Bogumila T. Konieczny

Selective expression of the interleukin 7 receptor identifies effector CD8 T cells that give rise to long-lived memory cells

A major unanswered question is what distinguishes the majority of activated CD8 T cells that die after an acute viral infection from the small fraction (5–10%) that survive to become long-lived memory cells. In this study we show that increased expression of the interleukin 7 receptor α-chain (IL-7Rα) identifies the effector CD8 T cells that will differentiate into memory cells. IL-7Rhi effector cells contained increased amounts of antiapoptotic molecules, and adoptive transfer of IL-7Rhi and IL-7Rlo effector cells showed that IL-7Rhi cells preferentially gave rise to memory cells that could persist and confer protective immunity. Thus, selective expression of IL-7R identifies memory cell precursors, and this marker may be useful in predicting the number of memory T cells generated after infection or immunization.

Functional and genomic profiling of effector CD8 T cell subsets with distinct memory fates

An important question in memory development is understanding the differences between effector CD8 T cells that die versus effector cells that survive and give rise to memory cells. In this study, we provide a comprehensive phenotypic, functional, and genomic profiling of terminal effectors and memory precursors. Using killer cell lectin-like receptor G1 as a marker to distinguish these effector subsets, we found that despite their diverse cell fates, both subsets possessed remarkably similar gene expression profiles and functioned as equally potent killer cells. However, only the memory precursors were capable of making interleukin (IL) 2, thus defining a novel effector cell that was cytotoxic, expressed granzyme B, and produced inflammatory cytokines in addition to IL-2. This effector population then differentiated into long-lived protective memory T cells capable of self-renewal and rapid recall responses. Experiments to understand the signals that regulate the generation of terminal effectors versus memory precursors showed that cells that continued to receive antigenic stimulation during the later stages of infection were more likely to become terminal effectors. Importantly, curtailing antigenic stimulation toward the tail end of the acute infection enhanced the generation of memory cells. These studies support the decreasing potential model of memory differentiation and show that the duration of antigenic stimulation is a critical regulator of memory formation.

Immunologic 'ignorance' of vascularized organ transplants in the absence of secondary lymphoid tissue.

Secondary lymphoid organs (the spleen, lymph nodes and mucosal lymphoid tissues) provide the proper environment for antigen-presenting cells to interact with and activate naive T and B lymphocytes. Although it is generally accepted that secondary lymphoid organs are essential for initiating immune responses to microbial antigens and to skin allografts, the prevailing view has been that the immune response to primarily vascularized organ transplants such as hearts and kidneys does not require the presence of secondary lymphoid tissue. The assumption has been that the immune response to such organs is initiated in the graft itself when recipient lymphocytes encounter foreign histocompatibility antigens presented by the grafts endothelial cells. In contrast to this view, we show here that cardiac allografts are accepted indefinitely in recipient mice that lack secondary lymphoid tissue, indicating that the alloimmune response to a vascularized organ transplant cannot be initiated in the graft itself. Moreover, we demonstrate that the permanent acceptance of these grafts is not due to tolerance but is because of immunologic ‘ignorance’.

Recall and propagation of allospecific memory T cells independent of secondary lymphoid organs

The allospecifc T cell population responding to a transplanted organ consists of both naïve and memory lymphocytes. Although it is established that naive T cells are activated by antigen within the organized structures of secondary lymphoid organs (the spleen, lymph nodes, and mucosal lympoid tissues), it is not clear whether memory T cell activation and propagation depend on homing to these organs. To answer this question, we investigated whether allospecific naïve or memory T cells can mediate acute cardiac allograft rejection in mutant mice that lack all of their secondary lymphoid tissues. The results of our experiments demonstrated that antigen-experienced memory T cells have two advantages over naïve T cells: (i) memory T cells mount a vigorous immune response that leads to allograft rejection independent of secondary lymphoid organs; and (ii) memory T cells generate more memory T cells without homing to secondary lymphoid organs. These unique properties of memory T cells were further confirmed by showing that memory-like T cells that arise from the homeostatic proliferation of naive T cells in the absence of antigenic stimulation are suboptimal at rejecting allografts and do not generate memory T cells in mice devoid of secondary lymphoid tissues.

Autophagy is essential for effector CD8 + T cell survival and memory formation

The importance of autophagy in the generation of memory CD8+ T cells in vivo is not well defined. We report here that autophagy was dynamically regulated in virus-specific CD8+ T cells during acute infection of mice with lymphocytic choriomeningitis virus. In contrast to the current paradigm, autophagy decreased in activated proliferating effector CD8+ T cells and was then upregulated when the cells stopped dividing just before the contraction phase. Consistent with those findings, deletion of the gene encoding either of the autophagy-related molecules Atg5 or Atg7 had little to no effect on the proliferation and function of effector cells, but these autophagy-deficient effector cells had survival defects that resulted in compromised formation of memory T cells. Our studies define when autophagy is needed during effector and memory differentiation and warrant reexamination of the relationship between T cell activation and autophagy.

