Background & Aims Chimeric antigen receptor engineered T cells (CARTs) for hepatocellular carcinoma (HCC) and other solid tumors are not as effective as they are for blood cancers. CARTs may lose function inside tumors due to persistent antigen engagement. The aims of this study are to develop low-affinity monoclonal antibodies (mAb) and low-avidity CARTs for HCC and to test the hypothesis that low-avidity CARTs can resist exhaustion and maintain functions in solid tumors, generating durable antitumor effects. Methods and results New human glypican-3 (hGPC3) mAbs were developed from immunized mice. We obtained 3 hGPC3-specific mAbs that stained HCC tumors, but not the adjacent normal liver tissues. One of them, 8F8, bound an epitope close to that of GC33, the frequently used high-affinity mAb, but with ~17 fold lower affinity. We then compared the 8F8 CARTs to GC33 CARTs for their in vitro function and in vivo antitumor effects. In vitro, low-avidity 8F8 CARTs killed both hGPC3high and hGPC3low HCC tumor cells to the same extent as high-avidity GC33 CARTs. 8F8 CARTs expanded and persisted to a greater extent than GC33 CARTs, resulting in durable responses against HCC xenografts. Importantly, compared to GC33 CARTs, there were 5 folds more of 8F8-BBz CARTs in the tumor mass for a longer period of time. Remarkably, the tumor infiltrating 8F8 CARTs were less exhausted and apoptotic, and more functional than GC33 CARTs. Conclusion The novel low-avidity 8F8-BBz CART resists exhaustion and apoptosis inside tumor lesions, demonstrating a greater therapeutic potential than high-avidity CARTs.
Autologous T cells engineered with T receptor genes (TCR-T) are being studied to treat cancers. We have recently identified a panel of mouse TCRs specific for the HLA-A0201/alpha fetoprotein epitope (AFP158) complex and have shown that the TCR-engineered human T cells can eradicate hepatocellular carcinoma xenografts in NSG mice. In this current study, we evaluate their off-target toxicity. We found that 3 AFP158-specific TCR-Ts could be cross-activated by ENPP1436 peptide and that the TCR3-Ts could also be activated by another off-target peptide, RCL1215. However, compared to AFP158, it requires 250 times more ENPP1436 and 10,000 times more RCL1215 peptides to achieve the same level of activation. The EC50 of ENPP1436 peptide for activating TCR-Ts is approximately 17–33 times higher than AFP158. Importantly, the ENPP1+ tumor cells did not activate TCR1-Ts and TCR2-Ts, and only weakly activated TCR3-Ts. The IFNγ produced by TCR3-Ts after ENPP1+ cell stimulation was 22 times lower than that after HepG2 cells. And, all TCR-Ts did not kill ENPP1+ tumor cells. Furthermore, ectopic over-expression of ENPP1 protein in HLA-A0201+ tumor cells did not activate TCR-Ts. In silico analysis showed that the ENPP1436 peptide affinity for HLA-A0201 was ranked 40 times lower than AFP158 and the chance of ENPP1436 peptide being processed and presented by HLA-A0201 was 100 times less likely than AFP158. In contrast, the two off-targets (Titin and MAGE-A3) that did cause severe toxicity in previous trials have the same or higher MHC-binding affinity and the same or higher chance of being processed and presented. In conclusion, our data showed that these TCR-Ts, especially TCR1-Ts and TCR2-Ts, will unlikely cause significant off-target toxicity.
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