The B2M Knockout HAP1 Polyclonal Cells are a CRISPR/Cas9-edited polyclonal knockout cell population derived from the HAP1 cell line, engineered through targeted disruption of the B2M gene. This product provides a heterogeneous pool of cells harboring loss-of-function alleles at the B2M locus, enabling the study of beta-2-microglobulin deficiency in a near-haploid genetic background. The polyclonal format ensures that diverse genetic perturbations are represented, facilitating robust screening applications without the constraints of clonal selection. These cells serve as a versatile tool for investigating the molecular requirements for MHC class I antigen presentation and immune recognition pathways.
The HAP1 host cell line is a near-haploid derivative of the KBM-7 chronic myeloid leukemia cell line, characterized by expression of the BCR-ABL fusion protein and an adherent growth morphology. Its haploid state simplifies CRISPR-based genetic screens by reducing gene copy number, enabling straightforward disruption of single alleles and clear loss-of-function phenotypes. HAP1 cells are widely adopted for functional genomics studies, particularly in cancer and immune-related signaling, due to their stable karyotype and compatibility with high-throughput screening platforms. This background provides a well-suited context for interrogating B2M-dependent processes relevant to immune evasion and leukemia progression.
The B2M gene encodes beta-2-microglobulin, the invariant light chain that non-covalently associates with HLA-A, HLA-B, and HLA-C heavy chains to form functional MHC class I complexes. Beta-2-microglobulin is essential for stable cell surface expression of MHC I molecules and plays a critical role in antigen presentation to CD8+ T cells. Its interaction with the peptide-loading complex, including tapasin, calreticulin, ERp57, and calnexin, facilitates optimal peptide binding and transport to the plasma membrane. Upstream, B2M expression is transcriptionally regulated by factors such as NLRC5, IRF1, and RFX5, which are themselves activated by IFN-?? and TNF-?? signaling cascades. Disruption of B2M consequently abolishes MHC I surface display, preventing CD8+ T cell engagement and licensing NK cell-mediated killing through missing-self recognition, thereby recapitulating tumor immune escape mechanisms.
In the HAP1 myeloid leukemia background, B2M knockout provides a physiologically relevant model for studying immune evasion in hematologic malignancies. The ablation of MHC class I surface expression mimics the downregulation often observed in leukemia cells undergoing immune selection, allowing dissection of the interplay between tumor cells and cytotoxic lymphocytes. Moreover, the haploid nature of HAP1 cells enhances the utility of this model for CRISPR-based suppressor or activator screens aimed at identifying novel regulators of MHC I trafficking, peptide loading, or alternative mechanisms of ??2-microglobulin function, such as its roles in iron homeostasis via HFE interaction and IgG recycling through FcRn binding.
Typical applications include cancer immunology studies focused on CD8+ T cell evasion and NK cell cytolysis, drug target validation for immunotherapies that restore MHC I expression, and investigation of protein misfolding diseases linked to ??2-microglobulin aggregation. Researchers regularly employ these cells in flow cytometry assays for surface MHC I, Western blot and RT-qPCR for B2M expression, CD8+ T cell activation and NK cell cytotoxicity assays, immunofluorescence to monitor MHC I trafficking, and peptide-MHC stability or co-immunoprecipitation experiments to assess complex assembly. The B2M Knockout HAP1 Polyclonal Cells thus represent a powerful resource for molecular and cellular immunology research. For further details, please contact Ascent Research.
