A combination of PD-1 and TIGIT immune checkpoint inhibitors elicits a strong anti-tumour response in mesothelioma

Abstract

Background: Finding effective and curative treatment for mesothelioma remains challenging. While the introduction of immunotherapy combinations using ipilimumab (anti-CTLA-4) and nivolumab (anti-PD-1) have offered hope for some patients, a large proportion of mesothelioma cases, particularly the epithelial subtype, have minimal benefit from this.

Methods: Our study was inspired by the results of the AdvanTG-105 phase I clinical trial, which showed partial response with anti-TIGIT/PD-1 treatment in two epithelioid mesothelioma patients. Here, we conducted a comprehensive in vivo experiment involving eight animal treatment groups administered with either PBS (control group), cisplatin/pemetrexed, anti-PD-1, anti-PD-1 + anti-CTLA-4, anti-TIGIT, anti-PD-1 + anti-TIGIT, anti-PD-1 + anti-CTLA-4 + anti-TIGIT, and cisplatin/pemetrexed + anti-PD-1 + anti-TIGIT.

Results: Our results indicate that animals receiving anti-PD-1 + TIGIT exhibited a superior anti-tumour response, with 90% of the treatment group exhibiting an objective response, compared to 60%, 20% and 40% for the standard-of-care anti-PD-1 + CTLA-4, single-agent anti-PD-1 and cisplatin/pemetrexed treatment groups, respectively. Animals receiving anti-PD-1 + TIGIT displayed a significantly reduced average tumour size, with improved weight and survival rates, and fewer adverse effects than those receiving anti-PD-1 + CTLA-4 treatment. Anti-PD-1 + TIGIT-treated animals achieved complete tumour regression, with heightened effector CD8 + T cell and NK cell activity, remaining tumour-free for over 300 days without immune-related adverse events. After initial tumour elimination, anti-PD-1 + TIGIT-treated animals showed no tumour regrowth in the rechallenge experiment.

Conclusion: These findings provide rationale for the development of an anti-PD-1 + TIGIT combination immunotherapy trial for mesothelioma patients.

Fig. 1

Radiological responses to tislelizumab and ociperlimab for the two PM patients. 1A and 1B represent PET-CT images of patient number one, and 1C and 1D correspond to patient number two. A Axial section at the level of the right superior pulmonary vein at baseline (1 = 18 mm, 2 = 10 mm) and 12 weeks after treatment (1 = 5 mm, 2 = 5 mm) (B) Axial section at T9 vertebra level at baseline (1 = 10 mm, 2 = 11 mm) and 12 weeks after treatment (1 = 8 mm, 2 = 8 mm). C Axial section at the level of right 9.^th rib at baseline (1 = 14 mm) and 9 months after treatment (1 = 8 mm). D Axial section at the level of T9 vertebra at baseline (1 = 14 mm) and 9 months after treatment (1 = 6 mm)

Fig. 2

Anti-tumour effect of TIGIT immune checkpoint inhibitor in an epithelioid PM mouse model. a Schematic illustration of the anti-TIGIT combination treatment design to inhibit tumour growth in an epithelioid PM mouse model​. b Representative photographs showing the size and morphology of tumour nodules harvested at the end of the experiment (Day 30). c Representative in vivo bioluminescence images showing the size and distribution of tumour growth following, i.p., injection of AC29 mesothelioma cells in the mice after different treatments. d Average weights of tumours and e Tumor volume, measured by the IVIS imaging system after different treatments, is presented using violin plots to show the frequency distribution of the data. A total of ten mice were utilized per treatment group and experiments were repeated once. Error bars reflect the SD of each treatment group; statistical significances were calculated via paired t-test and two-way ANOVA, *P < 0.05, **P < 0.01

Fig. 3

Tumour volume measured by the IVIS imaging systems after different treatments. In vivo tumour growth and immunotherapy responses of individuals after a) standard care and b) novel TIGIT treatments. Anti-PD-1 single-armed treatment was presented in supplementary Fig. 5. Numbers indicate tumour-regression animals/total animals at completion. c Overall survival at the end of treatments (Day 30). N = 5–10 mice were utilized per treatment group

Fig. 4

Anti-PD-1 plus anti-TIGIT combination therapy activating systematic anti-tumour immunity. a, b, c Representative flow-cytometry plots (Day 13) showing the tumour-infiltrating CD4 + , CD8 + , CD4 + FoxP3 + (Treg) cells. d Enumeration of CD4 + , CD8 + , T reg cells in tumour. Representative flow-cytometry plots and relative percentage of e) NK cells and f) PD-1, g CTLA-4, h TIGIT expression on CD8 + T cells in tumour. N = 4–5 mice were used per group and per timepoints. Error bars reflect the SD determined from each treatment group. Statistical significances were calculated by two-way ANOVA. * P < 0.05, **P < 0.01, ***P < 0.01, ****P < 0.0001

Fig. 5

Effects of Anti-PD-1 plus TIGIT combination therapy further enhanced tumour CD8 + effector and memory T cell activation. a Representative flow-cytometry plots of tumour naïve (Q1), memory(Q2) and effector(Q3) CD4 + (bottom row) and CD8 + (top row) T cells in tumour b) Relative percentages of naïve CD4 + /CD8 + , effector CD4 + /CD8 + and memory CD4 + /CD8 + cells in tumour. ​c Schematic illustration of the experiment design to assess the immunological memory response triggered by Anti-PD-1 plus TIGIT combination therapy. d Representative in vivo bioluminescence images showing the size and distribution of tumour growth following the second inoculation of AC29 tumour cells at Day 300 without any treatment. Tumour naïve mice were used as control (N = 5). Statistical significances were calculated by two-way ANOVA. N = 4–5 for flow cytometry, N = 5–9 for tumour rechallenge. * P < 0.05, **P < 0.01, ****P < 0.0001

Fig. 6

Anti-PD-1 plus TIGIT combination therapy reduced the tumoral PD-L1 expression without any observed histological adverse effects. a Representative H&E staining of tumour at day 30 post tumour inoculation. b representative IHC staining of PD-L1 expression in tumour under different treatments. Yellow arrows indicate PD-L1 positive tumour cells. c Representative H&E staining of lung, liver and kidney harvested at the end of combination checkpoint blocked immunotherapy