Pushing the frontiers of T-cell vaccines: accurate measurement of human T-cell responses

Abstract

There is a need for novel approaches to tackle major vaccine challenges such as malaria, tuberculosis and HIV, among others. Success will require vaccines able to induce a cytotoxic T-cell response – a deficiency of most current vaccine approaches. The successful development of T-cell vaccines faces many hurdles, not least being the lack of consensus on a standardized T-cell assay format able to be used as a correlate of vaccine efficacy. Hence, there remains a need for reproducible measures of T-cell immunity proven in human clinical trials to correlate with vaccine protection. The T-cell equivalent of a neutralizing antibody assay would greatly accelerate the development and commercialization of T-cell vaccines. Recent advances have seen a plethora of new T-cell assays become available, including some like cytometry by time-of-flight with extreme multiparameter T-cell phenotyping capability. However, whether it is historic thymidine-based proliferation assays or sophisticated new cytometry assays, each assay has its relative advantages and disadvantages, and relatively few of these assays have yet to be validated in large-scale human vaccine trials. This review examines the current range of T-cell assays and assesses their suitability for use in human vaccine trials. Should one or more of these assays be accepted as an agreed surrogate of T-cell protection by a regulatory agency, this would significantly accelerate the development of T-cell vaccines.

Activation-induced Markers Detect Vaccine-Specific CD4+ T Cell Responses Not Measured by Assays Conventionally Used in Clinical Trials

“…A number of assays are conventionally used to measure the quantity and quality of antigen-specific T cells in humans [ 11 ]. The assays most frequently used for this purpose in clinical vaccine trials are the enzyme-linked immunospot (ELISpot) and intracellular cytokine staining (ICS) assays [ 12 , 13 , 14 ]. The ELISpot assay involves stimulating peripheral blood mononucleocyte (PBMC) with antigen in 96-well plates with membranes coated in the anti-cytokine capture antibody.…”

T-cell assays confirm immunogenicity of tungsten-induced erythropoietin aggregates associated with pure red cell aplasia

“…13 Because specific high-affinity IgG1 and IgG4 antibody responses to rhEPO point to T-cell-dependent isotype switching, 2,16 we focused our investigations on the question whether T-cell responses can differentiate nonaggregated from aggregated rhEPO. In vitro T-cell assays have been successfully used to evaluate the mechanism of immune responses to biotherapeutics, 5-9 vaccines, 17,18 and selfantigens. 19,20 Besides preexisting nonneutralizing IgM and IgG1 anti-EPO antibodies across various clinical indications, 14,15 EPOspecific T cells are part of the T-cell repertoire in healthy individuals.…”

“…15 Specific high-affinity neutralizing IgG1 and IgG4 antibody responses to rhEPO indicate T-cell-dependent isotype switching. 2,16 Because in vitro T-cell assays have been successfully used to evaluate the mechanism of immune responses to biotherapeutics, [5][6][7][8][9] vaccines, 17,18 and self-antigens in vitro, 19,20 we investigated in vitro T-cell responses to experimentally heat-induced rhEPO aggregates, and tungsteninduced rhEPO aggregates in clinical lots associated with rhEPOneutralizing antibodies and PRCA. Furthermore, we studied ex vivo T-cell recall responses of patients treated with rhEPO without PRCA, and of patient P1 who developed PRCA after treatment with a clinical batch with elevated levels of tungsten and aggregates.…”

A fresh perspective from immunologists and vaccine researchers: Active vaccination strategies to prevent and reverse Alzheimer's disease

“…H 3 Td incorporation or CFSE flow cytometry assay); detection by ELISPOT of T cells producing specific cytokines (e.g. IFNγ ELISPOT assays); flow cytometric analyses of intracellular cytokines or measurement of antigen-specific T-cell frequencies using MHC tetramers[104]. Such evaluations are particularly important as in elderly people with immunosenescence the number of T cells that respond to vaccination is dramatically decreased[70, 105, 106].…”