Middle East Fertility Society Journal xxx (2017) xxx–xxx
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Original Article
Co-culture of human embryos with autologous cumulus cell clusters and
its beneficial impact of secreted growth factors on preimplantation
development as compared to standard embryo culture in assisted
reproductive technologies (ART) q
Alexandros Vithoulkas a, Michael Levanduski b, Vasilios T. Goudas a,⇑, Karl Illmensee a
a
b
Genesis Fertility Center, Patras 264 42, Greece
Embryoserv Inc., NJ 07675, USA
a r t i c l e
i n f o
Article history:
Received 23 January 2017
Revised 7 May 2017
Accepted 29 May 2017
Available online xxxx
Keywords:
IVF
IVF outcome
Human embryo co-culture
Standard embryo culture
Standard culture media
Autologous cumulus cell clusters
Embryo culture supernatant
Uterine transfer
Follicular aspiration
Cumulus-oocyte complex
Vitrification
Preimplantation embryo
Human early embryo
Human preimplantation embryo
development
Grade-1 embryo
Grade-1 blastocyst
Cellular fragmentation
a b s t r a c t
Objective: To analyze the concentration of growth factors secreted by autologous cumulus cell clusters
during in vitro human embryo co-culture and investigate the impact of culture supplementation with
autologous cumulus cell clusters on embryo development and pregnancy rate as compared to standard
culture procedure.
Design: Randomized prospective comparative study.
Setting: Private IVF clinic.
Patients: 90 IVF patient couples ranging at the age between 35 and 40 (mean age of 36.5) agreed to participate in this study. In this IVF group, 64 first trials, 22 s trials and 4 third trials were included. 48 cases
have been terminated at day 3 of culture and 42 of them have been continued up to day 5. Of the 48 cases
assigned for day-3 culture, 208 MII-oocytes were randomly assigned for co-culture and 197 MII-oocytes
were assigned for standard culture. The selection was done by alternating the oocyte immediately after
stripping to co-culture or control, starting always with co-culture.
Interventions: All samples were analyzed with Milliplex factor-specific magnetic-bead panels with phycoerythrin fluorescent factor-specific antibodies using immunofluorescence cytometry technology by Lab
Supplies Inc. laboratories in Athens, Greece. The MFI (Mean Fluorescence Intensity) values were calibrated and the readings were translated in pg/ml and calculated against the background values of culture
medium alone. The statistical analysis of all data were processed with the Two-tailed T-test form.
Main outcome measures: 36 IVF cases terminated at day 3 were randomly chosen. Supernatants from 17
cases were analyzed for seven different growth factors, namely, epidermal growth factor (EGF), fibroblast
growth factor 1 and 2 (FGF-1 and FGF-2), vascular endothelial growth factor A, C and D (VEGF-A, VEGF-C
and VEGF-D) and Leptin. Supernatants from 19 cases were analyzed for Insulin-like Growth Factor I and II
(IGF-I and IGF-II).
Results: VEGF-A and VEGF-C were found at statistically significant levels (p < 0.005) in culture supernatant samples where the autologous cumulus clusters were present but were not detectable in supernatants of embryos cultured alone. IGF-I was detected at considerable levels in supernatant samples
where the autologous cumulus clusters were present. IGF-I was not detectable in supernatant samples
of embryos cultured alone. IGF-II was detected in significant amounts (p < 0.05) in samples of all groups.
The highest concentration level of IGF-II was detected in supernatant samples of embryos in standard culture.
Conclusion(s): The investigated factors, among other substances, may be causally connected to the beneficial effect observed on embryo development. Our findings suggest that co-culture with autologous
cumulus cell clusters improves the outcome of embryo culture in IVF programs.
Ó 2017 Middle East Fertility Society. Production and hosting by Elsevier B.V. This is an open access article
under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer review under responsibility of Middle East Fertility Society.
