Murine Allogeneic CAR-T Cells Integrated Before or Early After Posttransplant Cyclophosphamide Exert Anti-Tumor Effects

The direct integration of chimeric-antigen-receptor (CAR) T cell with allogeneic hematopoietic cell transplantation (allo-HCT) carries the risk of graft-versus-host disease (GVHD) induction by allogeneic CAR-T cells. Based on our past experiments, it has been shown that post-transplantation cyclophosphamide (PTCy) prevents GVHD induction by other cell infusions after T-cell-replete MHC-haploidentical murine allo-HCT models. In this study, we investigated whether CAR-T cells, given in a similar manner in the same MHC-haploidentical murine allo-HCT model, could safely exert anti-tumor effects. We showed that anti-CD19 CAR-T cells administered early after (day +5 of transplant) or prior to (day 0 of transplant) PTCy for allo-HCT cleared leukemia without toxicity or GVHD exacerbation. Using next generation single-cell RNA sequencing approaches, we demonstrated that in comparison to CAR-T cells infused early after PTCy (day +5), CAR-T cells infused prior to PTCy (day 0) exhibited transcriptional changes consistent with increased CD4+ T-cell activation and CD8+ T-cell cytotoxicity. Next-generation sequencing approaches on a large data set enabled the identification of transcription factors associated with increased CD4 activation and CD8 cytotoxicity in CAR-T cells administered on mice prior to PTCy transplantation.