Background/Purpose: T cell engagers (TCEs) redirect T cells to bind target cells by linking T cells with target-associated antigens expressed on cells responsible for disease pathology. Most TCEs to-date target alpha-beta (αβ) T cells, binding both an antigen such as CD20 on the cell of interest and CD3 on the T cell. This approach is complex, requiring CD3 de-tuning due to the risks of T cell exhaustion and severe, potentially life-threatening complications such as cytokine release syndrome (CRS). Gamma delta (γδ) T cells offer a promising alternative due to their innate MHC-independent cell killing and low production of CRS-associated cytokines. INB-619, a novel pan-γδ TCE that exhibits specific targeting of CD19+ B cells, including those from SLE patients with active disease. INB-619 induces potent cytotoxicity and drives robust activation and expansion of Vδ1and Vδ2 T cells. These unique properties potentially solve the challenge of current B cell depleting TCE’s, where dysfunctional immune cells, tissue-resident B cells and potential toxicities may limit the depth of B cell depletion. These findings position INB-619 as a promising therapeutic candidate for autoimmune indications.

Methods: INB-619 binding and activation specificity were confirmed by co-incubation of a 1:1 ratio of NALM-6 ALL (CD19+) or CD19- cell lines with expanded γδ T cells at increasing concentrations of INB-619. PBMC from healthy donors (n=2) and from subjects with active SLE (n=3) were exposed at DAY 0 to 5nM of INB-619 and assessed over 10 days for lymphocyte phenotype, expression of cell surface activation/ degranulation markers, and secreted cytokines (N = 3).

Results: INB-619 bound specifically to CD19+ NALM-6 and to γδ T cells and induced specific and dose-dependent γδ T cell cytotoxicity and upregulation of CD107a, PD-1, and CD69 at EC50 values from 26 to 51 pM but showed no specific activity against a CD19- cell line. Complete depletion of B cells from healthy and SLE donor PBMC were shown over a 10-day incubation period. In all cases, γδ T cells showed robust expansion of both CD27+CD45RA+ and CD27+/-CD45RA- populations reflecting the Vδ1 and Vδ2 populations, respectively. INB-619-expanded PBMC also exhibited a favorable cytokine release profile, with no detectable or minimal release of cytokines associated with CRS such as IL-4, IL-6, IL-10, and IL-17α. Concentrations of IgG1 and IgM in the coculture supernatants of all three SLE donors significantly decreased in TCE treatment groups concurrent with B cell depletion, with a correlation between the level of B cell depletion and γδ T expansion.

Conclusion: INB-619 is a novel CD19-targeting γδ TCE that expands both major γδ T cell subtypes sufficiently to eliminate a large population of B cells in vitro. The combined expansion and activation of tissue-resident Vδ1 and circulating Vδ2 populations, with the favorable cytokine pattern evidenced here, suggests that INB-619 could provide deep B cell depletion with a clinically relevant improvement in safety over current methods.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/inb-619-a-novel-gamma-delta-%ce%b3%ce%b4-t-cell-engager-to-target-b-cells-in-autoimmune-diseases/