JNJ-79032421, a Novel Membrane-Restricted Mesothelin-Targeting T Cell-Engaging Bispecific Antibody for the Treatment of Mesothelin-Positive Cancers

Our plain-English summary of JNJ-79032421, a Novel Membrane-Restricted Mesothelin-Targeting T Cell-Engaging Bispecific Antibody for the Treatment of Mesothelin-Positive Cancers, by K. Smans, T. Nesspor, S. De Breucker, et al (Molecular Cancer Therapeutics, 2026).

The study

• Authors: K. Smans, T. Nesspor, S. De Breucker, E. van Heerde, A. Valckx, N. Van Slycken, K. Sproesser, B.M. Cypert, K. Packman, G. Chu, J. Fisher, N. Mazzanti, T. Petley, W. Chan, B. Del Rosario, T. Liu, S. Ember, P.L. Shaffer, J.S. Clawson, J.M. Bauml, S. Moores, S. Laquerre, P.R. Gavine
• Journal: Molecular Cancer Therapeutics
• Published: 2026;25(10):1585-1598
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Mesothelin (MSLN) is a cell membrane-anchored glycoprotein overexpressed in several cancers, including pancreatic cancer, ovarian cancer, and mesothelioma. MSLN is protease-cleaved at the membrane proximal region, releasing shed MSLN (sMSLN) into the tumor microenvironment, leaving behind a membrane-bound stub. sMSLN in the tumor microenvironment is hypothesized to create a "sink" that could limit tumor binding of MSLN-targeted anticancer therapies. We describe JNJ-79032421, a bispecific antibody (BsAb) targeting cluster of differentiation (CD) 3 on T cells and the membrane-restricted, non-shed region of full-length MSLN on cancer cells. Crystal structure analysis confirmed JNJ-79032421 binding to the membrane-restricted, non-shed C-terminal region of MSLN. Using Western blotting, enzyme-linked immunosorbent assay (ELISA), fluorescence-activated cell sorting (FACS), and immunohistochemistry (IHC), elevated levels of sMSLN were detected in blood, serosal fluids, and tumor tissue of patients and tended to increase with MSLN tumor expression. Binding and cytotoxicity of JNJ-79032421 against cancer cell lines were unaffected by the presence of sMSLN. In cancer cell lines and cell line-derived and patient-derived xenograft mouse models, increasing levels of MSLN expression led to increased JNJ-79032421 potency. In contrast, MSLNxCD3 BsAbs, binding of which is non-membrane-restricted, demonstrated a loss of cytotoxicity in the presence of sMSLN. This "sink" effect was most pronounced for high-affinity non-membrane-restricted BsAbs. Increases in CD45+ and CD8+ T-cell infiltration, as well as CD8+ T-cell activation, observed in xenograft tumor tissues were time-dependent and JNJ-79032421 dose-dependent. Overall, these data suggest that JNJ-79032421 may offer meaningful clinical activity by avoiding binding to sMSLN.

©2026 The Authors; Published by the American Association for Cancer Research.

In plain English

This was a preclinical study describing JNJ-79032421, a bispecific antibody binding CD3 on T cells and the membrane-restricted, non-shed C-terminal region of mesothelin (MSLN) on tumour cells. Shed MSLN (sMSLN) was measured by ELISA in sera, ascites and pleural effusions and by Western blotting in tumour and xenograft tissue; crystallography mapped the binding epitope, flow cytometry measured cell-surface MSLN, and killing assays and mouse xenografts tested activity. Serosal fluids contained up to 179-fold more sMSLN than healthy-donor serum, and sMSLN in xenograft lysates rose with membrane MSLN (0.04, 0.2 and 3.1 nmol/L in low, medium and high expressing models). JNJ-79032421 bound full-length MSLN (KD 4.64 nmol/L) but not recombinant sMSLN lacking the seven most C-terminal amino acids, and its cytotoxicity was unchanged by up to 100 nmol/L sMSLN, whereas non-membrane-restricted bispecifics lost potency (up to 283-fold for MNC3B321 in high-expressing cells). In mice, 0.1 mg/kg gave 173% and 150% delta tumour growth inhibition relative to DPBS controls in high and medium MSLN cell-line-derived xenografts, with 89% and 69% tumour regression. The authors concluded the preclinical profile supports an ongoing phase I study.

