LEITERS TO THE EDITOR HETEROGENOUS DISTRIBUTION OF CIDMERISM PRODUCED BY RAT ORGAN AND BONE MARROW ALLOTRANSPLANTATION

We recently described a striking association of organ allograft acceptance and the quantity and quality of immunocytochemically detectable donor leukocyte chimerism caused by previous ("priming") transplants (1). In these experiments, 1.0 mg/kg/day tacrolimus on days 0-13 and single supplemental doses on days 20 and 27 were given intramuscularly to Brown Norway (EN, RT1n) recipients of primary Lewis (LEW, RT1l) orthotopic livers, bone marrow infusions, abdominally placed heart allografts (the Ono-Lindsey model [2J) and other kinds of organs and leukocyte suspensions. On day 100. after a drug-free interval of 73 days, the liver, bone marrow, and heart recipients accepted "challenge" liver and cardiac allografts from LEW strain donors for another 100 days. At day 200, significant histopathologic findings of chronic rejection in the challenge hearts were absent, mini· mal. and most obvious in the animals originally primed with the livers, bone marrow, and hearts, respectively (1). Although the results in this investigation correlated generally with the degree and kind of chimerism produced by the priming allograft. the substantial but incomplete tolerance at 100 days produced in primary heart recipients in whom donor leukocytes could no longer be found with immunocytochemical techniques prompted the following experiments. Hearts. livers. or bone marrow cells from male LEW donors were transplanted to female BN reCIpients under the same conditions as reported previously, including the short course uf tacrolimus. At 100 days. the animals were killed and their ! Issues WE're studied with polvmerase chain reaction (PCR) . 111d ~()uthern hvbrldizatlOn. using rat Y-chromosome (sex determining ! legion Y [SRY))-specific primers (3). This procedure allowed detection of small numbers of male cells (to 1150,000 recipient cells, 0.002%) in female recipients. Donor DNA was found in the spleen, native heart, liver, or thymus of the three heterotopic heart recipients treated by the previous protocol (group 1, Table 1). Five of the 14 samples, but only one in five from the spleen and lymph nodes, were positive. In two of the three animals, donor DNA was present at more than one site. As reported before (1), no cells were detected with immunocytochemistry. Three additional heart recipients (group 2) also were administered 180 J.Lg/kglday rmGM-CSF (n=2) or 250 J.Lg/kglday rhG·CSF (n= 1) for 14 days (day 0-13l. Four of six spleen or lymph node samples contained donor DNA (Table 1) and two of these (in a GM-CSF-treated animal) were positive with immunocytochemistry. Although not conclusive, the greater yield from the spleen and lymph nodes of the growth factortreated heart recipients was consistent with our speculation (1) that the better control of rejection in liver transplant recipients treated with G-CSF reported by Foster et a1. (4) was due to an augmentation of spontaneous chimerism. In rats submitted to liver replacement (group 3), three of six samples from the spleen or a lymph node tested positive for donor DNA (Table 1l. In animal 357, the donor DNA was found only in the bone marrow (footnote d in tablel. Donor bone marrow infusion (group 4) produced the most ubiqui· tous chimerism of any kind of allograft with or without ! _,'Towth factor therapy: 13 of 15 samples wer.e positive I Table 1) .