Cryopreservation of red blood cells: effect of freezing on red cell quality and residual lymphocyte immunogenicity.

Aims: To investigate treatment with glycerol/washing as a potential substitute for freeze-thawing in the production of leucocyte depleted red cell concentrates for patients with a history of non-haemolytic reactions following transfusion.

Methods: The standard procedure of treatment with glycerol/-80 degrees C freezing/thawing/washing was compared with a similar procedure in which freezing was omitted. The quality of the resulting red cell products was assessed in relation to: (1) standard red cell biochemical parameters; (2) leucocyte and lymphocyte subset composition using flow cytometry with fluorescent labelled monoclonal antibodies; and (3) immunogenicity of the residual lymphocytes in mixed lymphocyte culture.

Results: Compared with red cells subjected to the standard freeze-thaw technique, red cells undergoing the non-freezing procedure and suspended in additive solutions had significantly better biochemical preservation after 21 days of storage (p < 0.001). Both procedures removed an average 98% of the initial leucocytes at the expense of 18-20% of the red cells. The non-freezing procedure resulted in higher residual concentrations of HLA class II bearing lymphocytes (p < 0.01), but not higher numbers of dendritic cells. Both procedures were equally effective in annulling the residual lymphocytes' ability to act as stimulator cells in one-way mixed lymphocyte culture.

Conclusions: The non-freezing procedure produces a superior product for the provision of red cells to patients with granulocyte antibodies. These products may also offer a lower risk of HLA alloimmunisation to previously unexposed patients.