Description
HHLA2: A Tumor-Associated Antigen and B7-Family Checkpoint
- Gene Information: HHLA2 (B7-H5/B7-H7) is on human chromosome 3q13.13 and encodes a type I transmembrane protein with three extracellular Ig-like domains (IgV-IgC-IgV), unlike other typical two-domain B7 members. It is absent in rodents.
- Protein Expression: HHLA2 is limited in normal tissues (mainly intestinal) and has low expression on human APCs. It is broadly overexpressed in multiple cancers (NSCLC, TNBC, melanoma, RCC, HCC, PDAC, urothelial), making it a promising tumor-associated antigen (TAA).
- Signaling Pathway: HHLA2 signals via TMIGD2 on naive T/NK cells for AKT-dependent co-stimulation, and via KIR3DL3 on activated/exhausted CD8⁺ T and CD56ᵈⁱᵐ NK cells for co-inhibition. Repeated activation shifts the balance toward KIR3DL3-mediated inhibition.
- Therapeutic Engagement: HHLA2-targeting strategies exploit either its checkpoint function (blocking HHLA2–KIR3DL3 to restore T/NK effector function) or its TAA properties (ADCs, bispecific engagers, CARs). Its absence in mice makes humanized HHLA2 mice essential for preclinical evaluation.
Targeting strategy
HHLA2
- The full coding sequences of human HHLA2 gene that is driven by human HHLA2 promoter are inserted into mouse Gt(ROSA)26Sor locus in B-hHHLA2 mice.
HHLA2 mRNA Expression Analysis by RT-PCR
Strain specific analysis of HHLA2 mRNA expression in wild-type C57BL/6JNifdc mice and homozygous B-hHHLA2 mice by RT-PCR. Small intestine RNA was isolated from wild-type C57BL/6JNifdc mice (+/+) and homozygous B-hHHLA2 mice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with human HHLA2 primers. Sequencing of the PCR products confirmed that the amplified sequences were consistent with database reference sequences.
HHLA2 Protein Expression by WB
Strain specific HHLA2 expression analysis in homozygous B-hHHLA2 mice by western blot. The colon, spleen, lung, stomach and small intestine samples were collected from wild-type C57BL/6JNifdc mice (+/+) and homozygous B-hHHLA2 mice (H/H) and then analyzed by western blot with the species-specific anti-human HHLA2 antibody (abcam, ab315994). 40 μg total proteins were loaded for western blotting analysis.
* When publishing results obtained using this animal model, please acknowledge the source as follows: The animal model [B-hHHLA2 mice] (Cat# 113732) was purchased from Biocytogen.