⇑ Corresponding author.
http://dx.doi.org/10.1016/j.mefs.2017.05.009
1110-5690/Ó 2017 Middle East Fertility Society. Production and hosting by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: A. Vithoulkas et al., Co-culture of human embryos with autologous cumulus cell clusters and its beneficial impact of
secreted growth factors on preimplantation development as compared to standard embryo culture in assisted reproductive technologies (ART), Middle
East Fertil Soc J (2017), http://dx.doi.org/10.1016/j.mefs.2017.05.009
2
A. Vithoulkas et al. / Middle East Fertility Society Journal xxx (2017) xxx–xxx
1. Introduction
During the past twenty years many scientific reports have been
published on the subject of improving in vitro culture of human
embryos in ART [1–4]. With the addition of feeder layers or helper
cells from various tissue types (e.g. endometrium, fallopian tube,
ovarian follicle, oviduct epithelium, vero cells, fibroblasts,
granulosa-cumulus cells) a positive effect on quality and quantity
of developing embryos has been observed in comparison to standard culture conditions for in vitro fertilization (IVF) cycles [5–
11]. In particular, cumulus cells that support the growing oocyte
and are physiologically linked to oocyte maturation are instantly
available after follicular aspiration of cumulus-oocyte complexes
for IVF. They can be easily harvested and successfully used to assist
in embryo culture [12–16]. During such co-culture these cells not
only seem to be responsible for ameliorated embryo morphology
but also may provide a beneficial effect on embryo implantation
and pregnancy rates in IVF programs [17–19].
It has been demonstrated that various growth factors secreted
by feeder cells can promote oocyte maturation and support development of early embryos during in vitro culture, analogously, as
they take part in cross-cellular processes under in vivo conditions.
Significant progress in growth factor-related effectiveness through
co-culture has been reported for reduced fragmentation and
improved cleavage in early embryos, for increased numbers of
developing embryos and elevated pregnancy rates [20–22]. The
composition and cooperation of growth factors may vary among
different helper cell types by synthesizing these factors in
embryo-unrelated or less physiological concentrations. The presence of undesirable growth factors secreted during co-culture
can also lead to uncontrolled in vitro conditions resulting in developmental alterations during early embryogenesis [23].
As alternative approach individual growth factors at defined
concentrations have been added deliberately to standard culture
medium to evaluate their efficacy on embryo development and
IVF outcome. The insulin-like growth factor (IGF-I) when provided
to the culture medium has reduced cellular apoptosis and
increased the proportion of morphologically normal embryos
[24,25]. The granulocyte-macrophage colony-stimulating factor
(GM-CSF) supplemented to culture medium has improved blastocyst development and IVF outcome [26–28]. Exposure of early
human embryos to the platelet activating factor (PAF) during
in vitro culture has led to increased birth rates in ART [29,30].
The heparin-binding epidermal growth factor (HB-EGF) significantly improved development and hatching ability of human blastocysts [31]. The leukemia-inhibiting factor (LIF) has increased
implantation and pregnancy rates [32].
The addition of only single factors to culture media remains in
opposite to the complex mixture of multiple autocrine/paracrine
factors interacting with oocytes and embryos in vivo. Therefore,
supplementation of several key growth factors to the culture medium has been propagated and resulted in a substantial increase of
high quality blastocysts in comparison to standard culture conditions [33]. Such beneficial effect most likely was due to the additive
action of multiple growth factors. The detection of multiple receptors for different growth factors on the surface of early embryos
documents the importance of manifold exchange and selective
impact of stage-specific morphogenetic products between developing embryo and surrounding cells during preimplantation [34].
Such molecular cross-communication can only insufficiently take
place in standard culture media that deprive embryos of vital
growth factors. This may imply potential risks associated with
standard IVF since early embryos via their receptors cannot
respond to and interact with the respective growth factors
[23,35]. It therefore seems reasonable to assume that follicular
cumulus cells with their particular assortment of secreted growth
factors more closely resemble and re-enact the physiological environment in support of sustaining embryo culture in vitro [36].
About five years ago we reported that supplementation of
autologous cumulus cell clusters to the culture medium has
improved embryo morphology and increased the number of
embryos available for uterine transfer in ART [37]. Moreover, we
detected the presence of several growth factors during co-culture
that most likely have contributed to this qualitative and quantitative amelioration of embryogenesis [38,39]. In the study presented
here we have further investigated the impact of autologous cumulus clusters co-culture on embryo development and pregnancy rate
as compared to standard culture procedure. We also have analyzed
the concentration of growth factors secreted by cumulus cells during in vitro culture. We suggest that these factors, among other
substances, might be causally connected to the beneficial effect
observed on embryo development. Our findings support the concept of co-culture with autologous cumulus cell clusters and will
contribute to continuously optimize embryo culture in IVF
programs.
