T-cell costimulation via CD28-CD80/CD86 and CD40-CD40 ligand interactions

Translating B cell immunology to the treatment of antibody-mediated allograft rejection

Antibody-mediated rejection (AMR), including chronic AMR (cAMR), causes ~50% of kidney allograft losses each year. Despite attempts to develop well-tolerated and effective therapeutics for the management of AMR, to date, none has obtained FDA approval, thereby highlighting an urgent unmet medical need. Discoveries over the past decade from basic, translational and clinical studies of transplant recipients have provided a foundation for developing novel therapeutic approaches to preventing and treating AMR and cAMR. These interventions are aimed at reducing donor-specific antibody levels, decreasing graft injury and fibrosis, and preserving kidney function. Innovative approaches emerging from basic science findings include targeting interactions between alloreactive T cells and B cells, and depleting alloreactive memory B cells, as well as donor-specific antibody-producing plasmablasts and plasma cells. Therapies aimed at reducing the cytotoxic antibody effector functions mediated by natural killer cells and the complement system, and their associated pro-inflammatory cytokines, are also undergoing evaluation. The complexity of the pathogenesis of AMR and cAMR suggest that multiple approaches will probably be required to treat these disease processes effectively. Definitive answers await results from large, double-blind, multicentre, randomized controlled clinical trials.

The role of the oviduct environment in embryo survival

CONTEXT

Declining fertility is an issue in multiple mammalian species. As the site of fertilisation and early embryo development, the oviduct plays a critical role in embryo survival, yet there is a paucity of information on how the oviduct regulates this process.

AIMS

We hypothesised that differences in steroid hormone signalling and/or immune function would be observed in a model of poor embryo survival, the peripubertal ewe.

METHODS

We examined expression of steroid hormones in systemic circulation, oviductal expression of oestrogen receptorαand genes important in steroid hormone signalling, and immune function in pregnant and cyclic peripubertal and adult ewes on day 3 after oestrus.

KEY RESULTS

Concentrations of progesterone, but not oestradiol, were decreased in the peripubertal ewe compared to the adult ewe. Oestrogen receptorαprotein expression was increased in the peripubertal ewe, but pathway analysis of gene expression revealed downregulation of the oestrogen signalling pathway compared to the adult ewe. Differential expression of several genes involved in immune function between the peripubertal and adult ewe was consistent with an unfavourable oviductal environment in the peripubertal ewe lamb. Oestradiol concentration was positively correlated with the expression of multiple genes involved in the regulation of immune function.

CONCLUSIONS

Differences in the immune environment of the oviduct, potentially linked to differential modulation by steroid hormones, may partially underly the poor fertilisation and early embryo survival observed in the peripubertal ewe.

IMPLICATIONS

A unfavourable oviductal environment may play an important role in limiting reproductive success.

Role of Surgical Pathologist for the Detection of Immuno-oncologic Predictive Factors in Non-small Cell Lung Cancers

