The proteasome inhibitor bortezomib enhances the susceptibility to viral infection

Bortezomib Improves Adoptive T-cell Therapy by Sensitizing Cancer Cells to FasL Cytotoxicity

Cancer immunotherapy shows great promise but many patients fail to show objective responses, including in cancers that can respond well, such as melanoma and renal adenocarcinoma. The proteasome inhibitor bortezomib sensitizes solid tumors to apoptosis in response to TNF-family death ligands. Because T cells provide multiple death ligands at the tumor site, we investigated the effects of bortezomib on T-cell responses in immunotherapy models involving low-avidity antigens. Bortezomib did not affect lymphocyte or tissue-resident CD11c(+)CD8(+) dendritic cell counts in tumor-bearing mice, did not inhibit dendritic cell expression of costimulatory molecules, and did not decrease MHC class I/II-associated antigen presentation to cognate T cells. Rather, bortezomib activated NF-κB p65 in CD8(+) T cells, stabilizing expression of T-cell receptor CD3ζ and IL2 receptor-α, while maintaining IFNγ secretion to improve FasL-mediated tumor lysis. Notably, bortezomib increased tumor cell surface expression of Fas in mice as well as human melanoma tissue from a responsive patient. In renal tumor-bearing immunodeficient Rag2(-/-) mice, bortezomib treatment after adoptive T-cell immunotherapy reduced lung metastases and enhanced host survival. Our findings highlight the potential of proteasome inhibitors to enhance antitumor T-cell function in the context of cancer immunotherapy.

Inhibition and deficiency of the immunoproteasome subunit LMP7 attenuates LCMV-induced meningitis

In addition to antigen processing, immunoproteasomes were recently shown to exert functions influencing cytokine production by monocytes and T cells, T-helper cell differentiation, and T-cell survival. Moreover, selective inhibition of the immunoproteasome subunit LMP7 ameliorated symptoms of autoimmune diseases including CD4(+) T-cell mediated EAE. In this study, we show that LMP7 also plays a crucial role in the pathogenesis of lymphocytic choriomeningitis virus (LCMV)-induced meningitis mediated by CTLs. Mice lacking functional LMP7 display delayed and reduced clinical signs of disease accompanied by a strongly decreased inflammatory infiltration into the brain. Interestingly, we found that selective inhibition and genetic deficiency of LMP7 affect the pathogenesis of LCMV-induced meningitis in a distinct manner. Our findings support the important role of LMP7 in inflammatory disorders and suggest immunoproteasome inhibition as a novel strategy against inflammation-induced neuropathology in the CNS.

The ubiquitin-like modifier FAT10 in antigen processing and antimicrobial defense

The ubiquitin-like modifier (ULM) HLA-F adjacent transcript 10 (FAT10) is encoded in the MHC locus, is up-regulated during dendritic cell maturation, is highly expressed in lymphoid tissues, and strongly induced by interferon (IFN)-γ and tumor necrosis factor (TNF)-α. FAT10 is the only ULM known to date which directly targets its hundreds of substrates for degradation by the proteasome. This implies a role for FAT10 in antigen presentation. Indeed, fusion of FAT10 to viral proteins enhanced their presentation along the proteasome dependent MHC class I presentation pathway. In this review we discuss the FAT10 conjugation system as an alternative and distinct pathway for MHC class I and II antigen processing. Furthermore, we review the recent finding that FAT10 plays a role in antimicrobial defense against intracellular pathogens.

Hepatitis B virus reactivation in patients with multiple myeloma receiving bortezomib-containing regimens followed by autologous stem cell transplant

To investigate hepatitis B virus (HBV) reactivation and survival in patients with multiple myeloma (MM) receiving bortezomib-containing regimens, we analyzed 139 patients with MM receiving bortezomib-containing regimens in our hospital. Twenty-seven/139 patients were hepatitis B surface antigen positive (HBsAg+) with nine having DNA levels > 500 IU/mL, including four > 1000 IU/mL. All but five HBsAg+ patients were treated with lamivudine or entecavir before chemotherapy until at least 6 months after chemotherapy or autologous stem cell transplant (ASCT). HBV reactivation occurred in six HBsAg+ patients and two HBsAg- patients, including six who received ASCT. Overall survival and progression-free survival of HBsAg- patients were significantly longer than for HBsAg+ patients (both p < 0.01). From these results, we confirmed that the incidence of HBV reactivation was notable in patients with MM receiving bortezomib-containing regimens, especially those who underwent ASCT. HBsAg+ patients with MM had a poorer prognosis than HBsAg- patients. Prophylactic treatment should be prescribed to all patients with HBsAg+ MM for a minimum duration of 12 months.

