Contamination Rate of Cryopreserved Umbilical Cord Blood Is Inverse Correlated with Volume of Sample Collected and Is also Dependent on Delivery Mode

Abstract

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.

Full text

Contamination Rate of Cryopreserved Umbilical Cord
Blood Is Inverse Correlated with Volume of Sample
Collected and Is also Dependent on Delivery Mode
Susanne Reuther, Kathrin Floegel, Gunther Ceusters, Veronica Albertini, Jakub
Baran, Wolfram Dempke
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Stem Cells Translational Medicine, 2022, XX, 1–9
https://doi.org/10.1093/stcltm/szac020
Advance access publication 29 April 2022
Original Research
Received: 9 December 2021; Accepted: 6 March 2022.
© The Author(s) 2022. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/),
which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Contamination Rate of Cryopreserved Umbilical Cord
Blood Is Inverse Correlated with Volume of Sample
Collected and Is also Dependent on Delivery Mode
SusanneReuther,1,4 KathrinFloegel,1 GuntherCeusters,1,2 VeronicaAlbertini,2 JakubBaran,3
WolframDempke,4,5,*,
1Eticur Germany GmbH, Munich, Germany
2Famicord SA Suisse, Contone, Switzerland
3PBKM FamiCord Group, Warsaw, Poland
4Ludwig-Maximillians University Munich, Munich, Germany
5Worldwide Clinical Trials, Nottingham, United Kingdom
*Corresponding author: Wolfram Dempke, MD, PhD, MBA, Professor of Hematology & Oncology, Worldwide Clinical Trials, Waterfront House, Beeston
Business Park, Nottingham NG9 1LA, UK. Tel: +41 797 836 706; Fax: +44 207 121 6160; Email: wolfram.dempke@worldwide.com
Abstract
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 posi-
tive 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.
Key words: umbilical cord blood; sample volume; contamination; bacterial strains; delivery mode.
Graphical Abstract
Introduction
Umbilical cord blood (UCB) stem cells have been established
as an alternative stem cell source for pediatric and adult
patients with various oncologic, hematologic, immunologic,
and inherited metabolic disorders, especially by lacking a re-
lated or unrelated donor.1-3 Cord blood is also a very attrac-
tive alternative stem cell source because of the increased level
of HLA disparity that can be tolerated. This is of particular
importance for patients from racial and ethnic minorities, as
for those it can be difcult to nd a donor.1,4.
Numerous retrospective studies from recent years have
shown that UCB transplantation in patients with hemato-
logical malignancies can result in disease-free survival (DFS)
comparable to that of adult donor transplants.5,6 In addi-
tion, few studies have conrmed that the relapse rate after
UCB transplantation is low compared to unrelated donor
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2Stem Cells Translational Medicine, 2022, Vol. XX, No. XX
transplants, indicating that UCB may be the preferred source
for patients at high risk of relapse.7 UCB transplantation has
the advantage of a lower rate of chronic graft-versus-host
disease (GvHD) compared to hematopoietic stem cells from
peripheral blood, which is reected in lower long-term mor-
bidity and mortality.7 Research studies have shown that cord
blood transplants can also be performed in cases even when
the donor and the recipient are partially matched, so cord
blood increases the patient’s chance to nd a more suitable
donor.8,9 However, with increasing differences in the donor
and recipient HLA systems, the risk of delayed or absent he-
matopoietic reconstitution also increases in UCB transplan-
tation.8,10 In contrast, the greater availability of high-quality
and high-cell-content UCB units has resulted in increasingly
improved engraftment and survival outcomes after UCB
transplantation.11,12
There are various providers worldwide, which accom-
pany or sometimes even offer the process from collection to
storage. Importantly, the collection of UCB always bears a risk
of microbiological contamination, both in spontaneous/vag-
inal birth and in cesarean section.13 Cord blood preparations
with latent virus and environmental toxin contaminations
are lower than those with a bone marrow transplant, but ap-
pear to be more highly contaminated by bacteria than those
from bone marrow and peripheral blood are, which may
be due to the collection technique.14-16 Bacterial contami-
nation of human blood products is another challenge as it
occurs quite frequently and it is observed that bacteria devel-
oped resistance, which can be life-threatening, especially in
immune-compromised patients.17,18 Therefore, sterility testing
is mandatory according to the guideline standards to pre-
vent transplantation transmitted bacterial infections causing
severe transfusion-associated sepsis in immune-suppressed
patients.19,20
Moreover, bacterial contamination of hematopoietic stem
cells obtained from UCB may cause a rejection of a stem
cell graft.21 In case of contamination, a bacterial determina-
tion should be carried out again from a suitable reference
sample to exclude second contamination or higher risk of
unsuccessful clinical outcome, so high quality and safety of
hematopoietic stem cells are required for any successful trans-
plantation.16 Using sterile techniques and a closed system
during the whole preparation process is usually used to re-
duce the risk of any bacterial contamination.8,16 Freezing bags
or tubes must comply with the current state of technology
and exclude cross-contamination between different samples
during storage.16
The aim of this study was to investigate the bacterial con-
tamination rate related to the delivery mode including collec-
tion experiences of the staff and collection sample volume. In
addition, the most commonly detected bacterial strains were
determined.
