Discovery of the Selective Protein Kinase C-θ Kinase Inhibitor, CC-90005

The PKC-θ isoform of protein kinase C is selectively expressed in T lymphocytes and plays an important role in the T cell antigen receptor (TCR)-triggered activation of mature T cells, T cell proliferation, and the subsequent release of cytokines such as interleukin-2 (IL-2). Herein, we report the synthesis and structure-activity relationship (SAR) of a novel series of PKC-θ inhibitors. Through a combination of structure-guided design and exploratory SAR, suitable replacements for the basic C4 amine of the original lead (3) were identified. Property-guided design enabled the identification of appropriately substituted C2 groups to afford potent analogs with metabolic stability and permeability to support in vivo testing. With exquisite general kinase selectivity, cellular inhibition of T cell activation as assessed by IL-2 expression, a favorable safety profile, and demonstrated in vivo efficacy in models of acute and chronic T cell activation with oral dosing, CC-90005 (57) was selected for clinical development.

Imaging of Activated T Cells as an Early Predictor of Immune Response to Anti-PD-1 Therapy

Compelling evidence points to immune cell infiltration as a critical component of successful immunotherapy. However, there are currently no clinically available, noninvasive methods capable of evaluating immune contexture prior to or during immunotherapy. In this study, we evaluate a T-cell-specific PET agent, [18F]F-AraG, as an imaging biomarker predictive of response to checkpoint inhibitor therapy. We determined the specificity of the tracer for activated T cells in vitro and in a virally induced model of rhabdomyosarcoma. Of all immune cells tested, activated human CD8⁺ effector cells showed the highest accumulation of [18F]F-AraG. Isolation of lymphocytes from the rhabdomyosarcoma tumors showed that more than 80% of the intratumoral signal came from accumulation of [18F]F-AraG in immune cells, primarily CD8⁺ and CD4⁺. Longitudinal monitoring of MC38 tumor-bearing mice undergoing anti-PD-1 treatment revealed differences in signal between PD-1 and isotype antibody-treated mice early into treatment. The differences in [18F]F-AraG signal were also apparent between responders and nonresponders to anti-PD-1 therapy. Importantly, we found that the signal in the tumor-draining lymph nodes provides key information about response to anti-PD-1 therapy. Overall, [18F]F-AraG has potential to serve as a much needed immunomonitoring clinical tool for timely evaluation of immunotherapy. SIGNIFICANCE: These findings reveal differences in T-cell activation between responders and nonresponders early into anti-PD-1 treatment, which may impact many facets of immuno-oncology, including patient selection, management, and development of novel combinatorial approaches.

An essential role for Scurfin in CD4+CD25+ T regulatory cells

The molecular properties that characterize CD4+CD25+ regulatory T cells (TR cells) remain elusive. Absence of the transcription factor Scurfin (also known as forkhead box P3 and encoded by Foxp3) causes a rapidly fatal lymphoproliferative disease, similar to that seen in mice lacking cytolytic T lymphocyte-associated antigen 4 (CTLA-4). Here we show that Foxp3 is highly expressed by T(R) cells and is associated with T(R) cell activity and phenotype. Scurfin-deficient mice lack T(R) cells, whereas mice that overexpress Foxp3 possess more T(R) cells. In Foxp3-overexpressing mice, both CD4+CD25- and CD4-CD8+ T cells show suppressive activity and CD4+CD25- cells express glucocorticoid-induced tumor-necrosis factor receptor-related (GITR) protein. The forced expression of Foxp3 also delays disease in CTLA-4-/- mice, indicating that the Scurfin and CTLA-4 pathways may intersect and providing further insight into the T(R) cell lineage.

The amount of scurfin protein determines peripheral T cell number and responsiveness

In the absence of the recently identified putative transcription factor scurfin, mice develop a lymphoproliferative disorder resulting in death by 3 wk of age from a pathology that resembles TGF-beta or CTLA-4 knockout mice. In this report, we characterize mice that overexpress the scurfin protein and demonstrate that these animals have a dramatically depressed immune system. Mice transgenic for the Foxp3 gene (which encodes the scurfin protein) have fewer T cells than their littermate controls, and those T cells that remain have poor proliferative and cytolytic responses and make little IL-2 after stimulation through the TCR. Although thymic development appears normal in these mice, peripheral lymphoid organs, particularly lymph nodes, are relatively acellular. In a separate transgenic line, forced expression of the gene specifically in the thymus can alter thymic development; however, this does not appear to affect peripheral T cells and is unable to prevent disease in mice lacking a functional Foxp3 gene, indicating that the scurfin protein acts on peripheral T cells. The data indicate a critical role for the Foxp3 gene product in the function of the immune system, with both the number and functionality of peripheral T cells under the aegis of the scurfin protein.

