Human PD1 Knockout Cell Line-Jurkat

Staphylococcus aureus (S. aureus) presents a significant challenge in the clinic due to its well-defined ability to select mutations that increase antibiotic resistance and immune evasion. However, the molecular mechanisms remain poorly understood, especially for adaptive immunity. Cancer immunotherapy targeting programmed cell death protein 1 (PD-1) enhances T cell activity and is being used to treat certain viral infections, whereas its potential against bacterial infections remains elusive. Here researchers show that S. aureus clpP mutants selected during clinical antibiotic therapy suppress T cell activity by directly interacting with PD-1 on human T cells. The specificity of the interaction was confirmed using recombinant PD-1 as well as PD-1 overexpressing and knockout cells. Furthermore, PD-1 binding to S. aureus inhibited intracellular calcium mobilization, T cell proliferation, CD25 expression, and IL-2 secretion, whereas antibody-mediated PD-1 blockade using an engineered IgG1-based anti-PD-1 antibody mitigated the major effects. These results suggest that clpP mutant S. aureus directly targets PD-1 to evade immune activation and that therapeutic targeting of PD-1 could be useful against certain staphylococcal infections.

Here, the researchers used a panel of five (SADR-1, SADR-2, SADR-3, SADR-4, and SADR-5) methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from the same patient during persistent bacteremia. Using fluorescently labeled S. aureus, they found that SADR-2, SADR-3, and SADR-4 interacted significantly more with Jurkat-PD1 than with Jurkat-WT, whereas SADR-1, SADR-5, and USA300JE2 showed significantly lower PD-1-specific interactions (Figure 1a). The interaction of SADR-2 with Jurkat-PD1 was verified by confocal microscopy (Figure 1b). Jurkat-PD1, Jurkat-WT, and Jurkat-PD1 knockout (KO) T cells were treated with PBS or AF647-labeled SADR-1 or SADR-2. Interactions were analyzed by flow cytometry 2 hours later (Figure 1c). The study showed that knockout (KO) of PD-1 greatly reduced the interaction of SADR-2 with Jurkat T cells, further confirming that PD-1 is essential for binding to SADR-2 (Figure 1c). In fact, the binding of the clpP mutant SADR-2 to IgG-fc was significantly increased, while the interaction between PD-1-Fc and SADR-1 was significantly reduced (Figure 1d). As expected, no interaction was observed with the control chimeric protein CD44-Fc (Figure 1d). These data strongly suggest that the suppressive phenotype of T cells exposed to SADR-2 is caused by a direct inhibitory interaction with PD-1.

Figure 1. ClpP mutant S. aureus interacts directly with PD-1. (Mellergaard M, et al. 2023)