Search

The possible therapeutic benefits of B-cell depletion in combating tumoral immune escape have been debated. In support of this concept, metastasis of highly aggressive 4T1 breast cancer cells in mice can be abrogated by inactivation of tumor-evoked regulatory B cells (tBreg). Here, we report the unexpected finding that B-cell depletion by CD20 antibody will greatly enhance cancer progression and metastasis. Both murine and human tBregs express low levels of CD20 and, as such, anti-CD20 mostly enriches for these cells. In the 4T1 model of murine breast cancer, this effect of enriching for tBregs suggests that B-cell depletion by anti-CD20 may not be beneficial at all in some cancers. In contrast, we show that in vivo–targeted stimulation of B cells with CXCL13-coupled CpG oligonucleotides (CpG-ODN) can block cancer metastasis by inhibiting CD20Low tBregs. Mechanistic investigations suggested that CpG-ODN upregulates low surface levels of 4-1BBL on tBregs to elicit granzyme B–expressing cytolytic CD8+ T cells, offering some explanative power for the effect. These findings underscore the immunotherapeutic importance of tBreg inactivation as a strategy to enhance cancer therapy by targeting both the regulatory and activating arms of the immune system in vivo. Cancer Res; 73(7); 2127–38. ©2013 AACR.

Thymus, brain, and testes-associated (Tbata) is a negative control cell-cycle gene highly expressed in murine thymic epithelial cells (TECs). Tbata protein binds to Uba3, inhibiting formation of Nedd8 E1 and subsequent target degradation via neddylation of several cell cycle control proteins needed for G2/M transition, which may be a major mechanism of TEC growth arrest during thymic involution. Etoposide is a cytotoxic drug which targets the enzyme toposimerase II — increased 2-3 fold during the G2 phase. To further characterize effect of Tbata on the cell cycle, we modified p53 wild-type U2OS cells derived from human osteosarcoma to express a Tbata/mCherry fusion protein when mifepristone is added to culture media. Tbata-expressing cells identified on flow cytometry did exhibit growth arrest, with quantitative assessment of DNA content in U2OS cells by flow cytometry establishing that 32% of Tbata/mCherry-expressing cells were in the G2 phase when exposed to mifepristone for 24 hours, compared to 11% of mCherry-expressing cells. Gene expression studies were consistent with these results. Cells expressing Tbata/mCherry were also more sensitive to etoposide at 0.5, 1, and 5 times the IC50 dose. To test whether p53 function was required, we further modified the cells to overexpress a dominant negative p53 mutant along with Tbata/mCherry. Similar G2 arrest and increased sensitivity to etoposide were observed, indicating that the effects of Tbata did not require normal p53 function. Potential Tbata analogues or mimetics may therefore be used as an adjunct to G2-targeted chemotherapy. Citation Format: Milos D. Miljkovic, Francis A. Flomerfelt, Ronald E. Gress. Tbata induces G2/M cell cycle arrest and sensitizes osteosarcoma cells to etoposide in a p53-independent manner [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 313. doi:10.1158/1538-7445.AM2017-313

Human T cell lymphomas of an immature phenotype with mediastinal origin are classified as T cell lymphoblastic lymphomas (T-LBL) and comprise 85-90% of all lymphoblastic lymphomas. Treatment of T-LBL can be challenging because of the metastasizing nature of the disease, which commonly localizes to the bone marrow and can be found in other organs such as liver and spleen. We have developed a mouse T-LBL model by establishing a cell line from a spontaneous mediastinal tumor found in a T cell receptor (TCR) transgenic mouse strain. The resulting T-LBL like cell line, JMR4, has a known TCR (2C), known alloreactivity (H-2Ld), and known stimulating self-peptide (SIYR). JMR4 has an immature T cell phenotype, which includes a mixture of CD4+/CD8+, CD4lo/CD8+, CD4+/CD8lo and CD4+ cells. Other T cell markers, such as CD5, CD24 and CD69 are expressed at various levels depending on the phenotypic subset. The 2C TCR, which can be detected using the 1B2 idiotypic mAb, has been shown to be functional using flow cytometric analysis following TCR stimulation using peptide loaded thymic stromal feeder cells. In addition, JMR4 can be phenotypically altered (CD4/CD8/CD5/CD69 expression levels) differentially in vitro using the bone marrow stromal cell line OP9 and OP9DL, suggesting that it has pluripotency. Finally, when JMR4 is injected into sub-lethally irradiated mice, it develops into a multi-organ lymphoma. Interestingly, the phenotype of the JMR4 cells, based on CD4 and CD8 expression levels, is differentially regulated depending on organ type and MHC of the host, making JMR4 an ideal model to study the complex interactions of a tumor with its microenvironment. Understanding the mechanisms involved in tumor microenvironment (TME) induced changes to tumor cells should be important in understanding metastatic tumor progression and in designing new treatment regimens. Citation Format: Philip J. Lucas, Ronald E. Gress. Differential effect of microenvironment on tumor phenotype using an immature T cell lymphoma mouse model. [abstract]. In: Proceedings of the Fourth AACR International Conference on Frontiers in Basic Cancer Research; 2015 Oct 23-26; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2016;76(3 Suppl):Abstract nr B09.

Cancer metastasis is a leading cause of cancer morbidity and mortality. More needs to be learned about mechanisms that control this process. In particular, the role of chemokine receptors in metastasis remains controversial. Here, using a highly metastatic breast cancer (4T1) model, we show that lung metastasis is a feature of only a proportion of the tumor cells that express CCR4. Moreover, the primary tumor growing in mammary pads activates remotely the expression of TARC/CCL17 and MDC/CCL22 in the lungs. These chemokines acting through CCR4 attract both tumor and immune cells. However, CCR4-mediated chemotaxis was not sufficient to produce metastasis, as tumor cells in the lung were efficiently eliminated by natural killer (NK) cells. Lung metastasis required CCR4+ regulatory T cells (Treg), which directly killed NK cells using β-galactoside–binding protein. Thus, strategies that abrogate any part of this process should improve the outcome through activation of effector cells and prevention of tumor cell migration. We confirm this prediction by killing CCR4+ cells through delivery of TARC-fused toxins or depleting Tregs and preventing lung metastasis. [Cancer Res 2009;69(14):5996–6004]

Tumorigenesis in rodents, as well as in humans, has been shown to be a multistep process, with each step reflecting an altered gene product or gene regulatory process leading to autonomy of cell growth. Initial genetic mutations are often associated with dysfunctional growth regulation, as is demonstrated in several transgenic mouse models. These changes are often followed by alterations in tumor suppressor gene function, allowing unchecked cell cycle progression and, by genomic instability, additional genetic mutations responsible for tumor metastasis. Here we show that reduced transforming growth factor-β signaling in T lymphocytes leads to a rapid expansion of a CD8+ memory T-cell population and a subsequent transformation to leukemia/lymphoma as shown by multiple criteria, including peripheral blood cell counts histology, T-cell receptor monoclonality, and host transferability. Furthermore, spectral karyotype analysis of the tumors shows that the tumors have various chromosomal aberrations. These results suggest that reduced transforming growth factor-β signaling acts as a primary carcinogenic event, allowing uncontrolled proliferation with consequent accumulation of genetic defects and leukemic transformation.