Lymphoproliferative disorder in CTLA-4 knockout mice is characterized by CD28-regulated activation of Th2 responses

Mice lacking CTLA-4 die at an age of 2-3 wk due to massive lymphoproliferation, leading to lymphocytic infiltration and destruction of major organs. The onset of the lymphoproliferative disease can be delayed by treatment with murine CTLA4Ig (mCTLA4Ig), starting day 12 after birth. In this study, we have characterized the T cells present in CTLA-4-deficient mice before and after mCTLA4Ig treatment. The T cells present in CTLA-4-deficient mice express the activation markers, CD69 and IL-2R; down-regulate the lymphoid homing receptor, CD62L; proliferate spontaneously in vitro and cannot be costimulated with anti-CD28 mAb consistent with a hyperactivated state. The T cells from CTLA-4-deficient mice survive longer in culture correlating with higher expression of the survival factor, Bcl-xL, in these cells. Most significantly, the CD4+ T cell subset present in CTLA-4-deficient mice secretes high levels of IL-4 and IL-5 upon TCR activation. Treatment of CTLA-4-deficient mice treated with mCTLA4Ig reverses the activation and hyperproliferative phenotype of the CTLA-4-deficient T cells and restores the costimulatory activity of anti-CD28 mAb. Furthermore, T cells from mCTLA4Ig-treated mice are not skewed toward a Th2 cytokine phenotype. Thus, CTLA-4 regulates CD28-dependent peripheral activation of CD4+ T cells. This process results in apoptosis-resistant, CD4+ T cells with a predominantly Th2 phenotype that may be involved in the lethal phenotype in these animals.

Lymphoproliferative Disorder in CTLA-4 Knockout Mice Is Characterized by CD28-Regulated Activation of Th2 Responses

Mice lacking CTLA-4 die at an age of 2–3 wk due to massive lymphoproliferation, leading to lymphocytic infiltration and destruction of major organs. The onset of the lymphoproliferative disease can be delayed by treatment with murine CTLA4Ig (mCTLA4Ig), starting day 12 after birth. In this study, we have characterized the T cells present in CTLA-4-deficient mice before and after mCTLA4Ig treatment. The T cells present in CTLA-4-deficient mice express the activation markers, CD69 and IL-2R; down-regulate the lymphoid homing receptor, CD62L; proliferate spontaneously in vitro and cannot be costimulated with anti-CD28 mAb consistent with a hyperactivated state. The T cells from CTLA-4-deficient mice survive longer in culture correlating with higher expression of the survival factor, Bcl-xL, in these cells. Most significantly, the CD4+ T cell subset present in CTLA-4-deficient mice secretes high levels of IL-4 and IL-5 upon TCR activation. Treatment of CTLA-4-deficient mice treated with mCTLA4Ig reverses the activation and hyperproliferative phenotype of the CTLA-4-deficient T cells and restores the costimulatory activity of anti-CD28 mAb. Furthermore, T cells from mCTLA4Ig-treated mice are not skewed toward a Th2 cytokine phenotype. Thus, CTLA-4 regulates CD28-dependent peripheral activation of CD4+ T cells. This process results in apoptosis-resistant, CD4+ T cells with a predominantly Th2 phenotype that may be involved in the lethal phenotype in these animals.

Molecular basis of T cell inactivation by CTLA-4

CTLA-4, a negative regulator of T cell function, was found to associate with the T cell receptor (TCR) complex zeta chain in primary T cells. The association of TCRzeta with CTLA-4, reconstituted in 293 transfectants, was enhanced by p56(lck)-induced tyrosine phosphorylation. Coexpression of the CTLA-4-associated tyrosine phosphatase, SHP-2, resulted in dephosphorylation of TCRzeta bound to CTLA-4 and abolished the p56(lck)-inducible TCRzeta-CTLA-4 interaction. Thus, CTLA-4 inhibits TCR signal transduction by binding to TCRzeta and inhibiting tyrosine phosphorylation after T cell activation. These findings have broad implications for the negative regulation of T cell function and T cell tolerance.

