Intragraft Mechanisms Associated With the Immunosuppressive Versus the Tolerogenic Effect of CD3 Antibodies in a Mouse Model of Islet Allografts

We previously demonstrated the ability of CD3-specific antibodies (Abs) to induce tolerance of fully mismatched pancreatic islets when administered at the time of effector T-cell priming (day +7). When administered on day −1, CD3 Abs only displayed an immunosuppressive effect with no permanent acceptance. Here we show that rejection correlates with progressive migration of CD4+ and CD8+ T cells into the graft. In contrast, the day +7 CD3 Ab tolerogenic effect is associated with absence of de novo accumulation of CD8+ T cells within the allograft while CD4+ T-cell migration is not altered. Furthermore, the increased proportion in T-regulatory cells, observed both in the draining lymph nodes and in the transplanted islets, was more pronounced after the delayed (day +7) than the early (day −1) CD3 Ab course. Last, tolerance-promoting (day +7), but not immunosuppressive (day −1) CD3 Ab treatment was associated with an elevated in situ Foxp3/α-1,2-mannosidase gene expression ratio, identified as a biomarker predicting tolerance in renal transplant patients. In conclusion, intragraft-enhanced regulation over effector function after the delayed but not the early CD3 antibody therapy discriminates between the tolerance-promoting and immunosuppressive effect of CD3 Ab treatment and further highlights the importance of the therapeutic window.