Splenic Counterparts Research Articles

Tumor vaccine composed of C-class CpG oligodeoxynucleotides and irradiated tumor cells induces long-term antitumor immunity

BackgroundAn ideal tumor vaccine should activate both effector and memory immune response against tumor-specific antigens. Beside the CD8+ T cells that play a central role in the generation of a protective immune response and of long-term memory, dendritic cells (DCs) are important for the induction, coordination and regulation of the adaptive immune response. The DCs can conduct all of the elements of the immune orchestra and are therefore a fundamental target and tool for vaccination. The present study was aimed at assessing the ability of tumor vaccine composed of C-class CpG ODNs and irradiated melanoma tumor cells B16F1 followed by two additional injections of CpG ODNs to induce the generation of a functional long-term memory response in experimental tumor model in mice (i.p. B16F1).ResultsIt has been shown that the functional memory response in vaccinated mice persists for at least 60 days after the last vaccination. Repeated vaccination also improves the survival of experimental animals compared to single vaccination, whereas the proportion of animals totally protected from the development of aggressive i.p. B16F1 tumors after vaccination repeated three times varies between 88.9%-100.0%. Additionally, the long-term immune memory and tumor protection is maintained over a prolonged period of time of at least 8 months. Finally, it has been demonstrated that following the vaccination the tumor-specific memory cells predominantly reside in bone marrow and peritoneal tissue and are in a more active state than their splenic counterparts.ConclusionsIn this study we demonstrated that tumor vaccine composed of C-class CpG ODNs and irradiated tumor cells followed by two additional injections of CpG ODNs induces a long-term immunity against aggressive B16F1 tumors.

Licensing of naïve T cells for rapid TNF production (138.14)

Abstract TNF is a potent inflammatory cytokine with numerous immunological functions, including the ability to limit the magnitude of virus-specific T cell responses during infection. Naïve T cells in secondary lymphoid organs (SLOs) exhibit a unique ability to produce TNF rapidly after activation and prior to acquiring other effector functions. Peripheral T cells are a heterogeneous population of cells at various stages of post-thymic development. To determine how maturation influences the licensing of T cells to produce TNF, we compared cytokine profiles of single positive thymic T cells, recent thymic emigrants (RTEs) and matured-naïve T cells during TCR activation. Thymic T cells exhibited a poor ability to produce TNF when compared to splenic T cells, despite possessing a similar potential for activation. Moreover, thymic T cells had significantly reduced levels of TNF message and phosphorylated MAPK (Erk1/2) when compared to their splenic counterparts. Stimulation of thymic T cells in the presence of splenic B cells and APCs partially licensed the T cells to produce TNF but not to the same extent as peripheral T cells. RTEs had a significantly enhanced ability to produce TNF as compared to thymic T cells, but fully matured naïve T cells were the most efficient TNF producers. Together, these findings suggest that TNF expression by naïve T cells is regulated via a gradual licensing process that requires functional maturation in peripheral lymphoid organs.

Resident IL10-competent peritoneal B cells regulate colitis severity (84.18)

Abstract B cells mediate multiple functions that influence immune and inflammatory responses. A rare subset of splenic CD1dhiCD5+ B cells has been found to modulate T cell responses, contact hypersensitivity and experimental autoimmune encephalitis by secreting IL10. However, equal numbers of B cells producing IL10 are found in the peritoneal cavity (PC). In this study, the phenotypic and functional characteristics of PC IL10-competent B cells were characterized. PC IL10-competent B cells share several phenotypic markers with their splenic IL10-competent counterparts, and were found within the B1a (47%), B1b (28%), and B2 (5%) subsets. Stimuli that promote in-vitro IL10 production differ between the spleen and PC populations, with PC B1 cells spontaneously producing IL10 without exogenous stimulation, while splenic B cell IL10 production is increased upon TLR stimulation. In a Rag-/- colitis model, the transfer of IL10-competent PC B cells dramatically reduced disease progression, reduced the number of activated and memory CD4+ T cells in the PC and total CD8+ T cells in the mesenteric lymph nodes. Together, these data reveal that IL-10 competent B cells in the peritoneal cavity significantly modulate T cell pathogenicity.

