Sources and sequelae of bacterial contamination of hematopoietic stem cell components: implications for the safety of hematotherapy and graft engineering

Viral contamination of embryos cryopreserved in liquid nitrogen

Despite the worldwide application of embryo-freezing technology as the means of preserving germplasm of mammalian species, there is no information available on the possible transmission of infectious agents to cryopreserved embryos via contaminated liquid nitrogen (LN). Recently, it has been reported that new methods of cryopreservation which employ ultrarapid freezing or vitrification require direct contact between the freezing medium containing oocytes or embryos and liquid phase nitrogen (LPN). As models for human and animal viral pathogens three bovine viruses, bovine viral diarrhea virus (BVDV), bovine herpesvirus-1 (BHV), and bovine immunodeficiency virus (BIV), were employed to study the potential for their transmission by experimentally contaminated LN to embryos frozen and stored in open freezing containers. Bovine embryos in a mixture of 20% ethylene glycol, 20% ME(2)SO, and 0.6% sucrose were vitrified in either unsealed standard 0.25 ml or modified open pulled straws or in plastic cryovials and then plunged into contaminated LPN. After 3-5 weeks of storage in LN, embryos were thawed and sequentially washed and only those with intact ZP were pooled together and tested in batches of three for viral contamination. From this pool of 83 batches, 13 of 61 (21.3%) batches exposed to BVDV and BHV-1 tested positive for viral association while all 22 batches exposed to BIV in unsealed containers tested negative. All control embryos vitrified in sealed cryovials and straws were free from viral contamination.

Clinical scale expansion of cryopreserved small volume whole bone marrow aspirates produces sufficient cells for clinical use

Ex vivo expansion of bone marrow (BM) mononuclear cells (MNC) in a perfused culture system produces stem-progenitor cell type(s) in sufficient number(s) for hematopoietic reconstitution. The limitations in using fresh BM MNC for ex vivo expansion include additional cell processing and inflexibility in patient treatment. Cryopreservation of whole bone marrow (WBM) eliminates processing costs of MNC or CD34+ cell selection and allows for flexibility in patient treatment. We developed a convenient system to cryopreserve and thaw small volume WBM aspirations (n = 13) and then compared the expandability of unprocessed normal cryopreserved/thawed (C/T) WBM to that of fresh BM MNC cultured in the presence of erythropoietin, PIXY 321, and Flt3-ligand. Ex vivo expansion potential was retained in WBM aspirates after C/T. When initiated with 225 million viable nucleated cells, clinical scale expansion cultures (n = 6) yielded 9.7+/-2.8 x 10(8) total cells, which contained 10.4+/-5.8 x 10(6) colony-forming units-granulocyte-macrophage (CFU-GM), 1.3+/-1.4 x 10(4) LTCIC, and 2.2 x 10(6) CD34+Lin- cells, sufficient cell numbers for clinical use. These studies demonstrate that ex vivo perfusion culture expansion of unfractionated C/T WBM (< or =30 ml) provides doses of stem-progenitor cells similar in composition to expanded fresh BM MNC, previously demonstrated to achieve hematopoietic reconstitution.

Saponin, an inhibitory agent of carbon dioxide production by white cells: its use in the microbiologic examination of blood components in an automated bacterial culture system

BACKGROUND

Blood components with a white cell count > 100 x 10(9) per L may cause false-positive results when the BacT/Alert system is used for the microbiologic examination. The effects of different concentrations of saponin on bacterial growth and on carbon dioxide production by blood fractions with a high white cell count, in particular peripheral blood progenitor cells and buffy coats, were investigated.

STUDY DESIGN AND METHODS

The effect of saponin on carbon dioxide production was studied by adding different fractions of white cell-rich material (buffy coat or leukapheresis material) to BacT/Alert culture bottles with or without saponin and incubating these bottles. Five bacterial strains were used to inoculate the culture bottles at four levels ranging from about 1 colony-forming unit per mL to about 10(3) colony-forming units per mL. Aerobic and anaerobic bottles with and without saponin were used.

RESULTS

It was demonstrated that the addition of 0.5 percent saponin to BacT/Alert culture bottles effectively inhibited carbon dioxide production, without affecting bacterial growth.

CONCLUSION

Saponin at a concentration of 0.5 percent is a valuable additive to BacT/Alert culture media because it prevents false-positive results in the examination of white cell-rich blood components.

Sequential CD34+ and CD4+ cell selection from leukapheresis components

We tested the feasibility of sequential selection of CD34+ and CD4+ cell-enriched fractions from aliquots of five autologous leukapheresis components. CD34+ cells were selected from a median 8.0 x 10(8) mononuclear cells using the CellPro CEPRATE LC cell separation system. All cells in the CD34-depleted fraction (median 4.8 x 10(8), range 0.6-10.0 x 10(8) were then incubated with the appropriate antibodies for CD4+ cell selection and passed through a second LC column. Median target cell purities of the CD34+ cell-enriched fraction and CD4+ cell-enriched fraction were 90.5% and 86.0%, respectively. This study demonstrates that high purity CD34+ and CD4+ cell-enriched fractions can be isolated sequentially from leukapheresis components. In addition, CD8+ lymphocytes, implicated in graft-versus-host disease, were depleted in the course of both positive selection procedures. This approach could decrease the number of donor procedures by providing separate CD34(+)-enriched and CD4(+)-enriched populations for allogeneic peripheral blood progenitor cell transplantation and subsequent donor lymphocyte infusion from the same leukapheresis component.