Risk factors for microbial contamination of peripheral blood stem cell products

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.

Impact of microbial contamination of haematopoietic stem cells on post-transplant outcomes: A retrospective study from tertiary care centre in India

BACKGROUND

Haematopoietic stem cells (HSC) may act as a source of infection for the recipient due to manipulation at multiple levels from collection to infusion. Due to the high risk of contamination cultures are usually taken during multiple steps. The clinical significance of microbial contamination of HSC on the post-transplant course and the role of prophylactic antibiotics is relatively unknown.

AIMS AND METHODS

The aim of our study is to investigate the incidence of microbial contamination of haematopoietic stem cell and to assess its impact on the post-transplant febrile neutropenia, engraftment kinetics, hospitalisation and day 100 mortality. Details of all patients admitted in the bone marrow transplantation unit of a tertiary care centre in India between January 2014 and December 2018 were collected from case records.

RESULTS

Of the 1306 stem cell harvests from 503 patients sent for culture, 17 harvests (1.3%) were found to have a culture positive report. Sixteen patients had undergone autologous transplant. Multiple myeloma was most common indication of HSC transplant followed by Non-Hodgkin Lymphoma (NHL). Twelve of 17 HSC cultures were positive at the time of infusion and five were positive at the time of harvest. The five HSC that were culture positive at the time of harvest were culture negative at the time of infusion. Gram-positive organisms were isolated in six cultures and gram-negative in rest. All patients developed febrile neutropenia post-transplantation between day 1 and day 7. The median time of onset of fever was day +5 (1-7), the median duration of fever was 4 days (2-7), the median duration of antibiotic use was 11 days (9-16). Median day for neutrophil engraftment was 11 days (9-16), the median day for platelet engraftment was 14 days (10-25) and median duration of hospitalisation was 15 days (12-78). All patients were alive at day 100 of transplant.

CONCLUSION

This study shows that there appears to be minimal impact of culture positive HSC on transplant related outcomes in terms of engraftment kinetics, duration of hospitalisation and day 100 mortality. Discarding of contaminated HSC may not be required, though on development of febrile neutropenia appropriate antibiotics should be administered based on sensitivity pattern of HSC culture. Larger prospective studies are needed to determine the clinical relevance of such contaminations. Emphasis should be laid on better infection control practices to minimise contamination rates.

Microbial contamination risk in hematopoietic stem cell products: retrospective analysis of 1996–2016 data

Quality assurance and safety of hematopoietic stem cells (HSC) with special emphasis on bacterial and fungal contamination is the prerequisite for any transplantation procedure. The aim was to determine the incidence rate of such contamination during processing of transplantation material with regard to HSC source: peripheral blood stem cell (PBSC), bone marrow (BM), or cord blood (CB). Analysis involved autologous and allogenic products dedicated for patients and comprised in all 4135 donations, including 112 BM (2.70%), 3787 PBSC (91.60%), and 236 CB (5.70%) processed in cell bank over the period 1996–2016. Aerobic and anaerobic contamination was determined.

Analysis of the 20-year data revealed 42 contaminated products: 25 PBSC (0.66% of tested units) and 17 CB (7.20% of tested units). No microbial contamination of BM products was detected. Overall percentage of contaminated products was 1.01%, mostly with Staphylococcus epidermidis (61.36%). Bacterial contamination rate at cell bank is relatively low and processing in a closed system does not seem as crucial as might be expected. This is particularly true for BM components. Equally important are evaluation of donor’s medical status and condition of the puncture site for collection of source material. Implementation of appropriate sample collection procedures should help minimize the risk of false-positive results due to environmental contamination.

Sterility release testing of peripheral blood stem cells for transplantation: impact of culture bottles and incubation temperature

BACKGROUND

Sterility testing of peripheral blood stem cells (PBSCs) is mandatory before release. As antibiotic treatment of the PBSC donor may result in false-negative results, PBSC matrix validation must be carried out.

STUDY DESIGN AND METHODS

Three spiked PBSCs and a buffy coat (BC; control matrix) were analyzed using the blood culture device BacT/ALERT 3D with the low-temperature module. Samples were spiked with Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Candida albicans, Aspergillus brasiliensis, Clostridium sporogenes, and Propionibacterium acnes. Standard iAST/iNST culture bottles and iFA/iFN Plus bottles, which include resorbing polymers, were incubated for 14 days. All aerobic bottles were incubated at 22.5°C and for a direct comparison also at 35°C while all anaerobic bottles were incubated at 35°C.

RESULTS

The BacT/ALERT 3D system detected all microbes in iAST/iNST culture bottles according to their growth behavior in the BC matrix. Detection of microbes differed significantly in PBSC products using standard iAST/iNST culture bottles and iFA/iFN Plus bottles with resorbing polymers: In Graft 1 no growth was detected in spiked bottles with S. aureus (iAST), B. subtilis (iAST/iNST), C. sporogenes (iNST), and P. acnes (iNST) compared to iFA Plus and iFN Plus bottles wherein growth of spiked microbes was confirmed. Graft 2, with another antibiotic treatment, showed no growth in iAST/iNST bottles spiked with P. aeruginosa, B. subtilis, and C. sporogenes. However, using iFA/iFN Plus bottles all spiked microbes were detectable. The comparison of incubation temperature showed an expected slower growth at 22.5°C.

