actual virus. inactivated viruses are killed viruses that present a form of the antigen to the host. however, long-term immune response is limited. cancer treatment viral immunotherapy in the context of cancer stimulates the body's immune system to better fight against cancer cells. rather than preventing causes of cancer, as one would traditionally think in the context of vaccines, vaccines against cancer are used to treat cancer. the mechanism is dependent upon the virus and treatment. oncolytic viruses, as discussed in previous section, is stimulate host immune system through the release of tumor-associated antigens upon lysis as well as through the disruption of the cancer's microenvironment which helps them avoid the host immune system. car t cells, also mentioned in previous section, is another form of viral immunotherapy that uses viruses to genetically engineer immune cells to kill cancer cells. other projects and products protozoal virotherapy viruses have been explored as a means to treat infections caused by protozoa. one such protozoa that potential virotherapy treatments have explored is naegleria fowleri, which causes primary amebic meningoencephalitis (pam). with a mortality rate of 95%, this disease-causing eukaryote has one of the highest pathogenic fatality rates known. chemotherapeutic agents that target this amoeba for treating pam have difficulty crossing blood-brain barriers. however, the driven evolution of virulent viruses of protozoal pathogens (vvpps) may be able to develop viral therapies that can more easily access this eukaryotic disease organism by crossing the blood-brain barrier in a process analogous to bacteriophages. these vvpps would also be self-replicating and therefore require infrequent administration, with lower doses, thus potentially reducing toxicity. while these treatment methods for protozoal disease may show great promise in a manner similar to bacteriophage viral therapy, a notable hazard is the evolutionary consequence of using viruses capable of eukaryotic pathogenicity. vvpps will have evolved mechanisms of dna insertion and replication that manipulate eukaryotic surface proteins and dna editing proteins. vvpp engineering must therefore control for viruses that may be able to mutate and thereby bind to surface proteins and manipulate the dna of the infected host.