Aquaporins are water channels present on mammalian cells. We previously reported that aquaporin 4 (AQP4) blockade with small molecule inhibitor AER270/271 significantly prolongs survival of heart allografts subjected to 8h cold ischemia. The goal of this study was to determine the effects of AQP4 blockade on alloreactive T cells.

To test the role of AQP4 in memory T cell responses, we sensitized B6 mice against Balb/c alloantigens 5 weeks prior to heart transplantation. Balb/c heart donors were treated with 250[micro]g AER270/271, and 0.5h later hearts were harvested, perfused and stored for 0.5h in UW solution plus 10[micro]M AER270. Sensitized B6 recipients received α-CD154 mAb (MR-1, 1mg i.v. on d. -1) with or without AER271 (250 [micro]g i.p. every 6 h on d. 0-4). AQP4 blockade plus MR-1 significantly prolonged allograft survival compared to MR-1 alone (MST 21d, n=7 vs. 6d, n=8). Recall IFNγ ELISPOT assay showed similar frequencies of donor specific T cells in both groups at rejection.

Using qRT-PCR and flow cytometry, we found that both CD4 and CD8 T cells express AQP4 with increased expression on activated CD44^hi cells. In contrast, B cells did not express AQP4. To assess the effect of AQP4 blockade on T cells in vivo naïve B6 mice were treated with AER271 (d 0-4) and T cell numbers were analyzed in various compartments. 6 h after the first AER271 injection, the numbers of Annexin V⁺ CD4 and CD8 T cells in the spleen were increased compared to untreated controls. Unexpectedly, we observed altered T cell distribution in AER271 treated mice at later time points, up to 20 days after the treatment cessation. AQP4 blockade markedly decreased frequencies of both CD4 and CD8 T cells, but not B cells, in peripheral blood compared to untreated mice (6.2% vs. 17.6%, CD4, and 3.9%, vs. 12.3%, CD8, p<0.0001). In contrast, the frequencies and numbers of CD4 and CD8 T cells in the spleen and the lymph nodes were not significantly affected by AQP4 blockade, suggesting that the lack of circulating T cells is not due to systemic depletion but rather to altered T cell trafficking.

Our data suggest that initial T cell apoptosis along with long-lasting changes in T cell trafficking may account for prolonged allograft survival in AER270/271 treated recipients. Therefore, AQP4 blockade may be an attractive therapeutic strategy in transplantation.

CITATION INFORMATION: Nicosia M, Fan R, Farr G, Pelletier M, McGuirk P, Ayasoufi K, Valujskikh A. Aquaporin 4 Blockade Alters T Cell Anatomical Distribution and Prolongs Cardiac Allograft Survival in Sensitized Recipients. Am J Transplant. 2017;17 (suppl 3).

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