Correlation of human CD56+ cell cytotoxicity and IFN-gamma production

CD200/CD200R: Bidirectional Role in Cancer Progression and Immunotherapy

As an immune checkpoint molecule, CD200 serves a foundational role in regulating immune homeostasis and promoting self-tolerance. While CD200 expression occurs in various immune cell subsets and normal tissues, its aberrant expression patterns in hematologic malignancies and solid tumors have been linked to immune evasion and cancer progression under pathological conditions, particularly through interactions with its cognate receptor, CD200R. Through this CD200/CD200R signaling pathway, CD200 exerts its immunosuppressive effects by inhibiting natural killer (NK) cell activation, cytotoxic T cell functions, and M1-polarized macrophage activity, while also facilitating expansion of myeloid-derived suppressor cells (MDSCs) and Tregs. Moreover, CD200/CD200R expression has been linked to epithelial-to-mesenchymal transition and distant metastasis, further illustrating its role in cancer progression. Conversely, CD200 has also been shown to exert anti-tumor effects in certain cancer types, such as breast carcinoma and melanoma, indicating that CD200 may exert bidirectional effects on cancer progression depending on the specific tumor microenvironment (TME). Regardless, modulating the CD200/CD200R axis has garnered clinical interest as a potential immunotherapeutic strategy for cancer therapy, as demonstrated by early-phase clinical trials. However, further research is necessary to fully understand the complex interactions of CD200 in the tumor microenvironment and to optimize its therapeutic potential in cancer immunotherapy.

Antibodies conjugated with viral antigens elicit a cytotoxic T cell response against primary CLL ex vivo

Chronic lymphocytic leukemia (CLL) is the most frequent B cell malignancy in Caucasian adults. The therapeutic armamentarium against this incurable disease has recently seen a tremendous expansion with the introduction of specific pathway inhibitors and innovative immunotherapy. However, none of these approaches is curative and devoid of side effects. We have used B-cell-specific antibodies conjugated with antigens (AgAbs) of the Epstein-Barr virus (EBV) to efficiently expand memory CD4⁺ cytotoxic T lymphocytes (CTLs) that recognized viral epitopes in 12 treatment-naive patients with CLL. The AgAbs carried fragments from the EBNA3C EBV protein that is recognized by the large majority of the population. All CLL cells pulsed with EBNA3C-AgAbs elicited EBV-specific T cell responses, although the intensity varied across the patient collective. Interestingly, a large proportion of the EBV-specific CD4⁺ T cells expressed granzyme B (GrB), perforin, and CD107a, and killed CLL cells loaded with EBV antigens with high efficiency in the large majority of patients. The encouraging results from this preclinical ex vivo study suggest that AgAbs have the potential to redirect immune responses toward CLL cells in a high percentage of patients in vivo and warrant the inception of clinical trials.

1,25-Dihydroxy-vitamin D3 regulates NK-cell cytotoxicity, cytokine secretion, and degranulation in women with recurrent pregnancy losses

Vitamin D has a pivotal role in regulating immune responses by promoting Th2 immune responses and suppressing Th1 responses. Propensities to a Th1 immune response and increased NK-cell levels and cytotoxicity have been reported in women with recurrent pregnancy losses (RPL). In women with RPL, vitamin D deficiency is prevalent; however, the effect of vitamin D on NK cells is largely unknown. In this study, we demonstrated that CD69(+) activating receptor expression on NK cells was significantly decreased by incubation with 1,25(OH)2 D3 in a dose-dependent manner, while CD158a and CD158b inhibitory receptor expression was upregulated. The degranulation marker CD107a was significantly downregulated on NK cells following incubation with 1,25(OH)2 D3 . NK-cell conjugation with K562 target cells was not affected by 1,25(OH)2 D3 ; however, depolarization of perforin granules in conjugated NK cells was significantly increased. TLR4 expression on NK cells was significantly decreased and TNF-α and IFN-γ production was significantly reduced by 1,25(OH)2 D3 through interference with NF-κB. Our results suggest 1,25(OH)2 D3 has immune regulatory effects on NK cell cytotoxicity, cytokine secretion and degranulation process as well as TLR4 expression. Potential therapeutic application of 1,25(OH)2 D3 for dysregulated NK-cell immunity should be explored in the future.

