Nanobody-based chimeric antigen receptor (NbCAR) T cells for in-vivo cancer immunotherapy: A systematic review

Background : Conventional chimeric antigen receptor (CAR) construct is produced using the ScFv of a target specific antibody and has encountered significant challenges in treating cancer, e.g., adverse effects, T cell exhaustion, safety concerns, and sub optimal efficacy in solid tumors. An alternative approach could be to use the outer portion of a nano antibody, named the VHH, for CAR production. The CAR construct produced with this method is named the "nanobody CAR." Nanobody CAR T cells are less immunogenic, more efficient, and easier to manufacture, and thus might be a reliable alternative approach to overcome the barriers associated with conventional CAR T therapy. Materials and methods : Following a comprehensive search on PubMed, Scopus, Web of Sciences, and Google Scholar, available preclinical animal model studies which focused on the safety and efficacy of nanobody CAR T therapy in cancer were included. Results : 338 studies were identified (up to September 15th, 2023), of which 17 studies used nanobody CAR T cells against tumor cells in animal models of different malignancies, including acute leukemia (seven studies), lymphoma (foure studies), hepatocellular carcinoma (three studies), multiple myeloma (two studies), melanoma (one study), colon adenocarcinoma (one studies), TNBC (one study), lung tumor (one study), ovarian adenocarcinoma (one study), multiple myeloma (two studies), and pancreatic cancer (one study). The most common CAR structure was the second generation and, in some cases, the third generation. CD28, 4 1BB, and ICOS were used as co stimulatory domains in the structure. Compared to the control groups, nanobody CAR T cells had a better performance in reducing tumor volume and improving survival. The included studies incorporated significant heterogeneity regarding their reported outcomes and study design, making it impossible to conduct a meta analysis. The Systematic Review Centre for Laboratory animal Experimentation (SYRCLE) tool was used to assess the risk of bias, which showed potential bias in the included studies. Conclusion : According to small size, ideal stability, high affinity, and manufacturing practicality, nanobody CAR T cells serve as a promising strategy to improve in vivo mice survival and reduce tumor size. To obtain more reliable results, future studies should focus on diminishing the heterogeneity of study design and bias. Protocol registration : PROSPERO; registration number CRD42023425817, registered June 13th, 2023