LTBR CARs as next-generation therapies for R/R lymphoma

PROJECT SUMMARY Up to 50% of patients with diffuse large B-cell lymphoma (DLBCL) relapse after first-line treatment. Chimeric antigen receptor (CAR) T-cells have recently emerged as a curative therapy for relapsed or refractory (R/R) DLBCL. However, only 35% of R/R DLBCL patients treated with CAR T-cells have a durable response, and survival is measured in months for patients who fail to benefit. Improvements in CAR T-cells are urgently required to improve outcomes. Recently, we identified the cell surface lymphotoxin beta receptor (LTBR) as a positive T- cell regulator that enhances CD19 CAR T-cell efficacy in vitro and in vivo. LTBR is typically expressed in a subset of myeloid cells but absent in lymphocytes; however when expressed in T-cells, LTBR induces proinflammatory cytokine release, and improves antigen-specific CAR T- and γδ T-cell responses with no appreciable off-target toxicity. Based on these observations, we hypothesize that LTBR can effectively potentiate anti-tumor activity in R/R lymphoma T-cells, reducing markers of T cell exhaustion and outperforming current FDA-approved CAR-Ts across R/R DLBCL subtypes. In Aim 1, we characterize differences in expression of T-cell differentiation, activation, and exhaustion markers and myeloid populations in 25 treatment-naive and 25 R/R DLBCL patient samples. To understand if LTBR can similarly improve CAR-T response in the R/R context, we will use single- cell profiling and functional assays to test autologous CD19+ cell killing, with and without LTBR. In Aim 2 we will evaluate the impact of DLBCL subtype on CAR T-cell activity by introducing LTBR and CAR T-cells into mice xenotransplanted with multiple germinal center B-cell (GCB) and activated B-cell (ABC) cell lines. Since T-cell activation and kinetics are further influenced by patient tumor burden, we will also investigate the efficacy of LTBR-CAR T-cell therapy in a high tumor burden context and test for durable immune memory after complete tumor regression. Recently, by fusing the intracellular signaling domain of LBTR directly to existing (CD28 and 4-1BB) CARs, we have developed a novel CAR construct with more potent antitumor response. In Aim 3 using comprehensive scanning mutagenesis of the LTBR domain, we will create a library of CAR variants and test their ability to improve tumor killing, resistance to exhaustion and cytokine section. We will also measure changes in T-to-B cell immune synapses and resistance to immunosuppression by myeloid-derived suppressor cells (MDSCs) in the most promising LTBR-CARs. This project is the first to comprehensively characterize T cells states in treatment-naive and R/R DLBCL and evaluate LTBR as a T-cell activating strategy to maximize intrinsic anti-tumor activity in R/R DLBCL. There is substantial potential for our work to serve as a bridge from laboratory studies to clinical trials and to help the 40,000 patients per year with R/R DLBCL and other B-cell NHLs.