ELISPOT Assay for Monitoring Cytotoxic T Lymphocytes (CTL) Activity in Cancer Vaccine Clinical Trials

The profiling and monitoring of immune responses are key elements in the evaluation of the efficacy and development of new biotherapies, and a number of assays have been introduced for analyzing various immune parameters before, during, and after immunotherapy. The choice of immune assays for a given clinical trial depends on the known or suggested immunomodulating mechanisms associated with the tested therapeutic modality. Cell-mediated cytotoxicity represents a key mechanism in the immune response to various pathogens and tumors. Therefore, the selection of monitoring methods for the appropriate assessment of cell-mediated cytotoxicity is thought to be crucial. Assays that can detect both cytotoxic T lymphocytes (CTL) frequency and function, such as the IFN-γ enzyme-linked immunospot assay (ELISPOT) have gained increasing popularity for monitoring clinical trials and in basic research. Results from various clinical trials, including peptide and whole tumor cell vaccination and cytokine treatment, have shown the suitability of the IFN-γ ELISPOT assay for monitoring T cell responses. However, the Granzyme B ELISPOT assay and Perforin ELISPOT assay may represent a more direct analysis of cell-mediated cytotoxicity as compared to the IFN-γ ELISPOT, since Granzyme B and perforin are the key mediators of target cell death via the granule-mediated pathway. In this review we analyze our own data and the data reported by others with regard to the application of various modifications of ELISPOT assays for monitoring CTL activity in clinical vaccine trials.

CD200 expression suppresses natural killer cell function and directly inhibits patient anti-tumor response in acute myeloid leukemia

Upregulation of the immunosuppressive cell surface glycoprotein, CD200, is a common feature of acute myeloid leukemia (AML) and is associated with poor patient outcome. We investigated whether CD200 overexpression on AML cells could specifically compromise patient natural killer (NK) cell anti-tumor responses. We found that CD200(hi) patients showed a 50% reduction in the frequency of activated NK cells (CD56(dim)CD16(+)) compared with CD200(lo) patients. Additionally, NK receptor expression (NKp44 and NKp46) on these cells was also significantly downregulated in CD200(hi) patients. To assess whether NK cell activity was directly influenced by CD200 expression, we examined the effect of ectopic expression of CD200. These assays revealed that both NK cell cytolytic activity and interferon-γ response were significantly reduced toward CD200(+) leukemic targets and that these targets showed increased survival compared with CD200(-) cells. Similarly, NK cells isolated from AML patients were less functionally active toward CD200(hi) autologous blasts from both cytolytic and immunoregulatory perspectives. Finally, blocking CD200 alone was sufficient to recover a significant proportion of NK cell cytolytic activity. Together, these findings provide the first evidence that CD200 has a direct and significant suppressive influence on NK cell activity in AML patients and may contribute to the increased relapse rate in CD200(+) patients.

