PDCD1 and infection: We found strong evidence that PD-1+ cells had a higher infection frequency per 106 cells of intact nef compared to CTLA-4+ cells, DP cells and DN cells within this data (all p<0.00001; Figure 3A), with evidence that these differences varied across participants (participant effect modification; PD-1+ vs CTLA-4+: p=0.0001, PD-1+ vs DP: p=0.0095, and PD-1+ vs DN: p<0.00001; Table 1).