The role of the enzyme indoleamine 2.3-dioxygenase in inducing a specific immune response against tumor cells treated with photodynamic therapy.

Photodynamic therapy (PDT) is an example of a method of cancer treatment in which activation of the immune system is one of the key elements responsible for the treatment effectiveness. By activating the photosensitizer and creating reactive oxygen species, PDT causes the breakdown of cancer cells. In this way, inflammation within the tumor is induced, and the activated elements of the non-specific immune response are able to initiate an effective specific response only in special cases. Due to the immune tolerance, despite the presence of cancer antigens, the immune system does not fight the disease effectively. The enzyme indoleamine 2.3-dioxygenase (IDO) inhibits the immune response both within the neoplastic lesion and promotes the development of immune tolerance to neoplastic antigens. IDO is synthesized by cancer cells, but its main source in the body are dendritic cells and macrophages. The enzyme inhibits the proliferation and activation of cytotoxic T cells and causes the differentiation of CD4 + T cells into regulatory cells. The aim of the project is therefore to investigate whether inhibition of IDO activity will affect the long-term effect of PDT. The research hypothesis assumes that abolition of the immunomodulatory effect of IDO will result in the destruction of both the tumor and secondary neoplastic lesions.