In vivo characterization of the adjuvant effect of Mycobacterium tuberculosis hsp70

For the purpose of rationally designing heat shock protein vaccines against cancer the adjuvant effect of Mycobacterium tuberculosis hsp70 (TBhsp70) was studied using an adoptive transfer system. The vaccine used in this work contains a fragment of the model antigen chicken ovalbumin (OVA) fused to the amino terminus of TBhsp70. In order to track the CD8 + T cell response, congenic mice were adoptively transferred with OT-I/PL cells and immunized. OT-I cells respond to this vaccine because the OVA fragment contains SIINFEKL, the peptide for which the OT-I TCR is specific. At different times following immunization draining lymph node and spleen suspensions were examined. OVA.TBhsp70 causes the rapid activation and proliferation of almost all OT-1 cells as compared to other adjuvants. In addition, more memory cells are generated and survive better. Memory cell generation and survival was shown to be dependent on interleukin 15, but independent of CD4 +T cell help. In the absence of IL-15 expression of Bcl-2 by OT-1 memory cells is less. OVA.TBhsp70 caused an upregulation of the IL-15Ralpha chain on OT-1 cells, offering an explanation for their increased survival in the presence of IL-15. The memory cells generated are phenotypically (CD62L +, CCR7+, CD127+, CD44high and CD122high) and functionally characteristic of central memory cells. The cells produce IFN-gamma and proliferate upon rechallenge but exhibit low levels of direct ex vivo cytotoxicity. More cells survive following peptide rechallenge when OT-1 cells are primed in mice immunized with OVA.TBhsp70 than in mice that received OVA plus LPS indicating that T cells are programmed early in the immune response. To begin to understand the early events that dictate long-term survival of T cells experiments were done to identify the antigen-presenting cell responsible for uptake and presentation following OVA.TBhsp70 immunization. Both CD11b+ and CD11b- dendritic cells (DC) but not macrophages took up antigen and processed it for presentation by MHC class I molecules. In addition, OVA.TBhsp70 upregulated CD40 on these cells. Future experiments will be needed to establish if both sets of DC can interact with T cells and how the initial interaction determines the long-term fate of the T cell.