L.Zhang1, S.Kozlowski2, 1DMA, OTRR, CBER, FDA, 2DMA, OTRR, FDA
Peptide-based vaccine for cancer or autoimmunity have many attractive features such as ease of manufacturing and characterization as well as excellent safety documentation in clinical trials. However, ambiguous results from initial clinical trials suggest that peptide-base vaccine are far from optimal. The insufficient immunity generated by peptide vaccines can be attributed to many problems inherent for any peptide-based immune manipulation including identification and selection of the most appropriate T cells epitopes, lack of immunogenicity, generating immune tolerance and apoptosis of antigen specific T cells.
Recent years of studies on T cell migration and chemokine/cytokine expression have clear established that microenvironment surrounding antigen-specific T cells in second lymphoid organ or in inflamed site play critical role in the outcome of T cells (activation, anergy, apoptosis or type of cytokine production). Where the T cells located decide what signals or cytokine of APC can be received. By using TCR transgenic T cells (CD4 and CD8+) adoptive transfer model, we in situ examined the dynamic homing of transgenic T cells in second lymphoid organ, spleen and lymph nodes after immunization with appropriate peptides and protein and the location of cytokine and chemokines production and apoptosis. The major findings of the study are 1) there is a distinct difference in homing of DO11 TCR-transgenic T cells in spleen between immunization with ova peptide and with ova protein (both in CFA). DO11 T cells immunized with peptide were found exclusively in red pulp but not in T and B zone (white pulp), while 90% of DO11 T cells (in ova protein immunization) were found in T and B zone. 2) distribution of cytokine production were very different though both type of immunizations induce strong expression of IL-4, IL-2 and IFN-gamma. With peptide immunization, cytokine producing cells were found exclusively in red pulp but not in T and B zones. In contrast, with ova protein immunization, significant numbers of cells producing cytokines IL-4, IL-2 and IFN-gamma were found in T and B zone. The similar distribution patterns were also observed for cells expressing CD40 ligand. 3) Fas ligand expressing cells were found exclusively in red pulp with ova peptide or protein immunization. The difference between the two types of immunization is that lot more cells expressing fas ligand were observed in ova peptide immunization and lot more in 10 day compared with 5 days post (only a few Fas ligand expressing cells in red pulp can be found in 2C/peptide). 4) in model of 2C T cells, the similar results as with ova peptide immunization were obtained in QY5 or SYIR peptide immunization (not protein challenge), suggesting that the peptide immunization-induced migration or distribution of antigen specific T cells are not just limited to CD4+ T cells. 5) very different apoptotic dynamics of transgenic T cells were found between 2C and DO11 peptide immunization (DO11 protein immunization of apoptosis still ongoing experiment). While there are basically few apoptotic cells observed in 5 days postimmunization 2C/peptide, DO11/peptide and DO11/protein, a huge numbers of apoptotic cells were found 10 days post immunization in DO11/peptide in red pulp exclusively but not in 2C /peptide (it is interesting to see DO11/protein at 10 days). These results have tremendous significance in our understanding and design of peptide based immune manipulation. It has been established that it is important for T cells to be antigen presented by professional DC in T zone. Bypassing this may result in suboptimal activation and dysfunction of T cells. The unique homing of cytokine producing cells and antigen specific T cells in peptide immunization may partially explained the ineffectiveness of peptide based manipulation and strong suggest that any design of peptide vaccine should have a consideration of appropriate homing property of T cell.