Steering Siglec–Sialic Acid Interactions on Living Cells using Bioorthogonal Chemistry

Article abstract of DOI:10.1002/anie.201612193

Sialic acid sugars that terminate cell-surface glycans form the ligands for the sialic acid binding immunoglobulin-like lectin (Siglec) family, which are immunomodulatory receptors expressed by immune cells. Interactions between sialic acid and Siglecs regulate the immune system, and aberrations contribute to pathologies like autoimmunity and cancer. Sialic acid/Siglec interactions between living cells are difficult to study owing to a lack of specific tools. Here, we report a glycoengineering approach to remodel the sialic acids of living cells and their binding to Siglecs. Using bioorthogonal chemistry, a library of cells with more than sixty different sialic acid modifications was generated that showed dramatically increased binding toward the different Siglec family members. Rational design reduced cross-reactivity and led to the discovery of three selective Siglec-5/14 ligands. Furthermore, glycoengineered cells carrying sialic acid ligands for Siglec-3 dampened the activation of Siglec-3⁺ monocytic cells through the NF-κB and IRF pathways.

Full text of DOI:10.1002/anie.201612193

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International Edition: DOI: 10.1002/anie.201612193
German Edition: DOI: 10.1002/ange.201612193
Bioorthogonal Chemistry
Steering Siglec–Sialic Acid Interactions on Living Cells using
Bioorthogonal Chemistry
Christian Bꢀll+, Torben Heise+, Niek van Hilten, Johan F. A. Pijnenborg, Victor Bloemendal,
Lotte Gerrits, Esther D. Kers-Rebel, Tina Ritschel, Martijn H. den Brok, Gosse J. Adema†,* and
Thomas J. Boltje†*
Abstract: Sialic acid sugars that terminate cell-surface glycans
form the ligands for the sialic acid binding immunoglobulin-
like lectin (Siglec) family, which are immunomodulatory
receptors expressed by immune cells. Interactions between
sialic acid and Siglecs regulate the immune system, and
aberrations contribute to pathologies like autoimmunity and
cancer. Sialic acid/Siglec interactions between living cells are
difficult to study owing to a lack of specific tools. Here, we
report a glycoengineering approach to remodel the sialic acids
of living cells and their binding to Siglecs. Using bioorthogonal
chemistry, a library of cells with more than sixty different sialic
acid modifications was generated that showed dramatically
increased binding toward the different Siglec family members.
Rational design reduced cross-reactivity and led to the discov-
ery of three selective Siglec-5/14 ligands. Furthermore, glyco-
engineered cells carrying sialic acid ligands for Siglec-3
dampened the activation of Siglec-3+ monocytic cells through
the NF-kB and IRF pathways.
cell-surface glycan chains and regulate the immune system by
interacting with the sialic acid binding immunoglobulin-like
lectin (Siglec) family.[2] In humans, 14 Siglecs (Siglecs-1–11
and Siglecs-14–16) are expressed on immune cells. Siglecs
contain an extracellular sialic acid binding domain and most
Siglecs contain an intracellular immunoreceptor tyrosine-
based inhibitory motif (ITIM; Scheme 1).[3] Alternatively,
Siglecs-14–16 can recruit an immunoreceptor tyrosine-based
activation motif (ITAM). Siglecs can bind to sialic acids
present on the same cell (cis binding) or sialic acids present on
an adjacent cell (trans binding), and in general, these
interactions dampen immune-cell activation.[2c,3–5] Aberra-
tions in sialic acid and Siglec expression have been associated
with autoimmunity, inflammatory diseases, neurodegenera-
tion, and cancer.[4,6] Although the importance of the sialic
acid/Siglec interaction in immune regulation is well docu-
mented, its role in physiological and pathological processes is
still poorly understood.[4] To elucidate the function of sialic
acid/Siglec interactions, tools are needed to specifically target
Siglecs in a cellular context. This is difficult since sialic acids
bind Siglecs in a monovalent manner with low affinity (0.1–
3 mm).[2c] Chemical modification of sialic acids can augment
Siglec binding affinity and selectivity, and such modifications
can be introduced through copper-catalyzed azide–alkyne
cycloaddition (CuAAC).[7,8] However, these approaches are
often not applicable to cell-based assays and lack multivalent
presentation in a natural context, which is a crucial determi-
nant in Siglec binding.[9] Recently, sialoglycan-decorated
polymers have been developed that can be integrated into
the cell surface to bind Siglec-7.[10] However, the use of
unnatural polymers does not provide a natural context and is
labor-intensive.