Rescue of exhausted CD8 T cells by PD-1-targeted therapies is CD28-dependent

Immunotherapeutic PD-1–targeted therapies require CD28 to promote cancer cell killing. CD28 is a critical target for PD-1 blockade PD-1–targeted therapies have been a breakthrough for treating certain tumors and can rejuvenate T cells to unleash the anticancer immune response (see the Perspective by Clouthier and Ohashi). It is widely believed that PD-1 suppresses signaling through the T cell receptor (TCR). However, Hui et al. find instead that the TCR costimulatory receptor, CD28, is the primary target of PD-1 signaling. Independently, Kamphorst et al. show that CD28 is required for PD-1 therapies to kill cancer cells efficiently and eliminate chronic viral infections in mice. Lung cancer patients that responded to PD-1 therapy had more CD28+ T cells, which suggests that CD28 may predict treatment response. Science, this issue p. 1428, p. 1423; see also p. 1373 Programmed cell death–1 (PD-1)–targeted therapies enhance T cell responses and show efficacy in multiple cancers, but the role of costimulatory molecules in this T cell rescue remains elusive. Here, we demonstrate that the CD28/B7 costimulatory pathway is essential for effective PD-1 therapy during chronic viral infection. Conditional gene deletion showed a cell-intrinsic requirement of CD28 for CD8 T cell proliferation after PD-1 blockade. B7-costimulation was also necessary for effective PD-1 therapy in tumor-bearing mice. In addition, we found that CD8 T cells proliferating in blood after PD-1 therapy of lung cancer patients were predominantly CD28-positive. Taken together, these data demonstrate CD28-costimulation requirement for CD8 T cell rescue and suggest an important role for the CD28/B7 pathway in PD-1 therapy of cancer patients.

Acute rejection of vascularized heart allografts in the absence of IFNgamma.

It is generally assumed that IFNgamma plays a central role in acute allograft rejection. To test this hypothesis, we transplanted fully allogeneic (MHC class I and II incompatible) C3H/HeJ (H2k) murine hearts to IFNgamma-/- (IFNgamma gene-knockout) and IFNgamma+/+ BALB/c (H2d) mice. The phenotype of IFNgamma-/- mice was confirmed by demonstrating absent IFNgamma protein production by Con A stimulated IFNgamma-/- splenocytes. Both IFNgamma-/- and IFNgamma+/+ strains rejected transplanted hearts acutely: graft survival (mean +/- SD) was 5.2+/-0.4 and 6.0+/-0.0 days, respectively. Histologic examination revealed similar patterns of acute cellular rejection in both mouse groups. IFNgamma mRNA was present in hearts rejected by IFNgamma+/+ mice but was absent in those rejected by IFNgamma-/- mice. IL-2, IL-4, IL-10, and TNFalpha mRNA expression, on the other hand, was similar in grafts rejected by either strain. We also observed that hapten-induced delayed-type hypersensitivity (DTH) response was significantly reduced but not absent in IFNgamma-/- mice. Our results demonstrate that IFNgamma is not required for acute cellular rejection of fully allogeneic murine hearts. We propose that non-DTH mechanisms of allograft destruction could be enhanced in the absence of IFNgamma and thus lead to robust acute rejection.

Interplay between regulatory T cells and PD-1 in modulating T cell exhaustion and viral control during chronic LCMV infection.

T reg cells effectively maintain CD8 T cell exhaustion during chronic LCMV infection, but blockade of PD-1 is critical for elimination of infected cells.

The Dual Role of IL-2 in the Generation and Maintenance of CD8+ Memory T Cells

The mechanisms responsible for the generation and maintenance of T cell memory are unclear. In this study, we tested the role of IL-2 in allospecific CD8+ T cell memory by analyzing the long-term survival, phenotype, and functional characteristics of IL-2-replete (IL-2+/+) and IL-2-deficient (IL-2−/−) CD8+ TCR-transgenic lymphocytes in an adoptive transfer model. We found that IL-2 is not essential for the in vivo generation, maintenance, or recall response of CD8+ memory T cells. However, IL-2 increased the size of the CD8+ memory pool if present at the time of initial T cell activation but reduced the size of the pool if present during memory maintenance by inhibiting the proliferation of CD8+ memory T cells. Thus, IL-2-based vaccine strategies or immunosuppressive regimens that target IL-2 should take into account the divergent roles of IL-2 in CD8+ T cell immunity.

4-1BB Signaling Synergizes with Programmed Death Ligand 1 Blockade To Augment CD8 T Cell Responses during Chronic Viral Infection

Previous studies have identified the inhibitory role that the programmed death 1 (PD-1) pathway plays during chronic infection. Blockade of this pathway results in rescue of viral-specific CD8 T cells, as well as reduction of viral loads in mice chronically infected with lymphocytic choriomeningitis virus (LCMV). We tested the effect of combining PD ligand 1 (PD-L1) blockade with an agonistic regimen that induces 4-1BB costimulation during chronic LCMV infection. There is a boosting effect in the rescue of LCMV-specific CD8 T cell responses after dual treatment with PD-L1 blockade and 4-1BB agonistic Abs when the amount and timing of 4-1BB costimulation are carefully controlled. When PD-L1–blocking Abs are given together with a single low dose of anti–4-1BB agonistic Abs, there is an enhanced and stable expansion of viral-specific CD8 T cells. Conversely, when blocking Abs to PD-L1 are given with a repetitive high dose of anti–4-1BB, there is an initial synergistic expansion of viral-specific CD8 T cells by day 7, followed by dramatic apoptosis by day 14. Viral control paralleled CD8 T cell kinetics after dual treatment. By day 7 posttreatment, viral titers were lower in both of the combined regimens (compared with PD-L1 blockade alone). However, whereas the high dose of anti–4-1BB plus PD-L1 blockade resulted in rebound of viral titers to original levels, the low dose of anti–4-1BB plus PD-L1 blockade resulted in a stable reduction of viral loads. These findings demonstrate the importance of carefully manipulating the balance between activating and inhibitory signals to enhance T cell responses during chronic infection.