Freezing characteristics of genetically modified lymphocytes for the treatment of MPS II

The freezing characteristics of genetically modified lymphocytes obtained from a donor with mucopolysaccharidosis type II (MPS II) were determined using cryomicroscopy and controlled rate freezing studies to determine postthaw viability. The cells from a donor with MPS II used in this investigation were cultured and transduced with a retroviral vector for the iduronate-2-sulfatase (IDS) enzyme for clinical studies for human gene therapy. The water transport and intracellular ice formation (IIF) characteristics of the cells were determined after completion of the culture and transduction protocol. The water transport parameters, L(pg) and E(lp), for the cultured and transduced cells were determined to be 4.4 ± 1.3 x 10^{- 14} m³/Ns and 173 ± 25 kJ/mol, respectively. The IIF nucleation parameters, κ and Ω, were 5.5 x 10¹⁰ K⁵ and 3.5 x 10¹¹ (1/m² s), respectively. The postthaw viability of the genetically modified cells was less than the viability of the freshly isolated cells from the same donor. The postthaw viability of the cultured and transduced cells from a donor with MPS II was also less than that observed with cells from a normal donor that were frozen and thawed under the same conditions. These studies are essential in understanding the biophysical changes resulting from the ex vivo culture of cells and the manner in which these changes influence the ability of the cells to be cryopreserved.