Beyond PD-1? The Potential and Breakthroughs of the Emerging Immune Checkpoint BTLA

Immune checkpoint inhibitors, particularly those targeting the PD-1/PD-L1 pathway, have achieved groundbreaking progress in the field of cancer therapy. However, their limited response rates, the emergence of resistance, and insufficient efficacy in certain indications highlight the urgent need to explore new targets to enrich therapeutic strategies. Against this backdrop, B and T lymphocyte attenuator (BTLA), an inhibitory immune checkpoint with unique structural and functional characteristics, is garnering increasing attention.

Compared to classic checkpoints like PD-1, BTLA exhibits distinct differences in ligand selectivity, signal transduction mechanisms (such as HVEM-dependent bidirectional signaling), and its regulatory network across various immune cell types. Do these properties suggest that BTLA might overcome certain limitations of current therapies? Is its upregulation in the tumor microenvironment related to novel mechanisms of immune escape? Furthermore, does BTLA play a unique protective role in autoimmune diseases?

This article will systematically analyze the molecular basis, signaling network, and key functions of BTLA in various diseases including cancer, autoimmune disorders, and inflammation. It will also review the latest progress in drug development targeting BTLA, aiming to explore its potential to lead the next generation of immunotherapy innovations.

1. The Emerging Role of BTLA in Immune Regulation

2. Molecular Structure, Gene Locus, and Expression Pattern of BTLA

3. BTLA Signaling Pathways and Immune Regulatory Mechanisms

4. Functional Role of BTLA in Disease Pathogenesis

5. Latest Research Progress on BTLA-Targeting Drugs

6. BTLA Research Tools

1. The Emerging Role of BTLA in Immune Regulation

As an important inhibitory immune checkpoint of the B7-CD28 family, BTLA is expressed on T cells, B cells, NK cells, and myeloid cells. It limits excessive immune responses and maintains immune homeostasis by inducing negative signals. Compared to classic checkpoints like PD-1 and CTLA-4, BTLA possesses uniqueness in structural features, ligand selectivity, and bidirectional signaling, making its role in tumor immunity, autoimmune regulation, and inflammatory responses increasingly significant. Growing evidence indicates that abnormal BTLA expression or signaling imbalance may lead to impaired immune tolerance, immune exhaustion, or persistent tissue inflammation, thereby driving the progression of multiple diseases. Therefore, systematic research on BTLA's structure, signaling, and function is crucial for designing more precise immunotherapy strategies.

2. Molecular Structure, Gene Locus, and Expression Pattern of BTLA

2.1 Molecular Structure and Intracellular Signaling Motifs of BTLA

BTLA (B and T lymphocyte attenuator) mediates inhibitory signals through its intracellular ITIM and ITSM motifs ^[1]. The core sequence of ITIM contains a phosphorylated tyrosine followed by a hydrophobic residue, which is crucial for SH2 domain binding. Studies show BTLA primarily recruits the N-terminal SH2 domain (nSH2) of SHP1 via its ITIM, initiating the dominant inhibitory signal ^[2]. Further analysis indicates that the molecular volume of the residue at the pY+1 site in ITIM exhibits a bell-shaped dependence on SHP1 recruitment, and the conserved alanine in BTLA helps stabilize its specific binding to SHP1 ^[2].

In contrast, the ITSM of PD-1 is its primary functional motif, achieving selective recruitment through high-affinity binding to the C-terminal SH2 (cSH2) of SHP2, while its ITIM has a weak effect on SHP1 recruitment due to the presence of glycine at pY+1. Replacing this glycine with alanine can significantly enhance PD-1's binding to SHP1 ^[2]. These differences illustrate that subtle amino acid changes in structure can significantly influence the selectivity of checkpoint receptors for SHP1/2, thereby determining their immunosuppressive efficacy.

2.2 Expression Pattern and Regulatory Mechanisms of BTLA

BTLA is expressed on various immune cells, and its expression level is controlled by multiple factors including gene regulation, epigenetics, and intracellular regulators. For example, the T cell lineage protein THEMIS can restrict BTLA's inhibitory capacity, providing a "regulatory threshold" for T cell development ^[3]. Additionally, miR-155-5p affects BTLA expression in CLL B cells but does not have a significant impact in T cells ^[4].

