Antonio Madejón, Eduardo Sanz-de-Villalobos, Joaquín Miquel, Alejandro González-Praetorius, Trinidad Parra-Cid, Dolores Subirá, Javier García-Samaniego, Juan-Ramón Larrubia, Antonio Olveira, Elia Moreno-Cubero
Hepatitis C virus (HCV)-specific CD8(+) T cells suffer a progressive exhaustion during persistent HCV infection (PI). This process could involve the positive immune checkpoint 4-1BB/4-1BBL, through the loss of its signal transducer TRAF1. To address this issue, peripheral HCV-specific CD8(+) T cells (Pentamer(+)/CD8(+)) from patients with PI and resolved infection after treatment (RI) were studied. Duration of HCV infection and liver fibrosis progression rate inversely correlated with the likelihood of detecting peripheral pentamer(+)/CD8(+) cells. In PI, pentamer(+)/CD8(+) cells had impaired antigen-specific reactivity that worsened when these cells were not detectable ex-vivo Short/mid-lasting PI was characterized by detectable peripheral PD-1(+) CD127(low) TRAF1(low) cells. After TCR triggering, TRAF1 level positively correlated with CD127, Mcl-1, CD107a and proliferation intensity, but negatively with PD-1, linking TRAF1(low) to exhaustion. IL-7 in-vitro treatment up-regulated TRAF1, while TGF-β1 did the opposite, suggesting that IL-7/TGF-β1 balance, besides TCR stimulation, could be involved in TRAF1 regulation. In fact, TGF-β1 serum concentration was higher in PI than in RI patients, and it negatively correlated with TRAF1 expression. In line with IL-7 increasing TRAF1 level, IL-7/4-1BBL in-vitro treatment enhanced T cell reactivity in short/mid-lasting infection. However, in long-lasting PI, anti-PD-L1 in addition to IL-7/4-1BBL combination was necessary to re-establish T cell proliferation in slow fibrosers, but had no effect in rapid fibrosers. In conclusion, a peripheral hypo-reactive TRAF1(low) HCV-specific CD8(+) T cell response, restorable by IL-7/4-1BBL treatment, characterizes short/mid-length PI. In long-lasting disease, HCV-specific CD8(+) T cells are rarely detectable ex-vivo, but IL-7/4-1BBL/anti-PD-L1 treatment recovers their reactivity in-vitro in slow fibrosers.IMPORTANCE Hepatitis C virus (HCV) infects 71 million people worldwide. Two thirds develop a chronic disease that can lead to cirrhosis and hepatocellular carcinoma. Direct-acting antivirals clear the infection but there are still patients who relapse. In these cases, additional immunotherapy could play a vital role. A successful anti-HCV immune response depends on virus-specific CD8(+) T cells. During chronic infection, these cells are functionally impaired, which could be due to co-stimulation failure. This study describes exhausted specific T cells, characterized by low expression of the signal transducer TRAF1 of the positive co-stimulatory pathway 4-1BB/4-1BBL. IL-7 up-regulated TRAF1 and improved T cell reactivity in short/mid duration disease, while in long-lasting infection, it was also necessary to block the negative checkpoint PD-1/PD-L1. Taken together, this work supports novel ways of restoring specific CD8(+) T cell response, shedding light on the importance of TRAF1 signaling. This could be a promising target for future immunotherapy.