LACK OF GVHD ACROSS CLASSICAL SINGLE MINOR HISTOCOMPATIBILITY (MIH) LOCUS BARRIERS IN MICE

To determine whether a disparity at a single miH genetic loci are suff icient to generate GVHD in mice, we focused on well-known genetic alle leic differences at the miH gene loci, H3 and H4, For H3 congenic GVHD studies, C57BL/10 (H2(b)) mice were used as recipients of miH-dispara te B10.LP-H3(b) donor cells, For H4 congenic GVHD studies, C57BL/10 we re used as recipients for miH-disparate B10.129 (21M)-H4(b). To overco me the low frequency of miH-reactive CTLs in naive mice, multiple immu nizations of the donor strains with host lymphohematopoietic cells wer e used, Peripheral blood cells from immunized mice were shown to have potent CTL activity against their respective host-type stimulator cell s when analyzed 1 week prior to obtaining donor splenocytes for GVHD i nduction, Lethally irradiated C57BL/6 recipients of either 50 x 10(6) donor B10.LP-H3(b) or B10.129 (21M)-H4(b) splenocytes did not develop acute or chronic GVHD as assessed by monitoring the animals for surviv al, weight loss, splenic flow cytometry, and histological examination of skin, liver, colon, and lung in long-term survivors, Engraftment wa s documented in long-term chimeras in both strain combinations by usin g the post-BMT cells as alloantigen targets for cloned CTL lines speci fic for donor and not host-type miH antigens (H3(b) or H4(b)). On day 6 post-BMT, donor antihost CTL activity could not be detected in the s pleen, although third-party responses were intact, These results sugge st a rapid downregulation or disappearance of miH antigen-reactive CTL after BMT. These data have implications for the use of in vitro assay s to predict GVHD risk in recipients of miH loci-disparate donor graft s.