CONCLUSION

The use of iFA/iFN Plus culture bottles incubated at different temperatures safely detected microbes in spiked PBSCs.

Does microbial contamination influence the success of the hematopoietic cell transplantation outcomes?

INTRODUCTION

Microbial contamination can be a marker for faulty process and is assumed to play an important role in the collection of hematopoietic progenitor cell (HPC) and infusion procedure. We aimed to determine the microbial contamination rates and evaluate the success of hematopoietic cell transplantation (HCT) in patients who received contaminated products.

PATIENTS-METHODS

We analyzed microbial contamination records of HPC grafts between 2012 and 2015, retrospectively. Contamination rates of autologous donors were evaluated for at three steps: at the end of mobilization, following processing with dimethyl sulfoxide, and just before stem cell infusion. Grafts of allogeneic donors were assessed only before HCT.

RESULT

A total of 445 mobilization procedures were carried out on 333 (167 autologous and 166 allogeneic) donors. The microbiological contamination of peripheral blood (323/333 donations) and bone marrow (10/333 donations) products were analyzed. Bacterial contamination was detected in 18 of 1552 (1.15 %) culture bottles of 333 donors. During the study period 248 patients underwent HCT and among these patients microbial contamination rate on sample basis was 1.3 % (16/1212). Microbial contamination detected in nine patients (7 autologous; 2 allogeneic). In 8 of 9 patients, a febrile neutropenic attack was observed. The median day for the neutropenic fever was 4 days (0-9). None of the patients died within the post-transplant 30 days who received contaminated products.

CONCLUSION

The use of contaminated products with antibiotic prophylaxis may be safe in terms of the first day of fever, duration of fever, neutrophil, platelet engraftment and duration of hospitalization.

Cryopreservation in Closed Bag Systems as an Alternative to Clean Rooms for Preparations of Peripheral Blood Stem Cells

Autologous and allogeneic stem cell transplantation (SCT) represents a therapeutic option widely used for hematopoietic malignancies. One important milestone in the development of this treatment strategy was the development of effective cryopreservation technologies resulting in a high quality with respect to cell viability as well as lack of contamination of the graft.Stem cell preparations have been initially performed within standard laboratories as it is routinely still the case in many countries. With the emergence of cleanrooms, manufacturing of stem cell preparations within these facilities has become a new standard mandatory in Europe. However, due to high costs and laborious procedures, novel developments recently emerged using closed bag systems as reliable alternatives to conventional cleanrooms. Several hurdles needed to be overcome including the addition of the cryoprotectant dimethylsulfoxide (DMSO) as a relevant manipulation. As a result of the development, closed bag systems proved to be comparable in terms of product quality and patient outcome to cleanroom products. They also comply with the strict regulations of good manufacturing practice.With closed systems being available, costs and efforts of a cleanroom facility may be substantially reduced in the future. The process can be easily extended for other cell preparations requiring minor modifications as donor lymphocyte preparations. Moreover, novel developments may provide solutions for the production of advanced-therapy medicinal products in closed systems.

Long-term experiences in cryopreservation of mobilized peripheral blood stem cells using a closed-bag system: a technology with potential for broader application

BACKGROUND

In several European countries, preparation of cellular products with open manufacturing systems as used for cryopreservation of peripheral blood stem cells (PBSCs) needs to be performed in a clean-room facility. However, this form of manufacturing is highly expensive and laborious. Thus, safe techniques providing improved efficacy regarding time and material, which are in accordance with legal requirements are highly desirable.

STUDY DESIGN AND METHODS

We have developed, validated, and applied a simple method for cryopreservation of PBSCs within a functionally closed-bag system using the closed cryo freeze prep set. This process fulfills good manufacturing practice requirements and allows for the cryopreservation of PBSCs without a clean-room facility. In addition to cryopreservation of PBSCs, we have recently successfully modified our system for processing, portioning, and cryopreservation of allogeneic donor lymphocytes.

RESULTS

Since 2010, cryopreservation of PBSCs using a closed-bag system has been performed in our facility on a routine basis and 210 patients and healthy donors have been included in this analysis. No significant reduction in viability of CD34+ cells and no process-related contamination were observed. Outcome of hematopoietic stem cell transplantation regarding time of engraftment and infectious complications is comparable to products manufactured in conventional clean-room facilities.

CONCLUSION

Our data confirm that cryopreservation of PBSCs within a functionally closed-bag system is safe, effective, and economical. Furthermore, the system has the potential to be extended to other manufacturing processes of cellular products.