Evaluation of risk of symptomatic cytomegalovirus reactivation in myeloma patients treated with tandem autologous stem cell transplantation and novel agents: a single-institution study

The introduction of proteasome inhibitors and/or immunomodulators in the treatment of myeloma has led to an increase in viral infections, particularly in the Herpesviridae family. Previous studies about the risk of cytomegalovirus (CMV) reactivation after autologous stem cell transplantation (ASCT) have examined the clinical outcome after the first ASCT; however, only 1 study to date has investigated the risk of CMV reactivation after a second transplantation. To address this issue, we performed a retrospective chart review on 78 consecutive myeloma patients (median age 56 years) who underwent a tandem non-CD34(+) selected ASCT after induction treatment with either conventional chemotherapy (n = 42) or with novel agents (n = 36), respectively. All subjects had been mobilized and conditioned with cyclophosphamide plus granulocyte colony-stimulating factor and melphalan alone, respectively. CMV DNA load in the blood has been determined by polymerase chain reaction in the case of a clinical suspicion of CMV reactivation; therefore, routine monitoring was not performed. Considering the outcome of both the first and the second transplantations, we observed a total of 13 episodes of symptomatic CMV reactivation (13/156, 8%), in 12 subjects (12/78, 15%), all successfully treated. Eight subjects experienced a CMV reactivation after the first ASCT (8/78, 10%); however, only 1 of them (1/8, 12%) experienced a CMV reactivation after the second transplantation. Conversely, 4 CMV reactivations (6%) were observed after the second transplantation in the group of 70 patients who did not experience a CMV reactivation after the first ASCT. No statistically significant difference was observed between first and second ASCT (8/78, 10% vs. 5/78, 6%; P = 0.767). Univariate analysis showed that a pre-transplant treatment with novel agents was the only baseline factor significantly associated with the occurrence of post-ASCT CMV symptomatic reactivation after the first transplant (odds ratio [OR]: 9.897; 95% confidence interval [CI]: 1.154-84.840; P = 0.021) but not after the second transplant (OR: 5.125; 95% CI: 0.546-48.119; P = 0.115). No end-organ disease or primary infection was documented. Our data suggest that second transplantation does not increase the risk of CMV reactivation in our patient population, when compared with the first one, and confirm the role of a pre-transplant treatment with novel agents as a risk factor for CMV symptomatic reactivation.

Changing treatment paradigms for patients with plasma cell myeloma: impact upon immune determinants of infection

Plasma cell myeloma (PCM) is increasing in prevalence in older age groups and infective complications are a leading cause of mortality. Patients with PCM are at increased risk of severe infections, having deficits in many arms of the immune system due to disease and treatment-related factors. Treatment of PCM has evolved over time with significant impacts on immune function resulting in changing rates and pattern of infection. Recently, there has been a paradigm shift in the treatment of PCM with the use of immunomodulatory drugs and proteasome inhibitors becoming the standard of care. These drugs have wide-ranging effects on the immune system but their impact on infection risk and aetiology remain unclear. The aims of this review are to discuss the impact of patient, disease and treatment factors on immune function over time for patients with PCM and to correlate immune deficits with the incidence and aetiology of infections seen clinically in these patients. Preventative measures and the need for clinically relevant tools to enable infective profiling of patients with PCM are discussed.

