318 Skin rash composition after checkpoint inhibitor therapy varies by therapeutic regimen

Cancer patients treated with immune checkpoint inhibitors can experience adverse events affecting different organ systems. Among related events, skin rash develops relatively early and might serve as a biomarker of downstream responses to therapy. We questioned whether the cellular composition vary according type treatment applied, interfere PD1 signaling alone or combined CTLA-4 blockade. Skin samples were obtained from consenting adults perform mono-and multiplex OPAL immunostaining Vectra imaging snap frozen paraffin-embedded (n=9) control (n=8) samples. The composition, intercellular interactions proliferation evaluated compared healthy skin. CD4 CD8 T cells prime contributors rash, macrophages interacting proliferating on site. Combination therapy offers greater therapeutic benefit patients, here combination increased cytotoxic cell content decreased macrophage abundance was associated dual inhibition over alone. Type 1, 2 17, but not 9 regulatory among inflammatory infiltrates, enhanced epithelial -thickening. conclude that is defined in part by course treatment, wherein reduced contact are inhibitor