CD4 and small cell lung carcinoma: Both CD3+CD8+ and CD3+CD4+ T-cells from LS-SCLC (CD8: p = 0.030; CD4: p = 0.033) and ES-SCLC (CD8: p = 0.0006; CD4: 0.0002) patients were found to express elevated levels of PD-1 compared to HD (Figure 2).