• Gene Information: The human TFR1 gene is located on chromosome 3q29, containing multiple exons that encode transferrin receptor 1. It bears conserved iron-responsive elements for transcriptional control and maintains fundamental iron metabolism across mammalian tissues.
• Protein Expression: TFR1 membrane protein is abundant in proliferative cells with high iron demand. Its expression is boosted under iron deficiency, while excess iron triggers degradation to avoid toxic intracellular iron accumulation dynamically.
• Signaling Pathway: TFR1 coordinates iron homeostasis signaling with IRP1/IRP2. It binds circulating transferrin to import iron, and feedback signaling modulates its abundance to stabilize cellular iron levels under fluctuating iron supply.
• Therapeutic Inhibition: TFR1 (CD71) links to multiple diseases, including diverse malignancies, Alzheimer’s disease, iron-deficiency anemia and osteoarthritis. Tumors overexpress TFR1 to sustain rapid proliferation. Major therapies include TFR1-targeted ADCs, neutralizing antibodies triggering ADCC, bispecific antibodies crossing blood-brain barrier for CNS disorders, and iron chelators suppressing its iron uptake to curb lesion progression.

Gene targeting strategy for B-hTFR1 Mice Plus(C).

• The exons 4-19 of mouse Tfr1 gene that encode extracellular domain are replaced by human counterparts in B-hTFR1 Mice Plus(C). The genomic region of mouse Tfr1 gene that encodes cytoplasmic portion is retained.
• The promoter, 5’UTR and 3’UTR region of the mouse gene are also retained. The chimeric TFR1 expression is driven by endogenous mouse Tfr1 promoter, while mouse Tfr1 gene transcription and translation will be disrupted.

Strain specific TFR1 expression analysis in wild-type BALB/cCrSlcNifdc and heterozygous humanized B-hTFR1 mice plus(C) by flow cytometry. Bone marrow was collected from wild-type BALB/cCrSlcNifdc mice (+/+) and heterozygous B-hTFR1 mice plus(C) (H/+) and analyzed by flow cytometry. Protein expression was analyzed with anti-mouse CD71 antibody (Biolegend, 113808) and anti-human CD71 antibody (Biolegend, 334108) by flow cytometry. Mouse TFR1 was detectable in wild-type BALB/cCrSlcNifdc mice and heterozygous B-hTFR1 mice plus(C). Human TFR1 was exclusively detectable in heterozygous B-hTFR1 mice plus(C), but not in wild-type mice.

Western blot analysis of TFR1 protein expression in wild-type BALB/cCrSlcNifdc mice and homozygous B-hTFR1 plus (C) mice. Various tissues were collected from wild-type BALB/cCrSlcNifdc mice (+/+) and homozygous B-hTFR1 plus (C) mice (H/H) (female, 8-week-old) and then analyzed by western blot with an anti-TFR1 antibody (Abcam, ab214039). 40 μg total proteins were loaded for western blot analysis. GAPDH and β-actin were detected as internal controls. M, marker.

Frequency of leukocyte subpopulations by flow cytometry. Splenocytes (A), blood (B), and lymph node cells (C) were isolated from wild-type BALB/cCrSlcNifdc mice (female, n=3, 8-week-old) and homozygous B-hTFR1 plus (C) mice (female, n=3, 8-week-old). Flow cytometry analysis was performed to assess the frequency of leukocyte subpopulations. The frequencies of T cells, B cells, NK cells, DCs, neutrophils, monocytes, and macrophages in homozygous B-hTFR1 plus (C) mice were similar to those in wild-type BALB/cCrSlcNifdc mice. Humanization of TFR1 did not change the overall frequency or distribution of immune cell types in the spleen, blood, and lymph nodes. Values are expressed as mean ± SEM. Significance was determined by two-way ANOVA.

Frequency of T cell subpopulations by flow cytometry. Splenocytes (A), blood (B), and lymph node cells (C) were isolated from wild-type BALB/cCrSlcNifdc mice (female, n=3, 8-week-old) and homozygous B-hTFR1 plus (C) mice (female, n=3, 8-week-old). Flow cytometry analysis was performed to assess the frequency of T cell subpopulations. The frequencies of CD4+ T cells, CD8+ T cells, and Tregs in homozygous B-hTFR1 plus (C) mice were similar to those in wild-type BALB/cCrSlcNifdc mice. Humanization of TFR1 did not change the overall frequency or distribution of T cell types in the spleen, blood, and lymph nodes. Values are expressed as mean ± SEM. Significance was determined by two-way ANOVA.