When incubated with GvHD Balb/c-derived splenocytes from B6 recipients, the proliferation of naïve B6 splenocytes was completely abrogated whereas it was restored by supplementation with CD8+-depleted naïve Balb/c splenocytes, supporting the notion that allogeneic antigen-presenting cells (APCs) are essential for the activation of alloreactive CD8+ T cells, and that APCs in mice with acute GvHD were functionally debilitated. This evidence concerns the gene CD8A and graft versus host disease.