NOD2 Ligation Subverts IFN-α Production by Liver Plasmacytoid Dendritic Cells and Inhibits Their T Cell Allostimulatory Activity via B7-H1 Up-Regulation

The nucleotide-binding oligomerization domain (NOD)2/CARD15 protein, which senses muramyl dipeptide (MDP), a product of bacterial peptidoglycan, appears to play an important role in regulating intestinal immunity. Although the liver is exposed to gut-derived MDP, the influence of NOD2 ligation on hepatic APC, in particular dendritic cells (DC), is unknown. Freshly isolated mouse liver and spleen plasmacytoid (p)DC expressed higher levels of NOD2 message than conventional myeloid (m)DC. Following MDP stimulation in vivo, liver pDC, but not mDC, up-regulated expression of IFN regulatory factor 4 (IRF-4), a negative regulator of TLR signaling, and induced less allogeneic T cell proliferation and IFN-gamma production. The adoptive transfer of liver pDC from MDP-treated mice failed to prime allogeneic T cells in vivo. By contrast, splenic DC IRF-4 levels and T cell stimulatory activity remained unchanged. Liver pDC from MDP-stimulated mice also displayed greater IkappaBalpha, cell surface B7-H1, and B7-H1 relative to CD86 than control liver pDC. No similar effects were observed for liver mDC or spleen DC. Absence of B7-H1 on liver pDC reversed the inhibitory effect of MDP. After ex vivo stimulation with LPS or CpG, liver pDC but not mDC from MDP-treated animals secreted less IL-12p70, IL-6, and TNF-alpha and induced weaker allogeneic T cell proliferation than those from controls. Moreover, CpG-stimulated liver pDC from MDP-treated mice secreted less IFN-alpha than their splenic counterparts, and systemic levels of IFN-alpha were reduced in MDP-treated animals after CpG administration. These findings suggest that differential effects of NOD2 ligation on liver pDC may play a role in regulating hepatic innate and adaptive immunity.

Bone Marrow T Cells Are More Effective Than Peripheral T Cells in Inducing Chimeric Conversion Following MHC-Mismatched Nonmyeloablative Bone Marrow Transplantation

Background & Objectives: Recently, T cells in BM have attracted renewed interest because they are now known to have different surface phenotypes, subsets, and activation states from those in the periphery. Memory T cells undergo extensive migration from the blood to the BM and vice versa. The BM plays an important role in preferential homing and extensive proliferation of memory T cells, and contributes considerably to the longlived memory T cell pool. BM T cells are more activated than their splenic counterparts and have a higher rate of local proliferation. Although BM-T (NK1.1– CD4+ or CD8+) cells did not induce lethal GVH disease, even at high cell numbers, BM-T cells mediated vigorous graft-versus-tumor activity and facilitated engraftment of hematopoietic progenitor cells. These studies suggested that BM-T cells could be a useful cellular source for adoptive immunotherapy following ABMT, instead of peripheral T cells. Non-myeloablative bone marrow transplantation (NMT) and allogeneic mixed chimerism can provide an environment adequate for diminishing susceptibility to DLI-mediated GVHD and an immunological platform for DLI in both mouse and human models. In patients treated with DLI, a successful GVL effect is often associated with conversion to complete donor chimerism, supporting the concept of a graft-versus-host (GVH) response as part of the GVL effect. Thus, a quiet chimeric conversion following DLI is desirable to reach an optimal DLI-mediated GVL effect, without the occurrence of GVHD. Although in a mouse model, the administration of non-tolerant donor spleen cells to established mixed chimeras has been shown to convert mixed hematopoietic chimerism to full donor chimerism, without the concomitant development of GVHD, DLI in humans frequently results in serious GVHD and life-threatening complications. However, the use of BM-T cells, as compared with spleen T cells (SP-T), as the DLI source has not been investigated in allogeneic mixed chimerism prepared with NMT. In this study, we evaluated the beneficial alloreactivity of DLI using cryopreserved BM-T cells, a by-product obtained during the T cell depletion (TCD) procedure in BM grafting, to effectively induce chimeric conversion without the occurrence of GVHD in MHC-mismatched NMT.Methods: Cells were prepared using established procedures. During the T cell depletion (TCD) procedure in BM grafting, BM-T cells were obtained as a by-product and then cryopreserved for subsequent DLI using BM-T cells 21 days after the bone marrow transplant.Results: The administration of 5–10 × 105 BM-T (Thy1.2+) cells in mixed chimeras resulted in complete chimeric conversion, with self-limited graft-versus-host disease (GVHD) and no pathological changes. However, the administration of 5–10 × 105 SP-T (Thy1.2+) cells resulted in persistent mixed chimerism, with pathological GVHD signs in the liver and intestine.Conclusion: Our results suggest that DLI using BM-T cells, even in small numbers, could be more potent for inducing chimeric conversion in mixed chimerism than DLI using SP-T cells. Further study is needed to determine whether cryopreserved BM-T cells are an effective cell source for DLI to consolidate donor-dominant chimerism in clinical practice, without concerns about GVHD.

