Development of an AI-based cytokine-score to predict early recurrence or progression in melanoma patients undergoing immune checkpoint inhibition

Background: Tebentafusp (tebe), targeting gp100, is the first TCR-CD3 bispecific to demonstrate overall survival (OS) benefit and is approved for the treatment of mUM.We have previously shown B cell recruitment into the tumor associated with OS on tebe [1].We explored further formation of lymphoid aggregates (LA) within the tumor microenvironment in response to tebe.Methods: HLA-A*02:01+ 2L+ adult patients (pts) with mUM were treated with tebe (NCT02570308).Paired tumor biopsies were collected at baseline (n=70), after 3 doses of tebe (n=48), and at radiographical progression (n=17).Presence of B cells, T cells and macrophages was assessed by immunohistochemistry, using antibodies against CD20, CD3 and CD163 respectively, and digitally quantified.Using density analysis, aggregates of 10 CD20+ B cells within CD3+ T cell area in a 100m radius were defined as LA.At progression pts were categorized by OS 12 or <12 months.Mean fold change (FC) was used.Results: At baseline, B cells were detected in 90% of pts (median 5 B cells/mm 2 ) with those pts having no more than 2 LA/mm 2 (17% pts with 1 LA/mm 2 and 3% pts with 2 LA/mm 2 ).The median number of B cells in the biggest LA per sample was 24.B cells were recruited into the tumor after 3 doses of tebe (median 32 B cells/mm 2 , FC 3, p=6.5e-05).The LA density increased up to 6 LA/mm2 (23% pts with 1 LA/mm 2 , 8% pts with 2 LA/mm 2 , 6% pts with 3 LA/mm 2 and 2% pts with 6 LA/mm 2 ) with a trend for an increase in LA size (median B cell number in biggest LA = 30, p = 0.67).Tumors with a low baseline CD163+ macrophage to CD3+ T cell ratio, which was previously associated with longer OS on tebe, tended to have more LA/mm 2 at baseline and on-treatment than those with a high ratio.At progression, pts with long OS had more B cells in the tumor compared to short OS (median 20 vs 2 B cells/mm 2 ; FC 5, p=0.05).Additionally, more pts with long OS had LA than pts with short OS (6/12 pts vs 1/5 pts respectively) with a density not exceeding 1 LA/ mm 2 .LA in the short OS pt was found in the normal adjacent tissue compared to the LA in long OS pt which were located in the tumor and invasive margin.Conclusions: Tebe enhanced the formation of LA in the tumour microenvironment, notably in low immunosuppressed tumors, consistent with the hypothesis that it results in epitope spread.These observations provide deeper insight into the mechanism of action of tebe and helps to explain prolonged survival of mUM pts beyond radiographical progression.