreservation followed by storage in mechanical freezers.

STUDY DESIGN AND METHODS

Peripheral blood stem cells (PBSCs) were collected from normal donors by apheresis and allocated to one of four preservation and storage conditions: 1) 10% DMSO with freezing in liquid nitrogen and storage in liquid nitrogen, 2) 5% DMSO and 6% HES with freezing and storage in a -80 degrees C mechanical freezer, 3) 5% DMSO and 6% HES with freezing in a -80 degrees C mechanical freezer and storage in a -135 degrees C mechanical freezer, or 4) 5% DMSO and 6% HES with freezing and storage both in a 135 degrees C mechanical freezer. Cells were stored for 5 years during which total nucleated cells (TNCs), cell viability, CD34+ cell content, and colony-forming unit-granulocyte-macrophage content were determined.

RESULTS

There were some significant differences in the variables measured during freezing and the 5 years of storage compared to the values before freezing and storage; however, these differences were not consistent and do not favor one protocol over the others. Samples stored for 24 hours before cryopreservation showed a significant decrease in TNCs, but no other significant changes during the 5 years.

CONCLUSION

In vitro measurements indicate that PBSCs can be successfully frozen and stored using a combination of DMSO and HES providing smaller amounts of DMSO and allowing simplified freezing and storage conditions.

Long-term storage does not alter functionality of in vitro generated human erythroblasts: implications for ex vivo generated erythroid transfusion products

BACKGROUND

Cultured human erythroid cells derived in vitro may represent alternative transfusion products. It is unknown, however, if these ex vivo expanded erythroid cells remain functional or develop genetic abnormalities after storage.

STUDY DESIGN AND METHODS

Using mononuclear cells from four adult blood donors, erythroblasts were generated ex vivo in expansion cultures supplemented with stem cell factor, interleukin-3, erythropoietin (EPO), dexamethasone, and estradiol. The viability and in vitro function of freshly expanded or short (1-2 months)- and long (8 years)-term-stored erythroblasts cryopreserved in dimethyl sulfoxide were compared. Erythroblast function was defined as ability to proliferate in expansion media and mature in response to EPO. Cell number was determined manually and expressed as fold increase. Viability was assessed by trypan blue and propidium iodide exclusion. Maturation was evaluated by morphologic analyses and CD36/CD235a expression profiling. Cytogenetic evaluation included karyotype and multicolor fluorescence in situ hybridization analyses.

RESULTS

Equivalent numbers (>80%) of erythroblasts were viable after short- and long-term storage. Freshly expanded and short- and long-term-stored erythroblasts equally doubled in number (fold increase, 2.4) retaining an immature phenotype (23% of the cells were CD36(high)CD235a(neg)) when cultured for 4 days under expansion conditions. The numbers of freshly expanded and short-term-stored erythroblasts that matured when exposed for 4 days to EPO were also similar (approx. 22% of the cells became CD36(neg)CD235a(high)). In spite of the massive amplification, ex vivo generated erythroblasts demonstrated a normal (46,XY) karyotype with no obvious genomic rearrangements.

CONCLUSION

Ex vivo expanded erythroblasts remain functional and genetically normal after long-term storage.

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.

Evaluation of Hematological Reconstitution Potential of Autologous Peripheral Blood Progenitor Cells Cryopreserved by a Simple Controlled-Rate Freezing Method

A novel and simple procedure for the controlled-rate cryopreservation of peripheral blood progenitor cells (PBPCs) was introduced. A freezing bag housed in a protective aluminum canister was placed on top of a styrene foam box in the -85 degrees C electric freezer. A second set of samples was kept in cryotubes placed in a double styrene foam box in the same electric freezer. Measurement of the freezing rate in the PB bags and cryotubes demonstrated that this simple method for PBPC cryopreservation provided optimal conditions for both large-scale and small-scale cryopreservation. Within several days after autologous peripheral blood stem cell transplantation, we thawed the cells in the small sample tubes and evaluated the cell viability, the cell recovery, and the recovery rates of hematopoietic progenitor cells (HPCs), such as CD34+ cells and colony-forming unit-granulocyte/macrophage (CFU-GM) colonies. The median duration of cryopreservation was 59 days (range, 14-365 days). According to our analysis, infusions of more than 2 x 10(6) CD34+ cells/kg body weight and 0.5 x 10(6) CFU-GM colonies/kg body weight after thawing had favorable influences on the neutrophil engraftment. We have therefore established a simple freezing method for cryopreservation of human PBPCs, which ensures the transplantability of hematopoietic progenitors even after thawing. In vitro HPC assay after thawing is important to evaluate the quality of cryopreservation procedures.

