Oral Presentation 33rd Lorne Cancer Conference 2021

Dynamic changes in T cell receptor diversity correlate with successful responses to immune checkpoint blockade outcomes in murine tumour models (#4)

Joel Kidman 1 , Nicola Principe 1 , Rachael Zemek 2 , Wee Loong Chin 1 , Catherine Forbes 2 , Vanessa Fear 2 , Abha Chopra 3 , Scott Fisher 1 , Ayham Zaitouny 4 , Emma de Jong 2 , Debora Correa 4 , Robert Holt 5 , Anna Nowak 1 , Mark Watson 3 , Timo Lassmann 2 , Richard Lake 1 , Willem Lesterhuis 2 , Jonathan Chee 1
  1. National Centre of Asbestos Related Diseases, University of Western Australia, Perth, Western Australia, Australia
  2. Telethon Kids Institute, Perth, Western Australia, Australia
  3. Institute for Immunology and Infectious Diseases, Murdoch University, Perth, Western Australia, Australia
  4. Department of Mathematics Complex Systems, University of Western Australia, Perth, Western Australia, Australia
  5. British Columbia Cancer Genome Center, Vancouver, British Columbia, Canada

Checkpoint blockade immunotherapy (CPB) causes durable tumour responses in a minority of patients. Profiling immune changes in responders and non-responders to CPB provides mechanistic insight that will guide the development of treatment biomarkers, and novel immunotherapies. Our study profiled T cell repertoires of responding and non-responding animals with T cell receptor beta (TCRβ) sequencing. We hypothesize that differential dynamics of the TCRβ repertoire define CPB responses.

We utilised an established bilateral, transplantable tumour model that controlled variation in host genetics and tumour antigen expression. In this model, bilateral tumours either grow or regress symmetrically following treatment with anti-CTLA4 + anti-PD-L1. A source of variation comes from the naturally diverse TCRβ repertoire found between animals, allowing us to assess TCRβ repertoire’s contribution to CPB outcome. The symmetry of response allows for excision of one tumour as a readout for immune status, whilst leaving the other as a readout for CPB outcome. Tumours and peripheral blood were sampled one hour prior to CPB, or 2, 4 or 6 days after, and underwent TCRβ sequencing.

Despite limited variation in tumour antigen, each animal expanded unique tumour TCRβ clones. Expanded tumour T cell clones were primarily activated CD8+ T cells. There were no shared TCRβ clones that correlated with CPB response. However, responding animals displayed similar clonal dynamics, as they exhibited reduced TCRβ diversity and clonal expansion before non-responding mice. Using modified greedy clustering, we clustered similar TCRβ sequences based on CDR3 amino acid edit distance and delineated different tumour models with these clusters. We tracked TCRβ clusters dynamically, and identified increased expression of particular clusters over time that correlated with CPB response. Lastly, we validated these clonal dynamics by studying sequential peripheral blood samples from mice and patient samples in relation CPB responses. We propose that dynamic changes in TCRβ repertoire early in treatment, such as the clonal proliferation of relevant T cell clones, are possible predictors of CPB response.