Inhibition of the immunoproteasome ameliorates experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic demyelinating immune mediated disease of the central nervous system. The immunoproteasome is a distinct class of proteasomes found predominantly in monocytes and lymphocytes. Recently, we demonstrated a novel function of immunoproteasomes in cytokine production and T cell differentiation. In this study, we investigated the therapeutic efficacy of an inhibitor of the immunoproteasome (ONX 0914) in two different mouse models of MS. ONX 0914 attenuated disease progression after active and passive induction of experimental autoimmune encephalomyelitis (EAE), both in MOG_35–55 and PLP_139–151-induced EAE. Isolation of lymphocytes from the brain or spinal cord revealed a strong reduction of cytokine-producing CD4⁺ cells in ONX 0914 treated mice. Additionally, ONX 0914 treatment prevented disease exacerbation in a relapsing-remitting model. An analysis of draining lymph nodes after induction of EAE revealed that the differentiation to Th17 or Th1 cells was strongly impaired in ONX 0914 treated mice. These results implicate the immunoproteasome in the development of EAE and suggest that immunoproteasome inhibitors are promising drugs for the treatment of MS.

Invariant chain as a vehicle to load antigenic peptides on human MHC class I for cytotoxic T-cell activation

Protective T-cell responses depend on efficient presentation of antigen (Ag) in the context of major histocompatibility complex class I (MHCI) and class II (MHCII) molecules. Invariant chain (Ii) serves as a chaperone for MHCII molecules and mediates trafficking to the endosomal pathway. The genetic exchange of the class II-associated Ii peptide (CLIP) with antigenic peptides has proven efficient for loading of MHCII and activation of specific CD4(+) T cells. Here, we investigated if Ii could similarly activate human CD8(+) T cells when used as a vehicle for cytotoxic T-cell (CTL) epitopes. The results show that wild type Ii, and Ii in which CLIP was replaced by known CTL epitopes from the cancer targets MART-1 or CD20, coprecipitated with HLA-A*02:01 and mediated colocalization in the endosomal pathway. Furthermore, HLA-A*02:01-positive cells expressing CLIP-replaced Ii efficiently activated Ag-specific CD8(+) T cells in a TAP- and proteasome-independent manner. Finally, dendritic cells transfected with mRNA encoding IiMART-1 or IiCD20 primed naïve CD8(+) T cells. The results show that Ii carrying antigenic peptides in the CLIP region can promote efficient presentation of the epitopes to CTLs independently of the classical MHCI peptide loading machinery, facilitating novel vaccination strategies against cancer.

Proapoptotic effects of the novel proteasome inhibitor b-AP15 on multiple myeloma cells and natural killer cells

The small molecule b-AP15 is a novel inhibitor of proteasome deubiquitination. Recent studies have shown that b-AP15 displays antitumor activity in several preclinical, solid tumor models. In this study, we show that b-AP15 triggers time- and dose-dependent apoptosis of the human multiple myeloma (MM) cell lines RPMI8226 and U266, as determined by phosphatidylserine exposure. Apoptosis was dependent on caspase activation and was partially dependent on cathepsin D. Furthermore, b-AP15 triggered processing of pro-caspase-3 and cleavage of poly (ADP-ribose) polymerase in MM cells. b-AP15 also induced caspase-independent apoptosis in primary human natural killer cells. We also demonstrate that b-AP15 induces activation of the mitochondrial apoptosis pathway in MM cells, with activation of the proapoptotic protein Bax and a pronounced loss of the mitochondrial transmembrane potential. The latter events, however, appeared largely independent of caspase activation. Our data suggest that proteasome deubiquitinase inhibitors may have potential for treatment of multiple myeloma patients.

High incidence of post-transplant cytomegalovirus reactivations in myeloma patients undergoing autologous stem cell transplantation after treatment with bortezomib-based regimens: a survey from the Rome transplant network

