Further Phenomena

Abstract

We thank our colleagues for their clear position statement. In conclusion: “Cord blood is not the fountain of eternal youth in our time!”—and the ethical implications of “combined donations” should not be underestimated. The statement: “Autologous stem cells from cord blood have poor prospects for use in regenerative medicine, because they have to be cryopreserved until use [and it isn’t possible to produce clinically relevant amounts of non-hematopoietic stem cells from cryopreserved material],” however, cannot be left unchallenged. In addition to the two main mechanisms of cell damage during cryopreservation (namely osmotic dehydration and intracellular ice formation), further phenomena occur during the cooling, storage, and rewarming of biological cells (for example, toxicity of the cryoprotectives, “cold shock,” pH shifts, phase transitions and separations, lipid peroxidation, vesiculation, protein denaturation, “free” radicals, thermoelastic stress, embrittlement, crack formation, devitrification, recrystallization), all of which are the current subjects of cryobiological research. Such known damaging factors are likely to be responsible for the authors’ lack of success in culturing relevant amounts of non-hematopoietic stem cells (1). In a scenario of growth rates of 13% or 19% however, it is possible to grow non-hematopoietic stem cells from cord blood. The authors seem to have been using a similar cryopreservation procedure as that published 15 years ago (2) and have not introduced variations with regard to known factors of influence (for example, the type and concentration of the cryoprotective, cooling and rewarming rates, cell concentration, and methods to remove the cryoprotective. We should therefore not overemphasize the detail “cryopreservation does not turn out well”—this was assumed before 1949 (3). Instead we should better concentrate on ethical aspects when advising our patients not to store cord blood for autologous use.