Therefore, we investigated the possibility of using bio-
orthogonal chemistry to modify sialic acids on living cells to
enhance their binding to Siglecs whilst maintaining their
natural multivalent presentation on the cell surface
(Scheme 1). To this end, alkyne- or azide-modified sialic
acids were metabolically incorporated into living cells and
reacted with over sixty different azides/alkynes using
CuAAC.[11] The obtained library of glycoengineered cells
was screened for binding to the human Siglec family and this
led to the identification of modifications that dramatically
increase Siglec binding (> 100 fold). Using structure-guided
design, sialic acid modifications highly selective for Siglec-5
and its homologue Siglec-14 were developed. Finally, func-
tional analysis showed that the glycoengineered cells pro-
grammed to bind Siglec-3 are able to dampen the activation of
Siglec-3+ immune cells.
T
he immune system defends the host from pathogens and
cancer yet must discriminate between self and non-self to
avoid damage to healthy tissue. An important differentiator
in this respect is the presence or absence of sialic acid sugars
on the cell surface.[1] Sialic acids are found on the terminus of
[*] T. Heise,[+] J. F. A. Pijnenborg, V. Bloemendal, L. Gerrits, Dr. T. J. Boltje
Institute for Molecules and Materials
Heyendaalseweg 135, 6525 AJ, Nijmegen (The Netherlands)
E-mail: t.boltje@science.ru.nl
C. Bꢀll,[+] E. D. Kers-Rebel, Dr. M. H. den Brok, Prof. Dr. G. J. Adema
Department of Radiation Oncology
Radiotherapy & OncoImmunology Laboratory
Radboud University Medical Center
Geert Grooteplein Zuid 32, 6525 GA, Nijmegen (The Netherlands)
E-mail: G.Adema@radboudumc.nl
N. van Hilten, Dr. T. Ritschel
Computational Discovery and Design Group
Centre for Molecular and Biomolecular Informatics
Radboud University Medical Center
Geert Grooteplein 26–28, 6525 GA, Nijmegen (The Netherlands)
Dr. M. H. den Brok
Department of Anesthesiology, Pain and Palliative Medicine
Radboud University Medical Center
Geert Grooteplein 10, 6525 GA, Nijmegen (The Netherlands)
[+] These authors contributed equally to this work.
[†] These authors contributed equally to this work.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
http://dx.doi.org/10.1002/anie.201612193.
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Scheme 1. Sialic acid glycoengineering on living cells to modulate Siglec-mediated immune responses.
Glycoengineering was achieved by culturing Jurkat cells
in the presence of Ac5NeuNPoc or Ac5NeuNAz, which results
in the expression of alkyne and azide sialoglycans on the cell
surface (Figure S1a; Ac5Neu = N-acetylneuraminic acid,
Poc = propargyloxycarbonyl, Az = azidoacetyl.[11a] Jurkat
cells were used because they express a2,3- and a2,6-sialic
acids but do not express Siglecs thereby circumventing cis
binding (Figures S2,S3 in the Supporting Information). To
confirm the efficient incorporation of alkyne- and azide-
modified sialic acids, the cells were reacted with azide- or
alkyne-conjugated biotin (azide/alkyne-biotin) using CuAAC
in the presence of histidine to minimize cytotoxicity.[12] Biotin-
tagged surface glycans were detected with streptavidin-
conjugated phycoerythrin (streptavidin-PE) by flow cytom-
etry. As expected, high fluorescence was detected for
Ac5NeuNPoc and Ac5NeuNAz but not for the control sialic
acid Ac5NeuNAc (Figure S1b). Next, cells carrying alkyne- or
azide-modified sialoglycans were reacted with 49 different
azides (L1–L49) and 15 different alkynes (L50–L64; Figures
S4,S5), respectively. To determine the reaction efficiency,
a second reaction was performed with azide/alkyne-biotin to
detect remaining alkynes/azides. All azides and alkynes tested
showed reaction efficiencies of more than 78% (Figure 1).
