E (1 mCi/ well, Amersham Pharmacia Biotech, UK) was added to the culture for the final 18 h and Cell proliferation was measured by 3Hthymidine incorporation using a liquid scintillation counter (Wallac, Turku, Finland).Cardiac transplantation and histopathological examinationDonor hearts (BALB/c) were heterotopically (intra-abdominally) transplanted into recipient mice (C57BL/6). The aorta and pulmonary arteries of the donor hearts were end-to-side anastomosed to the recipient’s abdominal aorta and inferior vena cava, respectively. Survival of cardiac allografts was evaluated by daily palpation; cessation of beating was interpreted as rejection. Recipient mice received a subtherapeutic regimen of 1 mg/kg/ day i.p. Rapamycin (Sigma-Aldrich) in a vehicle containing 0.02 Tween 80 and 0.26 polyethylene glycol (both from SigmaAldrich) for 10 consecutive days (days 0?), and/or two dose of freshly isolated CD4+CD252Nrp1+T cell on day 0 and day 7. The study endpoint was defined as complete cessation of cardiac beat. Survival of cardiac grafts was monitored by palpitation by two independent observers without prior knowledge of the treatment protocol, which was always confirmed with histology. Cardiac grafts were harvested whenever necessary, fixed 
in 10 formalin and embedded in paraffin. Sections were cut at 4 mm, and were counterstained for 1 min with hematoxylin and eosin.Materials and Methods Mice and ethics statementBALB/c (H2d), and C57BL/6 (H2b) mice (6? wk, weight 20?25 g) were obtained from Joint Ventures Sipper BK Experimental Animal Company (Shanghai, China). All animal experiments were performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals, with the approval of the Scientific Investigation Board of Second Military Medical University (Shanghai, China).ReagentsRapamycin was obtained from Sigma-Aldrich. A Mouse CD4+ T cell Isolation Kit, CD4+CD25+ Regulatory T Cell Isolation Kit and goat anti-rabbit IgG microbeads were purchased from Miltenyi Biotec Company (Aubum, CA). Anti-Nrp1 ML-240 antibody was provided by the Abcam Company (Cambridge, MA). Fluorescent dye-conjugated monoclonal antibodies that specifically recognize CD4, Foxp3 and isotype IgG were purchased from BioLegend Company (San Diego, CA) and eBioscience (San Diego, CA). PCR primers were synthesized by Fudan Yueda Biotechnology Company (Shanghai, China). ELISA kits for measuring mouse IFN-c, IL-17, IL-10 and TGF-b were purchased from eBioscience. RPMI 1640 and fetal calf serum (FCS) were obtained from Invitrogen Life Technologies. Intracellular Foxp3 staining was performed using the relevent Fix/Perm Buffer set (Biolegend or eBioscience) according to manufacturer’s recommendations. The cell fluorescence was measured using LSR II (BD) and data were analyzed using Flowjo software (TreeStar).Quantitative real-time PCR (qRT-PCR)Total tissue RNA was extracted using TRIzol (Invitrogen) reagent according to the manufacturer’s SMER28 instructions. cDNA was synthesized using oligo d(T) (Applied Biosystems) and a SuperScript III Reverse Transcriptase Kit (Invitrogen). A StepOneTM Real-Time PCR System (Applied Biosystems) and a SYBR RTPCR kit (Takara) were used for quantitative real-time RT-PCR analysis. All reactions were conducted in a 20 ul reaction volume in triplicate. The relative expression levels for a target gene were normalized by GAPDH. Specificity of qRT-PCR was verified by melting curve analysis and agarose gel electrophoresis.E (1 mCi/ well, Amersham Pharmacia Biotech, UK) was added to the culture for the final 18 h and Cell proliferation was measured by 3Hthymidine incorporation using a liquid scintillation counter (Wallac, Turku, Finland).Cardiac transplantation and histopathological examinationDonor hearts (BALB/c) were heterotopically (intra-abdominally) transplanted into recipient mice (C57BL/6). The aorta and pulmonary arteries of the donor hearts were end-to-side anastomosed to the recipient’s abdominal aorta and inferior vena cava, respectively. Survival of cardiac allografts was evaluated by daily palpation; cessation of beating was interpreted as rejection. Recipient mice received a subtherapeutic regimen of 1 mg/kg/ day i.p. Rapamycin (Sigma-Aldrich) in a vehicle containing 0.02 Tween 80 and 0.26 polyethylene glycol (both from SigmaAldrich) for 10 consecutive days (days 0?), and/or two dose of freshly isolated CD4+CD252Nrp1+T cell on day 0 and day 7. The study endpoint was defined as complete cessation of cardiac beat. Survival of cardiac grafts was monitored by palpitation by two independent observers without prior knowledge of the treatment protocol, which was always confirmed with histology. Cardiac grafts were harvested whenever necessary, fixed in 10 formalin and embedded in paraffin. Sections were cut at 4 
mm, and were counterstained for 1 min with hematoxylin and eosin.Materials and Methods Mice and ethics statementBALB/c (H2d), and C57BL/6 (H2b) mice (6? wk, weight 20?25 g) were obtained from Joint Ventures Sipper BK Experimental Animal Company (Shanghai, China). All animal experiments were performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals, with the approval of the Scientific Investigation Board of Second Military Medical University (Shanghai, China).ReagentsRapamycin was obtained from Sigma-Aldrich. A Mouse CD4+ T cell Isolation Kit, CD4+CD25+ Regulatory T Cell Isolation Kit and goat anti-rabbit IgG microbeads were purchased from Miltenyi Biotec Company (Aubum, CA). Anti-Nrp1 antibody was provided by the Abcam Company (Cambridge, MA). Fluorescent dye-conjugated monoclonal antibodies that specifically recognize CD4, Foxp3 and isotype IgG were purchased from BioLegend Company (San Diego, CA) and eBioscience (San Diego, CA). PCR primers were synthesized by Fudan Yueda Biotechnology Company (Shanghai, China). ELISA kits for measuring mouse IFN-c, IL-17, IL-10 and TGF-b were purchased from eBioscience. RPMI 1640 and fetal calf serum (FCS) were obtained from Invitrogen Life Technologies. Intracellular Foxp3 staining was performed using the relevent Fix/Perm Buffer set (Biolegend or eBioscience) according to manufacturer’s recommendations. The cell fluorescence was measured using LSR II (BD) and data were analyzed using Flowjo software (TreeStar).Quantitative real-time PCR (qRT-PCR)Total tissue RNA was extracted using TRIzol (Invitrogen) reagent according to the manufacturer’s instructions. cDNA was synthesized using oligo d(T) (Applied Biosystems) and a SuperScript III Reverse Transcriptase Kit (Invitrogen). A StepOneTM Real-Time PCR System (Applied Biosystems) and a SYBR RTPCR kit (Takara) were used for quantitative real-time RT-PCR analysis. All reactions were conducted in a 20 ul reaction volume in triplicate. The relative expression levels for a target gene were normalized by GAPDH. Specificity of qRT-PCR was verified by melting curve analysis and agarose gel electrophoresis.