Michael Lemon

Ox-40 and Ox-40 ligand (Ox-40L) are thought to be involved in T cell-APC interactions. However, their exact role in T cell responses is undefined. Using fibroblast transfectants expressing Ox-40L and/or B7-1, and CD4 cells from TCR transgenic mice, we investigated the effect of Ox-40 signaling on primary responses to the Ag pigeon cytochrome c. Ox-40 expression on naive CD4 cells peaked 2 to 3 days after activation, and was lost by 4 to 5 days. APCs with Ox-40L promoted partial activation of naive T cells with some IL-2 secretion, but were unable to enhance proliferation, unlike those with B7-1. APCs coexpressing Ox-40L with B7-1 induced large quantities of IL-2 and promoted proliferative responses that persisted for several days. Effector cells taken 5 days after naive T cell activation reexpressed Ox-40 within 4 h and responded strongly to APCs expressing Ox-40L, whereas B7-1 had little effect. Synergy was also seen between Ox-40L and B7-1, with primarily IL-2 being elevated, although IL-4 and IL-5 were also up-regulated. The most striking action was on effector T cell proliferation, which continued at high levels for up to 4 days, with little proliferation evident at this time in the absence of Ox-40 signals. These data suggest that Ox-40/Ox-40L interactions act after initial activation events to prolong clonal expansion and enhance effector cytokine secretion, and may be involved in promoting long-lived primary CD4 responses.

The concern about bioterrorism with smallpox has raised the possibility of widespread vaccination, but the greater prevalence of immunocompromised individuals today requires a safer vaccine, and the mechanisms of protection are not well understood. Here we show that, at sufficient doses, the protection provided by both modified vaccinia Ankara and NYVAC replication-deficient vaccinia viruses, safe in immunocompromised animals, was equivalent to that of the licensed Wyeth vaccine strain against a pathogenic vaccinia virus intranasal challenge of mice. A similar variety and pattern of immune responses were involved in protection induced by modified vaccinia Ankara and Wyeth viruses. For both, antibody was essential to protect against disease, whereas neither effector CD4+ nor CD8+ T cells were necessary or sufficient. However, in the absence of antibody, T cells were necessary and sufficient for survival and recovery. Also, T cells played a greater role in control of sublethal infection in unimmunized animals. These properties, shared with the existing smallpox vaccine, provide a basis for further evaluation of these replication-deficient vaccinia viruses as safer vaccines against smallpox or against complications from vaccinia virus.

The V beta 8.2 T cell receptor (TCR) component is the predominant V beta gene product associated with antigen specific CD4+ T cell response to the major encephalitogenic epitope of myelin basic protein (MBP) in Lewis rats. Lewis rats were actively immunized with MBP in complete Freund's adjuvant and the V beta 8.2 positive and negative cells were analyzed for IFN-gamma mRNA production and OX-40 cell surface expression during the onset of EAE. The V beta 8.2+ T cells isolated from the spinal cord produced the majority of mRNA for IFN-gamma and also showed a marked enhancement for OX-40 expression compared to V beta 8.2+ T cells isolated from the lymph nodes. Only a fraction of IL-2 receptor positive T cells examined ex vivo from the inflammatory compartments co-expressed the OX-40 antigen. These results suggested that OX-40 cell surface expression could be used to identify and isolate the most recently activated T cells ex vivo. OX-40+ T cells isolated from the spinal cord were highly enriched for the V beta 8.2 T cell receptor component compared to OX-40- or unsorted spinal cord lymphocytes. OX-40+ T cells isolated from the spinal cord had an enhanced response to MBP, whereas OX-40+ cells isolated from the lymph nodes responded to both MBP and purified protein derivative. These data suggest that activated T cells can be isolated and characterized with the OX-40 antibody which only respond to the antigens present at the local site. The data also imply that isolation of OX-40+ T cells will be useful in identifying V beta biases and autoantigen specific cells within inflamed tissues even when the antigen specificity is unknown.