Longitudinal analysis of MART-1/HLA-A2-reactive T cells over the course of melanoma progression

An HLA-A2-positive patient with advanced stage IV melanoma was vaccinated with dendritic cells (DCs) pulsed with melanoma antigens, whereby the rapid progression of disease stalled for a period of 10 months. Monitoring of the cellular immune response against one of the vaccinated HLA-A2-restricted epitopes demonstrated both induction and subsequent decline in the number of interferon-gamma (IFN-gamma)-producing MART-1-reactive cells present in the blood. Enumeration of reactive T cells by MART-126-35/HLA-A2 tetramer staining revealed an induction of such cells after three vaccinations and a subsequent decline that most prominent at times of rapid disease progression. However, a substantial number of reactive cells were present even when no MART-1 reactivity was detectable by functional assays. Isolation of such MART-126-35-reactive T cells by means of peptide/HLA-A2-coated magnetic beads demonstrated the persistence of a TCRVbeta14+ T-cell clone in this population over the whole observation period. Intracellular fluorescence-activated cell sorter staining of such TCRVbeta14+ T cells for IFN-gamma and interleukin-2 after maximal stimulation with phorbol 12-myristate 13-acetate/ionomycin revealed an impairment in their capacity to produce cytokines at the end of the observation period. Thus, functional changes of individual T-cell clones, e.g. clonal exhaustion, seem to be responsible for the known discrepancy between functional and phenotype assays for immune monitoring of tumour patients.

In vitro production and characterization of partly assembled human CD3 complexes

Pairwise assembly of human CD3 chains takes place in the endoplasmic reticulum of T cells. Subsequently, the CD3 heterodimers form complexes with Ti alpha and Tiss chains forming hexameric Ti alpha beta CD3 gamma epsilon delta epsilon complexes. Finally, association with the zeta 2 homodimer occurs in Golgi apparatus before the fully assembled T-cell receptor is transported to the cell surface. To study the structural properties of the human CD3 chains, we have developed new methods to produce and fold the extracellular domains of CD3 gamma, CD3 delta and CD3 epsilon. Proteins were expressed in Escherichia coli as denatured chains and de novo folded in vitro. CD3 gamma and CD3 epsilon folded as soluble monomers, whereas CD3 delta did not yield any soluble proteins. When folding the chains pairwise, soluble CD3 gamma epsilon and CD3 delta epsilon heterodimers could be isolated, whereas CD3 gamma delta heterodimers were not produced. Using antibodies as structural probes, we identified two different types of antigenic epitopes that were dependent on heterodimerization. Our data indicate that CD3 epsilon undergoes a conformational change after dimerization with CD3 gamma or CD3 delta. Furthermore, we demonstrated that the CD3 gamma epsilon heterodimer could be purified using immunoaffinity chromatography.

Establishment of a quantitative ELISA capable of determining peptide - MHC class I interaction

Many different assays for measuring peptide-MHC interactions have been suggested over the years. Yet, there is no generally accepted standard method available. We have recently generated preoxidized recombinant MHC class I molecules (MHC-I) which can be purified to homogeneity under denaturing conditions (i.e., in the absence of any contaminating peptides). Such denatured MHC-I molecules are functional equivalents of "empty molecules". When diluted into aqueous buffer containing beta-2 microglobulin (beta2m) and the appropriate peptide, they fold rapidly and efficiently in an entirely peptide dependent manner. Here, we exploit the availability of these molecules to generate a quantitative ELISA-based assay capable of measuring the affinity of the interaction between peptide and MHC-I. This assay is simple and sensitive, and one can easily envisage that the necessary reagents, standards and protocols could be made generally available to the scientific community.