November 28
PROGRAM

06

Glycoscience : diversity and integration

Regulatory circuits mediated bylectins and glycans in
immune tolerance and inflammation
Gabriel A. Rabinovich, Ph.D.

Gabriel A. RabinovichProfileDr. Gabriel Adrián Rabinovich obtained
his BSc Biochemist degree in 1993 followed by his Ph.D. degree both from theSchool of Chemical Sciences of the National University of Córdoba. Curreently, he is
a Principal Investigator of the Argentinean
National Research Council (CONICET),
Head of the Laboratory of Immunopathology and Vicedirector of the Institute of Biology and Experimental Medicine, andProfessor of Immunology at the Faculty ofExact and Natural Sciences (University ofBuenos Aires). Also Dr. Rabinovich is Visiting Professor at the University of Maryland, Dana Farber Cancer Institute in Harvard Medical School and University of Miami. He serves as Editor of several journals
including Glycobiology, Cell Death andDifferentiation, Oncoimmunology, Immunology and Cell Biology and Emerging Infectious Diseases. Using an interdisciplinary approach, Dr. Rabinovich’s lab aims toidentify different therapeutic targets,based on protein-glycan interactions, todifferentially modulate immune-mediated disorders including cancer, autoimmunity and chronic inflammation. For
his scientific and professional achievements Dr. Rabinovich was awarded withthe John Simon Guggenheim fellowship(USA), Third World Academy of Sciences(TWAS) Award in Medical Research (Italy), Bunge Born Award (Argentina), Bernardo Houssay Award (Argentina), andCancer Research Institute InvestigatorAward (USA). He has published 145 articles in international leading journals including Cancer Cell, Nature Immunology,
Nature Medicine, Immunity, Journal ofExperimental Medicine, Nature Rev Immunol, PNAS, J Immunol and Annu RevImmunol, has written several chapters inbooks, and presented eight patents of hiswork.

Laboratorio de Inmunopatología
Instituto de Biología y Medicina Experimental (IBYME)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET),
ARGENTINA

Homeostatic signals delivered in the formof immunosuppressive cytokines or inhibitory receptors are integrated into regulatory
circuits that sustain peripheral tolerance
mechanisms. These mechanisms serve toprevent collateral tissue damage resulting
from over-exuberant immune responses topathogens or seemingly-innocuous environmental stimuli 1). Disruption of single
pathways underlying these circuits leads tosubstantial inflammatory and autoimmune
states. Conversely, their aberrant activation
represents a significant hurdle for the development of anti-tumor immunity. Although
under-appreciated for many years, exciting
findings underscore the essential contribution of cell surface glycosylation and lectinglycan signaling to these regulatory circuits
operating in immune homeostasis. Indeed,endogenous glycan-binding proteins or
lectins specifically decode glycan-containing information and convey this information into functional cellular responses 2).
Galectins are a family of soluble lectinscharacterized by a conserved carbohydrate
recognition domain (CRD) that recognizes
N- and O-glycans expressing the disaccharide N-acetyllactosamine (Galβ(1-4)GlcNAc or LacNAc) 2). Secreted galectins,
in contrast to cytokines or chemokines, do
not have specific receptors, but can mediated cellular communication through recognition of a preferred set of cell surface
glycoconjugates 3). In our laboratory, we
work at the interface of immunology andglycobiology using in vitro and in vivo
approaches to understand the role ofglycans and glycan-binding proteins in
immune tolerance and inflammation.
Research over the past decade revealed
a prominent expression of galectin-1 intumor cells and its association with malignant progression. These observations
led us to investigate the role of galectin1-glycan interactions in tumor biology.

