CD37 Human

What is CD37 and what is its expression pattern in normal and malignant cells?

CD37 is a tetraspanin family protein predominantly expressed on the surface of mature B cells with B-cell receptor (BCR) expression. At the molecular level, CD37 is downregulated in plasma cells, which aligns with its diminished expression during terminal B-cell differentiation .

In malignancies, CD37 shows high expression in B-cell non-Hodgkin lymphoma (B-NHL) . Research has demonstrated its presence in diffuse large B-cell lymphoma (DLBCL), with expression varying significantly between molecular subtypes . More recent investigations have detected CD37 expression in acute myeloid leukemia (AML), providing potential new therapeutic avenues . CD37 has also been reported in specific T-cell lymphomas .

Methodologically, researchers should be aware that CD37 detection efficiency may vary depending on the antibody clone used, with HH1 antibody showing reliable detection in certain contexts .

How does CD37 expression correlate with other B-cell markers?

CD37 expression significantly correlates with other B-cell markers, most notably CD20 (MS4A1). Research has demonstrated both protein and mRNA level correlations between these markers:

• CD37 protein levels show significant correlation with CD20 protein levels (Spearman rank correlation: r = 0.209, P = 8.16e-6)

• CD37 mRNA levels correlate strongly with CD20 mRNA levels (r = 0.406, P = 3.40e-21)

• In DLBCL cell lines tested by flow cytometry, CD20 and CD37 protein levels demonstrated strong correlation (r = 0.771, P = 0.002)

This correlation likely reflects that both CD37 and CD20 are expressed in mature B cells with BCR and are downregulated in plasma cells. Notably, in six DLBCL cell lines (three CD20-/CD37- and three CD20+/CD37+), the correlation was confirmed using two different CD37 monoclonal antibodies (WR17, HH1) with linear regression R² = 0.9737 .

The table below illustrates gene expression changes in CD37- versus CD37+ DLBCL subtypes:

What methodological approaches are available for measuring CD37 expression?

Research protocols for CD37 detection include:

• Flow cytometry: The gold standard for protein-level detection on cell surfaces, using specific antibody clones like HH1 and WR17

• Immunohistochemistry (IHC): Applied to tissue sections for spatial context of expression

• mRNA expression analysis: Transcriptomic approaches including qPCR and RNA sequencing, with single-cell RNA-seq providing cellular resolution of expression patterns

• Western blotting: For total protein quantification and analysis

Each method provides different insights. For example, while bulk RNA-seq data from AML patients shows CD37 mRNA expression, protein detection by flow cytometry may be antibody-dependent . Single-cell RNA-seq analysis of 28,404 cells from 15 AML patients confirmed that CD37 mRNA is predominantly expressed in malignant cell populations .

How does CD37 expression impact clinical outcomes in lymphoma patients?

CD37 expression status serves as a significant prognostic marker in DLBCL. Research has demonstrated:

The prognostic impact persisted in multivariate analysis, indicating CD37 status provides additional prognostic information beyond established risk factors. Researchers investigating DLBCL patients should consider CD37 assessment as part of comprehensive molecular profiling.

What are the current approaches for targeting CD37 in CAR-T cell therapy?

Research on CD37-directed CAR-T cells has progressed significantly, with several approaches under investigation:

• Novel mouse monoclonal anti-CD37 CAR: Developed using clone 2B8D12F2D4 with high binding affinity (KD = 1.6 nM)

• Humanized CD37 CAR: Generated from humanized CD37 variable heavy (VH) and variable light (VL) chains, incorporating 4-1BB costimulatory and CD3 activation domains

• Bi-specific humanized CD37-CD19 CAR: Combines humanized CD37 ScFv and mouse CD19 FM63 ScFv for dual-targeting capabilities

Functionally, CD37 CAR-T cells demonstrated specific cytotoxicity against CD37-positive targets:

• Humanized CD37 CAR-T cells showed 95.3% ± 0.8% cytotoxicity against CHO-CD37 cells compared to 17.5% ± 1.3% for non-transduced T cells

• Bi-specific CD37-CD19 CAR-T cells effectively killed both CD37+ and CD19+ targets

• Both constructs showed activity in xenograft models, reducing tumor burden and increasing median survival

How does CD37 expression in AML compare to established AML targets?

