Human peripheral blood leukocytes transplanted on CB17 scid-scid mice are transferred to their offspring.

Severe combined immunodeficient (scid) mice are deficient in functional T cells and B cells. Hence, scid mice reconstituted with human peripheral blood leukocytes (scid-huPBL) provide an excellent model for analysis of the human immune response under in vivo conditions. We have investigated this model further by analyzing human immune responses in the progeny of scid-huPBL (termed scid-humo). We find markedly elevated levels of human immunoglobulins (Ig) in the serum of scid-humo for more than 12 weeks indicating materno-fetal transfer of human B lymphocytes. Consistent with this finding we obtained evidence for the existence of human lymphocytes in scid-humo. Murine Ig levels in scid-humo were also elevated and surface Ig-expressing cells (probably B cells) were demonstrable. In this respect scid-humo resembled "leaky" scid. In contrast to "leaky" scid, scid-humo accepted transfer of human blood leukocytes. Not only leukocytes from autologous but also those from heterologous donors were accepted. Human Ig levels in scid-humo increased more rapidly as compared to normal scid mice. Thus, despite these increased B cell activities in scid-humo, transferred human leukocytes were not affected indicating that materno-fetal transfer of human cells had caused tolerization or conditioning. This is in contrast to scid mice in which elevated Ig levels correlate with increased failure rates of reconstitution with human blood leukocytes. We propose that scid-humo provide an improved model for studying the human immune responses in an in vivo setting.