0002: KITE-363: An Autologous Anti-CD19/CD20 CAR-T Product for the Treatment of Autoimmune Rheumatic Diseases

Background/Purpose: B-cell dysregulation is a key factor in the development and progression of autoimmune diseases, and B-cell inhibition has been a cornerstone of treatment for decades. Recent studies on B-cell depletion using chimeric antigen receptor (CAR) T-cell therapies in autoimmune diseases highlight the potential for reestablishing immune tolerance and achieving rapid, sustained remission without chronic use of systemic immunosuppressants (Taubmann J, et al. Arthritis Rheumatol. 2024). Both CD19 and CD20 are transmembrane proteins expressed on B-cells with variable expression throughout B cell development and thus, targeting both CD19 and CD20 may provide more comprehensive B-cell depletion than what could be achieved by targeting either antigen alone. KITE-363 is a dual-targeting anti-CD19/CD20 CAR T-cell therapy with 2 costimulatory domains, CD28 and 41BB, and is being evaluated in a Phase 1 clinical study of relapsed/refractory B-cell lymphoma (KT-US-499-0150).

Methods: CD19 and CD20 expression on B cell subsets from healthy donors and patients with systemic lupus erythematosus (SLE) with and without lupus nephritis (LN), systemic sclerosis (SSc), and idiopathic inflammatory myopathy (IIM) were analyzed by flow cytometry. Using a bicistronic lentiviral vector and T cells from patients, we generated anti-CD19/CD20 CAR-T cells (KITE-363). The bicistronic lentiviral vector encodes for an anti-CD19 CAR, containing the FMC63 binder and CD28 costimulatory domain, and anti-CD20 CAR, containing a novel CD20 binder and 41BB costimulatory domain. The final products were characterized via immunophenotyping and functionally assessed in vitro.

Results: Most B cells in the peripheral blood co-expressed CD19 and CD20 (CD19⁺CD20⁺), albeit at variable expression levels. Subsets of both CD19⁺CD20^– and CD19^–CD20⁺ B cells were observed in all autoimmune conditions. Plasmablasts were abundantly CD19⁺CD20^–, while double negative (IgD^–CD27^–) B cells were enriched for CD19^–CD20⁺ compared to other B cell subsets. Patient-derived KITE-363 T cell products exhibited high expression of both the anti-CD19 and anti-CD20 CARs and demonstrated CAR- and antigen-specific T-cell functionality including cytokine production, proliferation, and cytotoxicity against autologous B cells and cell lines expressing either CD19 and/or CD20 antigens.

Conclusion: Highly variable expression of CD19 and/or CD20 in B cell subsets, jointly with antigen-specific and B-cell depleting activity of KITE-363, support clinical development of KITE-363 in B cell-mediated auto-immune conditions. With dual-antigen targeting and optimized co-stimulation, KITE-363 has the potential to induce a more comprehensive B-cell depletion and achieve durable, drug-free remission in these diseases. A Phase 1 open-label, multicenter study is underway to evaluate the safety and efficacy of KITE-363 in participants with refractory autoimmune rheumatic diseases.