Rogelio Antonio Hernández-López

T cell proliferative capacity and persistence determine the therapeutic efficacy of chimeric antigen receptor (CAR) T cells. However, strategies to externally enhance CAR-T cell expansion without genetic rewiring are lacking. Here, we engineer CAREp, programmable DNA-scaffolded PLGA microparticles displaying CAR-targeting antigens and CD28-costimulatory antibodies, to repeatedly stimulate human CD8⁺ CAR-T cells ex vivo. CAREp sustains a-EGFR CAR-T cell expansion for over 100 days across both 4-1BBζ and CD28ζ constructs, achieving up to 10¹⁸-fold cumulative expansion and surpassing tumor-cell or CD3/CD28-Dynabeads stimulation. Expanded cells retain effector function and mitochondrial fitness while exhibiting clonal enrichment, initially preserved memory-associated progenitor states, delayed exhaustion, and transiently activated telomerase delaying telomere attrition. Early transcriptomic responses show coordinated activation of DNA repair, chromatin remodeling, telomere maintenance, and mitochondrial function while restricting differentiation-associated signaling programs, mirroring long-term functional outcomes. These findings demonstrate that nanoscale ligand organization synchronizes acute CAR-T signaling with durable proliferative and metabolic states.

SynNotch-CAR circuits improve T cell specificity by coupling antigen recognition to inducible CAR expression. However, basal CAR expression without receptor activation, termed here as leakiness, can reduce the separation between killing of intended target cells and sparing of antigen-positive off-target cells, limiting target-cell discrimination. Here, we systematically quantified basal CAR expression for several synNotch-CAR designs and developed a coupled ordinary differential equation model to show that discrimination depends on basal output, CAR potency, and effector-to-target ratio. We introduced C-terminal tags such as fluorescent proteins, degron domains, endocytosis signals, and endoplasmic reticulum retention motifs as a strategy to reduce CAR leakiness. We found that fluorescent proteins and degron-containing tags reduced basal CAR surface expression while preserving antigen-induced CAR expression, improving discrimination of antigen-density sensing and combinatorial circuits in vitro . In xenograft models, fluorescent protein-tagged CARs improved discrimination by reducing activity against off-target cells while retaining activity against high-antigen tumors. Degron-containing constructs reduced basal CAR expression in vitro but showed suboptimal performance in vivo , revealing a trade-off between basal CAR suppression and induced CAR persistence. Together, these findings demonstrate that basal output expression is a key parameter for inducible genetic circuit designs and establish layered transcriptional and post-translational regulation as a strategy to improve the fidelity of inducible T cell circuits.

Natural killer (NK) cell-based immunotherapies are promising for cancer treatment due to their ability to eliminate cancer cells independently of antigen presentation and “off-the-shelf” utility. However, molecular determinants governing tumor susceptibility to NK cytotoxicity remain incompletely understood. Here we employ CRISPR activation (CRISPRa) screening to identify cancer cell surface regulators of NK killing. Using a surfaceome-focused library, we screen human and murine cancer cell lines co-cultured with NK cells, identifying known and novel ligands modulating NK cytotoxicity. Screens reveal established factors including CD43 and previously uncharacterized regulators CD44, PDPN, and Siglec-1/CD169. Validation with orthogonal approaches confirm that disruption of these factors alters NK killing susceptibility in vitro and in humanized mouse models. Mechanistically, we find that CD43-mediated NK resistance operates independently of its proposed interaction with Siglec-7, and that targeting CD43 on NK cells or CAR T cells substantially enhances cytotoxic activity against leukemia. These results establish gain-of-function surfaceome screening as a powerful tool for identifying therapeutic targets for NK cell-based immunotherapy.

Figure S8. In vitro and in vivo activity of low a7inity scFv-guided CAR (KD = 3910 nM).

Figure S13. SKOV3 ovarian tumor volume measurements of individual mice treated with T cells expressing constitutive or inducible Sb1205 anti-HER2 CAR (related to Figure 5B and C).

Figure S3. Antigen expression and HER2 knock-down in a panel of cancer cell lines and additional Jurkat T cell reporter activation (NFAT-GFP) assays in co-culture with 293T* (HER2 KD) cells transfected with tumor associated antigens (related to Figure 2C, 2D.

Figure S5. Cytotoxic activity of Sb CARs expressed in human primary CD8+ T cells (related to Figure 2E)

Figure S9. Tumor volume measurement of individual mice treated with T cells expressing Sb1205 anti-HER2 CAR (related to Figure 4C and E).

Nucleotide sequences of constructs used in the study

Figure S4. NFAT-EGFP reporter activation in Jurkat T cells exposed to phorbol myristateacetate (PMA) and ionomycin or co-cultured with target cells expressing the cognate tumor associated antigen.