The incidence of cytomegalovirus (CMV) reactivations in patients with multiple myeloma (MM) receiving autologous stem cell transplantation (ASCT) is relatively low. However, the recent increased use of novel agents, such as bortezomib and/or immunomodulators, before transplant, has led to an increasing incidence of Herpesviridae family virus infections. The aim of the study was to establish the incidence of post-engraftment symptomatic CMV reactivations in MM patients receiving ASCT, and to compare this incidence with that of patients treated with novel agents or with conventional chemotherapy before transplant. The study was a survey of 80 consecutive patients who underwent ASCT after treatment with novel agents (Group A). These patients were compared with a cohort of 89 patients treated with VAD regimen (vincristine, doxorubicin, and dexamethasone) before ASCT (Group B). Overall, 7 patients (4.1%) received an antiviral treatment for a symptomatic CMV reactivation and 1 died. The incidence of CMV reactivations was significantly higher in Group A than in Group B (7.5% vs. 1.1%; P = 0.048). When compared with Group B, the CMV reactivations observed in Group A were significantly more frequent in patients who received bortezomib, whether or not associated with immunomodulators (9.4% vs. 1.1%; P = 0.019), but not in those treated with immunomodulators only (3.7% vs. 1.1%; P = 0.396). These results suggest that MM patients treated with bortezomib-based regimens are at higher risk of developing a symptomatic CMV reactivation after ASCT.

Brain abscess caused by Nocardia cyriacigeorgica in two patients with multiple myeloma: novel agents, new spectrum of infections

OBJECTIVE AND IMPORTANCE

Introduction of high-dose chemotherapy and the novel agents including bortezomib, Lenalidomide, and Thalidomide has provided a significant progress in the treatment of multiple myeloma (MM) with an increase in median overall survival up to 6-8 years. However, the advances in myeloma treatment comes at a price with new spectrum of treatment-related infectious complications which should be taken into consideration while treating these patients.

CLINICAL PRESENTATION

We report here two patients with Ig G λ MM presenting with intracerebral mass lesions in the abscence of constitutional symptoms that would suggest an infectious etiology. Both patients had severe hypogammaglobulinemia and lymphopenia, which was attributed to treatment regimens including bortezomib. Intervention The surgical intervention-revealed abscess in both cases caused by Nocardia cyriacigeorgica, a relatively new pathogen which rarely causes infections in humans and also an unexpected pathogen in myeloma patients.

CONCLUSION

Although every aspect of immune system is known to be affected in MM, humoral immune deficiency is the hallmark of the inherent immune defect in this disease. Introduction of the novel agents, bortezomib in particular seems to have changed the characteristics of the immune dysfunction and the spectrum of the opportunistic infections by causing qualitative and quantitative changes in cellular immunity. The new spectrum of infectious agents might not be limited to hepatitis B and herpes zoster. Monitoring lymphopenia and administration of prophylactic antimicrobial agents accordingly could be considered in patients treated with bortezomib.

The effect of proteasome inhibition on the generation of the human leukocyte antigen (HLA) peptidome

The Major histocompatibility complex (MHC) class I peptidome is thought to be generated mostly through proteasomal degradation of cellular proteins, a notion that is based on the alterations in presentation of selected peptides following proteasome inhibition. We evaluated the effects of proteasome inhibitors, epoxomicin and bortezomib, on human cultured cancer cells. Because the inhibitors did not reduce the level of presentation of the cell surface human leukocyte antigen (HLA) molecules, we followed their effects on the rates of synthesis of both HLA peptidome and proteome of the cells, using dynamic stable isotope labeling in tissue culture (dynamic-SILAC). The inhibitors reduced the rates of synthesis of most cellular proteins and HLA peptides, yet the synthesis rates of some of the proteins and HLA peptides was not decreased by the inhibitors and of some even increased. Therefore, we concluded that the inhibitors affected the production of the HLA peptidome in a complex manner, including modulation of the synthesis rates of the source proteins of the HLA peptides, in addition to their effect on their degradation. The collected data may suggest that the current reliance on proteasome inhibition may overestimate the centrality of the proteasome in the generation of the MHC peptidome. It is therefore suggested that the relative contribution of the proteasomal and nonproteasomal pathways to the production of the MHC peptidome should be revaluated in accordance with the inhibitors effects on the synthesis rates of the source proteins of the MHC peptides.