2. Material and methods
2.1. Co-culture and standard culture
90 IVF patient couples ranging at the age between 35 and 40
(mean age of 36.5) agreed to participate in this study. In this IVF
group, 64 first trials, 22 s trials and 4 third trials were included
(Table 1). As prerequisite, patients with prospective eight or more
oocytes were considered for this study. After follicular aspiration
the cumulus-oocyte complexes were kept shortly in follicular fluid
in order to cut off equal pieces of cumulus using fine syringe needles. The oocyte complexes together with the isolated cumulus
clusters were washed in Human Tubal Fluid buffered with HEPES
(HTF-HEPES) (IrvineScientific, Waalwijk, The Netherlands) supplemented with 10% Serum Substitute Supplement (SSS) (Santa Ana,
CA, US) and transferred to Human Tubal Fluid (HTF) (IrvineScientific, Waalwijk, The Netherlands) for one hour. Subsequently,
oocytes were stripped from their adhering cumulus cells with Hyaluronidase (Cook, Limerick, Ireland), washed in HTF-HEPES supplemented with 10% SSA and kept in Continuous Culture medium
(CSC) (IrvineScientific, Waalwijk, The Netherlands) for 15 min.
For each case, the prepared MIIoocytes were divided randomly in
two groups. Half of the MII-oocytes were assigned to co-culture
(group I) and the other half were assigned to culture in regular
medium (group II). As control, isolated autologous cumulus clusters were assigned to be cultured alone (group C). This was done
by assigning the first oocyte after stripping to the co-culture group
and thereafter alternating to the control standard (no co-culture)
group.
After ICSI treatment, MII-oocytes of group I and II were transferred separately to microdrops of CSC medium covered with FertiCult Mineral Oil (FertiPro NV, Beemem, Belgium). For each
microdrop of group I and group C one equally sized piece of isolated cumulus cluster was added. One microdrop of pure culture
medium was kept empty as additional background control. For
each case, all microdrop samples were kept on the same culture
dish. On day-3 of culture, 50.l of supernatants from embryo cultures of group I and II were collected and stored frozen at -20oC.
Supernatants from cultured cumulus clusters (group C), as well
as microdrops of pure culture medium were similarly collected
and stored frozen as controls.
At day 3 or day 5 of embryo culture, grade-1 embryos or blastocysts from group I were selected for embryo transfer (ET). The
Please cite this article in press as: A. Vithoulkas et al., Co-culture of human embryos with autologous cumulus cell clusters and its beneficial impact of
secreted growth factors on preimplantation development as compared to standard embryo culture in assisted reproductive technologies (ART), Middle
East Fertil Soc J (2017), http://dx.doi.org/10.1016/j.mefs.2017.05.009
3
A. Vithoulkas et al. / Middle East Fertility Society Journal xxx (2017) xxx–xxx
Table 1
Clinical data for the 90 IVF cases assigned for co-culture and standard culture comparison.
Transfer day
IVF cases, n
3
48
5
42
Patient mean age
First trials
Second trials
Third trials
Total embryos transferred
Embryos per transfer
38.4
33
11
4
144
3
36.6
31
11
0
97
2
Metaphase II (MII) oocytes
2PN/Fertilization rate
Grade 1 embryos/embryo development rate
Grade 1 blastocysts/blastulation rate
Pregnancies/pregnancy rate
Ongoing pregnancies/ongoing pregnancy rate
Co-culture
Standard culture
Co-culture
Standard culture
208
186/89.4%
157/84.4%
–
19/39.6%
18/37.5%
197
159/80.7%
106/66.7%
–
–
–
232
223/96%
208/93.3%
145/65%
23/55.8%
20/47.6%
228
198/86.8%
164/82.8%
70/35.4%
–
–
remaining grade-1 embryos or blastocysts of group I and II were
vitrified using KITAZATO Vitrification Media (KITAZATO BioPharma
Co., Ltd, Japan) and stored in liquid nitrogen.
group I and II were vitrified and cryostored. The pregnancy rate
for day-5 ETs was 55.8% (Table 1).
3.2. Growth factors associated with co-culture
2.2. Growth factor analysis
From the 36 randomly chosen IVF cases terminated at culture
day-3, supernatants from 17 cases were analyzed for seven different growth factors, namely, epidermal growth factor (EGF), fibroblast growth factor 1 and 2 (FGF-1 and FGF-2), vascular endothelial
growth factor A, C and D (VEGFA, VEGF-C and VEGF-D) and Leptin
using immunofluorescence cytometry with a factor-specific
magnetic-bead panel. Supernatants from 19 cases were analyzed
for Insulin-like Growth Factor I and II (IGF-I and IGF-II) with
another growth factor-specific magnetic-bead panel. All samples
were analyzed with Milliplex factor-specific magnetic-bead panels
with phycoerythrin fluorescent factor-specific antibodies by Lab
Supplies Inc. laboratories in Athens, Greece. The MFI (Mean Fluorescence Intensity) values for group I, group II and group C supernatants were calibrated and the readings were translated in pg/ml
and calculated against the background values of culture medium
alone. The statistical analysis of all data were processed with the
Two-tailed T-test form.
