Molecular characterization of microbial contaminants isolated from Umbilical Cord Blood Units for transplant

Sterility Testing for Hematopoietic Stem Cells

Over the last two decades, rapid technological advances have led to the wide adoption of cell and gene therapy products for the treatment of a variety of disease states. In this study, we reviewed the literature between 2003 and 2021 to provide a summary of overarching trends associated with microbial contamination in hematopoietic stem cells (HSCs) derived from peripheral blood, bone marrow, and cord blood. We provide a brief background on the regulatory context for human cells, tissues, and cellular and tissue-based products (HCT/Ps) as regulated by the US Food and Drug Administration (FDA), sterility testing expectations for autologous (Section 361) and allogeneic (Section 351) HSC products, and discuss clinical risks associated with the infusion of a contaminated HSC product. Finally, we discuss the expectations for current good tissue practices (cGTP) and current good manufacturing practices (cGMP) for the manufacturing and testing of HSC based on Section 361 and Section 351 categorization, respectively. We provide commentary on what is practiced in the field and discuss the critical need for updates to professional standards that keep pace with advancing technologies with an aim to clarify expectations for manufacturing and testing facilities to improve standardization across institutions.

OUP accepted manuscript

Cord blood (CB) collected at birth has become a valuable stem cell source for hematopoietic stem cell transplantation (HSCT). However, the collection of umbilical cord blood always bears a risk of microbiological contamination, both in vaginal birth and in cesarean section. A total of 10 054 umbilical cord stem cell samples were successfully cryopreserved between 2010 and 2020, of which 783 (8%) samples were tested positive for bacterial contamination. Umbilical CB with a volume of less than 60 mL showed a bacterial contamination rate of 12%, and above 60 mL volume a rate of 6% was found demonstrating an inverse relationship between sample volume and contamination rate (correlation coefficient r = −0.9). The contamination rate was associated with the mode of delivery and showed a significantly higher contamination rate of 9.7% when compared with cesarean deliveries (1.4%). The 10-year period consistently shows an average contamination rate between 4% and 6% per year. It is conceivable that the inverse relationship between volume and contamination rate might be related to thinner veins although no scientific evidence has been provided so far. The lower contamination rate in cesarean sections appears to be related to the sterile operating setting. Overall, the rate of bacterial contamination varies and depends on the type of birth, the way of delivery, and probably the experience of the staff.

Standards efforts and landscape for rapid microbial testing methodologies in regenerative medicine

The Standards Coordinating Body for Gene, Cell, and Regenerative Medicines and Cell-Based Drug Discovery (SCB) supports the development and commercialization of regenerative medicine products by identifying and addressing industry-wide challenges through standards. Through extensive stakeholder engagement, the implementation of rapid microbial testing methods (RMTMs) was identified as a high-priority need that must be addressed to facilitate more timely release of products. Since 2017, SCB has coordinated efforts to develop standards for this area through surveys, weekly meetings, workshops, leadership in working groups and participation in standards development organizations. This article describes the results of these efforts and discusses the current landscape of RMTMs for regenerative medicine products. Based on discussions with stakeholders across the field, an overview of traditional culture-based methods and limitations, alternative microbial testing technologies and current challenges, fit-for-purpose rapid microbial testing and case studies, risk-based strategies for selection of novel rapid microbial test methods and ongoing standards efforts for rapid microbial testing are captured here. To this end, SCB is facilitating several initiatives to address challenges associated with rapid microbial testing for regenerative medicine products. Two documentary standards are under development: an International Organization for Standardization standard to provide the framework for a risk-based approach to selecting fit-for-purpose assays primarily intended for cell and gene therapy products and an ASTM standard guide focused on sampling methods for microbial testing methods in tissue-engineered medical products. Working with the National Institute of Standards and Technology, SCB expects to facilitate the process of developing publicly available microbial materials for inter-laboratory testing. These studies will help collect the data necessary to facilitate validation of novel rapid methods. Finally, SCB has been working to increase awareness of, dialog about and participation in efforts to develop standards in the regenerative medicine field.

