Xiang H, Mortenson GP, Lang SB, Jakkaraju S, Chirala A, Zhu Y, Jia M, Wen J, Chen Y, Baghela A, Chen YC, Sze MA, Hegde LG, Zhang-Hoover J, Willingham A, Handa M, Chi A, Baltus GA, Kamath RV, Levesque M, Vollmann EH (2026) uPAR-targeting cytotoxic antibody–drug conjugates selectively deplete proinflammatory myeloid cells for autoimmune indications. Cells 15(9):803. doi: 10.3390/cells15090803
Objective: To explore uPAR as a cell-surface marker to target and eliminate proinflammatory monocytes and macrophages using antibody–drug conjugates (ADCs).
Summary: Using recent scRNA-seq findings from RA patients, the authors identified the urokinase plasminogen activator receptor (uPAR), encoded by PLAUR, as a highly expressed cell surface marker on an inflammation-associated IL1B+ proinflammatory myeloid subset. an anti-uPAR mAb conjugated with monomethyl auristatin F (MMAF) was employed to demonstrate selective depletion of uPARhigh-expressing macrophages in a myeloid-rich rodent model.
Usage: Fab-ZAP rat (IT-55) was used to test the internalization capacity of anti-mouse uPAR mAbs. Saporin and Fab-IgG-ZAP were used as control.
Hamakubo S, Komatsu N, Kosai A, Kuroda M, Sawada M, Shimizu R, Ohashi R, Suenaga H, Hamakubo T, Abe T (2026) Enhanced antitumor efficacy of a combination of immunotoxin and photosensitizer under illumination in xenograft mice. Biomedicines 14:573. doi: 10.3390/biomedicines14030573
Objective: To investigate the in vivo therapeutic efficacy of intelligent Targeted Antibody Phototherapy (iTAP), utilizing light as a spatiotemporal trigger to promote the cytoplasmic release of toxins.
Summary: The authors investigated the in vivo therapeutic efficacy of iTAP using an EGFR-targeted IT composed of cetuximab conjugated to saporin (IT-Cmab), administered in combination with the clinically used photodynamic therapy (PDT) photosensitizer NPe6, in a xenograft mouse model. Findings indicate that iTAP represents a promising therapeutic strategy for HNSCC.
Usage: Biotinylated Cmab was mixed with streptavidin-saporin (IT-Cmab). Mice received intraperitoneal IT-Cmab (0.5 mg/kg), followed 72 h later by intravenous NPe6 (5 mg/kg).
Tendler S, De Gregorio R, Balderes P, Michel AL, Hoang TT, Bauer D, Tully KM, Korsen JA, Lorenz IC, Khan AG, Carter L, Vergnolle O, Lebedeva IV, Nyakatura EK, Bodei L, Morris MJ, Poirier JT, Rudin CM, Lewis JS (2026) Next-generation anti-DLL3 radiopharmaceuticals targeting high-grade neuroendocrine lung and prostate cancers. Proc Natl Acad Sci U S A 123(6):e2505785123. doi: 10.1073/pnas.2505785123 PMID: 41628333
Objective: To report on the development of anti-DLL3 radioimmunoconjugates for use as either a diagnostic imaging tracer or a therapeutic agent. Delta-like ligand 3 (DLL3) is a tumor-selective cell surface protein upregulated in high-grade neuroendocrine tumors, including small-cell lung cancer (SCLC) and neuroendocrine prostate cancer (NEPC).
Summary: The authors generated a panel of human monoclonal antibodies targeting human DLL3 by immunizing transgenic mice engineered with a human immunoglobulin repertoire. Six select candidates were reformatted as human IgG4 anti-DLL3 mAbs.
Usage: NCI-H82 cells were seeded in a 96-well plate and incubated with serial dilutions of tested antibodies, premixed with the Fab–ZAP (IT-48) for 72 h.