L1–L64 were selected on the basis of known structures and
in silico docking experiments (see below).[8a,13]
Figure 1. Generation of a sialic acid modified cell library using click
chemistry.
To maximize the exploration of chemical space neighbor-
ing the sialic acid binding domain, aromatic, aliphatic, and
charged azides or alkynes were synthesized. In addition,
functional groups that can engage in hydrogen bonding were
included (Figures S4,S5). Having demonstrated that L1–L64
react efficiently with the clickable sialic acids, the binding of
available recombinant human Siglecs in the form of Silglec–
Fc chimeras (Fc = fragment crystallizable region of an anti-
2
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Figure 2. Screening of the sialic acid modified cell library for binding to the human Siglec family.
body) to the modified cells was assessed. To detect binding,
the recombinant Siglec–Fc chimeras were precomplexed to
Alex Fluor 647 (AF647)-conjugated anti-human-Fc antibod-
ies. The AF647-conjugated anti-human-Fc antibodies alone
showed no binding to L1–L64-modified Jurkat cells, but
significant changes in binding of the precomplexed Siglec–Fc
chimeras to the glycoengineered cell library was observed
(Figure 2 and Table S1 in the Supporting Information). The
addition of L1–64 to alkyne and azide sialic acid treated cells
in the absence of CuSO4 had no effect on Siglec binding, as
expected (Figures S6,S7). From the data shown in Figure 2, it
is clear that chemical modification of the sialic acids on living
cells drastically alters their interaction with Siglecs. Based on
the binding patterns, the Siglec family could be roughly
divided into two main groups. The first group includes Siglecs-
2, -3, -6, -8, -10, and -11, which reacted with only a few (1–6) of
the sialic acid modifications presented by the cells. The
second group, which includes Siglecs-5/-14, -7, and -9, reacted
with many (11–49) glycoengineered cells. In contrast, no
significant change in the binding of Siglec-4 to any of the
modified cells was found. To confirm applicability across
different cells lines, HEK293 kidney cells treated with
Ac5NeuNPoc were reacted with a selection of azides and
screened for Siglec binding. Similar results to those in the
Jurkat cell were obtained, which confirmed that the sialic acid
modifications specifically enhance Siglec binding (Figure S6).
Except for Siglec-4, glycoengineered cells were identified for
each Siglec family member tested, including the orphan
Siglecs, Siglecs-6, -8, and -11. Some modifications showed
affinity to multiple Siglecs. While these modifications could
be useful to target different Siglecs at the same time, selective
targeting is required to study or manipulate an individual
Siglec family member. Siglecs-5/-14, -7, and -9 showed similar
binding preferences for sialic acids modified with benzyl
azides (Figure 2).
To investigate the possibility of selectively targeting
individual Siglecs, we modeled the benzyl derivatives into
the crystal structure of Siglec-5.[14] This revealed an aspartic
acid residue (D130) in the F-G turn close to the sialic acid
modification. Sequence alignment of Siglecs-7 and -9 showed
that neither of them shares a negatively charged amino acid at
this position (Figure S8). We reasoned that positively charged
modifications such as L24–L26 could form a salt bridge with
D130 and might allow for the selective binding of Siglec-5/-14,
which was confirmed by docking experiments (Figure 3a,
Figure S11). We therefore synthesized L24–L26, and as
predicted, the presence of these positively charged groups
on the surface of Jurkat cells strongly enhanced binding to
Siglec-5 and its homologue Siglec-14 but not to Siglecs-7 and
-9 or any other Siglec family member (Figure 3b). These data
demonstrate that, depending on the structure of the V-set
domain, clickable molecules can be produced that alter sialic
acids selectivity for a particular Siglec member. Moreover,
other single (C-2, C-4, C-9) or multiple modifications of the
sialic acid backbone could further improve Siglec binding
affinity and avidity.[15]
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of Siglec-3 in reducing Toll-
like receptor and IRF sig-
naling. To further show that
the dampening effect of the
glycoengineered cells was
mediated by Siglec signal-
ing, the reporter cells were
pre-treated with the SHP-
1/-2 inhibitor NSC-87877,
which abrogated the inhib-
iting effects of both the
anti-Siglec-3
antibodies
and the L4, L39, and L57-
modifed Jurkat cells (Fig-
ure S10). These findings
suggest that glycoengi-
neered T-cells can induce
immune inhibitory Siglec-3
signaling that counteracts
the activation of immune
cells through the NF-kB
and IRF pathways. Possibly,
the glycoengineered T-cells
cross-link Siglec-3, thereby
leading to SHP-1/-2 recruit-
Figure 3. Structure-guided design to obtain selective sialic acid ligands for Siglec-5/14.