3. Results
3.1. Embryo co-culture versus standard culture
From 90 investigated cases that were considered for co-culture
and standard culture, 48 of them have been terminated at day 3 of
culture and 42 of them have been continued up to day 5. From 48
cases randomly assigned for day-3 culture, 208 MII-oocytes were
assigned for co-culture (group I) and 197 MII-oocytes were
assigned for standard culture (group II). After ICSI treatment the
fertilization rates were 89.4% (group I) versus 80.7% (group II).
The total number of developing grade-1 embryos was 157 (group
I) and 106 (group II). For day-3 ET, 144 embryos were selected from
co-culture (group I). The remaining 119 embryos from groups I and
II were vitrified and cryostored.
The pregnancy rate for day-3 ETs was 39.6% (Table 1). From 42
cases randomly assigned for day-5 culture, 232 MII-oocytes were
assigned for co-culture (group I) and 228 MII-oocytes were
assigned for standard culture (group II). After ICSI treatment the
fertilization rates were 96.1% (group I) versus 86.8% (group II).
The total number of developing grade-1 blastocysts was 145
(group I) versus 70 (group II). For day-5 ET, 97 blastocysts were
selected from co-culture. The remaining 118 blastocysts from
From 17 investigated cases, VEGF-A and VEGF-C were found at
statistically significant levels in supernatant samples where the
autologous cumulus clusters were present (group I and group C)
but were not detectable in samples of group II where embryos
were cultured alone (Fig 1). For VEGFA, the p values were <0.005
and <0.01 from samples of group I and group C respectively. For
VEGF-C, the p values were <0.05 and <0.01 from samples of group
I and group C respectively. FGF-2 was detected in considerable
concentration levels in samples of group I and C (Fig 1). However,
differences in concentration of FGF-2 between group I and C were
not statistically significant. Among the 17 cases investigated, variations in concentration levels were detected for the three growth
factors. The mean values of VEGF-A, VEGF-C and FGF-2 concentrations for all groups are presented in Table 2. EGF and FGF-1 were
only detectable in very low concentrations in group I and C values
ranging from 0.5 to 1.5 pg/ml. VEGF-D and Leptin could not be
detected in any of the analyzed samples within the concentration
sensitivity range of the immunofluorescence cytometry technology
used. From 19 investigated cases, IGF-I was detected at considerable levels in samples of group I and group C where cumulus clusters were present. The difference in concentration levels of IGF-I
between group I and C was not statistically significant. IGF-I was
not detectable in samples of group II, where embryos were cultured alone (Fig 2). IGF-II, on the contrary, was detected in significant amounts in samples of all groups. Unexpectedly, the highest
concentration level of IGFII was detected in samples of group II (Fig
2). For IGF-II, the p values of group I (<0.05) and C (<0.04) were at
statistically significant lower levels when compared to group II.
Among the 19 cases investigated, variations in concentration levels
have been observed for both growth factors. The mean values of
IGF-I and IGF-II concentrations for all groups are presented in
Table 3.
4. Discussion
There is currently evidence that standard culture media used
for IVF are optimal for human early embryos. Morphometric observations on preimplantation embryos cultured in standard media
have revealed that some embryos showed retarded cleavage divisions, reduced growth rates and increased proportion of lesscompacted inner cell mass (ICM) in blastocysts [23]. Disruption
of normal genomic imprinting during embryogenesis due to
inferior culture conditions may contribute to developmental
Please cite this article in press as: A. Vithoulkas et al., Co-culture of human embryos with autologous cumulus cell clusters and its beneficial impact of
secreted growth factors on preimplantation development as compared to standard embryo culture in assisted reproductive technologies (ART), Middle
East Fertil Soc J (2017), http://dx.doi.org/10.1016/j.mefs.2017.05.009
4
A. Vithoulkas et al. / Middle East Fertility Society Journal xxx (2017) xxx–xxx
Fig. 2. Graph showing the concentration distribution of growth factors IGF-I and
IGF-II in all studied groups.
Table 3
Mean concentration (pg/ml) of growth factors IGF-I and IGF-II in supernatants of
human embryo culture supplemented with (group I) and without (group II) cumulus
cell clusters, and in controls (group C). Differences in concentration of IGF-I between
group I and C were not statistically significant. For IGF-II, the p values of group I
(<0.05) and C (<0.04) were at statistically significant lower levels when compared to
group II (Two-tailed T-test).
