Human cytotoxic CD8(+) T-lymphocyte clones engraft in severe combined immunodeficient (SCID) mice but show diminished function

Mice with severe combined immunodeficiency (SCID) provide an in vivo model for studying interactions between human tumor cells and effector cells of the immune system. We studied the behavior of human alloreactive cytotoxic T lymphocytes (CTLs) in SCID mice, including the migration pattern of CD8(+) or CD4(+) CTL clones to various murine tissues, their engraftment in the absence or presence of recombinant human interleukin 2 (rhIL-2) compared with the engraftment of lymphokine activated killer (LAK) cells, and the in vitro as well as the in vivo function of the engrafted CTL clones. The polymerase chain technique using T-cell-receptor-gamma specific primers revealed the presence of human CD8(+) CTL clones in the blood, lungs, and liver of mice receiving rhIL-2 for 14 days, for at least 18 days after intravenous inoculation. Human T cells were transiently detected in the bone marrow, lymph nodes, thymus, and spleen. Although the three CD8+ CTL clones and two CTL lines tested required rhIL-2 for their engraftment, the four LAK cell populations also engrafted in the absence of rhIL-2. In contrast to CD8(+) T cells, only low frequencies (<1%) of CD4(+) cells could be detected in the blood of the SCID mouse. Engrafted human T cells recovered from the murine blood showed absent or diminished cytotoxicity in vitro against human target cells in five or six experiments, respectively. In addition, when the antitumor activity of engrafted CD8(+) clones was investigated in vivo using a xenotransplantation model of human B-cell lymphoma in SCID mice, no significant prolongation of the mean survival time of six treated animals was observed compared with animals treated with rhIL-2 alone. Our results illustrate that although in vitro primed and cultured human CD8(+) T cells engraft in SCID mice, their in vitro and in vivo function is impaired.