Effect of cryopreservation on adhesion molecule expression in peripheral blood derived CD34+ cells

Abstract

Homing of stem cells to the bone marrow after grafting is essential for hematopoietic recovery and supposedly depends on cellular adhesion molecules (CAMs). Since cryopreservation may affect expression of CAMs, members from integrin-(CD11a, CD49d), immunoglobulin-(CD54, CD58), selectin-(CD62L), and CD44 families were analyzed on CD34+ cells in fresh leukapheresis products (LKP) and after their cryopreservation. Two parameters were compared: the percentage of CD34+ cells with CAM expression, and the degree of CAM antigen expression; the latter can be estimated by quantitating the number of molecules of monoclonal antibody (MAb) that bind to the cell surface, and is called antibody-binding capacity (ABC). In fresh LKP 100% of CD34+ cells were positive for CD44 and CD58; the majority of CD34+ cells coexpressed CD11a, and CD49d; 73% coexpressed CD62L (L-selectin). CD54 was expressed with remarkable inter-individual variability. In thawed LKP the percentage of CD34+ cells coexpressing adhesion molecules CD54, CD11a was slightly (but not significantly) lower than in fresh samples. When the ABC is compared, generally a slightly lower expression of CAMs was observed. A marked difference was found for expression of CD62L; in the thawed LKP the surface antigen density and fraction of CD62+ cells was significantly reduced. Our results show that freezing-thawing process influences on qualitative change of the graft reflected by the decrease of CAMs on CD34+ cells, especially L-selectin. This might hamper homing, and possibly lead to suboptimal duration of aplasia.