CD28/CD154 blockade prevents autoimmune diabetes by inducing nondeletional tolerance after effector t-cell inhibition and regulatory T-cell expansion

Distinct peripheral blood molecular signature emerges with successful tacrolimus withdrawal in kidney transplant recipients

Tacrolimus (Tac) is an effective anti-rejection agent in kidney transplantation, but its off-target effects make withdrawal desirable. Although studies indicate that Tac can be safely withdrawn in a subset of kidney transplant recipients, immune mechanisms that underlie successful vs unsuccessful Tac removal are unknown. We performed microarray analyses of peripheral blood mononuclear cells (PBMC) RNA from subjects enrolled in the Clinical Trials in Organ Transplantation-09 study in which we randomized stable kidney transplant recipients to Tac withdrawal or maintenance of standard immunosuppression beginning 6 months after transplant. Eight of 14 subjects attempted but failed withdrawal, while six developed stable graft function for ≥2 years on mycophenolate mofetil plus prednisone. Whereas failed withdrawal upregulated immune activation genes, successful Tac withdrawal was associated with a downregulatory and proapoptotic gene program enriched within T cells. Functional analyses suggested stronger donor-reactive immunity in subjects who failed withdrawal without evidence of regulatory T cell dysfunction. Together, our data from a small, but unique, patient cohort support the conclusion that successful Tac withdrawal is not simply due to absence of donor-reactive immunity but rather is associated with an active immunological process.

Selective CD28 Inhibition Modulates Alloimmunity and Cardiac Allograft Vasculopathy in Anti-CD154-Treated Monkeys

BACKGROUND

Selective CD28 inhibition is actively pursued as an alternative to B7 blockade using cytotoxic T lymphocyte antigen 4 Ig based on the hypothesis that the checkpoint immune regulators cytotoxic T lymphocyte antigen 4 and programmed death ligand 1 will induce tolerogenic immune signals. We previously showed that blocking CD28 using a monovalent nonactivating reagent (single-chain anti-CD28 Fv fragment linked to alpha-1 antitrypsin [sc28AT]) synergizes with calcineurin inhibitors in nonhuman primate (NHP) kidney and heart transplantation. Here, we explored the efficacy of combining a 3-week "induction" sc28AT treatment with prolonged CD154 blockade.

METHODS

Cynomolgus monkey heterotopic cardiac allograft recipients received sc28AT (10 mg/kg, d0-20, n = 3), hu5C8 (10-30 mg/kg, d0-84, n = 4), or combination (n = 6). Graft survival was monitored by telemetry. Protocol biopsies and graft explants were analyzed for International Society of Heart and Lung Transplantation acute rejection grade and cardiac allograft vasculopathy score. Alloantibody, T-cell phenotype and regulatory T cells were analyzed by flow cytometry. Immunochemistry and gene expression (NanoString) characterized intra-graft cellular infiltration.

RESULTS

Relative to modest prolongation of median graft survival time with sc28AT alone (34 days), hu5C8 (133 days), and sc28AT + hu5C8 (141 days) prolonged survival to a similar extent. CD28 blockade at induction, added to hu5C8, significantly attenuated the severity of acute rejection and cardiac allograft vasculopathy during the first 3 months after transplantation relative to hu5C8 alone. These findings were associated with decreased proportions of circulating CD8 and CD3CD28 T cells, and modulation of inflammatory gene expression within allografts.

CONCLUSIONS

Induction with sc28AT promotes early cardiac allograft protection in hu5C8-treated NHPs. These results support further investigation of prolonged selective CD28 inhibition with CD40/CD154 blockade in NHP transplants.

Cutting Edge: Dual TCRα Expression Poses an Autoimmune Hazard by Limiting Regulatory T Cell Generation

Despite accounting for 10-30% of the T cell population in mice and humans, the role of dual TCR-expressing T cells in immunity remains poorly understood. It has been hypothesized that dual TCR T cells pose an autoimmune hazard by allowing self-reactive TCRs to escape thymic selection. We revisited this hypothesis using the NOD murine model of type 1 diabetes. We bred NOD mice hemizygous at both TCRα and β (TCRα^+/- β^+/-) loci, rendering them incapable of producing dual TCR T cells. We found that the lack of dual TCRα expression skewed the insulin-specific thymocyte population toward greater regulatory T (T_reg) cell commitment, resulting in a more tolerogenic T_reg to conventional T cell ratio and protection from diabetes. These data support a novel hypothesis by which dual TCR expression can promote autoimmunity by limiting agonist selection of self-reactive thymocytes into the T_reg cell lineage.