The immunoproteasome in antigen processing and other immunological functions

Treatment of cells with interferon-γ leads to the replacement of the constitutive catalytic proteasome subunits β1, β2, and β5 by the inducible subunits LMP2 (β1i), MECL-1 (β2i), and LMP7 (β5i), respectively, building the so-called immunoproteasome. The incorporation of these subunits is required for the production of numerous MHC class-I restricted T cell epitopes. Recently, new evidence for an involvement of the immunoproteasome in other facets of the immune response emerged. Investigations of autoimmune diseases in animal models and a genetic predisposition of β5i in human autoimmune disorders suggest a crucial function of the immunoproteasome in proinflammatory diseases. The recent elucidation of the high-resolution structure of the immunoproteasome will facilitate the design of immunoproteasome selective inhibitors for pharmacological intervention.

Incompatible kidney transplantation: a brief overview of the past, present and future

Live kidney donor transplantation across immunological barriers, either blood group or positive crossmatch [ABO- and human leucocyte antigens (HLA)-incompatible kidney transplantation, respectively], is now practised widely across many transplant centres. This provides transplantation opportunities to patients that hitherto would have been deemed contra-indicated and would subsequently have waited indefinitely for a suitably matched kidney. Protocols have evolved with time as experience has grown and now a variety of desensitization strategies are currently practised to overcome such immunological barriers. In addition, desensitization protocols are complemented by kidney paired donation exchange schemes and therefore incompatible patients now have strategies to either confront or bypass immunological barriers, respectively. As the field expands it is clear that non-transplant clinicians will be exposed to incompatible kidney transplant recipients outside of experienced centres. It is therefore timely to review the evolution of practice that have led to current desensitization modalities, contrast protocols and outcomes of current regimens and speculate on future direction of incompatible kidney transplantation.

Can we change the disease biology of multiple myeloma?

Despite improvements in disease management, multiple myeloma (MM) remains incurable. Conventional treatment methods are unsatisfactory, leading to a pattern of regression and remission, and ultimately failure. This pattern suggests that one of the possible strategies for improving outcomes is continuous therapy to maintain suppression of the surviving tumor cells. Optimal management of MM requires potent agents and modalities with direct tumoricidal activity, which can also provide continuous suppression of the residual tumor to prevent disease relapse. Immunomodulatory agents exert immunomodulatory and tumoricidal effects, and cause disruption of stromal cell support from the bone marrow microenvironment. Therefore continuous therapy with immunomodulatory agents may be able to provide both tumor reduction and tumor suppression, enabling physicians to consider the possibility of incorporating continuous therapy into the treatment paradigm of patients with MM.

Why the structure but not the activity of the immunoproteasome subunit low molecular mass polypeptide 2 rescues antigen presentation

The proteasome is responsible for the generation of most epitopes presented on MHC class I molecules. Treatment of cells with IFN-γ leads to the replacement of the constitutive catalytic subunits β1, β2, and β5 by the inducible subunits low molecular mass polypeptide (LMP) 2 (β1i), multicatalytic endopeptidase complex-like-1 (β2i), and LMP7 (β5i), respectively. The incorporation of these subunits is required for the production of numerous MHC class I-restricted T cell epitopes. The structural features rather than the proteolytic activity of an immunoproteasome subunit are needed for the generation of some epitopes, but the underlying mechanisms have remained elusive. Experiments with LMP2-deficient splenocytes revealed that the generation of the male HY-derived CTL-epitope UTY(246-254) was dependent on LMP2. Treatment of male splenocytes with an LMP2-selective inhibitor did not reduce UTY(246-254) presentation, whereas silencing of β1 activity increased presentation of UTY(246-254). In vitro degradation experiments showed that the caspase-like activity of β1 was responsible for the destruction of this CTL epitope, whereas it was preserved when LMP2 replaced β1. Moreover, inhibition of the β5 subunit rescued the presentation of the influenza matrix 58-66 epitope, thus suggesting that a similar mechanism can apply to the exchange of β5 by LMP7. Taken together, our data provide a rationale why the structural property of an immunoproteasome subunit rather than its activity is required for the generation of a CTL epitope.