Therapeutic efficacy of antitumor dendritic cell vaccinations correlates with persistent Th1 responses, high intratumor CD8+ T cell recruitment and low relative regulatory T cell infiltration.

Despite the increasing number of immunotherapeutic strategies for the treatment of cancer, most approaches have failed to correlate the induction of an anti-tumor immune response with therapeutic efficacy. We therefore took advantage of a successful vaccination strategy-combining dendritic cells and irradiated GM-CSF secreting tumor cells-to compare the immune response induced against 9L gliosarcoma tumors in cured rats versus those with progressively growing tumors. At the systemic level, the tumor specific cytotoxic responses were quite heterogeneous in uncured vaccinated rats, and were surprisingly often high in animals with rapidly-growing tumors. IFN-gamma secretion by activated splenic T cells was more discriminative as the CD4+ T cell-mediated production was weak in uncured rats whereas high in cured ones. At the tumor level, regressing tumors were strongly infiltrated by CD8+ T cells, which demonstrated lytic capacities as high as their splenic counterparts. In contrast, progressing tumors were weakly infiltrated by T cells showing impaired cytotoxic activities. Proportionately to the T cell infiltrate, the expression of Foxp3 was increased in progressive tumors suggesting inhibition by regulatory T cells. In conclusion, the main difference between cured and uncured vaccinated animals does not depend directly upon the induction of systemic cytotoxic responses. Rather the persistence of higher CD4+ Th1 responses, a high intratumoral recruitment of functional CD8+ T cells, and a low proportion of regulatory T cells correlate with tumor rejection.

Accelerated T Cell Memory Development in the Peritoneal Cavity (85.24)

Abstract Acute virus infection results in the expansion of the number of virus-specific CD8 T cells, virus clearance, followed by the death (contraction) of 90% of the expanded antigen-specific CD8 T cell population ultimately resulting in a stable memory population. Memory cells are characterized by their enhanced ability to expand in number after secondary infection, enhanced cytokine production (IL-2, TNF-α) and surface expression of the IL-7Rα (CD127), CD27, and the lymph node homing molecule CD62L. Most of what’s known about the kinetics of memory development is from data acquired from the spleen, however it is unclear if other peripheral tissues share those same kinetics. We demonstrate here that CD8 T cells isolated from the peritoneal cavity (PECs) after intraperitoneal or intravenous infection with lymphocytic choriomeningitis virus (LCMV) display enhanced IL-2 and TNF-α production as well as a greater frequency of cells expressing the memory markers CD127 and CD27 compared to their splenic counterparts. Interestingly, PECs demonstrated prolonged expression of the activation marker CD43 and similar levels of CD62L compared to splenic memory cells. PEC cells adoptively transferred into naïve mice maintain their phenotype in all tissues found, whereas splenic memory cells adopt the phenotype of their host tissue. These data suggest that the generation of memory CD8 T cells is controlled by tissue-specific signals.

Low TLR4 Expression by Liver Dendritic Cells Correlates with Reduced Capacity to Activate Allogeneic T Cells in Response to Endotoxin

Signaling via TLRs results in dendritic cell (DC) activation/maturation and plays a critical role in the outcome of primary immune responses. So far, no data exist concerning TLR expression by liver DC, generally regarded as less immunostimulatory than secondary lymphoid tissue DC. Because the liver lies directly downstream from the gut, it is constantly exposed to bacterial LPS, a TLR4 ligand. We examined TLR4 expression by freshly isolated, flow-sorted C57BL/10 mouse liver DC compared with spleen DC. Real-time PCR revealed that liver CD11c+CD8alpha- (myeloid) and CD11c+CD8alpha+ ("lymphoid-related") DC expressed lower TLR4 mRNA compared with their splenic counterparts. Lower TLR4 expression correlated with reduced capacity of LPS (10 ng/ml) but not anti-CD40-stimulated liver DC to induce naive allogeneic (C3H/HeJ) T cell proliferation. By contrast to LPS-stimulated splenic DC, these LPS-activated hepatic DC induced alloantigen-specific T cell hyporesponsiveness in vitro, correlated with deficient Th1 (IFN-gamma) and Th2 (IL-4) responses. When higher LPS concentrations (> or =100 ng/ml) were tested, the capacity of liver DC to induce proliferation of T cells and Th1-type responses was enhanced, but remained inferior to that of splenic DC. Hepatic DC activated by LPS in vivo were inferior allogeneic T cell stimulators compared with splenic DC, whereas adoptive transfer of LPS-stimulated (10 ng/ml) liver DC induced skewing toward Th2 responses. These data suggest that comparatively low expression of TLR4 by liver DC may limit their response to specific ligands, resulting in reduced or altered activation of hepatic adaptive immune responses.