Of the multiple mechanisms leading to type 1 diabetes, T cell receptor revision may play a prominent role (is type 1 diabetes more than a single disease?)

A single determinant factor for autoimmunity does not exist; disease development probably involves contributions from genetics, the environment and immune dysfunction. Type 1 diabetes is no exception. Genomewide-associated studies (GWAS) analysis in T1D has proved disappointing in revealing contributors to disease prediction; the only reliable marker has been human leucocyte antigen (HLA). Specific HLAs include DR3/DR4/DQ2/DQ8, for example. Because HLA molecules present antigen to T cells, it is reasonable that certain HLA molecules have a higher affinity to present self-antigen. Recent studies have shown that additional polymorphisms in HLA that are restricted to autoimmune conditions are further contributory. A caveat is that not all individuals with the appropriate 'pro-autoimmune' HLA develop an autoimmune disease. Another crucial component is autoaggressive T cells. Finding a biomarker to discriminate autoaggressive T cells has been elusive. However, a subset of CD4 helper cells that express the CD40 receptor have been described as becoming pathogenic. An interesting function of CD40 on T cells is to induce the recombination-activating gene (RAG)1/RAG2 T cell receptor recombination machinery. This observation is contrary to immunology paradigms that changes in TCR molecules cannot take place outside the thymic microenvironment. Alteration in TCR, called TCR revision, not only occurs, but may help to account for the development of autoaggressive T cells. Another interesting facet is that type 1 diabetes (T1D) may be more than a single disease; that is, multiple cellular components contribute uniquely, but result ultimately in the same clinical outcome, T1D. This review considers the process of T cell maturation and how that could favor auto-aggressive T cell development in T1D. The potential contribution of TCR revision to autoimmunity is also considered.

Targeting the alternatively spliced soluble isoform of CTLA-4: prospects for immunotherapy?

CTLA-4 is an inhibitory protein that contributes to immune homeostasis and tolerance, a role that has led to its exploitation as a therapeutic in several clinical settings including cancer and autoimmune disease. Development of CTLA-4 therapies focused largely on the full-length receptor isoform but other CTLA-4 isoforms are also expressed, including a secretable form of CTLA-4 (soluble CTLA-4 [sCTLA-4]). The contribution of sCTLA-4 to immune regulation has been less well studied, primarily because it was identified some years after the original description of CTLA-4. Here, we examine how sCTLA-4 might contribute to immune regulation and ask whether it might be a biomarker to inform current CTLA-4 therapies or represent a novel CTLA-4 target for future therapeutics.

CTLA4-Ig preserves thymus-derived T regulatory cells

BACKGROUND

CTLA-4 immunoglobulin fusion proteins (CTLA4-Ig) suppress immune reactions by blocking the T-cell costimulatory CD28-CD80-86 pathway and are used in clinical trials for diseases featuring exaggerated T-cell reactivity including autoimmune diseases and allograft rejection. However, because CTLA4-Ig has been suspected to interfere with T regulatory (Treg) cell homeostasis and function, recently, substantial concerns on CTLA4-Ig's potentially antitolerogenic effects have been raised.

METHODS

We tested immunoregulatory CTLA4-Ig explicitly for its effect on Treg cell numbers, frequencies and function in an in vitro murine major histocompatibility complex mismatched setting using C57BL/6 bone marrow-derived dendritic cells as stimulators of allogeneic Balb/c Foxp3 T cells, which allowed for tracing Treg cells in a straightforward fashion.

RESULTS

The presence of CTLA4-Ig in mixed leukocyte reactions-while dampening the global proliferative response of allostimulated Balb/c T cells-resulted in a relative increase of the frequency of thymus-derived CD4CD25Foxp3 Treg cells with intact suppressive activity. This relative increase was caused by a selective inhibitory effect of CTLA4-Ig on proliferating conventional T cells, whereas the proliferative capacity of Treg cells in cell cultures remained unaffected. Additionally, in the presence of CTLA4-Ig, the frequency of apoptosis was decreased in these cells.

