Recombination activating gene 2 (RAG2) deficiency / T-B- NK+ SCID due to RAG2 defect

Base Editing (ABE8e) via RNP electroporation (ex vivo) delivery is a rationale-driven therapeutic strategy for Recombination activating gene 2 (RAG2) deficiency / T-B- NK+ SCID due to RAG2 defect targeting the RAG2 c.686G>A (p.Arg229Gln) variant (Pathogenic, missense variant). The editing system (ABE8e-nSpCas9 (adenine base editor)) converts the pathogenic A back to G on the target strand, restoring the wild-type codon. Target tissue: Blood/HSC. Therapeutic goal: Correct loss-of-function or severely hypomorphic RAG2 alleles in autologous hematopoietic stem/progenitor cells at the endogenous RAG2 locus to restore sufficient V(D)J recombination activity for dura. Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Medium, immunogenicity Low.

1. Molecular basis: RAG2 NM_000536.4(RAG2):c.686G>A (p.Arg229Gln) is classified as Pathogenic (ClinVar variation ID 13130). Molecular consequence: missense variant. Protein change: R229Q. 2. Epidemiology: RAG1/2-related T-B- NK+ SCID is an ultrarare autosomal recessive primary immunodeficiency. Orphanet describes severe combined immunodeficiency due to complete RAG1/2 deficiency with prevalence 1–9 per 100,000 for SCID as a group (WEB-01), while a multicentre cohort of 82 RAG-deficient patients from 3. Standard of care: Authoritative web and clinical sources (WEB-02, WEB-03, WEB-04, PAPER-04, PAPER-07) agree that hematopoietic stem cell transplantation (HSCT) is the current standard curative treatment for RAG2-SCID and other severe RAG deficiencies. Infants typically present within the first months of life with sev 4. Pipeline: For RAG2 deficiency specifically, Orphanet lists multiple orphan medicinal product designations for ex vivo autologous CD34+ HSCT products transduced with self-inactivating lentiviral vectors carrying functional RAG genes, largely in preclinical or early Phase I/II stages (WEB-05, WEB-07). Preclinic 5. ABE clinical validation: ABE8e (Richter et al. 2020, Nat Biotechnol) achieves ~1.7x higher editing efficiency than ABE7.10. VERVE-101 demonstrated first-in-human LNP-ABE liver editing with 55-66% PCSK9 reduction (Raal et al. 2025, NEJM). Beam Therapeutics is advancing multiple ABE programs.

1. No published data specifically correcting RAG2 c.686G>A (p.Arg229Gln) with Base Editing (ABE8e); strategy is based on general principles and must be validated preclinically. 2. PAM availability and bystander base analysis for the specific genomic context have not been performed. If no canonical NGG PAM positions the target within the editing window, PAM-flexible variants (SpRY) may be needed. 3. Long-term durability, off-target genome-wide effects, and immunogenicity in the target patient population require thorough preclinical and clinical evaluation.

For RAG2 c.293del (p.Thr98fs), lentiviral gene addition to autologous hematopoietic stem cells is the most clinically mature variant-specific approach because early preclinical and clinical data show that restoring functional RAG2 cDNA rescues T/B development without needing allele-specific editing.

Historically, lentiviral vectors encoding codon-optimized RAG2 (RAG2co) corrected Rag2−/− mice, restoring lymphocyte subsets and humoral responses (Blood 2012; PMID:22692499; PMC3464632). Recent reviews summarize that GMP-grade RAG2 lentiviral platforms are entering first-in-human trials and that CRISPR-based insertion of codon-optimized RAG2 is also active in HSPCs (Blood Adv 2024; PMID:40829114; PMC10367010). Observations across these models and vectors align with the MB-110 program for RAG1 SCID, which already treats RAG1-deficient infants with LV-RAG1 CD34+ cells (Mustang Bio press release 2022) and demonstrates durable immune reconstitution, supporting that the same platform logic applies for RAG2 null alleles.

Almost all human experience is still in early-phase or preclinical stages; comprehensive safety, conditioning optimization, and long-term surveillance for integration-related events remain under study. The variant c.293del merely defines diagnosis; clinical benefit depends on early detection, conditioning quality, and infection control because irreversible neurologic damage can arise before gene correction. This argument is therefore mechanistically strong but requires the usual gene-therapy translational safeguards before regarded as proven clinical efficacy for this allele.