#hybridoma technology

Immunological Applications

Myeloma cells used in hybridoma technology are selected to be:

Establishing stringent selection requires myeloma background auxotrophic for purine salvage, achieved by exposure to 8-azaguanine, purine analogue structurally similar to guanine. Salvage competent cells convert 8-azaguanine via HGPRT to 8-azaguanosine monophosphate incorporated into mRNA and rRNA causing miscoding, translational errors, and lethal proteotoxicity triggering unfolded protein response. Spontaneous HPRT1 mutants survive because they cannot metabolize analogue, accumulating no toxic nucleotides. Surviving subclones harbor frameshift, nonsense, or missense mutations in coding exons 2-9, leading to premature stop codon and nonsense mediated mRNA decay, enzymatic activity undetectable via radiometric assay. In complete medium containing folate, deficiency tolerated because de novo purine synthesis via amidophosphoribosyltransferase using glutamine nitrogen supplies sufficient IMP via ten-step pathway. Once switched to HAT where aminopterin blocks that pathway, reliance shifts entirely to salvage, now impossible in mutants. ATP depletion, accumulation of PRPP, activation of AMPK, inhibition of mTORC1, and caspase 9 mediated apoptosis eliminate myeloma. Clones SP2/0-Ag14, P3X63-Ag8.653 routinely used worldwide ensure background below 1 per million, maximizing hybrid recovery efficiency.

Ref: Szybalski & Szybalska 1962 HGPRT negative mutants 8-azaguanine; ATCC SP2/0 Ag14 datasheet selection mechanism.

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Immunological Applications

Hybridoma cells survive in HAT medium because they:

Survival in HAT environment demands functional purine and pyrimidine salvage enzymes inherited from normal B parent. B lymphocytes express HPRT1 locus on X chromosome encoding 24 kDa hypoxanthine-guanine phosphoribosyltransferase that catalyzes phosphoribosyl transfer from PRPP to hypoxanthine yielding IMP plus pyrophosphate and to guanine yielding GMP, bypassing de novo steps requiring folate. They also express cytosolic thymidine kinase 1 cell-cycle regulated peaking in S phase and mitochondrial kinase 2 constitutive, phosphorylating thymidine supplied in medium to TMP using ATP. Hybridoma cells retain active alleles, enabling uptake of exogenous bases via equilibrative nucleoside transporters ENT1 and ENT2 and concentrative transporters CNT, generating nucleotides sufficient for DNA synthesis even when de novo synthesis ablated by aminopterin. Energy charge maintained allowing progression through G1/S checkpoint via cyclin E CDK2. Myeloma parents selected with 8-azaguanine lack HGPRT activity, cannot recycle hypoxanthine, undergo purine starvation, decrease in ATP and GTP pools activates p53 and causes mitochondrial depolarization. Unfused B cells possess salvage enzymes but inherently short lived due to withdrawal of BAFF and CD40L, undergoing apoptosis within seven days, leaving only hybrids as long-term proliferating population capable of indefinite expansion in selective medium.

Ref: Janeway Immunobiology salvage pathway HGPRT; Freshney Animal Cell Culture hybrids survive HAT via HGPRT TK from B cell.

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Immunological Applications

Myeloma cells used in hybridoma technology are selected to be:

Trastuzumab humanized IgG1 kappa mAb 148 kDa targets HER2 proto-oncogene extracellular domain IV juxtamembrane receptor overexpressed due ERBB2 amplification 17q12 20 percent breast gastric cancers poor prognosis. HER2 no known ligand but dimerizes HER1 HER2 HER3 after EGF binding autophosphorylating intracellular tyrosines Tyr1221 Tyr1222 recruiting Grb2 Shc activating PI3K Akt survival phosphorylating Bad Forkhead preventing apoptosis plus RAS RAF MEK ERK proliferation cyclin D1. Trastuzumab binds KD 5 nM sterically hindering dimerization preventing proteolytic cleavage shedding ECD generating constitutively active p95 truncated lacking ectodomain and inducing internalization clathrin-mediated requiring c-Cbl E3 ubiquitin ligase ubiquitination lysosomal degradation reducing surface density. Fc human IgG1 engages Fc gamma RIIIa CD16a NK cells triggering perforin granzyme ADCC and macrophage ADCP phagocytosis. Combination taxane docetaxel increased response 32 to 50 percent overall survival prolongation establishing HER2 testing companion diagnostic immunohistochemistry score 3+ FISH ratio >2.0 guiding patient selection achieving paradigm targeted immunotherapy solid tumors effective safe with cardiac monitoring due occasional LV dysfunction.

Ref: NEJM Trastuzumab HER2 Mechanism Slamon 2001 Clinical; FDA Herceptin Package Insert MOA Description; Janeway ADCC Trastuzumab Immune Mechanism NK Chapter 14.

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Basic Applied Biology

Hybridoma technology produces:

Hybridoma technology developed by Georges Köhler and César Milstein in 1975 and awarded Nobel 1984 created paradigm shift by immortalizing antibody-producing B lymphocytes through somatic cell fusion. Mice immunized with antigen develop germinal center reaction where B cells undergo VDJ recombination, somatic hypermutation and class switching to generate high affinity plasma cells. Splenic lymphocytes harvested shortly after boost are fused with HGPRT-deficient myeloma partner such as SP2/0-Ag14 or NS0 using polyethylene glycol 1500 that perturbs lipid bilayers promoting membrane fusion forming heterokaryons containing nuclei from both parents. Resulting hybrid cells combine immortal growth driven by myeloma oncogenes like c-myc deregulation with functional immunoglobulin heavy and light chain transcription from B cell. Clonal expansion and selection yields everlasting lines secreting monospecific antibody of defined isotype typically IgG1 kappa recognizing single epitope, known as monoclonal antibody. Such reagents revolutionized diagnostics, research tools like western blotting, and therapeutics by提供 unlimited standardized antibody with consistent affinity replacing heterogeneous polyclonal sera plagued by batch variation.

Ref: Köhler & Milstein Nature 1975 Continuous cultures of fused cells; Abbas Cellular and Molecular Immunology 10th ed. monoclonal antibody generation.

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