Clinical evaluation of HuDo-CSPG4 DNA electroporation as adjuvant treatment for canine oral malignant melanoma: comparison of two vaccination protocols

Canine oral malignant melanoma (OMM) is an aggressive, spontaneously occurring tumor carrying a poor to guarded prognosis and relatively limited therapeutic strategies. In this landscape, chondroitin sulfate proteoglycan (CSPG)4 represents a promising immunotherapeutic target. The objective of this bi-center prospective study was to examine the clinical outcome of OMM-bearing dogs treated with surgery and adjuvant electroporation using a DNA vaccine (HuDo-CSPG4) encoding both human (Hu) and canine (Do) portions of CSPG4 through two different vaccination protocols. Dogs with stage I-III surgically resected CSPG4-positive OMM underwent HuDo-CSPG4 plasmid electroporation starting at the 3rd-4th post-operative week; electrovaccination was repeated after 2 weeks. In protocol 1, electrovaccination was then delivered monthly while in protocol 2, electrovaccination was performed monthly four additional times followed by semestral boosters. The survival rates of HuDo-CSPG4-vaccinated dogs were estimated and compared with a control group treated with surgery alone. Significantly longer overall survival times were observed in HuDo-CSPG4 vaccinated dogs as compared with non-vaccinated controls. Dogs receiving protocol 2 showed similar outcomes to those of dogs undergoing protocol 1, despite fewer vaccinations. The comparable humoral response against CSPG4 resulting from the administration of protocol 1 and 2 appears to have similar clinical relevance, highlighting protocol 2 as the optimal vaccination schedule.