We sought to investigate some of the requirements for tolerance induction to cardiac allografts utilizing αLFA-1 mAb monotherapy. Having previously demonstrated that CD8 T-cells are required for induction but not maintenance of tolerance, we investigated the possibility that CD8⁺CD28^– suppressor T-cells might be involved and that there might be an associated increase of immunoglobulin like transcript 3 (ILT3) expression on antigen presenting cells (APCs).

Methods: BALB/c hearts were transplanted into B6 mice and were untreated or treated with αLFA-1 or αLFA-1 and αCD8. Draining lymph nodes were analyzed by flow cytometry for CD8 T-cell phenotype and expression of ILT3 on APCs on POD7, while those tissues harvested for in-vivo proliferation studies were observed on POD10 (day 5 post transfer of eFluor labeled TCR Tg 4C [direct CD4 anti-BALB/c] cells).

Results: αLFA-1 treated B6 recipients demonstrated significant increases in CD8⁺CD44^hiCD28^– cells compared to controls (64.6+/-1.6% vs. 25.5+/-1.7%). APCs from the draining lymph node showed an increased expression of ILT3 from 17.3+/-4.9% in controls to 31.1+/-0.6% when treated with αLFA-1. When CD8 cells were depleted from αLFA-1 treated animals ILT3 expression returned to control levels (17.5+/-0.5%). There was a significant decrease in the proportion (control; 31.7+/-4.7 % vs. 26.1+/-1.7%) and number (6390+/-1949 vs. 659+/-381) of anti-BALB/c CD4⁺Vβ13⁺ cells under αLFA-1 administration, which was reversed when CD8 cells were depleted (31.9+/-4.7%, and 1729+/-434). There was also a significant decrease in in-vivo proliferation of these cells with αLFA-1 administration (47.7+/-12.2% for control vs. 21.0+/-4.9% for αLFA-1 mAb monotherapy). Interestingly, this was not reversed by depletion of CD8 cells.

Conclusion: αLFA-1 mAb monotherapy produces potent tolerance-induction in recipients of fully vascularized cardiac allografts. CD8 T-cells (via host MHC class I expression) are critical for the induction of this tolerance. We have found that this is associated with a significant increase in T-cells of a suppressor (CD8⁺CD28^–) phenotype, an increase in ILT3 expression on host derived APCs and a decrease in BALB/c-reactive CD4 T-cells.

CITATION INFORMATION: Plenter R, Coulombe M, Grazia T, Gill R, Zamora M, Pietra B. αLFA-1 Monotherapy Induced Tolerance Is Dependent on Indirect CD8 T-Cells and Augments a Population of CD8 Cells with a Suppressor Phenotype. Am J Transplant. 2016;16 (suppl 3).

« Back to 2016 American Transplant Congress