Limitations of checkpoint inhibitor cancer immunotherapy include induction of autoimmune syndromes and resistance of many cancers. Since CD318, a novel CD6 ligand, is associated with aggressiveness and metastatic potential of human cancers, we tested the effect of an anti-CD6 monoclonal antibody, UMCD6, on killing of cancer cells by human lymphocytes. UMCD6 augmented killing of breast, lung or prostate cancer cells through direct effects on both CD8+ T cells and natural killer (NK) cells, increasing cancer cell death and lowering cancer cell survival in vitro more robustly than monoclonal antibody checkpoint inhibitors that interrupt the PD-1/PD-L1 axis. UMCD6 also augmented in vivo killing by human peripheral blood lymphocytes of a human breast cancer line xeno-transplanted into immunodeficient mice. Mechanistically, UMCD6 upregulated the expression of the activating receptor NKG2D and down-regulated expression of the inhibitory receptor NKG2A on both NK cells and CD8+ T cells, with concurrent increases in perforin and granzyme-B production. The combined capabilities of an anti-CD6 monoclonal antibody to control autoimmunity through effects on CD4+ lymphocyte differentiation, while enhancing killing of cancer cells through distinct effects on CD8+ and NK cells, opens a potential new approach to cancer immunotherapy that would suppress rather than instigate autoimmunity.
Objective CD6 is an important regulator of T cell function that interacts with the ligands CD166 and CD318. To further clarify the significance of CD6 in rheumatoid arthritis (RA), we examined the effects of targeting CD6 in the mouse model of collagen‐induced arthritis (CIA), using CD6‐knockout (CD6‐KO) mice and CD6‐humanized mice that express human CD6 in lieu of mouse CD6 on their T cells. Methods We immunized wild‐type (WT) and CD6 gene–KO mice with a collagen emulsion to induce CIA. For treatment studies using CD6‐humanized mice, mice were immunized similarly and a mouse anti‐human CD6 IgG (UMCD6) or control IgG was injected on days 7, 14, and 21. Joint tissues were evaluated for tissue damage, leukocyte infiltration, and local inflammatory cytokine production. Collagen‐specific Th1, Th9, and Th17 responses and serum levels of collagen‐specific IgG subclasses were also evaluated in WT and CD6‐KO mice with CIA. Results The absence of CD6 reduced 1) collagen‐specific Th9 and Th17, but not Th1 responses, 2) the levels of many proinflammatory joint cytokines, and 3) serum levels of collagen‐reactive total IgG and IgG1, but not IgG2a and IgG3. Joint homogenate hemoglobin content was significantly reduced in CD6‐KO mice with CIA compared to WT mice with CIA (P < 0.05) (reduced angiogenesis). Moreover, treating CD6‐humanized mice with mouse anti‐human CD6 monoclonal antibody was similarly effective in reducing joint inflammation in CIA. Conclusion Taken together, these data suggest that interaction of CD6 with its ligands is important for the perpetuation of CIA and other inflammatory arthritides that are T cell driven.
Cancer immunotherapy is a rapidly advancing and viable approach to treating cancer along with more traditional forms of therapy. Real-time cell analysis technologies that examine the dynamic interactions between cancer cells and the cells of the immune system are becoming more important for assessment of novel therapeutics. In this report, we use the IncuCyte® imaging system to study the killing potential of various immune cells on cancer cell lines. The IncuCyte® system tracks living cells, labeled by a red fluorescent protein, and cell death, as indicated by the caspase-3/7 reagent, which generates a green fluorescent signal upon activation of apoptotic pathways. Despite the power of this approach, obtaining commercially fluorescent cancer cell lines is expensive and limited in the range of cell lines that are available. To overcome this barrier, we developed an inexpensive method using a lentiviral construct expressing nuclear localized mKate2 red fluorescent protein to stably label cancer cells. We demonstrate that this method is effective in labeling a wide variety of cell lines, allowing for analyses of different cancers as well as different cell lines of the same type of cancer.
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