Comparison of human fetal liver, umbilical cord blood, and adult blood hematopoietic stem cell engraftment in NOD-scid/γc^−/−, Balb/c-Rag1^−/−γc^−/−, and C.B-17-scid/bg immunodeficient mice

Abstract

Immunodeficient mice bearing components of a human immune system present a novel approach for studying human immune responses. We investigated the number, phenotype, developmental kinetics, and function of developing human immune cells following transfer of CD34⁺ hematopoietic stem cell (HSC) preparations originating from second trimester human fetal liver (HFL), umbilical cord blood (UCB), or granulocyte colony-stimulating factor-mobilized adult blood (G-CSF-AB) delivered via intrahepatic injection into sublethally irradiated neonatal NOD-scid/γc^−/−, Balb/c-Rag1^−/−γc^−/−, and C.B-17-scid/bg mice. HFL and UCB HSC provided the greatest number and breadth of developing cells. NOD-scid/γc^−/− and Balb/c-Rag1^−/−γc^−/− harbored human B and dendritic cells as well as human platelets in peripheral blood, whereas NOD-scid/γc^−/− mice harbored higher levels of human T cells. NOD-scid/γc^−/− mice engrafted with HFL CD34⁺ HSC demonstrated human immunological competence evidenced by white pulp expansion and increases in total human immunoglobulin following immunization with T-dependent antigens and delayed-type hypersensitivity-infiltrating leukocytes in response to antigenic challenge. In conclusion, we describe an encouraging base system for studying human hematopoietic lineage development and function utilizing human HFL or UCB HSC-engrafted NOD-scid/γc^−/− mice that is well suited for future studies toward the development of a fully competent humanized mouse model.

Introduction

Immunodeficient mice harboring human cells or tissues, frequently referred to as “humanized mice,” are promising tools for studying complex processes in human biology. Mice bearing human immune systems, in particular, are being developed to investigate immune-mediated disease pathogenesis [1], [2] and allogeneic tissue rejection and tolerance in vivo[3], [4], [5]. Two decades ago, the original “SCID-hu” model was developed by McCune and co-workers using C.B-17-scid mice as recipients for human hematopoietic tissues including fetal liver, bone, and/or thymus originating from second-trimester human fetuses [6], [7], [8]. The engrafted human hematopoietic tissues gave rise to low levels of human T and B cells that were capable of producing a primary antibody response when autologous fetal skin, serving as an additional source of dendritic cells, was coengrafted along with thymus, bone marrow, and lymph node [9]. Adoptive transfer of peripheral blood mononuclear cells (PBMC) in this same mouse strain supported low levels of engraftment of T, B and dendritic cells [10]. Further compromising the innate immune system of C.B-17-scid animals by either introducing a beige mutation or crossing with mice of the NOD background allowed recipients to accept higher levels of mature human T and B cells [11], [12].

Two major technical advances enhance the applicability of humanized mice for studying the human immune system. First, isolated hematopoietic stem cells (HSC) engrafted in C.B-17-scid [[13], [14]] and NOD-scid mice [14]. Second, the development of more severely immunodeficient mouse lines lacking the common cytokine receptor gamma chain (γc) [15], [16] and thus more profoundly deficient in the innate immune system supported even higher levels of HSC engraftment and de novo differentiation of T, B, and dendritic cells [17]. Most recent work has centered on HSC engraftment in neonatal γc-deficient mice on either the NOD-scid[18] or the Balb/c-Rag1^−/−[19] background. Although such animals demonstrate varying levels of splenic lymphoid development, human immune system function is incomplete. Nevertheless, these systems offer great promise for routine use as humanized mouse models, especially if HSC can be reproducibly generated from embryonic stem cells [20], [21] or inducible pluripotent stem cells [22]. In addition to the requirement of severe defects in both innate and adaptive immunity in the recipient mouse, engraftment efficiency also appears dependent on the genetic background and age of the recipient mouse, route of engraftment and conditioning regime, and type and individual aliquot of injected HSC (for review, see [2]). We were interested in comparing the NOD-scid/γc^−/− and Balb/c-Rag1^−/−γc^−/− mouse strains for preparing humanized mice for our ongoing transplant immunology and disease pathogenesis studies. To this end, we performed a side-by-side comparison of the kinetics and breadth of the developing immune system following intrahepatic, neonatal transplantation using matched aliquots of HSC originating from human fetal liver (HFL), umbilical cord blood (UCB), and granulocyte colony-stimulating factor-mobilized adult blood (G-CSF-AB) in NOD-scid/γc^−/− and Balb/c-Rag1^−/−γc^−/− mice and also considered engraftment of our currently utilized strain, C.B-17-scid/bg.