2.3 HVEM, the Primary Ligand of BTLA, and Its Multi-Ligand Network

The primary ligand for BTLA is HVEM (TNFRSF14), a member of the tumor necrosis factor receptor family ^[5]. HVEM not only binds to BTLA but also interacts with various ligands such as LIGHT and CD160 ^[6], forming a complex network of co-stimulatory and co-inhibitory signals. HVEM-LIGHT/CD160 interactions can enhance the co-stimulatory function of HVEM, while BTLA-HVEM interaction primarily delivers inhibitory signals ^[6]. Research suggests an imbalance in the HVEM/BTLA axis in autoimmune diseases like RA and AITD ^[7]. Furthermore, this axis can achieve bidirectional signaling through cis or trans interactions; cis complexes can inhibit HVEM's co-stimulatory activity without affecting BTLA's inhibitory function, while trans binding is the main pathway for regulating T cell activation ^[8].

3. BTLA Signaling Pathways and Immune Regulatory Mechanisms

3.1 ITIM/ITSM Phosphorylation and SHP1/SHP2 Recruitment

Upon T cell activation, the ITIM and ITSM motifs of BTLA become phosphorylated, recruiting SHP1/2 and inhibiting early T cell activation events ^[1]. BTLA primarily relies on ITIM to recruit SHP1, whereas PD-1 prefers recruiting SHP2 via ITSM ^[2].

3.2 Impact of BTLA on T Cell Differentiation and Fate

SHP1/2 inhibit the differentiation of naïve T cells into both effector and central memory types, with SHP1 being the primary effector molecule ^[9]. BTLA expression shows an inverse relationship with CD5 expression. BTLA signaling can regulate CD5 levels in thymic and peripheral T cells, thereby affecting the T cell recognition threshold for self-antigens ^[8]. BTLA deficiency leads to RTE cells triggering multi-organ autoimmunity ^[8]. In memory CD8 T cell formation, BTLA/HVEM signaling has a positive co-stimulatory role; BTLA can act as a trans ligand promoting HVEM-dependent memory T cell development ^[10].

3.3 Regulation of B Cells, NK Cells, and Macrophages

BTLA has a potential role in BCR signal regulation and affects B cell activation. In NK cells, BTLA correlates with cytotoxicity levels and may influence their immune surveillance function in tumors ^[11]. In macrophages, BTLA expression is associated with M1/M0 infiltration patterns, but its molecular mechanisms require further investigation.

3.4 Cross-Regulation with Other Immune Checkpoints

BTLA, together with PD-1, CTLA-4, TIGIT, LAG-3, TIM-3, and others, constitutes a multidimensional immune regulatory network ^[12]. Their expression differences and functional specificity suggest that different checkpoints are not simply redundant in disease progression. In NSCLC and Sézary syndrome, multiple checkpoint receptors change concurrently but exhibit heterogeneous expression patterns ^[12]. Combined targeting strategies show that BTLA synergistically regulates immune tolerance with CTLA-4 and PD-1, demonstrating synergistic effects in transplant tolerance and autoimmune regulation ^[13]. Furthermore, BTLA expression in the tumor microenvironment can be linked to the CD47-macrophage axis, and exhausted BTLA+ CD4 T cells are closely associated with immune escape ^[14].

4. Functional Role of BTLA in Disease Pathogenesis

4.1 Tumor Immune Escape and BTLA

BTLA is upregulated in various tumors and is associated with immune exhaustion, disease progression, and poor prognosis. For example:

In NSCLC, high BTLA expression correlates with advanced tumor stage, lymph node invasion, and poorer OS/RFS ^[15].
In OSCC, BTLA shows strong positive correlation with checkpoints like PD-1/PD-L1 and CD96, participating in local immunosuppression ^[16].
In prostate cancer, high HVEM/BTLA expression indicates poor prognosis ^[17].
In CLL patients, elevated BTLA is associated with earlier time to treatment ^[10].
In MF/SS, BTLA is closely related to T cell exhaustion ^[12].

This evidence underscores the inhibitory role of BTLA in tumor immune escape and its value as a potential therapeutic target.

4.2 Protective Role of BTLA in Autoimmune Diseases

In autoimmune diseases, BTLA typically plays an inhibitory, protective role:

The BTLA 590C SNP is associated with RA susceptibility; the mutant BTLA loses its ability to inhibit IL-2 ^[11].
In SLE, HVEM levels decrease while BTLA remains stable, suggesting therapeutic potential for BTLA agonists ^[9].
In Sjögren's syndrome patients, the co-expression of BTLA/HVEM/CD160 in peripheral blood is significantly reduced, indicating dysregulation of the BTLA/HVEM axis ^[18].