Peripheral blood and BM CD34+ CD38− cells show better resistance to cryopreservation than CD34+ CD38+ cells in autologous stem cell transplantation

BACKGROUND

We and others have shown a critical role for CD34+ CD38- cells in hematopoietic recovery after autologous stem cell transplantation (ASCT), in particular for platelet reconstitution. Thus a routine assessment of CD34+ CD38- cells in freezing-thawing procedures for autografting could represent an important tool for predicting poor engraftment.

METHODS

To compare the impact of cryopreservation on CD34+ CD38+ and CD34+ CD38- hematopoietic stem cell subsets, 193 autograft products collected in 84 patients with malignancies were assessed before controlled-rate cryopreservation in 10% DMSO and after thawing for autografting.

RESULTS

Cell counts after thawing were significantly different from the pre-freezing counts for total CD34+ (P<0.0001) and CD34+ CD38+ (P<0.0001) cells, but not for CD34+ CD38- cells (P=0.252). Median losses for CD34+, CD34+ CD38+ and CD34+ CD38- cells were, respectively, 11.8%, 11.4% and 0.0%. The magnitude of fresh/post-thawing percentage cell variation was significantly different when comparing between the CD34+ CD38+ and CD34+ CD38- cell subsets (P<0.001). Moreover, CD34+ CD38- cells exhibited recovery values > or =100% in 85/160 graft products, compared with 51/193 in CD34+ CD38+ cells (P<0.0001). Also, recovery values > or =90% were significantly better in the CD34+ CD38- (98/160 grafts) than in the CD34+ CD38+ subsets (89/193 grafts) (P<0.01).

DISCUSSION

In this work we have demonstrated that CD34+ cells that do not express the CD38 Ag show a significantly better resistance to cryopreservation. This could represent another example of the particular ability of less committed progenitor cells to overcome environmental injuries. Moreover, we consider routine assessment of CD34+ CD38- cells before freezing as clinically relevant, but post-thawing controls may be avoided because of their good resistance to freezing.

Supplementation of conventional freezing medium with a combination of catalase and trehalose results in better protection of surface molecules and functionality of hematopoietic cells

Our previous studies had shown that a combination of the bio-antioxidant catalase and the membrane stabilizer trehalose in the conventional freezing mixture affords better cryoprotection to hematopoietic cells as judged by clonogenic assays. In the present investigation, we extended these studies using several parameters like responsiveness to growth factors, expression of growth factor receptors, adhesion assays, adhesion molecule expression, and long-term culture-forming ability. Cells were frozen with (test cells) or without additives (control cells) in the conventional medium containing 10% dimethylsulfoxide (DMSO). Experiments were done on mononuclear cells (MNC) from cord blood/fetal liver hematopoietic cells (CB/FL) and CD34(+) cells isolated from frozen MNC. Our results showed that the responsiveness of test cells to the two early-acting cytokines, viz. interleukin-3 (IL-3) and stem cell factor (SCF) in CFU assays was better than control cells as seen by higher colony formation at limiting concentrations of these cytokines. We, therefore, analyzed the expression of these two growth factor receptors by flow cytometry. We found that in cryopreserved test MNC, as well as CD34(+) cells isolated from them, the expression of both cytokine receptors was two- to three-fold higher than control MNC and CD34(+) cells isolated from them. Adhesion assays carried out with CB/FL-derived CD34(+) cells and KG1a cells showed significantly higher adherence of test cells to M210B4 than respective control cells. Cryopreserved test MNC as well as CD34(+) cells isolated from them showed increased expression of adhesion molecules like CD43, CD44, CD49d, and CD49e. On isolated CD34(+) cells and KG1a cells, there was a two- to three-fold increase in a double-positive population expressing CD34/L-selectin in test cells as compared to control cells. Long-term cultures (LTC) were set up with frozen MNC as well as with CD34(+) cells. Clonogenic cells from LTC were enumerated at the end of the fifth week. There was a significantly increased formation of CFU from test cells than from control cells, indicating better preservation of early progenitors in test cells. Our results suggest that use of a combination of catalase and trehalose as a supplement in the conventional freezing medium results in better protection of growth factor receptors, adhesion molecules, and functionality of hematopoietic cells, yielding a better graft quality.

