Objective: Renal fibroblasts were isolated from nephrectomy of control (n=3) and renal allograft rejection patients (n=3).  Fibroblasts were incubated with TGF-β1 (10 ng/ml) for 1 hour, later with TGF-β1 (10 ng/ml) and [Sildenafil (10µM) plus SB204741 (1µM)] for 24 hours (post-treatment strategy). In the pre-treatment strategy, fibroblasts were pre-treated with [Sildenafil (10 µM) plus SB204741 (1 µM)] for 1 hour and later with only TGF-β1 (10 ng/ml) for 24 hours. Similar strategies were followed for individual treatments of inhibitors. Real-time qPCR for pro-fibrotic genes, COL1A1, ACTA2, CTGF, and fibronectin1, and anti-fibrotic genes, TIMP1, MMP2 was performed.  Type 1 collagen and α-SMA proteins were examined by western blotting. Methods: In TGF-β1 stimulated fibroblasts, significant up-regulation of pro-fibrotic gene expression was observed, significantly reducing co-culture with PDE-5 plus 5-HT2B inhibitors. The ratio of anti-fibrotic genes (MMP2/TIMP1) was restored significantly. The expression of type 1 collagen was decreased significantly. Furthermore, near-complete amelioration of ACTA2, as well as α-SMA protein, was observed significantly (Table 1). Results: Dual inhibition combination of PDE-5 plus 5-HT2B inhibitors lead to near-complete attenuation of conversion of resident fibroblasts to myo-fibroblasts and thus may have the prospective for treatment of fibrosis of renal allograft rejection patients. Conclusions: Objective: Despite improvements in immunosuppressive therapy, long-term allograft survival after kidney transplantation remains as low as 50%. The primary cause of chronic allograft nephropathy is “interstitial fibrosis and tubular atrophy” (IF/TA). Serotonin (5-HT; 5-Hydroxytryptamine) produces extracellular matrix proteins in presence of TGF-β1 dependent manner. TGF-β1 activates resident fibroblasts, trans-differentiate into myo-fibroblasts, which is the hallmark of the pathogenesis of fibrosis. Here we evaluate the anti-fibrotic efficacy of phosphodiesterase-5 (PDE-5) inhibitor, Sildenafil, and 5-HT2B inhibitor, SB204741 in combination, on renal fibroblast isolated from renal allograft rejection patients. Methods: Renal fibroblasts were isolated from nephrectomy of control (n=3) and renal allograft rejection patients (n=3).  Fibroblasts were incubated with TGF-β1 (10 ng/ml) for 1 hour, later with TGF-β1 (10 ng/ml) and [Sildenafil (10µM) plus SB204741 (1µM)] for 24 hours (post-treatment strategy). In the pre-treatment strategy, fibroblasts were pre-treated with [Sildenafil (10 µM) plus SB204741 (1 µM)] for 1 hour and later with only TGF-β1 (10 ng/ml) for 24 hours. Similar strategies were followed for individual treatments of inhibitors. Real-time qPCR for pro-fibrotic genes, COL1A1, ACTA2, CTGF, and fibronectin1, and anti-fibrotic genes, TIMP1, MMP2 was performed.  Type 1 collagen and α-SMA proteins were examined by western blotting. Results: In TGF-β1 stimulated fibroblasts, significant up-regulation of pro-fibrotic gene expression was observed, significantly reducing co-culture with PDE-5 plus 5-HT2B inhibitors. The ratio of anti-fibrotic genes (MMP2/TIMP1) was restored significantly. The expression of type 1 collagen was decreased significantly. Furthermore, near-complete amelioration of ACTA2, as well as α-SMA protein, was observed significantly (Table 1). Conclusions: Dual inhibition combination of PDE-5 plus 5-HT2B inhibitors lead to near-complete attenuation of conversion of resident fibroblasts to myo-fibroblasts and thus may have the prospective for treatment of fibrosis of renal allograft rejection patients.