Session: (0001–0018) B Cell Biology & Targets in Autoimmune & Inflammatory Disease Poster I
0016: Pharmacology Analyses of Sail’s In Vivo hCD19 CAR-T Product Reveal Mechanistic Insights Underlying its Optimal Dose Efficiency Profile in Both Healthy Donors and SLE Patient Samples
Sail Biomedicines Cambridge, Massachusetts, United States
Disclosure information not submitted.
Background/Purpose: Ex vivo chimeric antigen receptor (CAR) T cell therapy has demonstrated encouraging clinical efficacy in small trials enrolling patients with B cell driven autoimmune diseases (AID), such as Systemic Lupus Erythematosus (SLE). However, existing autologous CAR-T therapies suffer from challenges in manufacturing complexity, scalability and safety. Sail Biomedicines is developing a targeted lipid nanoparticle (tLNP) encapsulating Endless RNA (eRNATM)-encoded hCD19 CAR for in vivo transient reprogramming of pan-T cells. Methods: Sail’s tLNP-eRNA platform was assessed in peripheral blood mononuclear cells (PBMCs) from a cohort of healthy donors and SLE patients in an in vitro assay. The mechanistic contribution of various CAR expression variables as well as CD4 and CD8 CAR-T cells to autologous B cell killing was assessed in PBMCs from multiple healthy donors that were depleted of either CD4 or CD8 T cells prior to treatment with tLNP-eRNA. Using humanized mice, in vivo engineered T cells were characterized to further understand possible mechanisms underlying the deep B cell depletion observed in blood and lymphoid tissues. Results: By assessing a large cohort of healthy donors in our in vitro PBMC assay, we determined the CAR expression levels required to achieve maximal B cell killing in terms of frequency of CAR+ T cells, CAR+ T:B ratio and number of CAR molecules per cell. We observed no correlation between the CD4:CD8 ratio of CAR+ T cells and potency of B cell depletion. To investigate the contribution of each T cell subset, we transfected PBMCs depleted of either CD4 or CD8 T cells and found similar dose efficiency relationships in absence of CD4 or CD8 T cells. Healthy donors and SLE patients demonstrated comparable dose-expression and dose-functional potency relationships following treatment with our tLNP-eRNA in vitro. We optimized our dosing regimen in a B cell repopulating humanized mouse model and were able to observe deep B cell depletion in blood and lymphoid tissues, including B cell progenitors in the bone marrow. Detailed immunophenotyping and characterization of in vivo engineering kinetics revealed mechanisms underlying deep depletion of B cells in lymphoid tissues. Conclusion: Here we explored the mechanisms underlying the optimal dose efficiency profile demonstrated by Sail’s pan-T cell tLNP-eRNA. Efficient engineering of both CD4 and CD8 T cells, including T cell memory subsets with tissue migrating potential, likely explains the profound level of B cell depletion in primary and secondary lymphoid tissues and effective immune reset observed in vivo. Importantly, in vitrotLNP-eRNA engineered CD4 CAR T cells exhibited a comparable capacity to eliminate autologous B cells as CD8 CAR T cells, further supporting our pan-T targeting approach. Moreover, comparable in vitro pharmacology relationships in PBMCs from healthy donors and SLE patients suggest a similar dose efficiency profile will be observed in patients. Sail’s tLNP-eRNA off-the-shelf IV injectable CAR-T product is poised to transform the care of patients with AID by increasing access, reducing safety risk and negating the need for lymphoablative conditioning while bearing the potential of lentiviral CAR-T efficacy.
