BTLA transcriptomic expression correlates with high levels of PD-1, PD-L2, and CTLA-4 checkpoints and with its ligand, HVEM, across diverse solid cancers.
Authors: Choi Sharon , Kurzrock Razelle , O'Keefe Thomas , Nishizaki Daisuke , Miyashita Hirotaka , Lee Suzanna , Nikanjam Mina , Eskander Ramez Nassef , Patel Hitendra , Botta Gregory P. , Pabla Sarabjot , Nesline Mary K , Conroy Jeffrey M. , DePietro Paul , Sicklick Jason K. , Kato Shumei 
Published: June 2023

e14641 Background: B and T lymphocyte attenuator (BTLA) is an immune checkpoint that is highly expressed on tumor-specific T cells and has been shown to be upregulated in several cancer types. The binding of BTLA to its ligand herpesvirus entry mediator (HVEM, also known as TNFRSF14) inhibits activation and proliferation of T lymphocytes, leading to decreased tumor killing. Early clinical trials of BTLA inhibitors are ongoing with preliminary results showing modest effects in advanced solid tumors. More recent clinical data suggests that combination checkpoint therapy with anti-BTLA and anti-PD-1 treatment provides greater benefit compared to monotherapy in patients with lymphoma. Methods: We analyzed RNA expression levels of 397 genes in various solid tumor types from 514 patients with various types of solid tumors seen at University of San Diego (UCSD), Moores Cancer Center. RNA expression was quantified at a CLIA-approved laboratory Omniseq (https://www.omniseq.com). Transcript abundance was normalized to internal housekeeping gene profiles and ranked (0-100 percentile) in a standardized manner to a reference population of 735 tumors spanning 35 histologies. We analyzed tumors with “High” (75-100 percentile rank) BTLA expression profiles. Odds ratio for high BTLA expression was calculated and multivariate analysis was utilized to determine significant correlations for multiple genes. Results: A total of 96 (18.7%) tumors had high BTLA (>75) expression across 32 different histologies. Cancers with the highest proportion of BTLA expression were small intestine (42%), breast (31%), pancreatic (29%), stomach (24%), neuroendocrine (20%), lung (20%), head and neck (17%) and colorectal (13%). There was significant association for BTLA and high PD-1 (p < 0.001), high CTLA-4 (p < 0.001), high PD-L2 (p = 0.05) and its ligand HVEM (p < 0.01). There was no significant association between BTLA expression and PD-L1, gender or stomach, neuroendocrine, head and neck, and lung histologies. Conclusions: High BTLA expression was found in a large number of tumor samples and significantly associated with other immune checkpoints with FDA-approved drugs. Furthermore, HVEM expression (ligand for BTLA) significantly correlates with high BTLA transcriptome levels. The BTLA/HVEM pathway has been associated with suppression of T cell-mediated anti-tumor activity and resistance to anti-PD-1 immunotherapy leading to poor clinical outcomes. The utilization of combination checkpoint therapy involving BTLA inhibitors and specific checkpoint blockade is currently being explored. Our results suggest that patient selection based on the RNA expression level of immune markers matched to corresponding immunotherapy agent, rather than a population-based approach, may be ideal for optimizing treatment response.