DNA cloning is an essential technique in life sciences research, which is used to make multiple, identical copies of a particular piece of DNA. Most of these DNA fragments are produced by digestion of existing DNA fragments by restriction endonuclease enzymes, or by PCR amplification. Cloning involves preparation of vectors and inserted DNA, ligation of the insert into the vector, transformation of cell of interest, and identification of positive clones.

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Major histocompatibility complex (MHC) class I and class II molecules share the task of presenting peptides on the cell surface for recognition by T cells and play a pivotal role in the adaptive immune system.

Peptide-MHC (pMHC) complexes are recognized by CD4+ and CD8+ T cells expressing a repertoire of hypervariable αβ T cell receptors (TCRs). The interaction between the pMHC complex and a cognate TCR is short lived and of low affinity. By the multimerization of four pMHC molecules on a streptavidin scaffold, the tetramer binds to TCR with high affinity and specificity. Thus, pMHC tetramers can be used to identify, monitor, and handle T cells through direct and specific staining.

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