Background/Purpose: Regulatory T cells (Tregs) play an important role in maintaining immune system homeostasis. Antigen-specific Tregs potently and specifically suppress autoreactivity, suggesting their potential to be engineered to treat autoimmune diseases. Lupus nephritis (LN) is a severe manifestation of SLE associated with the presence of anti-Smith (Sm) autoantibodies as well as the HLA haplotypes DR15 and DR3, with the majority of patients DR15. Due to the strong association of LN with anti-Sm and HLA-DR15, we developed Sm-specific Tregs for potential treatment of LN.

Methods: We identified DR15-restricted Sm T cell epitopes using a physical affinity binding assay. T cell receptors (TCRs) specific for Sm epitopes were identified by co-culturing CD4+ T cells with dendritic cells from HLA-DR15+ healthy donors and Sm epitopes, and sequencing proliferating CD4+ T cells using high-throughput 10X single cell V(D)J sequencing. TCRs were ranked based on clonal expansion, cloned into a lentiviral vector then transduced onto primary SLE patient Tregs. Sm-specific Tregs were evaluated for suppression of T effector cell function in vitro and in a humanised model of LN created by the transfer of PBMCs from anti-Sm positive HLA-DR15+ SLE patient into NSG-MHC-null mice.

Results: The top three Sm epitopes identified were SmB/B’_58-72, SmB/B’_1-15, and SmD3_43-57; the respective stability indices (SI) were 16.0, 1.4 and 1.2. Highly reactive TCRs specific for SmB/B’_58-72 were identified and the highest ranked SmB/B’_58-72 reactive TCR was cloned into a lentiviral vector then transduced onto primary SLE patient Tregs, resulting in Sm-Tregs. In in vitro co-cultures of SLE patient PBMCs with SmB/B’_58-72, Sm-Tregs, but not polyclonal Tregs induced 90% suppression of pro-inflammatory cytokine secretion (IFN-g (pg/mL): control 39.7±11.4, polyclonal Tregs 37.3±12.6, Sm-Tregs 2.7±1.0, p< 0.05; IL-17A (pg/mL): control 26.3±2.9, polyclonal Tregs 17.0±2.7, Sm-Tregs 2.4±0.6, p< 0.01) while Sm-Tregs produced significantly more IL-10 (p< 0.01). Transfer into NSG-MHC-null mice of Sm+ HLA-DR15+SLE patient PBMCs, but not healthy HLA-DR15+ PBMC, induced an LN phenotype characterised by proteinuria and histological glomerular necrosis. Treatment with Sm-Tregs halted the progression of functional and histological injury in this model (proteinuria: control 3.6±0.2, polyclonal Tregs 3.2±0.2, Sm-Tregs 1.2±0.2, p< 0.01; glomerular segmental necrosis: control 75.2±2.9%, polyclonal Tregs 61.2±6.3%, Sm-Tregs 14.4±1.9%, p< 0.001).

Conclusion: Antigen-specific Tregs generated against an immunodominant Sm peptide were highly efficient at suppressing Sm-specific T effector responses. HLDA-DR15+Sm+ SLE patient PBMC induced a model of LN, in which Sm-Tregs were therapeutic. Autologous Sm-Treg cell therapy is a promising treatment for LN, and other antigen-specific autoimmune diseases could be similarly targeted.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/development-of-engineered-smith-specific-regulatory-t-cells-to-treat-lupus-nephritis/