30

the 20th Anniversary of the Mizutani Foundation for Glycoscience

By a combination of in vitro and in vivo
experiments we identified a crucial rolefor galectin-1 in tumor-immune escape 4).
We found that both human and murine
melanoma cells secrete functional galectin-1, which substantially contributes tothe immunosuppressive activity of thesecells. Targeted inhibition of galectin-1
gene expression rendered mice resistantto tumor challenge and stimulated thegeneration of a tumor-specific Th1-type
response 4). Supporting these findings, wefound that Hodgkin lymphoma cells selectively overexpress galectin-1, favoring thesecretion of Th2-type cytokines and blunting specific T-cell immunity 5). Notably, theobserved role for galectin-1-glycan interactions in the establishment of immune privileged microenvironments was important
not only in tumor settings but also at thefetomaternal interface 6). In an establishedmodel of stress-induced failing pregnancy,
galectin-1 had a critical role in preventing
fetal loss and restoring tolerance in vivo.
Galectin-1-deficient (Lgals1-/-) female mice
showed higher rates of fetal loss comparedto their wild-type counterparts in allogeneic, but not in syngeneic matings. Investigation of the mechanisms underlying theseregulatory effects revealed the ability of
galectin-1 to restore the Th1/Th2 cytokine
balance and promote the expansion of IL10-producing Treg cells 6). These effects wererecently confirmed in several autoimmune,
inflammatory and tumor settings 7).
To understand the cellular mechanisms
underlying these immunoregulatory effects,
we performed in vitro and in vivo studies.
We found a link between differential glycosylation of T helper cells, susceptibility
to galectin-1-induced cell death and termination of the inflammatory response 8).
While Th1- and Th17-differentiated cells
expressed the repertoire of cell surface glycans that are critical for galectin-1 binding
and cell death, Th2 cells were protectedfrom galectin-1 through differential α2,6 sialylation of cell surface
glycoproteins 8). More recently,
we investigated the relevance ofgalectin-glycan lattices within thedendritic cell (DC) compartment.
Notably, DCs differentiated in a
galectin-1-enriched microenvironment acquired a distinctive ‘regulatory signature’ characterized byabundant secretion of IL-27 andIL-10 9). When transferred in vivo,
these DCs promoted antigen-specificT-cell tolerance, blunted Th1 andTh17 responses and halted autoimmune neuroinflammation throughmechanisms involving DC-derived
IL-27 and T cell-derived IL-10.
Thus, using IL-27 receptor-deficient (Il27ra-/-) and IL-10-deficient(Il10-/-) mice, we have identified an
immunoregulatory circuit linking
Figure 1. Tumour secreted galectin-1 promotes tumour immune escape through modulation of DCs difgalectin-1 signaling, IL-27-producferentiation and functionality and regulation of T cell homeostasis.
ing tolerogenic DCs and IL-10 secretDCs differentiated in a galectin-1-enriched microenvironment acquire a tolerogenic phenotype charing Treg cells. Remarkably, galectin-1
acterized by abundant secretion of IL-27 and induction of IL-10 secreting Treg. In addition, galectin-1
differentially regulates apoptosis of T cell populations. While Th1- and Th17-differentiated cells express
expression increased during thethe repertoire of cell surface glycans that are critical for galectin-1 binding and cell death, Th2 cells arepeak and recovery phases of experiprotected from galectin-1 through differential α2,6 sialylation of cell surface glycoproteins .
mental autoimmune encephalomyelitis (EAE), and animal model ofmultiple sclerosis (MS), and wasthrough mechanisms involving microglia
CREB-dependent pathways and hierarchidramatically up-regulated by tolerogenic
de-activation 10). Thus, similar to the effects
cally controlling downstream pro-inflamstimuli. Moreover, galectin-1-sufficient but
observed at the peripheral compartment,
matory mediators such as iNOS, TNF andnot galectin-1-deficient DCs were able toour results show that galectin-1-glycan
CCL2. Mechanistically galectin-1 acted byrestore tolerance and contribute to EAEinteractions are key mediators of different
specifically interacting on core 2 O-glycans
recovery 9), suggesting a crucial role ofcellular processes central to immune reguon CD45 and retaining this glycoprotein
endogenous galectin-1 in ‘fine-tuning’ thelation in the central nervous system.
on the surface of microglia cells, thus favorimmunogenic function of DCs. Furthering its phosphatase activity and amplifying
more, we recently identified an essential
Taken together, our findings set the bases
its inhibitory effect. Targeted deletion ofrole of galectin-1-glycan interactions infor the design of novel therapeutic stratgalectin-1 resulted in pronounced inflamtempering microglia activation, brain
egies aimed at potentiating antitumor
mation-induced neurodegeneration in an
inflammation and neurodegeneration withresponses, preventing fetal loss and favoranimal model of multiple sclerosis. Morecritical therapeutic implications in MS 10).
ing the resolution of chronic inflammation
over, adoptive transfer of astrocytes secretWe found that galectin-1 limits M1 microgand autoimmune disorders.
ing galectin-1 or administration of recomlia activation and neurodegeneration, bybinant galectin-1 rescued this phenotype
targeting the activation of p38MAPK- andReferences1) 	Bluestone JA, Thomson AW, Shevach EM, Weiner HL. What does the future
hold for cell-based tolerogenic therapy? Nat. Rev. Immunol. (7): 650-654,2007.
2) 	Rabinovich GA, Croci DO. Regulatory circuits mediated by lectin-glycan interactions in autoimmunity and cancer. Immunity. (36):322-335, 2012.
3) 	Rabinovich GA, Toscano MA. Turning ‘sweet’ on immunity: galectin-glycan
interactions in immune tolerance and inflammation. Nat. Rev. Immunol. (9):338-352, 2009.
4) 	Rubinstein N, Alvarez M, Zwirner NW, Toscano MA, Ilarregui JM, Bravo A,Mordoh J, Fainboim L, Podhajcer OL, Rabinovich GA. Targeted inhibition ofgalectin-1 gene expression in tumor cells results in heightened T cell-mediated rejection; A potential mechanism of tumor-immune privilege. Cancer Cell(5): 241-251, 2004.
5) 	Juszczynski P, Ouyang J, Monti S, Rodig SJ, Takeyama K, Abramson J, ChenW, Kutok JL, Rabinovich GA, Shipp MA. The AP1-dependent secretionof galectin-1 by Reed Sternberg cells fosters immune privilege in classicalHodgkin lymphoma. Proc. Natl. Acad. Sci. U S A (104): 13134-13139, 2007.
6) 	Blois SM, Ilarregui JM, Tometten M, Garcia M, Orsal AS, Cordo-Russo R,Toscano MA, Bianco GA, Kobelt P, Handjiski B, Tirado I, Markert UR, Klapp

