Wolfgang Dummer

T cell homeostatic proliferation elicits effective antitumor autoimmunity

Development of tumor immunotherapies focuses on inducing autoimmune responses against tumor-associated self-antigens primarily encoded by normal, unmutated genes. We hypothesized that such responses could be elicited by T cell homeostatic proliferation in the periphery, involving expansion of T cells recognizing self-MHC/peptide ligands. Herein, we demonstrate that sublethally irradiated lymphopenic mice transfused with autologous or syngeneic T cells showed tumor growth inhibition when challenged with melanoma or colon carcinoma cells. Importantly, the antitumor response depended on homeostatic expansion of a polyclonal T cell population within lymph nodes. This response was effective even for established tumors, was characterized by CD8(+) T cell-mediated tumor-specific cytotoxicity and IFN-gamma production, and was associated with long-term memory. The results indicate that concomitant induction of the physiologic processes of homeostatic T cell proliferation and tumor antigen presentation in lymph nodes triggers a beneficial antitumor autoimmune response.

Cutting Edge: Recent Immune Status Determines the Source of Antigens That Drive Homeostatic T Cell Expansion

Homeostatic proliferation of naive T cells transferred to T cell-deficient syngeneic mice is driven by low-affinity self-MHC/peptide ligands and the cytokine IL-7. In addition to homeostatic proliferation, a subset of naive T cells undergoes massive proliferation in chronically immunodeficient hosts, but not in irradiated normal hosts. Such rapid T cell proliferation occurs largely independent of homeostatic factors, because it was apparent in the absence of IL-7 and in T cell-sufficient hosts devoid of functional T cell immunity. Strikingly, immunodeficient mice raised under germfree conditions supported only slow homeostatic proliferation, but not the marked T cell proliferation observed in conventionally raised immunodeficient mice. Thus, polyclonal naive T cell expansion in T cell-deficient hosts can be driven predominantly by either self-Ags or foreign Ags depending on the host’s previous state of T cell immunocompetency.

Ocrelizumab, a humanized anti-CD20 monoclonal antibody, in the treatment of patients with rheumatoid arthritis: A phase I/II randomized, blinded, placebo-controlled, dose-ranging study†

OBJECTIVE Ocrelizumab, a humanized anti-CD20 monoclonal antibody, was studied in a first-in-human trial in rheumatoid arthritis (RA) patients receiving concomitant methotrexate (MTX). METHODS The ACTION trial was a combined phase I/II study of placebo plus MTX versus ocrelizumab plus MTX in 237 RA patients (intent-to-treat population). During phase I, 45 patients were treated with 1 of 5 escalating doses of study drug (infusions on days 1 and 15, 10-1,000 mg per each infusion). An additional 192 patients were randomized during phase II. Eligible patients had active disease, an inadequate response to treatment with at least MTX, rheumatoid factor positivity, and elevated levels of acute-phase reactants. The total study duration was 72 weeks. B cell pharmacodynamics over time was investigated. RESULTS Baseline demographics were similar among the treatment groups. Based on the entire 72-week data set, the incidence of serious adverse events in the ocrelizumab-treated patients was 17.9%, as compared with 14.6% in placebo-treated patients. The incidence of serious infections was 2.0% in all ocrelizumab-treated patients and 4.9% in placebo-treated patients. Infusion-associated adverse events were mostly grade 1 or grade 2 and were more frequent around the time of the first infusion. No serious infusion-associated adverse events were reported in the ocrelizumab group. Evidence of clinical activity was observed at all doses evaluated. Peripheral B cell depletion after infusion was rapid at all doses, with earlier repletion of B cells at doses of 10 mg and 50 mg. Human anti-human antibodies were detected in 19% and 10%, respectively, of those receiving 10 mg and 50 mg of ocrelizumab, compared with 0-5% of those receiving 200, 500, and 1,000 mg. CONCLUSION Ocrelizumab therapy in combination with MTX was well tolerated. Doses of 200 mg (2 infusions) and higher showed better clinical responses, better reduction of C-reactive protein levels, and very low immunogenicity.

Autologous Regulation of Naive T Cell Homeostasis Within the T Cell Compartment

Naive T cells undergo spontaneous slow proliferation on adoptive transfer into syngeneic T cell (T)-deficient hosts. Recent work has shown that such “homeostatic” T cell proliferation is driven by MHC molecules loaded with self-peptides rather than foreign peptides. Because naive T cells in normal T-sufficient hosts remain in interphase despite continuous contact with self-MHC/peptide ligands, T cells apparently inhibit homeostatic proliferation of neighboring T cells. To address this, we have investigated the requirements necessary for “bystander” T cells to inhibit homeostatic proliferation of other T cells. Three key findings are reported. First, homeostatic proliferation of T cells only occurs in specific microenvironments, namely the T cell compartment of the secondary lymphoid tissues. Second, direct entry into T cell compartments is also required for bystander inhibition of homeostatic proliferation. Third, bystander inhibition is mediated largely by naive rather than activated/memory T cells and does not require proliferation or TCR ligation. These findings suggest that homeostasis of naive T cells is unlikely to be regulated through competition for systemic soluble factors or for specific stimulatory self-MHC/peptide ligands. Rather, the data favor mechanisms that involve competition for local non-MHC stimulatory factors or direct cell-to-cell interactions between the T cells themselves within the T cell compartment.

