Blood samples are obtained periodically and examined by immunoenzyme techniques for mixed lymphocyte reaction (as a surrogate marker for alloreactivity) and cytokine levels (TH1 [i.e., interleukin (IL)-2 and interferon-gamma], TH2 [i.e., IL-10 and IL-4], and inflammatory cytokines [i.e., tumor necrosis factor-alpha and IL-1]). Tissue specimens are examined by CD45 immunohistochemistry and fluorescent in situ hybridization to detect hematopoietic and nonhematopoietic cells.