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Commercial providers have developed tools and solutions for every step of the CRISPR genome editing workflow and these are listed in Table 4.1. The most popular form of editing involves use of the Streptococcus pyogenes Cas9 (SpCas9) enzyme, which can be delivered to cells in one of five formats: (i) as protein (in complex with gRNA), (ii) expressed through a plasmid expression vector, (iii) via lentiviral particles, (iv) via AAV particles, or (v) via mRNA. The format of choice depends on the cell type and type of experiment that is to be performed. For example, before conducting screening experiments in cancer cell lines, one needs to generate cells stably expressing Cas9. In this case, Cas9 lentiviral particles are the format of choice, as they facilitate Cas9 integration into the genome, which allows for stable, long‐term expression of Cas9 driven by promoter sequences contained within the vector. Multiple lentiviral construct options are available. For example, Horizon Discovery offers the choice of CMV, EF1a, PGK, and CAG promoters. Also, Merck offers a range of antibiotic resistance or fluorescent reporters in their lentiviruses (blasticidin, hygromycin, neomycin, zeocin, or GFP/RFP fluorophores). Other providers like Takara Bio offer the choice between constitutive or Tet‐inducible Cas9 expression. Therefore, the choice of vendor may depend on the type of construct that best suits your experimental design. In addition, if the desired construct is not available off‐the‐shelf, several companies offer custom vector generation (Table 4.1), thus there is a lot of flexibility. However, there is a trade‐off. Off‐the‐shelf products arrive quickly and tend to be less expensive, whereas custom reagents need time for production and will typically cost more.

Table 4.1 Major providers of CRISPR reagents.

Company	Location	Reagents
Agilent	Santa Clara, CA	Oligo library synthesis; synthetic gRNA and libraries
Cellecta	Mountain View, CA	Cas9 and gRNA expression vectors, lentiviral gRNA libraries
GenScript	Jiangning, China	Cas9 nuclease; Cas9 and gRNA expression vectors; lentiviral gRNA libraries
Horizon Discovery	Cambridge, United Kingdom	Cas9 nucleases; Cas9 and gRNA expression vectors; synthetic, plasmid, and lentiviral gRNA and libraries
Integrated DNA Technologies	Coralville, IA	Oligo library synthesis; Cas9 nucleases; Cpf1 nuclease; Cas9 and gRNA expression vectors; synthetic gRNA libraries
Merck KGaA	Darmstadt, Germany	Cas9 nucleases; Cas9 and gRNA expression vectors; synthetic, plasmid, and lentiviral gRNA and libraries
New England Biolabs	Ipswich, MA	Cas9 nucleases
Oxgene	Oxford, United Kingdom	Plasmid and lentiviral gRNA libraries
Synthego	Redwood City, CA	Synthetic gRNA and libraries
System Biosciences	Palo Alto, CA	Cas9 and gRNA expression vectors
Takara Bio	Mountain View, CA	Cas9 nucleases; Cas9 and gRNA expression vectors; synthetic, plasmid, and lentiviral gRNA and libraries
ThermoFisher	Carlsbad, CA	Cas9 nucleases; Cas9 and gRNA expression vectors; synthetic and lentiviral gRNA and libraries
Transomic Technologies	Huntsville, AL	Cas9 and gRNA expression vectors; plasmid and lentiviral gRNA libraries
Twist Bioscience	San Francisco, CA	Oligo library synthesis

For many editing experiments including one‐off editing and gene KO for arrayed screening, use of Cas9/gRNA ribonucleoprotein complex (RNP) is preferred, as it has been reported to demonstrate higher efficacy as compared with other delivery formats, together with simpler protocols and reduced toxicity, because RNP pipelines do not require delivery of foreign DNA, or enrichment/selection. Moreover, use of RNP has been reported to help reduce off‐target effects (OTEs), because unlike Cas9 delivered as plasmid or lentivirus which remains expressed beyond 72hours, Cas9 introduced as RNP is cleared rapidly by 48hours (Kim et al. 2014; Liang et al. 2015). For therapeutic genome editing applications, several improved Cas9 enzymes have been described which improve on‐target editing specificity and/or reduce off‐target editing. Two of these, eSpCas9 (Slaymaker et al. 2016) and high‐fidelity (HiFi) Cas9 (Vakulskas et al. 2018) are commercially available through Merck and IDT.