Methods
A total of 10 054 UCB samples for potential autologous use
was cryopreserved in the transfusion medicine and hemostasis
department from September 2010 to September 2020 in co-
operation with the Erlangen University Hospital (Germany).
Institutions that manufacture, test, process, store, or
market stem cell products in Germany must ensure com-
pliance with legal requirements, maintain a quality man-
agement system in accordance with Section 3 AMWHV
(“Arzneimittel- und Wirkstoffherstellungs-verordnung”) and
the principles of “good manufacturing practice” (EU GMP
Guideline). The UCB collection was carried out in all ma-
ternity clinics in Germany that had signed a contract with
the Eticur GmbH Germany company in accordance with the
current SOP “Guidelines for Transplantation of Stem Cells
Part III, Umbilical Cord Stem Cells, 3.1 Collection” and
the individual preparations were carried out by the transfu-
sion medicine and hemostasis department of the University
Hospital Erlangen in accordance with the SOP “Guidelines
for Transplantation of Stem Cells, Part III Umbilical Cord
Stem Cells, 4th CB Stem Cell Preparation.” The University
Hospital of Erlangen is licensed by the Federal Agency PEI
(Paul Ehrlich Institute). Eticur GmbH Germany is a 100%
subsidiary of Famicord Europe and has established collabo-
ration with the University Hospital Erlangen. In this regard,
the applied methods for cryopreservation and microbiology
testing were identied and described in SOPs (validated ac-
cording to Ph.Eur. section 2.6.27).
Informed consent from the parents, a prescribed anamnesis
questionnaire, and a production protocol were mandatory for
the collection of UCB. All clinics and the University Hospital
Erlangen provided a valid manufacturing permit. Approval for
the pre-drug stage was carried out by the “Qualied Person”
in accordance with § 14 AMG (German Medical Law).
Cord blood samples were transported immediately
after birth to the stem cell laboratory were analyzed and
cryopreserved (10% v/v DMSO) within 48 h from the de-
livery time. Every sample was analyzed in terms of total
blood volume, a total count of CD34+ cells, total nucleated
cell (TNC, CD45+) count, and colony-forming units (CFU).
The CFU method was performed according to the protocol
described by Dempke et al,22 which shows the in vitro ca-
pacity of the proliferation of hematopoietic stem cells.
CD34+ and CD45+ cells were analyzed by immunouorescence
on FACSCalibur (Becton Dickenson, Heidelberg) using anti-
CD34-PE and anti-CD45-FITC (Becton Dickenson, Heidelberg)
according to the protocol described by Cassens et al.23
To check the quality parameters such as the microbiolog-
ical control, the purity, and the vitality of the product as well
as to control the manufacturing process or cryopreservation,
sufcient preparation samples according to Section 18 (1)
AMWHV must be ensured until clinical use. These samples
must be stored under conditions comparable to those of the
umbilical cord blood stem cells.
In an attempt to determine the contamination with bac-
teria samples were taken from the incoming cord blood bag
as well as the processed stem cell preparation followed by
microbiological cultures were performed by using BD Bactec
Standard Anaerobic/F 40 mL culture vials (REF 442024)
and BD Bactec Standard/10 Aerobic/F 40 mL culture vials
(REF442027) (Becton Dickenson, BD, Heidelberg) to de-
tect anaerobic and aerobic bacteria after 7 incubation days.
The sample volume was identical for all samples (percentage
volume). The method validation included a slow grower and
all standard bacteria and fungi. Each bag was tested twice
and both assays (primary and secondary contamination rates)
were comparable (data not shown).
