Controlled rate freezing of human marrow in a constant temperature cooling gradient in air

A new instrument which utilizes a computer controlled freezing platform moving in a constant air temperature gradient generated over liquid nitrogen (LN2) was evaluated for cryopreservation of human marrow. Marrows were placed horizontally on the freezing platform which was suspended over LN2 in a cylindrical freezing chamber. The platform was raised or lowered to maintain a predetermined fixed cooling rate in response to temperature monitored and recorded by the computer from a thermocouple placed at platform level. Separate freezing programs were created for different marrow volumes. The viability of normal marrow was tested in vitro before and after freezing. Recovery of marrow cells after freezing and thawing, as measured by cell counts and CFU-GM assays, were the same for the constant air gradient instrument as for a conventional freezing instrument. Thirteen patients received autologous marrow transplants utilizing marrow cryopreserved in the constant air gradient instrument and engraftment results were indistinguishable from those obtained for marrow cryopreserved with a conventional instrument.