Oral Presentation Asia-Pacific Vaccine and Immunotherapy Congress 2024

Anti-CD40 is effective in immune cold colorectal cancer (#45)

Stephen J Blake 1 2 , Yee T Chern 1 2 , Susan Woods 1 3 , David Lynn 1 2
  1. SAHMRI, Adelaide, SOUTH AUSTRALIA, Australia
  2. College of Medicine and Public Health, Flinders University, Bedford Park, South Australia, Australia
  3. School of Medicine, Adelaide University, Adelaide, South Australia, Australia

Colorectal cancer (CRC) has a devastating toll, with more than 17,000 Australians diagnosed and >5,000 deaths annually. PD1/L1 immune checkpoint blockade (ICB) have provided hope to CRC patients, as they are able to induce tumour reduction in ~33% of patients with microsatellite instable (MSI) CRC. Unfortunately, the vast majority (~95%) of advanced CRC is microsatellite stable (MSS), which is almost completely unresponsive to anti-PD1/L1 treatment. We have developed a novel orthotopic preclinical model of MSS-CRC by introducing common CRC mutations; KRASG12D, AKP and P53 deletions into murine colonic organoids via CRISPR-Cas9 targeting. Following colonoscope injection into the distal colon, these tumour organoids accurately recapitulate the MSS-CRC disease seen in patients, with immune effector cells excluded from a tumour microenvironment dominated by suppressive macrophages, neutrophils, and fibroblasts. Consistent with observations in patients, our model is resistant to anti-PD1 and anti-CTLA4 treatments. Excitingly then, we have found that the immune agonist antibody anti-CD40 drives a robust infiltration of activated effector immune cells into CRC tumours, including a 20-fold increase in CD8+ T-cells. Anti-CD40 monotherapy had significant anti-tumour efficacy against established CRC tumours, inducing tumour shrinkage and significantly extending survival. Efficacy of anti-CD40 was dependent on CD8+ T-cells while depletion of CD4+ T-cells improved anti-CD40 efficacy, likely via effects on regulatory T-cells. Spatial transcriptomic and metabolomic analysis determined that anti-CD40 induced tumour intrinsic activation of innate and adaptive immune cells, including the upregulation of multiple suppressive pathways including PDL1-PD1 and CD28-CTLA4, suggesting we may observe synergy with immune checkpoint blockade. Despite these observations, we found no increase in efficacy when combining anti-CD40 with either anti-PD1 or CTLA4 and further evaluation with other combinations is currently underway. In summary, we have developed a novel mouse model of MSS CRC that may more closely model the outcomes of immunotherapies observed in human disease than the commonly used 2D tumour models of CRC, such as CT-26 or MC38 cells. We propose this model will be useful as a “second round” preclinical model to identify the most potent, clinically applicable immunotherapy combinations to take into clinical trials.