T cell homeostasis and systemic autoimmunity

The exact mechanisms by which homeostatic anti-self proliferation of peripheral T cells is controlled are not yet well understood. Nevertheless, evidence exists that self-MHC/peptide recognition, necessary for T cell survival in a resting state, may become overt under certain conditions associated with lymphopenia and lead to T cell expansion and generation of effector cells (Figure ​(Figure1).1). Several factors may influence whether this expansion is beneficial or detrimental to the host, including genetic background, intensity, frequency and duration of lymphocyte disturbances, and previous inflammatory damage of the target organs. We further postulate that if the T cell repertoire and expanded clones primarily have low self-affinity, then the expansion will be largely innocuous, whereas if composed of cells with high self-affinity, clinically evident autoaggression may be the outcome. Validation of this hypothesis may provide a new paradigm for understanding autoimmune syndromes, including lupus.

Depletion of B cells by a humanized anti-CD20 antibody PRO70769 in Macaca fascicularis.

PRO70769 is a humanized IgG1 monoclonal antibody against the CD20 molecule that is present on normal and malignant B cells. PRO70769 is being evaluated for treatment of B-cell-mediated diseases and is in a phase 1 trial for rheumatoid arthritis. As part of the preclinical toxicology evaluation, B-cell depletion profiles and safety of PRO70769 were assessed in cynomolgus monkeys. Animals were administered drug (IV) on days 1 and 15 with 10, 50, or 100 mg/kg PRO70769 and killed 2 weeks after the second dose and after a 3-month recovery period. In a parallel study, animals were not necropsied but instead were retreated with a second cycle of PRO70769 administered under an identical regimen. PRO70769 suppressed B cells in the blood to undetectable levels and significantly reduced B cells in lymphoid tissues. Splenic B cells were depleted to a greater extent compared with lymph node B cells. A second cycle of treatment resulted in a greater extent of depletion in lymphoid tissues compared with the depletion observed after one cycle of treatment; however, residual B cells in lymphoid tissues were still detectable, even at the highest dose. The rate of B-cell recovery in peripheral blood appeared similar between one and two cycles of treatment. Upon depletion there was a change in the profile of lymph node B-cell subsets. After recovery, B-cell subsets were reconstituted to normal levels. Depletion of CD20-expressing cells and lymphoid follicular atrophy were the only treatment-related effects.

Role of cyclin kinase inhibitor p21 in systemic autoimmunity.

The cyclin kinase inhibitor protein p21 affects multiple processes relevant to the immune system, including cell cycle progression, replicative senescence, hemopoietic stem cell quiescence, and apoptosis. Therefore, malfunction of this protein may be a contributor to the pathogenesis of systemic autoimmunity. Here, we report that mixed background p21-deficient 129/Sv × C57BL/6 mice showed increased in vitro and in vivo T cell cycling and activation, moderate hypergammaglobulinemia and, at low penetrance, anti-chromatin autoantibodies. Homeostatic anti-self MHC/peptide ligand-induced proliferation of p21-deficient T cells was also enhanced. However, lymphoid organ enlargement was very mild, presumably due to increased apoptosis of the rapidly dividing cells. Moreover, the older p21-deficient mice had kidney pathology representing a similar, but slightly more advanced, state than that seen in the control mice. The timing and severity of the above serologic, cellular, and histologic manifestations in p21-deficient mice were unaffected by gender. Thus, p21 deficiency significantly enhances T cell activation and homeostatic proliferation, and can induce mild autoimmune manifestations at a low incidence without gender bias, but does not in itself generate the full spectrum of lupus-like disease.

