Background Activated T cells have limited antigen presenting capability due to inefficient capture.1 This process can be enhanced through novel chimeric engulfment receptors (CERs) expressing a human Tim-4 phagocyte receptor that recognizes phosphatidylserine (Ptd-Ser)2 fused to T cell and macrophage/dendritic cell-derived signaling domains. CERs can facilitate antigen capture, processing, and presentation, and impart target-dependent cytotoxic function when expressed in T cells. This combined function is hypothesized to improve tumor clearance and durability of response, making CER T cell products ideal clinical candidates.
Methods We generated Tim-4 receptors fused to toll-like receptor (TLR)-2 or -8, CD28 or CD3 zeta and tested phagocytic, antigen presentation and cytotoxic function in healthy donor T cells. To assess phagocytosis, target cells treated with a small molecule to induce Ptd-Ser externalization were labeled with pH-Rodo followed by co-culture with CER T cells. Activated CER T cells were evaluated by transmission electron microscopy (TEM) or flow cytometry (FC) for lysosomal uptake of cell fragments. Antigen capture and presentation were characterized by FC for the capacity of human papilloma virus 16 (HPV 16) E7 peptide-pulsed CER T cells to activate and induce proliferation of autologous HPV 16 E7-TCR transduced T cells. Cytotoxic function was evaluated in co-culture assays of CER T cells in the presence of subtherapeutic doses of BTKi (ibrutinib)-treated JeKo-1 lymphoma cells.
Results TEM imaging demonstrated that CER T cells engulfed target cell fragments, illustrated by multi-vesicular bodies containing tumor fragments (some measuring >0.5 uM) and pseudo-pod like formations around apoptotic target cell blebs. RNA analysis revealed upregulation of TLR, myeloid differentiation, and antigen presentation pathways. In the HPV 16 E7 co-culture model, T-cell surface activation markers CD25 and CD69 were upregulated 41% and 23%, respectively, on E7-TCR-T cells relative to controls. In addition, the percentage of dividing E7-TCR-T cells was increased (44% vs 8%) after 6 days in co-culture. Addition of CER T cells to JeKo- 1 target cells in the presence of BTKi at low effector: target ratios enhanced cytotoxicity by over 99%, demonstrating synergy with a targeted small molecule to fully eliminate lymphoma cells.
Conclusions Novel Tim-4/TLR containing CERs can capture tumor cell fragments and present soluble antigen, a function previously demonstrated to be a barrier to effective antigen presentation in T cells. Enhanced T-cell antigen capture and presentation capability alongside inducible and target-specific cytotoxic function in single T cells represents a significant advancement in the potential for chimeric receptor-based therapies.
Lanzavecchia A, Roosnek E, Gregory T, Berman P, Abrignani S. T cells can present antigens such as HIV gp120 targeted to their own surface molecules. Nature 1988 Aug 11;334(6182):530–2.
Caronni N, Piperno GM, Simoncello F, Romano O, Vodret S, Yanagihashi Y, et al. TIM4 expression by dendritic cells mediates uptake of tumor-associated antigens and anti-tumor responses. Nat Commun 2021 Apr 14;12(1):2237.
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