Application of PD-1, PD-L1, and CTLA-4 inhibitors in the treatment of solid tumors: a basic approach in the immunotherapy of oncology diseases

Immune checkpoint proteins like PD-1/PD-L1 and CTLA-4 represent significant scientific discoveries in the immunotherapy of solid tumors. Humanized monoclonal antibodies, known as PD-L1 inhibitors, suppress the binding of PD-L1, a human transmembrane protein referred to as a checkpoint protein. PD-L1 is involved in the signaling of programmed cell death through the receptor PD-1, a cell surface receptor that plays a crucial role in immune system suppression and promotes tolerance to host cells. The two main pathways that are specifically targeted in clinical practice are cytotoxic T-lymphocyte antigen-4 (CTLA-4) and the protein "programmed cell death 1" (PD-1). Humanized monoclonal antibodies targeting these immunological checkpoint proteins have shown success in patients with non-small cell lung cancer (NSCLC), renal cell carcinoma, metastatic melanoma, and head and neck carcinoma. The FDA has approved three categories of immune checkpoint inhibitors: PD-1 inhibitors (Pembrolizumab, Nivolumab, and Cemiplimab), PD-L1 inhibitors (Durvalumab, Atezolizumab, and Avelumab), and CTLA-4 inhibitors (Ipilimumab). Not all patients responded positively, which highlights the role of biomarkers such as PDL-1 expression in predicting the response to immunotherapy with checkpoint inhibitors. This literature review aims to present the latest developments in the field of immunotherapy for the treatment of solid tumors.