Until very recently, surgery, chemotherapy, and radiation therapy have been the mainstay of treatment in non-small cell carcinomas (NSCLCs). However, recent advances in molecular immunology have unveiled some of the complexity of the mechanisms regulating cellular immune responses and led to the successful targeting of immune checkpoints in attempts to enhance antitumor T-cell responses. Immune checkpoint molecules such as cytotoxic T-lymphocyte associated protein-4, programmed cell death protein-1, and programmed death ligand (PD-L) 1 have been shown to play central roles in evading cancer immunity. Thus, these molecules have been targeted by inhibitors for the management of cancers forming the basis of immunotherapy. Advanced NSCLC has been the paradigm for the benefits of immunotherapy in any cancer. Treatment decisions are made based on the expression of PD-L1 on the tumor cells and the presence or absence of driver mutations. Patients with high PD-L1 expression (≥50%) and no driver mutations are treated with single-agent immunotherapy whereas, for all other patients with a lower level of PD-L1 expression, a combination of chemotherapy and immunotherapy is preferred. Thus, PD-L1 blockers are the only immunotherapeutic agents approved in advanced NSCLC without any oncogenic driver mutations. PD-L1 immunohistochemistry, however, may not be the best biomarker in view of its dynamic nature in time and space, and the benefits may be seen regardless of PD -L1 expression. Each immunotherapy molecule is prescribed based on the levels of PD-L1 expression as assessed by a Food and Drug Administration-approved companion diagnostic assay. Other biomarkers that have been studied include tumor mutational burden, the T-effector signature, tumor-infiltrating lymphocytes, radiomic assays, inflammation index, presence or absence of immune-related adverse events and specific driver mutations, and gut as well as local microbiome. At the current time, none of these biomarkers are routinely used in the clinical decision-making process for immunotherapy in NSCLC. However, in individual cases, they can be useful adjuncts to conventional therapy. This review describes our current understanding of the role of biomarkers as predictors of response to immune checkpoint molecules. To begin with a brief on cancer immunology in general and in NSCLC, in particular, is discussed. In the end, recent advancements in laboratory techniques for refining biomarker assays are described.

Cytotoxic T lymphocyte antigen-4 regulates development of xenogenic graft versus host disease in mice via modulation of host immune responses induced by changes in human T cell engraftment and gene expression

Graft versus host disease (GvHD) is a major clinical problem with a significant unmet medical need. We examined the role of cytotoxic T lymphocyte antigen-4 (CTLA-4) in a xenogenic GvHD (xeno-GvHD) model induced by injection of human peripheral mononuclear cells (hPBMC) into irradiated non-obese diabetic (NOD) SCID gamma (NSG) mice. Targeting the CTLA-4 pathway by treatment with CTLA-4 immunoglobulin (Ig) prevented xeno-GvHD, while anti-CTLA-4 antibody treatment exacerbated the lethality and morbidity associated with GvHD. Xeno-GvHD is associated with infiltration of hPBMCs into the lungs, spleen, stomach, liver and colon and an increase in human proinflammatory cytokines, including interferon (IFN)-γ, tumor necrosis factor (TNF)-α and interleukin (IL)-5. Infiltration of donor cells and increases in cytokines were attenuated by treatment with CTLA-4 Ig, but remained either unaffected or enhanced by anti-CTLA-4 antibody. Further, splenic human T cell phenotyping showed that CTLA-4 Ig treatment prevented the engraftment of human CD45⁺ cells, while anti-CTLA-4 antibody enhanced donor T cell expansion, particularly CD4⁺ (CD45RO⁺ ) subsets, including T box transcription factor TBX21 (Tbet)⁺ CXCR3⁺ and CD25⁺ forkhead box protein 3 (FoxP3) cells. Comprehensive analysis of transcriptional profiling of human cells isolated from mouse spleen identified a set of 417 differentially expressed genes (DEGs) by CTLA-4 Ig treatment and 13 DEGs by anti-CTLA-4 antibody treatment. The CTLA-4 Ig regulated DEGs mapped to down-regulated apoptosis, inflammasome, T helper type 17 (Th17) and regulatory T cell (T_reg ) pathways and enhanced Toll-like receptor (TLR) receptor signaling, TNF family signaling, complement system and epigenetic and transcriptional regulation, whereas anti-CTLA-4 antibody produced minimal to no impact on these gene pathways. Our results show an important role of co-inhibitory CTLA-4 signaling in xeno-GvHD and suggest the therapeutic utility of other immune checkpoint co-inhibitory pathways in the treatment of immune-mediated diseases driven by hyperactive T cells.

