IL-21 is an antitolerogenic cytokine of the late-phase alloimmune response.
OBJECTIVE
Interleukin-21 (IL-21) is a proinflammatory cytokine that has been shown to affect Treg/Teff balance. However, the mechanism by which IL-21 orchestrates alloimmune response and interplays with Tregs is still unclear.


METHODS
The interplay between IL-21/IL-21R signaling, FoxP3 expression, and Treg survival and function was evaluated in vitro in immunologically relevant assays and in vivo in allogenic and autoimmune models of islet transplantation.


RESULTS
IL-21R expression decreases on T cells and B cells in vitro and increases in the graft in vivo, while IL-21 levels increase in vitro and in vivo during anti-CD3/anti-CD28 stimulation/allostimulation in the late phase of the alloimmune response. In vitro, IL-21/IL-21R signaling (by using rmIL-21 or genetically modified CD4(+) T cells [IL-21 pOrf plasmid-treated or hIL-21-Tg mice]) enhances the T-cell response during anti-CD3/anti-CD28 stimulation/allostimulation, prevents Treg generation, inhibits Treg function, induces Treg apoptosis, and reduces FoxP3 and FoxP3-dependent gene transcripts without affecting FoxP3 methylation status. In vivo targeting of IL-21/IL-21R expands intragraft and peripheral Tregs, promotes Treg neogenesis, and regulates the antidonor immune response, whereas IL-21/IL-21R signaling in Doxa-inducible ROSA-rtTA-IL-21-Tg mice expands Teffs and FoxP3(-) cells. Treatment with a combination of mIL-21R.Fc and CTLA4-Ig (an inhibitor of the early alloimmune response) leads to robust graft tolerance in a purely alloimmune setting and prolonged islet graft survival in NOD mice.


CONCLUSIONS
IL-21 interferes with different checkpoints of the FoxP3 Treg chain in the late phase of alloimmune response and, thus, acts as an antitolerogenic cytokine. Blockade of the IL-21/IL-21R pathway could be a precondition for tolerogenic protocols in transplantation.
Transplantation Research Center, Children’s Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Alessandra
A
Petrelli
Michele
M
Carvello
Andrea
A
Vergani
Kang Mi
KM
Lee
Sara
S
Tezza
Ming
M
Du
Sonja
S
Kleffel
Liu
L
Chengwen
Bechara G
BG
Mfarrej
Patrick
P
Hwu
Antonio
A
Secchi
Warren J
WJ
Leonard
Deborah
D
Young
Mohamed H
MH
Sayegh
James F
JF
Markmann
Allan J
AJ
Zajac
Paolo
P
Fiorina
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism; D018106:CD28 Antigens / Q000276:immunology / Q000378:metabolism; D017252:CD3 Complex / Q000276:immunology / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D016207:Cytokines; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D007378:Interleukins / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D053655:Receptors, Interleukin-21 / Q000235:genetics / Q000378:metabolism*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D050378:T-Lymphocytes, Regulatory / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D000098546:Interleukin-21
D000906:Antibodies; D018106:CD28 Antigens; D017252:CD3 Complex; D016207:Cytokines; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; D007378:Interleukins; D053655:Receptors, Interleukin-21; D000098546:Interleukin-21