New flow cytometric assays for monitoring cell-mediated cytotoxicity

The exact immunologic responses after vaccination that result in effective antitumor immunity have not yet been fully elucidated and the data from ex vivo T-cell assays have not yet defined adequate surrogate markers for clinical efficacy. A more detailed knowledge of the specific immune responses that correlate with positive clinical outcomes should help to develop better or novel strategies to effectively activate the immune system against tumors. Furthermore, clinically relevant material is often limited and, thus, precludes the ability to perform multiple assays. The two main assays currently used to monitor lymphocyte-mediated cytoxicity in cancer patients are the (51)Cr-release assay and IFN-gamma ELISpot assay. The former has a number of disadvantages, including low sensitivity, poor labeling and high spontaneous release of isotope from some tumor target cells. Additional problems with the (51)Cr-release assay include difficulty in obtaining autologous tumor targets, and biohazard and disposal problems for the isotope. The ELISpot assays do not directly measure cytotoxic activity and are, therefore, a surrogate marker of cyotoxic capacity of effector T cells. Furthermore, they do not assess cytotoxicity mediated by the production of the TNF family of death ligands by the cytotoxic cells. Therefore, assays that allow for the simultaneous measurement of several parameters may be more advantageous for clinical monitoring. In this respect, multifactor flow cytometry-based assays are a valid addition to the currently available immunologic monitoring assays. Use of these assays will enable detection and enumeration of tumor-specific cytotoxic T lymphocytes and their specific effector functions and any correlations with clinical responses. Comprehensive, multifactor analysis of effector cell responses after vaccination may help to detect factors that determine the success or failure of a vaccine and its immunological potency.

Lipopolysaccharide-mediated mast cell activation induces IFN-gamma secretion by NK cells

Mast cells (MCs) that are well known for their important effector function in IgE-associated immune responses play a key role in innate immune defenses. In this study, we investigate the interaction between MCs and NK cells in vitro and in vivo. We show that mouse bone marrow-derived cultured MCs activated with LPS, polyinosinic-polycytidylic acid, or CpG can stimulate NK cells to secrete increasing concentrations of IFN-gamma. MCs induce a 20-fold increase in IFN-gamma release from NK cells after LPS stimulation. This enhancement of IFN-gamma secretion is cell contact dependent and TNF-alpha independent. Furthermore, we show that this interaction is in part mediated by OX40 ligand on MCs. NK cell-mediated cytotoxicity was not affected by the presence of MCs. Intracellular IFN-gamma levels in splenic NK cells are significantly decreased after i.p. injection of LPS in mast cell-deficient (C57BL/6 Kit(wsh/wsh)) mice in comparison with wild-type mice. In conclusion, our data show for the first time a direct mast cell-dependent NK cell activation. This interaction might play an important role in innate immune defense, as it is dependent on the presence of stimulators relevant in innate immune responses.

Retention of viability, cytotoxicity, and response to IL-2, IL-15, or IFN-alpha by human NK cells after CD107a degranulation

NK cells represent a critical component of the host innate immune response to viral infection and tumor transformation. Nevertheless, the fate of recently degranulated NK cells subsequent to a primary target cell interaction remains largely unexplored. Here, we investigated the long-term viability and killing potential of human NK cells following target cell lysis using live-sorting of CD107a-degranulated NK cells. We observed that sorted CD107a+ NK cells exhibited continued lytic potential against a wide variety of target cells, including tumor and virally infected target cells. CD107a-positive- and CD107a-negative-sorted NK cells displayed similar long-term viability, killing potential, and response to inflammatory cytokines such as IL-2, IL-15, and IFN-alpha. Interestingly, we observed that the CD107a signature is remarkably stable over time and that recently degranulated NK cells exhibit an amplification of CD107 expression immediately following a target cell interaction. Together, our data expand previous data showing that NK cells retain the capacity to kill multiple target cells in succession and reveal that NK viability, cytotoxicity, and response to inflammatory cytokines are not altered following a primary target cell interaction. Overall, our data argue for the strength of the NK cell compartment in the continuous surveillance of tumor and virally infected cells in the body and highlight the use of using CD107a expression as a stable marker for NK cytotoxicity.

