Abstract 2271: Tebentafusp recognition of melanoma cells is restricted by HLA-A0201 presentation of a gp100 peptide
Authors: Cole David , Robinson Ross , Srikannathasan Velupillai , Karuppiah Vijay , Harper Stephen , Coles Charlotte , Patel Viren , Jevanthan Anitha , Harper Jane , Berman David , Powesland Alex 
Published: September 2020

Abstract
Introduction:
Presentation of dysregulated or neoantigen peptides by human leukocyte antigens (pHLA) are a key source of novel targets for cancer immunotherapy. ImmTAC molecules are a novel class of T cell redirecting bispecific fusion protein that utilize an affinity enhanced TCR to target tumor selective pHLA. Tebentafusp, our lead clinical candidate, is an ImmTAC molecule that targets a gp100-derived peptide presented by HLA-A*02:01. The aim of this study was to investigate whether the gp100 peptide could be presented by other HLA alleles (i.e. alloreactivity), and whether this presentation could be detected by tebentafusp.
Experimental procedures:
Using mass spectrometry, gp100 presentation in HLA-A*02:01+ and HLA-A*02:01- melanoma cell lines was investigated. T cell redirection assays were performed against gp100+ HLA-A*02:01+ and gp100+ HLA-A*02:01- tumor cells as well as a panel of HLA-A*02:01- B cells with broad HLA allele presentation. X-ray crystallography was used to solve the structure of tebentafusp in complex with HLA-A*02:01-gp100 peptide to understand the mechanisms underpinning target selectivity to tumor cells expressing both gp100 and HLA-A*02:01.
Summary of the data:
Our data demonstrate that the gp100 peptide targeted by tebentafusp was only detectable on HLA-A*02:01+ tumor cells. Tebentafusp-mediated T cell redirection was only observed on target cells expressing both gp100 and HLA-A*02:01 and recognition of gp100+ HLA-A*02:01- cells could be re-established via lentiviral expression of HLA-A*02:01. Additionally, tebentafusp did not generate a T cell response against a panel of B cells representing major HLA types that cover ~90% of the human population. Further investigation revealed that although gp100 could bind to some other HLA-A*02 subfamily members, tebentafusp was able to discriminate between these pHLA complexes in binding and cellular assays. The 3D crystal structure of tebentafusp in complex with HLA-A*02:01-gp100 peptide revealed the complex was stabilized through specific interactions with residues unique to HLA-A*02:01.
Conclusions:
The lack of alloreactivity by tebentafusp towards other HLA alleles was driven by both restricted presentation of the target gp100 peptide by HLA-A*02:01 and direct molecular interactions between tebentafusp and unique residues on the HLA-A*02:01 surface. These data have implications for the selection of patient populations that are likely to benefit from treatment with this novel bispecific drug.
Citation Format: David Cole, Ross Robinson, Velupillai Srikannathasan, Vijay Karuppiah, Stephen Harper, Charlotte Coles, Viren Patel, Anitha Jevanthan, Jane Harper, David Berman, Alex Powesland. Tebentafusp recognition of melanoma cells is restricted by HLA-A0201 presentation of a gp100 peptide [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2271.