Elevated CD8+Tscm proportion in HCV monoinfected and HIV/HCV coinfected patients
To determine the role of CD8+Tscm during HCV monoinfection or HIV/HCV coinfection, we firstly analyzed the proportion of this compartment in untreated HCV + and HIV-virologically suppressed with viral load of < 50 copies/ml but HCV-untreated HIV/HCV coinfected individuals. HESN and ART-experienced HIV + patients with viral load of < 50 copies/ml were used as controls. The gating strategy for CD8+Tscm analysis was shown in Fig. 1a. CD8+T subpopulation was defined as CD3+CD8+, and were further divided into three memory compartments according to CD45RA, CCR7, CD27, and CD95 expression on the cell surface: central memory (cm, CD45RA−CCR7+), effector memory (em, CD45RA−CCR7−), and stem cell-like memory (scm, CD45RA+CCR7+CD27+CD95+). As shown in Fig. 1b and c, compared to HESN, the proportion of CD8+Tscm in both HCV + and HIV/HCV significantly increased (all p < 0.001), however, there was no difference of this CD8+T compartment between HCV + and HIV/HCV (p = 0.715). HIV + had the lowest CD8+Tscm frequency among four groups (all p < 0.001). HCV + had the highest CD8+Tcm and the lowest CD8+Tem frequencies among four groups (Fig. 1b).
CD8+Tscm involved in T memory cell maintenance during HCV infection
The frequency of CD8+Tscm had a positive correlation with that of CD8+Tcm in HIV+ (r = 0.640, p < 0.001) and HCV+ (r = 0.425, p = 0.024), and a similar correlation was found when considering that in HIV/HCV (r = 0.445, p = 0.086) (Fig. 2a). Oppositely, negative correlation between the frequency of CD8+Tscm and that of CD8+Tem was observed in HESN (r=-0.630, p < 0.001), HIV+ (r=-0.538, p = 0.005), and HCV+ (r=-0.447, p = 0.016), and a similar trend in HIV/HCV (r=-0.418, p = 0.084) (Fig. 2b). These findings indicated that, as the initial stage of memory T cell differentiation, Tscm compartment may support the Tcm development, which subsequently further differentiated into Tem in HCV infection.
Association between CD8+Tscm and HCV clinical parameters
Next, we investigated the possible influence of CD8+Tscm on the virological progression in HCV + and HIV/HCV infected patients. There was no significant difference in plasma HCV viral load between HCV+ (median:5.33 log10IU/ml) and HIV/HCV (median:5.92 log10IU/ml) (Table 1). Reverse relationships were observed between plasma HCV viral load and the proportion of CD8+Tscm, CD8+Tcm, respectively, in HCV+ (CD8+Tscm: r=-0.563, p = 0.002; CD8+Tcm: r=-0.401, p = 0.034), but not in HIV/HCV (CD8+Tscm: r = 0.133, p = 0.599; CD8+Tcm: r=-0.256, p = 0.338) (Fig. 3a and b). In addition, the proportion of CD8+Tem was not related to HCV viral load in both HCV+ (r = 0.163, p = 0.407) and HIV/HCV (r=-0.280, p = 0.261) (Fig. 3c).
Since immune activation was an independent predictor for HIV-1 disease progression, as well as an key factor to drive liver injury and fibrosis in HCV infected patients[26], we consequently analyzed the possible connection between CD8+Tscm and the level of immune activation that were represented by the frequency of CD38 and HLA-DR coexpression on CD8+T cell surface in HCV + and HIV/HCV. As shown in Fig. 4a, HCV + had the highest level of CD38+HLA-DR+CD8+T cell among four groups (all p ≤ 0.001). Moreover, compared to HESN and HIV+, the frequency of CD38+HLA-DR+CD8+T cell in HIV/HCV was increased (all p ≤ 0.001). Of note, the level of immune activation in HIV + was still higher than HESN, although virological suppression after successful ART in HIV + individuals (p < 0.001). There was a trend of positive relationship between the frequency of CD38+HLA-DR+CD8+T cell and plasma HCV viral load in HCV+ (r = 0.347, p = 0.070), but not in HIV/HCV (r = 0.107, p = 0.705) (Fig. 4b), indicating that HCV replication may drive the elevated the level of immune activation in HCV infected patients. Correlation analysis revealed that within HCV+, the frequency of CD38+HLA-DR+CD8+T cell was reversely related to that of CD8+Tscm (r=-0.387, p = 0.041) (Fig. 5a), and CD8+Tcm (r=-0.379, p = 0.046) (Fig. 5b). Similar relationship was not found when considering same parameters in HESN, HIV+, and HIV/HCV. Besides, there was no association between the frequency of CD38+HLA-DR+CD8+T cell and that of CD8+Tem within all groups, with the exception of a positive correlation in HESN (r = 0.509, p = 0.002) (Fig. 5c). We also analyzed the association between the memory CD8+T cell compartments and the level of alanine aminotransferase (ALT) or aspartate aminotransferase (AST) in HCV + and HIV/HCV groups. However, no significant correlation but a negative trend was observed between ALT or AST and the proportion of CD8+Tscm, CD8+Tcm, as well as CD8+Tem in both HCV + and HIV/HCV groups (data not shown).