Long-term hematologic reconstitution after autologous peripheral blood progenitor cell transplantation: a comparison between controlled-rate freezing and uncontrolled-rate freezing at 80 degrees C

BACKGROUND

The most widely used system for peripheral blood progenitor cell (PBPC) cryopreservation is controlled-rate freezing (CRF). Uncontrolled-rate freezing (URF) at -80 degrees C has also been used, but its clinical impact has not been studied sufficiently yet.

STUDY DESIGN AND METHODS

Two groups of patients were compared: Group A consisted of 69 patients autotransplanted with PBPCs cryopreserved with CRF; Group B consisted of 192 patients autotransplanted with PBPCs cryopreserved with URF at -80 degrees C. The same cryoprotectant solution and storage system were used.

RESULTS

A significant delay of hematologic reconstitution (HR) in the URF group was observed for neutrophils greater than 0.5 x 10(9) per L and for platelets greater than 20 x 10(9) per L and greater than 50 x 10(9) per L; we did not observe any differences in the clinical course. The long-term HR was comparable in the two groups, all patients showed stable engraftment, and no late graft failures were observed.

CONCLUSION

Our study confirms that URF is safe and allows sustained long-term engraftment without increasing the risks of transplantation, even though the early engraftment after URF is slower.

Cryopreserved human haematopoietic stem cells retain engraftment potential after extended (5-14 years) cryostorage

Harvesting of stem cells during the early phases of treatment with no immediate intention to perform a stem cell transplant is becoming an increasingly common practice. Such "insurance" harvests are often stored for many years before being needed for transplant in a subsequent relapse. The effect of long-term cryostorage (5-14 years) on the viability and functional capacity of haematopoietic stem cells (HSCs) was investigated in 40 bone marrow and peripheral blood harvests using standard in vitro methods, the colony forming unit-granulocyte/macrophage (CFU-GM) assay and a single platform viable CD34(+) cell absolute count by flow cytometry. Forty percent of harvests had CD34(+) HSC counts of at least 0.7 x 10(6)/kg bodyweight and 85% had CFU-GM counts of at least 1.0 x 10(5)/kg bodyweight, these values representing our institutional minimum requirements for safe transplantation. Based on these results, it appears that HSC collections can remain adequate for safe transplantation after up to 14 years of cryostorage. However, as deterioration of HSC quality and viability may occur, some precautions may be warranted, namely harvesting higher than normal numbers of HSCs in collections intended for long-term storage and repeating in vitro assays on harvests after long-term storage prior to transplantation.

Long-term engraftment stability of peripheral blood stem cells cryopreserved using the dump-freezing method in a -80 degrees C mechanical freezer with 10% dimethyl sulfoxide

In this study, we summarize our long-term follow-up data of 24 patients who underwent autologous peripheral blood stem cell transplantation (PBSCT) using the dump-freezing method in a -80 degrees C freezer. Collected peripheral blood mononuclear cells were mixed with a cryoprotectant solution consisting of autologous plasma and 20% dimethyl sulfoxide, then placed in a -80 degrees C freezer. The recovery rate of mononuclear cells (MNCs), colony-forming unit-granulocyte/macrophage (CFU-GM) colonies, and CD34+ cells were calculated. Engraftment time (with neutrophil count > 0.5 x 10(9)/L, platelet count > 50 x 10(9)/L) and normal hemopoiesis (neutrophil count > 2 x 10(9)/L, platelet count > 100 x 10(9)/L) were evaluated. Median duration of cryopreservation was 76 days. The mean recovery rates of MNCs, CFU-GM colonies, and CD34+ cells were 93.4%, 78.4%, and 95.3%, respectively. The median engraftment times of neutrophils and platelets were 8 and 27 days, respectively. The median normal hemopoiesis times of neutrophil and platelet were 31 and 45 days, respectively. Nine patients are alive and in complete remission (CR). Seven patients in first CR sustained normal hemopoiesis with a median duration of 35 months. Two patients, who achieved second CR after salvage chemotherapy due to a leukemia relapse after PBSCT, maintained engraftment status for 24 and 28 months, and 1 reached normal hemopoiesis. These results demonstrate that PBSCT using the dump-freezing method in a -80 degrees C freezer leads to acceptable long-term engraftment stability.

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.