Suppression of human T-cell activation and expansion of regulatory T cells by pig cells overexpressing PD-ligands.
BACKGROUND
Genetic modification of pigs (e.g., transgenic expression of human complement regulatory molecules or inactivation of alpha1,3galactosyltransferase) enabled the development of promising strategies to overcome hyperacute rejection after pig-to-primate xenotransplantation. However, cellular rejection still remains a hurdle for successful xenograft survival. This report tested the hypothesis that overexpression of human negative costimulatory PD-Ligands (PD-L) in pig antigen presenting cells might be an approach to prevent human anti-pig T-cell responses.


METHODS
The pig B-cell line L23 was transfected with the pIRES-AcGFP vector containing human PD-L1 or PD-L2. Stable transfectants (L23-PD-L1, L23-PD-L2 cells) were established and used for in vitro stimulation of purified human CD4+ T cells.


RESULTS
Human CD4+ T cells responded with significantly reduced proliferation to L23-PD-L1 or L23-PD-L2 cells and produced less IL-2, IFNgamma, TNFalpha, IL-4, and IL-5 than cells stimulated with mock-transfected B cells. The concentration of IL-10, however, was increased in CD4+ T cells responding to stimulation with PD-L1 or PD-L2 transfectants. Furthermore, in cultures of CD4+ T cells stimulated for 3 weeks with PD-L1 or PD-L2 transfectants a CD4+CD25(high)Foxp3+ subset showed up that effectively suppressed the activation of conventional CD4+ T cells.


CONCLUSIONS
These findings imply that PD-1/PD-Ligand pathways are interesting targets to prevent human anti-pig T-cell responses after xenotransplantation, and also suggests that PD-1/PD-Ligand interactions may play a role in the control of the activity and/or homeostasis of regulatory T cells.
Transplantationslabor, Klinik für Viszeral- und Transplantationschirurgie, Medizinische Hochschule Hannover, Hannover, Germany.
Annegret
A
Plege
Katja
K
Borns
Wiebke
W
Baars
Reinhard
R
Schwinzer
D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology*; D060890:B7-H1 Antigen; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D005434:Flow Cytometry; D005784:Gene Amplification; D006084:Graft Rejection / Q000276:immunology*; D006085:Graft Survival / Q000276:immunology; D006801:Humans; D007165:Immunosuppression Therapy; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000276:immunology; D008213:Lymphocyte Activation; D016133:Polymerase Chain Reaction; D011323:Primates; D061027:Programmed Cell Death 1 Ligand 2 Protein; D013552:Swine; D013601:T-Lymphocytes / Q000276:immunology*; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D014162:Transfection; D014183:Transplantation, Heterologous / Q000276:immunology
D015703:Antigens, CD; D060890:B7-H1 Antigen; C423236:CD274 protein, human; D036341:Intercellular Signaling Peptides and Proteins; C556977:PDCD1LG2 protein, human; D061027:Programmed Cell Death 1 Ligand 2 Protein