The secret ally: immunostimulation by anticancer drugs

It has recently become clear that the tumour microenvironment, and in particular the immune system, has a crucial role in modulating tumour progression and response to therapy. Indicators of an ongoing immune response, such as the composition of the intratumoural immune infiltrate, as well as polymorphisms in genes encoding immune modulators, have been correlated with therapeutic outcome. Moreover, several anticancer agents--including classical chemotherapeutics and targeted compounds--stimulate tumour-specific immune responses either by inducing the immunogenic death of tumour cells or by engaging immune effector mechanisms. Here, we discuss the molecular and cellular circuitries whereby cytotoxic agents can activate the immune system against cancer, and their therapeutic implications.

Acyclovir prophylaxis against varicella zoster virus reactivation in multiple myeloma patients treated with bortezomib-based therapies: a retrospective analysis of 100 patients

BACKGROUND

Previous studies have indicated that, in patients with multiple myeloma (MM), bortezomib is associated with an increased incidence of herpes zoster, resulting from reactivation of latent varicella zoster virus (VZV).

OBJECTIVE

Our objective was to determine whether increased risk of VZV reactivation could be abrogated by using prophylactic acyclovir.

METHODS

We retrospectively evaluated 100 consecutive MM patients treated with bortezomib-based therapies at the Roswell Park Cancer Institute for development of herpes zoster. Frontline and relapsed/refractory patients were included, and patients received bortezomib alone or in combination with agents such as doxorubicin, melphalan, or dexamethasone. All patients received >4 weeks of acyclovir prophylaxis (400 mg twice daily), which was initiated prior to starting treatment with bortezomib and discontinued 4 weeks following bortezomib.

RESULTS

Median patient age was 62 years, 57% were male, and most (56%) had Durie-Salmon stage IIIA MM. None of the 100 MM patients receiving acyclovir prophylaxis developed herpes zoster during treatment with bortezomib, irrespective of patients receiving a wide variety of concomitant antimyeloma therapies and regardless of response to bortezomib-based therapy. One additional patient, found to be noncompliant with acyclovir therapy, experienced VZV reactivation, having received 3 cycles of bortezomib (3 weeks each cycle) in combination with cyclophosphamide and dexamethasone.

LIMITATIONS

Limitations of the study include its small size and retrospective nature.

CONCLUSIONS

The increased risk of VZV reactivation observed in previous studies of bortezomib-based therapy was completely abrogated in this series of patients who received prophylaxis with acyclovir.

Inhibition of intraerythrocytic proteasome retards the generation of hemorphins

Hemorphins are a set of hemoglobin-derived opioid peptides. The production mechanism of these structural overlap peptides remains unclear. Based on the sequences of hemorphins, it could be inferred that hemorphins are probably generated by cleavage of hemoglobin β chain at sites favored by the chymotrypsin-like protease. 20S proteasome possesses the chymotrypsin-like activity and still persists in mature erythrocytes. This study attempts to clarify whether the intraerythrocytic proteasome involves in the formation of hemorphins. Hemorphins containing hemorphin-7 and V-hemorphin-7 are isolated by immunoprecipitation from culture supernatant of human erythrocytes. Bortezomib inhibits the chymotrypsin-like activity of intraerythrocytic proteasome and prevents the yield of hemorphins in a dose-dependent manner. The present study suggests that intraerythrocytic proteasome contributes to the generation of hemorphins.

Pharmacological targets in the ubiquitin system offer new ways of treating cancer, neurodegenerative disorders and infectious diseases

Recent advances in the development and discovery of pharmacological interventions within the ubiquitin-proteasome system (UPS) have uncovered an enormous potential for possible novel treatments of neurodegenerative disease, cancer, immunological disorder and microbial infection. Interference with proteasome activity, although initially considered unlikely to be exploitable clinically, has already proved to be very effective against haematological malignancies, and more specific derivatives that target subsets of proteasomes are emerging. Recent small-molecule screens have revealed inhibitors against ubiquitin-conjugating and -deconjugating enzymes, many of which have been evaluated for their potential use as therapeutics, either as single agents or in synergy with other drugs. Here, we discuss recent advances in the characterisation of novel UPS modulators (in particular, inhibitors of ubiquitin-conjugating and -deconjugating enzymes) and how they pave the way towards new therapeutic approaches for the treatment of proteotoxic disease, cancer and microbial infection.