Results
A total of 10 054 UCB stem cell samples were successfully
cryopreserved between September 2010 and September 2020.
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Stem Cells Translational Medicine, 2022, Vol. XX, No. XX 3
Most cord blood samples had volumes between 50 and
100mL. The overall distribution of all cord blood samples
taken shows a Gaussian-like distribution with the maximum
at less than or equal to 70mL volume (Fig. 1).
From 10 054, 783 (7.8%) samples were tested positive
for bacterial contamination. UCB with a volume of less than
60 mL showed a contamination rate of 12%, and above
60mL volume, a rate of 6% was found demonstrating an in-
verse relationship between sample volume and contamination
rate (correlation coefcient r = −-0.9) (Fig. 2A).
Considering all samples with a volume of 50–100mL, an
inverse correlation between sample volume and contamina-
tion rate is clearly shown, the higher the volume collected, the
lower the contamination rate (Fig. 2B).
Furthermore, the results show that vaginal birth is much
more frequently performed than cesarean section, and a
Gaussian-like distribution can also be seen for both birth
modes, where a maximum is seen with the highest number
of collections is at a sample volume of 60–90mL (Fig. 2C).
Regarding the contamination rate related to collection
sample volume as well as delivery mode, both birth modes
showed the inverse correlation between sample volume
and contamination rate (Fig. 2D). For spontaneous birth,
depending on the volume, the contamination rate ranges from
14.1% for less than 30mL to 4.17% for more than 150mL
of cord blood collected. In contrast, cesarean sections showed
a contamination rate between 3.3% for less than 30mL and
0% for more than 150mL volume (Table 1).
In addition, the contamination rate associated with the
mode of delivery showed a signicantly higher average con-
tamination rate of 8.4% compared with cesarean deliveries
with only 1.5% (Table 1; Fig. 2D).
Considering all 783 non-sterile samples the most detected
bacterial strains were Staphylococcus- (37.7%), Bacteroides-
(22.1%), and Enterococcus-strains (21.8%), as well as
Escherichia coli species (13.5%) (Table 2A). All detected
bacteria strains are shown in Fig. 3A. The 3 largest bacterial
strains show the following subfamilies as the most identied:
In the staphylococcus group, the Staphylococcus epidermidis
subfamily is the most detected with 38.9%; Bacteroides
reveal Bacteroides vulgatus as the most found subfamily with
43.3%. Enterococcus faecalis is the most determined in its
family with 82.8%. No unexpected ndings were found ac-
cording to the standards of the European Pharmacopoeia
(Table 2Bi–iii).
At cesarean section, the most frequent strains in collected
UCB is the propionibacterium acnes with 40% as well as
34% of staphylococcus species, 6% of Enterococcus spe-
cies, and E. coli species with 6% were detected (Table 3;
Fig. 3B). The quality of the umbilical cord stem cell prep-
aration is also determined using the cell number of TNC
(CD45+) as well as the CD34+ stem cells that are included in
the TNC population. In addition, the viability of both cell
populations is indicative of the quality of the stem cells. It
is clearly shown that the higher the volume of the umbil-
ical cord blood, the higher is the TNC cell count (Fig. 4A) .
Regarding the CD34+ stem cells, this correlation cannot be
clearly identied. A clear range of variation is shown in Fig.
4B. A direct correlation between sample volumes and the
vitality of TNC as well as CD34+ stem cells could not be
established as the vitality of both cell populations does not
primarily depend on the volume but also on the transport
and storage conditions as well as on the processing of the
cord blood into the stem cell preparation (internal quality
data, not shown).
Regarding the TNC, it became apparent that a vitality of
70%-80% was tendentially achieved with smaller volumes,
in contrast to the CD34+ stem cells, which (with a few
exceptions) display a very good vitality of over 90% inde-
pendent of the sample volume (Fig. 4C, 4D). Considering the
10-year period, a contamination rate between 6% and 9.5%
per year was found (Fig. 5). Although it appears that the con-
tamination rates are higher after 5 years, the differences are
not signicant (P > .1, Student t-test).
Discussion
The main objective of this study was the investigation of
bacterial contamination rate under a routine condition in
the cord blood stem cell products after vaginal delivery and
Figure 1. Number of cord blood samples related to sample volume (mL) showing a Gaussian-like distribution.
