The fate of human peripheral blood lymphocytes after transplantation into SCID mice

Human peripheral blood lymphocytes (hu-PBL) can be adoptively transferred by intraperitoneal injection into mice with severe combined immunodeficiency (SCID). The transplanted lymphocytes can produce immunoglobulin (Ig), respond to antigens, and survive for months in this chimeric model (hu-PBL SCED). However, whether the lymphocytes actually repopulate and reconstitute lymphoid structures and organs has been subject of some debate. To address this question and to characterize the hu-PBL SCID model better, we employed a novel technique for the identification of human cells in xenogeneic mice. We used fluorescence in situ hybridization (FISH) with a biotinylated DNA probe to all human centromeres. We demonstrated that FISH could be used to detect human cells when they accounted for less than 1 % of human/mouse cell mixtures; it could also be employed for the identification and localization of individual human cells in tissue sections. By using FISH, we studied 31 SCID mice injected with 1.5 × 10⁷ ?4 × 10⁷ hu-PBL via intravenous (i.v.) or intraperitoneal (i.p.) routes. In the 6 i.v -injected mice, we found that the human cells were removed from the circulation into the lung within 1 h. In 22 of 25 i.p -injected animals, 90–3716 μg/ml of human IgG was found in the sera at 3 to 13 weeks after transplantation (a.t.). Human cells colonized the peritoneal cavity and persisted for up to 13 weeks a.t. and, in the 12 mice studied, accounted for 4 % to 57 % of the cells in the peritoneal fluid. However, only rare, isolated human cells were found in the spleen, blood, bone marrow, lung or Peyer's patches. In 7 of 19 mice that received hu-PBL i.p. from Epstein-Barr virus-seropositive donors, we found masses of human cells usually beneath the peritoneal lining but sometimes infiltrating normal tissue. We conclude that FISH offers a simple means for accurate identification of human cells in the xenogeneic mouse. Although there is colonization of the peritoneal cavity in most mice, and development of lymphoid masses in some, there is no reconstitution of lymphoid structures and only minimal engraftment of lymphoid organs by human cells in conventionally-prepared hu-PBL SCID constructs.