Camrelizumab-induced oral lichenoid reaction with subepithelial CD4+T-cell infiltration

Introduction: Camrelizumab is a novel anti-programed cell death-1 (PD-1) antibody that has been investigated for the treatment of various malignancies. Increasing immune-related adverse events have been reported in clinical practice, with CD4+ T-cell-mediated-reactive cutaneous capillary endothelial proliferation being the most common. Camrelizumabinduced oral lichenoid reaction (OLR) appears to be a rare adverse effect compared with other anti-PD therapies induced OLR, with the main pathogenesis of activated CD8+ T cells mediating autoimmune reactions. Herein, we report a rare case of camrelizumab-induced OLR and a possible pathogenic mechanism of subepithelial CD4+ T-cell infiltration. Case report: A 57-year-old male patient, who was diagnosed with metastatic esophageal squamous cell carcinoma three years prior, presented with a two-month history of oral erosion that developed while under camrelizumab therapy. Diffuse erythematous and erosive lesions surrounded by bilateral white lesions on the buccal mucosa were detected in his physical examination. Hematoxylin and eosin staining of the lesions revealed the presence of basal keratinocyte degeneration and band-like subepithelial T-cell infiltration. The immunostaining for CD4 on T-cell was positive, while CD8 were sporadically positive. Flow cytometry showed a gradual increase in the CD4+ T-cell proportion in the peripheral blood, with the CD8+ T-cell percentage almost unchanged and in the normal range. We obtained a score of 6 based on the Naranjo algorithm, which means a probable adverse drug reaction. Management and Outcome: The patient exhibited notable improvement after two weeks of treatment with topical glucocorticoid without regulating his immunotherapy, and remained in stable condition in the follow-up. Discussion: This case may offer new insight to clinicians on the pathogenesis of anti-PD-1-induced OLR. More critically, it may provide some ideas for a more precise anti-PD therapy or corresponding combination therapy for patients becoming resistant to immunotherapy due to exhausted CD4+ T-cell responses in the tumor microenvironment.