Having established the ability to drastically improve
Siglec binding affinity and selectivity using bioorthogonal
chemistry, we next investigated the functional consequences
of such modifications. To this end, we investigated the effect
of the interaction between glycoengineered Jurkat T-cells that
show high binding to Siglec-3, and Siglec-3-expressing mono-
cytic THP1-DUAL cells. Siglec-3 is normally expressed on
myeloid cells, monocytes, myeloid leukemia cells, and micro-
glia cells and contains an intracellular ITIM.[4,7a] THP1-
DUAL cells express Siglec-3 but no other Siglec family
member (Figure S9) and secrete alkaline phosphatase (AP) in
response to immune activation through the NF-kB pathway,
and luciferase (Luc) in response to signaling through the IRF
pathway.[16] The two pathways play distinct roles in the
activation of the immune system and can be triggered by Toll-
like receptor (TLR) ligands. Therefore, this reporter cell
model allowed us to study the effect of sialic acid/Siglec-3
interactions on the activation of monocytic cells through the
NF-kB and IRF pathways.[16b,17] From our glycoengineered
cell library (Figure 2), we selected three sialic acid modifica-
tions (L4, L39, and L57) that strongly enhance Siglec-3
binding. As a positive control, anti-Siglec-3 antibodies were
used that have been shown to cross-link Siglec-3, thereby
inducing signaling and SHP-1/-2 recruitment to the ITIM.[18]
As a negative control, Jurkat cells modified with L40, which
showed no Siglec-3 binding, and unconjugated Jurkat cells
were used (Figure 2). Next, the THP1-DUAL cells were
activated by TLR ligands LPS and Pam3CSK4, resulting in
high production of AP and Luc (Figure 4). Co-culture with
unmodified Jurkat cells or Jurkat cells modified with L40 had
no significant effect on THP1-DUAL cell activation, whereas
cross-linking of Siglec-3 with antibodies reduced AP and Luc
secretion. Intriguingly, co-culture with L4, L39, or L57-
modifed Jurkat cells was as effective as antibody cross-linking
ment and suppression of activation through the TLR pathway.
Altogether, the described glycoengineering approach can be
used to modulate sialic acid/Siglec interactions on a cellular
level and may hold therapeutic potential in the context of
autoimmune diseases and allergies.
In conclusion, we have developed a glycoengineering
approach to readily modify the surface sialic acids of living
cells and their Siglec binding. Next to being applied as a type
of “glycan array”, the glycoengineered cells can be used to
study and steer sialic acid/Siglec interactions between living
cells. The observed immune suppressive activity of the
glycoengineered cells may be applicable to dampen the
immune response in autoimmune diseases and allergies.
Finally, the general principle of using bioorthogonal chemis-
try to edit the glycocalyx and to alter its interaction with
lectins may be extended to other classes of sialic acid binding
lectins (e.g., selectins, hemagglutinin) or other classes of
glycan/lectin interactions (e.g., galectins).
Acknowledgements
This work was supported by a Radboud University Medical
Center PhD Grant awarded to C.B., a VENI grant from the
Netherlands Organization for Scientific Research (NWO)
awarded to T.J.B., the Netherlands Research School for
Chemical Biology (NRSCB) and a KWF grant (KUN2015-
7604) awarded to G.J.A., T.J.B. and C.B.
Conflict of interest
The authors declare no conflict of interest.
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Haider, I. Netravali, S. Le, R. Elia, E. Dow, A. Lee, J.
Freudenberg, P. L. De Jager, Y. Chretien, A. Varki, M. E.
MacDonald, T. Gillis, T. W. Behrens, D. Bloch, D. Collier, J.
Korzenik, D. K. Podolsky, D. Hafler, M. Murali, B. Sands, J. H.
Stone, P. K. Gregersen, S. Pillai, Nature 2010, 466, 243 – 247; b) T.
