Identification of a major susceptibility locus for lethal graft-versus-host disease in MHC-matched mice

Fine mapping of the Bmgr5 quantitative trait locus for allogeneic bone marrow engraftment in mice

To identify novel mechanisms regulating allogeneic hematopoietic cell engraftment, we used forward genetics and previously described identification, in mice, of a bone marrow (BM) engraftment quantitative trait locus (QTL), termed Bmgr5. This QTL confers dominant and large allele effects for engraftment susceptibility. It was localized to chromosome 16 by quantitative genetic techniques in a segregating backcross bred from susceptible BALB.K and resistant B10.BR mice. We now report verification of the Bmgr5 QTL using reciprocal chromosome 16 consomic strains. The BM engraftment phenotype in these consomic mice shows that Bmgr5 susceptibility alleles are not only sufficient but also indispensable for conferring permissiveness for allogeneic BM engraftment. Using panels of congenic mice, we resolved the Bmgr5 QTL into two separate subloci, termed Bmgr5a (Chr16:14.6-15.8 Mb) and Bmgr5b (Chr16:15.8-17.6 Mb), each conferring permissiveness for the engraftment phenotype and both fine mapped to an interval amenable to positional cloning. Candidate Bmgr5 genes were then prioritized using whole exome DNA sequencing and microarray gene expression data. Further studies are warranted to elucidate the genetic interaction between the Bmgr5a and Bmgr5b QTL and identify causative genes and underlying gene variants. This may lead to new approaches for overcoming the problem of graft rejection in clinical hematopoietic cell transplantation.

Alloimmune response results in expansion of autoreactive donor CD4+ T cells in transplants that can mediate chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is considered an autoimmune-like disease mediated by donor CD4(+) T cells, but the origin of the autoreactive T cells is still controversial. In this article, we report that the transplantation of DBA/2 donor spleen cells into thymectomized MHC-matched allogeneic BALB/c recipients induced autoimmune-like cGVHD, although not in control syngeneic DBA/2 recipients. The donor-type CD4(+) T cells from the former but not the latter recipients induced autoimmune-like manifestations in secondary allogeneic BALB/c as well as syngeneic DBA/2 recipients. Transfer of donor-type CD4(+) T cells from secondary DBA/2 recipients with disease into syngeneic donor-type or allogeneic host-type tertiary recipients propagated autoimmune-like manifestations in both. Furthermore, TCR spectratyping revealed that the clonal expansion of the autoreactive CD4(+) T cells in cGVHD recipients was initiated by an alloimmune response. Finally, hybridoma CD4(+) T clones derived from DBA/2 recipients with disease proliferated similarly in response to stimulation by syngeneic donor-type or allogeneic host-type dendritic cells. These results demonstrate that the autoimmune-like manifestations in cGVHD can be mediated by a population of donor CD4(+) T cells in transplants that simultaneously recognize Ags presented by both donor and host APCs.