Anti-mesothelin immunotoxin induces mesothelioma eradication, anti-tumor immunity, and the development of tertiary lymphoid structures

Our plain-English summary of Anti-mesothelin immunotoxin induces mesothelioma eradication, anti-tumor immunity, and the development of tertiary lymphoid structures, by W. Liu, C.H. Tai, X. Liu, et al (Proceedings of the National Academy of Sciences of the United States of America, 2022).

The study

• Authors: W. Liu, C.H. Tai, X. Liu, I. Pastan
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Published: 2022;119(48):e2214928119
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

LMB-100 is a recombinant immunotoxin composed of a Fab linked to a toxin. It kills cells expressing human mesothelin (hMSLN), which is highly expressed on the surface of mesothelioma and many other cancer cells. Clinically, we observed some patients had delayed responses to an anti-hMSLN immunotoxin treatment, suggesting the induction of anti-tumor immunity. We aimed to develop a mouse model to investigate whether immunotoxin alone can induce anti-tumor immunity and to study the mechanism of this immunity. An immunocompetent transgenic mouse was used to grow mouse mesothelioma AB1 cells expressing hMSLN in the peritoneal cavity. Mice were treated with LMB-100, and mice with complete responses (CRs) were rechallenged with tumor cells to determine whether anti-tumor immunity developed. Changes in gene expression profiles were evaluated by Nanostring, and changes in cytokines and chemokines were checked by protein arrays. The distribution of various immune cells was assessed by immunohistochemistry. Our results show that the mice with tumor reached CRs and developed anti-tumor immunity after LMB-100 treatment alone. The primary response requires CD8+ T cells, CD4+ T cells, and B cells. Transcriptional profiling shows that LMB-100 treatment reshapes the tumor immune microenvironment by upregulating chemotaxis signals. LMB-100 treatment upregulates genes associated with tertiary lymphoid structures (TLS) development and induces TLS formation in tumors. In sum, immunotoxin-mediated cell death induces anti-tumor immunity and the development of TLS, which provides insights into how immunotoxins cause tumor regressions.

In plain English

This was a laboratory experiment in mice. The authors grew mouse mesothelioma AB1 cells engineered to express human mesothelin (AB1-L9) in the peritoneal cavity of BALB/c TPO-MSLN transgenic mice, which do not reject cells carrying human mesothelin, and treated them with the anti-mesothelin recombinant immunotoxin LMB-100. In culture, LMB-100 killed AB1-L9 cells with an IC50 of 19 ng/ml, while cells without human mesothelin were not killed. A single intraperitoneal dose on day 5 gave complete responses in 9/19 mice (47%) and two doses in 11/22 (50%); an inactive immunotoxin (LMB-255) and a non-targeting immunotoxin (LMB-34) produced no complete responses. Surviving mice that had reached complete responses were re-challenged subcutaneously with AB1-L9 cells about 1.5 months after the initial inoculation, and tumours failed to form in 9/9 of those given one dose and 17/19 of those given two doses. Depleting CD8+ T cells lowered the complete response rate from 14/22 to 2/17, and depleting B cells from 12/17 to 3/13; NK cell depletion did not significantly change survival (P = 0.28). Tertiary lymphoid structure density rose 1.5-fold at 24 h and 7.9-fold at 48 h after LMB-100.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: animal (mouse) experiment with in vitro cell culture work
• Who was studied: BALB/c TPO-MSLN transgenic mice (10-20 weeks old) given five million AB1-L9 mouse mesothelioma cells intraperitoneally, plus cultured AB1 and AB1-L9 cells; laboratory study at the US National Cancer Institute
• Exposure: Treatment with the anti-human-mesothelin immunotoxin LMB-100 (mostly 3 mg/kg intraperitoneally), compared with the inactive immunotoxin LMB-255, the non-targeting immunotoxin LMB-34 (anti-hBCMA), or PBS
• Main results:
  • In culture, LMB-100 killed AB1-L9 cells with an IC50 of 19 ng/ml, while AB1 cells lacking human mesothelin stayed viable up to 1,000 ng/ml
  • Complete responses in tumour-bearing mice: 9 of 19 (47%) with one dose of LMB-100 on day 5 and 11 of 22 (50%) with two doses
  • Delaying treatment reduced complete responses: 3/11 (27%) with doses on days 7 and 11, and 1/11 (9%) with doses on days 9 and 13
  • Neither the inactive immunotoxin LMB-255 nor the non-targeting immunotoxin LMB-34 produced any complete responses in treated mice
  • Among mice that had achieved complete responses and were re-challenged subcutaneously about 1.5 months after initial inoculation, AB1-L9 cells failed to form tumours in 9/9 mice treated with one dose and 17/19 mice treated with two doses
  • Of complete-response mice challenged with AB1 cells not expressing human mesothelin, 8/10 rejected them, indicating immunity to other tumour antigens
  • CD8+ T cell depletion lowered the complete response rate from 64% (14/22) with control antibody to 12% (2/17)
  • B cell depletion lowered complete remissions from 12/17 (71%) to 3/13 (23%) and shortened survival (P = 0.002); CD4+ T cell depletion gave a 32% (7/22) complete response rate
  • NK cell depletion did not significantly change survival of LMB-100-treated mice (P = 0.28)
  • Tertiary lymphoid structure density in tumours rose 1.5-fold at 24 h and 7.9-fold at 48 h after LMB-100
  • Tumour cells killed by LMB-100 in culture and then injected did not generate protective immunity in the mice
  • Ccl20 showed the largest transcript increase after LMB-100 treatment of tumours
• The authors' conclusion: The authors concluded that immunotoxin-mediated cell death caused complete regression of orthotopic mesothelioma and anti-tumour immunity in this mouse model, requiring CD8+ T cells, CD4+ T cells and B cells and accompanied by tertiary lymphoid structure formation, and they suggested agents stimulating B cells, stroma and TLS might combine with LMB-100
• Limitations the authors state:
  • The authors stated that it remains unknown which non-malignant cells produce the cytokines and what signals pass from tumour cells to them
  • The authors noted that for Nanostring analysis only the top 50% most responsive tumours were analysed
  • The authors noted that one TLS signature gene could not be measured in this mouse system

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelin, Mesothelioma, Peritoneal Cavity, Cytokine, Immunohistochemistry.

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