Abstract A12: The Eevaluation of syngeneic animal models for the development of immunotherapeutics in cancer
Authors: Batey Michael A. , Alzabin Saba , Hoyle Sarah , Otto Sarah , Bowden Emma 
Published: May 2016

Background. Cancer immunotherapies are designed to work in conjunction with a patient's immune system to increase native anti-tumour responses, and immunotherapeutic approaches to treating cancer have been evaluated during the last few decades with limited success. An understanding of the checkpoint signaling pathway involving the programmed death 1 (PD-1) receptor and its ligands (PD-L1/2) has focused efforts in targeting tumour-induced immune suppression to advance immunotherapeutic drug development, with the PD-1/PD-L1 pathway being shown to be a promising therapeutic target. Early clinical experience has shown encouraging activity of these agents in a variety of human tumours, with further results awaited from completed and ongoing studies.

One of the most important aspects in anti cancer drug development is the availability of robust preclinical models which allow the efficacy of novel therapies to be examined. Conventional xenograft models lack relevance in this area due to the immunocompromised status of the strains used. Several Humanised mouse models have been developed, but these can be difficult to manage and expensive to run. Syngeneic mouse models (murine cancer growing in a mouse) however can provide an effective mechanism for studying of cancer therapy in the presence of a fully functional immune system. As they retain intact immune systems, syngeneic mouse models representing a variety of hematological and solid tumors (including leukemia, melanoma, lung, colon and breast cancer) can be particularly relevant for studies of immunologically-based targeted therapies, either used alone or in combination with other drugs that modulate the immune system's ability to seek out and destroy cancer cells. As well as allowing the evaluation of tumour burden and tumour growth delay, these models allow the assessment of immune-modulatory phenotypes. Here we discuss the response of syngeneic tumours to the checkpoint inhibitor PD-L1 using the colorectal syngeneic tumour model CT26, and outline the development of strategies to optimise tissue disaggregation and FACs analysis of relevant markers in this and other syngeneic tumour models.

Materials and Methods. Female BalB/C mice aged between 6-8 weeks were inoculated sub cutaneously with CT26 cells at a variety of concentrations between 1 × 106 to 5×106 cells per mouse. Tumours were allowed to grow to 100mm3 and then animals were administered with vehicle control or anti PD-L1 at a variety of doses and schedules. At sacrifice, spleen and tumour were collected, and tissues were processed using a variety of conditions to provide single cell suspensions which were then labelled for FACs analysis using a panel of markers including CD3, CD4, CD8, Foxp3, CD11b, B220 and CD44 to evaluate the influence of anti-PD-L1 treatment on immune cell populations such as regulatory T cells (Tregs), and effector T cells.

Conclusion.CT26 syngeneic tumours grow well as a sub cutaneous model, with palpable tumours forming within one week of implantation. Administration of anti PD-L1 shows some efficacy in the model. Careful attention must be paid to the methodology of tumour disaggregation and cellular staining, to retain the viability of all cell populations within the tumour for subsequent FACs analysis, and so as not to bias results. These methods can be readily used to examine the influence of immunotherapy in syngeneic tumour models.

Citation Format: Michael A. Batey, Saba Alzabin, Sarah Hoyle, Sarah Otto, Emma Bowden. The Eevaluation of syngeneic animal models for the development of immunotherapeutics in cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A12.