Expression, Clinical Significance, and Receptor Identification of the Newest B7 Family Member HHLA2 Protein

Clin Cancer Res. 2015 May 15;21(10):2359-66. doi: 10.1158/1078-0432.CCR-14-1495. Epub 2014 Dec 30.


Purpose: HHLA2 (B7H7/B7-H5/B7y) is a newly identified B7 family member that regulates human T-cell functions. However, its protein expression in human organs and significance in human diseases are unknown. The objective of this study was to analyze HHLA2 protein expression in normal human tissues and cancers, as well as its prognostic significance, to explore mechanisms regulating HHLA2 expression, and to identify candidate HHLA2 receptors.

Experimental design: An immunohistochemistry protocol and a flow cytometry assay with newly generated monoclonal antibodies were developed to examine HHLA2 protein. HHLA2 gene copy-number variation was analyzed from cancer genomic data. The combination of bioinformatics analysis and immunologic approaches was established to explore HHLA2 receptors.

Results: HHLA2 protein was detected in trophoblastic cells of the placenta and the epithelium of gut, kidney, gallbladder, and breast, but not in most other organs. In contrast, HHLA2 protein was widely expressed in human cancers from the breast, lung, thyroid, melanoma, pancreas, ovary, liver, bladder, colon, prostate, kidney, and esophagus. In a cohort of 50 patients with stage I-III triple-negative breast cancer, 56% of patients had aberrant expression of HHLA2 on their tumors, and high HHLA2 expression was significantly associated with regional lymph node metastasis and stage. The Cancer Genome Atlas revealed that HHLA2 copy-number gains were present in 29% of basal breast cancers, providing a potential mechanism for increased HHLA2 protein expression in breast cancer. Finally, Transmembrane and Immunoglobulin Domain Containing 2 (TMIGD2) was identified as one of the receptors for HHLA2.

Conclusions: Wide expression of HHLA2 in human malignancies, together with its association with poor prognostic factors and its T-cell coinhibitory capability, suggests that the HHLA2 pathway represents a novel immunosuppressive mechanism within the tumor microenvironment and an attractive target for human cancer therapy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • 3T3 Cells
  • Amino Acid Sequence
  • Animals
  • CD28 Antigens / chemistry
  • CD28 Antigens / metabolism
  • Cell Line, Tumor
  • DNA Copy Number Variations
  • Female
  • Gene Expression
  • Glycosylation
  • Humans
  • Immunoglobulins / genetics
  • Immunoglobulins / metabolism*
  • Lymphatic Metastasis
  • Mice
  • Middle Aged
  • Molecular Sequence Data
  • Protein Processing, Post-Translational
  • Triple Negative Breast Neoplasms / metabolism*
  • Triple Negative Breast Neoplasms / pathology


  • CD28 Antigens
  • HHLA2 protein, human
  • Immunoglobulins
  • TMIGD2 protein, human