Q: Is the dosage of Fab-ZAP always enough for any level of antibody concentration?
A: The 4.5 nM dosage of Fab-ZAP is the recommended concentration. We do not typically see unspecific killing at 4.5 nM on most cell lines. If the concentration of Fab-ZAP is increased, it may undergo bulk-phase endocytosis and kill cells indiscriminately. A lower concentration of Fab-ZAP may lead to antibody competition, resulting in a lack of killing of cells at the highest concentration of antibody.
Q: Each concentration is suggested to perform 6 replications, can it be adjusted more or less in practice?
A: Yes, the assay design is meant to be a thorough approach but can be adjusted by the user. We recommend 6 replications based on our 96-well plate template design. The concentration of Fab-ZAP is 4.5 nM in the suggested protocols.
Q: Can Fab-ZAP detect the targeted antibody still in supernatant?
A: As long as there is nothing in the supernatant inhibiting the reactivity of Fab-ZAP, it should work. We do not typically recommend this, but in theory it should be possible. I would be cautious of this approach based off of the presumed lack of established concentration of antibody.
Q: Instead of performing the reaction between our biotinylated peptide and Streptavidin-ZAP at the initially provided concentration of Strep-ZAP (20 µM), is it OK if the reaction is done at a 10-fold more dilute concentration? This request is to ensure we don’t have any solubility problems with our very tricky lipophilic peptide. Our protocol would be to first dilute Streptavidin-ZAP to 2 µM with PBS and then add the peptide in DMSO (10% final), and store the aliquoted resulting 1.82 µM solution?
A: In regards to your question, while keeping in mind your solubility concerns, we suggest that you:
Proceed with diluting the Streptavidin-ZAP to 2 uM with PBS as you suggest, BUT, only react the amount of Streptavidin-ZAP necessary for the next step.
Store the undiluted and unreacted Streptavidin-ZAP at -80°C until you’re ready for more conjugate.
We understand the solubility of the peptide is a concern, and rightfully so. However, we also do not want to compromise the Streptavidin-ZAP during storage, considering its value.
Q: We have your ZAP internalization kit and I have a question regarding the concentrations used in the cytotoxicity assay. The Hum-ZAP used in the assay (mentioned in the PDF protocol) is 4.5 nM and the target agent was 10 nM to 1 fM. Is there a stoichiometric relation between Hum-ZAP and the target agent concentrations?
A: To answer your question simply, yes, there is a stoichiometric relation between a secondary conjugate and the targeting agent.
Q: If I use higher concentrations of the target antigen, then should I also increase the concentration of Hum-ZAP?
A: It may be intuitive to think that using a higher dose of primary antibody induces a higher amount of cell death, but as seen in the attached figure, at the highest concentration of 192-IgG (10 nM = Log -8) there is a lessened amount of killing, at a 25-fold lower concentration, as compared to the antibody. The explanation for this is that, at the higher concentrations of primary antibody, there is more unconjugated 192-IgG and fewer 192-IgG+Fab-ZAP complexes. The free 192-IgG then out-competes the conjugates for cell surface binding sites which, in turn, decreases the amount of Saporin being internalized, hence less cell death.
Ancheta LR, Shramm PA, Bouajram R, Higgins D, Lappi DA (2022) Saporin as a commercial reagent: its uses and unexpected impacts in the biological sciences-tools from the plant kingdom. Toxins (Basel) 14(3):184. doi: 10.3390/toxins14030184
Hickerson BT, Daniels-Wells TR, Payes C, Clark LE, Candelaria PV, Bailey KW, Sefing EJ, Zink S, Ziegenbein J, Abraham J, Helguera G, Penichet ML, Gowen BB (2022) Host receptor-targeted therapeutic approach to counter pathogenic New World mammarenavirus infections. Nat Commun 13(1):558. doi: 10.1038/s41467-021-27949-3 PMID: 35091550
Objective: Demonstrate that a fusion protein of the antibody (ch128.1/IgG1) directed against the apical domain of human transferrin receptor 1 (hTfR1) and the Machupo virus (MACV) can inhibit infection of attenuated and pathogenic New World mammarenaviruses (NWMs).
Summary: NWMs cause life-threatening hemorrhagic fever (HF) and these viruses enter into cells via hTfR1. Use of ch128.1/IgG1 with other promising direct-acting small molecule antivirals or antibodies targeting the viral envelope glycoprotein would provide a complementary therapeutic strategy that would increase efficacy and reduce the emergence of drug resistance.
Usage: References MonoBiotin-ZAP reacted with avidinylated anti-hTfR (ch128.1Av) in a 1:1 molar ratio on ice for 30 minutes.
Objective: To demonstrate that biotinylated anti-CD45-SAP or anti-cKit-SAP mixed with Streptavidin-Saporin along with Janus kinase 1/2, enables alloengraftment on murine allo-hematopoietic stem cell transplantation (HSCT) models.
Summary: HSCT has therapeutic potential. However, the transplantation requires first depletion and secondly, for allogeneic-HCST, host and immune responses need to be controlled to prevent graft rejection. The allo-HSCT conditioning strategy exemplifies the promise of immunotherapy to improve the safety of HSCT for treating hematologic diseases.
Usage: Antibodies were incubated with Streptavidin-ZAP (1:1 molar ratio) for 15 minutes at 20°C and . The doses of CD45.2 and cKit conjugates were injected retroorbitally (41.8 μg and 33.2 μg, respectively).
Martin Perez C, Conceição M, Raz R, Wood MJA, Roberts TC (2022) Enhancing the therapeutic potential of extracellular vesicles using peptide technology. (eds. Langel Ü). In: Cell Penetrating Peptides. Methods in Molecular Biology 2383:119-141. Humana, New York, NY. doi: 10.1007/978-1-0716-1752-6_8
Objective: To modify EVs with peptides which confer specific advantageous properties, thus enhancing their therapeutic potential.
Summary: The authors provide an overview of the applications of peptide technology with respect to EV therapeutics. We focus on the utility of EV-modifying peptides for the purposes of promoting cargo loading, tissue-targeting and endosomal escape, leading to enhanced delivery of the EV cargo to desired cells/tissues and subcellular target locations. Both endogenous and exogenous methods for modifying EVs with peptides are considered.
Usage: Streptavidin-ZAP is combined with biotinylated peptides to make a targeted saporin conjugate.
