The immune response to tumor can be enhanced by targeting costimulatory molecules on T cells. As the CD70-CD27 costimulatory axis plays an important role in the activation, survival and differentiation of lymphocytes, we have examined the efficacy of agonistic anti-CD27 antibodies as monotherapies for established melanoma in a murine model. We demonstrate that this approach leads to a substantial reduction in the outgrowth of both experimental lung metastases and sub-cutaneous tumors. Anti-CD27 treatment supports the maintenance of tumor-specific CD8 + T cells within the tumor, reduces the frequency of FoxP3-expressing CD4 + T cells within tumors, and potentiates the ability of NK1.1 + and CD8 + tumor infiltrating cells to secrete IFNγ upon coculture with tumor cells. The enhanced effector function correlated with lower levels of PD-1 expression on CD8 + T cells from anti-CD27 treated mice. Despite the modulating effect of anti-CD27 on multiple cell types, only CD8 + T cells were absolutely required for tumor control. CD4 + T cells were dispensable, while NK1.1 + cells were needed during early stages of tumor growth but not for the effectiveness of anti-CD27. Thus, CD27-mediated costimulation provides a potent boost to multiple aspects of the endogenous responses to tumor, and may be exploited to enhance tumor immunity.

Fully functional CD8+ T cell memory is highly dependent upon CD4+ T cell support. CD4+ T cells play a critical role in inducing the expression of CD70, the ligand for CD27, on dendritic cells. Here we demonstrate that CD27 stimulation during primary CD8+ T cell responses regulates the ability to mount secondary CD8+ T cell responses. CD27 stimulation during vaccinia and dendritic cell immunization controls the expression of the IL-7 receptor (CD127), which has been shown to be necessary for memory CD8+ T cell survival. Further, CD27 stimulation during primary CD8+ T cell responses to vaccinia virus restrained the late expression on memory precursor cells of cytokine receptors that support terminal differentiation. The formation of CD8+ T cell memory precursors and secondary CD8+ T cell responses were restored in the absence of CD27 costimulation when endogenous IL-12 was not available. Similarly, the lesion in CD8+ T cell memory that occurs in the absence ofCD4+ T cells did not occur in mice lacking IL-12. These data indicate that CD4+ T cell help and, by extension, CD27 stimulation supports CD8+ T cell memory by modulating the expression of cytokine receptors that influence the differentiation and survival of memory CD8+ T cells.

CD70-mediated stimulation of CD27 is an important cofactor of CD4+ T cell licensed dendritic cells. However, it is unclear how CD70-mediated stimulation of T cells is integrated with signals that emanate from Signal 3 pathways, such as type-1 interferon (IFN-1) and IL-12. We find that while stimulation of CD27 in isolation drives weak EomesoderminhiT-betlo CD8+ T cell responses to OVA immunization, profound synergistic expansion is achieved by co-targeting TLR. This cooperativity can substantially boost anti-viral CD8+ T cell responses during acute infection. Concomitant stimulation of TLR significantly increases per-cell IFNγ-production and the proportion of the population with characteristics of short-lived effector cells, yet also promotes the ability to form long-lived memory. Notably, while IFN-1 contributes to the expression of CD70 on dendritic cells, the synergy between CD27 and TLR stimulation is dependent upon IFN-1’s effect directly on CD8+ T cells, and is associated with the increased expression of T-bet. Surprisingly, we find that IL-12 fails to synergize with CD27 stimulation to promote CD8+ T cell expansion, despite its capacity in driving effector differentiation. Together these data identify complex interactions between Signal 3 and costimulatory pathways, and identify opportunities to influence the differentiation of CD8+ T cell responses.