A GFP-Transfected HFWT Cell Line, GHINK-1, as a Novel Target for Non-RI Activated Natural Killer Cytotoxicity Assay

An anchorage-dependent Wilms' tumor cell line, HFWT, has been found to be extremely susceptible to human natural killer (NK) cells. Here we established a transfectant of HFWT with the green fluorescence protein (GFP) gene, designated GHINK-1 cells, to apply to the activated NK cytotoxicity assay without radioisotope labeling. After being co-cultured with CD3 CD56+ NK cells, GHINK-1 cells released GFP into the medium. The intensity of the fluorescence from the released GFP correlated almost exactly with the radioactivity of a standard 51Cr-release assay performed with suspension-cultured K562 cells. Because it does not require separation of the remaining live target cells by centrifugation, the non-radioisotopic GFP release assay with GHINK-1 cells is a convenient alternative for monitoring human activated NK killing activity.

LNFPIII/LeX-stimulated macrophages activate natural killer cells via CD40-CD40L interaction

Lacto-N-fucopentaose III (LNFPIII) is a human milk sugar containing the biologically active Lewis X (LeX) trisaccharide. LNFPIII/LeX is also expressed by immunosuppressive helminth parasites, by bacteria, and on a number of tumor/cancer cells. In this report, we first demonstrate that LNFPIII activates macrophages in vitro as indicated by upregulation of Gr-1 expression on F4/80(+) cells. Further, we investigated the effect of LNFPIII-activated macrophages on NK cell activity. We found that LNFPIII-stimulated F4/80(+) cells were able to activate NK cells, inducing upregulation of CD69 expression and gamma interferon (IFN-gamma) production. The experiments show that NK cell activation is macrophage dependent, since NK cells alone did not secrete IFN-gamma in response to LNFPIII. Furthermore, we found that activation of NK cells by glycan-stimulated macrophages required cell-cell contact. As part of the cell-cell contact mechanism, we determined that CD40-CD40L interaction was critical for IFN-gamma secretion by NK cells, as the addition of anti-CD40L antibodies to the coculture blocked IFN-gamma production. We also demonstrated that LNFPIII-stimulated macrophages secrete prostaglandin E(2), interleukin-10 (IL-10), and tumor necrosis factor alpha (TNF-alpha) but a very low level of IL-12. Interestingly, addition of anti-TNF-alpha, anti-IL-10, or anti-IL-12 monoclonal antibodies did not significantly alter NK cell activity. Our data show that these soluble mediators are not critical for LNFPIII-stimulated macrophage activation of NK cells and provide further evidence for the importance of cell-cell contact and CD40-CD40L interactions between macrophages and NK cells.

Vaccination with Ep-CAM protein or anti-idiotypic antibody induces Th1-biased response against MHC class I- and II-restricted Ep-CAM epitopes in colorectal carcinoma patients

PURPOSE

The tumor-associated antigen Ep-CAM (epithelial cell adhesion molecule) is overexpressed in colorectal carcinoma (CRC). The aim of the present study was to evaluate and compare the safety and immunogenicity of a recombinant Ep-CAM protein and a human anti-idiotypic antibody (anti-Id) mimicking Ep-CAM.

EXPERIMENTAL DESIGN

Patients with resected American Joint Committee on Cancer stages II-IV CRC without remaining macroscopic disease received intradermal/subcutaneous injections of Ep-CAM (400 microg/dose; n = 7) or anti-Id (500 microg/dose; n = 6) at weeks 0, 2, and 6 in combination with granulocyte macrophage colony-stimulating factor (75 microg/day, for 4 consecutive days).

RESULTS

Adverse reactions were mild (grade I-II). All patients immunized with the Ep-CAM protein produced Ep-CAM-specific IgG antibodies, predominantly IgG1 and IgG3 subclasses, whereas no humoral response was induced by the anti-Id vaccine. All patients, with one exception in each group, mounted an Ep-CAM-specific proliferative T-cell response. The immune response was more rapid, potent, and protracted after Ep-CAM in comparison with anti-Id vaccination. Interferon-gamma-secreting cells (ELISPOT) were detected in both immunization groups against the Ep-CAM protein as well as various Ep-CAM-derived MHC class I- and II-restricted peptides. Flow cytometry analysis showed that Ep-CAM-specific interferon-gamma- and perforin-producing cells predominantly resided within CD8(+)CD56- and CD8(dim)CD56+ T cells.

