Exploiting the immune system in order to treat malignancy has been a longstanding field of interest. On the one hand, antibodies against a variety of more or less tumour specific antibodies have been developed, starting with anti CD20 or Rituximab. Nowadays, the field has moved forward, and a variety of different approaches is now available for the clinician, varying from biclonal antibodies, through CART cells, to small molecules targeted to proteins mutated in some malignancies but necessary for a functional immune system as well. As more and more patients survive, the interest to gain more insight in the behaviour of the immune system after therapy is growing. The lecture will talk you through the different therapies and the types of secondary immunodeficiency's that have been described. A second niche to be discussed is the growing insight in the evolution of the immune system after stemcell transplantation.