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4Stem Cells Translational Medicine, 2022, Vol. XX, No. XX
cesarean section related to sample volume and bacterial
strains. Additionally, the correlation between the cell num-
bers, sample volume, and delivery mode has been established.
The quality and associated safety of hematopoietic stem
cells are one of the most important requirements for successful
transplantation. Another important factor is considered the
high concentration of adult pluripotent progenitor stem cells
with increased proliferative potency, which are usually not yet
affected by environmental factors and are young and vital. It
is possible that due to the relative immaturity of the T cells
in the CB, greater immunological tolerance can be expected
after transplantation.2,24 This is probably one reason for fewer
cases of acute or chronic GvHD. It has also been reported that
not all HLA characteristics need to be matched in allogeneic
hematopoietic stem cell transplantation, making cord blood
an alternative to bone marrow or peripheral blood stem cell
transplantation.3,8,9,24-27
In our study, 10 054 UCB stem cell preparations were
cryopreserved between 2010 and 2020, with all volumes
showing a Gaussian normal distribution. Thereby, most of
the UCB samples have a volume of 50-100mL and peaked
at approximately 70 mL (Fig. 1), whereas according to the
applicable standard operation procedure (SOP) a minimum
volume of at least 60mL had to be collected. Although nu-
merous samples contained less blood volume, storage was still
requested after the parents had become aware of the reduc-
tion in quality, provided that the parents had been informed
of the reduction in quality beforehand, which is required by
the transfusion law. Although the TNC cell concentration is
proportional to the blood volume (Fig. 4A), this is not the
same for the CD34+ stem cells (Fig. 4B), so that the storage
of smaller volumes is also acceptable. In general, a minimum
concentration of ≥2.5×108 TNC and of ≥1.0×106 of CD34+
stem cells with a respective viability of ≥90% and ≥95% was
required, in accordance with the German stem cell guideline
current at the time.28
No difference was found between vaginal birth and ce-
sarean section in terms of obtained cord blood sample
volumes. This is in line with the results of other studies.29,30
In contrast, other authors report that more blood volume
was collected during cesarean section than during vaginal
birth.31,32 Moreover, no difference between the birth modes
in the cell concentrations of TNC and CD34+ stem cells were
found, consistent with the reports of other researchers.30,33
However, it contradicts the statements of some researchers
who found a higher CD34+ stem cell concentration at vaginal
birth or cesarean section.32,34 Mancinelli et al32 postulated that
in spontaneous deliveries an increase in CD34+ cells due to
the narrow birth canal, as pressure is applied to the thorax
and abdomen of the child and this pressure allows more cells
Table 1. Contamination rate (%) related to delivery mode and collection
sample volume.
Cord blood collection
volume (mL)
Cesarian
section (%)
Vaginal
delivery (%)
<30 3.33 14.10
30-60 2.53 12.10
60-90 1.31 9.05
90-120 1.06 5.63
120-150 0.75 5.48
>150 0.00 4.17
Average of contami-
nation rate
1.50 8.42
Figure 2. Contamination rate (%) in correlation with cord blood volume,
correlation coefficient r = −0.9 (A), in correlation of all cord blood
samples with a volume between 50 and 100mL (B). Number of cord
blood samples in correlation to sample volume (mL) and delivery mode
(C) and related to delivery mode and collection sample volume (D).
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Stem Cells Translational Medicine, 2022, Vol. XX, No. XX 5
to circulate compared to cesarean deliveries.35 In contrast,
Yamada et al34 conrmed a larger volume and higher con-
tent of CD34+ cells in collections from cesarean sections.34
It was hypothesized that the difference was due to the pos-
ition of the umbilical cord and the infant before clamping.
When the newborn is placed on the maternal abdomen after
delivery, the volume and content of CD34+ cells in the cord
blood increases.34,36
Some reports also described that vaginal delivery was asso-
ciated with higher TNC counts than at cesarean section.28,37,38
In agreement with Platz et al13 their study showed that cord
blood collections may have comparable amounts of nec-
essary cells in both vaginal births and cesarean sections.13
Additionally, it is also hypothesized that the causes of the lower
cell content in primary cesarean sections can be attributed
to for instance preoperative hemodilution.13 These results of
contamination rates in this study are well within the range
of those values reported in the literature (0.9%-8.6%).18,39-44
The inverse relationship between volume and contamina-
tion rate might be related to small veins, especially for smaller
volumes. Small veins may result in a longer collection time,
which may have some (albeit limited) impact on the com-
plete sterility of the cord throughout the collection process.