Immune checkpoints and their inhibitors: Reappraisal of a novel diagnostic and therapeutic dimension in the urologic malignancies

Advances in molecular immunology have unveiled some of the complexity of the mechanisms regulating cellular immune responses and led to the successful targeting of immune checkpoints in attempts to enhance antitumor T cell responses. Surgery, chemotherapy, and radiation therapy have been the mainstay of treatment in urologic malignancies. Immune checkpoint molecules such as cytotoxic T-lymphocyte associated protein-4, programmed cell death protein-1, and programmed death-ligand 1 have been shown to play central roles in evading cancer immunity. Thus these molecules have been targeted by inhibitors for the management of cancers forming the basis of immunotherapy. Immunotherapy is now among the first line therapeutic options for metastatic renal cell carcinomas. In advanced bladder cancer, immunotherapy is the standard of care in the second line and the first line for cisplatin ineligible patients. There continues to be ongoing research to identify the role if any of immunotherapy in testicular, prostatic, and penile cancers. The ideal biomarker for response to immunotherapy is still elusive. Although programmed death-ligand 1 immunohistochemical testing has been widely used across the globe as a biomarker for immunotherapy, companion diagnostic tests have inherent issues with testing and reporting and cannot have universal applicability. Additional biomarkers including, tumor mutational burden, deficient mismatch repair, high microsatellite instability, and immune gene expression profiling are being evaluated in various clinical trials. This review appraises the data of immunotherapy in the management of urologic malignancies.

Targeting Negative and Positive Immune Checkpoints with Monoclonal Antibodies in Therapy of Cancer

The immune checkpoints are regulatory molecules that maintain immune homeostasis in physiological conditions. By sending T cells a series of co-stimulatory or co-inhibitory signals via receptors, immune checkpoints can both protect healthy tissues from adaptive immune response and activate lymphocytes to remove pathogens effectively. However, due to their mode of action, suppressive immune checkpoints may serve as unwanted protection for cancer cells. To restore the functioning of the immune system and make the patient’s immune cells able to recognize and destroy tumors, monoclonal antibodies are broadly used in cancer immunotherapy to block the suppressive or to stimulate the positive immune checkpoints. In this review, we aim to present the current state of application of monoclonal antibodies in clinics, used either as single agents or in a combined treatment. We discuss the limitations of these therapies and possible problem-solving with combined treatment approaches involving both non-biological and biological agents. We also highlight the most promising strategies based on the use of monoclonal or bispecific antibodies targeted on immune checkpoints other than currently implemented in clinics.

A study of the immune properties of human umbilical cord lining epithelial cells

BACKGROUND AIMS

Our previous study has demonstrated the stem cell-like properties of human umbilical cord lining epithelial cells (CLECs) and their capability for epidermal reconstitution in organotypic skin culture; however, the immunogenicity of these cells has not been clearly defined. We assessed several aspects of the immune properties of CLECs in vitro.

METHODS

We examined CLECs for their immunoregulatory function in a mixed lymphocyte culture experiment. We characterized the expression patterns of the major histocompatibility complex (MHC), co-stimulatory molecules and the pro-/anti-inflammatory cytokines and growth factors in CLECs by means of reverse transcription-polymerase chain reaction, Western blotting, flow cytometry and FlowCytomix multiple analyte detection assays.

RESULTS

CLECs were found not to induce but to suppress the proliferation response of the peripheral blood mononuclear cells in a mixed lymphocyte culture assay. They did not express the MHC class II antigen HLA-DR but the non-classic MHC class I antigens HLA-G and HLA-E and lacked the expression of the co-stimulatory molecules CD40, CD80 and CD86. In addition, they produced less interleukin-1β and transforming growth factor-β1 but more interleukin-4 and hepatocyte growth factor than did adult keratinocytes, a pattern in favor of wound healing with less inflammation response.

CONCLUSIONS

Our data suggest that CLECs have an immunosuppressive function in addition to their low immunogenicity. This could be at least partially explained by their expression of HLA-G and HLA-E molecules associated with immune tolerance and absence of HLA-DR and co-stimulatory molecules. The demonstration that CLECs produce a favorable pattern of cytokines and growth factors for wound healing provides further support for their potential clinical application in allogeneic cell therapy.