CONCLUSION

Our findings unequivocally demonstrate that CTLA4-Ig does not negatively affect Treg cell frequencies and function in vitro.

Targeting CD44 augments the efficacy of Tregs in autoimmune diabetes

Curing type 1 diabetes (T1D) will require lasting control of the autoimmune response that destroys insulin-producing islet β-cells. Re-establishing tolerance by restoring/replacing Tregs has significant potential for treatment of T1D but will require strategies to augment and maintain their efficacy. We previously showed that polyclonal in vitro-induced Tregs can reverse recent onset of T1D in ∼ 50% of NOD mice. Here we report that treatment of newly hyperglycemic animals with a short course of anti-CD44 at the time of Treg transfer improved diabetes reversal to >90%. Anti-CD44 treatment alone delayed diabetes onset and increased the frequencies of pancreatic CD4(+) T cells producing IL-2 or TGF-β, cytokines that support Treg function and survival, without altering production of IFN-γ. These anti-CD44 effects on endogenous T cells were also observed in the context of polyclonal Treg transfer, and the combination treatment also reduced pancreatic infiltrates. The results provide compelling evidence that approaches to modulate the pancreatic milieu to support Treg function and counteract inflammation in the pancreas can greatly enhance the efficacy of adoptively transferred Tregs, and suggest that approaches achieving these outcomes hold promise for long-term control of autoimmunity in T1D.

Targeted immune interventions for type 1 diabetes: not as easy as it looks!

PURPOSE OF REVIEW

Although insulin is lifesaving and sustaining for those with type 1 diabetes (T1D), curing the disease will be much more complex than simple replacement of this hormone. T1D is an autoimmune disease orchestrated by T cells, and includes many arms of the immune response. Tremendous effort has gone into understanding its underlying immune, genetic, and environmental causes, and this progress has led to immunologically based clinical trials in T1D. This review will focus primarily on the clinical trials of the past decade that have attempted to translate these fundamental findings.

RECENT FINDINGS

It is known that powerful, nonspecific immune suppressants can temporarily slow the course of newly diagnosed T1D, yet are too toxic for long-term use, especially in children. Recent clinical trials to reverse T1D have used newly developed therapies that target specific components of the immune process believed to be involved with T1D. Although well justified and designed, no recent approach has resulted in clinical remission and few have had any effect on disease course.

SUMMARY

Advances in our fundamental understanding of how the human diabetes immune response is activated and regulated coupled with lessons that have been learnt from the most recent era of completed trials are guiding us toward the development of more effective, multipronged therapies to ablate diabetes autoimmunity, restore immune tolerance, preserve β cells, and, ultimately, improve the lives of patients with T1D.

Central memory CD8+ T lymphocytes mediate lung allograft acceptance

Memory T lymphocytes are commonly viewed as a major barrier for long-term survival of organ allografts and are thought to accelerate rejection responses due to their rapid infiltration into allografts, low threshold for activation, and ability to produce inflammatory mediators. Because memory T cells are usually associated with rejection, preclinical protocols have been developed to target this population in transplant recipients. Here, using a murine model, we found that costimulatory blockade-mediated lung allograft acceptance depended on the rapid infiltration of the graft by central memory CD8+ T cells (CD44(hi)CD62L(hi)CCR7+). Chemokine receptor signaling and alloantigen recognition were required for trafficking of these memory T cells to lung allografts. Intravital 2-photon imaging revealed that CCR7 expression on CD8+ T cells was critical for formation of stable synapses with antigen-presenting cells, resulting in IFN-γ production, which induced NO and downregulated alloimmune responses. Thus, we describe a critical role for CD8+ central memory T cells in lung allograft acceptance and highlight the need for tailored approaches for tolerance induction in the lung.

Targeting co-stimulatory pathways: transplantation and autoimmunity

The myriad of co-stimulatory signals expressed, or induced, upon T-cell activation suggests that these signalling pathways shape the character and magnitude of the resulting autoreactive or alloreactive T-cell responses during autoimmunity or transplantation, respectively. Reducing pathological T-cell responses by targeting T-cell co-stimulatory pathways has met with therapeutic success in many instances, but challenges remain. In this Review, we discuss the T-cell co-stimulatory molecules that are known to have critical roles during T-cell activation, expansion, and differentiation. We also outline the functional importance of T-cell co-stimulatory molecules in transplantation, tolerance and autoimmunity, and we describe how therapeutic blockade of these pathways might be harnessed to manipulate the immune response to prevent or attenuate pathological immune responses. Ultimately, understanding the interplay between individual co-stimulatory and co-inhibitory pathways engaged during T-cell activation and differentiation will lead to rational and targeted therapeutic interventions to manipulate T-cell responses and improve clinical outcomes.