Conventional liver CD4 T cells are functionally distinct and suppressed by environmental factors†

The contribution of intrahepatic conventional T cells to the unique immunologic properties of the liver has not been clearly defined. We isolated bulk and CD4 T cells from mouse liver and compared their functions with each other and with their splenic counterparts. Unlike bulk spleen T cells, bulk liver T cells reacted minimally to allogeneic or antigen-loaded syngeneic dendritic cells. However, after exclusion of natural killer T cells (NKTs) and gammadelta T cells by FACS, liver and spleen CD4 T cells actually proliferated to a similar extent upon allogeneic or antigen-specific stimulation. Liver CD4 T cells were more sensitive to interleukin 2 (IL-2) than were spleen CD4 T cells, but had a similar proliferative potential based on their response to CD3 ligation. In addition, activated liver CD4 T cells produced higher levels of IL-4, IL-5, IL-10, and interferon gamma (IFN-gamma) than did splenic CD4 T cells. Therefore, liver CD4 T cells are intrinsically different from spleen CD4 T cells. In vitro, liver or spleen NKTs and gammadelta T cells suppressed liver and spleen CD4 T-cell proliferation in a dose-dependent fashion. In conclusion, unconventional T cells constrain liver CD4 T-cell function. Our findings have implications for pathological conditions of the liver that involve the response of conventional CD4 T lymphocytes.

Changes in integrin expression are associated with altered homing properties of Lin(-/lo)Thy1.1(lo)Sca-1(+)c-kit(+) hematopoietic stem cells following mobilization by cyclophosphamide/granulocyte colony-stimulating factor.

Although migration of hematopoietic stem cells (HSC) is essential for normal hematopoiesis and successful hematopoietic cell transplantation, little is known about the mechanisms that underlie this movement. We have sought to characterize the factors that regulate HSC migration by analyzing changes in expression of particular adhesion receptors associated with cyclophosphamide/granulocyte colony-stimulating factor (Cy/G-CSF)-induced HSC mobilization. Expression by Lineage(-/lo)Thy1.1(lo)Sca-1(+)c-kit(+) HSC of members of the beta1 integrin family of adhesion molecules was assessed in untreated or Cy/G-CSF-treated mice by multiparameter flow cytometry. In parallel, the in vivo homing properties of normal and mobilized HSC were compared following intravenous transfer of fluorescently marked HSC. Normal adult HSC express high levels of several beta1 integrin family members. Following Cy/G treatment, bone marrow HSC selectively downregulate alpha 2 integrin expression and upregulate alpha 5 expression. HSC found in the blood following Cy/G-CSF treatment express significantly lower levels of multiple integrins than their bone marrow and/or splenic counterparts. Changes in integrin expression by blood-borne HSC correlate with a 50% decrease in their ability to home to the bone marrow in short-term assays, and with previously observed defects in competitive engraftment by these HSC. Similar reductions in bone marrow (BM) homing are observed for BM HSC treated with alpha 4 integrin function blocking mAb prior to injection. Modulation of integrin expression induced by mobilization was not associated with cell-cycle progression. Changes in integrin expression and function are associated with HSC mobilization and likely significantly affect the engraftment potential of hematopoietic stem cells.

Migration of primary and memory CD8 T cells.

Our results indicate that a substantial proportion of the antimicrobial CD8 and CD4 T cell response is focused in non-lymphoid tissues. This finding makes teleological sense since maximum protection against infection is better served by the widespread presence of effector and memory cells. In the case of CD8 T cells, it appears that irrespective of the site at which initial activation of naive cells occurs, the end result is production of effector cells with broad migratory capabilities. Memory T cells perhaps have more restricted migratory abilities as compared to effector cells, although this needs to be tested definitively. Our results suggest that memory CD8 T cells in the intestinal LP may not be part of the recirculating pool of memory cells, though our data does not preclude the possibility that migrants from outside the mucosa contribute to the LP memory pool. Our data also demonstrates that CD8 memory T cells in non-lymphoid tissue exhibit heightened effector function as compared to their splenic counterparts. Whether these findings indicate the existence of distinct lineages of memory cells remains to be seen. The functional abilities of migrating memory cells could be modulated by the migration process and/or by the environmental milieu of a particular tissue. Although the development of CD8 memory T cells is a complex process requiring multiple signalling pathways, we identified IL-7 as an important player in memory generation. Much further work is needed to decipher the cellular and molecular mechanisms of memory induction as well as to learn the in vivo functional significance of memory cell subsets.

