HIGH-LEVEL FUNCTIONAL ENGRAFTMENT OF SEVERE COMBINED IMMUNODEFICIENT MICE WITH HUMAN PERIPHERAL-BLOOD LYMPHOCYTES FOLLOWING PRETREATMENT WITH RADIATION AND ANTI-ASIALO G(M1)

The severe combined immunodeficient (SCID) mouse engrafted with human peripheral blood lymphocytes (PBLs) is a potentially useful model for the study of cancer immunotherapy. For this application, rapid, consis tent, and high level engraftment of SCID mice with functional human cy totoxic effector cells is necessary. To date, short term human lymphoi d cell engraftment in SCID mice has generally been low and variable. F urther, most of the human cells detected within the first 30 days are found in the peritoneal cavity. The purpose of the present study was t o improve short term reconstitution of human PBLs in the SCID mouse. W hen untreated SCID mice were injected with human PBLs, the mean level of CD3(+) cells in the spleens was <5% on days 6-32 after injection, a s determined by flow cytometry (FCM). Depletion of SCID mouse natural killer (NK) cells with anti-asialo G(M1) only marginally improved shor t term reconstitution with human CD3(+) cells. Preirradiation of SCID mice with 3 Gy improved reconstitution to over 16% CD3(+) cells on day s 12-14 following engraftment. However, the combination of pretreatmen t with anti-asialo G(M1) plus radiation, significantly increased the m ean percentage of human CD3(+) cells in the spleen to 40% within 2 wee ks following injection of PBLs. Human T cells positive for CD4, CD8, T cR alpha beta, and TcR gamma delta, and human NK and B cells were dete cted in the spleens of irradiated plus anti-asialo G(M1) pretreated SC ID mice. The presence of human lymphoid cells was confirmed by immunoh istologic staining. The human immune cells in these mice were shown to be functional by the in vivo demonstration of an appropriate secondar y immune response to the injection of tetanus toroid and by an in vivo proliferative response to phytohemagglutinin. Human NK cells could be found in the spleens and peripheral blood of irradiated plus anti-asi alo G(M1) pretreated mice. These cells were also shown to be competent by their ability to lyse the human NK sensitive tumor targets K562 an d MOLT-4 in Cr-51 release assays. Thus, pretreatment of SCID mice with radiation plus anti-asialo G(M1) significantly improves short term hu man PBL engraftment and provides a potentially useful model for the st udy of cancer immunotherapy.