../../cms/~chanatt/125187892742471/visual-08.jpg

Vapor phase liquid nitrogen storage approach eliminates cross-contamination of cryopreserved cord blood unit

Anthony C.F. Chan, Ph.D. (Cantab)

The cryopreservation of invaluable samples for long-term has been accomplished by using liquid nitrogen phase storage approach to maintain temperatures below glass transition (Tg) temperature -132oC at which all biological activity ceases. However, cross-contamination of submersed samples has surfaced and become one of the major concerns worldwide.

Previous study has shown that infective viruses were detectable in liquid nitrogen which is indicative of the potential contamination problem of liquid nitrogen (Schafer et al., 1976). This potential problem has been confirmed by the cross-contamination of liquid nitrogen phase stored bone marrow stem cells with Hepatitis B virus (HBV), resulting in the outbreak of HBV infection (Tedder et al., 1995). Microbial contamination is commonly found in cryopreserved stem cells that liquid nitrogen tank might potentially serve as a media for cross-contamination (Foutain et al., 1997; Prince et al., 1995; Lazarus et al., 1991; Stroncek et al., 1991; Webb et al., 1996). Most of the cord blood banks nowadays have addressed this potential problem by implementation of quarantine system such as storing samples in a designated quarantine liquid nitrogen tank, or sealing overwrap that acts to quarantine each unit, or both. All of these method can potentially prevent possible cross-contamination.

To eliminate the risk of cross-contamination from other samples that can potentially occur in liquid phase storage, vapor phase liquid nitrogen storage tank has promise in eliminating this problem as transmission media is no longer exist. In addition, with advancing technology in vapor phase liquid nitrogen storage approach, vapor phase tanks are able to maintain a consistent temperature significantly below critical temperature (-150 oC) throughout the tanks as the liquid phase does.

References
[1] Schafer T et al., 1976. Biohazard: Virus-contaminated liquid nitrogen (letter). Science 191: 24-26.
[2] Tedder R et al., 1995. Hepatitis B transmission from contaminated cryopreservation tank. Lancet 346: 137-140.
[3] Foutain D et al., 1997. Liquid nitrogen freezers: A potential source of microbial contamination of hematopoietic stem cell components. Transfusion 37: 585-591.
[4] Prince H et al., 1995. Microbial contamination of harvested bone marrow and peripheral blood. Bone Marrow Transplant 15: 87-91.
[5] Lazarus H et al., 1991. Contamination during in vitro processing of bone marrow for transplantation: Clinical Significance. Bone Marrow Transplant 7: 241-246.
[6] Stroncek D et al., 1991. Adverse reactions in patients transfused with cryopreserved marrow. Transfusion 31:521-526.
[7] Webb I et al., 1996. Sources and sequence of bacterial contamination of hematopoietic stem cell components: Implications for the safety of hematotherapy and graft engineering. Transfusion 36: 782-788.