Background: With the advancement of genetics and hematopoiesis resulting in therapeutic applications, a growing focus has developed on the quality assessment of biological products generated for various cellular therapies. Endotoxin is a critical measure for the presence of Gram-negative bacteria, known to cause endotoxemia. Cellular products are currently regulated as medical devices. Each location engaged in clinical protocols is responsible for establishing a quality assurance program.
Methods: In this study, endotoxin levels were assayed using both the gel-clot and kinetic chromogenic Limulus amebocyte lysate (LAL) assays on 33 patients' cellular products, produced in clinical laboratory settings as part of a clinical trial or approved protocol. These patient samples include tumor infiltrating lymphocytes (HSVtk). We sought to identify the more reliable and informative method for the determination of endotoxin levels in a variety of cellular products, to meet the growing demand for standardization of product quality assessment. Comparison of the most sensitive gel-clot LAL test (0.03 EU/mL), with the kinetic chromogenic LAL test, with a lysate sensitivity of 0.005 EU/mL, found many advantages of the more sensitive method.
Results: The kinetic chromogenic LAL test, which has the greatest sensitivity, increased the percentage of samples with valid spike recoveries compared with the gel-clot LAL test from 65% to 70% at a 1:10 sample dilution; and from 81% to 88% at a 1:100 sample dilution. Ata sample dilution of 1:50 the kinetic chromogenic LAL test provided valid spike recoveries on 81% of all samples tested.
Discussion: In the interest of providing the highest quality and safety in the finished cellular product, the determination of endotoxin by the kinetic chromogenic LAL test is a rapid, effective, easy-to-use method to detect the presence of Gram-negative bacterial contamination.