Maria NI, Xia Y, Raparia C, Lin K, Martinez S, Yi Z, Zhang W, Aziz M, Wang P, Guerra M, Salmon, J, Sones JL, Arazi A, Hoover P, Davidson A (2026) Pregnancy loss due to early developmental defects in lupus mice expressing human TLR8. bioRxiv 2026.02.07.701591. doi: 10.64898/2026.02.07.701591
Objective: To explore human TLR8 (huTLR8) in anti-phospholipid (APL) antibody-mediated placental injury.
Summary: The authors used a novel mouse model of pregnancy loss in SLE-prone mice expressing huTLR8. Findings indicate huTLR8, likely through myeloid cell activation and cytolytic T cell recruitment, drives placental injury in the context of SLE and APL autoantibodies.
Usage: 8- to 10-week-old Sle1.CD45.1 mice were treated with biotin anti-CD117 and streptavidin-saporin
ZAP conjugates allow you to screen targeting agents in a quick and cost-efficient way, looking for specificity, functional binding, internalization, and EC50 determination.
Here we have a closer look at the typical in vitro data you can expect to see from a cytotoxicity assay. In this example, you are looking at the cytotoxicity curves using various secondary conjugates when compared to the direct conjugate, 192-IgG-SAP.
Mab-ZAP, our bivalent secondary antibody that recognizes whole IgG, reacted with primary antibody, produces a similar potency to the directly linked conjugate of saporin to the same antibody.
Fab-ZAP and FabFc-ZAP, which both use a monovalent secondary antibody, reacted with primary antibody produced a cytotoxic effect greater than 12-fold over the direct conjugate.
In this example, you will also see an interesting phenomenon with ZAP secondary conjugates. It may be intuitive to think that using a higher dose of primary antibody induces a higher amount of cell death, but at the highest concentration of 192-IgG (10 nM = Log (-8)) there is a lessened amount of killing, at a 25-fold lower concentration when compared to the antibody. The explanation is that at the higher concentrations of primary antibody, there are more unconjugated 192-IgG and fewer 192-IgG plus Fab-ZAP complexes. So, this free 192-IgG can then out-compete the conjugates for cell surface binding sites, which, in turn, decreases the amount of saporin being internalized, hence less cell death.
Our publication in the Journal of Toxins, provides a nice review of this phenomenon.
We are continuing to highlight our ZAP antibody internalization kits and our line of secondary antibody saporin conjugates.
ZAP conjugates allow you to screen targeting agents in a quick and cost-efficient way, looking for specificity, functional binding, internalization, and EC50 determination.
We also highlighted a publication that did a great job in showcasing how they can be used to screen antibodies for the best candidate, and then proceed with having us perform a custom conjugation of that antibody directly to saporin.
Here is information about the chemistry and why we offer conjugates that use whole, bivalent, IgG as well as monovalent Fab IgG.
Our first release of ZAP conjugates utilized whole-molecule IgG, bivalent secondary antibodies that recognized both heavy and light chains of primary antibodies. In theory though, this presented a possible limitation if the bivalent nature of an antibody suggested that cross-linking could occur on the cell surface and contribute to a phenomenon known as ‘cap formation’. The ‘cap’ could potentially induce some level of endocytosis that would lead to cytotoxicity and produce a false positive for internalization of a primary antibody.
We designed new secondary conjugates (given the moniker Fab-ZAP) which used monovalent antibodies that would continue to recognize whole IgG, but lacked components that would contribute to capping.
We now offer 3 main categories: (1) Conjugates made with bivalent antibodies that recognize whole IgG, (2) conjugates made with monovalent antibodies that recognize whole IgG, and (3) conjugates made with monovalent antibodies that recognize only the Fc region of IgG.
Objective: To develop and validate a modular streptavidin based antibody drug conjugate platform for optimizing antibody mediated hematopoietic stem cell transplant conditioning.