4.3 Role of BTLA in Infectious Diseases and Inflammation

HVEM/BTLA signaling plays an important regulatory role in processes such as liver injury, intestinal immune homeostasis, and stem cell differentiation. For example:

MSCs expressing HVEM can inhibit immune responses and promote bone formation ^[19].
HVEM/BTLA deficiency leads to impaired hepatobiliary repair in a DDC-induced liver injury model and is associated with gut microbiota dysbiosis ^[20].

4.4 Protective Role of BTLA in Cardiovascular Diseases and Nephritis

In atherosclerosis, a BTLA agonist (3C10) can reduce follicular B2 cells, increase the proportion of regulatory cells, and enhance plaque stability ^[21].
In experimental crescentic glomerulonephritis, BTLA deficiency exacerbates the disease, while a BTLA agonist can inhibit Th1 cells and promote Tregs, thereby protecting renal function.

5. Latest Research Progress on BTLA-Targeting Drugs

Currently, the development of BTLA-targeting drugs shows distinct trends of strategic diversification and expansion into disease areas. Research entities are exploring the therapeutic potential of the BTLA target through various technological pathways, including monoclonal antibodies, small molecule drugs, recombinant proteins, and peptides. In terms of disease application, two clear directions have emerged: First, in the field of oncology, research is most active, especially for monoclonal antibody drugs targeting various solid tumors like lymphoma, non-small cell lung cancer, and melanoma. Among these, Junshi Biosciences' monoclonal antibody is at the leading clinical phase III stage. Second, in autoimmune diseases such as rheumatoid arthritis and atopic dermatitis, several projects have entered early clinical research stages. Overall, BTLA-targeting drugs are extending from cancer immunotherapy to a broader disease spectrum. Some pipelines under research are summarized in the table below:

Drug	Drug Type	Indications Under Research	Research Institution	Highest R&D Stage
Recombinant Humanized Anti-BTLA Monoclonal Antibody (Shanghai Junshi Biosciences)	Monoclonal Antibody	Classical Hodgkin Lymphoma \| Refractory Classical Hodgkin Lymphoma, etc.	Shanghai Junshi Biosciences Co., Ltd. \| Shanghai Pulmonary Hospital	Clinical Phase 3
GS-0272	Small Molecule	Rheumatoid Arthritis	Gilead Sciences, Inc.	Clinical Phase 1
Pegylated Recombinant Human Endostatin Injection (Simcere)	Recombinant Protein	Metastatic Non-Small Cell Lung Cancer	Simcere Biopharma Co., Ltd. \| China Pharmaceutical University \| Jiangsu Simcere Pharmaceutical Co., Ltd.	Clinical Phase 1
ANB-032	Monoclonal Antibody	Atopic Dermatitis	AnaptysBio, Inc.	Clinical Phase 1
HFB-200603	Monoclonal Antibody	Advanced Malignant Solid Tumors \| Colorectal Cancer \| Melanoma \| Non-Small Cell Lung Cancer \| Renal Cell Carcinoma \| Gastric Cancer	Hifibio SAS	Clinical Phase 1
MB-272	Monoclonal Antibody	Autoimmune Diseases	MiroBio Ltd.	Clinical Phase 1
HFB-200604	Monoclonal Antibody	Autoimmune Diseases	HiFiBio Therapeutics (Hangzhou) Co., Ltd.	IND Approved
CD160-Derived Peptide A5 (University of Gdańsk)	Synthetic Peptide	Immune System Diseases	University of Gdańsk	Preclinical
MG-B-28	Small Molecule	Tumors	Weill Cornell Medicine \| Mansoura University	Preclinical

(Data as of December 24, 2025, sourced from Synapse)

6. BTLA Research Tools

As a key immune checkpoint molecule, BTLA maintains immune homeostasis by regulating immune cell activity and plays a central role in the pathogenesis of various diseases including cancer, autoimmune disorders, and infections. It is considered a highly promising target for next-generation immunotherapy. Wuhan Huamei Biotech provides BTLA recombinant proteins, antibodies, and ELISA kits to support your related mechanism research and targeted drug development.