Miltefosine effectively modulates the cytokine milieu in Indian post kala-azar dermal leishmaniasis

BACKGROUND

The increasing incidence of unresponsiveness to antimonials in leishmaniasis prompted the use of newer drugs such as miltefosine. Miltefosine influences macrophage effector functions, but its effect on patients with post kala-azar dermal leishmaniasis (PKDL) has not been evaluated.

METHODOLOGY

The immunomodulatory activity of miltefosine was evaluated in patients with PKDL by studying the expression of activation markers (CD14 and CD16) and costimulatory molecules (CD80 and CD86) on circulating monocytes, levels of pro-inflammatory cytokines (tumor necrosis factor α, interleukin 6, interleukin 1β, and interleukin 8) and anti-inflammatory cytokines (interleukin 10, transforming growth factor β, interleukin 4, and interleukin 13) in serum and peripheral blood mononuclear cell culture supernatants, and serum nitrite and arginase activity.

RESULTS

Miltefosine on circulating monocytes upregulated expression of CD16 and CD86 and reduced that of CD14. Miltefosine also induced a significant increase in circulating levels of pro-inflammatory cytokines with a concomitant decrease in anti-inflammatory cytokines. Its macrophage activating potential was evidenced by its ability to decrease serum arginase activity and increase serum nitrite.

CONCLUSIONS

Miltefosine increased the proportion of monocytes that have a pro-inflammatory phenotype, which was accompanied by an enhanced secretion of pro-inflammatory cytokines and increased levels of serum nitrite. The decrease in anti-inflammatory cytokine levels and serum arginase activity collectively indicated that miltefosine triggered a robust T-helper 1 response that facilitated parasite elimination.

Acinetobacter lwoffii and Lactococcus lactis strains isolated from farm cowsheds possess strong allergy-protective properties

BACKGROUND

Children who grow up in a farming environment show lower levels of atopic sensitization, hay fever, and asthma than children of the same age not living in such an environment. A number of investigations provided good evidence that this is due to an early-life contact with cowsheds, farm animals, and/or consumption of products like raw milk. Also, it had been indicated that microorganisms might have an important effect on the development of allergies, and thus the question arose of which farm microbial organisms, their products, or both might induce or influence allergy-protective mechanisms.

OBJECTIVE

We sought to gain further insight into the potential allergy-protective properties of microbes isolated from the farming environment.

METHODS

Of a number of bacterial species identified in cowsheds of farms, 2 were selected, isolated, and characterized, namely Acinetobacter lwoffii F78 and Lactococcus lactis G121. The isolates were investigated with regard to their activation of pattern-recognition receptors, the maturation of human monocyte-derived dendritic cells, the upregulation of inflammatory cytokines, the T(H)1-polarizing Notch ligand expression, and their influence on the allergic phenotype.

RESULTS

It is shown that both bacterial isolates were able to reduce allergic reactions in mice, to activate mammalian cells in vitro, and to induce a T(H)1-polarizing program in dendritic cells.

CONCLUSION

Our data strongly support the hygiene hypothesis, which states that an environment rich in microbiologic structures, such as a farming environment, might protect against the development of allergies.

CLINICAL IMPLICATIONS

This work provides the first data on a potential application of cowshed bacteria in allergy protection.

CD40-induced aggregation of MHC class II and CD80 on the cell surface leads to an early enhancement in antigen presentation

Ligation of CD40 on B cells increases their ability to present Ag and to activate MHC class II (MHC-II)-restricted T cells. How this occurs is not entirely clear. In this study we demonstrate that CD40 ligation on Ag-presenting B cells (APC) for a short period between 30 min and 3 h has a rapid, augmenting effect on the ability of a B cell line and normal B cells to activate T cells. This is not due to alterations in Ag processing or to an increase in surface expression of CD80, CD86, ICAM-1, or MHC-II. This effect is particularly evident with naive, resting T lymphocytes and appears to be more pronounced under limiting Ag concentrations. Shortly after CD40 ligation on a B cell line, MHC-II and CD80 progressively accumulated in cholesterol-enriched microdomains on the cell surface, which correlated with an initial enhancement in their Ag presentation ability. Moreover, CD40 ligation induced a second, late, more sustained enhancement of Ag presentation, which correlates with a significant increase in CD80 expression by APC. Thus, CD40 signaling enhances the efficiency with which APC activate T cells by at least two related, but distinct, mechanisms: an early stage characterized by aggregation of MHC-II and CD80 clusters, and a late stage in which a significant increase in CD80 expression is observed. These results raise the possibility that one important role of CD40 is to contribute to the formation of the immunological synapse on the APC side.

