SIRPD Antibody

What is the functional role of SIRPα in immune regulation, and how do antibodies modulate this interaction?

SIRPα (Signal Regulatory Protein α) is an inhibitory transmembrane receptor expressed on myeloid cells (e.g., macrophages, dendritic cells). It binds to CD47, a ubiquitously expressed "don't eat me" ligand, to suppress phagocytosis of healthy cells . Antibodies targeting SIRPα disrupt this interaction, thereby enhancing macrophage-mediated phagocytosis of CD47-expressing tumor cells .

Methodological Insight:
To validate SIRPα's role, researchers often use:

• Flow cytometry to quantify SIRPα expression on myeloid subsets.

• Phagocytosis assays with tumor cell lines (e.g., Raji lymphoma) co-cultured with macrophages ± anti-SIRPα antibodies .

• Surface plasmon resonance (SPR) to measure binding kinetics between SIRPα antibodies and CD47 .

How do SIRPα allelic variants (e.g., V1, V2, V8) influence antibody cross-reactivity?

SIRPα exhibits genetic polymorphism, with V1 (common in Europeans/Africans) and V2 (common in East Asians) representing major variants differing in their immunoglobulin variable (IgV) domain . Pan-allelic antibodies (e.g., BYON4228, BR105) bind all variants, whereas others (e.g., GenHunter’s mAbs) are allele-specific .

Experimental Design:

• Use SNP genotyping (e.g., TaqMan assays) to identify donor SIRPα haplotypes.

• Validate cross-reactivity via ELISA with recombinant SIRPα-Fc fusion proteins .

What techniques are recommended for detecting SIRPα expression in tissue samples?

Proteintech’s 14482-1-AP antibody detects SIRPα at 75–85 kDa (post-glycosylation) across human, mouse, and rat samples . Key applications include:

Validation Tip: Include controls like SIRPα-knockout macrophages to confirm specificity .

How do researchers address off-target binding of SIRPα antibodies to SIRPγ on T cells?

SIRPγ shares 73% homology with SIRPα but is expressed on T cells and mediates CD47-dependent adhesion . Antibodies like BR105 and BYON4228 avoid SIRPγ binding via epitope engineering:

• BR105: Binds SIRPα IgV domain with <5% cross-reactivity to SIRPγ .

• BYON4228: Targets a conformational epitope absent in SIRPγ .

Assay: Perform competitive binding with recombinant SIRPγ-Fc and flow cytometry on Jurkat T cells .

How can allelic variation confound preclinical-to-clinical translation of SIRPα antibodies?

Problem: Murine models (e.g., NSG mice) often express a single SIRPα variant, whereas human populations exhibit polymorphism . A therapy optimized for V1 may fail in V2-dominant cohorts.

Resolution:

• Use transgenic mice expressing human SIRPα variants .

• Screen clinical trial participants for SIRPα haplotypes via PCR-RFLP .

What strategies improve tumor selectivity of SIRPα-targeted therapies?

SIRPabodies (SIRPα fused to tumor-targeting antibodies like rituximab) localize CD47 blockade to malignancies, sparing RBCs :

Experimental Validation:

• Competitive binding assays with excess RBC lysates .

• Xenograft models (e.g., Raji-luciferase) to quantify tumor burden via bioluminescence .

Why do some SIRPα antibodies show differential efficacy in hematologic vs. solid tumors?

Hypothesis: Solid tumors exhibit higher CD47 expression and immunosuppressive stromal cells .

Data Comparison:

Methodological Adjustments:

• Add hypoxia-mimetic agents (e.g., CoCl₂) to upregulate CD47 in vitro .

• Use patient-derived organoids to model stromal interactions .

How do contradictory findings about T-cell inhibition arise with SIRPα antibodies?

Conflict: Some pan-SIRP antibodies (e.g., HEFLB) inhibit T-cell activation via SIRPγ binding, while BR105/BYON4228 do not .

Resolution:

• Include CFSE dilution assays to quantify T-cell proliferation .

• Test antibody candidates in mixed lymphocyte reactions .

What metrics define successful SIRPα antibody engineering?

Key Parameters:

• Affinity: KD ≤10 nM for SIRPα (SPR) .

• Allelic Coverage: ≥95% human population (genotype databases) .

• Safety: <10% RBC depletion in primate models .

Case Study: BYON4228 achieved:

• KD = 2.1 nM for SIRPαV1/V2 .

• 0% RBC lysis at 30 mg/kg in cynomolgus monkeys .