Growth factor
IGF-I
IGF-II
Group I (pg/ml)
Group II (pg/ml)
Group C (pg/ml)
6 ± 3.5
0.1 ± 0
9 ± 0.6
28 ± 16.4
68 ± 9.3
27 ± 14.6
n = 19.
Fig. 1. Graph showing the concentration distribution of growth factors VEGF-A,
VEGF-C and FGF-2 in all studied groups.
Table 2
Mean concentration (pg/ml) of growth factors VEGF-A, VEGF-C and FGF-2 in
supernatants of human embryo culture supplemented with (group I) and without
(group II) cumulus cell clusters, and in controls (group C). For VEGF-A, the p values
were <0.005 and <0.01 from samples of group I and group C respectively. For VEGF-C,
the p values were <0.05 and <0.01 from samples of group I and group C respectively.
Differences in concentration of FGF-2 between group I and C were not statistically
significant (Two-tailed T-test).
Growth factor
VEGF-A
VEGF-C
FGF-2
Group I (pg/ml)
Group II (pg/ml)
Group C (pg/ml)
2889 ± 418.6
24.4 ± 10.2
1209.5 ± 214.9
67.92 ± 24
0.1 ± 0
15.25 ± 5.9
46 ± 19.5
0.5 ± 0
256.42 ± 92.7
n = 17.
abnormalities. Imprinting errors caused by altered DNA methylation could be initiated in preimplantation embryos. There have
been studies indicating minor elevated risks for genetic imprinting
diseases [40–42] and for two systemic syndromes caused by epige-
netic alterations through abnormal imprinting in ART programs
[43,44]. Substantial improvements for embryo culture in IVF have
been achieved by co-culture with cumulus cells. Positive effects of
such co-culture have been observed on accelerated cleavage divisions, reduced cellular apoptosis and increased number of high
quality blastocysts. Embryo co-cultures have been shown to
increase embryo implantation and pregnancy rates in IVF patients
[18]. It also seems to improve blastocyst transfer in IVF patients
with repeated implantation failures [19]. Cumulus cells have
shown to remain viable up to ten days in culture as estimated from
morphological criteria and therefore continue to be viable beyond
embryo implantation [18]. Preferably for each IVF case autologous
cumulus cells should be selected from the same patient. Isolated
cumulus cells are quite homogeneous and their protein expression
profiles are very similar between cumulus cells from different
oocytes retrieved from the same patient. On the contrary, dissimilarities in protein profiles of cumulus cells have been detected
between patients depending on their particular ovarian stimulation protocols [45]. In fact, there seems to be a good correlation
between specific synthesis of cumulus cell proteins and oocyte
maturity required for normal embryo development. Cumulus
Please cite this article in press as: A. Vithoulkas et al., Co-culture of human embryos with autologous cumulus cell clusters and its beneficial impact of
secreted growth factors on preimplantation development as compared to standard embryo culture in assisted reproductive technologies (ART), Middle
East Fertil Soc J (2017), http://dx.doi.org/10.1016/j.mefs.2017.05.009
A. Vithoulkas et al. / Middle East Fertility Society Journal xxx (2017) xxx–xxx
cell-specific gene products can therefore lead to the discovery of
new biomarkers predictive of embryo quality and pregnancy outcome in IVF [46,47].
In our comparative study of embryos cultured with (group I)
and without (group II) autologous cumulus clusters we found that
under co-culture conditions the cleavage divisions of early
embryos were accelerated with more equally sized blastomeres,
embryo morphology was improved giving rise to increased numbers of grade-1 embryos and blastocysts available for ET and
cryo-storage for further IVF trials. On the contrary, embryos cultured in standard medium showed a decreased growth rate with
more unequal cleavage divisions and cellular fragmentation. The
total number of grade-1 embryos was reduced substantially with
increased numbers of arrested embryos. Only embryos and blastocysts of high quality were kept frozen as supplementary reserve for
future ETs. In addition, we obtained a significant increase in the
number of grade-1 blastocysts derived from co-culture when compared to standard culture conditions (65% versus 35.4%). Previously, under standard culture conditions in IVF, our overall
pregnancy rate had been 24%. Since the introduction of coculture with autologous clusters in IVF, our overall pregnancy rate
increased to 36%. Therefore, based on these observations, we have
routinely shifted to the co-culture system in our IVF practices for
embryo culture in vitro. Our findings are in good agreement to
other comparable studies where cumulus cells instead of cumulus
clusters have been used for co-culture of human embryos in ART
[18,19].