The antiviral immune response in mice devoid of immunoproteasome activity

The replacement of the catalytically active proteasome subunits β1, β2, and β5 by the immunoproteasome subunits low molecular mass polypeptide (LMP) 2 (β1i), multicatalytic endopeptidase complex-like-1 (MECL-1) (β2i), and LMP7 (β5i) is required for the production of numerous class I ligands. Hitherto, investigation of the immunoproteasome was confined to the analysis of mice deficient for one or two immunosubunits. In this study, we characterized LMP2(-/-)/MECL-1(-/-) double-deficient mice and used the well-defined LMP7-selective inhibitor ONX 0914 in these mice to generate mice lacking the activity of all immunoproteasome subunits. LMP2(-/-)/MECL-1(-/-) double-deficient mice had strongly reduced numbers of CD8(+) T cells in the spleen. Nevertheless, infection with the lymphocytic choriomeningits virus induced a normal cytotoxic T cell response in these mice, although the T cell response to several class I epitopes was altered. Treatment of LMP2(-/-)/MECL-1(-/-) double-deficient mice with the LMP7-selective inhibitor ONX 0914 elicited a strong CTL response in lymphocytic choriomeningitis virus-infected mice. Thereby, the T(CD8+) response to nucleoprotein 205-212, which is barely detectable in LMP2(-/-)/MECL-1(-/-) double-deficient mice, could be reverted to normal levels by LMP7 inhibition. Additional experiments could demonstrate that the increased CTL response to the nucleoprotein 205-212 in mice lacking functional immunoproteasome is due to an altered class I presentation of this epitope. Taken together, to our knowledge, this is the first study investigating viral infection in mice lacking activity of all three immunoproteasome subunits.

Viral takeover of the host ubiquitin system

Like the other more well-characterized post-translational modifications (phosphorylation, methylation, acetylation, acylation, etc.), the attachment of the 76 amino acid ubiquitin (Ub) protein to substrates has been shown to govern countless cellular processes. As obligate intracellular parasites, viruses have evolved the capability to commandeer many host processes in order to maximize their own survival, whether it be to increase viral production or to ensure the long-term survival of latently infected host cells. The first evidence that viruses could usurp the Ub system came from the DNA tumor viruses and Adenoviruses, each of which use Ub to dysregulate the host cell cycle (Scheffner et al., 1990; Querido et al., 2001). Today, the list of viruses that utilize Ub includes members from almost every viral class, encompassing both RNA and DNA viruses. Among these, there are examples of Ub usage at every stage of the viral life cycle, involving both ubiquitination and de-ubiquitination. In addition to viruses that merely modify the host Ub system, many of the large DNA viruses encode their own Ub modifying machinery. In this review, we highlight the latest discoveries regarding the myriad ways that viruses utilize Ub to their advantage.

Drug-mediated and cellular immunotherapy in multiple myeloma

Multiple myeloma is an immunologically relevant disease, which subverts and suppresses immunity, but that may also be amenable to immunological control. Novel drug and cell-based therapies provide an opportunity for the design of antimyeloma immunotherapy. Reversing the immunosuppression associated myeloma remains a substantial challenge. The minimal residual disease setting achieved by autologous stem cell transplant or highly efficacious induction therapy may reverse this immunoparesis and provide a setting for induction of antimyeloma T-cell responses. Adoptive cytotoxic T-lymphocyte/NK therapy and comprehensive treatment with immunomodulatory drug therapy represent means by which antimyeloma immune responses may be promoted. In addition, apoptosis-inducing therapies may prime endogenous antigen presentation via immunogenic cell death, which again may be enhanced by the addition of immunomodulatory drug therapy.

Poxvirus exploitation of the ubiquitin-proteasome system

Ubiquitination plays a critical role in many cellular processes. A growing number of viruses have evolved strategies to exploit the ubiquitin-proteasome system, including members of the Poxviridae family. Members of the poxvirus family have recently been shown to encode BTB/kelch and ankyrin/F-box proteins that interact with cullin-3 and cullin-1 based ubiquitin ligases, respectively. Multiple members of the poxvirus family also encode ubiquitin ligases with intrinsic activity. This review describes the numerous mechanisms that poxviruses employ to manipulate the ubiquitin-proteasome system.

