Generation Of Cytotoxic Effectors Research Articles

CD39: A complementary target to immune checkpoints to counteract tumor-mediated immunosuppression

We report that CD39–expressing-melanoma cells inhibited both T-cell proliferation and the generation of cytotoxic effectors in an adenosine-dependent manner, and that treatment with a CD39-blocking antibody alleviated tumor-mediated immunosuppression. Thus, blocking CD39 ectonucleotidase may represent a novel immunotherapeutic strategy to restore antitumor immunity.

The imidazoquinolines — mechanism of action and therapeutic potential in HPV-associated disease

AbstractDendritic cells and macrophages have a central role as a bridge between innate and adaptive immunity and pharmacological agents that modulate the functions of these cells could have therapeutic value. The imidazoquinoline compounds of which imiquimod, formulated as Aldara™, is the best characterised to date are such molecules. Imiquimod and its homologues are agonists of TLR7 and TLR8 thereby inducing secretion of pro-inflammatory cytokines, predominantly IFN-α, TNF-α and IL-12. This locally generated cytokine milieu biases to a Th1-cell-mediated immune response with the generation of cytotoxic effectors and this has been exploited clinically in the treatment of both benign and neoplastic HPV-associated disease. Imiquimod has been shown to be significantly more effective than placebo in clearing genital warts and mechanism of action studies indicate that this is related to the ability to generate pro-inflammatory cytokines and a Th1 response. Intra-epithelial neoplasms of cutaneous and mucosal sur...

Imiquimod and the imidazoquinolones: mechanism of action and therapeutic potential.

A central development of the past decade has been in our understanding of the interactions between, and interdependence of, the innate and adaptive immune responses. Innate immunity recognizes 'danger' signals and activates adaptive immunity in a targeted, appropriate and effective response. Dendritic cells and macrophages have a central role in this process, and pharmacological agents that modulate the functions of these cells could have therapeutic value. The imidazoquinolone compounds, of which imiquimod, formulated as Aldara trade mark, is the best characterized to date, are such molecules. Imiquimod and its homologues act by activating macrophages and other cells via binding to cell surface receptors, such as Toll receptor 7, thereby inducing secretion of pro-inflammatory cytokines, predominantly interferon (IFN)-alpha, tumour necrosis factor (TNF)-alpha and interleukin (IL)-12. This locally generated cytokine milieu biases towards a Th1 cell mediated immune response with the generation of cytotoxic effectors, and this has been exploited clinically in the treatment of viral infections (human papillomavirus, herpes simplex virus, molluscum contagiosum) and nonmelanoma skin cancer. Imiquimod has been shown to be significantly more effective than placebo in clearing genital warts, and mechanism of action studies indicate that this is related to the ability to generate proinflammatory cytokines and a Th1 response. Intra-epithelial neoplasms of cutaneous and mucosal surfaces are associated with human papillomavirus infection and there is some evidence that immune response modifiers may have therapeutic value for these lesions. Topical immunotherapy with immunomodulators shows potential for effective and patient-friendly treatment of cutaneous viral infections. These compounds also have adjuvant properties that could significantly enhance conventional vaccine strategies.

IL-4 Inhibits IL-2 Induction of LAK Cytotoxicity in Lymphocytes from a Variety of Lymphoid Tissues

The purpose of this study was to determine the influence of recombinant human interleukin-4 (IL-4) on the regulation of lymphokine-activated killer (LAK) and mixed lymphocyte culture cytotoxic activity. Lymphocytes from several lymphoid tissues were studied including human peripheral blood leukocytes (PBL), spleen cells, thymocytes, and thoracic duct lymphocytes. Cells were cultured with IL-4 in the presence or absence of recombinant human interleukin-2 (IL-2) in 4-day cultures. LAK and natural killer (NK) activities were measured in a standard chromium release cytotoxicity assay against LAK-sensitive, NK-resistant M14 melanoma targets and NK-sensitive K562 erythroleukemic cells. IL-4 alone does not increase NK or LAK activity under the conditions studied. However, IL-4 does inhibit the induction of cytotoxic activity by IL-2. IL-4 inhibits IL-2-induced thymidine incorporation in 3-day PBL cultures, suggesting that the inhibition of cytotoxicity is not a dilution effect due to the proliferation of noncytotoxic cell populations. IL-4 also inhibits the development of LAK and NK-like activities generated in mixed lymphocyte culture (MLC) while augmenting MLC-generated allospecific cytotoxic T lymphocyte activity. Thus, IL-4 appears to inhibit the induction of nonspecific cytotoxic effectors while augmenting the generation of MHC-specific responses. This confirms an important regulatory function for this lymphokine in the generation of cytotoxic effectors.

Pgp-1hi T lymphocytes accumulate with age in mice and respond poorly to concanavalin A.

Aging is associated with an accumulation of T cells functionally hyporesponsive to the effects of mitogens such as concanavalin A. Recent studies in mice and human have identified surface markers useful for distinguishing antigen-stimulated memory T cells from virgin T cells. In mice, memory T cells within the CD8+ cell population have been shown to express relatively high levels of the cell surface glycoprotein Pgp-1. On the theory that aging might diminish the supply of virgin thymic emigrants without compromising the production of memory T cells, we examined the proportion of Pgp-1hiCD4+ and CD8+ cells in the spleen, blood and lymph nodes of mice of varying age. We found a dramatic (2.5-fold) age-associated increase in the percentage of cells with the Pgp-1hi phenotype. By limiting dilution methods, the frequency of concanavalin A-responsive T cells was found to be significantly reduced in the Pgp-1hi cell pool, whether measured by interleukin 2-dependent proliferation, interleukin 2 production or generation of cytotoxic effectors. Pgp-1hi and Pgp-1lo T cells from young mice proliferate equally well when stimulated by optimal doses of phorbol myristate acetate and ionomycin suggesting that the poor responses to concanavalin A do not simply reflect low viability. Aging leads both to an increase in mitogen-hyporesponsive Pgp-1hi T cells, and also to lower responsiveness of cells in the Pgp-1hi subset.

