Rapid lymphocyte reconstitution of unconditioned immunodeficient mice with non-self-renewing multipotent hematopoietic progenitors

Abstract

The replacement of abnormal hematopoietic stem cells (HSCs) with normal transplanted HSCs can correct a wide range of hematologic disorders. Here, we provide evidence that transplantation of more differentiated progenitor cells can be used to more rapidly correct lymphoid deficiencies in unconditioned immunocompromised mice. Transplantation of flk2+ multipotent progenitors led to robust B and T cell reconstitution that was maintained for at least 16 weeks. Antigenic challenge at 16 weeks post-transplantation revealed that reconstituted lymphocytes maintained a functional repertoire. In contrast to the persistent lymphocytic engraftment, myeloid chimerism was lost by 12 weeks post-transplantation consistent with the fact that flk2+ progenitors are non-self-renewing. Thus, while more differentiated progenitors are capable of rescuing lymphoid deficiencies, transplantation of HSCs must be used for the correction of non-lymphoid disorders, and, we propose, very long-term immune reconstitution. Based on recent evidence, we discuss novel strategies to achieve the replacement of abnormal HSCs without the use of cytotoxic conditioning regimens.

Figure 1. Rapid B cell and transient granulocyte reconstitution after transplantation of non-self-renewing multipotent progenitor cells in unconditioned immunodeficient animals

Unconditioned CD45.2+ RAG2^−/− γc^−/− animals were transplanted with 180 CD45.1+ c-kit+ lineage− Sca-1+ CD34+ flk2+ (KLS flk2+) or 500 c-kit+ lineage− Sca-1+ CD34− flk2− (HSC) cells and peripheral blood was analyzed for donor contribution at 3 and 12 weeks post-transplantation. Representative plots for KLS flk2+ cell-transplanted animals (n=5) and HSC-transplanted animals (n=14) are shown. Donor B lymphocytes were identified as CD45.1+ CD45.2− CD45R+ CD11b− cells. Donor granulocytes were identified as CD45.1+ CD45.2− CD45R− CD11b+ side scatterhigh cells. The subset of cells upon which each plot is gated is listed above every column.

Figure 2. Functional donor lymphocytes persist after transplantation of non-self-renewing progenitor cells

Unconditioned RAG2^−/−γc^−/− mice were transplanted with 180 KLS FLK2+ cells from wild type mice and immunized with 100µg of the T-dependent antigen NP-CGG 14 weeks after transplantation. NP-specific antibody levels were measured 1 week after immunization in 5 mice that had been immunized and 1 wild type untransplanted mouse that had not been immunized. Serum from each mouse was tested in triplicate and the standard deviations for each sample are shown. ND=not detectable.