Suppressive efficacy and proliferative capacity of human regulatory T cells in allogeneic and xenogeneic responses.
BACKGROUND
An understanding of the mechanisms that suppress the human anti-pig cellular response is key for xenotransplantation. We have compared the ability of human regulatory T cells (Tregs) to suppress xenogeneic and allogeneic responses in vitro.


METHODS
Human peripheral blood mononuclear cells (PBMC), CD4+ T cells, or CD4+ CD25- T cells were stimulated with irradiated human or wild type (WT) or alpha1,3-galactosyltransferase gene-knockout (GT-KO) pig PBMC in the presence or absence of human CD4+ CD25 high Tregs. In separate experiments, 5- (and 6)-carboxyfluorescein diacetate succinimidyl ester-labeled human CD4+ T cells were stimulated with human or pig PBMC. The expansion and precursor frequencies of allo- and xenoreactive Tregs were assessed by labeling with FoxP3 mAb and flow cytometric analysis.


RESULTS
The responses of human PBMC, CD4+ T cells, and CD4+ CD25- T cells to pig PBMC were stronger than to human PBMC (P<0.05). Human anti-GT-KO responses were weaker than anti-WT responses (P<0.05). Human CD4+ CD25 high Tregs suppressed proliferation of CD4+ CD25- T cells to both human and pig PBMC stimulator cells with the same efficiency. Alloreactive CD4+ CD25+ FoxP3 high responder T cells proliferated more than their xenoreactive counterparts (P<0.05), although xenoreactive CD4+ CD25+ T cells proliferated more than alloreactive cells (P<0.05). There was no difference in precursor frequency between allo- and xeno-reactive CD4+ CD25+ FoxP3 high cells.


CONCLUSIONS
Human T-cell responses to pig cells are stronger than to allogeneic cells. The human response to GT-KO PBMC is weaker than to WT PBMC. Although human Tregs can suppress both responses, expansion of CD4+ CD25+ FoxP3 high cells against pig PBMC is weaker than against human PBMC. More human Tregs may be required to suppress the stronger xenogeneic response.
Lin
Yih-Jyh
YJ
Thomas E. Starzl Transplantation Institute, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15261, USA.
Hara
Hidetaka
H
Tai
Hao-Chih
HC
Long
Cassandra
C
Tokita
Daisuke
D
Yeh
Peter
P
Ayares
David
D
Morelli
Adrian E
AE
Cooper
David K C
DK
D000818:Animals; D030801:Animals, Genetically Modified; D015703:Antigens, CD / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D005700:Galactosyltransferases / Q000172:deficiency / Q000235:genetics; D006084:Graft Rejection / Q000235:genetics / Q000276:immunology; D006801:Humans; D007165:Immunosuppression Therapy / Q000379:methods; D053645:Interleukin-2 Receptor alpha Subunit / Q000276:immunology; D013552:Swine / Q000235:genetics / Q000276:immunology; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D014183:Transplantation, Heterologous / Q000276:immunology*; D014184:Transplantation, Homologous / Q000276:immunology*
D015703:Antigens, CD; D053645:Interleukin-2 Receptor alpha Subunit; D005700:Galactosyltransferases