Cell-mediated cytotoxicity in glioma-bearing patients: differential responses of peripheral blood mononuclear cells to stimulation with interleukin-2 and microbial antigen.

Peripheral blood mononuclear cells (PBMC) of malignant glioma-bearing patients were stimulated in vitro with Interleukin-2 (IL-2) or a glucomannan-protein antigen of Candida albicans (GMP) then assayed for proliferation, production of IFN-gamma, and generation of cytotoxic effectors against either K562 tumor cell line or freshly-cultured allogenic glioma cells. PBMC of healthy, age and sex-matched subjects were the controls. PBMC of glioma-bearing patients did not differ, as a whole, from PBMC of healthy donors in IL-2 or GMP-induced proliferation. However, they showed a lesser ability to produce IFN as well as a substantial inability to generate cytotoxic effectors following GMP stimulation. PBMC of glioma patients were fully responsive to IL-2 in cytotoxicity generation, as were the PBMC from normal subjects. The results suggest that glioma patients may have a defective antigen-mediated activation of natural cytotoxic effectors. This hyporesponsiveness is not accompanied by depressed lymphoproliferation and does not apparently involve a reduced response to IL-2.

Heterogeneity of long-term cultured activated killer cells induced by anti-T3 antibody.

The present study has characterized the short term and long term cultured murine-activated killer (AK) cells that are induced by antibody directed against the epsilon-chain of T3 complex. The conventional lymphokine AK (LAK) cells were generated by culturing normal B6 spleen cells with purified human rIL-2. The alpha T3-induced AK cells (T3AK) were induced by culturing normal B6 spleen cells with alpha T3 and were then maintained in culture medium supplemented with human rIL-2 and/or alpha T3. After initial activation with alpha T3, lymphocyte proliferation and generation of cytotoxic effectors (T3AK) were noted, and these events were related to the endogenous production of IL-2 and IL-4. Addition of alpha IL-2 and/or alpha IL-4 suppressed both the proliferative response and the cytotoxic response induced by alpha T3. In comparing the T3AK cells with the conventional LAK cells, there were many similarities as well as some distinct differences. Both cells displayed a similar cytotoxic spectrum against a variety of tumor targets. The T3AK cells usually gave much higher levels of cytotoxic activity against susceptible targets. However, the susceptibility of different tumor targets to conventional LAK cells and T3AK cells varied. The time course for the generation of lytic activity also differed between the conventional LAK and T3AK cells. One distinct difference was their ability to survive in vitro. The conventional LAK cells survived in culture for only 1 wk. The T3AK cells could survive for at least 4 to 5 wk with active growth. The serologic phenotype of the LAK precursors was asialo GM1 (AsGM1+) cells, but the T3AK precursors could be either AsGM1+ or AsGM1-, depending on the target cell. The LAK effectors were both Lyt-2+ and Lyt-2-, but the short-term T3AK effectors were exclusively Lyt-2+. The long term T3AK cells (cultured for more than 2 wk) were found to consist of Lyt-2+ and Lyt-2- cells, and these subsets of T3AK cells showed different target specificities. These findings demonstrate the heterogeneity of LAK and T3AK cells, and this heterogeneous property may contribute to their diversity in specificity against different tumor targets and thus may affect their effectiveness in the immunotherapy of cancer.

Inhibition of in vitro generation of cytotoxicity against tumor cells by monoclonal antibody to Thy-1.

The Thy-1 molecule on murine T lymphocytes has been suggested to play a role in cellular activation events leading to a variety of immunologic functions. We present evidence that this molecule may be involved in signals leading to the in vitro generation of cytotoxic T cells against several tumor cell lines used as stimulators in mixed tumor-lymphocyte culture. The presence of monoclonal antibody against a polymorphic determinant on the Thy-1 molecule markedly reduced the generation of cytotoxicity after three days of culture of murine splenocytes with stimulator tumor cells bearing low levels of Ia antigen. In contrast, no effect was seen when the stimulators were either allogeneic splenocytes, or a tumor cell line expressing large amounts of Ia. These results suggest that the Thy-1 molecule is critically involved in events leading to the generation of cytotoxic effectors under some, but not all conditions.

Natural regulatory cells in murine bone marrow: inhibition of in vitro proliferative and cytotoxic responses to alloantigens.

A lymphocyte-enriched fraction of murine bone marrow (BML), obtained by sucrose density fractionation, contains natural regulatory cells that can profoundly suppress the proliferative and cytotoxic response of syngeneic lymph node cells to irradiated alloantigens in a mixed lymphocyte culture (MLC). A close correlation exists between the inhibition of alloantigen-induced proliferation and the generation of cytotoxic effectors. The suppression of proliferation is dependent on the dose of BML added to the cultures but is not due to cell crowding, since red blood cells, thymocytes, and irradiated splenocytes, all syngeneic to the lymph node responders, do not inhibit proliferation to the degree observed with BML. The addition of BML to cultures does not cause the maximum proliferative response to change from the usual day 5 peak, indicating that there is no change in culture kinetics. The release of nonradioactive thymidine by BML cannot explain the suppression. The target of suppression is maximally affected during the first 24 hr of culture, since adding BML to MLC later than this resulted in negligible inhibition of proliferation. Thus, the natural regulatory cell-mediated suppression reflects inhibition of "early" events in the proliferative response to alloantigens.