Abstract A07: Changes in immune profiles of osteosarcoma dogs receiving a GD3-based vaccine concurrently with carboplatin chemotherapy and surgery

Introduction: The disialyl gangliosides GD2/GD3 have been implicated in the enhancement of malignancy in a number of human and animal cancers and as a tumor antigen target for immunotherapy. In a recent abstract presented at an AACR Conference we reported on the coexpression of GD2/GD3 in four canine osteosarcoma (OSA) cell lines (1). In a prospective IACUC approved clinical trial we vaccinated dogs with a GD3-based vaccine with naturally occurring OSA receiving surgery and carboplatin chemotherapy to investigate the expression profiles of immune modulating cells overtime. Methods: Dogs will be entered into the study only if they meet the following inclusion criteria: have a confirmed diagnosis of OSA and no other life-threatening diseases. The study will accrue 40 cases; 20 will receive the vaccine plus standard of care and 20 dogs will receive only the standard of care (amputation and intent to treat with 6 doses of carboplatin). On admission blood will be collected according to the protocol for monitoring of the immune response. The dogs will then be vaccinated according to a predetermined protocol during chemotherapy and staged. The immune response profile of the vaccine group will be compared to dogs receiving standard of care alone and normal dogs. Flow cytometric platforms were developed to monitor changes in immune cells (CD5, CD21, CD4, CD8, CD14, CD11b, MHCII, and Foxp3). In addition, IHC arrays and RNA Scope will be developed for checkpoints of immunity PD1, PDL-1 and expression of intratumoral immune cells. Results: Currently twenty dogs with osteosarcoma have enrolled into the study and have received standard of care and vaccination. Complete flow cytometric immune profiles are available for nine dogs with osteosarcoma. On admission, all dogs with OSA showed elevated cell counts of Treg (FoxP3+/CD4+) cells, Monocytic (m-) and Granulocytic (g-) myeloid derived suppressor cells (MDSCs) when compared to normal dogs (all dogs had normal CBCs). All m-MDCSs and g-MDSCs and Treg cells decreased significantly after the first dose of chemotherapy. Serial sampling over weeks showed sustained inhibition even after chemotherapy was completed (18 weeks). Two OSA cases which relapsed with metastasis to the lungs showed significant increases in Treg cells at the time of restaging. Complete necropsy post-therapy in three dogs showed changes in metastatic profiles; 2/3 showed no metastatic disease to the lungs, but metastases occurred to bone and kidneys. Discussion: MDSCs series of cells and Treg cells are increased in OSA compared to normal dogs and may be a factor in maintaining a welcoming tumor microenvironment and resistance to immunotherapy. MDSCs are reported to be elevated in other cancers, but not in naturally occurring OSA. Furthermore, canine OSA cell lines show increased expression of CCL2 and COX2 (data not shown). Recruitment of MDSCs to the cancer micro-tumor environment are thought to be mediated by the chemokine CCL2 and COX2. Abrogation of these pathways with chemotherapy and possibly immunotherapy may enhance overall survival. Early necropsy data seem to support the attenuation of the metastatic profile in dogs receiving standard of care and GD3-based vaccine. Conclusions: Anticipated results from the study will be used to adjust the vaccine protocol according to the changes in immune profiles. Data is not mature enough to evaluate survival at this time. Acknowledgment: The study is funded by a grant from the American Kennel Club Health Foundation and The UF CVM. Reference: 1. Milner RJ, Chimura N, Bowles KD, Salute M. Abstract A29: Differential expression of the gangliosides GD3 and GD2 in canine and human osteosarcoma cell lines: An immunotherapy target. Cancer Immunol Res 2015 Oct 1;3(10 Supplement):A29. Citation Format: Bikash Sahay, Shana Hutchison, Matt Cascio, Amandine Lejeune, Carlos Souza, Anna Szivek, Keijiro Shiomitsu, Kayla Harding, Stacey Fox-Alvarez, Mia Livaccarri, Lindsay Powers, Rowan James Milner. Changes in immune profiles of osteosarcoma dogs receiving a GD3-based vaccine concurrently with carboplatin chemotherapy and surgery [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A07.