S. Kusaka et al., Clonotype analysis of human alloreactive T cells: A novel approach to studying peripheral tolerance in a transplant recipient, J IMMUNOL, 164(4), 2000, pp. 2240-2247
The recognition of allo-MHC and associated peptides on the surface of graft
-derived APC by host T cells (direct pathway allorecognition) plays an impo
rtant role in acute rejection after organ transplantation. However, the sta
tus of the direct pathway T cells in stable long term transplants remains u
nclear. To detect alloreactive T cell clones in PBL and the allograft durin
g the transplant tolerance, we utilized RT-PCR instead of functional assays
, which tend to underestimate their in vivo frequencies. We established all
oreactive CD4(+) and CD8(+) T cell clones from peripheral blood sampled dur
ing the stable tolerance phase of a patient whose graft maintained good fun
ction for 9 years, 7 without immunosuppression, We analyzed the sequence of
TCR V beta and V alpha genes and made clonotype-specific probes that allow
ed us to detect each clone in peripheral blood or biopsy specimens obtained
during a 1-year period before and after the rapid onset of chronic rejecti
on. We found an unexpectedly high level of donor HLA-specific T cell clonot
ype mRNA in peripheral blood during the late tolerance phase. Strong signal
s for two CD4(+) clonotypes were detected in association with focal T cell
infiltrates in the biopsy. Chronic rejection was associated with a reductio
n in direct pathway T cell clonotype mRNA in peripheral blood and the graft
. Our data are inconsistent with the hypothesis that direct pathway T cells
are involved only in early acute rejection events and suggest the possibil
ity that some such T cells may contribute to the maintenance of peripheral
tolerance to an allograft.