TCR-gamma delta cells in CD3 zeta-deficient mice contain Fc epsilon RI gamma in the receptor complex but are specifically unresponsive to antigen

Unlike TCR-alpha beta cells, TCR-gamma delta cells express a distinct member of the zeta family, the gamma-chain of Fc epsilon RI (Fc epsilon RI gamma) within the TCR complex. To study the role of the Fc epsilon RI gamma-chain in TCR-gamma delta cells, a TCR-gamma delta transgenic mouse (G8) has been crossed with CD3 zeta-chain-deficient mice (G8.zeta-/-). Thy-1+ spleen and lymph node cells of these animals expressed low levels of CD3/TCR. These results suggested that the zeta-chain is required for effective TCR transport to the cell surface. In contrast, intraepithelial TCR-gamma delta cells of G8.zeta-/- mice expressed high levels of TCR. Immunoprecipitation with anti-CD3 showed that Fc epsilon RI gamma-chains were associated with the TCR complex in T cells isolated from zeta-deficient mice. Although the Fc epsilon RI gamma-expressing T cells proliferated in response to stimulation by TCR-specific Abs including anti-CD3 epsilon, anti-pan gamma delta, and anti-V gamma 2 mAb, the G8.zeta-/- T cells did not respond to the G8-specific Ag (T10b), anti-Thy-1 mAb, or Con A. The unresponsiveness to the Ag was not due to the reduced TCR expression, because intraepithelial TCR-gamma delta cells from the zeta-deficient mice did not respond to Ag. The inability of the G8.zeta-/- T cells to respond to Ag could not be overcome by providing an anti-CD28 costimulatory signal or by adding exogenous rIL-2. Taken together, our data suggest that the Fc epsilon RI gamma-chain associates with the TCR-gamma delta complex in the absence of the zeta-chain, but it is not able to substitute for the zeta-chain for effective transport of TCR to the cell surface or functional responses to Ag.

TCR-gamma delta cells in CD3 zeta-deficient mice contain Fc epsilon RI gamma in the receptor complex but are specifically unresponsive to antigen

Unlike TCR-alpha beta cells, TCR-gamma delta cells express a distinct member of the zeta family, the gamma-chain of Fc epsilon RI (Fc epsilon RI gamma) within the TCR complex. To study the role of the Fc epsilon RI gamma-chain in TCR-gamma delta cells, a TCR-gamma delta transgenic mouse (G8) has been crossed with CD3 zeta-chain-deficient mice (G8.zeta-/-). Thy-1+ spleen and lymph node cells of these animals expressed low levels of CD3/TCR. These results suggested that the zeta-chain is required for effective TCR transport to the cell surface. In contrast, intraepithelial TCR-gamma delta cells of G8.zeta-/- mice expressed high levels of TCR. Immunoprecipitation with anti-CD3 showed that Fc epsilon RI gamma-chains were associated with the TCR complex in T cells isolated from zeta-deficient mice. Although the Fc epsilon RI gamma-expressing T cells proliferated in response to stimulation by TCR-specific Abs including anti-CD3 epsilon, anti-pan gamma delta, and anti-V gamma 2 mAb, the G8.zeta-/- T cells did not respond to the G8-specific Ag (T10b), anti-Thy-1 mAb, or Con A. The unresponsiveness to the Ag was not due to the reduced TCR expression, because intraepithelial TCR-gamma delta cells from the zeta-deficient mice did not respond to Ag. The inability of the G8.zeta-/- T cells to respond to Ag could not be overcome by providing an anti-CD28 costimulatory signal or by adding exogenous rIL-2. Taken together, our data suggest that the Fc epsilon RI gamma-chain associates with the TCR-gamma delta complex in the absence of the zeta-chain, but it is not able to substitute for the zeta-chain for effective transport of TCR to the cell surface or functional responses to Ag.

