Background
Transplant tolerance induction through conventional costimulation blockade (CoB) remains an elusive goal. Recent evidence suggests that inflammatory cytokines (IC) contribute to the activation of alloreactive T cells in a CD28- and CD40-independent manner. We aimed to delineate the possible synergism between CoB and inhibition of IC signaling via JAK/STAT inhibition.
Methods
Murine T cell activation was assessed through a CFSE proliferation assay. Activation in an inflamed environment was simulated through addition of supernatant (MATSup) from maturing dendritic cells. Jak inhibition was exerted with the inhibitor Tofacitinib (Tofa). Differential expression of DC maturation markers in response to LPS +/− Tofa was analyzed by flow cytometry. In vivo synergism between Tofa and CTLA4-Ig was tested in B6 to BALB/c heart and skin graft models.
Results
As hypothesized, MATSup addition counteracted the anti-proliferative effect of CTLA4-Ig on CD4 and CD8 T cells in our CFSE-proliferation assay. Tofa addition was able to restore CTLA4-Ig inhibition in presence of MATSup. Tofa also reduced DC expression of costimulatory molecules (CD40, CD80, and CD86) in response to LPS. Our skin transplant model showed that a short course of Tofa (d0–12) synergized with CTLA4-Ig improving graft survival (MST untreated: 9.5 d, CTLA4-Ig only: 13 d, Tofa+CTLA4: 18 d). Heart transplant survival in mice treated with CTLA-4Ig was significantly improved by a short course of Tofa (MST untreated: 9 d, CTLA4-Ig only: 36 d, Tofa+CTLA4-Ig: 4/5 vital grafts at 74 d, currently ongoing) This improvement was even more pronounced in parallel groups receiving hearts kept ischemic for 4 h before transplantation –a clinically relevant scenario– (MST untreated: 9 d, CTLA4-Ig only: 26.5 d, Tofa+CTLA4-Ig: 5/5 vital grafts at 74 d, currently ongoing).
Conclusion
Our results clearly indicate that the stimulatory effect of inflammatory cytokines counteracts the efficacy of CoB. However, this effect is neutralized through inhibition of Jak signaling that targets both T cells and DC. Our transplant survival data suggest that combining Jak inhibition with CoB is a promising strategy for promotion of transplant acceptance.