Mice xenotransplanted with human cells and/or expressing human gene products (also known as “humanized mice”) recapitulate the human evolutionary specialization and diversity of genotypic and phenotypic traits. These models can provide a relevant in vivo context for understanding of human‐specific physiology and pathologies. Humanized mice have advanced toward mainstream preclinical models and are now at the forefront of biomedical research. Here, we considered innovations and challenges regarding the reconstitution of human immunity and human tissues, modeling of human infections and cancer, and the use of humanized mice for testing drugs or regenerative therapy products. As the number of publications exploring different facets of humanized mouse models has steadily increased in past years, it is becoming evident that standardized reporting is needed in the field. Therefore, an international community‐driven resource called “Minimal Information for Standardization of Humanized Mice” ( MISHUM ) has been created for the purpose of enhancing rigor and reproducibility of studies in the field. Within MISHUM , we propose comprehensive guidelines for reporting critical information generated using humanized mice.

The toxicity of preparative regimens render neonatal bone marrow transplantation (BMT) for progressive childhood diseases a controversial treatment. Ablative BMT in neonatal mice with or without the lysosomal storage disease mucopolysaccharidosis type VII (MPS VII) show high morbidity and developmental disruption of both brain and bone structure. In this investigation, BMT was performed with a high dose of congenic, normal bone marrow into nonablated newborn mice. Recipients had lifelong, multilineage, peripheral blood chimerism with the donor ␤-glucuronidase-positive (GUS ؉ ) cells that was both well tolerated and therapeutic. Three daily injections of normal adult marrow increased the average life span by at least 6 months and corrected the functional breeding deficits typical of the MPS VII mice. Twelve months after injection, several structural features of femurs were more like that of normal mice than of untreated MPS VII mice. Periosteal circumference and bone cortical thickness were significantly improved in males and cortical density did not differ significantly from values in normal females. Signifi- IntroductionA growing number of genetic disorders respond therapeutically to bone marrow transplantation (BMT). 1,2 BMT can restore immune function 3 and stabilize multiple forms of anemia and hemoglobinopathies. 4 For some metabolic diseases, myeloablative transplantation with normal hematopoietic tissues delivers cells carrying protein that, by cross-correction, stabilize cellular biochemistry and alleviate disease in surrounding tissues. A significant proportion of diseases that respond to BMT, such as the lysosomal storage diseases, 5 are highly progressive in nature and show improved response when BMT is performed early in development. [6][7][8][9] When treatment occurs in the first few years of life, BMT halts progressive neuropsychological retardation 10 and can reverse the hepatosplenomegaly and corneal clouding 1 commonly observed in the lysosomal storage diseases. Currently, most transplantation protocols use chemical ablative preparatory regimens to obtain high levels of engraftment. These techniques are highly toxic in the neonatal period and can cause developmental malformations as well as increased mortality. 8,11 Optimization of the transplantation regimen as well as donor cell type (both ontologically and phenotypically) are clearly paramount to the successful treatment of young children with life-threatening genetic disorders.The homing and engraftment of donor hematopoietic stem cells (HSCs) in the rapidly expanding and developing neonatal environment is not well understood. Early experiments in murine adult BMT led to the hypothesis that HSC reside in marrow "niches" that require "opening" with irradiation or cytoreductive reagents. 12 This idea was supported by experiments performed without marrow ablation that showed poor engraftment of donor cells. [13][14][15] The concept of the HSC "niche" was put into question when Brecher and colleagues 16 successfully engrafted male donor cells i...

The aerobic nitrogen-fixing cyanobacterium, Cyanothece sp. BH68K produces non-mucoid variants defective in exopolysaccharide (EPS) production at a high frequency. The EPS-producing wild-type colonies (EPS(+)) have a characteristic smooth and shiny appearance which allows them to be easily distinguished from the EPS(-) variants. When grown on agar plates lacking a source of combined nitrogen, the EPS(-) variants exhibited a yellow phenotype typical of nitrogen starvation. These EPS(-) variants showed varying degrees of reversion back to the EPS(+) phenotype. After reversion, they exhibited normal diazotrophic growth on agar plates. Alcian blue and ruthenium red staining indicated that the EPS is an acidic polysaccharide, which is present as a loose network around the cell, and which can be completely removed by low speed centrifugation. The accumulation of EPS takes place mainly during the stationary phase. All EPS(-) variants failed to produce any EPS. Analysis of growth of wild-type and EPS(-) variants revealed that EPS production is beneficial for diazotrophic growth on solid medium, but not in liquid medium. In addition, EPS phenotypic alteration may have some advantage in the dispersal of cells from one place to another in the natural environment.

Lysosomal storage diseases (LSDs), due to deficiency of a lysosomal enzyme, are inherited, progressive disorders that are often fatal during childhood. The mucopolysaccharidoses (MPS) are LSDs caused by deficiency of a lysosomal enzyme needed for the stepwise degradation of glycosaminoglycans. A murine model of MPS VII shares many clinical, biochemical, and pathologic features with human MPS and has proved valuable for the study of the pathophysiology of MPS and for evaluation of therapies for LSDs. Early therapy of MPS VII mice, initiated in the first weeks of life, is much more effective in decreasing clinical and morphologic evidence of disease than treatment begun in mature animals. Whether such early therapy decreases existing storage or prevents its accumulation is incompletely investigated. We performed an analysis of storage in very young MPS VII mice to define the extent of disease at and before the time of initiation of early treatments. MPS VII pups from 12 days postcoitus (dpc) to 31 days postnatal (dpn) were studied. Storage accumulated in fixed tissue macrophages in the liver and cartilage as soon as 12 dpc and was present in central nervous system glia, leptomeninges, and perivascular cells by 15 dpc. Osteoblast and primitive neocortical cell storage was apparent at 18 to 19 dpc. At 2 dpn, lysosomal distention appeared in circulating leukocytes. Abundant lysosomal storage was present in many sites by 14 dpn. Secondary accumulation of beta-hexosaminidase paralleled increasing glycosaminoglycan storage. These results confirm the presence of widespread storage even in utero and in the very young MPS VII mouse and highlight the importance of early treatment to prevent storage accumulation.