Tebentafusp induces a T cell driven rash in melanocyte-bearing skin as an adverse event consistent with the mechanism of action

Abstract

Tebentafusp is a gp100xCD3 bispecific ImmTAC designed to redirect polyclonal T cells against cells presenting the melanocyte lineage specific antigen gp100 on HLA-A*02:01. Skin-related adverse events, predominantly rash, are frequent and occur within a few hours after initial infusions, yet the mechanisms are unknown. Here we analysed clinical data from the randomised phase 3 trial (NCT03070392) of tebentafusp (n=252) versus investigator's choice (n=126). Translational analyses were performed on paired on-treatment skin samples from 19 patients collected in the phase 1 trial (NCT01211262). Our analyses showed that rash is a clinical manifestation of tebentafusp-induced recruitment of T cells to cutaneous melanocytes. Development of rash depended on baseline expression levels of gp100 and other melanin pathway genes in the skin. On treatment, melanocyte number was reduced and expression of melanocytic genes decreased, while gene expression related to immunity and cytokine signalling increased. When adjusted for baseline prognostic features, patients with rash within the first week of tebentafusp treatment had the same overall survival compared to patients without a rash in the phase 3 randomized trial IMCgp100-202 (HR 0.84; 95% CI 0.53-1.32). In summary, skin rash is an off-tumour, on-target effect of tebentafusp against gp100+ melanocytes, in line with the mechanism of action.