Pretransplant detection of human minor histocompatibility antigen-specific naive and memory interleukin-2-secreting T cells within class I major histocompatibility complex (MHC)-restricted CD8+ and class II MHC-restricted CD4+ T-cell subsets.

Recent studies have shown that host-reactive interleukin-2 (IL-2)-secreting donor T lymphocytes (TI) are critically involved in the development of acute graft-versus-host disease (GVHD) after allogeneic HLA-identical sibling bone marrow transplantation (BMT). To further characterize the responding TI, we determined the frequency of pretransplant IL-2-secreting TI-precursors (TI-p) between eight HLA-A, -B, -C, -DR, and -DQ-identical sibling donor-host pairs in both the graft-versus-host (GVH) and the host-versus-graft (HVG) direction. High frequencies of pretransplant host-reactive donor TI-p (1/18,000 to 1/49,000) were detectable in five patients with grade II acute GVHD. Donor-reactive host TI-p (1/3,700 to 1/31,000) were observed in previously in vivo primed (n = 5) and unprimed (n = 1) patients. In two pairs tested after previous in vivo priming, pretransplant donor-reactive host TI-p were highly enriched within the CD45RO+ memory T-cell subset. Previously unprimed host-reactive donor TI-p occurred in almost equal frequencies within CD45RO+ and CD45RO- T cells. Both CD4+ and CD8+ T-cell subsets contributed in comparable frequencies to host- and donor-reactive TI-p. Recognition of minor histocompatibility (mH) antigens by CD8+ TI-p appeared to be class I major histocompatibility complex (MHC)-restricted, whereas CD4+ TI-p operated in a class II (HLA-DR) MHC-restricted fashion. Even between oligonucleotide-defined HLA-DPB1-disparate sibling donor-host pairs (n = 3), either responding T-cell subset was found to recognize cellularly defined mH antigens. These data indicate that various T-cell subsets contribute to host- and donor-reactive IL-2-secreting TI in allogeneic sibling BMT.