Bacterial safety of cell‐based therapeutic preparations, focusing on haematopoietic progenitor cells

Abstract

Bacterial safety of cellular preparations, especially haematopoietic progenitor cells (HPCs), as well as advanced therapy medicinal products (ATMPs) derived from stem cells of various origins, present a challenge for physicians, manufacturers and regulators. The article describes the background and practical issues in this area and illustrates why sterility of these products cannot currently be guaranteed. Advantages and limitations of approaches both for classical sterility testing and for microbiological control using automated culture systems are discussed. The review considers novel approaches for growth-based rapid microbiological control with high sensitivity and faster availability of results, as well as new methods for rapid bacterial detection in cellular preparations enabling meaningful information about product contamination within one to two hours. Generally, however, these direct rapid methods are less sensitive and have greater sampling error compared with the growth-based methods. Opportunities for pyrogen testing of cell therapeutics are also discussed. There is an urgent need for development of novel principles and methods applicable to bacterial safety of cellular therapeutics. We also need a major shift in approach from the traditional view of sterility evaluation (identify anything and everything) to a new thinking about how to find what is clinically relevant within the time frame available for the special clinical circumstances in which these products are used. The review concludes with recommendations for optimization of microbiological control of cellular preparations, focusing on HPCs.

Validation of shortened 2-day sterility testing of mesenchymal stem cell-based therapeutic preparation on an automated culture system

“…Later the bacteria can enter the product during the manufacturing process and exposure to environmental contaminants. Finally the storage, transport and administration may also lead to microbial impurity (Störmer et al 2014). Despite the utilization of aseptic techniques, clean room facilities and controlled manufacturing conditions, the risk of microbial contamination of ATMPs cannot be completely minimized.…”

Prospective Evaluation of a Practical Guideline for Managing Positive Sterility Test Results in Cell Therapy Products

“…For products including gene therapies and more-than-minimally- manipulated cell therapies in prolonged cultures, regulations further specify sterility testing for bacteria and fungi using microbial testing methods equivalent to or better than those described in 21 CFR 610.12 9 . In our institution, traditional USP<71> testing for cell therapy products was replaced in 2004 with direct inoculation of aerobic and anaerobic plus bottles incubated at 30– 35°C for 14 days on the Bactec FX automated blood culture system (Becton Dickinson, Sparks, MD) 10,11 .…”

“…And, due to the need to maximize cell suspension for infusion, only a small volume (~1 mL; 1–10% of the cellular product) may be available for sterility testing and this may compromise culture sensitivity. Automated systems, such as blood culture instruments, have demonstrated faster time detection compared with the manual compendial USP<71> method in some studies 9–11 . Hence, aseptic processing in a controlled, clean facility (per International Standards Organization (ISO) standards), and rigorous in-process sterility sampling paired with an active environmental monitoring program are critical in reducing risk of product contamination, and can provide investigative data in the event of a positive sterility result that requires antimicrobial intervention.…”

Biomedical Applications of Untethered Mobile Milli/Microrobots

“…Immunogenicity concerns of muscle-cell-actuated microrobots could be successfully evaded by producing functional cells from patient-derived induced pluripotent stem cells (iPSC) [185]. On the other hand, during microrobot fabrication, biohybrid constructs are highly prone to microbial contamination, which should be given a special emphasis [186], [187]. Bacteria-propelled micro robots must be sterilized from any sort of pathogenicity.…”