Upregulation of costimulatory molecules induced by lipopolysaccharide and double-stranded RNA occurs by Trif-dependent and Trif-independent pathways

Both lipopolysaccharide (LPS) and double-stranded RNA (dsRNA) are adjuvants for the adaptive immune response, inducing upregulation of costimulatory molecules (UCM) on antigen-presenting cells. Trif, an adapter protein that transduces signals from Toll-like receptor 4 (TLR4) and TLR3, permits the induction of many cytokines, including interferon-beta, which signals through the type I interferon receptor. We show here that LPS-induced UCM was strictly dependent on the TLR4-->Trif axis, whereas dsRNA-induced UCM was only partly dependent on the TLR3-->Trif axis. But both LPS- and dsRNA-induced UCM were entirely dependent on type I interferon receptor signaling. These findings show that UCM involves an autocrine or paracrine loop, and indicate that an alternative TLR3-independent, Trif-independent pathway contributes to dsRNA-induced UCM.

Vaccines for colorectal cancer

Despite recent advances in the treatment of colorectal cancer, the overall survival rate for those patients with advanced locoregional disease remains less than 50%. Although adjuvant systemic chemotherapy has improved survival of these patients, more effective therapies are needed. Immunotherapy is an approach that could have a particular role in the adjuvant therapy of colorectal cancer. There is now convincing evidence that the immune system can specifically recognize and destroy malignant cells. Although both antibody- and T-cell-mediated anti-tumor responses have been documented, the cellular immune response with its direct cytotoxic mechanisms is felt to be the principal anti-tumor arm of the immune system. Analysis of the T cells that recognize tumors has led to the identification and characterization of many tumor-associated antigens including several colorectal antigens. Current approaches to developing a vaccine for colorectal cancer use our expanded understanding of these tumor-associated antigens and the conditions that allow development of an effective cellular immune response to them.

In vitro analysis of CD40-CD154 and CD28-CD80/86 interactions in the primary T-cell response to allogeneic "nonprofessional" antigen presenting cells

BACKGROUND

Recently, several ligand interactions have been examined in detail as potential mediators of costimulatory signaling. The CD154/CD40 and CD28/B7 interactions have been highlighted as being among the more-significant contributors to proper activation of unprimed T lymphocytes. Human keratinocytes (HK) and human dermal fibroblasts (HF) are capable of expressing Class II HLA and CD40 antigens after interferon-gamma exposure, yet neither express significant levels of B7. HK and HF have been characterized as "nonprofessional" antigen presenting cells (APC) and their poor APC function has been partially attributed to deficient costimulatory activity.

METHODS

In this study, we examined whether substituting for costimulatory signaling events through the addition of cross-linked monoclonal antibodies against the T-cell ligand/s (CD28 and/or CD154) could restore allostimulation. Mixed lymphocyte reactions were performed combining enriched human peripheral blood T cells and allogeneic HK or HF with or without stimulatory anti-CD28 and/or anti-CD154 antibodies.

RESULTS

The results show that the addition of anti-CD28 alone permitted HF but not HK to present alloantigen effectively. In contrast, addition of both anti-CD154 and anti-CD28 was required to generate even a moderate proliferative response to allogeneic HK. Further, adding a monomorphic anti-HLA-DR antibody substantially inhibited these responses. Additional experiments suggest that signaling through CD40/CD154 directs HK to produce TGF-beta, which would adversely affect T-cell activation.

