Low-affinity anti-HER2-CAR T cells efficiently eradicate HER2+ and HER2low cancer cells with reduced toxicity on healthy tissue

Chimeric antigen receptor (CAR) T cell therapy is considered a therapeutic breakthrough in hematological malignancies. However, its translation to metastasized solid tumors remains limited by the paucity of “druggable” targets and the limited therapeutic potency of the cell therapeutics in solid cancers. Human epidermal growth factor receptor 2 (HER2), a promising target for treatment of metastasized solid cancers, is amplified in around 3% (HER2 + cancer) and overexpressed without amplification in ∼40% (HER2 low cancer) of all carcinomas, yet the physiological expression of HER2 on healthy tissues poses the risk of on-target off-tumor effects. To address this, we utilized low-affinity (LA) Anti-HER2-CAR T cells. These CAR T cells exhibited efficient lysis of HER2 + SKOV3 ovarian cancer cells even at low effector-to-target ratios. Following stimulation through cancer cells, LA Anti-HER2-CAR T cells showed rapid proliferation and elevation of pro-inflammatory cytokines markers. Low numbers of CAR T cells were sufficient to induce durable complete remissions of systemically seeded ovarian cancer in NOD- Prkdc scid -IL2rg Tm1 /Rj mice. LA Anti-HER2 CAR T cells also exhibited tumor regression and lasting tumor control in a subcutaneous in vivo model of HER2 low LS174T cells. Additionally, the LA and high-affinity (HA) CAR T cells could effectively combat HER2 low human colorectal cancer (CRC) cell lines and primary CRC organoids, while LA Anti-HER2-CAR T cells showed a trend-wise reduced lysis of healthy colon organoids. Our results suggest that LA Anti-HER2-CAR T cells provide a novel treatment option for HER2-overexpressing advanced systemic tumors. Importantly, they effectively distinguished between healthy colon tissue and HER2 low cancer, broadening the scope of HER2-directed CAR T cells to this frequent cancer subset.