CC chemokine receptor (CCR) 7 and cognate CCR7 ligands, CCL21 (formerly secondary lymphoid tissue chemokine [SLC]) and CCL19 (formerly Epstein-Barr virus-induced molecule 1 ligand chemokine [ELC]), were known to establish microenvironment for the initiation of immune responses in secondary lymphoid tissue. As described previously, coadministration of DNA vaccine with CCR7 ligand-encoding plasmid DNA elicited enhanced humoral and cellular immunity via increasing the number of dendritic cells (DC) in secondary lymphoid tissue. The author hypothesized here that CCR7 ligand DNA could effectively expand memory CD4+ T cells to protect from viral infection likely via increasing DC number.

To evaluate the effect of CCR7 ligand DNA on the expansion of memory CD4+ T cells, DO11.10.BALB/c transgenic (Tg)-mice, which have highly frequent ovalbumin (OVA)_323-339 peptide-specific CD4+ T cells, were used. Tg-mice were previously injected with CCR7 ligand DNA, then immunized with OVA_323-339 peptide plus complete Freund's adjuvant. Subsequently, memory CD4+ T cells in peripheral blood lymphocytes (PBL) were analyzed by FACS analysis for memory phenotype (CD44^high and CD62 L^low) at memory stage. Memory CD4+ T cells recruited into inflammatory site induced with OVA-expressing virus were also analyzed. Finally, the protective efficacy against viral infection was evaluated.

CCR7 ligand DNA-treated Tg-mice showed more expanded CD44^high memory CD4+ T cells in PBL than control vector-treated animals. The increased number of memory CD4+ T cells recruited into inflammatory site was also observed in CCR7 ligand DNA-treated Tg-mice. Such effectively expanded memory CD4+ T cell population increased the protective immunity against virulent viral infection.

These results document that CCR7 and its cognate ligands play an important role in intracellular infection through establishing optimal memory T cell. Moreover, CCR7 ligand could be useful as modulator in DNA vaccination against viral infection as well as cancer.