Human CD4 super(+)CD25 super(low) Adaptive T Regulatory Cells Suppress Delayed-Type Hypersensitivity during Transplant Tolerance

Adaptive T regulatory (T sub(R)) cells mediate the suppression of donor-specific, delayed-type hypersensitivity (DTH) in tolerant organ transplant recipients. We hypothesized that cells belonging to the CD4 super(+)CD25 super(+) T cell subset but distinct from natural T sub(R) cells may fulfill this role. To test this hypothesis, PBMC and biopsy samples from two tolerant kidney transplant recipients (K1 and K2) were analyzed. When transferred with recipient APC into a SCID mouse footpad, CD4 super(+) T cells were hyporesponsive in DTH to donor type HLA-B Ags and derivative allopeptides. However, anti-human TGF- beta 1 Ab revealed a response to immunodominant allopeptides in both patients, suggesting that CD4 super(+) T effector (T sub(E)) cells coexisted with suppressive, TGF- beta 1-producing CD4 super(+) T sub(R) cells. During in vitro culture, allopeptide stimulation induced both IFN- gamma -producing and surface TGF- beta 1 super(+) T cells. The relative strength of the latter response in patient K1 was inversely correlated with the level of systemic anti-donor DTH, which varied over a 6-year interval. Allopeptide-induced surface TGF- beta 1 expression was found primarily in Forkhead box P3 (FoxP3)-negative CD4 super(+)CD25 super(low) T cells, which could adoptively transfer suppression of donor-specific DTH. Biopsy samples contained numerous surface TGF- beta 1 super(+) mononuclear cells that costained for CD4 and, less frequently CD25, but were negative for FoxP3. The CD4 super(+)TGF- beta 1 super(+) T cells were localized primarily to the tubulointerstitium, whereas TGF- beta 1 super(-)FoxP3 super(+)CD25 super(+) cells were found mainly in lymphoid aggregates. Thus, adaptive T sub(R) cells suppressing T sub(E) cell responses to donor allopeptides in two tolerant patients appear to be functionally and phenotypically distinct from CD4 super(+)CD25 super(high)FoxP3 super(+) T cells.