Toubai, G. Hou, N. Mathewson, C. Liu, Y. Wang, K. Oravecz-
Wilson, E. Cummings, C. Rossi, R. Evers, Y. Sun, J. Wu, S. W.
Choi, D. Fang, P. Zheng, Y. Liu, P. Reddy, Blood 2014, 123, 3512 –
3523; c) G. Y. Chen, X. Chen, S. King, K. A. Cavassani, J. Cheng,
X. Zheng, H. Cao, H. Yu, J. Qu, D. Fang, W. Wu, X. F. Bai, J. Q.
Liu, S. A. Woodiga, C. Chen, L. Sun, C. M. Hogaboam, S. L.
Kunkel, P. Zheng, Y. Liu, Nat. Biotechnol. 2011, 29, 428 – 435;
d) G. Y. Chen, J. Tang, P. Zheng, Y. Liu, Science 2009, 323, 1722 –
1725; e) K. Malpass, Nat. Rev. Neurol. 2013, 9, 360; f) C. Bꢀll,
M. H. den Brok, G. J. Adema, Biochim. Biophys. Acta Rev.
Cancer 2014, 1846, 238 – 246; g) C. Bꢀll, M. A. Stoel, M. H.
den Brok, G. J. Adema, Cancer Res. 2014, 74, 3199 – 3204.
[7] a) C. Bꢀll, T. Heise, G. J. Adema, T. J. Boltje, Trends Biochem.
Sci. 2016, 41, 519 – 531; b) T. Angata, C. M. Nycholat, M. S.
Macauley, Trends Pharmacol. Sci. 2015, 36, 645 – 660.
[8] a) C. D. Rillahan, E. Schwartz, R. McBride, V. V. Fokin, J. C.
Paulson, Angew. Chem. Int. Ed. 2012, 51, 11014 – 11018; Angew.
Chem. 2012, 124, 11176 – 11180; b) V. V. Rostovtsev, L. G.
Green, V. V. Fokin, K. B. Sharpless, Angew. Chem. Int. Ed.
2002, 41, 2596 – 2599; Angew. Chem. 2002, 114, 2708 – 2711.
[9] B. Belardi, C. R. Bertozzi, Chem. Biol. 2015, 22, 983 – 993.
[10] J. E. Hudak, S. M. Canham, C. R. Bertozzi, Nat. Chem. Biol.
2014, 10, 69 – 75.
[11] a) C. Bꢀll, T. Heise, D. M. Beurskens, M. Riemersma, A.
Ashikov, F. P. Rutjes, T. H. van Kuppevelt, D. J. Lefeber, M. H.
den Brok, G. J. Adema, T. J. Boltje, ACS Chem. Biol. 2015, 10,
2353 – 2363; b) N. J. Agard, C. R. Bertozzi, Acc. Chem. Res. 2009,
42, 788 – 797.
[12] D. C. Kennedy, C. S. McKay, M. C. Legault, D. C. Danielson,
J. A. Blake, A. F. Pegoraro, A. Stolow, Z. Mester, J. P. Pezacki, J.
Am. Chem. Soc. 2011, 133, 17993 – 18001.
[13] a) S. V. Shelke, G. P. Gao, S. Mesch, H. Gathje, S. Kelm, O.
Schwardt, B. Ernst, Bioorg. Med. Chem. 2007, 15, 4951 – 4965;
b) S. Kelm, J. Gerlach, R. Brossmer, C. P. Danzer, L. Nitschke, J.
Exp. Med. 2002, 195, 1207 – 1213.
Figure 4. Sialic acid glycoengineered cells that bind Siglec-3 dampen
immune activation. a,b) A Siglec-3 cross-linking antibody (positive
control) and Jurkat cells expressing L4-, L39-, and L57-modified sialic
acids as ligands for Siglec-3 inhibit activation of the NF-kB (a) and IRF
(b) pathways by LPS and Pam3CSK4 in Siglec-3+ monocyte reporter
cells as measured by the production of alkaline phosphatase or
luciferase, respectively. Unmodified or L40-expressing Jurkat cells that
are not recognized by Siglec-3 showed no effect on NF-kB or IRF
activation.
[14] M. A. Zhuravleva, K. Trandem, P. D. Sun, J. Mol. Biol. 2008, 375,
437 – 447.
