CD28 and small cell lung carcinoma: However, therapeutic interventions targeting the two best-described B7-CD28 family immunotherapy targets—T-lymphocyte protein 4 (CTLA-4) and programmed cell death protein-1 (PD-1)—have failed to achieve favorable results in patients with SCLC (14–16).Therefore, a better understanding of the TIME and immune checkpoint blockades has the potential to lead to promising new SCLC treatments.