Tumor location impacts immune response in mouse models of colon cancer

Abstract

Existing preclinical models of human colorectal cancer (CRC) that rely on syngeneic subcutaneous grafts are problematic, because of increasing evidence that the immune microenvironment in subcutaneous tissue is significantly different from the gastrointestinal tract. Similarly, existing orthotopic models that use a laparotomy for establishing grafts are also problematic, because the surgical procedure results in extensive inflammation, thereby creating a nonphysiologic tumor microenvironment. To facilitate the bench-to-bedside translation of CRC immunotherapy strategies, we developed a novel orthotopic model in mice that uses endoscopy-guided microinjection of syngeneic cancer cells. When we compared immune system infiltration, we found that tumors in the subcutaneous model had fewer T cells, B cells, and natural killer (NK) cells, but more immunosuppressive myeloid cells; in contrast, tumors in our orthotopic model had a higher number of tumor-infiltrating T cells, B cells, and NK cells, with fewer immunosuppressive myeloid cells. The number of immune-stimulating cytokines, such as interleukin (IL)-2, IL-6, interferon (IFN)-gamma, and granzyme B, was also higher in tumors in our model, as compared with the subcutaneous model. Those differences resulted in heightened sensitivity to immune checkpoint blockade therapy in our endoscopy-guided orthotopic CRC model. Our study indicates that tumor location affects immune response in CRC mouse models; choosing the appropriate preclinical model is important when testing immunotherapy in CRC.

Profiling the intratumoral immune landscapes of primary and syngeneic Kras-driven sarcoma mouse models

“…Of note, the majority of published studies of syngeneic models report a CD4/CD8 ratio equal to or above 1. [5][6][7][8][9][10] All our tumor models except the KRIMS-2 UPS syngeneic tumors followed this pattern. KRIMS-2 tumors, in contrast, favored CD8+ T cell enrichment with a CD4/CD8 of 0.6 ( Figure 4E).…”

“…Previously published reports from multiple syngeneic tumor models have found a wide diversity of immune cell composition. [5][6][7][8][9][10] Based on these studies and on our finding of differing levels of CD45+ immune infiltration, we hypothesized there would be broad differences in multiple immune cell populations between UPS primary and KRIMS-1 and KRIMS-2 syngeneic tumors.…”

“…Though there are extensive characterizations of diverse syngeneic models across multiple tumor types and mouse background strains [5][6][7][8][9][10] , there are few studies comparing the immune profiles of orthotopic allograft models with their originating primary tumor model to determine if the syngeneic tumors accurately recapitulate the primary tumors' intratumoral immune landscapes. We performed flow cytometry on five to nine similarly-sized orthotopic allograft tumors from each model and compared levels of CD45+ immune cell infiltration ( Figure 2F).…”

“…5 Even among the same syngeneic model, tumor location can alter the immune profile, as orthotopically injected CT26 tumors contain higher levels of T, B, and NK cells than tumors grown subcutaneously. 10 However, there are few studies that examine how well syngeneic models reflect the immune profile of their original primary tumors. Ultimately, a better understanding of immune infiltrates between primary tumors and their syngeneic counterparts will help prioritize selection of these models and aid in extrapolating their data to the clinic.…”

Of Mice, Dogs, Pigs, and Men: Choosing the Appropriate Model for Immuno-Oncology Research

“…[42][43][44][45] Moreover, orthotopically implanted tumors have provided a valuable system for evaluation and understanding of checkpoint inhibition in various preclinical cancer models. [46][47][48] To date, several types of orthotopically implanted tumor models have been established amongst others, including transplantation in the brain (GL261 cells), 49 the mammary fat pad (4T1 and EMT6 cells), 50,51 intrasplenic (Panc02 cells), 52,53 and in the bladder (MBT-2 cells). 54 Overall, these models may serve as more clinically relevant systems, although the technicality of transplanting the tumor cells is more complex and labor-intensive compared to subcutaneous administration.…”