Cells responsible for GVHD is -
Graft-versus-host disease (GVHD)

GVHD occurs when immunologically competent cells (T cells) or their precursors are transplanted into immunologically crippled recipients, and the transferred cells recognize alloantigens in the host and attack host tissues.
Most commonly involved tissues in graft versus host disease
Liver
Skin
Gut
Immunocompetent T Cell recipient
Immunocompetent B cell donor
Immunocompetent T cell donor
Immunocompetent B cell recipient