Summary: The authors demonstrate that a streptavidin drug conjugate system enables rapid comparison of antibody payload combinations for hematopoietic stem cell depletion and leukemia targeting. The study builds on prior work using CD45 targeted immunotoxins to achieve effective hematopoietic niche depletion in murine HSCT models.
Usage: This study references earlier conditioning experiments that utilized Streptavidin-ZAP (IT-27) in combination with biotinylated CD45 antibodies to selectively deplete hematopoietic stem cells in murine HSCT models, typically administered as a single intravenous dose of approximately 75 µg per mouse.
Park JS, Kenum C, He L, Khan AG, Pohl MA, White TE, Kodangattil SR, Rudin CM, Balderes PJ, Lorenz IC, Massagué J, anesh K (2025) Development of antibody-drug conjugates targeting L1CAM to treat metastatic cancer. bioRxiv 2025.10.01.679843. doi: 10.1101/2025.10.01.679843 PMID: 41256399
Objective: To develop L1CAM-targeted antibody-drug conjugates (ADCs) using high-affinity monoclonal antibodies and assess their therapeutic potential against metastatic cancer.
Summary: L1CAM ADCs conjugated with the potent payload PNU-159682 achieved strong cytotoxicity, tumor regression, and prolonged survival in models of metastatic breast and lung cancer. Safety studies indicated a favorable therapeutic window for clinical translation.
Usage: FabFc-ZAP Human (IT-65) was used to evaluate antibody internalization. FabFc-ZAP was incubated with L1CAM candidate antibodies or isotype control and applied to L1CAM-HEK293T cells, with viability measured after five days.
Diamantoudis SC, Miliotou AN, Galatou E, Telliou S, Sideris K, Grigoriadis N, Vizirianakis IS (2025) Assessing the hematological cancer stem cell landscape to improve immunotherapy clinical decisions. Biocell 49(10):1799-1858. doi: 10.32604/biocell.2025.067216
Objective: To combine existing information and clinical evidence to assess and bring to the spotlight targets related to Hematological cancer stem cells (HCSCs) that can be considered for the improvement of therapeutic interventions.
Summary: Targeting HCSCs represents one of the most promising advances toward achieving lasting remission and potential cure in hematologic malignancies. Next-generation immunotherapies—enabled by advances in molecular profiling, synthetic biology, and systems immunology—can shift the paradigm in blood cancers by overcoming current limitations.
Usage: CD117-ADC (carrying streptavidin–saporin) has shown dose-dependent results in mice, with a range from 0.3–1.5 mg/kg, as depletion of stem cells was noted with the subsequent successful engraftment of allogenic transplants.
I am using your Fab-ZAP Human (IT-51) and I want to know how many antibody molecules can a secondary antibody conjugate theoretically bind to?
Answer
A whole IgG (bivalent) secondary antibody in theory is capable of binding two antigen molecules. Since our Fab-ZAP conjugates actually use a monovalent secondary antibody, in theory they would be able to each bind one antigen molecule. Our Fab-ZAP human conjugates use polyclonal monovalent secondary antibodies raised against both heavy and light chain of IgG and can cross-react across immunoglobulin classes and subclasses of the same species since they share the same light chain. In theory it would be possible that your primary antibody could have several secondary conjugates attached.
Question
When exploring the usage concentration for Fab-ZAP Human, what is the recommended concentration range (for example, is it a few times the initial concentration of the analyte antibody / the highest test concentration)?
Answer
Our standard protocol (in vitro only) for our Fab-ZAP secondary conjugates is to maintain a constant concentration of 4.5 nM of the Fab-ZAP while titrating the primary antibody, usually in a range starting at 10 nM with 1:5 to 1:10 serial dilutions. The goal would be to have the primary antibody as a ‘variable’ and the Fab-ZAP as the ‘constant’. Also, it’s important to saturate the primary antibody with Fab-ZAP secondary conjugate, as any ‘free unreacted primary antibody’ would compete with ‘antibody+Fab-ZAP conjugate’ for binding sites on the cell. I have attached a publication that discusses this topic.
