Combined immunosuppression with cyclosporine and methotrexate in dogs given bone marrow grafts from DLA-haploidentical littermates.

We examined the effect of methotrexate (MTX) combined with cyclosporine (CSP) on the prevention of graft-versus-host disease (GVHD) in dogs. Ten recipients were prepared for grafting with 9 Gy of total-body irradiation and given marrow and buffy coat cells from littermate donors differing for one DLA haplotype (AA leads to AB or AB leads to AC). MTX (0.4 mg/kg) was given i.v. on days 1, 3, 6, and 11. CSP was given i.m. on days 0 to 7 and orally on days 8 to 100. The dose was 15 mg/kg/day on days 0 to 25, 10 mg/kg/day on days 26 to 50, 5 mg/kg/day on days 51 to 75, and 5 mg/kg every other day on days 75 to 100. All ten dogs had sustained engraftment. Three dogs died, one with pneumonia (day 57), one with pneumonia and GVHD (day 107), and one with convulsions (day 204). Seven dogs are surviving at 210 to 493 days, and all are complete chimeras; five are well and two have chronic GVHD that developed after immunosuppressive treatment had been stopped. These results with a combination of MTX and CSP as GVHD prophylaxis are superior to those obtained previously with MTX alone in dogs given marrow grafts from DLA-haploidentical littermates.