Transient immunological and clinical effectiveness of treating mice bearing premalignant oral lesions with PD‐1 antibodies

A carcinogen‐induced premalignant oral lesion model that progresses to oral cancer was used to examine the impact of blocking PD‐1 on cytokine expression and on progression of lesions to cancer. The results of this study show increased production of IL‐2 and the inflammatory cytokines IL‐6, IL‐17 and TNF‐α by spleen cells of lesion‐bearing mice that were treated with PD‐1 antibody for 1 week compared to cytokine production by spleen cells of lesion‐bearing mice treated with control antibody. Production of IFN‐γ increased at 3 weeks of PD‐1 antibody treatment, although production of the other Th1 and inflammatory mediators declined. By 5 weeks, levels of these cytokines declined for both control and PD‐1 antibody‐treated mice. Flow cytometric analysis for IFN‐γ‐expressing cells showed shifts in CD4(+) cells expressing IFN‐γ consistent with the changes in cytokine secretion. Whether or not treatment generated reactivity to lesions or HNSCC was determined. Spleen cells from PD‐1 antibody‐treated mice were stimulated by lysates of premalignant lesion and HNSCC tongue tissues to produce increased levels of Th1 and select inflammatory cytokines early in the course of PD‐1 antibody treatment. However, with continued treatment, reactivity to lesion and HNSCC lysates declined. Analysis of clinical response to treatment suggested an early delay in lesion progression but, with continued treatment, lesions in PD‐1 antibody‐treated mice progressed to the same degree as in control antibody‐treated mice. Overall, these results show an early beneficial response to PD‐1 antibody treatment, which then fails with continued treatment and lesion progression.