A policy for the disposal of autologous hematopoietic progenitor cells: report from an Italian consensus panel

BACKGROUND

Autologous stem cell transplantation (ASCT) requires collection and cryopreservation of hematopoietic progenitor cells (HPCs), which in turn may be partially or never reinfused. Thus, HPC storage has become a logistic, ethical, and economic issue. SIDEM, GITMO, and CNT/ISS endorsed a project aimed to define national criteria for HPC disposal aimed to guarantee appropriateness and equity.

STUDY DESIGN AND METHODS

A multidisciplinary panel was convened including HPC harvest and manipulation experts from apheresis units, hematologists with clinical expertise in ASCT, a representative of the national health authority, and a bioethicist. An analytic hierarchy process (AHP) was carried out to select disposal criteria.

RESULTS

The AHP selected two criteria for prompt disposal of freshly collected HPCs: an abnormal freezing procedure causing highly reduced viability or major microbiology contamination. Moreover, AHP selected six major criteria, each one of them allowing for the disposal of stored HPC units: patient death, withdrawal of consent to ASCT, contraindications or loss of indications to ASCT, a damaged label that prevents correct identification of the unit, and time elapsed since harvest longer than 10 years. Three minor criteria were additionally identified that allowed to anticipate disposal only provided that viability levels are below the limit of acceptance: a documented cold chain interruption, loss of bag integrity, and total amount of stored CD34+ cells lower than 1 × 10(6) /kg or lower than 2 × 10(6)/kg in patients with a successfully completed stem cell transplantation program.

CONCLUSIONS

A formal consensus process allowed SIDEM and GITMO to propose a policy for autologous HPC disposal that fulfills clinical, ethical, and economic criteria.

Microbial screening of unrelated cord blood units in a Chinese cord blood bank

BACKGROUND

Given limited sample volume available for sterility testing, optimal testing methods and algorithms of cord blood (CB) have not been established according to standards.

STUDY DESIGN AND METHODS

The volume of CB unit was reduced to 20 mL in a closed system. Hetastarch and cryopreservation solution was added to the processed CB unit in Class 100 environment. In the routine sterility testing, 20 mL of red blood cells (RBC) sample was cultured in aerobic and anaerobic culture bottles. In verification post-thaw culture of the final product, some of the discarded final product units were also sampled and cultured after thaw. All the culture bottles were incubated in the BacT/ALERT 3D system.

RESULTS

In the routine sterility testing, 139 of 7032 CB units (1·98%) were contaminated with microorganism. In 84 of these 139 units (60·4%) only the anaerobic bottle was positive. Lactobacillus spp. were the most prevalent contaminant. Sixty-two discarded CB stem cell units were recultured after thaw. Of these, 10 of 48 units with a positive culturing of RBC sample were negative in the post-thaw reculture. One of 14 units with negative culturing of RBC sample was contaminated with Bifidobacterium breve in special verification test.

CONCLUSION

Our study demonstrates the predominant organisms implicated in CB microbial contamination were part of the human intestinal and vaginal flora. The larger sample volume and anaerobic culture would significantly increase the detection rate of microbial contaminated CB. We also found that potential transfusion-transmitted bacterial infection risk still existed in final product although microbial screening was performed.

Microbial contamination of hematopoietic progenitor cell products

INTRODUCTION

Microbial screening for contamination is a part of hematopoietic progenitor cell (HPC) collection and infusion procedure. We aimed to find out our microbial contamination rates during collection, processing and infusion steps of HPC products. We also evaluated the clinical course of patients who received contaminated HPC products.

PATIENTS-METHODS

We retrospectively analyzed microbial contamination records of HPC grafts between 2010 and 2012. HPC products of autologous donors were evaluated for contamination at three steps: at the end of mobilization, following processing with DMSO and just before stem cell infusion. Grafts of allogeneic donors were assessed only before HPC transplantation (HCT). Microbiological analysis of HPC samples were performed with an automated system (BacT/Alert®).

RESULT

During the study period a total of 492 mobilization procedures were performed on 329 (214 autologous and 115 allogeneic) donors. Bacterial contamination has been detected in 103 of 1630 samples (6%). Ninety-seven out of 1162 blood samples (8%) from 265 patients who were treated with HCT were contaminated. Forty-six patients (41 autologous and 5 allogeneic) were transplanted with contaminated HPC products. During HCT 42 patients experienced febrile neutropenic attack and 34 of them had positive blood culture results. In none of these 34 patients the isolated pathogens were the same organisms with those found in the final contaminated stem cell product before stem cell infusion. None of the patients who received contaminated products died because of sepsis within the posttransplant 30days. There was no significant difference between patients who received contaminated and non-contaminated products in terms of the first day of fever, duration of fever, engraftment kinetics and duration of hospitalization.

CONCLUSION

Our results suggest that microbial contamination of HPC products is an issue to be prevented, although it may not have a major impact on the general success of HCT.