Investigating The Effects of Combined Chemotherapy and Subcutaneous Administration of Macrophage-like Monocyte-Derived Exosomes Carrying Tumor Antigens in a Female Dog with CTVT

Background: Canine Transmissible Venereal Tumor (CTVT) is a clonally transmissible malignant neoplasm primarily transmitted through mating or direct physical contact. It affects the genital mucosa and, in some cases, the extragenital sites. Conventional treatments include surgery and chemotherapy. Surgery often results in recurrence or metastasis to other organs, while chemotherapy based on vincristine has proven to be effective and is the standard procedure of treating CTVT. Our study investigated the outcome of combining vincristine chemotherapy with immunotherapy using macrophage-like monocyte–derived exosomes carrying CTVT tumor antigens and its effect on therapeutic efficacy and clinical recovery. Methods: A six-year-old, ۲۰ kg female mixed-breed dog (Jessie, Iranian native × Shih Tzu) with severe cachexia and a ۱۳ × ۲۰ cm genital mass was referred to University of Tehran’s Veterinary Hospital (April ۱۶, ۲۰۲۴). CTVT diagnosis was confirmed by performing cytology and histopathology. Baseline imaging and hematology showed no signs of metastasis. The dog received six weekly doses of vincristine alongside ondansetron, and three subcutaneous (SC) injections of macrophage-like monocyte–derived exosomes carrying CTVT tumor antigens (One injection every two weeks). Exosomes were produced by incubating patient-derived monocytes with CTVT tumor lysate for ۲۴ hours. After isolation they were characterized, and quantified using TEM, DLS/Zeta, and NanoDrop analyses. Nutritional support was also provided during hospitalization, and a full laboratory re-evaluation was performed after six weeks of treatment. Results: This Combined Chemo and immunotherapy demonstrated significant tumor necrosis and volume reduction from ۱۳ × ۲۰ cm to approximately ۴ × ۶ cm. The patient gained ۱۰ kgs of weight, showed improved health condition, and had no signs of systemic or local toxicity based on hematological, biochemical, radiological, or ultrasonographic parameters. Conclusion: The combined use of vincristine-based chemotherapy and subcutaneous administration of macrophage-like monocyte–derived exosomes carrying tumor antigens (Exosome-based Immunotherapy) led to a significant regression in the tumor and also improved