Describe the two pathways of resistance to checkpoints of tumors?

Resistance through CTLA4: — CTLA4 or CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), also known as CD152, is an analog of CD28 expressed on activated T cells and on Treg — It binds B7-1 or B7-2 and blocks signaling through C Resistance through PD1-PD1L: — The PD-1 (programmed cell death-1) receptor and its ligands, PDL1/PD-L2, are members of the family of immune checkpoint proteins: — PD-L1 and PD-L2 are commonly expressed by dendritic cells and macrophages — Normally, PD-1 is increasingly expressed on activated T cells to halt or inhibit immune responses — The PD-1/PD-L1 pathway is a resistance mechanism of tumor cells: — PD-L1 is overexpressed on tumor cells or on non-transformed cells in the tumor microenvironment — Its binding to PD-1 receptors on activated T cells leads to persistent CTL inhibition in the tumor microenvironment