Selective JAK3 inhibition by J1f prolongs cardiac allograft survival in mice and suppresses alloimmune responses.

BACKGROUND

Achieving potent immunosuppression while minimizing off-target and exposure-limiting toxicities remains a key goal in organ transplantation. JAK3 is a nonredundant mediator of γc-cytokine signaling and an attractive target for lymphocyte-restricted immunomodulation; however, existing JAK3 inhibitors may show incomplete isoform selectivity and/or uncertain durability of cellular pathway suppression. We therefore developed a novel JAK3 inhibitor, J1f, and performed a preclinical evaluation of its selectivity and immunosuppressive efficacy.

METHODS

J1f was evaluated by biochemical kinase profiling, cellular signaling analyses, and ex vivo studies of activated splenocytes and one-way mixed lymphocyte reactions. In vivo efficacy was assessed in a fully MHC-mismatched heterotopic cervical cardiac transplant model with graft survival, histology, intragraft cytokine expression, and systemic T-cell profiling. Safety was evaluated in OECD-aligned acute and subacute toxicity studies.

RESULTS

J1f potently inhibited JAK3 (IC50 6.6 ± 1.4 nM) with >1200-fold selectivity over JAK1 and JAK2 and negligible activity against TYK2. In washout assays, p-STAT5 suppression persisted after washout up to 6 h under the tested ex vivo conditions. J1f dose-dependently reduced ConA-induced T-cell proliferation and increased apoptosis ex vivo. In vivo, vehicle-treated allografts were rejected rapidly (median survival time [MST] 7 days), whereas J1f prolonged graft survival (MST 9.5 days at 30 mg/kg q.d.; MST 30.5 days at 30 mg/kg b.i.d.; n = 6/group) and reduced intragraft CD4+ and CD8+ T-cell infiltration and IFN-γ mRNA. No overt hematologic, hepatic, or renal toxicity signals were observed under the tested regimens.

CONCLUSIONS

J1f provides preclinical proof-of-concept for selective JAK3 inhibition in organ transplantation; further PK/PD, target-occupancy, and comparator studies are warranted.