In this study, we propose an enzymatically crosslinked hyaluronic acid (HA) hydrogel with tunable mechanical strength and gelation rate as a novel injectable system. The hydrogel composed of HA--tyramine conjugate (HA--Tyr) was formed using the oxidative coupling of tyramine moieties catalyzed by hydrogen peroxide (H 2 O 2 ) and horseradish peroxidase (HRP). The mechanical strength of the HA--Tyr hydrogel was tuned solely by the H 2 O 2 amount without affecting the gelation rate. The hydrogels formed more rapidly with increasing HRP concentration and the gelation time ranged from 1 s to 20 min. A faster gelling system yielded more localized gel formation than a slower gelling one at the site where it was administered through subcutaneous injection. Studies on the swelling ratio and scanning electron microscopy images of the hydrogel structure further demonstrated that the crosslinking density was controlled by the concentration of H 2 O 2 used. The mechanical strength of HA--Tyr hydrogels strongly affected the degradation rate in the presence of hyaluronidase in vitro; hydrogels degraded more slowly with increasing mechanical strength of the hydrogel. The independently tunable mechanical strength and gelation rate achieved by this enzymatically formed HA--Tyr hydrogel system will provide great advantages to a wide range of applications of injectable hydrogels, such as drug delivery and tissue regeneration.

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GALT can be subdivided into several compartments: (a) Peyer's patches (PP); (b) lamina propria (LP); and (c) intraepithelial leukocyte (IEL) spaces. The B-cell follicles of PP are quiescent in neonatal and germ-free (GF) adult mice. Germinal centers (GC), including sIgA+ blasts, appear in the B follicles of formerly GF adult mice about 10-14 days after monoassociation with various gut commensal bacteria. The GC wax and wane over about a 3-week period, although the bacterial colonizers remain in the gut at high density. Neonatal mice, born of conventionally reared (CV), immunocompetent mothers, display GC reactions in PP postweaning, although pups of SCID mothers display precocious GC reactions at about 14 days of life. Normally, gut colonization of neonates with segmented filamentous bacteria (SFB) leads to explosive development of IgA plasmablasts in LP shortly after weaning. Commensal gut bacteria and the immunocompetency of mothers also appears to control the rate of accumulation of primary B cells from “virgin” B cells in neonates. Enteric reovirus infection by the oral route can cause the activation of CD8+ T cells in the interfollicular regions of PP and the appearance of virus-specific precursor cytotoxic T lymphocytes (pCTL) in the IEL spaces. Such oral stimulation can also lead to “activation” of both CTL and natural killer (NK) cells in the IEL spaces. More normally, colonization of the gut with SFB also leads to similar activations of NK cells and “constitutively” cytotoxic T cells.

In this report, we show that expression of a NUP98-PHF23 (NP23) fusion, associated with acute myeloid leukemia (AML) in humans, leads to myeloid, erythroid, T-cell, and B-cell leukemia in mice. The leukemic and pre-leukemic tissues display a stem cell-like expression signature including Hoxa, Hoxb, and Meis1 genes. The PHF23 PHD domain is known to bind H3K4me3 residues, and chromatin immunoprecipitation experiments demonstrated that the NP23 protein bound chromatin at a specific subset of H3K4me3 sites, including Hoxa, Hoxb, and Meis1. Treatment of NP23 cells with disulfiram, which inhibits the binding of PHD domains to H3K4me3 residues, rapidly and selectively killed NP23 myeloblasts; cell death was preceded by decreased expression of Hoxa, Hoxb, and Meis1. Furthermore, AML driven by a related fusion gene, NUP98-JARID1A (NJL), was also sensitive to disulfiram. Thus, the NP23 mouse provides a platform to evaluate compounds that disrupt binding of oncogenic PHD proteins to H3K4me3.