The proteasome inhibitor bortezomib disrupts tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) expression and natural killer (NK) cell killing of TRAIL receptor-positive multiple myeloma cells

Bortezomib, a potent 26S proteasome inhibitor, is approved for the treatment of multiple myeloma (MM) and clinical trials are under way to evaluate its efficacy in other malignant diseases. However, cytotoxic effects of bortezomib on immune-competent cells have also been observed. In this study, we show that bortezomib downregulates cell surface expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on primary human interleukin (IL)-2-activated natural killer (NK) cells. Pharmacological inhibition of the transcription factor, NF-kappaB also profoundly decreased TRAIL expression, suggesting that NF-kappaB is involved in the regulation of TRAIL expression in activated human NK cells. Furthermore, perforin-independent killing of the human MM cell lines RPMI8226 and U266 by NK cells was markedly suppressed following bortezomib treatment. In addition, blocking cell surface-bound TRAIL with a TRAIL antibody impaired NK cell-mediated lysis of the TRAIL-sensitive MM cell line, RPMI8226. In conclusion, the proteasome is likely to be involved in the regulation of TRAIL expression in primary human IL-2-activated NK cells. Proteasome inhibition by bortezomib disrupts TRAIL expression and TRAIL dependent and/or independent pathway-mediated killing of myeloma cells, suggesting that bortezomib may potentially hamper NK-dependent immunosurveillance against tumors in patients treated with this drug.

Prevention of experimental colitis by a selective inhibitor of the immunoproteasome

The proteasome, a multicatalytic protease, is responsible for the degradation of intracellular proteins. Stimulation of cells with inflammatory cytokines, such as IFN-gamma, leads to the replacement of the constitutive catalytic proteasome subunits by the inducible subunits low molecular mass polypeptide (LMP)2 (beta1i), multicatalytic endopeptidase complex-like-1 (beta2i), and LMP7 (beta5i), which are required for the production of certain MHC class I-restricted T cell epitopes. In this study, we investigated the effect of immunoproteasomes on the development of dextran sulfate sodium-induced colitis. Colitis induction in LMP2-, LMP7-, and multicatalytic endopeptidase complex-like-1-deficient mice caused reduced weight loss compared with wild-type mice. Although colon lengths were shortened in wild-type mice, no reduction was observed in immunoproteasome-deficient mice. In accordance with this, proinflammatory cytokines, such as TNF-alpha and IL-1beta, were not upregulated in these mice. Blockage of LMP7 by a novel LMP7-selective inhibitor (PR-957) strongly reduced pathological symptoms of dextran sulfate sodium-induced colitis. Production of numerous cytokines in PR-957-treated mice was suppressed, resulting in reduced inflammation and tissue destruction. Taken together, these results demonstrate that an immunoproteasome-specific inhibitor can be used to attenuate autoimmune diseases like colitis.

Designing CD8+ T cell vaccines: it's not rocket science (yet)

CD8+ T cells play important roles in clearing viral infections and eradicating tumors. Designing vaccines that elicit effective CD8+ T cell responses requires a thorough knowledge of the pathways of antigen presentation in vivo. Here, I review recent progress in understanding the activation of naïve CD8+ T cells in vivo, with particular emphasis on cross-priming, the presentation of protein antigens acquired by dendritic cells from their environment. With the rapid advances in this area of research, the dawn of rational vaccine design is at hand.

The proteasome inhibitor Velcade enhances rather than reduces disease in mouse hepatitis coronavirus-infected mice

Many viruses, including coronaviruses (CoVs), depend on a functional cellular proteasome for efficient infection in vitro. Hence, the proteasome inhibitor Velcade (bortezomib), a clinically approved anticancer drug, shown in an accompanying study (M. Raaben et al., J. Virol. 84:7869-7879, 2010) to strongly inhibit mouse hepatitis CoV (MHV) infection in cultured cells, seemed an attractive candidate for testing its antiviral properties in vivo. Surprisingly, however, the drug did not reduce replication of the virus in mice. Rather, inhibition of the proteasome caused enhanced infection with lethal outcome, calling for caution when using this type of drug during infection.