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: preclinical in vitro and animal (xenograft) drug characterisation study, including crystallography and analysis of patient body-fluid and tumour samples
• Who was studied: Patient and healthy-donor samples (serum from healthy males n=60, pregnant females n=31, mesothelioma n=7, ovarian cancer n=9, lung cancer n=81; ovarian ascites n=6; lung cancer pleural effusions n=5), PDX protein lysates (lung n=88, pleura n=9, ovary n=7, pancreas n=48), 21 lung adenocarcinoma tissues, 17 cancer cell lines, and female NSG mice bearing cell line-derived or patient-derived xenografts
• Exposure: Treatment with the MSLNxCD3 bispecific antibody JNJ-79032421 (0.005 to 2.5 mg/kg in mice; 100 nmol/L to 0.01 pmol/L in vitro) compared with non-membrane-restricted MSLNxCD3 bispecifics (MNC3B232, MNC3B321, MNC3B597), membrane-restricted MNC3B319, nullxCD3 and DPBS controls, with or without added shed MSLN (0, 1, 10, 100 nmol/L)
• Main results:
  • Serosal fluids from patients with cancer contained up to 179-fold more sMSLN than serum from healthy individuals, and sMSLN was elevated in blood of patients with mesothelioma or ovarian cancer
  • sMSLN in xenograft tumour lysates increased with membrane-bound MSLN expression: 0.04 nmol/L in low, 0.2 nmol/L in medium and 3.1 nmol/L in high MSLN-expressing models
  • JNJ-79032421 bound full-length MSLN with KD 4.64 nmol/L but did not bind recombinant sMSLN lacking the seven most C-terminal amino acids (SMQEALS)
  • T cell-induced cytotoxicity with the membrane-restricted bispecifics JNJ-79032421 and MNC3B319 was unaffected by up to 100 nmol/L sMSLN, whereas the non-membrane-restricted MNC3B597 and MNC3B321 lost potency by up to 14.6-fold and 283-fold respectively in high MSLN-expressing cells
  • Across 17 cell lines, JNJ-79032421 killing EC50 values ranged from 0.04 to 88.59 nmol/L and correlated with MSLN receptor density; EC50 values for MNC3B232 (0.01-1.14 nmol/L) did not correlate with MSLN expression
  • In mice, JNJ-79032421 0.1 mg/kg produced 173% and 150% delta tumour growth inhibition versus DPBS controls in the high and medium MSLN-expressing cell line-derived xenografts
  • At 0.1 mg/kg, high MSLN-expressing tumours regressed by 89% with complete response in 10 of 10 mice, and medium-expressing tumours regressed by 69% with complete response in 2 of 10 mice
  • The non-membrane-restricted MNC3B232 at 0.1 mg/kg showed no significant antitumour effect in the high and medium MSLN models but gave 99% delta tumour growth inhibition in the low MSLN-expressing SK-OV-3 model
  • MSLN receptor density in ovarian ascites and pleural effusions was about 500 to 6,200 receptors/cell on benign mesothelial cells and about 1,100 to 32,000 receptors/cell on cancer cells
• The authors' conclusion: The authors concluded that JNJ-79032421 binds membrane-restricted MSLN and not shed MSLN, is efficacious against medium and high MSLN-expressing cancer cells while sparing low-expressing cells, and that this preclinical profile supports its ongoing phase I safety and tolerability study
• Limitations the authors state:
  • The membrane-restricted and non-membrane-restricted bispecifics compared in the cell-line panel differed in MSLN affinity, and no comparison was made between agents of similar affinity
  • Matched solid tumour tissue was not available from the patients whose effusion cells were analysed, so MSLN expression by flow cytometry could not be correlated with immunohistochemistry
  • The authors noted that the higher affinity of the comparator MNC3B232 likely contributed to its reduced potency in high MSLN-expressing cells
  • Tumours with heterogeneous and low MSLN expression might escape treatment, so patient selection by MSLN expression may need exploration

Topics

Medical terms in this study, explained in our Lexicon: Mesothelin, Glycoprotein, Ovarian Cancer, Mesothelioma, Tumor Microenvironment, Crystal Structure, Immunohistochemistry.

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