56P - Potent antitumor efficiency of CD19-CAR T cells self-secreting PD-L1 x CD3 BiTE against aggressive B-cell lymphoma

Background

Chimeric antigen receptor (CAR) and bispecific T-cell engagers (BiTEs) targeting CD19 had impressive antitumor efficacy for relapsed/refractory acute lymphoblastic leukemia but are limited responses for aggressive B-cell lymphoma (BCL). Programmed death-ligand 1 (PD-L1) overexpression on a tumor cell is a significant obstacle to objective responses after CAR-T cell therapy. Since immune checkpoint inhibitors combined with CAR-T cells may not wholly eradicate resistant solid tumors, redirecting PD-L1 and CD3 expressing cells using PD-L1 x CD3e BiTE may improve CAR-T cell antitumor functions.

Methods

To mitigate PD-L1 mediated CAR-T cell suppression, we engineered anti-CD19-CAR-T cells to secrete PD-L1 x CD3 BiTE (PD-L1 BiTE). A 4-1BB-based second-generation CD19-CAR comprising FMC63 scFv was linked with PD-L1 scFv x CD3e scFv (CD19-CAR.PD-L1 BiTE) via a T2A. PD-L1+/HeLa-CD19+ cell was used as a model to investigate whether the exogenous supply with PD-L1 BiTE or secreted by CAR-T can facilitate the antitumor activity of CD19-CAR T-cells.

Results

The antitumor activity of CD19-CAR T-cells co-incubated with recombinant PD-L1 BiTE showed superior cytolytic activity to CD19-CAR T-cells or PD-L1 BiTE alone. Primary human T cells expressing CD19-CAR.PD-L1 BiTE can secrete PD-L1 BiTE into the culture medium and exert bioactivities on specific binding to PD-L1 and CD3. CD19-CAR.PD-L1 BiTE significantly enhanced antitumor function and cytokine production against Raji/PD-L1 tumor cells. Taken together, these results proved the concept that a combination of CD19-CAR T-cells with either recombinant PD-L1 BiTE or self-secreted CAR-T cells could effectively enhance antitumor efficacies against PD-L1⁺/CD19⁺ tumor cells.

Conclusions

We demonstrated that PD-L1 blockade concomitant with redirecting CD3+ T cells mediated by PD-L1 BiTE secreted from anti-CD19-CAR2-T cells can improve CAR-T antitumor efficiency against PD-L1-positive tumors. This finding highlighted that concomitantly secreted PD-L1xCD3 BiTEs by CAR T-cells is a promising strategy to overcome PD-L1-mediated immune cell suppression to achieve synergistic efficacy for solid tumor treatment.

Legal entity responsible for the study

The authors.

Funding

The National Science and Technology Development Agency (NSTDA) (grant no. P1650727).

Disclosure

All authors have declared no conflicts of interest.