Furthermore, it should be noted that inexperienced staff may
also contribute to higher contamination rates. Although this
was not systematically evaluated in our study, there was a
trend to a higher contamination rate when blood samples
were drawn by less experienced staff and a separate study is
underway to further address this observation.
Also, re-attempting collection, especially if the umbilical
cord collapses quickly, can sometimes occur and sterility
may no longer be optimal. Beside the vaginal or as perianal
microbiomes source for contamination, kit contamination as
well as bacteria from skin cannot be excluded as source during
collection preparation and cryopreservation.15,16 Moreover, it
is evident that the preparation of CB for clinical use is another
challenge due to the small sample volume and special sterility
requirements that must be met. Studies are currently ongoing
to optimize UCB sample collection with a focus on diluting
the starting material, determining the best time for sample
collection, and collecting test samples from UCB residues, ie,
red blood cells.45 However, it should be noted that any sam-
pling for testing would reduce the quantity of stem cells avail-
able for transplantation.
Further results regarding the contamination rate related to
collection sample volume as well as delivery mode, both birth
modes showed also the inverse correlation between sample
volume and contamination rate (Fig. 2D). For spontaneous
birth, depending on the volume, the contamination rate
ranges from 14.1% for less than 30mL to 4.17% for more
than 150mL of cord blood collected. In contrast, cesarean
sections showed a contamination rate between 3.3% for less
than 30mL and 0% for more than 150mL volume (Table 1).
The dependence of contamination rate on the mode of de-
livery is even more evident in the signicantly higher average
contamination rate of 8.4% for vaginal deliveries compared
to 1.5% for cesarean deliveries (Table 1; Fig. 2D). The re-
lation of the results to each other is comparable to the one
described here, but the contamination rates in this study are
higher than other authors already showed contamination
rates of 4.1%, 5.31%, 5.6% at vaginal birth and 0.79% and
0.64% from cesarean sections are shown.13,21,39 The lower
Table 2. Most commonly detected bacterial strains in the 783 non-sterile
samples (A) and the most detected bacterial strains in all non-sterile cord
blood samples and the determined subfamilies (Bi-iii).
Bacterial strain Number of
cases
Percentage of
bacterial strains [%]
(A) 783 non-sterile samples
Staphylococcus species 295 37.68
Bacteroides species 173 22.09
Enterococcus species 171 21.84
Escherichia coli 106 13.54
Propionibacterium species 55 7.02
Corynebacterium species 42 5.36
Lactobacillus species 32 4.09
Parabacteroides species 29 3.70
Peptoniphilus species 23 2.94
Streptococcus species 21 2.68
(B i ) Staphylococcus subgroup
Staphylococcus epidermidis 115
Coagulase-negativeStaphy-
lococcusspecies
102
Staphylococcus hominis 27
Staphylococcus haemolyticus 20
Staphylococcus capitis 17
Staphylococcus lugdunensis 5
Staphylococcus
saccharolyticus
2
Staphylococcus caprae 1
Staphylococcus cohnii 1
Staphylococcus condimenti 1
Staphylococcus pettenkoferi 1
Staphylococcus warneri 1
Staphylococcus xylosus 1
Stapyhlococcus capitis 1
295 total
(B ii) Bacteroides subgroup
Bacteroides vulgatus 75
Bacteroides uniformis 38
Bacteroides species 14
Bacteroides fragilis 12
Bacteroides ovatus 10
Bacteroides stercoris 6
Bacteroides
thetaiotaomicron
5
Bacteroides cellulosilyticus 4
Bacteroides caccae 3
Bacteroides nordii 2
Bacteroides faecis 1
Bacteroides hetaiotaomicron 1
Bacteroides massiliensis 1
Bacteroides salyersiae 1
173 total
B (iii) Enterococcus subgroup
Enterococcus faecalis 99
Enterococcus species 12
Enterococcus faecium 7
Enterococcus avium 1
Enterococcus durans 1
Enterococcus hirae 1
121 total
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6Stem Cells Translational Medicine, 2022, Vol. XX, No. XX
contamination rate in cesarean sections is caused by the envi-
ronmental conditions of an operating room.13,21
In all non-sterile cord blood stem cell products (n = 783)
the most detected bacterial strains were Staphylococcus with
37.7% and Bacteroides species with 22.1% as well as E.