CONCLUSIONS

Ep-CAM protein in combination with granulocyte macrophage colony-stimulating factor induced a long-lasting, Th1-biased humoral and cellular immune response compared with anti-Id. Ep-CAM-specific T cells and natural killer-like T cells responding in a MHC class I- and II-restricted manner were also induced. Vaccination with Ep-CAM protein may warrant further investigation as a novel therapeutic approach to CRC.

Modified ELISPOT

The use of the IFN-γ ELISPOT assay to evaluate cellular immune responses has gained increasing popularity, especially as a surrogate measure for CTL responses. We developed and validated some modifications of the IFN-γ ELISPOT assay to optimize immunological monitoring of various cancer vaccine trials. Taking into consideration that the main mechanism of cell-mediated cytotoxicity is the release of cytolytic granules that contain, among others, cytolytic protein Granzyme B (GrB), we developed the GrB ELISPOT assay. Extensive studies demonstrated that the GrB ELISPOT assay is specific, accurately measures the rapid release of GrB, is more sensitive than the 51Cr-release assay, and that it may be successfully applied to measuring CTL precursory frequency in PBMC from cancer patients. Assuming that immunological assays that demonstrate recognition of native tumor cells (tumor-specific) may be more clinically relevant than assays that demonstrate recognition of tumor protein or peptide (antigen-specific), we developed and validated the Autologous Tumor IFN-γ ELISPOT assay using PBMC from idiotype vaccinated lymphoma patients as effectors and autologous B cell lymphoma tumor cells as targets. The precursor frequency of tumor-reactive T cells was significantly higher in the postvaccine PBMC, compared with prevaccine samples in all patients tested. Furthermore, the specificity of these T cells was established by the lack of reactivity against autologous normal B cells. These results demonstrate the feasibility of evaluating tumor-specific T cell responses when autologous, primary tumor cells are available as targets. Modifications of ELISPOT assay described in this chapter allow more comprehensive assessment of low frequency tumor-specific CTL and their specific effector functions and can provide valuable insight with regards to immune responses in cancer vaccine trials.

Evaluating the cytotoxicity of innate immune effector cells using the GrB ELISPOT assay

Background

This study assessed the Granzyme B (GrB) ELISPOT as a viable alternative to the ⁵¹Cr-release assay for measuring cytotoxic activity of innate immune effector cells. We strategically selected the GrB ELISPOT assay because GrB is a hallmark effector molecule of cell-mediated destruction of target cells.

Methods

We optimized the GrB ELISPOT assay using the human-derived TALL-104 cytotoxic cell line as effectors against K562 target cells. Titration studies were performed to assess whether the ELISPOT assay could accurately enumerate the number of GrB-secreting effector cells. TALL-104 were treated with various secretion inhibitors and utilized in the GrB ELISPOT to determine if GrB measured in the ELISPOT was due to degranulation of effector cells. Additionally, CD107a expression on effector cells after effector-target interaction was utilized to further confirm the mechanism of GrB release by TALL-104 and lymphokine-activated killer (LAK) cells. Direct comparisons between the GrB ELISPOT, the IFN-γ ELISPOT and the standard ⁵¹Cr-release assays were made using human LAK cells.

Results

Titration studies demonstrated a strong correlation between the number of TALL-104 and LAK effector cells and the number of GrB spots per well. GrB secretion was detectable within 10 min of effector-target contact with optimal secretion observed at 3–4 h; in contrast, optimal IFN-γ secretion was not observed until 24 h. The protein secretion inhibitor, brefeldin A, did not inhibit the release of GrB but did abrogate IFN-γ production by TALL-104 cells. GrB secretion was abrogated by BAPTA-AM (1,2-bis-(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid tetra(acetoxymethyl) ester), which sequesters intracellular Ca²⁺, thereby preventing degranulation. The number of effector cells expressing the degranulation associated glycoprotein CD107a increased after interaction with target cells and correlated with the stimulated release of GrB measured in the ELISPOT assay.