CONCLUSIONS

The data presented highlight significant differences in signaling capacities for HK versus HF and provide evidence for a partial mechanism by which allogeneic human skin equivalents might be immunologically null upon engraftment.

Comparison of thymocyte development and cytokine production in CD7-deficient, CD28-deficient and CD7/CD28 double-deficient mice

CD7 and CD28 are Ig superfamily molecules expressed on thymocytes and mature T cells that share common signaling 0mechanisms and are co-mitogens for T cell activation. CD7-deficient mice are resistant to lipopolysaccharide (LPS)-induced shock syndrome, and have diminished in vivo LPS-triggered IFN-gamma and tumor necrosis factor (TNF)-alpha production. CD28-deficient mice have decreased serum Ig levels, defective IgG isotype switching, decreased T cell IL-2 production and are resistant to Staphylococcus aureus enterotoxin-induced shock. To determine synergistic roles CD7 and CD28 might play in thymocyte development and function, we have generated and characterized CD7/CD28 double-deficient mice. CD7/CD28-deficient mice were healthy, reproduced normally, had normal numbers of thymocyte subsets and had normal thymus histology. Anti-CD3 mAb induced similar levels of apoptosis in CD7-deficient, CD28-deficient and CD7/CD28 double-deficient thymocytes as in control C57BL/6 mice (P = NS). Similarly, thymocyte viability, apoptosis and necrosis following ionomycin or dexamethasone treatment were the same in control, CD7-deficient, CD28-deficient and CD7/CD28-deficient mice. CD28-deficient and CD7/CD28-deficient thymocytes had decreased [3H]thymidine incorporation responses to concanavalin A (Con A) stimulation compared to control mice (P < or = 0.01 and P < or = 0.05 respectively). CD7/CD28 double-deficient mice had significantly reduced numbers of B7-1/B7-2 double-positive cells compared to freshly isolated wild-type, CD7-deficient and CD28-deficient thymocytes. Con A-stimulated CD4/CD8 double-negative (DN) thymocytes from CD7/CD28 double-deficient mice expressed significantly lower levels of CD25 when compared to CD4/CD8 DN thymocytes from wild-type, CD7-deficient and CD28-deficient mice (P < 0.05). Anti-CD3-triggered CD7/CD28-deficient thymocytes also had decreased IFN-gamma and TNF-alpha production compared to C57BL/6 control, CD7-deficient and CD28-deficient mice (P < or = 0.05). Thus, CD7 and CD28 deficiencies combined to produce abnormalities in the absolute number of B7-1/B7-2-expressing cells in the thymus, thymocyte IL-2 receptor expression and CD3-triggered cytokine production.

In vitro anti-tumour activity of anti-CD80 and anti-CD86 immunotoxins containing type 1 ribosome-inactivating proteins

Immunotoxins specific for the CD80 and CD86 antigens were prepared by linking three type 1 ribosome-inactivating proteins (RIPs), namely bouganin, gelonin and saporin-S6, to the monoclonal antibodies M24 (anti-CD80) and 1G10 (anti-CD86). These immunotoxins showed a specific cytotoxicity for the CD80/CD86-expressing cell lines Raji and L428. The immunotoxins inhibited protein synthesis by target cells with IC50s (concentration causing 50% inhibition) ranging from 0.25 to 192 pmol/l as RIPs. The anti-CD80 immunotoxins appeared 1-2 log more toxic for target cells than the anti-CD86 ones. Immunotoxins containing saporin and bouganin induced apoptosis of target cells. The toxicity for bone marrow haemopoietic progenitors of these conjugates was also evaluated. Bouganin and related immunotoxins at concentrations up to 100 nmol/l did not significantly affect the recovery of committed progenitors or of more primitive cells. The saporin-containing immunotoxins at concentrations >/= 1 nmol/l showed some toxicity on colony-forming unit cells (CFU-C). The expression of the CD80 and CD86 molecules is prevalently restricted to antigen-presenting cells and is also strong on Hodgkin and Reed-Sternberg cells in Hodgkin's disease. Present results suggest that immunotoxins targeting type 1 ribosome-inactivating proteins to these antigens could be considered and further studied for the therapy of Hodgkin's disease or other CD80/CD86-expressing tumours.