Recent research has identified CD37 as a potential target in AML, with important comparisons to established targets:

• CD37 was detected in the majority of AML patient samples studied

• Comparison of CD37 to established AML targets CD33 and CD123 showed similar positivity levels on bulk AML populations

• CD37 expression was also detected in AML leukemic stem cell (LSC) populations

• Unlike CD33, CD37 protein expression showed excellent correlation with European LeukemiaNet (ELN) 2017 patient prognostic stratification

Single-cell RNA sequencing data from 15 AML patients further confirmed CD37 expression predominantly in malignant cell populations . This suggests CD37 may serve as a complementary or alternative target to established markers in AML therapeutic development.

What is the significance of CD37 negativity in DLBCL?

CD37 negativity in DLBCL is associated with:

The molecular mechanisms underlying these associations remain under investigation, but may involve altered cellular signaling networks and potential immune evasion strategies. Researchers should consider CD37 status when designing studies targeting BCR signaling pathways in lymphoma.

What antibody clones are most effective for detecting CD37 in research settings?

Several antibody clones have demonstrated efficacy in CD37 detection:

• HH1: Successfully used in AML research and validated for flow cytometry applications

• WR17: Employed alongside HH1 in DLBCL cell line characterization with strong concordance

• 2B8D12F2D4: Novel mouse monoclonal antibody with high binding affinity (KD = 1.6 nM) specifically recognizing surface CD37 in lymphoma cells but not in multiple myeloma or other cancer types

When designing flow cytometry experiments, researchers should consider:

• Clone selection based on application (flow cytometry vs. IHC)

• Potential variability in epitope recognition between antibodies

• The need for multiple confirmatory antibodies in critical experiments

The detection efficiency may be restricted to specific antibodies, as observed in AML research where certain clones were necessary for reliable detection .

What technical challenges exist in developing CD37-targeted therapies?

Researchers developing CD37-targeted therapies face several technical challenges:

• CAR-T cell viability: Studies have observed a 30-40% decrease in viability of CD37 CAR-T cells 12 days post-transduction, affecting expansion capabilities

• Target density variability: CD37 expression can vary significantly between cell types and disease states, requiring careful consideration of CAR avidity

• Dual-targeting approaches: With bi-specific constructs (e.g., CD37-CD19), optimizing balanced recognition of both targets poses design challenges

• Humanization requirements: Converting mouse-derived antibodies to humanized constructs for clinical application requires careful preservation of binding properties

Despite these challenges, research has demonstrated that even CD37-low cell lines can induce specific CAR responses, suggesting high functional avidity of certain constructs .

How might bi-specific CD37-CD19 targeting address current limitations in CAR-T therapies?

Bi-specific CD37-CD19 CAR-T cells represent an innovative approach to overcome limitations in single-target therapies:

• Antigen escape prevention: Targeting both CD37 and CD19 simultaneously could prevent relapse due to antigen loss of either target

• Enhanced targeting efficiency: Dual-targeting may improve recognition of heterogeneous tumor populations

• Expanded target range: Bi-specific CARs could potentially address both CD19+ and CD37+ malignancies with a single product

Experimentally, bi-specific humanized CD37-CD19 CAR-T cells have demonstrated:

• Effective killing of Raji cells (expressing both antigens)

• Specific targeting of single-antigen expressing cells (CHO-CD37 and Hela-CD19)

• No activity against control cells lacking both antigens (CHO and Hela)

Different bi-specific CAR designs have been reported, and future clinical studies will be needed to determine the advantages of various structural approaches .

What is the potential for CD37 targeting in AML treatment?

CD37 represents a promising novel target for AML therapy based on recent research findings:

• Widespread expression: CD37 was detected in the majority of AML patient samples across the disease spectrum

• LSC targeting: Expression in leukemic stem cell populations suggests potential for targeting disease-initiating cells

• Prognostic correlation: CD37 protein expression showed excellent correlation with ELN 2017 patient prognostic stratification

• CAR-T feasibility: CD37-directed CAR-T cells demonstrated specific reactivity against CD37-low AML cell lines, suggesting potent recognition capability

Methodologically, researchers should note that while CD37 mRNA is translated and expressed at the surface of AML cells, its detection may be restricted to specific antibodies . This emerging area requires further research to establish optimal targeting approaches and combinatorial strategies.