[15] a) H. Prescher, A. Schweizer, E. Kuhfeldt, L. Nitschke, R.
Brossmer, ACS Chem. Biol. 2014, 9, 1444 – 1450; b) H. H. Abdu-
Allah, K. Watanabe, G. C. Completo, M. Sadagopan, K. Hay-
ashizaki, C. Takaku, T. Tamanaka, H. Takematsu, Y. Kozutsumi,
J. C. Paulson, T. Tsubata, H. Ando, H. Ishida, M. Kiso, Bioorg.
Med. Chem. 2011, 19, 1966 – 1971; c) S. Kelm, P. Madge, T. Islam,
R. Bennett, H. Koliwer-Brandl, M. Waespy, M. von Itzstein, T.
Haselhorst, Angew. Chem. Int. Ed. 2013, 52, 3616 – 3620; Angew.
Chem. 2013, 125, 3704 – 3708.
[16] a) B. Dey, R. J. Dey, L. S. Cheung, S. Pokkali, H. Guo, J. H. Lee,
W. R. Bishai, Nat. Med. 2015, 21, 401 – 406; b) K. Honda, T.
Taniguchi, Nat. Rev. Immunol. 2006, 6, 644 – 658.
[17] a) W. Chen, C. Han, B. Xie, X. Hu, Q. Yu, L. Shi, Q. Wang, D. Li,
J. Wang, P. Zheng, Y. Liu, X. Cao, Cell 2013, 152, 467 – 478;
b) G. Y. Chen, N. K. Brown, W. Wu, Z. Khedri, H. Yu, X. Chen,
D. van de Vlekkert, A. DꢁAzzo, P. Zheng, Y. Liu, elife 2014, 3,
e04066.
Keywords: bioorthogonal chemistry · immunology ·
molecular modeling · sialic acids · Siglecs
[1] a) A. Varki, Glycobiology 2011, 21, 1121 – 1124; b) B. S. Blaum,
J. P. Hannan, A. P. Herbert, D. Kavanagh, D. Uhrin, T. Stehle,
Nat. Chem. Biol. 2015, 11, 77 – 82.
[2] a) R. Schauer, Curr. Opin. Struct. Biol. 2009, 19, 507 – 514; b) A.
Varki, Nature 2007, 446, 1023 – 1029; c) P. R. Crocker, J. C.
Paulson, A. Varki, Nat. Rev. Immunol. 2007, 7, 255 – 266.
[3] S. Pillai, I. A. Netravali, A. Cariappa, H. Mattoo, Annu. Rev.
Immunol. 2012, 30, 357 – 392.
[4] M. S. Macauley, P. R. Crocker, J. C. Paulson, Nat. Rev. Immunol.
2014, 14, 653 – 666.
[5] Y. Ding, Z. Guo, Y. Liu, X. Li, Q. Zhang, X. Xu, Y. Gu, Y. Zhang,
D. Zhao, X. Cao, Nat. Immunol. 2016, 17, 1167.
[18] V. C. Taylor, C. D. Buckley, M. Douglas, A. J. Cody, D. L.
Simmons, S. D. Freeman, J. Biol. Chem. 1999, 274, 11505 – 11512.
[6] a) I. Surolia, S. P. Pirnie, V. Chellappa, K. N. Taylor, A. Cariappa,
J. Moya, H. Liu, D. W. Bell, D. R. Driscoll, S. Diederichs, K.
Manuscript received: December 15, 2016
Final Article published: && &&, &&&&
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Communications
Bioorthogonal Chemistry
Clicking the immune system off: We
report a method to rapidly reprogram the
binding of sialic acid sugars on living
cells to their cognate Siglec receptors
through glycoengineering and click
chemistry. Binding could be improved by
more than 100-fold and in a selective
manner. The modified cells showed
potent immunosuppressive activity
resulting from strong signaling through
Siglecs on immune cells.
C. Bꢁll, T. Heise, N. van Hilten,
J. F. A. Pijnenborg, V. Bloemendal,
L. Gerrits, E. D. Kers-Rebel, T. Ritschel,
M. H. den Brok, G. J. Adema†,*
T. J. Boltje†*
&&&& — &&&&
Steering Siglec–Sialic Acid Interactions
on Living Cells using Bioorthogonal
Chemistry
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