A protocol for umbilical cord tissue cryopreservation as a source of mesenchymal stem cells

Mesenchymal stem cells (MSC) differentiate into different cell types and have immunomodulatory and paracrine effects. Cryopreservation of umbilical cord tissue as a source of MSC is very promising for regenerative medicine. We aim to evaluate a protocol for cryopreserving this tissue sectioned into small fragments with viable MSC. A total of 723 samples were frozen, thawed and cultured to obtain primary cultures of MSC. These were followed until 90-100% confluence and flow cytometric analysis were performed to confirm the mesenchymal phenotype. Samples in which protocol alterations at the collection of the samples were reported, were excluded for microbial contamination analysis leaving a total of 634 samples composed of 181 vaginal and 453 cesarean births. All cultures reach confluence with a media of 22.57 days and 97% in 28 or fewer days. Evaluated cultures showed low percentage of CD45+ and high of CD73 and CD90. Eight samples were subcultured 4 or 5 times and differentiated to chondrocytes and osteocytes to test differentiation potential with positive results. Umbilical cord tissue collections showed similar microbial profile and risk factors to those reported of umbilical cord blood collections, but with higher contamination frequencies. Cryopreserved tissue samples had viable cells that can be expanded without losing differentiation potential. Higher contamination frequencies compared to umbilical cord blood collection are not surprising, however, microbial load and survival of microorganisms to cryopreservation are expected to be lower.

The role of microbiota in neonatal hyperbilirubinemia

Hyperbilirubinemia accounts for about 60% of full-term and 80% of preterm neonates globally, which is characterized by physiologically elevated unconjugated bilirubin in serum, but abnormally high levels of bilirubin have potential neurotoxic effects. Several factors contribute to the development of neonatal hyperbilirubinemia, including isoimmunization, dysregulated gut flora, genetic alteration and environmental factors. Animal studies have pinpointed the causal roles of several bacteria in bilirubin metabolism. Human studies have revealed microbiota composition in hyperbilirubinemia and found that gut microbiota affect newborns with different severity of hyperbilirubinemia. However, dysbiosis and subsequent changes in microbiota-related metabolic processes are not always considered. This review aims to describe the critical microbiota signatures for neonatal hyperbilirubinemia and focus on the underlying pathogenetic mechanism. These scientific bases give a new and accurate therapeutic strategy for the application of gut microbiota.

Development of a proof of principle for universal neutralization of antibiotics in cord blood by-products used for sterility testing

BACKGROUND

Bacterial contamination of cord blood (CB) represents a safety risk for transplantation patients. CB sterility testing at Canadian Blood Services' Cord Blood Bank is performed using a 1:1 mix of CB-derived plasma and red blood cells (RBCs). Culture bottles of an automated culture system, which lack antimicrobial neutralization properties, are used for bacterial screening of CB. This process is unsuitable for CB-containing antibiotics, potentially resulting in false-negative results. This study was aimed at developing a protocol for antibiotic neutralization in CB used for sterility testing.

STUDY DESIGN AND METHODS

Phase 1: four neutralizers-penicillinase, ion exchange resins L and A, lecithin + Tween80, and activated charcoal (AC)-were individually tested to neutralize penicillin or gentamicin in cultures of Staphylococcus epidermidis or Klebsiella pneumoniae, respectively, adjusted to 100 colony forming units/mL, in Müller-Hinton broth (MHB). Phase 2: combinations of penicillinase plus resin L or penicillinase plus AC were assayed for the simultaneous neutralization of both antibiotics in MHB. Phase 3: penicillinase plus resin L was used to neutralize both antibiotics in CB sterility testing samples (plasma + RBCs).

RESULTS

Phase 1: penicillin was neutralized by penicillinase and resin A, while gentamicin was neutralized by resin L and AC. Phase 2: the antibiotics were simultaneously neutralized by the two neutralizer combinations tested. Phase 3: neutralization of both antibiotics in CB was achieved with penicillinase and resin L.

CONCLUSION

A protocol for antibiotic neutralization in CB sterility testing samples has been successfully developed at Canadian Blood Services' Cord Blood bank. This in-house assay applies to any culture-based CB bacterial screening method.