117: Naive and memory T regulatory cells respond to mesenchymal cells regulation

In T cell replete bone marrow transplantation GvHD remains a major problem despite prophylaxis with immune suppressive agents. In animal models CD4(+)CD25(+)FoxP3(+) T regulatory (T reg) cells protected from rejection and GvHD after bone marrow transplantation. 70% of T reg are memory/effector cells with a CD45RO+ phenotype. The others are naive CD45RA+ T cell. When sorted and/or purified both subpopulations inhibit mixed lymphocyte cultures. T cells from healthy subjects were enriched by immnuselection to provide populations of CD45RA+ cells (95 % ± 2.9) and CD45RO+ cells (97 % ± 0.25). Naive and memory cells were cultured in presence of human mesenchymal cells (hMSC) (ratio 5:1). After 7 days’ culture, in the naive population the T reg starting fraction of 0.05 % ± 0.01 of CD4/CD25 positive cells, rose to 0.2 % ± 0.14 in presence of MSC. In the memory population the T reg starting fraction of 0.3 % ± 0.05 of CD4/CD25 positive cells, rose to 1.5 % ± 0.9 in the presence of MSC. The naive T reg starting fraction expressed 3 % ± 1.2 CD127 which was down-regulated to 0.29 % ± 0.2 with MSC. Memory T reg cells expressed CD127 in 15% ± 1.2 of the starting fraction which was down-regulated to 1.32 % ± 0.34 with MSC. FoxP3 expression was measured by real time quantitative PCR in sort-purified subsets of peripheral blood, identified by staining with a combination of CD4, CD25, CD45RA or CD45RO. FoxP3 expression increased 1.15 fold in the presence of MSC in naive T reg and 1.14 fold in memory T reg. Observing that naive and memory T regulatory cells respond to MSC regulation opens new perspectives for clinical use. Post transplant infusion of MSC and/or donor regulatory cells after co-culture with MSC might be a new option for GvHD treatment.