Poster Presentation 18th International Symposium on Dendritic Cells 2026

Dissecting the contributions of dendritic cell lineage and activation state to T cell responses in cancer (#254)

Erin Richardson 1 , Maria Koufaki 1 , Shih-Chieh Chiang 1 , Adam Flinders 2 , Richard Reeves 2 , Sudhakar Sahoo 2 , Duncan Smith 3 , Santiago Zelenay 1
  1. Cancer Inflammation and Immunity , CRUK Manchester Institute, Manchester, United Kingdom
  2. Computational Biology Support, CRUK Manchester Institute, Manchester, United Kingdom
  3. Biological Mass Spectrometry, CRUK Manchester Institute, Manchester, United Kingdom

Conventional dendritic cells (cDCs) promote anti-tumour immunity by presenting tumour antigens. Single-cell RNA sequencing identified a CCR7⁺ activated DC (actDC) cluster derived from both cDC1s and cDC2s. Using intersectional genetic models to label or deplete actDCs, we recently showed that actDCs are essential for CD8+ T cell priming and immunotherapy responses. However, the contributions of lineage and activation state to CD4⁺ T cell responses remain unclear.

To assess how lineage and state determine cDC identity, fluorescently tagged actDC1s, actDC2s, and matched resting cDCs were FACS-sorted for mass spectrometry. Activation induced a shared co-stimulatory and T cell activation programme, consistent with the transcriptomic actDC signature. Nevertheless, lineage remained the major determinant of the cDC proteomic landscape following actDC state acquisition. Although 408 proteins were differentially expressed between actDC1s and actDC2s, most reflected pre-existing lineage-specific features.

We next tested the functional contributions of lineage and activation state to CD4+ T cell priming. In contrast to CD8+ T cells, CD4⁺ T cell priming was actDC-independent, as actDC depletion did not alter activation or proliferation of naïve OT-II cells in mice bearing OVA-expressing tumours. Instead, proliferation was markedly reduced in cDC1-deficient mice, indicating a requirement for cDC1 lineage. OT-II priming was also reduced in cross-presentation deficient Wdfy4-/- mice, independently of the accompanying loss of antigen-specific CD8+ T cell responses. This defect was absent when cancer cells expressed OVA323-339 peptide, rather than full-length ovalbumin. Finally, CD4⁺ T cell priming declined rapidly during tumour progression across multiple models and was not restored by sustained antigen availability or immune checkpoint blockade.

Together, these analyses indicate that effective anti-tumour CD4⁺ T cell priming depends on the cDC1 lineage rather than acquisition of the actDC state. These findings reveal distinct requirements for dendritic cell lineage and activation state in driving CD4⁺ versus CD8⁺ T cell immunity in cancer.