Growth factors secreted by cumulus cells during co-culture
have shown to be partially responsible for the beneficial effect
observed on human embryo development in IVF [23,35]. In our
studies to investigate the presence of growth factors secreted by
cumulus clusters during embryo co-culture, we found significant
concentrations of VEGF-A and VEGF-C. Their concentration in samples of group I was significantly higher as compared to samples of
group C and was not detectable in samples of group II (Fig 1). We
assume that embryos in standard culture are not synthesizing
these two growth factors whereas embryos under co-culture conditions either seem to be capable of synthesizing VEGF-A and
VEGF-C or cumulus cells secreted a higher amount of these two
factors. Alternatively embryos together with cumulus cells are synergistically responsible for this concentration increase. Growth factor FGF-2 was not detected in samples of group II but was present
in samples of group I and C (Fig 1). We conclude that this growth
factor is not synthesized by embryos cultured in standard medium
but is secreted in considerable amount by the cumulus clusters
alone. Concerning the reduced concentration in samples of group
I we can only suspect that either embryos have consumed this
growth factor or a substantial amount of FGF-2 has been metabolized under co-culture conditions. For these three growth factors
that we have detected under co-culture conditions there is published evidence for their functional role in human preimplantation
embryo development and IVF outcome [23,35].
For growth factor IGF-I, we have detected considerable amounts
of this factor in samples of group I and C but not in samples of
group II (fig 2). We conclude that this factor is not being synthesized by the embryo but secreted by the cumulus cells. The
reduced amount of IGF-I in group I versus group C may be due to
either metabolic consumption and/or uptake by the embryos during co-culture. It was shown previously that the addition of IGF-I to
culture media prevented apoptosis in preimplantation embryos by
reducing cellular fragmentation, increasing the number of healthy
blastomeres and improving the morphology of the developing
blastocysts that resulted in increased implantation and pregnancy
rates [24,25,48].
For growth factor IGF- II, we detected significant amounts of
this factor in samples of all groups (Fig 2). Whereas the concentra-
5
tion of this factor is almost equally present in group I and C it is significantly increased in samples of group II. We assume that similar
levels of IGF-II in co-culture and cumulus-culture reflect the normal amount of this growth factor that is secreted and/or downregulated under co-culture conditions. It has been known for quite
some time that IGF-II is being synthesized by the embryo itself
[49]. However, when we compare the level of secreted IGF-II in
group II with the levels of group I and C we found a statistically significant elevated IGF-II concentration. We postulate that embryos
in standard culture (group II) are over synthesizing IGF-II leading
to altered concentration of this particular growth factor. On the
other hand, under co-culture conditions, secretion of IGF-II seems
to reach a more physiological level for embryos (group I) and
cumulus cells (group C). Based on these new findings, we suggest
that in standard medium early embryos with the appropriate surface receptors are deprived of external molecular cross-reactions
with gene products secreted by cumulus cells. Such unbalanced
IGF-II concentration may have a negative effect on regular embryogenesis [49,50]. It may also be linked to genetic imprinting diseases
and epigenetic abnormalities in ART programs [40–44].
To improve standard culture conditions, attempts have been
made by addition of individual growth factors [29–32]. However,
supplementation of culture media with individual growth factors
can only insufficiently fulfill the manifold metabolic requirements
needed for the developing embryos. New approaches to further
improve culture conditions have been introduced by supplementing the culture medium with a mixture of several key growth factors that improve embryo morphology and implantation potential
[33]. As alternative approach, supplementation of standard culture
medium with autologous cumulous clusters creates a physiological
environment which more closely support the biological needs for
the developing embryo. Despite of advanced knowledge about
the physiological contribution of growth factors, further investigations are needed to unveil the complexity of cross-communication
between growth factors and their receptors and their crucial role in
oocyte maturation and early embryo development. This may also
lead to predictive and specific biomarkers for high quality oocytes
and embryos applicable for IVF programs [50].
Conflict of interest
The authors declared that there is no conflict of interest.
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Please cite this article in press as: A. Vithoulkas et al., Co-culture of human embryos with autologous cumulus cell clusters and its beneficial impact of
secreted growth factors on preimplantation development as compared to standard embryo culture in assisted reproductive technologies (ART), Middle
East Fertil Soc J (2017), http://dx.doi.org/10.1016/j.mefs.2017.05.009