● BTLA Recombinant Protein

Recombinant Human B- and T-lymphocyte attenuator (BTLA), partial (Active); CSB-MP773799HU

Recombinant Human B- and T-lymphocyte attenuator(BTLA), partial (Active); CSB-MP773799HU1

Recombinant Macaca fascicularis B- and T-lymphocyte attenuator (BTLA), partial (Active); CSB-MP4897MOV

● BTLA Antibodies

BTLA Recombinant Monoclonal Antibody; CSB-RA773799MA1HU

● BTLA ELISA Kit

Human B- and T-lymphocyte attenuator(BTLA) ELISA kit; CSB-EL002868HU

References

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[2] Xiaozheng Xu, T. Masubuchi, Qixu Cai, Yunlong Zhao, E. Hui.(2021). Molecular features underlying differential SHP1/SHP2 binding of immune checkpoint receptors.

[3] Suzanne Mélique, Aurélie Vadel, Nelly Rouquié, Cui Yang, Cyrielle Bories, Coline Cotineau, Abdel Saoudi, N. Fazilleau, Renaud Lesourne.(2024). THEMIS promotes T cell development and maintenance by rising the signaling threshold of the inhibitory receptor BTLA.

[4] A. Kosmaczewska, L. Ciszak, Anna Andrzejczak, A. Tomkiewicz, Anna Partyka, Zofia Rojek-Gajda, Irena Frydecka, Dariusz Wołowiec, Tomasz Wróbel, A. Bojarska-Junak, Jacek Roliński, Lidia Karabon.(2025). miR-155-5p Silencing Does Not Alter BTLA Molecule Expression in CLL T Cells: Implications for Targeted Immunotherapy.

[5] Shane Atwell, T. Cheung, Elaine M Conner, Carolyn Ho, Jiawen Huang, Erin L Harryman, Ricky Lieu, Stacie Lim, Wai W Lin, Diana I Ruiz, Andrew C Vendel, Carl F Ware.(2025). Quantitative detection of the HVEM-BTLA checkpoint receptor cis-complex in human lymphocytes.

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[7] W. Hobo, W. J. Norde, N. Schaap, H. Fredrix, F. Maas, Karen Schellens, J. Falkenburg, A. Korman, D. Olive, R. van der Voort, H. Dolstra.(2012). B and T Lymphocyte Attenuator Mediates Inhibition of Tumor-Reactive CD8+ T Cells in Patients After Allogeneic Stem Cell Transplantation.

[8] Adeolu O. Adegoke, G. Thangavelu, Ting-Fang Chou, Marcos I. Petersen, K. Kakugawa, J. May, K. Joannou, Qingyang Wang, K. K. Ellestad, Louis Boon, Peter A. Bretscher, H. Cheroutre, Mitchell Kronenberg, T. Baldwin, Colin C. Anderson.(2024). Internal regulation between constitutively expressed T cell co-inhibitory receptors BTLA and CD5 and tolerance in recent thymic emigrants.

[9] Andrew C Vendel, L. Jaroszewski, Matthew D Linnik, Adam Godzik.(2024). B‐ and T‐Lymphocyte Attenuator in Systemic Lupus Erythematosus Disease Pathogenesis.

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[14] J. Chemnitz, R. Parry, K. Nichols, C. June, J. Riley.(2004). SHP-1 and SHP-2 Associate with Immunoreceptor Tyrosine-Based Switch Motif of Programmed Death 1 upon Primary Human T Cell Stimulation, but Only Receptor Ligation Prevents T Cell Activation1.

[15] Xiangmin Li, Zhaoguo Xu, Guoyuan Cui, Li Yu, Xiaoye Zhang.(2020). BTLA Expression in Stage I–III Non–Small-Cell Lung Cancer and Its Correlation with PD-1/PD-L1 and Clinical Outcomes.

[16] Minglei Yang, Chenxi Zheng, Yu Miao, Cuicui Yin, Longfei Tang, Chongli Zhang, Pu Yu, Qingfang Han, Yihui Ma, Shenglei Li, Guozhong Jiang, Wencai Li, Peiyi Xia.(2025). BTLA promoter hypomethylation correlates with enhanced immune cell infiltration, favorable prognosis, and immunotherapy response in melanoma.

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[19] Zhigang Rong, Fei Zhang, Zhengdong Wang, Weifeng He, S. Dong, Jianzhong Xu, F. Dai.(2018). Improved Osteogenesis by HVEM-Expressing Allogenic Bone Marrow-Derived Mesenchymal Stem Cells in an Immune Activation Condition and Mouse Femoral Defect Model.

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