Q36. Which one of the following cells lack hypoxanthine–guanine
phosphoribosyltransferase (HGPRT)?
(A) B Cell
(B) T Cell
(C) Macrophage
(D) Myeloma Cell

Myeloma cells lack hypoxanthine-guanine phosphoribosyltransferase (HGPRT). This enzyme deficiency is a key feature in hybridoma technology for monoclonal antibody production, where specially selected myeloma cells are used.

Correct Answer

(D) Myeloma Cell
In hybridoma technology, myeloma cells are deliberately engineered or selected to be HGPRT-deficient, making them unable to survive in HAT (hypoxanthine-aminopterin-thymidine) medium.

Option Analysis

(A) B Cell

B cells express functional HGPRT, enabling them to use the purine salvage pathway for nucleotide synthesis in HAT medium. They provide this enzyme to hybridomas during fusion, allowing hybrid survival.

(B) T Cell

T cells express HGPRT, as shown in studies of T cell proliferation and mutation rates where HGPRT activity supports DNA salvage synthesis. No natural deficiency occurs in normal T cells.

(C) Macrophage

Macrophages express HGPRT, demonstrated by successful fusions with HGPRT-deficient cell lines to create hybridomas. They rely on this enzyme for purine recycling.

(D) Myeloma Cell

Myeloma cells used in hybridoma production lack HGPRT due to selection with 8-azaguanine, blocking the salvage pathway. In HAT medium, aminopterin inhibits de novo synthesis, killing unfused myeloma cells while hybrids survive via B cell-derived HGPRT.

Introduction to HGPRT and Cell Deficiency

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is essential for the purine salvage pathway, recycling hypoxanthine and guanine into nucleotides. In hybridoma technology, cells lack HGPRT refers specifically to myeloma cells selected for deficiency, enabling selective hybridoma growth in HAT medium. This concept is crucial for CSIR NET Life Sciences exams focusing on biotechnology.

Role in Hybridoma Technology

Myeloma cells are cultured in 8-azaguanine to knock out HGPRT function, making them HAT-sensitive. Post-fusion with B cells:

• Unfused myeloma cells die due to blocked de novo (aminopterin) and salvage (HGPRT absence) pathways.

• B cells die from limited lifespan.

• Only HGPRT+ hybrids proliferate indefinitely.

Why Not Immune Cells?

• B cells: HGPRT-positive; donate enzyme to hybrids.

• T cells: Express HGPRT for proliferation; mutants studied but not naturally deficient.

• Macrophages: HGPRT-present; used in fusions requiring functional enzyme.

Exam Relevance for CSIR NET

This question tests understanding of hybridoma selection, a staple in molecular biology and biotechnology units. Myeloma cells’ engineered HGPRT deficiency ensures pure monoclonal antibody production.