The transmembrane protein receptor CD40, also known as TNFSFR5 (tumor necrosis factor super family receptor 5) is a member of the tumor necrosis factor (TNF) receptor super family and is involved in co-stimulation of immune cells. CD40 is expressed by antigen-presenting cells (APCs) including dendritic cells (DCs), B-cells, macrophages, and monocytes. It has the ability to “wake” DCs to prime effective cytotoxic T-cell responses. Binding of an anti-CD40 antibody to CD40 on antigen presenting cells (i.e., dendritic cells, monocytes and B-cells) is believed to initiate a multi-faceted immune response that enables multiple components of the immune system (e.g., T cells, macrophages) to work in concert against cancer.
CD40 is an important target for immunotherapy, as it plays a critical role in the activation of innate and adaptive immune responses. Effective CD40-targeted antibodies provide an ideal therapy alternative in combination with other immuno-oncology (IO) antibodies.
When delivered systemically, CD40 agonists have produced adverse events that may limit their use. A number of novel CD40 targeting biologics are in preclinical and clinical development using various constructs (multimeric, bispecific, targeted delivery) to overcome systemic safety issues by limiting activation to the tumor microenvironment.
The ligand of CD40, known as CD154 or CD40L, is a type II transmembrane protein that is constitutively expressed on hematopoietic cells such as dendritic cells, macrophages, and B cells. Engagement of CD40 by CD40L expressed on T cells results in the production of proinflammatory cytokines, induces T helper cell function, and promotes macrophage activation. The involvement of CD40 in chronic immune activation has resulted in CD40 being proposed as a therapeutic target for a range of chronic inflammatory diseases. CD40 antagonists are currently being explored for the treatment of autoimmune diseases.

