Moving forward with organ preservation in rectal cancer

Organ Preservation in Rectal Cancer: An Overview of the Dutch Perspective and Recent Developments

Although current guidelines on rectal cancer treatment often recommend rectal resection with or without neoadjuvant (chemo)radiotherapy, there is growing interest in organ-preserving treatment approaches among patients and clinicians in the Netherlands. Currently, multiple ongoing studies are investigating the value of different non-operative treatment modalities to improve tumour response rates and increase the chance of successful organ preservation. Papillon contact X-ray brachytherapy is a promising treatment modality to improve the chance of organ preservation, which seems especially relevant for elderly and frail patients unable or refusing to undergo total mesorectal excision surgery. The elderly and frail patient with rectal cancer poses a significant challenge and warrants a thorough multidisciplinary approach to provide the most optimal organ-preserving treatment. In this overview, an insight into the Dutch perspectives and developments within the field of organ preservation and the set-up of a Papillon facility to complete the spectrum of organ-preserving treatment options in a tertiary referral centre for rectal cancer treatment has been provided.

ATR-mediated CD47 and PD-L1 up-regulation restricts radiotherapy-induced immune priming and abscopal responses in colorectal cancer

Radiotherapy (RT) of colorectal cancer (CRC) can prime adaptive immunity against tumor-associated antigen (TAA)-expressing CRC cells systemically. However, abscopal tumor remissions are extremely rare, and the postirradiation immune escape mechanisms in CRC remain elusive. Here, we found that irradiated CRC cells used ATR-mediated DNA repair signaling pathway to up-regulate both CD47 and PD-L1, which through engagement of SIRPα and PD-1, respectively, prevented phagocytosis by antigen-presenting cells and thereby limited TAA cross-presentation and innate immune activation. This postirradiation CD47 and PD-L1 up-regulation was observed across various human solid tumor cells. Concordantly, rectal cancer patients with poor responses to neoadjuvant RT exhibited significantly elevated postirradiation CD47 levels. The combination of RT, anti-SIRPα, and anti-PD-1 reversed adaptive immune resistance and drove efficient TAA cross-presentation, resulting in robust TAA-specific CD8 T cell priming, functional activation of T effectors, and increased T cell clonality and clonal diversity. We observed significantly higher complete response rates to RT/anti-SIRPα/anti-PD-1 in both irradiated and abscopal tumors and prolonged survival in three distinct murine CRC models, including a cecal orthotopic model. The efficacy of triple combination therapy was STING dependent as knockout animals lost most benefit of adding anti-SIRPα and anti-PD-1 to RT. Despite activation across the myeloid stroma, the enhanced dendritic cell function accounts for most improvements in CD8 T cell priming. These data suggest ATR-mediated CD47 and PD-L1 up-regulation as a key mechanism restraining radiation-induced immune priming. RT combined with SIRPα and PD-1 blockade promotes robust antitumor immune priming, leading to systemic tumor regressions.