HIV-1 gp120-specific antibody-dependent cell-mediated cytotoxicity correlates with rate of disease progression

The Ab-dependent cell-mediated cytotoxicity (ADCC) activity of anti-gp120 Abs in serum from four groups of HIV-1-positive individuals in the Multicenter AIDS Cohort Study was evaluated at several time points over a 10-yr period. HIV-1-positive individuals who progressed to AIDS within 3 yr of seroconversion (rapid progressors) were compared with seroconverters who did not progress to AIDS within 6 yr (nonrapid progressors) and individuals who were seropositive when they entered the study and did not progress to AIDS within 9-10 yr (nonprogressors). At the visit closest to AIDS, rapid progressors had significantly lower titers of Abs that mediate ADCC against HIV-1 gp120 than those of nonrapid progressors at corresponding visits or those of nonprogressors at any visit. Nonprogressors generally had high titers of ADCC Abs at all visits. Differences between ADCC titers of rapid progressors and nonrapid progressors or nonprogressors remained when longitudinal changes within individuals were compared. Among seroconverters who were nonrapid progressors, those with low or declining ADCC titers lost significantly more CD4+ cells during the study than those whose ADCC titers were stable or increasing, even though both groups had similar serum virion RNA levels. This demonstrates that high titers of Abs that mediate ADCC correlate with a successful host defense against AIDS.

HIV-1 gp120-specific antibody-dependent cell-mediated cytotoxicity correlates with rate of disease progression

The Ab-dependent cell-mediated cytotoxicity (ADCC) activity of anti-gp120 Abs in serum from four groups of HIV-1-positive individuals in the Multicenter AIDS Cohort Study was evaluated at several time points over a 10-yr period. HIV-1-positive individuals who progressed to AIDS within 3 yr of seroconversion (rapid progressors) were compared with seroconverters who did not progress to AIDS within 6 yr (nonrapid progressors) and individuals who were seropositive when they entered the study and did not progress to AIDS within 9-10 yr (nonprogressors). At the visit closest to AIDS, rapid progressors had significantly lower titers of Abs that mediate ADCC against HIV-1 gp120 than those of nonrapid progressors at corresponding visits or those of nonprogressors at any visit. Nonprogressors generally had high titers of ADCC Abs at all visits. Differences between ADCC titers of rapid progressors and nonrapid progressors or nonprogressors remained when longitudinal changes within individuals were compared. Among seroconverters who were nonrapid progressors, those with low or declining ADCC titers lost significantly more CD4+ cells during the study than those whose ADCC titers were stable or increasing, even though both groups had similar serum virion RNA levels. This demonstrates that high titers of Abs that mediate ADCC correlate with a successful host defense against AIDS.

CD28 expression is not essential for positive and negative selection of thymocytes or peripheral T cell tolerance

Thymocyte development requires positive selection of clones that can recognize Ag presented by MHC molecules and negative selection of clones that are self-reactive. However, the costimulatory signals required for negative selection and cell death, or positive selection and the transition to the peripheral lymphoid system, are not well understood. Many molecular interactions that are important for T cell activation have also been found to play a role in thymocyte development. The importance of the CD28/B7 interaction in the activation of mature T cells and recent observations that CD28 may play a role negative selection of developing CD4+CD8+ thymocytes suggest that CD28 may also be involved in development and maintenance of T cell tolerance. CD28-deficient mice were crossed to alpha beta and gamma delta TCR transgenic as well as H-2k Mlsc-bearing animals and were used to address the role of CD28 in positive and negative selection of developing T cells. The CD28-deficient animals demonstrated no obvious deficiency in either positive or negative selection of developing thymocytes. However, when mixed bone marrow chimeras were created with cells derived from both CD28-deficient and wild-type mice, the CD28+ T cells had a selective advantage over the CD28-deficient T cells. Therefore, it appears that CD28, although not essential for the selection of T cells during development, may allow for additional signals that increase the efficiency of selection and/or expansion of peripheral T cell populations.

