Our immune system has several types of cells: those called effector T cells and those called regulatory T cells (Tregs).
The effector T cells are the ones that attack and destroy antigens foreign to our body, be they bacteria, viruses or tumor cells, but they need to be somehow authorized to attack by the regulatory T cells (Tregs). In cancer, these authorizing T cells are deceived by the tumor microenvironment and do not allow the effector T cells to attack.
With immunotherapeutic drugs what is achieved is that the number of these regulatory T cells (Tregs) decreases and also that they are exposed in their masking action of the tumor antigens.
Cancer is a very intelligent and sophisticated disease that "tricks" our immune system into believing that cancer cells are healthy cells, and therefore they are not attacked and destroyed by the T-lymphocytes of our immune system. Discovering and reversing this trickery is what can be achieved through cryoablation and intratumoral immunotherapy.