Biology Reference
In-Depth Information
ROLE OF TETRAMER STAINING FOR MONITORING VACCINE
IMMUNOGENICITY
The use of peptide/MHC tetramers for rapidly assessing the cellular immuno-
genicity of therapeutic or preventative vaccine candidates represents an impor-
tant development. Peptide/MHC tetramers have been used to monitor vaccine
responses in rhesus monkeys with a Mamu-A*01 MHC background (Letvin et
al., 1999). Antigen-speci®c CD8
T cells were ®rst identi®ed in SIVmac 251
infected animals using tetramers folded around the immunodominant epitope
in Gag: p11C.C-M ( Egan et al., 1999). These tetramers were then used to assess
the magnitude of the CTL response elicited by modi®ed vaccinia Ankara
(MVA) expressing the SIV gag and pol genes (Seth et al., 1998). Four of four
Mamu-A*01 positive animals possessed 0.6±4.9% p11C.C-M/Mamu-A*01 tet-
ramer binding cells 10 days after a second immunization with MVA (Seth et al.,
1998). Similar results have been shown in monkeys receiving a DNA prime
followed by an MVA boost ( Hanke et al., 1999). Use of peptide/MHC tet-
ramers in clinical vaccine trials has yet to be reported.
CONCLUSION
This chapter has shown that ¯ow cytometry coupled with peptide/MHC tet-
ramers can be used to measure the magnitude of MHC class I-restricted T-cell
responses directly in the peripheral circulation. The method is quick, and the
frequency of antigen-speci®c cells can be quanti®ed without the requirement for
labor-intensive culture conditions. The nature of HIV infection, as persistent
and chronic, results in clonally expanded numbers of antigen-speci®c CD8
T
cells. The use of peptide/MHC tetramers has shown that during the acute stage
of infection, large numbers of antigen-speci®c CD8
cells are functionally
active and are associated with control of HIV-1 replication (Ogg et al., 1999b;
Wilson et al., 2000). However, during the chronic stage of infection, in the
clinically asymptomatic stage, large numbers of tetramer-binding CD8
cells
are not functional and probably require persistently high levels of HIV-1 repli-
cation to maintain their numbers (Gray et al., 1999; Kelleher and Rowland-
Jones, 2000). This scenario has been gleaned from studies showing that
HAART results in signi®cant reductions in the frequencies of antigen-speci®c
cells as HIV-1 replication is suppressed. The hypofunctional nature of tetramer-
binding CD8
T cells has also been found in studies investigating melanoma-
speci®c T cells ( Lee et al., 1999) and in CD4-de®cient mice infected with
LCMV (Zajac et al., 1998). It is tempting to equate the progressive loss of CD4
help with loss of anti-HIV CD8 CTL function as HIV-1 disease progresses. A
recent study has shown that lack of perforin content and CTL killing capacity
during the chronic stage of disease may be related to a block in CD8
CTL
maturity (Appay et al., 2000). Whatever the reason for defective antigen-speci®c
CD8
T cells after initial viral infection, the use of peptide/MHC tetramers has
