Endogenous CCL21-Ser deficiency reduces B16-F10 melanoma growth by enhanced antitumor immunity.

The chemokine CCL21 regulates immune and cancer cell migration through its receptor CCR7. The Ccl21a gene encodes the isoform CCL21-Ser, predominantly expressed in the thymic medulla and the secondary lymphoid tissues. This study examined the roles of CCL21-Ser in the antitumor immune response in Ccl21a-knockout (KO) mice. The Ccl21a-KO mice showed significantly decreased growth of B16-F10 and YUMM1.7 melanomas and increased growth of MC38 colon cancer, despite no significant difference in LLC lung cancer and EO771 breast cancer. The B16-F10 tumor in Ccl21a-KO mice showed melanoma-specific activated CD8+ T cell and NK cell infiltration and higher Treg counts than wild-type mice. B16-F10 tumors in Ccl21a-KO mice showed a reduction in the positive correlation between the ratio of regulatory T cells (Tregs) to activated CD8+ T cells and tumor weight. In Ccl21a-KO tumor, the intratumoral Tregs showed lower co-inhibitory receptors TIM-3 and TIGIT. Taken together, these results suggest that endogenous CCL21-Ser supports melanoma growth in vivo by maintaining Treg function and suppressing antitumor immunity by CD8+ T cells.

CCL21-Ser expression in melanoma cells recruits CCR7+ naïve T cells to tumor tissues and promotes tumor growth.

CCL21-Ser, a chemokine encoded by the Ccl21a gene, is constitutively expressed in the thymic epithelial cells and stromal cells of secondary lymphoid organs. It regulates immune cell migration and survival through its receptor CCR7. Herein, using CCL21-Ser-expressing melanoma cells and the Ccl21a-deficient mice, we demonstrated the functional role of cancer cell-derived CCL21-Ser in melanoma growth in vivo. The B16-F10 tumor growth was significantly decreased in Ccl21a-deficient mice compared with that in wild-type mice, indicating that host-derived CCL21-Ser contributes to melanoma proliferation in vivo. In Ccl21a-deficient mice, tumor growth of melanoma cells expressing CCL21-Ser was significantly enhanced, suggesting that CCL21-Ser from melanoma cells promotes tumor growth in the absence of host-derived CCL21-Ser. The increase in tumor growth was associated with an increase in the CCR7+ CD62L+ T cell frequency in the tumor tissue but was inversely correlated with Treg frequency, suggesting that naïve T cells primarily promote tumor growth. Adoptive transfer experiments demonstrated that naïve T cells are preferentially recruited from the blood into tumors with melanoma cell-derived CCL21-Ser expression. These results suggest that CCL21-Ser from melanoma cells promotes the infiltration of CCR7+ naïve T cells into the tumor tissues and creates a tumor microenvironment favorable for melanoma growth.

Novel anti-GARP antibody DS-1055a augments anti-tumor immunity by depleting highly suppressive GARP+ regulatory T cells.

Regulatory T (Treg) cells, which are essential for maintaining self-tolerance, inhibit anti-tumor immunity, consequently hindering protective cancer immunosurveillance, and hampering effective anti-tumor immune responses in tumor-bearing hosts. Here, we show that depletion of Treg cells via targeting glycoprotein A repetitions predominant (GARP) induces effective anti-tumor immune responses. GARP was specifically expressed by highly suppressive Treg cells in the tumor microenvironment (TME) of multiple cancer types in humans. In the periphery, GARP was selectively induced in Treg cells, but not in effector T cells, by polyclonal stimulation. DS-1055a, a novel afucosylated anti-human GARP monoclonal antibody, efficiently depleted GARP+ Treg cells, leading to the activation of effector T cells. Moreover, DS-1055a decreased FoxP3+CD4+ T cells in the TME and exhibited remarkable anti-tumor activity in humanized mice bearing HT-29 tumors. We propose that DS-1055a is a new Treg-cell-targeted cancer immunotherapy agent with augmentation of anti-tumor immunity.

A Munc13-like protein in Arabidopsis mediates H+-ATPase translocation that is essential for stomatal responses.

Plants control CO2 uptake and water loss by modulating the aperture of stomata located in the epidermis. Stomatal opening is initiated by the activation of H(+)-ATPases in the guard-cell plasma membrane. In contrast to regulation of H(+)-ATPase activity, little is known about the translocation of the guard cell H(+)-ATPase to the plasma membrane. Here we describe the isolation of an Arabidopsis gene, PATROL1, that controls the translocation of a major H(+)-ATPase, AHA1, to the plasma membrane. PATROL1 encodes a protein with a MUN domain, known to mediate synaptic priming in neuronal exocytosis in animals. Environmental stimuli change the localization of plasma membrane-associated PATROL1 to an intracellular compartment. Plasma membrane localization of AHA1 and stomatal opening require the association of PATROL1 with AHA1. Increased stomatal opening responses in plants overexpressing PATROL1 enhance the CO2 assimilation rate, promoting plant growth.

Impaired osteoclast differentiation and function and mild osteopetrosis development in Siglec-15-deficient mice.

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) is a cell surface receptor for sialylated glycan ligands. Recent in vitro studies revealed upregulated Siglec-15 expression in differentiated osteoclasts and inhibition of osteoclast differentiation by anti-Siglec-15 polyclonal antibody, demonstrating Siglec-15 involvement in osteoclastogenesis. To discern the physiological role of Siglec-15 in skeletal development and osteoclast formation and/or function in vivo, we generated Siglec-15-deficient (siglec-15(-/-)) mice and analyzed their phenotype. The siglec-15(-/-) mice developed without physical abnormalities other than increased trabecular bone mass in lumbar vertebrae and metaphyseal regions of the femur and tibia, causing mild osteopetrosis. Histological analyses demonstrated that the number of osteoclasts present on the femoral trabecular bone of the mutant mice was comparable to that of the wild-type mice. However, urinary deoxypyridinoline, a systemic bone resorption marker, decreased in the siglec-15(-/-) mice, indicating that impaired osteoclast function was responsible for increased bone mass in the mutant mice. In addition, the ability of bone marrow-derived monocytes/macrophages from the siglec-15(-/-) mice to differentiate into osteoclasts was impaired, as determined in vitro by cellular tartrate-resistant acid phosphatase activity in response to the receptor activator of nuclear factor-κB ligand or tumor necrosis factor-α. These results reveal the importance of Siglec-15 in the regulation of osteoclast formation and/or function in vivo, providing new insights into osteoclast biology.