coli species with 13.5% (Fig. 3A; Table 2A) corresponding
to results of other authors.14-17,42,44,46 As bacterial subfamilies
S. epidermidis (38.9%, n = 295) and Bacteroides vulgatus
(43.4%, n = 173) were found (Table 2Bi and ii). The third
most common bacterial strain identied was Enterococcus
(21.8%, n = 121), especially Enterococcus faecalis as the most
common with 81.8% (Table 2Biii). The results are compa-
rable with those from other authors.16,18,21
The most frequently described bacterial strain Staphylococcus
species identied in cord blood samples from vaginal births
was also found in cesarean section samples, but it is remarkable
that propionibacterium acnes was the most frequently detected
with 40% (n = 50) in cesarean sections (Fig. 3B; Table 3).
Other authors also conrm the identication of relatively
high concentrations of propionibacterium acnes in cord
Figure 3. All detected bacterial strains in the 783 non-sterile samples (A). Detected percentage of bacterial strains in all cord blood samples and divided
into vaginal birth and cesarean section (B).
Table 3. Distribution of identified bacteria depended on the mode of
delivery.
Bacterial strain Percentage of bacterial strains (%)
All cases (independent
from delivery mode)
Vaginal
delivery
Cesarean
section
Staphylococcus species 37.68 37.93 34.00
Bacteroides species 22.09 23.60 0.00
Enterococcus species 21.84 22.92 6.00
Escherichia coli 13.54 14.05 6.00
Propionibacterium
species
7.02 4.77 40.00
Corynebacterium
species
5.36 5.73 0.00
Lactobacillus species 4.09 4.09 4.00
Parabacteroides species 3.70 3.96 0.00
Peptoniphilus species 2.94 2.14 0.00
Streptococcus species 2.68 2.73 2.00
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Stem Cells Translational Medicine, 2022, Vol. XX, No. XX 7
blood samples.20,44,47 Even if the average bacterial contamina-
tion rates is not higher than those of other studies, the anal-
ysis of the last 10 years shows an average contamination rate
between 6% and 9.5% (Fig. 5), which are comparable to the
described values from the literature.16
Even if not all bacteria survive the process of cryopreserva-
tion,44 it is clear the processes starting with the collection of the
umbilical cord blood, through the processing to the stem cell
preparation to the cryopreservation according to the national
guidelines and laws must be trained and optimized repeatedly
to be able to fulll the required parameters.14 Furthermore, it
must be ensured that multi-resistant bacteria, one of the great
challenges of our time, do not continue to advance.
Conclusion
The contamination rate of cryopreserved UCB is dependent
on delivery mode and is inversely correlated with the volume
of sample collected at birth. Based on the study presented here
several lines of evidence indicate that bacterial contamination
rates of UCB collected at birth for transplantation purposes
may be reduced by the collection of samples after cesarean
Figure 4. Number of TNC (A) and CD34+ stem cells (B) in correlation with the cord blood volume (mL). Vitality (%) of TNC (C) and vitality (%) CD34+
stem cells (D) both related to the sample volume respectively (mL).
Figure 5. History of the contamination rate (%) per year shown for the last 10 years.
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8Stem Cells Translational Medicine, 2022, Vol. XX, No. XX
delivery together with a high sample volume. In addition,
utilizing experienced and well-trained collection staff is able
to successfully complete the collection in a sterile manner even
in the presence of smaller veins, which can successfully reduce
insufcient puncture maneuver, which can clearly increase the
contamination rate.
Conflict of Interest
S.R., K.F., and C.G. are employees of the Famicord Group
Warsaw/Eticur GmbH Munich and Famicord Suisse SA. V.A.
is an employee of Famicord Group/Famicord Suisse SA. J.B.
is an employee of Polski Bank Komórek Macierzystych SA.
(PBKM) Famicord Group, Warsaw, Poland. W.D. is an em-
ployee at Worldwide Clinical Trials, United Kingdom.
Author Contributions
S.R.: conception and design, data analysis and interpretation,
manuscript writing. K.F.: data analysis and interpretation.
G.C., V.A., J.B.: proofreading and review of content. W.D.:
conception and design, manuscript writing.
Data Availability
The data that supports the ndings of this study are available
from the corresponding author upon reasonable request.
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