Conclusions

Because of its high sensitivity and ability to estimate cytotoxic effector cell frequency, the GrB ELISPOT assay is a viable alternative to the ⁵¹Cr-release assay to measure MHC non-restricted cytotoxic activity of innate immune cells. Compared to the IFN-γ ELISPOT assay, the GrB ELISPOT may be a more direct measure of cytotoxic cell activity. Because GrB is one of the primary effector molecules in natural killer (NK) cell-mediated killing, detection and enumeration of GrB secreting effector cells can provide valuable insight with regards to innate immunological responses.

The Granzyme B ELISPOT assay: an alternative to the 51Cr-release assay for monitoring cell-mediated cytotoxicity

Background

The interferon-γ (IFN-γ) ELISPOT assay is one of the most useful techniques for immunological monitoring of cancer vaccine trials and has gained increased application as a measure of specific T cell activation. However, it does not assess cell-mediated cytotoxicity directly as IFN-γ secretion is not limited to only cytolytic cells. Granzyme B (GrB) is a key mediator of target cell death via the granule-mediated pathway. Therefore, the release of GrB by cytolytic lymphocytes upon effector-target interaction may be a more specific indicator of CTL and NK cytotoxic ability than IFN-γ secretion.

Methods

We assessed whether the GrB ELISPOT assay is a viable alternative to the ⁵¹Cr-release and IFN-γ ELISPOT assays for measuring antigen-specific CTL cytotoxicity. Direct comparisons between the three assays were made using human CTL cell lines (αEN-EBV and αJY) and an in vitro stimulated anti-Flu matrix peptide (FMP)-specific CTL.

Results

When the GrB ELISPOT was directly compared to the IFN-γ ELISPOT and ⁵¹Cr-release assays, excellent cross-correlation between all three assays was shown. However, measurable IFN-γ secretion in the ELISPOT assay was observed only after 1 hour of incubation and cytotoxicity assessed via the ⁵¹Cr-release assay after 4 hours, whereas GrB secretion was detectable within 10 min of effector-target contact with significant secretion observed after 1 h. Titration studies demonstrated a strong correlation between the number of effector cells and GrB spots per well. Irrelevant targets or antigens did not induce significant GrB secretion. Additionally, GrB secretion was abrogated when CTL cultures were depleted of CD8+ cells.

Conclusion

Our findings demonstrate that the GrB ELISPOT assay is a superior alternative to the ⁵¹Cr-release assay since it is significantly more sensitive and provides an estimation of cytotoxic effector cell frequency. Additionally, unlike the IFN-γ ELISPOT assay, the GrB ELISPOT directly measures the release of a cytotolytic protein. Detection of low frequency tumor-specific CTL and their specific effector functions can provide valuable insight with regards to immunological responses.

Natural killer cell cytotoxicity: a methods analysis of 51chromium release versus flow cytometry

The purpose of this study is to describe design considerations for the use of flow cytometry (FC) compared to 51chromium (51Cr)-release assays utilizing cryopreserved peripheral blood mononuclear cells (PBMCs) to detect natural killer (NK) cell cytotoxicity. Subjects were 10 healthy women aged 18 to 39 years. Intra-assay variability between methods differed only at the lowest effector-target ratios evaluated. Interassay variability was wide but did not differ between methods. The relationship of lytic unit-10 between methods was strongly positive. Cytotoxicity detected by 51Cr release was higher than that detected by FC for all 10 subjects. Cost was comparable. However, had more assays been performed, technician time would have been greater with flow cytometry. More whole blood was needed to perform the flow cytometry cytotoxicity assay than 51Cr-release cytotoxicity assay. The authors found no compelling reason to adopt NK cell cytotoxicity by flow cytometry over 51Cr release.