CD40L-expressing recombinant vaccinia virus (rVV40L) : generation of central memory CD8+ T cells and induction of tumor cell death

Generation of immunological memory represents a key tenet of the adaptive immune system. CD8+ T cell memory compartment encompasses two main subsets, central (TCM) and effector memory (TEM) lymphocytes, displaying a differential expression of homing and chemokine receptors. Furthermore, TCM are characterized by high proliferative potential in response to antigen stimulation, high responsiveness to homeostatic cytokines and the ability to home into secondary lymphoid organs.In contrast, TEM produce higher levels of effector cytokines, preferentially home in non- lymphoid tissues and have limited proliferation capacity. Immune responses conferring protection against infectious agents or efficiently eradicating established tumors critically necessitate the generation of antigen specific TCM.
We have generated a recombinant vaccinia virus encoding human CD40 ligand (rVV40L) and used it here, in replication incompetent form, to promote the differentiation of naïve CD8+ T cells into TCM specific for viral and tumor associated antigens. Soluble CD40L recombinant protein (s40L) and wild-type vaccinia virus (VV WT) alone or in combination were used as controls. We have found that, in the absence of CD4+ T cells, a single antigenic stimulation “in vitro” of naïve CD8+ T cells by rVV40L-infected non-professional CD14+ antigen presenting cells (APCs) promotes the rapid generation of viral or tumor associated antigen specific CD8+ T cells displaying TCM phenotypic and functional properties. In particular these cells are able to respond with vigorous proliferation and IL-2 production to “in vitro” antigenic challenge.
In addition, we have also evaluated the capacity of rVV40L to mediate cytotoxic effect on tumor cells upon direct infection or by promoting the activation of myeloid cells of monocyte/macrophage lineage. Interestingly, rVV40L infection as compared to s40L treatment resulted in the inhibition of proliferative capacity of CD40 receptor expressing tumor cells. Furthermore, rVV40L-infection of tumor cells resulted also in the acquisition of tumorocidal activity, as indicated by the increased TNF-α gene expression, by CD14+ monocytes.
Taken together, these data fully support the use of CD40L-expressing recombinant vaccinia virus for clinical investigation in view of its direct cytotoxic activity on tumor cells and by its ability to to promote the generation of of effective and long-lasting antigen specific CD8+ T cell responses through the modulation of antigen presenting capacity of non-professional CD14+ antigen presenting cells.