UsEPs as a Possible Immunotherapy

Abstract

That usEPs could ablate tumors was a significant finding in the use of this technology for cancer therapy. The finding that usEPs could also induce immunity was a bonus for this treatment as possible immunotherapy. However, the data to support this immune induction by usEPs had several different sets of suggestive evidence. One approach showed slower tumor growth in immunocompetent mice vs. growth in immunodeficient mice. A second approach showed the slower growth of a secondary tumor after ablation of a primary tumor, suggesting that the primary treatment caused an immune response that slowed secondary tumor growth. The presence of CD4+ T-cells in the primary treated tumors and CD4+ cells in the untreated secondary tumor was used as evidence. However, the CD4+ cells require further characterization to differentiate CD4+ CD25+ Foxp3+ T-regulatory immunosuppressor cells (Tregs) from CD4+ CD44+ with the presence or absence of CD62L+ as T-central or T effector memory cells, respectively. The strongest evidence for usEP-induced immunity indicated the complete absence of secondary tumor growth after primary tumor treatment. Such responses were present in cancer models in the ectopic mouse liver, orthotopic mouse breast, and rat liver cancers. The absence of secondary tumor growth is called vaccine effects or in situ vaccination. Thus, the treatment of the primary tumor induces immunity and vaccinates the animals by the usEP treatment. The latter two cancers exhibited early decreases in immunosuppressor Tregs and myeloid-derived suppressor cells (MDSC), which resolve suppression of immune responses, and increases in dendritic cells (DCs) in the TME that could identify antigens and induced immunity. The rat liver cancer model also showed activation of the innate immune natural killer (NK) cells with specific activation markers in its TME and the presence of effector and central memory cells in the mouse breast and rat liver (TME), which were cytotoxic. An ectopic mouse pancreatic cancer model that did not show a vaccine effect failed to show a decrease in Tregs and MDSC in the TME and blood and did not show activated T-cells, suggesting immunosuppression prevented an immune response. Continued studies will determine immunity, cell death mechanisms, and ICD factors (calreticulin, ATP, and HMGB1) in other immunogenic cancer models.