Liquid biopsy for lung cancer immunotherapy

Abstract

The recent successful use of the immune checkpoint inhibitors (CPIs) anti-programmed death receptor-1 (PD-1)/PD-1 ligand 1 in clinical trials indicates their crucial role in obtaining an effective cancer immune therapy. These CPIs have been identified to have an effective therapeutic response, particularly in tumors with high tumor mutation burden. Targeting private somatic mutations encoding immunogenic neoantigens (neo-Ags) has been developed as an autologous gene therapy. T-cell receptor-engineered T cells targeting neo-Ags are a novel option for adoptive cell therapy used for the treatment of lung cancer. However, not all patients experience an effective response from immunotherapy. Although the resistance mechanism of CPIs has been reported, its association with other treatment methods during systemic anticancer therapy remains unclear, particularly the treatment options following the emergence of drug resistance in lung cancer. The potential biomarkers used for liquid biopsy may assist in the identification of patients who would benefit the most from immunotherapy. Attempts to identify potential biomarkers for predicting clinical response to immunotherapy are underway. With regard to liquid biopsy, the present review summarizes and discusses the lung cancer management of immunotherapy for precision medicine by reviewing recent literature and associated clinical trials.

Keywords: T cells; checkpoint inhibitors; liquid biopsy; lung cancer; neoantigens; prognosis; tumor mutation burden.

Figure 1.

Cancer-immunity cycle and immune checkpoint inhibitor resistance. (A) CPI resistance on the cancer-immunity cycle and TMB/neo-Ags. i) Early-stage cancer without/with fewer neo-Ags. ii) Cancer within major neo-Ags. iii) For resistance of immune response for major neo-Ag, cancer induces an increase in neo-Ags to render cancer less susceptible to the immune system. The CPIs will give a clinical response at this stage. iv) The CPIs, including anti-PD-1, are used. v) Adaptive resistance with upregulation of alternative immune checkpoints-TIM-3. The circular arrow indicates the cancer-immunity cycle. (B) Clinical therapy strategy using chemo-, TKI and CPI. CPI, checkpoint inhibitor; neo-Ag, neoantigen; TMB, tumor mutation burden; TKI, tyrosine kinase inhibitor; PD-1, programmed death receptor-1; PD-L1, PD-1 ligand 1; chem, chemotherapy; radio, radiotherapy; TIM-3, T cell immunoglobulin-3; IFN-γ, interferon γ; ab, antibody.

Figure 2.

Liquid biopsy for cancer immunotherapy based on PD-1 checkpoint inhibitor in lung cancer. (A) The four types of lung cancer, according to the immune status of tumor microenvironment: Type I, PD-L1+ with TIL+, indicating adaptive immune resistance; Type II, PD-L1- with TIL-, indicating immune ignorance; Type III, PD-L1+ with TIL-, indicating intrinsic induction in iTME; Type IV, PD-L1- with TIL+, indicating the role of other suppressor pathways in promoting immune tolerance. (B) Biomarkers associated with iTME in blood samples. With liquid biopsy by blood sample, the PD-L1 expression, including soluble PD-L1 and cell-free PD-L1 RNA, and surface biomarker expression (i.e., CTLA4, PD-1, LAG-3, TIM-3) on circulating T cells, provide a window into the antitumor reactivity of T cells in the TME. CTCs, ctDNA and cfDNA were used for the detection of TMB or bTMB. TIL, tumor-infiltrating lymphocyte; PD-1, programmed death receptor-1; TIM-3, hepatitis A virus cellular receptor 2; iTME, immune tumor microenvironment; CTLA4, cytotoxic T-lymphocyte-associated protein 4; CTCs, positive circulating tumor cells; ctDNA, circulating tumor DNA; cfDNA, circulating free DNA; TMB, tumor mutation burden; TCR, T-cell receptor; LAG-3, lymphocyte activating 3.

Figure 3.

TCR-engineered adoptive therapy targeting neoantigen in patients with lung cancer. i) Primary tumor biopsy or CTCs/ctDNA enriched from liquid biopsy, underwent whole-exome sequencing and RNA sequencing to identify non-synonymous somatic mutations or neo-Ags. ii) CD8+/PD-1+ T cells were sorted by flow cytometry. iii) Sorted CD8+/PD-1+ T cells were co-cultured with antigen-presenting cells with synthetic long peptides of neo-Ag. iv) T cells with upregulated activation markers, including 4-1BB, OX-40, were isolated and underwent paired TCR sequencing to identify TCRα/β sequences against neo-Ag. v) T cells isolated from the blood cells of the same patient were modified with the transfect vector to encode the identified TCRα/β. In this process, the patients' T cells acquired tumor-specificity that allowed them to attack cancer with specific neo-Ag. vi) Modified T cells were cultured and expanded in vitro to obtain sufficient numbers for the treatment and reinfusion into the same patient with cancer. TCR, T-cell receptor; CTCs, positive circulating tumor cells; ctDNA, circulating tumor DNA; neo-Ags, neoantigens; PD-1, programmed death receptor-1; NGS, next-generation sequencing; WES, whole exome sequencing; OX-40, tumor necrosis factor superfamily member 4; 4-1BB, tumor necrosis factor receptor superfamily member 9; CD, cluster of differentiation.