Endogenous memory CD8 T cells are activated within cardiac allografts without mediating rejection

Endogenous memory CD8 T cells infiltrate MHC-mismatched cardiac allografts within 12-24 h posttransplant in mice and are activated to proliferate and produce IFN-γ. To more accurately assess the graft injury directly imposed by these endogenous memory CD8 T cells, we took advantage of the ability of anti-LFA-1 mAb given to allograft recipients on days 3 and 4 posttransplant to inhibit the generation of primary effector T cells. When compared to grafts from IgG-treated recipients on day 7 posttransplant, allografts from anti-LFA-1 mAb-treated recipients had increased numbers of CD8 T cells but these grafts had marked decreases in expression levels of mRNA encoding effector mediators associated with graft injury and decreases in donor-reactive CD8 T cells producing IFN-γ. Despite this decreased activity within the allograft, CD8 T cells in allografts from recipients treated with anti-LFA-1 mAb continued to proliferate up to day 7 posttransplant and did not upregulate expression of the exhaustion marker LAG-3 but did have decreased expression of ICOS. These results indicate that endogenous memory CD8 T cells infiltrate and proliferate in cardiac allografts in mice but do not express sufficient levels of functions to mediate overt graft injury and acute rejection.

Elimination of T cell reactivity to pancreatic β cells and partial preservation of β cell activity by peptide blockade of LFA-1:ICAM-1 interaction in the NOD mouse model

In insulin dependent diabetes mellitus (T1D), self-reactive T cells infiltrate pancreatic islets and induce beta cell destruction and dysregulation of blood glucose. A goal is to control only the self-reactive T cells, leaving the remainder of the T cell population free to protect the host. One approach is blockade of the second signal for T cell activation while allowing the first (antigen-specific) signal to occur. This work proposes that small peptides that block interaction of second signals delivered through the counter receptors LFA-1:ICAM-1 will induce attacking T cells (receiving the antigen signal) to become anergic or undergo apoptosis. In NOD mice, the peptides eliminated T cell reactivity against pancreatic antigens and reduced cellular infiltration into islets, which retained stronger density of insulin staining at five weeks after cessation of therapy. In in vitro studies the peptides induced nonresponsiveness during activation of T cells from mice and from human peripheral blood.

Cytotoxic T lymphocyte antigen 4-immunoglobulin G is a potent adjuvant for experimental allergen immunotherapy

Allergen-specific immunotherapy (SIT) is the only treatment for allergic diseases that targets allergen-specific T helper type 2 (Th2) cells, which are the cause of the disease. There is an unmet requirement for adjuvants that increase the clinical efficacy of SIT allowing application of lower doses of the allergen, thereby reducing the risk of anaphylactic reactions. Cytotoxic T lymphocyte antigen 4-immunoglobulin (CTLA-4-Ig) has been shown to induce immunological tolerance in autoimmunity and allograft transplantation by blocking T cell co-stimulation and induction of the immunoregulatory enzyme indoleamine 2,3 dioxygenase (IDO). Previously, we showed that CTLA-4-Ig treatment at the time of allergen inhalation induced tolerance to subsequent allergen exposure in a mouse model of asthma. In this study, we test the hypothesis that CTLA-4-Ig acts as an adjuvant for experimental SIT. We evaluated the adjuvant effects of CTLA-4-Ig on SIT in a mouse model of ovalbumin-driven asthma. We used both wild-type and IDO-deficient mice to assess the role of IDO in the adjuvant effects of CTLA-4-Ig. Co-administration of CTLA-4-Ig strongly increased SIT-induced suppression of airway hyperreactivity (AHR), specific IgE in serum, airway eosinophilia and Th2 cytokine levels. Moreover, we found that CTLA-4-Ig, as an adjuvant for SIT, is equally effective in IDO-deficient and wild-type mice, demonstrating that the effect of CTLA-4-Ig is independent of IDO expression. We show that CTLA-4-Ig acts as a potent adjuvant to augment the therapeutic effects of SIT. As the adjuvant activity of CTLA-4-Ig is independent of IDO, we conclude that it acts by blocking CD28-mediated T cell co-stimulation.