B7-1 (CD80) and B7-2 (CD86) have complementary roles in mediating allergic pulmonary inflammation and airway hyperresponsiveness

We examined the roles of B7-1 (CD80) and B7-2 (CD86) in a model of allergic pulmonary inflammation and airway hyperresponsiveness (AHR) by using mice with germline deletions of the B7-1 and/or B7-2 molecules. Multiple parameters of the allergic response were affected to varying degrees by the absence of B7-1 and/or B7-2. Mice lacking both B7-1 and B7-2 had no elevation of serum immunoglobulin E, lack of airway eosinophilia, and no AHR. These same disease parameters were also reduced in mice lacking either B7-1 or B7-2. Lack of B7-1 and/or B7-2 resulted in an increase in T-helper 1 cytokine production. Our observations suggest that whereas B7-2 is quantitatively more significant in the induction of this response, B7-1 and B7-2 may have complementary roles in mediating the development of allergic pulmonary inflammation.

Ligation of CD28 In Vivo Induces CD40 Ligand Expression and Promotes B Cell Survival

Functional activation of T cells requires ligation of Ag receptors with specific peptides presented by MHC molecules on APCs concurrent with appropriate contacts of cell surface accessory molecules. Among these accessory molecules, interactions between CD28/CTLA-4 with B7 family members (CD80 and CD86) and CD40 with CD40 ligand (CD40L) play a decisive role in regulating the progression of balanced immune responses. However, most information regarding the role of accessory molecules in immune responses has been derived in the context of signals from the TCRs. Little understanding has been achieved regarding the consequence of ligation of costimulation molecules in absence of signals from the TCR. By employing an in vivo murine system, we show, herein, that ligation of CD28 alone with anti-CD28 Abs leads to a dramatic enlargement of the peripheral lymphoid organs characterized primarily by the expansion of B cells. B cells from anti-CD28-treated mice are resistant to spontaneous and anti-IgM-induced apoptosis. These cells are also unsusceptible to FasL-mediated apoptosis. Interestingly, this in vivo effect of CD28 on B cells is largely mediated by inducing the expression of CD40L, since coadministration of a blocking Ab against CD40L inhibited CD28-mediated B cell survival and expansion. Therefore, CD28-mediated expression of CD40L may play an important role in the regulation of lymphocyte homeostasis.

Novel therapies for inflammatory bowel disease

Looking back at successes and failures in newer approaches to treating IBD, it is tempting--although still difficult--to draw conclusions about pathogenesis. When a therapy proves effective, do clinicians truly know how it works? Even with a therapy as specific as anti-TNF antibody, it is not clear if the benefit is attributable to simple binding and clearance of TNF-alpha or to binding on the cell surface and subsequent deletion of the activated macrophage. When a drug appears to be less effective than preclinical models suggest, can failures in effectiveness from delivery or dosing be differentiated? The disappointing results of clinical trials with IL-10--so at odds with the prediction of benefit from animal models--bring into question the validity of those models as well as the soundness of design of the clinical trials on which efficacy of IL-10 is judged. The variability of response even to the most narrowly targeted agents suggests that these diseases are far more heterogeneous in humans than in their murine counterparts. Clinicians are only just beginning to recognize subclinical markers of response, and it may soon be possible to predict response on the basis of genetic composition. For the moment, however, the field of pharmacogenetics is embryonic. Challenges in developing new therapeutic strategies include not only identifying novel agents, but also improving the definitions of clinical endpoints and defining efficacy at the biologic level. Only through considered evaluation of clinical evidence may clinicians determine which therapies should remain novelties and which should become an accepted part of the armamentarium.