Preferential localization of effector memory cells in nonlymphoid tissue.

Many intracellular pathogens infect a broad range of host tissues, but the importance of T cells for immunity in these sites is unclear because most of our understanding of antimicrobial T cell responses comes from analyses of lymphoid tissue. Here, we show that in response to viral or bacterial infection, antigen-specific CD8 T cells migrated to nonlymphoid tissues and were present as long-lived memory cells. Strikingly, CD8 memory T cells isolated from nonlymphoid tissues exhibited effector levels of lytic activity directly ex vivo, in contrast to their splenic counterparts. These results point to the existence of a population of extralymphoid effector memory T cells poised for immediate response to infection.

Incidence and Subtype Specificity of API2-MALT1 Fusion Translocations in Extranodal, Nodal, and Splenic Marginal Zone Lymphomas

The t(11;18)(q21;q21) is thought to represent an important primary event in the development of marginal zone lymphomas, although an accurate estimation of the frequency and distribution of this genetic alteration among nodal, splenic, and extranodal marginal zone lymphoma types has yet to be determined. Recently, molecular genetic studies have shown that this translocation results in the fusion of the API2 gene on chromosome 11 and a novel gene termed MALT1 on chromosome 18. To investigate the incidence of API2-MALT1 fusion transcripts among marginal zone lymphomas and to determine possible marginal zone lymphoma subtype associations, we used reverse transcriptase-polymerase chain reaction to analyze RNAs extracted from frozen tissue samples of 99 marginal zone lymphomas. Fifty-seven involved diverse extranodal sites including 14 stomach, 11 lung, 7 orbit, 7 parotid, 5 thyroid, 5 lacrimal gland, 3 small intestine, 2 large intestine, 1 kidney, 1 paraspinal region and 1 skin. Twenty-one primary splenic and twenty-one primary nodal marginal zone lymphomas were also studied. API2-MALT1 fusion transcripts were detected in 12 of 57 extranodal marginal zone lymphomas (21%), but in none of the nodal or splenic cases. The cDNA sequences of the fusion transcripts were determined, revealing variation in the coding sequence fusion point for both API2 and MALT1. The findings suggest that t(11;18)(q21;q21) is restricted to extranodal marginal zone lymphomas and that these tumors have distinct genetic etiologies in comparison with their splenic and nodal counterparts.

Characterization of Peripheral Regulatory CD4+ T Cells That Prevent Diabetes Onset in Nonobese Diabetic Mice

The period that precedes onset of insulin-dependent diabetes mellitus corresponds to an active dynamic state in which pathogenic autoreactive T cells are kept from destroying beta cells by regulatory T cells. In prediabetic nonobese diabetic (NOD) mice, CD4+ splenocytes were shown to prevent diabetes transfer in immunodeficient NOD recipients. We now demonstrate that regulatory splenocytes belong to the CD4+ CD62Lhigh T cell subset that comprises a vast majority of naive cells producing low levels of IL-2 and IFN-gamma and no IL-4 and IL-10 upon in vitro stimulation. Consistently, the inhibition of diabetes transfer was not mediated by IL-4 and IL-10. Regulatory cells homed to the pancreas and modified the migration of diabetogenic to the islets, which resulted in a decreased insulitis severity. The efficiency of CD62L+ T cells was dose dependent, independent of sex and disease prevalence. Protection mechanisms did not involve the CD62L molecule, an observation that may relate to the fact that CD4+ CD62Lhigh lymph node cells were less potent than their splenic counterparts. Regulatory T cells were detectable after weaning and persist until disease onset, sustaining the notion that diabetes is a late and abrupt event. Thus, the CD62L molecule appears as a unique marker that can discriminate diabetogenic (previously shown to be CD62L-) from regulatory T cells. The phenotypic and functional characteristics of protective CD4+ CD62L+ cells suggest they are different from Th2-, Tr1-, and NK T-type cells, reported to be implicated in the control of diabetes in NOD mice, and may represent a new immunoregulatory population.