Targeting regulatory T cells in the treatment of type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is a T cell-mediated autoimmune disease resulting in islet β cell destruction, hypoinsulinemia, and severely altered glucose homeostasis. T1DM has classically been attributed to the pathogenic actions of auto-reactive effector T cells(Teffs) on the β cell. Recent literature now suggests that a failure of a second T cell subtype, known as regulatory T cells (Tregs), plays a critical role in the development of T1DM. During immune homeostasis, Tregs counterbalance the actions of autoreactive Teff cells, thereby participating in peripheral tolerance. An imbalance in the activity between Teff and Tregs may be crucial in the breakdown of peripheral tolerance, leading to the development of T1DM. In this review, we summarize our current understanding of Treg function in health and in T1DM, and examine the effect of experimental therapies for T1DM on Treg cell number and function in both mice and humans.

TGF-β blockade does not improve control of an established persistent viral infection

Acute resolving viral infections are often associated with a strong and multi-specific T-cell response, whereas in persistent viral infections T-cell responses are often impaired. It has been suggested that the resuscitation of the antiviral T-cell response could be a powerful tool to target persisting viruses. Several immunoregulatory pathways, such as IL-10 and TGF-β, have been shown to be involved in the induction of T-cell exhaustion and viral persistence. In this study, we sought to investigate whether TGF-β signaling is also relevant in the maintenance of T-cell exhaustion after viral persistence has been established, and whether blockade of TGF-β signaling could improve control of viral replication in a mouse model of persistent virus infection. Using the LCMV clone 13 model, we analyzed the frequency, function, and phenotype of virus-specific CD4 and CD8 T cells following therapeutic TGF-β signaling blockade. We show that in vivo blockade of the TGF-β receptor failed to substantially enhance the antiviral T-cell response, and was insufficient to mediate a therapeutically-relevant reduction of viral titers in different tissues. Thus, although TGF-β signaling has the ability to hamper antiviral immunity, its pharmacological blockade may not be sufficient to tackle persistent viruses.

Promoting long-term survival of insulin-producing cell grafts that differentiate from adipose tissue-derived stem cells to cure type 1 diabetes

BACKGROUND

Insulin-producing cell clusters (IPCCs) have recently been generated in vitro from adipose tissue-derived stem cells (ASCs) to circumvent islet shortage. However, it is unknown how long they can survive upon transplantation, whether they are eventually rejected by recipients, and how their long-term survival can be induced to permanently cure type 1 diabetes. IPCC graft survival is critical for their clinical application and this issue must be systematically addressed prior to their in-depth clinical trials.

METHODOLOGY/PRINCIPAL FINDINGS

Here we found that IPCC grafts that differentiated from murine ASCs in vitro, unlike their freshly isolated islet counterparts, did not survive long-term in syngeneic mice, suggesting that ASC-derived IPCCs have intrinsic survival disadvantage over freshly isolated islets. Indeed, β cells retrieved from IPCC syngrafts underwent faster apoptosis than their islet counterparts. However, blocking both Fas and TNF receptor death pathways inhibited their apoptosis and restored their long-term survival in syngeneic recipients. Furthermore, blocking CD40-CD154 costimulation and Fas/TNF signaling induced long-term IPCC allograft survival in overwhelming majority of recipients. Importantly, Fas-deficient IPCC allografts exhibited certain immune privilege and enjoyed long-term survival in diabetic NOD mice in the presence of CD28/CD40 joint blockade while their islet counterparts failed to do so.

CONCLUSIONS/SIGNIFICANCE

Long-term survival of ASC-derived IPCC syngeneic grafts requires blocking Fas and TNF death pathways, whereas blocking both death pathways and CD28/CD40 costimulation is needed for long-term IPCC allograft survival in diabetic NOD mice. Our studies have important clinical implications for treating type 1 diabetes via ASC-derived IPCC transplantation.

Embryonic pig pancreatic tissue for the treatment of diabetes: potential role of immune suppression with "off-the-shelf" third-party regulatory T cells

BACKGROUND

Xenogeneic embryonic pancreatic tissue can provide an attractive alternative for organ replacement therapy. However, immunological rejection represents a major obstacle. This study examines the potential of regulatory T cells (Tregs) in the prevention of E42 pancreas rejection.

