Polymorphic Sirpa is the genetic determinant for NOD-based mouse lines to achieve efficient human cell engraftment

Abstract

Key Points• NOD-specific Sirpa polymorphism is the genetic determinant of highly efficient xenograft activity in NOD-based immunodeficient mouse models.Current mouse lines efficient for human cell xenotransplantation are backcrossed into NOD mice to introduce its multiple immunodeficient phenotypes. Our positional genetic study has located the NOD-specific polymorphic Sirpa as a molecule responsible for its high xenograft efficiency: it recognizes human CD47 and the resultant signaling may cause NOD macrophages not to engulf human grafts. In the present study, we established C57BL/6.Rag2 nullIl2rgnull mice harboring NOD-Sirpa (BRGS). BRGS mice engrafted human hematopoiesis with an efficiency that was equal to or even better than that of the NOD.Rag1 nullIl2rgnull strain, one of the best xenograft models. Consequently, BRGS mice are free from other NOD-related abnormalities; for example, they have normalized C5 function that enables the evaluation of complement-dependent cytotoxicity of antibodies against human grafts in the humanized mouse model. Our data show that efficient human cell engraftment found in NOD-based models is mounted solely by their polymorphic Sirpa. The simplified BRGS line should be very useful in future studies of human stem cell biology. (Blood. 2013;121(8):1316-1325) IntroductionImmunodeficient mice are widely used to reconstitute human hematopoiesis by xenotransplantation of hematopoietic stem cells (HSCs). 1,2 This "humanized" mouse model provides a powerful tool with which to evaluate the biologic properties of human HSCs and progenitors in vivo. 3,4 Such xenotransplantation systems have also been used to study human cancer stem cells. [5][6][7][8] Elimination of the lymphoid system is the first step to achieving reconstitution of human hematopoiesis. To deplete T and B cells, the scid mutation in the Prkdc gene [9][10][11] or disruption of the recombination activating gene 1 or 2 (Rag1 and Rag2) 12,13 has been introduced into various mouse strains. In addition, to deplete natural killer (NK) cells or their functions, the IL-2 receptor common ␥ chain subunit (Il2rg) [14][15][16] or beta-2-microglobulin (B2m) [17][18][19] is disrupted.However, depletion of lymphoid cells is not sufficient and it has been shown empirically that additional strain-specific factors modulate human hematopoietic engraftment in the xenotransplantation setting. For example, within the SCID strain, the SCID with the NOD background was the gold standard for the xenotransplantation assay based on its high efficiency. 11 In fact, recent studies have shown that among the lymphoid-depleted mouse strains, the NOD-scid Il2rg null (NSG/NOG) 14,15 and NOD.Rag1 null Il2rg null (NOD-RG) 20 strains are the most efficient; the BALB/c.Rag2 null Il2rg null (BALB-RG) strain is the next efficient 21,22 ; and the C57BL/6 strains with scid, 23 Rag2 null , Rag2 null B2m null , Rag2 null Prf null , 24 or Rag2 null Jak3 null25 mutations are unable to reconstitute human hematopoiesis. The NOD strain has multiple immune deficiencies, ...

BLT-humanized C57BL/6 Rag2−/−γc−/−CD47−/− mice are resistant to GVHD and develop B- and T-cell immunity to HIV infection

“…18,19 Various methods have been used to surmount the problem of mouse SIRPa-human CD47 incompatibility to produce humanized mice in non-NOD strains. Legrand et al 20 showed that transgenic expression of mouse CD47 on human HSC facilitated engraftment in a BALB/c Rag2 17 successfully surmounted this obstacle in a HIS model using DKO mice expressing a NOD SIRPa transgene. These studies indicate that the lack of tolerization of the phagocytic compartment in C57BL/6 mice is an important barrier to successful humanization.…”

“…by guest www.bloodjournal.org From C57BL/6 mice express a form of the signal recognition protein a (SIRPa) receptor that does not recognize human CD47. 16,17 SIRPa-CD47 recognition transmits antiphagocytic signals necessary to prevent engulfment and clearance of transplanted human cells by macrophages. 18,19 Various methods have been used to surmount the problem of mouse SIRPa-human CD47 incompatibility to produce humanized mice in non-NOD strains.…”

Human Hematopoietic Reconstitution and HLA-Restricted Responses in Nonpermissive Alymphoid Mice

“…In addition, SIRPa was shown to express different alleles in both human and mice populations (11). Consistent with this function, the ability of NOD immune-deficient hosts to promote immune reconstitution upon hHSC engraftment was attributed to better xenogeneic hCD47/mouse SIRPa recognition, leading to the inhibition of human donor cell destruction by murine phagocytes both in vitro and in vivo (11,29).…”

Innate Response to Human Cancer Cells with or without IL-2 Receptor Common γ-Chain Function in NOD Background Mice Lacking Adaptive Immunity

“…CD47 binds to sirpa to send a signal inhibiting phagocytosis by self-macrophages. Although mouse macrophages basically eliminate xenogeneic cells due to inability of xenogeneic CD47 to bind to mouse sirpa, human CD47 can bind to sirpa encoded by the NOD-derived allele to avoid elimination of human cells by the NOD background macrophages (5,6). Resembling hepatic metastases of HCT116 cells transferred to NOG hosts in the present study, reconstitution of human platelets and erythrocytes in the periphery was suppressed by host macrophages in contrast to that of leukocytes in the periphery and of all lineages of hematopoietic cells in the marrow in NOG hosts in previous studies (20,21).…”

“…IL-2Rg c signaling is required for development of NK cells and a subset of dendritic cells (DCs) producing IFN-g represented by the CD11c + B220 + CD122 + phenotype (3,4). The allele of Sirpa gene in the NOD background mice allows human CD47 to bind to the encoded signal regulatory protein a (sirpa) to inhibit macrophage phagocytosis of human cells (5,6). The details of how such alteration in innate immunity contributes to the engraftment are of considerable interest but still remain to be elucidated.…”