CD28 expression is not essential for positive and negative selection of thymocytes or peripheral T cell tolerance

Thymocyte development requires positive selection of clones that can recognize Ag presented by MHC molecules and negative selection of clones that are self-reactive. However, the costimulatory signals required for negative selection and cell death, or positive selection and the transition to the peripheral lymphoid system, are not well understood. Many molecular interactions that are important for T cell activation have also been found to play a role in thymocyte development. The importance of the CD28/B7 interaction in the activation of mature T cells and recent observations that CD28 may play a role negative selection of developing CD4+CD8+ thymocytes suggest that CD28 may also be involved in development and maintenance of T cell tolerance. CD28-deficient mice were crossed to alpha beta and gamma delta TCR transgenic as well as H-2k Mlsc-bearing animals and were used to address the role of CD28 in positive and negative selection of developing T cells. The CD28-deficient animals demonstrated no obvious deficiency in either positive or negative selection of developing thymocytes. However, when mixed bone marrow chimeras were created with cells derived from both CD28-deficient and wild-type mice, the CD28+ T cells had a selective advantage over the CD28-deficient T cells. Therefore, it appears that CD28, although not essential for the selection of T cells during development, may allow for additional signals that increase the efficiency of selection and/or expansion of peripheral T cell populations.

TCR gamma delta cells: a specialized T-cell subset in the immune system

Specificity, memory, and self/nonself discrimination are the essential principles that underlie the acquired immune response. From birth through one's life, the immune system is continually responding to new environmental challenges (e.g. bacteria and viruses) and developing a specific, long-lasting immunity to those challenges. The first exposure to a pathogen results in the recruitment of multiple cell types, including macrophages, dendritic cells, and assorted leukocytes, that initiate an antigen nonspecific inflammatory response designed to attract T cells and B cells to the inflammatory sites including the draining lymph nodes. The foreign antigens are concentrated within the professional antigen-presenting cells (APCs) that process and present small antigenic peptides to CD4+ and CD8+ T cells in association with class II and class I major histocompatibility complex (MHC) molecules, respectively. The activated CD4+ T-cell receptor (TCR) alpha beta cells respond vigorously to the pathogen in an antigen-specific manner, liberating a barrage of cytokines that induce B cells to differentiate to antibody-secreting plasma cells and likewise cause CD8+ cells to differentiate into cytolytic effectors. The T cells and B cells expand in an evolving, highly specific manner to control the initial infection while developing long-term acquired immunity such that any further infection by that pathogen is virtually impossible. Thus TCR alpha beta T cells are the central lymphocyte in the immune system, providing specific pathogen recognition and long-term memory all within the context of distinguishing foreign from self antigens. Yet, during a primary immune response, there is a lag time of approximately 3 to 4 days before antigen-specific responses are evident, and TCR alpha beta responses do not peak until approximately day 7. Therefore, it is essential that other strategies are employed by the immune system in order to mount an aggressive early immune response.

Anti-C-reactive protein inhibits cytoskeletal rearrangement without altering calcium influx in natural killer cell activation

C-reactive protein (CRP), an acute phase protein in human serum, is present on large granular lymphocytes (LGL). Anti-CRP inhibits natural killer (NK) cell-mediated lysis. Our current study shows that anti-CRP also inhibits antibody-dependent cell-mediated cytotoxicity (ADCC) of LGL. Calcium influx and protein kinase C (PKC) activation are the early signal transduction events in NK activation. In the conjugates formed between LGL and targets (NK or ADCC), 75-90% of LGL respond with a calcium influx. Addition of anti-CRP had no effect on the percentage of LGL which respond to target cell binding or on the magnitude of the calcium response of LGL. This was true for both NK and ADCC effector cells. Crosslinking anti-CRP with a secondary antibody did not alter this result. Next, the effect of PMA, a PKC activator, and calcium ionophore, A23187, on anti-CRP-mediated inhibition of cytotoxicity were studied. PMA alone reversed most of the inhibition of lysis seen with anti-CRP. Based on previous observations that anti-CRP inhibited target cell-stimulated release of lytic factors, the effect of anti-CRP on release of lytic factors stimulated by PMA and calcium ionophore was evaluated. Anti-CRP blocked the release of lytic factors stimulated by PMA and ionophore. Release of lytic factors involves the rearrangement of cytoskeletal element of NK cell toward the target cell. The effect of anti-CRP on cytoskeletal reorganization was studied. In conjugates formed between effector and target cells, the polarization of cytoskeleton at the contact site of NK and target cell was significantly reduced in the presence of anti-CRP. Although anti-CRP inhibits both ADCC and NK lytic mechanisms, it does not alter target cell-induced Ca2+ influx. CRP interacts with the secretory mechanisms involved in granule exocytosis since anti-CRP inhibits the cytoskeletal polarization and the release of lytic factors and PMA might reverse anti-CRP-mediated inhibition by activating alternative mechanisms of cytotoxicity in effectors.