METHODS

To develop new approaches to combat rejection, we evaluated engraftment, growth, and development of E42 pig pancreatic tissue in mice treated with ex vivo expanded Tregs in combination with T-cell debulking and the conventional immunosuppressive drugs, rapamycin and FTY720.

RESULTS

Transplantation of E42 pig pancreas into C57BL/6 mice immunosuppressed by this protocol resulted in complete rejection within less than 6 weeks. In contrast, additional treatment with a single infusion of ex vivo expanded third-party Tregs markedly delayed the onset of graft rejection to 10 weeks. The infusion of Tregs was associated with a significant reduction in CD4 and CD8 expansion in the lymph nodes and other peripheral organs at the priming stages after implantation. Freezing and thawing of the Tregs did not affect their efficacy, indicating the potential of Tregs banking.

CONCLUSION

Considering the technical difficulties encountered in the generation of Tregs from patients or from specific donors, our results demonstrate the feasibility of using "off-the-shelf" fresh or frozen third-party Tregs to control rejection in organ transplantation.

Acquisition of regulatory function by human CD8(+) T cells treated with anti-CD3 antibody requires TNF

Anti-CD3 mAb can modulate graft rejection and attenuate autoimmune diseases but their mechanism(s) of action remain unclear. CD8(+) T cells with regulatory function are induced in vitro by Teplizumab, a humanized anti-CD3 antibody and inhibit responses of autologous and allogeneic T cells. They inhibit CD4(+) T-cell proliferation by mechanisms involving TNF and CCL4, and by blocking target cell entry into G2/M phase of cell cycle but neither kill them, nor compete for IL-2. CD8(+) Treg can be isolated from peripheral blood following treatment of patients with Type 1 diabetes with Teplizumab, but not from untreated patients. The induction of CD8(+) Treg by anti-CD3 mAb requires TNF and signaling through the NF-κB cascade. The CD8(+) Treg express CD25, glucocorticoid-induced TNF receptor family, CTLA-4, Foxp3, and TNFR2, and the combined expression of TNFR2 and CD25 identifies a potent subpopulation of CD8(+) Treg. These studies have identified a novel mechanism of immune regulation by anti-CD3 mAb and markers that may be used to track inducible CD8(+) Treg in settings such as chronic inflammation or immune therapy.

GVHD after haploidentical transplantation: a novel, MHC-defined rhesus macaque model identifies CD28- CD8+ T cells as a reservoir of breakthrough T-cell proliferation during costimulation blockade and sirolimus-based immunosuppression

We have developed a major histocompatibility complex-defined primate model of graft-versus-host disease (GVHD) and have determined the effect that CD28/CD40-directed costimulation blockade and sirolimus have on this disease. Severe GVHD developed after haploidentical transplantation without prophylaxis, characterized by rapid clinical decline and widespread T-cell infiltration and organ damage. Mechanistic analysis showed activation and possible counter-regulation, with rapid T-cell expansion and accumulation of CD8(+) and CD4(+) granzyme B(+) effector cells and FoxP3(pos)/CD27(high)/CD25(pos)/CD127(low) CD4(+) T cells. CD8(+) cells down-regulated CD127 and BCl-2 and up-regulated Ki-67, consistent with a highly activated, proliferative profile. A cytokine storm also occurred, with GVHD-specific secretion of interleukin-1 receptor antagonist (IL-1Ra), IL-18, and CCL4. Costimulation Blockade and Sirolimus (CoBS) resulted in striking protection against GVHD. At the 30-day primary endpoint, CoBS-treated recipients showed 100% survival compared with no survival in untreated recipients. CoBS treatment resulted in survival, increasing from 11.6 to 62 days (P < .01) with blunting of T-cell expansion and activation. Some CoBS-treated animals did eventually develop GVHD, with both clinical and histopathologic evidence of smoldering disease. The reservoir of CoBS-resistant breakthrough immune activation included secretion of interferon-γ, IL-2, monocyte chemotactic protein-1, and IL-12/IL-23 and proliferation of cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin-resistant CD28(-) CD8(+) T cells, suggesting adjuvant treatments targeting this subpopulation will be needed for full disease control.