Comparative phenotypes of peripheral blood and spleen cells from cancer patients

Low-intensity pulsed ultrasound activated the anti-tumor immunity by irradiating the spleen of mice in 4 T-1 breast cancer

Tumor immunotherapy is booming around the world. However, strategies to activate the immune system and alleviate the immunosuppression still need to be refined. Here, we demonstrate for the first time that low-intensity pulsed ultrasound (LIPUS, spatial average time average intensity (Isata) is 200 mW/cm2, frequency is 0.3 MHz, repetition frequency is 1 kHz, and duty cycle is 20%) triggers the immune system and further reverses the immunosuppressive state in the mouse models of breast cancer by irradiating the spleen of mice. LIPUS inhibited tumor growth and extended survival in mice with 4 T-1 tumors. Further studies had previously shown that LIPUS enhanced the activation of CD4+ and CD8+ T cells in the spleen and led to significant changes in cytokines, as well as induced upregulation of mRNA levels involved in multiple immune regulatory pathways in the spleen. In addition, LIPUS promoted tumor-infiltrating lymphocyte accumulation and CD8+ T cell activation and improved the dynamics of cytokines/chemokines in the tumor microenvironment, resulting in a reversal of the immunosuppressive state of the tumor microenvironment. These results suggest a novel approach to activate the immune response by irradiating the spleen with LIPUS.

Role of myeloid-derived suppressor cells in tumor recurrence

The establishment of primary tumor cells in distant organs, termed metastasis, is the principal cause of cancer mortality and is a crucial therapeutic target in oncology. Thus, it is critical to establish a better understanding of metastatic progression for the future development of improved therapeutic approaches. Indeed, such development requires insight into the timing of tumor cell dissemination and seeding of distant organs resulting in occult lesions. Following dissemination of tumor cells from the primary tumor, they can reside in niches in distant organs for years or decades, following which they can emerge as an overt metastasis. This timeline of metastatic dormancy is regulated by interactions between the tumor, its microenvironment, angiogenesis, and tumor antigen-specific T-cell responses. An improved understanding of the mechanisms and interactions responsible for immune evasion and tumor cell release from dormancy would help identify and aid in the development of novel targeted therapeutics. One such mediator of dormancy is myeloid derived suppressor cells (MDSC), whose number in the peripheral blood (PB) or infiltrating tumors has been associated with cancer stage, grade, patient survival, and metastasis in a broad range of tumor pathologies. Thus, extensive studies have revealed a role for MDSCs in tumor escape from adoptive and innate immune responses, facilitating tumor progression and metastasis; however, few studies have considered their role in dormancy. We have posited that MDSCs may regulate disseminated tumor cells resulting in resurgence of senescent tumor cells. In this review, we discuss clinical studies that address mechanisms of tumor recurrence including from dormancy, the role of MDSCs in their escape from dormancy during recurrence, the development of occult metastases, and the potential for MDSC inhibition as an approach to prolong the survival of patients with advanced malignancies. We stress that assessing the impact of therapies on MDSCs versus other cellular targets is challenging within the multimodality interventions required clinically.

Splenic and PB immune recovery in neoadjuvant treated gastrointestinal cancer patients

In recent years, immune therapy, notably immune checkpoint inhibitors (ICI), in conjunction with chemotherapy and surgery has demonstrated therapeutic activity for some tumor types. However, little is known about the optimal combination of immune therapy with standard of care therapies and approaches. In patients with gastrointestinal (GI) cancers, especially pancreatic ductal adenocarcinoma (PDAC), preoperative (neoadjuvant) chemotherapy has increased the number of patients who can undergo surgery and improved their responses. However, most chemotherapy is immunosuppressive, and few studies have examined the impact of neoadjuvant chemotherapy (NCT) on patient immunity and/or the optimal combination of chemotherapy with immune therapy. Furthermore, the majority of chemo/immunotherapy studies focused on immune regulation in cancer patients have focused on postoperative (adjuvant) chemotherapy and are limited to peripheral blood (PB) and occasionally tumor infiltrating lymphocytes (TILs); representing a minority of immune cells in the host. Our previous studies examined the phenotype and frequencies of myeloid and lymphoid cells in the PB and spleens of GI cancer patients, independent of chemotherapy regimen. These results led us to question the impact of NCT on host immunity. We report herein, unique studies examining the splenic and PB phenotypes, frequencies, and numbers of myeloid and lymphoid cell populations in NCT treated GI cancer patients, as compared to treatment naïve cancer patients and patients with benign GI tumors at surgery. Overall, we noted limited immunological differences in patients 6 weeks following NCT (at surgery), as compared to treatment naive patients, supporting rapid immune normalization. We observed that NCT patients had a lower myeloid derived suppressor cells (MDSCs) frequency in the spleen, but not the PB, as compared to treatment naive cancer patients and patients with benign GI tumors. Further, NCT patients had a higher splenic and PB frequency of CD4+ T-cells, and checkpoint protein expression, as compared to untreated, cancer patients and patients with benign GI tumors. Interestingly, in NCT treated cancer patients the frequency of mature (CD45RO+) CD4+ and CD8+ T-cells in the PB and spleens was higher than in treatment naive patients. These differences may also be associated, in part with patient stage, tumor grade, and/or NCT treatment regimen. In summary, the phenotypic profile of leukocytes at the time of surgery, approximately 6 weeks following NCT treatment in GI cancer patients, are similar to treatment naive GI cancer patients (i.e., patients who receive adjuvant therapy); suggesting that NCT may not limit the response to immune intervention and may improve tumor responses due to the lower splenic frequency of MDSCs and higher frequency of mature T-cells.

In Vivo Evaluation of Near-Infrared Fluorescent Probe for TIM3 Targeting in Mouse Glioma

PURPOSE

Current checkpoint inhibitor immunotherapy strategies in glioblastoma are challenged by mechanisms of resistance including an immunosuppressive tumor microenvironment. T cell immunoglobulin domain and mucin domain 3 (TIM3) is a late-phase checkpoint receptor traditionally associated with T cell exhaustion. We apply fluorescent imaging techniques to explore feasibility of in vivo visualization of the immune state in a glioblastoma mouse model.

PROCEDURES

TIM3 monoclonal antibody was conjugated to a near-infrared fluorescent dye, IRDye-800CW (800CW). The TIM3 experimental conjugate and isotype control were assessed for specificity with immunofluorescent staining and flow cytometry in murine cell lines (GL261 glioma and RAW264.7 macrophages). C57BL/6 mice with orthotopically implanted GL261 cells were imaged in vivo over 4 days after intravenous TIM3-800CW injection to assess tumor-specific uptake. Cell-specific uptake was then assessed on histologic sections.

RESULTS

The experimental TIM3-800CW, but not its isotype control, bound to RAW264.7 macrophages in vitro. Specificity to RAW264.7 macrophages and not GL261 tumor cells was quantitatively confirmed with the corresponding clone of TIM3 on flow cytometry. In vivo fluorescence imaging of the 800CW signal was localized to the intracranial tumor and significantly higher for the TIM3-800CW cohort, relative to non-targeting isotype control, immediately after tail vein injection and for up to 48 h after injection. Resected organs of tumor bearing mice showed significantly higher uptake in the liver and spleen. TIM3-800CW was seen to co-stain with CD3 (13%), CD11b (29%), and CD206 (26%).

CONCLUSIONS

We propose fluorescent imaging of immune cell imaging as a potential strategy for monitoring and localizing immunologically relevant foci in the setting of brain tumors. Alternative markers and target validation will further clarify the temporal relationship of immunosuppressive effector cells throughout glioma resistance.