Single-cell gene expression in Her2-specific CAR T cells in osteosarcoma mouse model.

Purpose: To compare cell states between control Her2-BBz and JUN-overexpression Her2-BBz human CAR T cells in a mouse model of osteosarcoma. Methods: 8-week old NSG mice were implanted with 1 million 143B osteosarcoma tumor cells intramuscularly in the right leg. 14 days post tumor implantation, mice were infused intravenously with 10 million human CAR+ T cells via tail vein injection. Before T cell transfer, mice were randomized for tumor size and treated with either control Her2-BBz or JUN-overexpressing Her2-BBz CAR T cells. T cells were 70% CAR+ at infusion for both groups. 14 days post T cell treatment (day 28 post tumor engraftment), 6 mice per group were euthanized, solid tumor tissue was collected, mechanically dissociated, and single cell suspensions were labeled with human-CD45 antibody and viability dye. Live hCD45+ tumor-infiltrating lymphocytes were sorted from each tumor and 6 samples were pooled for each group. ~35,000-40,000 sorted live cells (counted post sort) for each group were delivered to the Stanford Functional Genomics Facility for 3' single-cell RNA-sequencing on the 10X Genomics platform. Results: We found that substantially more JUN-overexpressing Her2-BBz CAR T cells were within the G2/M and S phases of the cell cycle than control Her2-BBz CAR T cells, consistent with increased in vivo proliferation of JUN-Her2-BBz CAR T cells. Furthermore, JUN-Her2-BBz CAR T cells also demonstrated a more activated transcriptional program (as measured by IL2RA and CD38), while many exhaustion-associated genes were downregulated (PDCD1, BTLA, TIGIT, CD200, ENTPD1, NR4A2) compared to control Her2-BBz CAR T cells. Finally, a small cluster of cells characterized by high IL7R expression (IL7R+ KLF2+ CD27+ TCF7+ SELL+) was apparent in JUN-overexpressing but not in control Her2-BBz CAR T cells, consistent with maintenance of a memory-like population capable of self-renewal. Conclusions: This study provides insights into cell states that could explain the improved efficacy of JUN-overexpression Her2-BBz CAR T cells compared to control Her2-BBz CAR T cells in a mouse model of osteosarcoma. A total of 17,931 Her2-BBz CAR T cells (control: 6,946, JUN-overexpressing: 10,985) were sequenced to an average of 49,542 post-normalization reads per cell capturing a median of 4,281 unique molecular identifier (UMI) counts per cell mapping to a median of 1,599 unique genes per cell.