Differential regulation of CD27 expression on subsets of CD4 T cells

Progression of carcinogen-induced fibrosarcomas is associated with the accumulation of naïve CD4+ T cells via blood vessels and lymphatics

The tumor microenvironment comprises newly formed blood and lymphatic vessels which shape the influx, retention and departure of lymphocytes within the tumor mass. Thus, by influencing the intratumoral composition of lymphocytes, these vessels affect the manner in which the adaptive immune system responds to the tumor, either promoting or impairing effective antitumor immunity. In our study, we utilized a mouse model of carcinogen-induced fibrosarcoma to examine the composition of tumor-infiltrating lymphocytes during tumor progression. In particular, we sought to determine whether CD4(+) Foxp3(+) regulatory T cells (Tregs) became enriched during tumor progression thereby contributing to tumor-driven immunosuppression. This was not the case as the proportion of Tregs and effector CD4(+) T cells actually declined within the tumor owing to the unexpected accumulation of naïve T cells. However, we found no evidence for antigen-driven migration of these T cells or for their participation in an antitumor immune response. Our data support the notion that lymphocytes can enter tumors via aberrantly formed blood and lymphatic vessels. Such findings suggest that targeting both the tumor vasculature and lymphatics will alter the balance of lymphocyte subpopulations that enter the tumor mass. A consideration of this aspect of tumor immunology may be critical to the success of solid cancer immunotherapies.

MUC1 is a novel costimulatory molecule of human T cells and functions in an AP-1-dependent manner

MUC1 mucin, primarily known as an epithelial antigen, has been demonstrated to be expressed on activated human T cells. In the present study, we first examined the expression of MUC1 on different subsets of T cells (naive, effector, effector/memory). MUC1 appears to be strongly upregulated on activated CD4(+) T cells in comparison with CD8(+) T cells. The cytoplasmic tail of MUC1 contains both immune tyrosine-based activation and inhibitory motifs; therefore, we investigated whether MUC1 can also act as a costimulatory molecule on human T cells. Nonpurified T-cell cultures from human peripheral blood exhibited enhanced proliferation and an increase in cytokine production when CD3 and MUC1 were cross-linked and coligated. The intracellular mechanism of MUC1-mediated costimulation was determined to be mediated by the calcium-dependent NF-AT pathway. We further demonstrated that the cytoplasmic tail of MUC1 binds to the AP-1 transcription factors c-Fos and c-Jun, with c-Fos binding constitutively and c-Jun binding only after MUC1 stimulation. Their nuclear migration is then facilitated in a CD3-dependent manner. Our findings clearly demonstrate that MUC1 is a novel T-cell costimulatory molecule involved in immune regulation. These studies delineate important mechanisms of T-cell activation and regulation.

Aberrant expression of CD27 and soluble CD27 (sCD27) in HIV infection and in AIDS-associated lymphoma

CD27 is a member of the tumor necrosis factor receptor superfamily that is expressed primarily on T cells, as well as on subsets of B cells and NK cells. CD70, which is expressed on activated B and T cells, but not on resting lymphocytes, is a ligand for CD27. Cell surface CD27 can be proteolytically cleaved to produce a 32-kDa soluble CD27 (sCD27) molecule. Elevated levels of sCD27 are seen in a number of disease states and malignancies. Although it has been reported that cerebrospinal fluid sCD27 levels were elevated in people who had AIDS dementia, little is known about CD27 expression in HIV disease. To determine if sCD27 levels were elevated in those with HIV infection, and/or in those with AIDS-associated non-Hodgkin's lymphoma (AIDS-NHL), sCD27 levels were measured in HIV-negative and HIV-positive subjects as well as in people who developed AIDS-NHL. Serum sCD27 levels were seen to be elevated in HIV+ subjects. Furthermore, sCD27 levels were particularly elevated in those subjects who went on to develop AIDS-NHL, with serum sCD27 levels in AIDS-NHL subjects being significantly higher than those in HIV+ subjects who did not develop lymphoma. Most AIDS-NHL cell lines and primary AIDS-NHL tumor specimens expressed both CD27 and its ligand, CD70. The proportion of circulating B cells that expressed cell surface CD27 was substantially reduced in those with HIV infection, and B cells from HIV-infected subjects produced decreased levels of sCD27 in culture. Together, these results indicate that CD27/sCD27 expression is abnormal in HIV infection and suggest that this molecule merits further examination as a potential marker for AIDS-NHL.