Cell-based models of 'Cytokine Release Syndrome' endorse CD40L and GM-CSF knockout in CAR T cells as mitigation strategy
Chimeric antigen receptor (CAR) T cells are engineered lymphocytes able to recognize and eradicate cancer cells. While CAR T cell therapy has shown promising outcomes in patients with hematologic malignancies, it can cause undesirable side-effects such as cytokine release syndrome (CRS). CRS is triggered by CAR T cell-based activation of monocytes, which are stimulated via the CD40L–CD40R axis or via uptake of GM-CSF to secrete pro-inflammatory cytokines. Mouse models have been used to model CRS but they are labor intensive and not amenable to screening approaches. To overcome this challenge, we established two cell-based CRS in vitro models that entail the co-culturing of leukemic B cells with CD19-targeting CAR T cells and primary monocytes from the same donor. Upon antigen encounter, CAR T cells upregulated CD40L and GM-CSF which stimulated the monocytes to release IL-6. To endorse these models, we demonstrated that neutralizing antibodies or genetic disruption of the CD40L and/or CSF2 loci in CAR T cells using CRISPR-Cas technology significantly reduced IL-6 secretion by bystander monocytes without affecting the cytolytic activity of the engineered lymphocytes. Overall, our cell-based models were able to recapitulate CRS in vitro, allowing us to validate mitigation strategies based on antibodies or genome editing. Overall design: CAR T cells, produced via lentiviral transduction were treated with two RNP complexes (Cas9) targeting close sites within CSF2 and/or CD40L. CAST-Seq was performed on cells treated with either one or both nuclease pairs looking at the targeted loci in each sample to assess the formation of stable translocations between the on-target site potential off-target sites.