BF, Poirier F, Szekeres-Bartho J, Rabinovich GA, Arck PC. A pivotal role forgalectin-1 in fetomaternal tolerance. Nat. Med. (13):1450-1457, 2007.
7) 	Cedeno-Laurent F, Watanabe R, Teague JE, Kupper TS, Clark RA, Dimitroff
CJ. Galectin-1 inhibits the viability, proliferation, and Th1 cytokine production of nonmalignant T cells in patients with leukemic cutaneous T-cell lymphoma. Blood. (119):3534-3538, 2012.
8) 	Toscano MA, Bianco GA, Ilarregui JM, Croci DO, Correale J, Hernandez JD,Zwirner NW, Poirier F, Riley EM, Baum LG, Rabinovich GA. Differential glycosylation of TH1, TH2 and TH-17 effector cells selectively regulates susceptibility to cell death. Nat. Immunol. (8): 825-834, 2007.
9) 	Ilarregui JM, Croci DO, Bianco GA, Toscano MA, Salatino M, Vermeulen
ME, Geffner JR, and Rabinovich GA. Tolerogenic signals delivered by dendritic cells to T cells through a galectin-1-driven immunoregulatory circuit
involving interleukin 27 and interleukin 10. Nat. Immunol. (10): 981-991,2009.
10) 	Starossom SC, Mascanfroni ID, Imitola J, Cao L, Raddassi K, Hernandez SF,Elyaman W, Bassil R, Croci DO, Cerliani JP, Wang Y, Khoury SJ, Rabinovich
GA. Galectin-1 deactivates classically-activated microglia and protects frominflammation-induced neurodegeneration. Immunity, 2012. in press.

Commemorative Symposium31