Childhood cancers present distinct challenges that require specialized therapeutic approaches, different from those used in adult cancers. Ground-breaking immunotherapies, known as immune checkpoint inhibitors, have shown limited efficacy in paediatric solid tumours despite remarkable success in some adult cancers such as melanoma. A key reason for this disparity is the lack of consideration for paediatric-specific immune responses during preclinical research. To address this critical issue, we developed preclinical models of sarcoma that allowed us to examine the effect of developmental age on the tumour immune microenvironment.
In this project, we sought to experimentally compare age-specific intratumoural immune microenvironmental differences between subcutaneous and intramuscular sites using an immune-competent age-appropriate allograft model of rhabdomyosarcoma.
We used a murine rhabdomyosarcoma cell line (M3-9-M; derived from a p53+/- mouse with systemic HGF overexpression) implanted either subcutaneously or orthotopically into the gastrocnemius muscle into juvenile and adult C57BL/6J mice. We compared the tumour immune microenvironment using multiparameter spectral flow cytometry, immunohistochemistry, and/or bioluminescence.
Surprisingly, we found significant differences in the abundance and types of immune cells infiltrating the tumours. Macrophages, neutrophils, CD4+ T, B and NK cell populations were significantly different between subcutaneous versus orthotopic rhabdomyosarcomas. Furthermore, orthotopic implantation resulted in altered tumour growth compared to subcutaneous implantation in both young and old recipients.
These results indicate that the implantation site and age of the preclinical model has profound effects on tumour biology, growth kinetics and the immune microenvironment, which may in turn influence preclinical therapeutic responses. Our findings support efforts to better model paediatric cancers in preclinical research, to help find novel (immune)therapies for children with cancer.