A Plasmablast Biomarker for Nonresponse to Antibody Therapy to CD20 in Rheumatoid Arthritis

Plasmablast biomarkers predict whether rheumatoid arthritis patients will respond to therapeutic antibodies to CD20. A Molecular Magic Eight Ball Ever wish you could predict the future? From children’s toys to psychic consultants, there’s an entire industry devoted to providing people with insight into upcoming events. This desire for precognition extends to clinical medicine—both doctors and patients wish they could predict whether a treatment will work for a particular disease in a particular patient. Thus, the search for biomarkers was born. However, many studies that claim to identify “biomarkers” have as little experimental validation as a late-night TV psychic, making the truly validated biomarker a rare gem. Owczarczyk et al. now develop such a predictor for nonresponsiveness to anti-CD20 antibody therapy for rheumatoid arthritis. Rituximab and ocrelizumab are therapeutic antibodies that bind to CD20 on the surface of effector and memory B cells, causing them to be depleted from the circulation. These antibodies can be helpful to rheumatoid arthritis patients who don’t fare well with more general antirheumatic drugs, such as nonsteroidal anti-inflammatory drugs, and disease-modifying antirheumatic drugs, such as hydroxychloroquine, sulfasalazine, leflunomide, or methotrexate. But not all patients respond to these expensive targeted biologics. Owczarczyk et al. observed that rheumatoid arthritis patients who don’t respond to anti-CD20 antibodies had elevated amounts of IgJ mRNA, a marker for antibody-secreting plasmablasts. They then performed prospective testing of IgJ mRNA concentrations in one ocrelizumab and two rituximab patient cohorts and found that this marker could predict nonresponse to anti-CD20 antibody therapy. Moreover, a combination mRNA biomarker, IgJhiFCRL5lo, improved test performance over IgJhi alone. Will these biomarkers also be useful in stratifying response rates in other diseases in which anti-CD20 antibody therapy has shown clinical activity such as relapsing-remitting multiple sclerosis and ANCA-associated vasculitis? Cannot predict now. Ask again later. An important goal for personalized health care is the identification of biomarkers that predict the likelihood of treatment responses. Here, we tested the hypothesis that quantitative mRNA assays for B lineage cells in blood could serve as baseline predictors of therapeutic response to B cell depletion therapy in subjects with rheumatoid arthritis (RA). In samples from the REFLEX trial of rituximab in inadequate responders to antibodies to tumor necrosis factor–α, a 25% subgroup of treated subjects with elevated baseline mRNA levels of IgJ, a marker for antibody-secreting plasmablasts, showed reduced clinical response rates. There were no significant efficacy differences in the placebo arm subjects stratified by this marker. Prospective testing of the IgJ biomarker in the DANCER and SERENE rituximab clinical trial cohorts and the SCRIPT ocrelizumab cohort confirmed the utility of this marker to predict nonresponse to anti-CD20 therapy. A combination mRNA biomarker, IgJ hiFCRL5lo, showed improved test performance over IgJ hi alone. This study demonstrates that baseline blood levels of molecular markers for late-stage B lineage plasmablasts identify a ~20% subgroup of active RA subjects who are unlikely to gain substantial clinical benefit from anti-CD20 B cell depletion therapy.

γδ T Cell Homeostasis Is Controlled by IL-7 and IL-15 Together with Subset-Specific Factors

Among T cell subsets, γδ T cells uniquely display an Ag receptor-based tissue distribution, but what defines their preferential homing and homeostasis is unknown. To address this question, we studied the resources that control γδ T cell homeostasis in secondary lymphoid organs. We found that γδ and αβ T cells are controlled by partially overlapping resources, because acute homeostatic proliferation of γδ T cells was inhibited by an intact αβ T cell compartment, and both populations were dependent on IL-7 and IL-15. Significantly, to undergo acute homeostatic proliferation, γδ T cells also required their own depletion. Thus, γδ T cell homeostasis is maintained by trophic cytokines commonly used by other types of lymphoid cells, as well as by additional, as yet unidentified, γδ-specific factors.

Lack of Intrinsic CTLA-4 Expression Has Minimal Effect on Regulation of Antiviral T-Cell Immunity

ABSTRACT CTLA-4 is considered one of the most potent negative regulators of T-cell activation. To circumvent experimental limitations due to fatal lymphoproliferative disease associated with genetic ablation of CTLA-4, we have used radiation chimeras reconstituted with a mixture of CTLA-4+/+ and CTLA-4−/− bone marrow that retain a normal phenotype and allow the evaluation of long-term T-cell immunity under conditions of intrinsic CTLA-4 deficiency. Following virus infection, we profiled primary, memory, and secondary CD8+ and CD4+ T-cell responses directed against eight different viral epitopes. Our data demonstrate unaltered antigen-driven proliferation, acquisition of effector functions, distribution of epitope hierarchies, T-cell receptor repertoire selection, functional avidities, and long-term memory maintenance in the absence of CTLA-4. Moreover, regulation of memory T-cell survival and homeostatic proliferation, as well as secondary responses, was equivalent in virus-specific CTLA4+/+ and CTL-A-4−/− T-cell populations. Thus, lack of CTLA-4 expression by antigen-specific T cells can be compensated for by extrinsic factors in the presence of CTLA-4 expression by other cells. These findings have implications for the physiologic, pathological, and therapeutic regulation of costimulation.