Leucyl-leucine methyl ester treatment of donor cells permits establishment of immunocompetent parent → F₁ chimeras that are selectively tolerant of host alloantigens

Treatment of murine lymphocytes wtih L-leucyl-L-leucine methyl ester (Leu-Leu-OMe) selectively removes natural killer cells, cytotoxic T lymphocyte precursors, and the capacity to cause lethal graft-vs-host disease, whereas bone marrow stem cell function and alloantigen-induced L3T4⁺ T helper function remains intact. The present studies assess the immunocompetence of allogeneic bone marrow chimeras established by reconstituting irradiated (C57BL/6 x DBA/2)F₁ (B6D2F₁) mice with Leu-Leu-OMe-treated C57BL/6 (B6) bone marrow and spleen cells. Spleen cells from such chimeras were found to have normal B and T cell mitogenic responses. Furthermore, levels of natural-killer cell function were comparable to those observed in B6 → B6 syngeneic radiation chimeras established without Leu-Leu-OMe treatment of donor cells. Spleen cells from B6 → B6D2F₁ mice were identical with B6 → B6 or B6 mice in allostimulatory capacity and thus contained no discernible cells of non-H-2(b) phenotype. Whereas B6 → B6D2F₁ spleen cells demonstrated alloproliferative and allocytotoxic responses toward H-2(k) bearing spleen cells, no H-2(d) specific proliferative or cytotoxic responses could be elicited. B6 → B6D2F₁ spleen cells did not suppress the generation of anti-H-2(d) or anti-H-2(k) proliferative or cytotoxic responses from control B6 spleen cells. Furthermore, addition of rat concanavalin A supernatants did not reconstitute anti-H-2(d) responses of B6 → B6D2F₁ chimeric spleen cells. Thus, Leu-Leu-OMe treatment of B6 donor cells not only prevents lethal graft-vs-host disease, but also permits establishment of long-lived parent→F₁ chimeras that are selectively tolerant of host H-2 disparate alloantigens, but fully immunocompetent with respect to natural killer cell function, B and T cell mitogenesis, and anti-third party alloresponsiveness.